Ti-V合金の変態に関する観察

Abstract

Using a hot stage microscope with cine-camera, the kinetics of β-α transformation during continuous cooling and isothermal holding, and β-α′ transformation by quenching in Ti-V alloys were observed by means of the surface relief associated with the martensitic transformation. The kinetics of the transformations showed the following results: (1) The isothermal β-α transformation in Ti-V alloys is the isothermal martensitic transformation and “Schiebung” martensitic transformation due to the nucleation and growth process. The growth rate of α needles is independent of the isothermal transformation temperature but decreases with the increasing content of V. Both the maximum height of surface relief of α needles and the hardness increase with the increasing temperature of isothermal transformation. (2) When the rate of cooling is below 20°C/min, the growth rate of α needles increases with the increasing rate of cooling during β-α transformation in continuous cooling. But at the same rate of cooling, the growth rate of α needles decreases with the increasing content of V. The maximum height of surface relief of α needles decreases but the hardness increases with the increasing rate of cooling. (3) The β-α′ transformation by quenching is the athermal and “Schiebung” martensitic transformation. The Ms point is independent of the rate of cooling but decreases with the increasing content of V. The structure is the Widmannstäten type, the α′ phase is coherent with the α phase and seem to be the α solution supersaturated in V.