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

Abstract

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 TiAl 3 and TiSi 2. 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. SiO 2 was also detectable in the oxide scale. It was inferred that during oxidation, the TiSi 2 in the coating was oxidized to SiO 2. In the meantime, the TiSi 2 was reduced to a lower silicide, Ti 5Si 4. The formation of the alumina-rich scale (containing silica) at the outermost surface accounted for the improvement in the oxidation resistance.