It was recalled that the α”-martensite phase of quenched Ti-40wt%Nb transformed reversibly into the β-phase during short-term aging (623K, 900s), resulting in a β+ω microstructure in aged specimens. The relationship between the tensile properties and the microstructure was investigated here by observing structural changes in quenched and aged specimens during tensile deformation. Products of the β-phase (which were similar to {332} twins), surrounded by an α”-martensite matrix, were formed in the quenched specimen during tensile deformation. In aged specimens, α”-martensite and {332} twins were formed upon tensile deformation. The amounts of α”-martensite in the 2 specimens were larger in the non-uniformly deformed area near to the fracture. In particular, concentrated slip occurred in the non-uniformly deformed area of the aged specimen; accompanied by the extinction of ω-phases. The results indicated that the α” transformation, and then the reverse α” → β transformation, were involved in the formation of {332} twins. It was suggested that the formation of such twins was due to lattice instability and that, besides playing a role in deformation resistance, ω-phases played a part in non-uniform deformation.

Formation of α” Martensite and {332}<113> Twin during Tensile Deformation in Ti-40wt%Nb Alloy. Y.Mantani, Y.Takemoto, M.Hida, A.Sakakibara: Journal of the Japan Institute of Metals, 2002, 66[10], 1022-9