Microstructure and hot corrosion resistance of Si-Al-Y coated TiAl alloy

Abstract

In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment, Si-Al-Y coatings were fabricated by pack cementation process at 1050 °C for 4 h. Corrosion behaviors of the TiAl alloy with and without Si-Al-Y coatings are compared to illustrate the factors and corresponding mechanism in molten salt environment of 25wt% K2SO4 and 75wt% Na2SO4 at 900 °C. The obtained Si-Al-Y coating was mainly composed of a TiSi2 outer layer, a (Ti, X)5Si4 and (Ti, X)5Si3 (X represents Nb or Cr element) middle layer, a TiAl2 inner layer and a Al-rich inter-diffusion zone. The inter-phase selective corrosion containing corrosion pits extending along α2 phase from lamellar interfaces in hot corrosion tested TiAl alloy was observed. However, by being coated with Si-Al-Y coating, the hot corrosion performance of TiAl alloy was improved remarkably.