In situ chemical vapour co-deposition of Al and Si to form diffusion coatings on TZM

Multilayer alumino-silicide and silicide coatings were formed by in situ chemical vapour co-deposition of Al and Si on TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy for improving its high-temperature oxidation resistance. MoSi2 and Mo (Si, Al)2 layers were formed in the inner and the outer layers, respectively in the case of alumino-silicide coating. Whereas silicide coating consisted of Mo5Si3 and MoSi2 phases in the inner and the outer layers, respectively. 24–100-μm thick coatings were formed by optimizing the pack mixture of Al and or Si, NH4F and Al2O3 powders and conducting the experiments at 1000 °C for 8–36 h. MoSi2 layer showed a faster growth rate and presence of columnar grains. A small weight gain at the initial stages was observed during the oxidation tests of the coated samples under continuous or cyclic heating at 1300 °C in air. Neither cracks nor peeling of the coating layers were noticed after oxidation tests.