The effect of coating composition on structural changes and oxidation behavior was studied using a Sn-Al spray-slurry system with tantalum, tantalum alloys, columbium, tungsten and molybdenum. In tests conducted at 3000°F it was found that increased .oxidation pro¬tection was most significantly related to the thickness of the tin-rich phase at the surface. The use of refractory metal powder additives plus excess aluminum to form aluminide particles served best to increase the thickness of this phase. Coating composition was opti¬mized and an extensive evaluation was carried out with Ta-10%W, Ta-30%Cb-7.5%V, and Cb-5%Zr. In oxidation tests at 1100° to over 3000°F protective life was significantly affected by substrate composi¬tion, coating thickness and thermal cycling. Tensile and stress rupture data were obtained on coated samples at 2000 to 3000°F and correlated fairly well with data in the literature for uncoated material. Preliminary studies were made of coating stability at air pressures in the micron to millimeter range. Oxidation and diffusion effects were explored by metallographic electron probe and x-ray analysis. A brief study of Ta-10Hf-5W in contact with AI2O3 at elevated temperatures showed that this alloy was unstable in contrast to pure tantalum, Ta-lOW, and Ta-30Cb-7.5V, which were quite stable.nOxidation data were obtained for several tantalum alloys coated with Ti-Si. A diluent system was sought for beryllide-type coatings in which Sn, Cu, Si, and Ag were investigated. The use of silver as a slurry base was found to be most promising, but was not extensively evaluated.
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