Effect of Oxygen Addition on the Formation of α′′ Martensite and Athermal ω in Ti–Nb Alloys

Abstract

The effect of the addition of oxygen on the formation of the microstructure quenched from the β phase of Ti–Nb alloy was investigated based on the solid solution treatment (SST) temperature in the β phase. The alloy ingots of Ti–(12, 14, and 18)-at% Nb–(0, 1, and 3)-at% O were arc-melted. They were homogenized at 1200°C for 3.6 ks and then hot-rolled at 850°C into 1.5-mm thick sheets. The specimens were solution-treated at 1050 to 1200°C for 0.6 ks and then quenched in iced brine. The microstructure of the Ti–(12, 14, and 18)-at% Nb alloys exhibited an α′′ phase regardless of the SST temperature. The addition of oxygen in the Ti–(14 and 18)-at% Nb alloys suppressed the β → α′′ martensitic transformation; therefore, the quenched structure became the β + ω_a phase. The further addition of oxygen suppressed the β → ω_a transformation during quenching. The effect of oxygen addition on the phase transformations of β → α′′ and β → ω_a during quenching from the β phase was weakened with an increasing SST temperature.