Liquid-phase aluminizing and siliconizing at the surface of a Ti60 alloy and improvement in oxidation resistance

A simple and inexpensive method to improve oxidation resistance of titanium alloys, liquid-phase aluminizing and siliconizing by an Al–Si alloy, has been proposed. The surface reaction at 1013 K for 20 min on a Ti60 alloy using Al–10 wt.%Si melt as reaction medium resulted in a modified layer with a thickness of about 50 μm, composed of TiAl3 and TiSi2. The coating significantly improved the isothermal oxidation resistance of the alloy at 1073 K. An approximately continuous alumina-rich scale was formed at the outermost surface after oxidation. SiO2 was also detectable in the oxide scale. It was inferred that during oxidation, the TiSi2 in the coating was oxidized to SiO2. In the meantime, the TiSi2 was reduced to a lower silicide, Ti5Si4. The formation of the alumina-rich scale (containing silica) at the outermost surface accounted for the improvement in the oxidation resistance.