Phase transformation of quenched α″ martensite by aging in Ti–Nb alloys

The purpose of this study is to investigate the phase transformation behavior of quenched orthorhombic α″ martensite during aging in titanium–niobium binary alloys. Four kinds of alloys with niobium concentrations of 25, 30, 35, and 40 (mass%) were used. Differential thermal analysis, optical microscopy, X-ray diffraction, and a Vickers hardness test were performed to investigate the phase transformation behavior of each alloy under different aging conditions. The phase transformations observed in this study were the reverse transformation of the α″ martensite to β, ω phase precipitation in the β matrix, and α phase precipitation. Based on these results, the phase transformation temperature ranges were discussed. It was pointed out that there existed a possibility of a difference in the aging transformation and hardening behavior between the α″ martensite structure and the α″ + β duplex phase structure.