HIGH-TEMPERATURE OXIDATION PROTECTIVE COATINGS FOR VANADIUM-BASE ALLOYS

Abstract : The objective of this program is the development of oxidation- protective coatings for vanadium-base alloys for use at 1800 to 2500F. The effect of pack-siliconizing on the mechanical properties of 0.020 in. thick sheet of V-60Cb-1Ti (weight per cent) is being studied. Results indicate that the siliconizing process has little effect on strength, but causes some reduction in tensile ductility. However, good ductility is noted at temperatures as low as -320F. Preliminary results indicate that there is no embrittlement of this coated sheet after twenty-five 4-hr oxidation cycles at temperatures up to 2300F. The development of an oxidation resistant slurry or liquid cementation type of coating for V-60Cb-1Ti is progressing. Slurry compositions containing tin, silicon, silver, copper, aluminum, and columbium have been investigated; several of these show good coverage, even at corners and edges. The static oxidation life of other vanadium-base alloys, coated by the pack-siliconizing process, is also being investigated. V-40Cb-30Ta-1Ti, the most promising of these alloys, has an oxidation life of about 50 hr at 2200F, and less under cyclic conditions.