Effects of Commercially Available Protective Coatings on Stress-corrosion Properties of Supersonic-transport Skin Materials Final Summary Report, 1 Jun. 1964 - 31 Jan. 1966

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Figure 12 shows the effects of the 550" F dry-salt environment on titanium -alloy specimens that were not previously damaged with scratches.

Part (a) of the figure contains the results from bare specimens and from those coated with Aluminum-Modified Silicone (ANIS) and with Catalytically Cured Silicone (CCS). A l l of the specimens within this group retained equiva- lently high ductilities except the bare specimens exposed to salt, which failed at low values of shortening. There is nothing in these r e s u l t s to confirm the visual observation that the CCS coating crazed and spalled from the specimens within 48 hours after exposure to the 550" F environment, and w e r e essentially bare f r o m that time on. The most logical explanation f o r the retention of high ductility by these specimerrs is +hat L l e salt deposits w e r e removed along with the spalled coating.

The apparent increase in ductility between 1000 and 3000 h r is a false effect caused by the previously explained change that w a s made in the location of the specimens within the bending fixture. It is likely that the ductile 1000- h r specimens would have exhibited ductilities equivalent to those from the longer exposures if they had been similarly located in the fixture. The change in loca- tion w a s made while bending the 3000-hr specimens after the bare, AMs, and CCS specimens unexposed to salt had already been tested. Therefore, these specimens appeared to have lower ductilities similar to those from the 1000-hr specimens. Although the actual shortening values obtained for these 3000-hr are reported in the appendix, they w e r e not used in no-salt'' specimens Figure 12 (a) because they presented a distorted value for comparison with the other 3000-hr specimens. F o r purposes of the plot, the more realistic shorten- ing values obtained with the 3000-hr AMS and CCS specimens exposed to salt w e r e considered to be representative of the "no salt" specimens and w e r e plotted a s such. The change of location in the fixture did not significantly effect the results obtained from embrittled specimens.

In Figure 12 (b) the results from the bare specimens are shown com- pared to those obtained from the specimens coated with Zinc in Silicate Vehicle (ZSV), Electrophoretically Deposited Aluminum (EDA), and Flame- Sprayed Aluminum (FSA). The specimens exposed to salt are shown by open data points connected with solid lines, and the specimens unexposed to salt by closed data points connected with dashed lines.

The results show that the specimens coated with ZSV w e r e similarly embrittled in both the "no salt" and salt-exposed conditions, and produced shortening values ranging between approximately 0.7 to 0.9 in. f r o m all speci- mens. Subsequent metallographic examination (see Figure 27) indicated that the embrittlement was caused by gross surface roughness that w a s probably inflicted when the coating supplier prepared the specimens f o r coating.

SOUTHERN RESEARCH INSTITUTE 13A 13 E EDA IPSA 0 1 5 7 Exposure Time, 1000 H r (b) B a r e and coated w i t h Zinc: in Silicate V e h i c l e (ZSV), Electrophoretically Deposited A h miriu m (EDA), and Flame-SprayedA luminum (FSA).

Figure 12.

E f f e c t s of 550" F Dry S a l t on UNSCRATCITED TITANIUM 8-1- 1 as Shown by Bend-Ductility Evaluations.

Specimens coated with FSA were embrittled similarly but to a lesser extent than those coated with ZSV, and although only one "no salt" data point w a s available for comparison, the lack or presence of salt apparently had in- significant effects on the embrittlement. Metallographic examination revealed that the surface of these specimens had also undergone roughening prior to coating.

The EDA specimens, on the other hand, exhibited considerable dif- ference between the ductilities of the "no salt'' and salt-exposed specimens.

The "no salt" specimens w e r e less ductile than the bare specimens , probably was applied to a different ?ct of tftantim alioy and because the EDA coating w a s given additional heat treatments to improve the adherence of the coating.

Because this coating w a s applied t o the substrate in sheet form, the edges of the specimens w e r e bare. The bare edges possibly account for the loss of ductility on salt-exposed specimens, which w e r e embrittled to the same ex- tent as bare specimens.

A l l results in Figure 12 and its companion figures show that all speci- mens affected by the s a l t had achieved their complete embrittlement to bend- ing within the first 1000-hr exposure period, and no further significant losses in ductility occurred beyond that duration.

Figure 13 shows the shortening results f o r titanium-alloy specimens that w e r e damaged with scratches before introduction to the 550" F exposure.

Except for the reductions in shortening caused by the scratches themselves, the results are quite consistent with the r e s u l t s from unscratched specimens (Figure 12). The r e s u l t s from unscratched bare specimens have been included in Figure 13 for purposes of comparison.

Figure 13 (a) compares the bare specimens with the Aluminum-Modified Silicone (AMS) and Catalytically Cured Silicone ( C C S ) .

The bare specimens not exposed to salt and the coated specimens with and without salt all had similar ductilities on the order of 1.5 in. shortening, which w a s apparently the ductility level dictated by the presence of the scratches. The bare specimens exposed to salt were further embrittled and had ductilities equivalent to the unscratched bare specimens that were exposed to salt. As with the unscratched specimens, the apparent protection furnished by CCS is not necessarily valid because the coating spalled off of the specimens shortly after heating to 550" F.

Figure 13 (b) shows the results from bare specimens compared to those from specimens coated with Zinc in Silicate Vehicle (ZSV), Electrophoretically Deposited Aluminum (EDA), and Flame-Sprayed Aluminum (FSA). These re- s u l t s were quite similar to the r e s u l t s obtained on the unscratched specimens (Figure 12).

A l l specimens coated with ZSV had equivalent lowered ductilities .

SOUTHERN RESEARCH INSTITUTE I I I 1 NOSALT SALT

0- - -0 0-0 BARE

0 1 3 5 7 Exposure Time, 1000 I f r B a r e and coatcd with Aluminum-Modified Silicone (AMS) (a) and Catalytically ( ' w e d Silicone (C'C'S). B a r e , undamaged r e s u l t s with 110 s a l t (N) and with s a l t (S) shown f o r com- parison.

SALT 0 1 3 5 7 Exposure T i m e , 1000 H r B a r e and coated with Zinc in Silicate Vehicle (ZSV), (b) Electrophoretic ally Deposited Aluminum (E DA), and Flame-Sprayed Aluminum (FSA). B a r e , undamaged (N) and with s a l t (S) shown for r e s u l t s with no s a l t com par is on.

F i g u r e 13.

Effects of 550" F d r y s a l t on SCRATCHED TITANIUM 8-1-1 a s shown by bend ductility evaluations.

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that were apparently not affected by the salt. The results from FSA speci- a similar relationship but with slightly better ductilities than the mens had ZSV specimens. Specimens coated with EDA had nearly complete ductility in the absence of salt but were completely embrittled in the presence of salt, presumably because of the bare edges.

Figure 14 shows the effects of t5e humid exposure on the bare and coated Ti-8-1-1 substrate. The results from the unscratched specimens a r e shown in Figure 14 (a). Although fewer data a r e available for the shorter- duration exposures, enough data a r e available to indicate the trends. It is evident, for example. that the humid environment, either -.vit.lii o r ---.'IL-- w 1 UlUUt salt, did not cause any embrittlement of the bare substrate. The two coatings, AMS and C C S , therefore, also exhibited maximum ductility. On the other hand, the surface roughness noted in the previous discussion of the 550" F exposures has apparently caused lower ductilities in the specimens coated with ZSV and with FSA. The specimens coated with EDA retained good ductility even though general corrosion of the aluminum coating itself w a s increasingly severe with increasing exposure times (see Table VIII). The increase in ductility of the EDA specimens between 5000 and 7000 h r (noted also in the scratched specimens shown in Figure 14 b) could not be explained by any of the known data.

Figure 14 (b) contains the data from the scratched specimens.

These data confirm that the presence of salt in this environment had no stress- corrosion effects on the titanium-alloy substrate, either in the bare o r A l l specimens exhibited some loss in ductility because coated conditions.

of the presence of the scratches but the losses were not as great as those caused by the scratches in the specimens exposed to the 550" F environ- ment (see Figure 13).

Figure 15 contains a plot of all of the results obtained from the AM 350 substrate-scratched and unscratched specimens in both 550" F and humid ex- posures. It was practical to summarize most of the data to form the upper curve in the figure because neither the scratches nor the 550" F exposures had any effect on the ductility of AM 350 substrate. Specimens coated with ZSV and exposed to salt had less ductility on the average than the ZSV speci- mens not exposed to salt. However, reference to the tabular data in the Ap- pendix will show that several of the salt-exposed specimens did retain maxi- mum ductility. The bare specimens exposed to salt also reacted in an e r r a t i c manner not revealed by the average shortening values. A s shown in Table V I I I and the tabulated data in the Appendix, the bare specimens exposed to salt either fractured completely within 800 h r after the start of exposure o r remained intact and exhibited maximum ductility at the end of the exposure.

Therefore, the plotted points a r e averages between zero shortening and maxi- mum shortening, with the average value depending upon the relative number of SOUTHERN RESEARCH INSTITUTE 0 1 3 5 7 Exposure Time, 1000 H r (a) Unscratched, Bare and Coated with Aluminum- Modified Silicone (AMS), Catalytically Cured Silicone (CCS), Zinc in Silicate Vehicle (ZSV), Electrophoretically Deposited Aluminum (EDA), and Flame-Sprayed Aluminum (FSA).

NOSALT SALT

.--- 0 0 - 0 BARE

M AMs e--- 0 0 - 0 ccs .---.

0-0 zsv

tt e---*

0 1 3 5 7 Exposure Time, 1000 Hr Scratched, Bare and Coated with Aluminum- (b) Modified Silicone (AMS), Catalytically Cured Silicone (CCS), Zinc in Silicate Vehicle (ZSV), and Electrophoretically Deposited Aluminum (EDA).

Figure 14. Effects of Humid Salt on TITANIUM 8-1-1 as shown by bend-ductility evaluations.

.--- COMBINATION'

N O S A L T S A L T

e--- 0 - 0 BARE'

.---* 0-0 zsvs

0 1 3 5 7 Exposure Time, 1000 H r Average of all data from the 550' F exposure and from the humid-exposure specimens coated with Aluminum-Modified Silicone and Catalytically Cured Silicone.

Data from all bare specimens in the humid exposure.

Data from all of the humid-exposure specimens coated with Zinc in Silicate Vehicle (ZSV).

Figure 15.

Effects of 550" F Dry Salt and of Humid Salt on A M 350 SCT STAINLESS S T E E L as shown by bend- ductility evaluations.

SOUTHERN RESEARCH INSTITUTE specimens having zero shortening. N o explanation could be found to account of the bare and ZSV-coated substrates in the humid- for the erratic behavior salt environment.

The results from Rene 41 specimens exposed at 550" F a r e shown in The e r r a t i c pattern of the plotted results, in which the salt- Figure 16.

exposed specimens were often more ductile than the "no-salt" specimens, indicates that the Rene 41 substrate was not affected by the hot salt. The r e - s u l t s shown in Figure 17 indicate the same lack of effects from the humid salt.

Both figures show that the specimens coated with ZSV had consistently less ductility than the other specimens, probably because of the previously men- tioned surface roughness found in all of the metallographic specimens involv- ing the ZSV coating.

Metallographic Exam inations : Although a thorough and comprehensive metallographic study w a s beyond the scope of this program, certain selected specimens were sub- jected to metallographic examination in a n effort to help explain the results from the corrosion exposures. The significant microstructures observed a r e reproduced in Figures 18 through 29.

Figure 18 shows the microstructure of the Ti-8-1-1 alloy in the as- A s shown in Figure 18 (a), the longi- received, duplex-annealed condition.

tudinal structure at lOOX magnification and bright-field illumination consisted

cy matrix with small p particles scattered throughout the

of a fine-grained section. The cy matrix itself, however, consists of two types of cy grains.

One type of cy grain is characterized by a clear white appearance, promi- nently etched grain boundaries, an absence of p particles in the grain interiors, of the elongation produced in rolling the material to sheet form.

and retention The other type of cy grain is characterized by a darker and mottled appearance,

less prominent grain boundaries, the presence of p particles in the grain in-

a more equiaxed structure. F o r purposes of discussion, the teriors, and clear, elongated grains were designated primary cy and the other secondary c y .

The differences between the primary and secondary0 , and the ap-

pearance of the p particles is more clearly seen in the 500X bright-field

view in Figure 18 (b). This view shows that the p particles appear in the

grain boundaries of either primary or secondary cy but in the grain interiors

of only the secondary cy . These structural phenomena a r e emphasized under

polarized illumination of the same field, a s shown in Figure 18 (c). Under polarized illumination the primary cy grains appear clear and black, the secondary0 grains a r e a mottled dark gray, and the j 3 particles have a bright crystalline appearance.

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0 1 3 5 7 Exposure Time, 1000 H r (a) Results f r o m USSCRATCHED Specimens B a r e and Coated with Aluminum-Modified Silicone (AMs), Catalytically Cured Silicone (CCS), and Zinc in Silicate Vehicle (ZSV).

N O S A L T SALT

.--- 0-0 BARE

. - - - I 0 - a AMs

I I I I I I I 0 1 3 5 7 Exposure Time, 1000 H r (b) ResuEts f r o m SCRATCHED Specimens Bare and Coated with Aluminum- Modified Silicone (AMs), Catalytically Cured Silicone (CCS), and Zinc in Silicate Vehicle (ZSV).

F i g u r e 16. E f f e c t s of 550" F Dry Salt on RENE 41 as shown by bend- ductility evaluations.

SOUTHERN RESEARCH INSTITUTE 0 1 3 5 7 Exposure Time, 1000 H r (a) Results f r o m UNSCRATCHED Specimens B a r e a n d Coated with Aluminum - Modified Silicone (A MS), Catalytically Cured Silicone (CCS), and Zinc in Silicate Vehicle (ZSV).

N O S A L T SALT 0 1 3 5 7 Exposure Time, 1000 H r (b) Results f r o m SCRATCHED Specimens Bare and Coated with Aluminurn- Modified Silicone (AMS), Catalytically C u r e d Silicone (CCS), and Zinc in Silicate Vehicle (ZSV).

F i g u r e 17. Effects of Humid S a l t on RENE 41 as shown by bend- ductility evaluations.

(a) Bright field.

lOOX (b) Bright field.

500X Figure 18. Ti-8-1-1 original structure p r i o r to exposure. Shows CY matrix with small

p particles and elongated islands of

I f p r i m a r y C Y . 1 1 Longitudinal section.

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The microstructures shown in Figure 18 indicate that there w a s segre- gation of the Q and b stabilizers during the preparation of the alloy. It was not conclusively determined whether this structure has significant influence on the susceptibility of Ti-8-1-1 and other titanium alloys to dry-salt stress corrosion, but the possibility that it does is worthy of further investigation.

Figure 19 presents a comparison of the surface and fracture appearances of two bare Ti-8-1-1 specimens subjected to the 550" F exposure. The speci- men shown in Figure 19 (a) w a s exposed for 5000 h r without salt and exhibited The specimen shown in Figure 19 (b) w a s subjected f u l l ductility in the bend test.

to the 550" F exposure for 1000 h r with salt and had extreme?- J t ' noor &-- ULtility.

The microstructures of these two specimens appear to be identical except for the surface cracks visible in the salt-exposed specimens.

The surface cracks in the embrittled specimen w e r e observed along the surface at areas remote from the fracture, indicating that the cracks w e r e produced by s t r e s s corrosion and were not opened up by the bending operation. In fact, the most severe cracking occurred remote from the fracture. This area of most severe cracking is shown in Figure 20 (a) at the s a m e magnification used for Figure 19 (b).

Some of the characteristics of the cracks are revealed at both lOOX Figure 20. One characteristic is the blunt con- and 500X magnifications in figuration of the ends of the cracks. In view of the apparent intergranular path of the cracks, these blunt ends a r e somewhat surprising. and no sug- gested explanation a p p e a r s to be completely satisfactory. Although the stresses in the self-loaded specimen would be expected to decrease below the threshold for s t r e s s corrosion with increasing depth below the surface, it is unlikely that this phenomenon would produce the blunt ends until all cracks had reached approximately the same depth.

Another characteristic of the cracks is that many of them are dis- continuous in the plane of the c r o s s section as shown in Figure 20 (b).

a further indication of the Such apparent discontinuities a r e undoubtedly intergranular path of the cracks, but it is interesting to note that the dis- continuities tend to occur at intersections with the p r i m a r y 0 grains, pro- viding a n indication that the p r i m a r y a might be more resistant to stress- corrosion cracking.

Figure 21 shows microsections of bare Ti-8-1-1 specimens that w e r e purposely damaged with scratches prior to 500 h r exposures at 550" F. The specimen in Figure 2 1 (a) exposed without salt w a s embrit- tled by the scratch (1.68 in. shortening) and the specimen in Figure 21 (b) was further embrittled by salt (0.21 in. shortening). Yet, no cracks w e r e SOUTHERN RESEARCH INSTITUTE (a) 5000 h r with no salt,. lOOX (b) 1000 h r with salt. 1OOX Figure 19. Ti-8-1-1 ductile and brittle f r a c t u r e s after ex- posure at 550" F. (a) Specimen TOUlHsA, 5000 h r with no salt and (b) Specimen TOU2H1C, 1000 h r with salt. Shows stress-corrosion cracks on surface of embrittled specimen (b).

(a) 1 0 0 ~ (b) 500X Figure 20. Ti-8-1-1 stress-corrosion cracks. Most s e v e r e cracks in bare specimen TOU2H1C subjected to Most s e v e r e crack- 1000 hr a t 550" F c.ith salt.

ing was a t location away from fracture.

(a) NO salt. IOOX (b) W i t h salt. 1ooX Ti-8-1-1 f r a c t u r e surfaces of scratched bare speci- Figure 21.

mens after 5000 hr exposure at 550" F.

(a) Specimen TODlHsA, no salt, 1.68 in. shortening.

(b) Specimen TODZHSB, with salt, 0.21 in. shortening.

found in the surface of the salt-embrittled specimen. It is indicated, there- fore, that either all surface cracks were accidentally missed in the plane of the c r o s s section o r that the stress-corrosion attack w a s confined to the scratches.

Sections of Ti-8-1-1 specimens coated with Aluminum-Modified Silicon (AMS) and with Zinc in Silicate Vehicle (ZSV) are shown in Figure 22. No stress-corrosion cracks were found in either specimen even though the AMS specimen, Figure 22 (a), was ductile and the ZSV specimen, Figure 22 (b), w a s embrittled. Figure 22 reveals that the surface of the embrittled speci- men has been rougnened and grossly disturbed, apparentiy in preparation for the ZSV coating. The surface under the ductile specimen coated with AMS w a s smooth and undisturbed.

Both sections a r e shown under polarized illumi- nation in order to make the coating more visible.

Specimens coated with Catalytically Cured Silicone were not metallo- graphically examined because the coating spalled from the substrate in the 550" F exposure, and all specimens from all exposures w e r e ductile in the bend test.

Microsections of a Ti-8- 1- 1 specimen coated with Electrophoretically Deposited Aluminum (EDA) and exposed to 550" F for 5000 h r with salt a r e shown in Figure 23. A view of the brittle fracture is shown in Figure 23 (a).

No outstanding stress corrosion cracks w e r e found in any part of this longi- tudinal section. A t higher magnification, 500X in Figure 23 (b), quite s m a l l openings perpendicular to the substrate surface were observed.

These openings w e r e s o small that their significance is doubtful, but they w e r e unique to this specimen. w e r e ex- Since the edges of the EDA specimens posed and the section shown is a longitudinal section through the interior of the specimen, the small openings might be lateral extensions of deeper edge 23 (c) shows the appearance of the coating a t lOOX magnifi- cracks. Figure cation under polarized light.

Figure 24 shows microsections of a Ti-8-1-1 specimen coated with 550" F for 5000 hr.

Flame-Sprayed Aluminum (FSA) and exposed with salt to Figure 24 (a) shows the a r e a near the brittle fracture and Figure 24 (b) is a polarized-light view showing the appearance of the coating and the disturbed surface. No stress-corrosion cracks w e r e observed and the em- substrate brittlement w a s probably caused by the substrate surface conditions.

Several specimens of ~ i - 8 - 1 - 1 exposed to the humid atmosphere w e r e examined but not photographed because there were no significant changes in A l l of the titanium-alloy specimens ex- the basic structure of the substrate.

posed to the humid atmosphere w e r e ductile unless embrittled by scratched o r roughened surfaces. The AM 350 SCT substrate, on the other hand, w a s SOUTHERN RESEARCH INSTITUTE (a) AMS coating. 1OOX (b) ZSV coating. 1ooX Figure 22. Coated Ti-8-1-1 exposed with salt at 550" F for 5000 hr. (a) Ductile specimen T1U2H5B coated with Aluminum-Modified Silicone (AMs).

(b) Brittle specimen T3U2H5C coated with Zinc in Silicate Vehicle (ZSV). Taken with polarized light.

(a) Fracture. 1ooX (b) Fine surface (c) Coating shown cracks. 500X with polarized light. lOOX Figure 23. Ti-8- 1- 1 coated with Electrophoretically Deposited Specimen T4U2H5B exposed 5000 Aluminum (EDA).

h r with salt a t 550" F. Brittle failure.

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(a) Fracture. 1ooX (b) Coating shown with polarized light. 1OOX Figure 24. Ti-8-1-1 coated with Flame-Sprayed Aluminum (FSA). Specimen T5U2H5B. Exposed 5000 h r with salt at 550" F. Brittle failure.

resistant to corrosion at 550" F but did undergo attack in some specimens in the humid atmosphere.

The structure of the SCT heat-treated AM 350 prior to corrosion ex- The posures is shown in Figure 25 at 1OOX (a) and 500X (b) magnifications.

structure consisted of small elongated ferrite grains in a fine martensitic matrix.

As previously shown in the r e s u l t s plotted in Figure 15, humid salt exposures had a n average embrittling effect on bare A M 350. The actual at- tack, however, w a s concentrated only OE c e r b k specimens and caused frac- t u r e s to occur within 800 h r at a location approximately 3/8 in. from a t a b end while the specimens w e r e still on the exposure rack. Other specimens, the f u l l exposure apparently identical in preparation and exposure, withstood times and retained f u l l ductility in the bend test.

Microsections in the vicinity of the fracture in one of the failed AM 350 specimens are shown in Figures 26 (a) and 26 (b).

The section in Figure 26 (a) shows a large crack extending angularly between the fracture surface and the surface of the specimen. Neither end of the crack extends to the surface in 26 (b) shows a portion of the crack at the plane of the microsection. Figure higher magnification and indicates that it is predominently intergranular, al- though the poor definition of the grain boundaries makes it difficult to be c e r - tain. The lack of perpendicular surface cracks and the position and direction of the large crack indicate that the attack w a s not stress corrosion but stress- accelerated general corrosion. Further evidence of the general corrosion was found in the specimen shown in Figure 26 (c). This view shows s m a l l corro- sion cracks extending into the specimen from the concave surface of one of the ductile bend specimens. The location of the cracks on the surface sub- jected to compressive stresses during the exposures indicates that tensile s t r e s s e s from external sources were not necessary for corrosive attack when it occurred.

The only coated specimens of AM 350 that had reduced ductility were some that w e r e coated with Zinc in Silicate Vehicle and exposed to humid salt.

Metallographic examination revealed no corrosive attack from the salt but did show that the substrate surfaces of ductile and embrittled specimens had been considerably distorted, apparently in preparation f o r the coating. A s shown in Figure 27, the maximum surface roughness w a s greater in the em- brittled specimen than in the ductile specimen. The metallographic examina- tion did not reveal, however, why the reduced ductilities w e r e confined to specimens exposed to salt.

The r e s u l t s from the bend-ductility tests of Rene 41 specimens (Figures 16 and 17) indicated that the inherent bend ductility of that substrate was lower SOUTHERN RESEARCH INSTITUTE

(2) 1oox

(b) 500X Figure 25. A M 350 S C T original structure prior to exposure.

Shows elongated f e r r i t e in martensitic matrix.

(a) Internal crack. lOOX (b) Internal crack.

(c) Cracks in concave 500X surface. 500X Figure 26. Cracks in b a r e unscratched AM 350 SCT exposed to humid salt at 95" F.

(a) and (b), Specimen AOU2L5A, show internal c r a c k at angle to brittle- f r a c t u r e surface. (c) shows s m a l l c r a c k s at con- cave surface on f u l l - ductility specimen AOU2L5B.

(a) Ductile specimen. 500X (b) Brittle Specimen. 500X Figure 27.

Maximum surface roughness of AM 350 SCT sub- s t r a t e coated with Zinc in Silicate Vehicle (ZSV).

(a) Specimen A3U2LlA with good bend ductility.

(b) Specimen A3D2L1B with poor bend ductility.

Both specimens exposed to humid salt at 95" F for 1000 hr.

and more e r r a t i c than the bend ductility of the other two substrates. The microstructure of Rene 41 in the heat-treated-and-aged condition prior to the exposures is shown in Figure 28. The view at lOOX magnification in Figure 28 (a) shows the s t r u c t u r e to consist of a matrix with small carbides precipitated at the grain and twin boundaries and more massive carbides scattered at random. The matrix, however, appears to consist of two sets of grains: one "old" set of large grain size on which the fine carbides are precipitated, and one set of "new" twins and small grains o r subgrains on are not precipitated. The distinction between the old and which carbides new grains is shown in Figure 28 (b), which is a higher magnification view of the subgrain complex at the 8 o'clock position on the large grain in the center of Figure 28 (a). Figure 28 (c) is an identical view taken with polarized illu- mination to emphasize the carbide locations. The s t r u c t u r e indicates that- the final solution heat treatment partially recrystallized the previous grain s t r u c t u r e but did not dissolve the carbides for f u r t h e r precipitation on the the subsequent aging treatment.

new twin and grain boundaries during Further investigation would be necessary to determine whether structure w a s influential in producing the wide scatter observed in the bend-ductility results.

The only consistent feature of the Rene 41 bend-ductility results w a s that the specimens coated with Zinc in Silicate Vehicle (ZSV) exhibited ducti- The metallographic exami- lities at the lower boundary of the scatter band.

nation failed to reveal the cause of lower ductilities in the ZSV specimens, but it may be logically surmised that they w e r e probably caused by the surface-roughening treatments observed to produce reduced bend ductilities in the other two substrates.

Figure 29 shows the s t r u c t u r e s at the fracture surfaces of two speci- mens exposed for 5000 h r at 550" F. The specimen in Figure 29 (a) w a s ex- posed with salt but produced no evidence of attack by the salt. The fracture in the unsalted specimen shown in Figure 29 (b) w a s quite similar to that of Some surface cracks like those visible in the salt-exposed specimen.

Figure 29 (b) w e r e present in the unsalted specimen but they w e r e located only near the fracture and w e r e probably opened up during the bend-ductility tests.

SOUTHERN RESEARCH INSTITUTE .

General view.

lOOX Bright- f ield view of old and new twins.

500X Polarized-light view of old and new twins.

500X Figure 28. Rene 41 original structure p r i o r to exposure.

Shows precipitated carbides in old grain and twin boundaries, and new grain and twin boundaries without precipitated carbides.

(a) With salt. 1 0 0 ~ (b) No salt. lOOX Figure 29. Rene 41 brittle fractures after exposure to 550" F f o r 5000 hr. Shows intergranular f r a c t u r e s in (a) Specimen ROU2H5A with salt and (b) Specimen ROU1H5B without salt.

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Survey of Airframe Manufacturers: Although the results from the survey of five airframe manufacturers were conflicting in several details, they did provide a valuable overall evalua- A tion of the coatings program and assessment of the needs for the future.

recapitulation of the questionnaire used in the survey, and of the answers given, are included in the Appendix. The following is a summary of the pre- valent opinions obtained from the formal interviews with the five airframe manufacturers and from an informal interview (questionnaire w a s not used as '-=le basis for the dracussion) with one eiigirie manufacturer, The conclusions reached by Southern Research Institute with respect to the most promising coatings, that is, Aluminum-Modified Silicone and Catalytically Cured Silicone w e r e considered to be generally correct. How- ever, because of SST requirements f o r high emissivity in the infra-red (IR) range, Aluminum-Modified Silicone, the first choice on the basis of the ex- perimental program, has been given little consideration f o r skin areas of Catalytically Cured Silicones with white pigmentation are, however, the SST.

the most promising formulations currently available. The spalling problem encountered with Catalytically Cured Silicone in the experimental program has been overcome in the formulations developed by various paint manufacturers working with the a i r f r a m e companies. In engine areas, where IR emissivity is not a critical consideration and temperature exposures might be on the o r - der of 800 to 900" F, Aluminum-Modified Silicones appear to be most advan- tageous.

Within the scope of the experimental program, no coatings are known to be superior to those found most promising by Southern Research Institute.

On the other hand, slight changes in requirements, o r specific requirements for local areas, could increase the feasibility of some of the types of coat- ings that have been screened out of the promising list. F o r example, it ap- pears possible that more refined SST design will allow large portions of the skin to operate at maximum temperatures on the order of 450" F. A t this maximum temperature, polyimide coatings appear promising if improvements can be made toward room-temperature curing and better color stability in pigments. Cermet types of coatings offer some possibilities in local engine areas where temperature o r abrasion requirements are too great f o r the Aluminum-Modified Silicones. Metallic coatings such as aluminum cladding offer some possibilities but, since IR emissivity control is a critical con- sideration, top coatings would still be necessary on the aluminum surface.

Among the properties not included in this investigation, the IR emissivity to absorptivity ratio is considered to be of primary importance.

High emissivity (0.8 o r greater) is a necessity not only for reducing the SOUTHERN RESEARCH INSTlTUTE temperature exposure of skin and coating materials but, more importantly, for weight reductions in insulation and cooling requirements for the interior of the aircraft. Therefore, the suitability of a skin coating will be largely determined by the temperature reductions the coating can provide by means of J R radiation. Solar reflectivity was considered to be of much less im- portance for temperature control.

A general consensus was not reached on the relative importance of These other properties, listed more or l e s s in other coating properties.

descending order of majority opinion of their importance, were: 1. Ultraviolet, weathering, and thermal-cycling resistance.

2. Resistance to hydraulic oils, fuels, and similar fluids.

3. Abrasion resistance.

4. Resistance to combinations of elevated temperature and reduced pres s u r e.

5 . Resistance to rain erosion.

6. Aerodynamic smoothing.

Flexibility a t high and low temperatures.

7.

8. Electrical conductivity.

9. Hardness before, during, and after temperature exposures.

In answer to the specific question pertaining to the importance of r e - sistance to rain erosion, most of respondents considered it to be of minor im- SST program. Most of the skin a r e a s of the SST will present a portance in the low angle of attack to the rain and will not be subject to erosion. Rain erosion w i l l be a problem on leading edges but the SST designs do not call for coatings at these areas.

The airframe manufacturers do not consider problems with hot-salt s t r e s s corrosion and with heat tinting of skin surfaces to be serious enough It was unanimously agreed that the lack in themselves to require coatings.

of known stress-corrosion effects in current aircraft using titanium alloys, the apparent ability of titanium alloys to r e s i s t s t r e s s corrosion from cyclic exposures, and the improvements in notch ductility produced by special heat treatments w i l l make coatings unnecessary for stress-corrosion protection.

Heat tinting discolorations of SST skins would be acceptable from a technical standpoint, b u t it was generally agreed that airlines would probably require coatings for the sake of appearance.

Opinions were somewhat divided on the probable effects of differences The majority in pressure between ground conditions and flight conditions.

opinion w a s that serious adhesion and stability problems would a r i s e with most coatings when they a r e heated to the 450-500" F temperature range in the reduced pressures existing at 65,000 to 75,000 ft. (30 mm Hg). There- fore, candidate coatings must be evaluated under these conditions. In the at minority opinion, however, coatings that meet temperature requirements ambient pressures w i l l meet the same temperature requirements in the par- tial vacuum at cruising altitudes, provided that the coating has been completely cured before subjection to the reduced pressure.

Titanium alloys, particularly Ti-8- 1-1, are the leading candidates for the skin material on SST aircraft. Both the Ti-8-1-1 and Ti-6A1-4V, the second leading candidate, will probably be used with special heat treat- ments for improving notch ductility and resistance to stress corrosion and wet crack propagation. Other titanium alloys mentioned w e r e Ti-4A1-3Mo-lV and Ti-5A1-2.5Sn. Ti-8-1-1 appears to be the leading candidate for engine applications also.

There w a s a wide range of opinions on whether it would be valuable for the Government to sponsor development of coatings, primers, and s u r - face preparations specifically oriented toward SST requirements. The majority opinion was that the sponsorship of development of improved resins and poly- m e r s would probably be valuable, whereas sponsorship of surface preparation and p r i m e r studies would be of doubtful value. There w e r e several expressions, however, of the need for the development of a target o r tentative specification that could be used by coating suppliers for evaluating imovations in vehicles, fillers, and formulations.

Preliminary Evaluation of Additional Coatings: The results from the preliminary evaluation of additional coatings not included in earlier parts of the program are listed in Table M. These coat- ings are identified by general t e r m s in the table, but more specific identifica- tion is available in Table X in the Appendix. On the basis of the preliminary of the ad- evaluation and visual observation of the as-received samples, none ditional coatings would be expected to be superior for SST service in compari- son with Aluminum-Modified Silicone or Catalytically Cured Silicones.

The Phenolic-Vinyl-Metallic Compound has some desirable characteris- tics in that it was reported to have high emissivity properties at 500" F, and it provided excellent protection of the substrate in salt spray. Its adherence to the Ti-8-1-1 substrate was poor, however, and this shortcoming must be cor- rected before it could be given further consideration f o r SST service.

The Ceramic-Bonded Aluminum adhered well to the titanium-alloy substrate and provided good protection in salt spray. In comparison with Aluminum-Modified Silicone, however, it requires excessively high curing SOUTHERN RESEARCH INSTITUTE , Effects of Temperature Cycling(l) and Salt Spray( a ) on Table IX.

Additional Coatings Temperature Cycling( Salt Spray(8) Phenolic-Vinyl-Metallic Compound, 0.7 mils thick, dull black color.

Undamaged Specimen: No rust or significant Coating lost adherence and spalled from sub- change in coating appearance strate during first cycle at temperature.

Damaged Specimen: Rust streaks from the damaged spots but no changes otherwise.

Ceramic-Bonded Aluminum, 650" F Cure, 2-3 mils thick, dull light-gray color.

slightly to darker gray. Undamaged Specimen: N o rust or significant Color changed change in coating appearance.

Adherence not affected.

Damaged Specimen: 3 pin-point spots o f rust apparently caused by external contamina- tion. Damaged spots showed no rust but had slight amount of white corrosion pro- duct from the coating.

Ceramic-Bonded Aluminum, 1000" F Cure, 2-3 mils thick, dull light-gray color.

I

Undamaged Specimen N o rust, but color No discernible changes.

darkened and fine white corrosion product formed.

Damaged Specimen N o rust, but color darkened and much fine white corrosion product formed, particularly at damaged spots.

Silicate-Bonded Zinc + Silicate Stainless, 5-6 mils thick, dull gray color.

Color changed toward light straw color. Undamaged Specimen: 3 pin-point spots of rust Adherence not affected. apparently caused by external contamina- Some staining from fine white corro- tion.

sion product.

Damaged Specimen: 8 pin-point spots of rust apparently caused by external contamina- tion. Light rust-colored stains and stain- ing from fine white corrosion product.

Light rusting at impact damage but none at penetrator damage.

Silicate Stainless, 5-6 mils thick, dull gray color.

I

Color changed toward straw color.

Undamaged Specimen: General rusting over Adherence not affected. complete surface.

Damaged Specimen: General rusting over com- plete surface but more severe below the Light rusting at impact damaged spots.

damage but none at penetrator damage.

( I ) Tested on Ti-8-1-1 panels. 4 cycles except that panels were Heated to 650" F for 1 hr, air cooled, for spray quenched after 3rd heating cycle.

( a ) Tested on 4130 steel panels, 1 a s received, and 1 damaged at 1 spot with 4 ft-lb impact blow and at 3 spots with Rockwell "C" hardness penetrations.

temperature f o r color retention and is not as smooth and attractive in appear- ance. In comparison with Catalytically Cured Silicone, it has low emittance as w e l l as the high curing temperature.

The double coating of Silicate-Bonded Zinc plus Silicate Stainless ad- hered w e l l and provided adequate corrosion protection, but its color stability when heated to 650" F on titanium-alloy was poor, Also, its original appear- ance is not as smooth o r attractive as the leading coatings. When used alone, the Silicate Stqinless provided inadequate corrosion protection and discolored when heated to 650" F, DISCUSSION Substrates : Among the three substrates included in this evaluation, the Ti-8-1-1 alloy w a s apparently the only one that w a s consistently susceptible to stress corrosion in one of the environmental conditions included in the program.

Rene 41 was apparently unaffected by salt, either in the humid or 550" F ex- posures, although its inherently erratic bend ductility resulted in some shortening values on the same order as those from the salt-embrittled tita- nium alloy. The AM 350 SCT substrate exhibited a consistent immunity to corrosion in the hot-salt environment (550" F) but was inconsistently attacked in the humid-salt environment. Although the few specimens that w e r e at- tac ke d might have failed by str es s - c orr os ion or s tr es s - a c c e le rated- cor r os ion the complete immunity of the other replicate specimens indi- mechanisms, cates that some uncontrolled factor (such a s , possibly, fortuitous mode of contact with the welding-rod supports in the exposure racks) was necessary in addition to the presence of humid salt. In accordance with prior expecta- tions, the '33-8-1-1 substrate w a s readily susceptible to s t r e s s corrosion f r o m dry salt at 550" F but was resistant to embrittlement from humid salt even when previously damaged with cross scratches. Apparently the notch these scratches was not severe enough to cause crack initiation formed by and propagation to parallel the reduced fracture toughness that has been ce- ported (5) for pre-cracked high-strength titanium alloys in the presence of wet salt.

The interviews with personnel employed by airframe manufacturers make it clear that Ti-8-1-1 or other high-strength titanium alloys are, by far, the most likely materials for use on the outer skin of SST aircraft. It is also clear that these personnel do not consider the stress-corrosion problem to be a critical one, despite the great susceptibility the favored alloys have shown in laboratory tests in hot-salt environment under sustained loads on SOUTHERN RESEARCH INSTITUTE This confidence in the ability of titanium to with- the order of 8 h r o r more.

stand the stress-corrosion threat is mostly based on the following factors: l. Special heat treatments improve the notch ductility of the titanium al- loys and reduce susceptibility to stress corrosion.

Stress corrosion has not arisen as a problem in existing supersonic 2.

aircraft using titanium alloys.

Laboratory tests using cyclic exposures similar to the cyclic condi- 3.

tions expected in SST service have not produced stress-corrosion cracking.

The "working" coatings necessary for temperature control of the 4.

outer skin will simultaneously protect the substrate from exposure to dry salt.

The maximum skin temperature expected to occur with the latest 5.

SST designs has been decreased to near the threshold temperature (approximately 450" F) below which stress corrosion of titanium alloys has not been found to occur.

Regardless of the above arguments to the contrary, the many laboratory demonstrations of the rapid deterioration of stressed titanium alloys when ex- posed to small quantities of hot salt make it imperative that the stress-corrosion problem be given serious consideration. In addition, reasonable arguments can be given to counter those used to depreciate the potential danger of stress- corrosion failures. Examples of such arguments are: 1. Special heat treatments that completely eliminate the susceptibility to s t r e s s corrosion have not yet been developed for the titanium al- loys most favored f o r SST service.

Existing supersonic aircraft a r e not subject to the s a m e operational, 2.

maintenance, and exposure conditions that will be imposed in com- mercial SST service.

3. Some SST flight schedules, particularly in future generations, are likely to exceed the cyclic exposure times that have been investigated in the laboratory, and could approach the shortest times that have produced stress corrosion in steady-state laboratory tests.

4. The high-emissivity "working'' coatings w i l l protect from stress corrosion only if they are applied and maintained on all areas sub- jected to stress corrosion exposure regardless of whether tempera- t u r e control is required in those areas.

5 . Maximum skin temperatures i n the latest SST designs are still above the threshold temperature f o r stress-corrosion failures and there is no assurance that the design temperatures will not sometimes be ex- ceeded on operating aircraft.

Embrittiernent Mechanisms: The several investigations that are underway to determine the mechanism of stress-corrosion cracking have not yet resulted in a satisfactory explanation (6). I t i s ell -b-nwn that stress corrosion cracks in the titanium alloys are intergranular, and there has been some indication that segregations of some of the alloyiig elements might contribute to the cracking.

The metallographic examinations made in this investigation confirm the intergranular path of the stress-corrosion cracks. A s shown in Figures 18 and 20, there is also some indication that segregations might be involved.

20 appear to occur at grains of the The crack interruptions shown in Figure elongated "primary a.

There is a possibility that the improvement in notch ductility (and heat treatments is stress-corrosion resistance) brought about by special due, at least in part, to greater homogeneity in the heat-treated structure, However, unless the heat treatments eliminate the characteristically elongated "primary a , complete homogeneity will not be achieved. It would appear, therefore, that special homogenizing treatments before o r during the reduction from billet to sheet form might be more effective than special heat treatments of the finished sheet. Homogenizing treatments at early stages in processing might make it possible to achieve stress-corrosion resistance with conventional heat treating of the final sheet, and without com- promising the optimum strength characteristics. Investigation of the possi- ble improvements from early homogenizing treatments would probably be worthwhile, SST Coating Requirements: In the opinions of the interviewed airframe representatives, high emissivity in the IR range will be the ruling criterion for choice of an SST skin coating from among those coatings that can withstand the exposure temperatures and that can be cured at room temperature, preferably, o r at reasonable elevated temperatures. The results of this and other investigations indicate that protection from stress corrosion might be of equal importance.

Fortunately, the same basic type of coating can s e r v e to meet both of these criteria in the temperature range of interest.

~~ SOUTHERN RESEARCH INSTITUTE From the standpoint of s t r e s s corrosion, it appears that any paint- type coating that is impervious to wet salt will protect titanium substrates from s t r e s s corrosion if it remains stable and retains adherence at the Aluminum-Modified Silicone is the only coating temperatures involved.

that has consistently withstood the exposures involved in the investigation Catalytically Cured Silicone has also per- at Southern Research Institute.

formed well until the current investigation, in which it shredded and spalled F. However, the a i r f r a m e companies from the substrate when exposed to 550" have found similar coatings to perform well and, in this investigation, the coating had withstood heating to 650" F in previous exposures on other sub- strates. It can be assumed, then, that Catalytically Cured Silicones are satisfactory if care is taken to assure that the application technique and formulation used w i l l provide adherence to titanium alloys. Because of the many concomitant requirements that have been mentioned previously in this report, it is doubtful that any of the other types of coatings involved in this investigation can successfully compete for SST service in their present form.

From the standpoint of IR emissivity, Aluminum-Modified Silicone, even if formulated to cure catalytically, is not a satisfactory coating be- cause of the low emissivity characteristics of the aluminum pigment. The white-pigmented Catalytically Cured Silicones, on the other hand, possess attractively high IR emissivities. Therefore, Catalytically Cured Silicone, properly pigmented and formulated for elevated- temperature adherence to titanium alloys, is judged to be the most promising coating f o r major a r e a s of the skin of SST aircraft. In local a r e a s where IR emissivity is not the controlling factor, coatings should be employed for stress-corrosion protec- w i l l probably provide superior protection tion. Aluminum-Modified Silicone for these a r e a s if it can be formulated to cure catalytically without compro- mising the properties available in the bake-cured coatings. Unpublished re- sults obtained in an investigation by a leading engine manufacturer have shown that a baked Aluminum - Modified Silicone provided meaningful s t r e s s - corrosion protection of engine components at temperatures up to 900" F.

The baked coatings a r e feasible f o r the relatively small engine components since their size makes oven- baking practical.

CONCLUSIONS Duplex annealed Ti-8-1-1 is readily susceptible to stress corrosion 1.

from hot salt at 550" F. It is apparently not attacked by humid salt at 95" F within 7000 hr. As measured by bend-ductility shortening, complete deterioration from stress corrosion occurred within 1000 h r of exposure to the hot salt.

The AM 350 SCT stainless steel is resistant to stress-corrosion at- 2.

tack from hot salt at 550" F but, depending upon other undefined con- ditions, can be rapidly attacked by humid salt a t 95" F.

Rene 41 is apparently resistant to stress-corrosion attack from salt 3 .

either in the hot condition at 550" F o r the humid condition at 95" F.

However, its inherent ductility, in the heat-treated condition used for these experiments, is frequently as low as salt-embrittled speci- mens of the other substrates.

Because of the demonstrated potential danger from stress corrosion 4 .

of titanium alloys in the presence of hot salt, all titanium areas of the SST will probably require protection with a suitable coating regard- less of whether coatings a r e needed for other reasons such as control of I R em is sivity.

All of the coatings evaluated in this investigation are apparently 5 .

capable of preventing s t r e s s corrosion of the three substrates evaluated. However, because of concomitant requirements f o r SST service, only Aluminum-Modified Silicone and Catalytically Cured Silicone appear to be satisfactory unless operating temperatures re- main below 450" F.

6. If SST operating temperatures remain below 450" F, other coatings previously screened out in earlier investigations of this program (polyimide coatings, for example) might become leading candidates f o r SST service.

7. Because of the need for coatings to provide high I R emissivity on large areas of the SST outer skin, white-pigmented Catalytically Cured Silicone is the most feasible commercially available coat- ing. In areas not subject to IR control, Aluminum-Modified Silicone is probably superior, especially in engine areas and on engine com- ponents exposed to temperatures up to 900" F.

~~~ SOUTHERN RESEARCH INSTITUTE Because of slight but significant differences in formulations from one 8 .

supplier to another, coatings for SST service must ultimately be evaluated on the basis of supplier or trade name rather than on the basis of fundamental type used in this investigation.

In order to provide standard requirements and test methods f o r 9.

f u t u r e evaluations and screening of attempted coating improvements, it would be desirable to develop a target specification for supersonic- aircraft coatings. Because of the difficulties in compromising dif- ferences of opinion among the various aircraft manufacturers and a specification must probably be de- coating manufacturers, such veloped by a neutral agency under Government sponsorship.

10. The current attempts to improve the stress-corrosion resistance of titanium alloys by special heat treatments of finish :d sheet should be supplemented by investigations of the feasibility of providing more homogeneous structures by means of complementary heating and roll- ing treatments in the early stages of sheet production.

Submitted by: A. Clyde Willhelm Re search Metallurgist W Assistant Metallurgist Approved:

/,/-

J. R. Kattus, Director Metallurgy R e search Birmingham, Alabama March 23, 1966 7685- 1417-XV REFERENCES 1. Holder, S . G . , Jr. and Willhelm, A. C., "Protective Coatings for Sheet Metals in Supersonic Transport Aircraft, It final summary r e - port f r o m Southern Research Institute to NASA on contract NASr-117, 15 June 1963.

Y I 2. Honeycutt, J. O . , Jr. and Willhelm, A. C., Evaluation of Protec- I # tive Coatings for Skin Materials on Supersonic Transport Aircraft, final summary report f r o m Southern Research Institute to NASA on Contract NASr-117, 24 June 1964.

3. Mallory-Sharon Titanium Corp., Pratt &Whitney Aircraft, e t al: I t P r o g r e s s Report on the Salt Corrosion of Titanium Alloys at Elevated Temperature and Stress, TML Report No. 88 (Contract No. A F 18(600)-1375), Battelle Memorial Institute, 20 Nov. 1957.

4. Braski, D. N., and Heimerl, G. J., "The Relative Susceptibility of Four Commercial Titanium Alloys to Salt Stress Corrosion at 550" F, " NASA Technical Note 0-2011, Langley Research Center, Hampton, Va., 1963.

1 1 5. Pellini, W. S . , et al, Review of Concepts and Status of Procedures f o r Fracture -Safe Design of Complex Welded Structures Involving Metals of Low to Ultra-High Strength Levels, '' NRL Report 6300, June 1965.

6. Minutes of the Twelfth Meeting of NASA Special Committee on Materials Research for Supersonic Transports, Washington, D. C. , February 1965.

SOUTHERN RESEARCH INSTITUTE

APPENDIX Page

-

Descriptionof Coatings . . . . . . . .

Questionnaire onSST Coatings . . . . . . .

Bend-Ductility Data Tables . . . . . . . .

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m SOUTHERN RESEARCH INSTITUTE QUESTIONNAIRE O N SST COATINGS The following questionnaire was used as the basis f o r personal interviews with technical personnel of five leading airframe manufacturers identified herein as companies A through E. The summary answers provided by the interviewed personnel are listed immediately following each question.

Of the five aircraft companies involved, companies A, C, and E have had extensive manufacturing or design experience with supersonic aircraft and companies B and D have not.

1 . The results from the investigations at Southern Research Institute

show that resin coatings of the silicone type (Aluminum-Modified Silicone and Catalytically cured silicone) show the most promise among existing coatings for SST service.

Based on your experience, what is your opinion of these results?

n Concur completely C Substantially correct Inconclusive

0 Disagree Other comment

Other Comment: A Polyimide coatings, cermet coatings offer possibilities.

B. Air-cured coatings necessary.

C. Desire catalytically cured system, stable decorative colors, Amount and choice of fillers good far-infra-red emittance.

effects on IR emissivity.

would be guided by D. No experience in this requirement range.

E. Flat white catalytically cured silicone is the best a t present.

2. Are you aware of a more promising coating not covered in the investigation at Southern Research Institute? If so, what?

A. Polyimide (up to 450°F).

B. No.

SOUTHERN RESEARCH INSTITUTE C. No. However, roll cladding o r dip-coating w i t h aluminum is Paint would still be needed f o r IR emittance.

a possibility.

Polyimides have some promise except f o r curing temperatures and pigment dis color at ion.

D. No.

E. Flat white catalytically cured silicone (also available in gloss and semi-gloss).

3. Of the properties not investigated by Southern Research Institute, w h i c h do you consider the most important f o r f u t u r e investigation?

Indicate order of importance by 1, 2, 3, etc.

Rain-erosion IR Absorpti- Hydraulic fluids

m

and fuels lD3) Electrical

Ultraviolet resistance conductivity resistance Others: C2. Flexibility at -65°F and at 500°F.

C3. Reduced pressure (30 mm Hg).

C5. Hardness before, during,and after temperature exposure.

C6. Weathering and thermal cycling.

El. Weight loss at elevated temperature and reduced pressure El. Aerodynamic smoothing.

4. Do you expect resistance to rain erosion to be important i n a coating f o r SST service ?

P r i m a r y importance Significant importance

Insignificant importance a N o importance

Other comment: A. Might be important on radomes.

C and E. Important only at leading edges where more effective materials might be used.

5. In the investigations at Southern Research Institute, comparisons have purposely been restricted mostly to coatings of different types. Do you believe comparisons should also be made between competitive coatings (trade names) that fall WitIiin the same type?

a No

~ Yes Other: B. Suppliers should work to pre -specified requirements.

C. Yes, particularly for paint coatings.

E. Many suppliers important to aircraft industry w e r e not included in the original survey.

6. Do you expect hot-salt s t r e s s corrosion to be such a serious problem that protective coatings will be required for that reason alone, if for no other reason?

D Yes

Other: A. Wet crack propagation important in engine areas.

B. Not convinced it is a serious problem but possibility of problem should be recognized.

D. Some possibility of problem, especially wet crack propagation.

SOUTHERN RESEARCH INSTITUTE 7. Do you expect heat-tinting to be such a serious problem that protective coatings w i l l be required for that reason alone, if for no other reason:

B Yes

Other: C. A i r l i n e customers might need convincing, however.

E. Coatings needed f o r appearance even if heat-tinting is not a problem.

8. Do you expect the differences in pressure between ground condi- tions and flight conditions to be significant in the performance of coatings ?

4 Y e s

Other: B. Effects on adhesion.

D. But should be considered.

9. In your poinion what a r e the three leading candidates for the skin material on SST aircraft?

A B C 1. Ti-8-1-1 Ti-8-1-1 Ti-6 -4 (Special Heat Treatment) 2. Ti-6-4 Ti-6 -4 Ti-4Al-3Mo-lV (Special Heat Treatment

3. - Ti-5A1-2.5Sn Ti-8-1 -1 (Mill Annealed)

D E

1. Ti-8-1-1 o r Ti-6-4 -

2. P H Stainless Steels -

3. INCO718 -

10. In your opinion would it be valuable for the Government to

sponsor coating development specifically oriented toward SST coating requirements ?

Ex t re mely valuable Valuable

Doubtfully valuable 0 N o v a l u e

Comment: C. Opinion divided, depending upon type of development.

D. Only in context of the question and current approach to SST development.

E. But problem not critical.

11. In your opinion would it be valuable for the Government to sponsor

a study of surface preparation and primers to improve the adherence (and, possibly, the performance) of the more promising c oat ings ?

Extremely valuable Valuable

Doubtfully valuable D No v a l u e

12. From the standpoint, of aircraft manufacture, which type of

coating would be most preferable? Designate order of preference with 1, 2, 3, etc.

n A solid, rolled, metal coating (such as electrophoretically

deposited aluminum) that would be obtained on the original sheet, that would be formed along with the sheet, that would require edge protection only, and that would not require replacement f o r the life of the aircraft.

SOUTHERN RESEARCH INSTITUTE

a A paint-type resin coating that would be sprayed on after

assembly, that would require heat curing at temperatures up to 45OoF, that would require replacement a t 2-year overhaul periods, and that would require occasional touch-up repair.

A paint-type resin coating that would be sprayed on after assembly, that would cure at room temperature, that would require replacement annually, and that would require more frequent touch-up repair.

An electroplated metallic coating that would be deposited after forming but before assembly, that would require replacement at 5-year periods, and that would require infrequent touch-up repair by a Dalic- type process.

A flame-sprayed ceramic coating that would be applied after assembly, that would require replacement at 5-year periods, and that would require occasional touch-up repair.

n A flame-sprayed metallic coating that would be applied after

assembly, that would require replacement at 2-yr overhaul periods, and that would require occasional touch-up repair.

: Additional Comment A1 and El. Answer should be altered to need replacement every few years and occasional repair.

Cl. Best listed answer, but subject to numerous qualifications because of assumptions made in the choices.

D. Opinions too divided to summarize.

13. In your opinion, should the NASA Special Committee on Materials Research for SST establish a suggested standard procedure (based upon the work at Southern Research Institute) for screening evaluation of p r e s e n t and f u t u r e candidate coatings f o r SST service ?

Yes a No

Other Comment: B. Aircraft companies could probably not get together on requirements but tentative specification would be helpful.

C . Doubtful of SRI specimen for w i d e use. General approach by SRI w a s good, but current SST designs indicate 550°F temperature is too high.

Need target specification that should be met before E.

coatings are submitted to aircraft manufacturers.

14. What additional comments, suggestions, o r information do you have to offer on the SST coatings problem in general, the work performed by Southern Research Institute, and the work remain- ing to be done in the future? We would appreciate your candid comments on your confidence in the data already accumulated; the additional information needed to meet design and manufac- turing problems; and the relative importance and restrictions for such factors as weight, visual apparance, reflectivity, thermal and electrical conductivity, erosion resistance, flame resistance, resistance to f u e l s and other solvents, edge exposure, joining methods, curing temperatures, material cost, and application costs.

A Interior coatings w i l l be required to obtain corrosion resistance, acid resistance, etc. (problems from coffee, urine, alcohol).

The temperature regime will be on the order of 550°F rather than 65OoF. Erosion resistance and thermal conductivity will be required on leading edges. Resistance to oils, f u e l s , and M a t e r i a l and application cleaning materials will be required.

costs are important b u t not as critical as obtaining satisfactory coatings.

Changes in absorptivity and emissivity for exterior coatings due to temperature or aging will be critical.

Ambient curing of coatings is very important.

Exterior coatings should not be more than two mils in total Temperature cycling tests thickness to minimize weight.

f r o m -65°F to 550°F will be required.

Surface preparation such a s descaling, anodizing, o r surface treating of titanium materials to obtain adhesion will be critical.

SOUTHERN RESEARCH INSTITUTE Have f u l l confidence in the data f r o m Southern Research B.

A l l factors mentioned a r e influential f o r coatings Institute.

but their importance varies depending upon the mission requirement.

Relative importance of the various vactors must be assessed as the design proceeds.

The hot-salt corrosion problem does not seem to be s o C.

severe a problem with the notch-ductile SST skin candidates now under consideration. The materials are more resistant, and the more probable exposure temperature is 425°F with occasional excursions to 500°F. SRI work was with continuous stress exposure to salt at 550°F. Our experience indicates no problems (on Ti-8-1-1) under cycle exposure to salt and at u r e .

temper A very important consideration is IR emittance of the coating.

Emittance must exceed 0.8. Reflectivity is relatively unimportant, although a high solar reflectance is desirable, Weight is a very important consideration, as is v i s u a l appearance and resistance to f u e l s and solvents. Material are rather important. Curing cycles cost and application cost Room-temperature and temperatures are quite important.

curing is very desirable.

Joining methods are important only if the coating would be applied prior to final assembly. In case the material was applied prior to final assembly, interference with weldability would be critical. Edge exposure would be important in such c a s e s also, with erosion of secondary importance. Thermal and electrical conductivity a r e important only if the material is applied prior to assembly and if the tendency of the coating to spa11 is affected.

Additional information needed is: 1. Flexibility of coatings at high and low temperatures both before, during, and after aging.

2. Resistance of coating to deterioration by weather, moisture, f u e l s , and solvents, thermal cycling, ultraviolate exposure, and possibly ozone.

3 . Effects of reduced pressure.

4. Ease of application.

5. cost.

6. Appearance before and after aging.

7. IR emittance and solar reflectance.

8. Hardness and abrasion resistance.

Concerning confidence in data gathered by SRI:

Question remains - how does continuous exposure to hot

1.

salt correlate with expected service exposure ?

2. The data presented appears valid within the rather limited scope of the examination.

Why - when the catalytically cured silicone coating spalled

3.

off e a r l y in exposure - was exposure of these specimens

continued?

What attempts were made to determine the reason for 4.

the spalling?

What surface pretreatment was used for each paint type of 5.

coating ?

D. None.

Optimum thickness (or weight) of the coating is very E .

important.

Our coating (flat white catalytically cured silicone) probably meets the requirements for outer skin but more critical problems are posed by materials for aerodynamic smoothing and for r a i n erosion.

A tentative general specification would be valuable for vendors to u s e as a guide or goal for developing suitable formulations.

Our own specification should provide a good start for a tent a t ive gene ral spec if ic a t ion.

Emissivity is one of the most important characteristics in a coating because these must be "working" coatings that the temperatures as much as possible.

hold down SOUTHERN RESEARCH INSTITUTE Table XI Bend-Ductility Data from UNSCRATCHED Ti-8-1 -1 After Exposure to 550°F WITHOUT SALT for Durations Shown T1U1H3A TlUlH5A 2.460 " I U 1 H 7 A 2.325 TlUlHlA 1.819 1.630 TlUlHlB 1.285 . T1U1IBB 1.635 T1UlH5B 2.365 "IUlH?B 2.465 T1UlmC 1.828 , J TlU1H3C 1.781 TlUlH5C 2.465 T l U l H 7 C 2.440 T2UfH3A 1.690 2.450 T2UlH7A 2.385 T2UlHlA 1.790 "2UlH5A T2UlHIB 1.794 T2U1H3B 1.670 T2UlH5B 2.460 T2UlH7B 2.470

T2U1HlC 1.730 d T2U1H3C 1.686 T2UlHFiC 2.395 T2UlH7C 2.455

T 3 U l H l A 0.719 T 3 U l H 3 A 0.670 T3UlH5A 0.890 T 3 U l H 7 A 0.798 T3U1H1B 0.748 T3U1mB 0.660 T3U1H5B 0.835 T3U1H?B 0.885 T3UlH1.C 0.660 p T3U1H3C 0.695 T3UlH5C 0.540 T3ulH7c 0.800

T4UlH1.A 0.554 ' T4U1H3A 2.100 ' T4U1H5A 1.490 T4UlmA 2.460

T4U1H5B 1.700 T4U1"?B 0.960 T4U1HIB 1.566 T4UlH3B 1.710

T4U1HlC 0.780 T4UlH3C 2.200 I T4U1H5C 1.940 T4UlMC 1.690

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(')Catalytically Cured Silicone spalled from substrate within 48 h r after exposure to 55OOF.

~~ SOUTHERN RESEARCH INSTITUTE Table XI1 Bend-Ductility Data from UNSCRATCHED Ti-8-1-1 After Exposure to 550°F WITH SALT for Durations Shown TOU2H7B 0.280

Coated with Aluminum -

Modified Silicone

TlU2HlA 1.810 11 T1U2H3A 2.336 11 T1U2H5A 2.110 11 T1U2H7A 2.420

TlUZHlB 1.405 TI U2H3B 2.481 T1U2H5B 2.450 TI U2H7B 2.255 TIU2H1C 1.790 T1U2H3C 2.470 T1U2H5C 2.470 T1U2H7C 2.300 Coated w i t h Catalytically Cured Silicone(') T2U2H1A 1.700 T2U2H3A 2.400 T2U2H5A 2.290 T2U2H7A 2.465 T2U2H1B 1.450 T2U2H3B 2.455 T2U2H5B 2.470 T2U2H7B 2.312 T2U2H1C 1.815 T2U2H3C 2.463 T2U2H5C 2.430 T2U2H7C 2.455 Coated w i t h Zinc in Silicate Vehicle T3U2H1A 0.700 T3U2H3A 0.990 T3U2H5A 0.950 T3U2H7A 0.580 T3UZH1B 0.720 T3U2H3B 1.000 T3U2H5B 0.540 T3U2"lB 0.895 T3U2H1C 0.775 T3U2H3C 0.688 T3U2H5C 0.620 T3U2H7C 0.895 Coated w i t h Electrophoretically Deposited Aluminum T4U2H1A 0.320 T4U2H3A 0.290 T4U2H5A 0.265 T4U2"lA 0.280 T4U2H1B 0.894 T4U2H3B 0.283 T4U2H5B 0.320 T4U2H7B 0.300 T4U2H1C 0.480 T4U2H3C 0.355 T4U2H5C 0.345 T4U2H7C 0.820 Coated w i t h Flame-Sprayed Aluminum T5U2H3A 1.259 T5U2H5A 1.185 T5U2H7A 1.120 ~ T5U2H3B 1.305 T5U2H5B 0.975 T5U2H7B 1.060 T5U2H5C 1.190 T5U2H7C 0.890 (')Catalytically Cured Silicone spalled f r o m substrate within 48 h r after exposure to 550°F

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t I I I C c 3 3 0 0 5 Ln 0 m 3 L ' : v D m ' N i a sazIJu1 u: ?uyua].xot~~ SOUTHERN RESEARCH INSTITUTE Table XI11 Bend-Ductility Data from SCRATCHED Ti-8-1-1 After Exposure to 55OOF WITHOUT SALT for Durations Shown T4D1D3A 2.275 T4D1H5A 2.365 T4D1H7A 2.460 T4D1mB 2.283 T4D1H5B 1.960 T4D1H7B 2.450 T4DlH6C 2.295 T4D1H7C 1.700 T5D1H5A 1.060 T5D1H7A 1.055 T5D1H5B 0.930 T5D1H7B 1.110 (')Catalytically Cured Silicone spalled from substrate within 48 h r after exposure to 550°F Table XIV Bend-Ductility Data from SCRATCHED .Ti-8-1 -1 After Exposure to 55OOF WITH SALT for Durations Shown Bare

TOD2HlA 0.236 11 TOD2H3A 0.590 11 TOD2H5A 0.205 ! I T@D2H?A 0.730

TOD2H?B 0.550 TOD2H3B 0.286 TOD2H5B 0.335 TOD2HlB 0.305 TOD2HlC 0.230 TOD2H3C 0.670 TOD2H5C 0.500 TOD2H7C 0.310

Coated with Aluminum - Modified Silicone

TlDZHlA 1.348 1 1 T1D2H3A 1.710 11 TlD2H5A 1.560 1 1 TlD2"IA 1.540

T1D2H1B 1.167 T1D2-B 1.960 T1D2H5B 1.730 TlD2H7B 1.665 TlD2HlC 1.230 T1D2mC 1.410 T1D2H5C 1.670 TlD2"IC 2.120 Coated with Catalytically Cured Silicone(')

T2D2H1A 1.444 11 T2D2-A 1.135 11 T2D2H5A 2.000 1 1 T2D2EflA 1.335

T2D2H1B 1.442 T2D2H3B 1.440 T2D2H5B 1.470 T2D2H7B 1.555 T2D2HlC 1.469 T2D2mC 1.925 T2D2H5C 1.750 T2D2H7C 2.080 T3D2HlA 0.630 T3D2H3A 0.580 T3D2H5A 0.830 T3D2"lA 0.910 T3D2HlB 0.815 T3D2H3B 0.925 T3D2H5B 0.860 'I3D2"IB 1.040 T3D2H1C 0.834 T3D2"3C 0.950 T3D2H5C 0.790 T3D2H7C 0.800 Coated w i t h Electrophoretically Deposited Aluminum

T4D2HlA 0.470 11 T4D2H3A 0.280 11 T4D2H5A 0.390 11 T4D2"IA 0.390

T4D2H1B 0.340 T4D2H3B 0.445 T4D2H5B 0.600 T4D2mB 0.600 I T4D2H1C 1.480 T4D2H3C 0.420 T4D2H5C 0.345 T4D2H7C 0.390 Coated w i t h Flame-Sprayed Aluminum T5DZH3A 1.290 T5D2H5A 0.910 T5D2H7A 1.260 T5D2H3B 1.090 T5D2H5B 1.245 l%D2H?B 1.230 (')Catalytically Cured Silicone spalled from substrate within 48 h r after exposure to 550°F SOUTHERN RESEARCH INSTITUTE 9 8 I

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Table XV Bend-Ductility Data from UNSCRATCHED Ti-8-1-1 After Exposure to HUMID conditions WITHOUT SALT for Durations Shown

Coated with Aluminum - Modified Silicone

T l U l L 5 A 2.462 T1UlL7A 2.455 TlUlL53 2.460 TlU1L7B 2.420

. TlU1L7C 2.430

Coated with Catalytically Cured Silicone T2UlL5A 2.430 T2UlL7A 2.428 T2U1L5B 2.425 T2U1L7B 2.415 T2UlL7C 2.270 Coated with Zinc in Silicate Vehicle

T3UlL5A 1.530 11 “3UlL7A 1.420

1 1 T3UlL5B 1.600 1 1 ”3mL?B 1.310

Coated with Electrophoretically Deposited Aluminum T4UlL5A 2.365 T4UlL7A 2.370 T4UlL5B 1.720 T4U1L7B 2.290

I )

Coated with Flame-Sprayed Aluminum “5UlL7A 1.790 T5UlL7B 1.720

I t

SOUTHERN RESEARCH INSTITUTE Table XVI Bend-Ductility Data f r o m UNSCRATCHED Ti-8-1-1 After Exposure to HUMID Conditions WITH SALT for Durations Shown TOU2 L5A 2.330 TOU2L7 A 2.435 TOU2L5B 2.465 TOU2L7B 2.250 TlU2L1A 1.750 T1U2aA 2.470 TlU2L5A 2.440 T1U2L7A 2.375 TlU2LlB 1.838 T 1 U 2 u B 2.340 T1U2L5B 2.360 T1U2L7B 2.455 TlU2LlC 1.795 T1U2L3C 2.370 T1U2L5C 2.457 T1U2L7C 2.460 T2U2LlA 1.500 T2U2-A 2.440 T2U2L5A 2.450 T2U2L7A 2.430 T2U2L1B 1.760 T2U2L3B 2.445 T2U2L5B 2.437 T2U2L7B 2.440 T2U2LlC 1.925 T2U2L3C 2.285 , T2U2L5C 2.429 T2U2L7C 2.442 T3U2L1A 1.100 T3U2L3A 1.450 T3U2L5A 1.675 T3U2L7A 1.545 T3U2LlB 1.225 T3U2L3B 1.490 T3U2L5B 1.675 T3U2L7B 1.530 T3U2L1C 1.162 T3U2-C 1.620 T3U2L5C 1.530 T3U2L7C 1.480 T4U2L5A 2.060 T4U2L7A 2.425 T4U2L5B 2.070 T4U2L7B 2.430 T5U2L5A 1.775 T5U2L7A 1.680 T5U2L5B 1.990 T5U2L7B 1.660 0 P-

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C C SOUTHERN RESEARCH !NST!TUTE Table XVII Bend-Ductility Data f r o m SCRATCHED T i - 8 - 1 - 1 After Exposure to HUMID Conditions WITHOUT SALT for Durations Shown(') (l)No specimens Coated with Flame-Sprayed Aluminum w e r e included in these exposures.

Table XVIII Bend-Ductility Data from SCRATCHED Ti-8-1-1 After Exposure to IIUMXD Conditiom WITH SALT for Durations Shown(') ( ' ) N o specimens Coated with Flame-Sprayed Aluminum were included in these exposures.

SOUTHERN RESEARCH INSTITUTE

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0 < L n < Table X M Bend-Ductility Data from UNSCRATCHED AM 350 SCT After Exposure to 55PF for Durations Shown Coated w i t h Catalytically Cured Silicone(') A2UlHlA 2.16111 A2UlH3A 2.50211 A2U1H5A 2.48511 A2UlH7A 2.497

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2.500 A3U1H5A 2.481 A3U1H7A 2.482 A 3 U l H l A 2.16 A3U1H3A A3U1H3B 2.504 A3U1H5B 2.482 A3UlmB 2.492 A3U1H1B 2.15 T H AlU2H3A 2.499 A1U2H5A 2.490 AlU2H"fA 2.493 AlU2HlA 2.165 A1U2H3B 2.500 A1U2H5B 2.480 A1U2mB 2.491 s AlU2H1B 2.165 A A1U2H3C 2.500 A1U2H5C 2.488, A1U2H7C 2.496 AlU2J3lC 2.166( L T 2.485 A2U2"7A 2.494 A2U2H3A 2.500 A2U2H5A A2U2HlA 2.163 A2U2H5B 2.488 A2mH"B 2.489 A2U2H3B 2.488 A2U2HlB 2.16C A2U2H5C 2.4881 A2U?Mi"7 2.500 A2U2H3C 2.486 A3U2H3A 2.500 A3U2H5A 2.484 A3U2"7A 2.492 2.144 A3U2H1A A 3 m H 3 B 2.500 A3U2H5B 2.483 A3U2"7B 2.480 A3U2H1B 2.145 A3U2H5C 2.482 A3U2H7C 2.480

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(Ikatalytically Cured Silicone spalled from substrate within 48 h r after exposure to 55PF SOUTHERN RESEARCH INSTITUTE 0 0 0 0 0 0 In 0 In 0 In 0 rT) e a N + + 0 saq3u1 U! Bu!ual.IoqS Table XX Bend-Ductility Data from SCRATCHED AM 350 SCT After Exposure to 550°F for Durations Shown Bare

I i AODlHlA 2.166ll AODlH3A 2.50211 AOD1H5A 2.485 11 AODlH7A 2.493 1

T Coated with Aluminum - Modified Silicone H AlD2HlA 2.167 AlD2H3A 2.500 A1D2H5A 2.490 A1D2"lA 2.492 AlD2IIlB 2.068 A1D2H3B 2.500 AlD2H5B 2.490 A1D2"lR 2.498 S A Coated with Catalytically Cured Silicone(') L T A2D2H1A 2.165 A2D2H3A 2.500 A2D2H5A 2.490 A2D2"7A 2.500 A2D2II1B 2.161 A2D2H3B 2.500 A2D2H5B 2.490 A2D2H7B 4.493 Coated with Zinc in Silicate Vehicle

A3D2H1A 2.155 A3D2H3A 2.495 A3D2H5A 2.480 I A3D2H7A 2.493

A3D2H1B 2.123 A3D2H3B 2.488 A3D2H5B 2.480 I A3D2H7B 2.488

& @)Catalytically Cured Silicone spalled from substrate within 48 h r after exposure to 550°F SOUTHERN RESEARCH INSTITUTE IO9 Table XXI Bend-Ductility Data f r o m UNSCRATCHED AM 350 SCT After E x p o s u r e to HUMID Conditions f o r Durations Shown AOUlL5A 2.490 AOUIL'IA 2.490 AOUl L1 A 2.194 A O U l U A 2.500 AOUlL'7B 2.490 AOUlUB 2.500 A O U l G B 2.486 AOUlL1B 2.218 W I T H A l U 1 L 3 A 2.500 AlUlL5A 2.486 AlUlL'JA 2.490 A l U l L l A 2.155 2.487 AIU1LTB 2.490 AlUlLlB 2.163 AlUlL3B 2.500 AlU1L5B U T S A L T

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- ( l ) S p e c i m e n f r a c t u r e d spontaneously within the f i r s t 800 h r of exposure.

SOUTHERN RESEARCH INSTITUTE

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Table XXII Bend-Ductility Data from SCRATCHED AM 350 SCT After Exposure to HUMID Conditions for Durations Shown F AOD1Lf.A 2.177 AODlaA 2.500 AODlL5A 2.486 AOD1L7A 2.490 AODlLfB 2.180 AODlL3B 2.500 AODl L5B 2.486 AODl L7B 2.487 W I T H A ~ D ~ L L A 2.170 A ~ D ~ L ~ A 2.494 A1D1L5A 2.474 AID1 L7A 2.481 A ~ D ~ L ~ B 2.167 A ~ D ~ L ~ B 2.500 A1DIL5B 2.480 AID1 L7B 2.487 U T S A A ~ D ~ L ~ A 2.167 A ~ D ~ U A 2.460 A Z D ~ L ~ A 2.445 A2D1L7A 2.456 A2D1L3B 2.462 A2D1L5B 2.450 A2DlL73 2.450 A2DlLlB 2.110 L T Coated with Zinc in Silicate Vehicle A ~ D ~ L ~ A 1.440 A ~ D ~ L ~ A 2.450 A3D1L5A 2.475 MD1L7A 2.487 A3DlLlB 1.705 A3DlUB 2.488 A3D1L5B 2.480 a D 1 L I B 2.482 - _.

Bare AOD2LlA O(') AOD2UA O(') AOD2L5A 2.487 AOD2L7A O(l) AOD2LlB O ( l ) AOD2L3B o(*) AOD2L5B 2.490 AOD2L7B 2.490 W I T H AlD2L3A 2.495 A1D2L5A 2.477 AlD2L7A 2.488 A ~ D ~ L ~ A 2.170 AlD2UB 2.495 A1D2L5B 2.480 A1D2L7B 2.490 d D 2 L l B 2.165 S A L T 1.975 A2D2UA . 3.457 A2D2L5A 2.450 A2D2L7A 2.452 A2D2L1A 2.161 A2D2L3B 2.460 A2D2L5B 2.450 A2D2L7B 2.456 A2D2L1B 1.390 A3D2L5A 2.110 A3D2L7A 2.477 A3D2LlA 1.330 A3D2L3A 1.795 A3D2L5B 1.690 A3D2L7B 2.140 A3D2L1B 1.000 A3D2L3B

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SOUTHERN RESEARCH INSTITUTE 1.1.2 I 0 0 0 0 0 In 0 Bend-Ductility Data from UNSCRATCHED RENE 41 Aiter Exposure io 550°F for Durations Shown Coated w i t h Catalytically Cured Silicone S A R2UlHlA 1.030 R2U1H3A 1.540 R2U1H5A 1.630 R2UlH7A 0.530 L R2UlHlB 0.824 R2U1H3B 1.310 R2U1H5B 1.530 R2U1H7B 1.035 T R2U1HlC 1.000 aU1H3C 1.115 R2UlH5C 1.02Od R2U1H7C 1.280 with Zinc in Silicate Vehicle Coated R3U1H1A 0.640 R3UlH3A 1.030 R3U1H5A 0.740 R3UlH7A 0.750 R3UfH1B 0.753 R3U1H3B 0.935 R3U1H5B 1.120 R 3 U l H " B 0.550 R3U1H1C 0.875- R3U1H3C 0.980 R3U1H5C 1.210 R3UI"IC 0.860 Bare ROUZHlA 1.284 ROU2H3A 1.585 ROU2H5A 0.500 ROU2H7A 0.460 W ROU2HfB 0.400 ROU2H3B 0.980 ROU2H5B 1.410 R O U ~ H ~ B 0.770 I r

Coated with Aluminum - Modified Silicone

H RlU2HlA 1.750 R1U2H3A 0.775 R1U2H5A 1.180 R1U2H7A 0.605 3 R1U2H1B 0.738 R1U2H3B 1.240 R1U2H5B 1.060 RlU2"lB 1.570 A R1U2HlC 0.715 R1U2H3C 1.090 R1U2H5C 1.140 R1U2H7C 1.040 L Coated with Catalytically Cured Silicone r R2U2H1A 1.784 R2U2H3A 1.835 R2U2H5A 0.750 R2U2H7A 0.985 R2U2HlB 1.148 R2U2H3B 1.832 R2U2H5B 2.230 R2U2H7B 0.710 R2U2H1C 1.400 R2U2H3C 1.055 R2U2H5C 1.940 R2U2H7C 0.990 Coated with Zinc in Silicate Vehicle R3U2H1A 0.558 R3U2H3A 0.745 R3U2H5A 0.640 R3U2H7A 1.040 R3U2fdR 0.744 R3U2H3B 1.085 R3U2H5R 0.780 R3U2H7B 1.020 R3U2HlC 0.670 R3U2H3C 0.777 R3U2H5C 0.600 R3U2H7C 0.775 SOUTHERN RESEARCH INSTITUTE

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Table XXIV Bend-Ductility Data from SCRATCHED RENE 4 1 After Exposure to 550°F for Durations Shown ROD1"IA 0.960 RODlHlA 1.264 ROD1H3A 0.360 ROD1H5A 0.740 0.270 ROD1H5B 1.145 RODlHTB 1.910 RODlHlB 1.620 RODlH3B

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I T Coated with Aluminum - Modified Silicone H R l D l H l A 0.980 R1D1H3A 1.180 R l D l H 5 A 0.840 R l D l H 7 A 1.415 R l D l H l B 0.858 RlDlH3B 1.010 RlDlH5B 1.100 R1D1"IB 0.880

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R1D1H5C 1.730 RlDfHTC 1.145 T , Coated with Catalytically Cured Silicone S R2D1H3A 1.495 R2D1H5A 1.120 RZDl"7A 1.160 R2DlHlA 1.232 A 1.130 R2D1mB 1.290 RZDlEdB 0.800 R2DlH3B 1.175 R2D1H5B L _I R2D1H7C 1.340 T , Coated with Zinc in Silicate Vehicle R3D1H3A 0.655 R3D1H5A 1.135 R3D1H7A 1.050 R3D1HlB 0.748 R3D1H3B 0.865 R3D1H5B 0.750 R3D1mB 0.630 R3D1H5C 0.640 Ri?DlMC 1.080 - T I I

Coated with Aluminum - Modified Silicone

H R1D2H5A 1.010 R1D2H?A 1.190 RlD2H1A 0.645 R1D2H3A 2.225 R1D2H3B 0.325 R1D2H5B 0.900 R1D2H7B 1.745 S R1D2H1B 0.904 A 0.755 R1D2H3C 2.025, RlD2H5C 0.990 RlDzH?C 1.530 RlD2EdC L Coated with Catalytically Cured Silicone T R2D2HlA 1.035 R2D2H3A (1 1 R2D2H5A 1.145 R2D2H7A 0.990 R2D2H1B 0.745 R2D2H3B 0.250 R2D2H5B 0.785 R2D2H7B 1.580 0.769 R2D2H3C 0.725 R2D2H5C 0.810 R2D2H7C 1.735 R2DZH1C Coated with Zinc in Silicate Vehicle R3D2H1A 0.540 R3D2H3A 0.800 R3D2H5A 0.960 R3D2H7A 0.360 R3D2HlB 0.687 mD2H3B 0.355 R3D2H5B 0.520 R3D2H7B 0.500 R3D2H1C 0.660 R3D2H3C 0.790 R3D2H5C 0.900 R3D2H7C 0.420 (')Weld parted during exposure.

~~ SOUTHERN RESEARCH INSTITUTE

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Table XXV Bend-Ductility Data from UNSCRATCHED RENE 41 After Exposure to HUMID Conditions for Durations Shown Bare 1.085 ROU2L3A 2.195 ROU2L5A 1.645 ROU2L?A 0.575 ROU2 L1 A 1.410 ROU2BB 0.340 1.005 W ROU2LlB 0.956 ROU2L3B ROU2L7B I T Coated with Aluminum - Modified Silicone H .

R1U2LlA 0.730 RlU2L3A 0.810 R1U2L5A 0.785 R1U2L7A 1.900 S R1U2LlB 0.985 R1U2L3B 1.080 R1U2L5B 0.880 R1U2L7B 0.975 A R1U2LlC 0.705 RlU2L3C 0.850 R1U2L5C 1.275. R1U2L7C 0.820 L Coated with Catalytically Cured Silicone T R2U2LlA 1.682 R2U2L3A 1.110 R2U2L5A 0.755 R2U2L7A 1.920 R2U2L1B 1.010 R2U2L3B 0.320 R2U2L5B 1.630 R2U2L7B 1.930 R2U2LlC 0.748 R2U2L3C 0.980 R2U2L5C 1.400 R2U2L7C 2.020 Coated w i t h Zinc in Silicate Vehicle R 3 U 2 L l A 0.651 R3U2L3A 0.405 R3U2L5A 0.350 R3U2L7A 0.430 R3U2LlB 0.645 R3U2L3B 0.375 R3U2L5B 0.650 mU2L7B 0.810 R 3 u 2 ~ 1 c 0.440 R3u2L3c 0.540- R3U2L5C 0.470 R 3 u 2 ~ 7 c 0.530 SOUTHERN RESEARCH INSTITUTE

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Table XXVI Bend-Ductility Data from SCRATCHED RENE 41 After Exposure to HUMID Conditions for Durations Shown

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R O D l L l A 1.465 RODlL3A 0.800 ROD1L5A 1.510 ROD1 L7A 1.360 0.910 RODlL3B 0.455 , RODlL1B RODlL5B 1.540 ROD1 L7B 0.900 W I T H H l D l L 1 A 1.350 R1D1L3A 1.060 R1D1L5A 0.690 R1D1L7A 0.540 R l D l L 1 B 0.813 U R1D1L3B 2.210 RID1L5B 0.970 RlDlL7B 1.320 T s A Ii2DlLlA 1.040 WD1L3A 1.720 R2DlL5A 1.190 R2D1L7A 2.030 L R2D1L1B 1.250 R2D1L3B 1.720 R2D1L5B 0.750 R2D1L7B 1.690 T 0.355 R3D1L1A R3D1L3A 0.670 FC3DlLsA 0.480 FGD1L7A 0.690 R3D1L1B 0.453 R3D1L3B 0.690 R3D1L5B 0.590 R3DlL7B 0.735 - - ROD2L1A 1.390 ROD2L3A 1.280 ROD2L5A 1.850 ROD2L7A 1.300 N 0.434 ROD2L3B 0.900 ROD2L1B ROD2L5B 0.960 ROD2L7B 1.060 I

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1.100 R1D2L3A 0.735 RlD2L5A 1.355 R1D2L7A 1.020 RlD2LlA 5 R1D2LA1B 0.720 RlD2L3B 1.020 RlD2L5B 1.600 R1D2L7B 0.780 9 R1D2L1C 0.795 R1D2aC 1.440 R1D2L5C 1.310 R1D2L7C 1.250 L

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R2D2L1A 1.710 R2D2L3A 1.510 R2D2L5A 1.030 R2D2L7A 0.990 1.249 R2D2L3B 0.750 R2D2L5B 0.790 mDzL7B 1.520 R2D2L1B R2D2L1C 1.000 R2D2L3C 0.925 R2D2L5C 1.465 R2D2L7C 0.680 R3D2L5A 0.410, MD2L7A 0.420 R3d2L1A 0.550 R3D2L3A 0.550 0.469 R3D2L3B 0.480 R3D2L5B 0.555 R3D2L7B 0.400 R3D2L1B 0.485 MD2L7C 0.510 R3D2L1C 0.423 R3D2L3C 0.455 R3D2L5C - - SOUTHERN RESEARCH INSTITUTE

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