Microstructure and high-temperature oxidation resistance of in-situ synthesized Ti-Al-Si composite coating by laser cladding

Abstract

Abstract According to the in situ reaction mechanism of Ti, Al, Si mixed powders and the Ti-Al-Si ternary phase diagram, two kinds of alloy systems with an atomic ratio of Ti: Al: Si=41:41:18 and Ti: Al: Si=35:35:30 was designed. The Ti-Al-Si composite coatings were in situ synthesized by laser cladding on Ti6Al4V titanium alloy (TC4) surface. The microstructure and phase composition of composite coating were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The microhardness and corrosion resistance of coating were investigated by microhardness tester and electrochemical workstation. The high-temperature oxidation resistance and anti-oxidation mechanism of coating at 800 °C × 24 h × 5 times cyclic oxidation was analyzed by oxidation mass gain and oxidation kinetics curves. The results show that the Ti-Al-Si composite coating has a good metallurgical bonding with titanium alloy substrate. The coating is mainly composed of Ti5Si3, Ti7Al5Si12, Ti3Al, TiAl and TiAl3 phases. The average microhardness of the two kinds of coating is 853.3 HV0.2 and 795.2 HV0.2, 2.37 times and 2.21 times that of the substrate, respectively. Compared with titanium alloy substrate, the corrosion resistance of the coating in artificial seawater has been improved significantly, and the coating with an atomic ratio of Ti: Al: Si=41:41:18 is better than the coating with an atomic ratio of Ti: Al: Si=35:35:30. The oxidation kinetics curves at 800 °C × 24 h × 5 times cyclic oxidation exhibit that the oxidation resistance of Ti: Al: Si=41:41:18 coating increase by 12.5 times. The oxide layer on titanium alloy surface is loose and composed of rod-like TiO2 and cluster islands Al2O3. However, on the surface of cladding composite coating, a uniform, dense and long rod-like oxide layer with a thickness of about 8 μm is formed. The oxide layer on cladding composite coating surface is mainly composed of TiO2, Al2O3 and SiO2. The in situ synthesized Ti-Al-Si laser cladding composite coating plays a positive role in improving the high-temperature oxidation resistance of titanium alloy.