Structure of orthorhombic martensite in the Ti92.5Nb5Mo2.5 alloy, its deformation and thermal stability

A ternary alloy Ti92.5Nb5Mo2.5 was obtained by arc melting on crystallization of water-cooled copper hearth followed by homogenization treatment, rolling, annealing and quenching in ice water. In this work, the formation of orthorhombic martensite alpha '' and its stability under deformation and in the course of thermal processing were investigated by a combination of X-ray diffraction, differential thermal analysis and optical microscopy. A set of the Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry. Experimental evidences indicate that a deformation-induced transformation of martensite to austenite (alpha '' -> beta) occurs after the above-mentioned heat treatment. It is also shown that during of DTA heating this martensite begins to transform into the beta-phase at the temperature of 724 degrees C. On cooling this beta-phase decomposes into a and b phases of nonequilibrium compositions. (C) 2020 Elsevier B.V. All rights reserved.