Preparation of TiAl_3-Al Composite Coating by Cold Spraying and Evaluation of Its High Temperature Oxidation Behavior

TiAl3-Al composite coating with an average thickness of 250 μm was prepared on γ-TiAl alloy by cold spraying and subsequent heat-treatment.The phase structure,morphology and composition of as-sprayed composite coating were analyzed using an X-ray diffractometer,a field emission electron microscope and an electron probe.The long time high-temperature oxidation behavior of the coating at 950 ℃ was investigated.It was found that cold-sprayed Al coating was compact and contained a small amount of micro-cracks and gas holes.TiAl3 phase was formed between TiAl 3-Al compo site coating and substrate,and pores existed at the interface of TiAl 3 and Al.The alloy substrate(γ-TiAl) lost weight after 70 h of oxidation at 950 ℃,generating TiO2 and Al2O3 as the mixed oxidized products.The composite coating gained weight slowly in the steady oxidation period where the oxidation kinetics curve approximately followed a parabolic rate law.Even after 1000 h of oxidation at 950℃,the composite coating kept almost intact,and its oxidized product consisted of alumina and trace of titanium dioxide and titanium nitrides.In general,the composite coating could significantly improve the oxidation resistance of γ-TiAl alloy at elevated temperature.