Study on the oxidation resistance of γ-TiAl intermetallic alloy coated via different diffusion coating processes

Abstract

Because of having attractive mechanical properties, γ-TiAl intermetallic alloys have been extensively utilized in gas turbines. However, their oxidation resistance is insufficient at temperatures above 800 °C. In this work, the oxidation resistance and microstructure of oxide scales formed during isothermal oxidation at 1000 °C for 300 h associated with γ-TiAl [Ti-48Al-2Nb-2Cr (at%)] samples coated with gas-phase pack cementation and liquid-phase slurry coating processes are investigated and compared. To accomplish this purpose, the mass gain during the isothermal oxidation as well as the cross-sectional scanning electron microscopy (SEM) images and x-ray radiation diffraction (XRD) patterns corresponding to each coated and oxidized sample and are obtained and compared to each other. It is revealed that the coated sample via liquid-phase slurry process has the best high-temperature oxidation resistance, and there is no spallation in this sample after the isothermal oxidation. Moreover, in the liquid-phase slurry coated sample, it seems that the formation of middle thin layer of Al2O3 + Ti5Si3 acts as a barrier toward the oxygen diffusion to the substrate which causes to improve significantly the high temperature oxidation of it.