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

Abstract

Niobium silicide coatings were prepared by molten salt on Nb-based alloys. The nanostructured out-layer ((Nb,Ti)Si2 or (Nb,Ti,Mo)Si2) and transition layer ((Nb,Ti)5Si3 or (Nb,Ti,Mo)5Si3) 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 SiO2. 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.

Keywords: Nb alloys, Silicide coatings, Molten salt, Oxidation