Co-deposition of Si and B to form oxidation-resistant coatings on an Nb–Ti–Si based ultrahigh temperature alloy by pack cementation technique

• Si–B co-deposition coating was applied to Nb based alloy by pack cementation.
• The Si–B co-deposition coating mainly consisted of (Nb,X)Si2 and (Nb,X)B2 phases.
• The mass gains are very low after oxidation at 900 and 1250 °C for 100 h.
• The good oxidation resistance is due to the formation of a dense glass-like scale.

In this work, we study the oxidation behavior of a B-modified silicide coating at 900–1350 °C. The coating was prepared by pack cementation, which mainly consisted of a (Nb,X)Si2 + (Nb,X)B2 outer layer, a (Nb,X)Si2 intermediate layer and an inner layer. At 900 and 1250 °C, the evolution of the mass gain versus time showed parabolic-like kinetics; while at 1350 °C, the evolution seemed to follow a linear-like kinetic, but could protect the alloy from oxidation for at least 60 h. The good oxidation resistance of the B-modified silicide coating was attributed to the formation of a dense glass-like scale.