OXIDATION BEHAVIOR OF TUNGSTEN AND GERMANIUM-ALLOYED MOLYBDENUM DISILICIDE COATINGS

[摘要] A multicomponent diffusion coating has been developed to protect niobium-base alloys from high temperature oxidation. A solid solution disilicide of molybdenum and tungsten doped with germanium provided the best protection and supported a slow-growing protective silica (SiO2) scale when exposed to high temperature oxidation. The (Mo, W)(Si,Ge)2 coating was made by reacting to a previously sputtered 70at.%Mo-30at.%W deposit in an NaF-activated cementation pack containing silicon and germanium. The germanium addition helped to improve the cyclic oxidation resistance by increasing the thermal expansion coefficient of the silica scale. The germanium also helped to avoid pesting (accelerated low temperature oxidation) by providing better sealant coverage at low temperatures. The results of cyclic oxidation tests performed on coated niobium coupons at 925, 1370 and 1540-degrees-C in air are presented. The coated niobium successfully passed 200 cyclic oxidation tests of 1 h at 1370-degrees-C and 60 cycles of 1 h at 1540-degrees-C. These results represent test termination points and not application limits. Accelerated low temperature oxidation and/or pest oxidation did not occur when the coatings were exposed to isothermal conditions of up to 200 h in air in the temperature range 500-700-degrees-C.

[发布日期] 1992-07-30

[效力级别]  Proceedings Paper