Oxidation resistance comparison of MoSi 2 and B‐modified MoSi 2 coatings on pure Mo prepared through pack cementation

A MoSi 2 coating and a B‐modified MoSi 2 coating were prepared on pure Mo by halide activated pack cementation (HAPC) method. The B‐modified MoSi 2 coating consisted of a thick MoSi 2 outer layer with MoB precipitates distributed in its inner part, a Mo 5 Si 3 second layer, a MoB third layer, and a Mo 2 B inner layer. Both coatings were oxidized isothermally at 873, 1523, and 1773 K. It was found that pest oxidation did not occur in both coatings at 873 K for full cover scales could form on their surfaces after 100 h oxidation. During oxidation, B atoms in the B‐modified MoSi 2 coating diffused outward to the coating surface and oxidized to low viscose B 2 O 3 , which promoted the formation of full cover scale and significantly reduced the volatilization of MoO 3 at 1523 K, while that effect was negligible at 1773 K for silica had good fluidity at such a high temperature. It was also found that the MoB layer of the B‐modified MoSi 2 coating retarded the inward diffusion of Si from MoSi 2 to the substrate, which could increase the coating oxidation‐resistant lifetime.