Microstructure and Cyclic Oxidation Behavior of Silicide Coatings Prepared by Molten Salt on Nb–Based Multiphase Alloys

Niobium silicide coatings were prepared by molten salt on Nb-based multiphase alloys. The nanostructured out-layer ((Nb,Ti)Si 2 or (Nb,Ti,Mo)Si 2 ) and transition layer ((Nb,Ti) 5 Si 3 or (Nb,Ti,Mo) 5 Si 3 ) silicides were formed at the surface of both multiphase alloys. The cyclic oxidation behavior at 850 °C and 1000 °C was adopted to investigate the high temperature oxidation resistance of the coatings. It is revealed that the silicide coatings protect efficiently the alloy substrate, and the excellent oxidation resistance of the coatings is attributed to the formation of the layer mainly consisting of SiO 2 . After oxidation at 1000 °C, the transition layer is thickened significantly due to the interdiffusion of Si in Nb solid solution. The formation and oxidation resistance mechanisms of silicide coatings are discussed in details based on a microstructural analysis of the as-deposited coatings and oxidized samples