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

The effect of the addition of oxygen on the formation of the microstructure quenched from the beta phase of Ti-Nb alloy was investigated based on the solid solution treatment (SST) temperature in the beta 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 degrees C for 3.6 ks and then hot-rolled at 850 degrees C into 1.5-mm thick sheets. The specimens were solution-treated at 1050 to 1200 degrees 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 alpha '' phase regardless of the SST temperature. The addition of oxygen in the Ti-(14 and 18)-at% Nb alloys suppressed the beta ->alpha '' martensitic transformation; therefore, the quenched structure became the beta + omega(a) phase. The further addition of oxygen suppressed the beta ->omega(a) transformation during quenching. The effect of oxygen addition on the phase transformations of beta ->alpha '' and beta ->omega(a) during quenching from the beta phase was weakened with an increasing SST temperature.