Composition-dependent magnitude of atomic shuffles in Ti–Nb martensites

In this work the structural characteristics of martensitic phases in the Ti–Nb system are studied in detail. While the distortion of the orthorhombic unit cell of α′′-martensite by the addition of β-stabilizing atoms is well documented in the literature, comprehensive experimental data on the detailed atomic positions and how they vary with chemical composition are missing. For this study, a series of binary Ti–Nb alloys were prepared by casting techniques, followed by homogenization treatment and water quenching. Rietveld-based analyses of X-ray diffraction data were used to study the gradual structural changes of α′- and α′′-martensites effected by the addition of Nb, and their compositional boundaries were determined. In the case of orthorhombic α′′, it was established that, besides the lattice parameters, the positions of the atoms on the (002)_α′′ planes respond very sensitively to the amount of Nb present.