Improving vacuum gas nitriding of a Ti-based alloy via surface solid phase transformation

Abstract

The traditional surface nitriding technology of titanium alloy usually adopts the temperature above 700 °C to ensure the nitriding effect, but the high temperature will lead to the deterioration of the Matrix structure and reduce the mechanical properties. In this paper, the metastable β phase was formed on the surface of TiZrAl alloy by laser quenching, compared with the 10 μm thick nitrided layer mainly composed of (TiZr)N and α-Ti phases under the traditional process, the thickness and nitrogen content of nitrided layer were increased by the thermodynamic driving force of β→α phase transformation and the kinetic diffusion of phase interface, the effective thickness of nitrided layer was increased to 15 μm via nitriding at 500 °C. the (TiZr)N and α-Ti phases were dominant in the surface layer, and (TiZr)N0.3 and α-Ti phases were dominant in the inner layer, nitriding layer hardness up to 1200HV. In this paper, a novel nitriding technology is used to achieve excellent nitriding effect at low temperature, which has important reference significance for surface nitriding and carburizing of titanium alloys and other alloy materials.