The Dependence of Isothermal ω Precipitation on the Quenching Rate in a Metastable β-Ti Alloy

The precipitation behavior of the alpha strengthening phase in metastable beta-Ti alloys is highly dependent on heat treatment parameters such as quenching rate, heating rate and ageing temperature. In this paper we have investigated the influence of quenching rate on the formation of isothermal omega precipitates that have been regarded as potent nucleant sites for alpha precipitation. The results show that the beta-solutionized alloy contains a beta matrix with a layer structured morphology. Regular atomic movement of the (002)(beta) plane along the <002> direction was observed in the alloy. The increase in quenching rate refines the thickness of layers, subsequently influencing the nucleation and growth of isothermal omega precipitates after ageing treatment. The high quenching rate promotes the occurrence of omega precipitation, broadens the stage of omega precipitation and increases the number density of omega precipitates. Since the isothermal omega phase provides a heterogeneous nucleation site for alpha precipitates, it is inferred that the quenching rate may indirectly influence the mechanical properties of metastable beta-Ti alloy.