抄録
A change of deformation modes in lattice instable Ti-14 mass%Mo alloy single crystals ((\bar110) plate and (\bar3\bar31) side) upon aging treatments at 623 K was investigated in the tensile test up to rupture. The tensile direction of these specimens was [116]β. The main deformation modes of as-quenched specimen (AQ) were {332}⟨113⟩ and {112}⟨111⟩ mechanical twins. Their Schmid factors (SF) were 0.321 and 0.156 in {332}⟨113⟩ twins and 0.447 in {112}⟨111⟩ twins. A specimen aged for a short time of nearly 250 s (AG(S)) showed a kind of transitional state of deformation mode which involved {332}⟨113⟩ twins, {112}⟨111⟩ twins and {112}⟨111⟩ slips. In this state AG(S) had been already poor in ductility. A specimen long aged for 1×105 s (AG(L)) showed a remarkable brittle fracture caused by the aged ω phase, but it was not the {001} cleavage fracture. The fracture surface had a chevron pattern induced by the operation of some {112} slip systems in the initial stage. Large grown aged ω variants caused the β matrix to remarkably increase the stress level for deformation and induced locally an ω→β inverse transformation. Local softening which occurred with the inverse transformation led to an extreme stress concentration and then to crack. In this way AG(L) apparently showed notable embritlement.
