抄録
The crystallography and morphology of quenched and aged metastable β-phase titanium alloys, Ti–15Mo–5Zr and Ti–15Mo–5Zr–3Al, were studied by transmission electron microscopy. In both alloys it was observed that there were two types of the α phase, Type 1α (obeying the well-known Burgers orientation relation between α and β phases) and Type 2α (not obeying the Burgers relation). Moreover, two types of α phase morphology were revealed: one is plate or needle-like and the other is raft-like. The precipitation sequence of Type 1α→Type 2α was confirmed in the Ti–15Mo–5Zr–3Al alloy aged at 773 and 623 K. The morphology of the Type 2α is platelike. The ω→2α transition was observed in the Ti–15Mo–5Zr alloy aged at 673 K. The morphology of the Type 2α is raft-like. The ω, Type 1α and Type 2α with platelet morphology were formed in the Ti–15Mo–5Zr alloy aged at 748 K. The effect of the crystallography and morphology of the precipitates on the mechanical properties is discussed in comparison with other metastable β-titanium alloys.
