Si-B co-deposition coatings on an Nb suicide based ultrahigh temperature alloy prepared by pack cementation technique

In order to improve the oxidation resistance of suicide coatings on an Nb suicide based alloy, Si-B co-deposition coatings were prepared at 1150 degrees C for 8 h by using pack mixtures containing different amounts of B powders. The microstructural characteristics of the coatings were studied. The results showed that all coatings had a triple-layer structure. The middle layers of all coatings were composed of (Nb,X)Si-2 (X represents Ti, Cr and Hf elements) and the inner layers of all coatings were composed of (Nb,X)(5)Si-3, but the outer layers of the coatings had different phase constituents and morphologies when the amount of B powders in the pack mixture changed. When the amount of B powders in the pack mixture ranged from 0.5 wt% to 12 wt%, the outer layers were composed of (Nb,X)B-2, with a few CrB2 particles. When the amount of B powders in the pack mixture was in the range of 0.05 similar to 0.1 wt%, the outer layers were composed of (Nb,X)B-2. However, when the amount of B powders in the pack mixture was in the range of 0.02 similar to 0.03 wt%, the outer layers were composed of (Nb,X)Si-2, with needle-like (Nb,X)B-2 particles dispersed in it.