Tailoring the Bain strain of martensitic transformations in Ti[sbnd]Nb alloys by controlling the Nb content

Abstract

The lattice (Bain) strain and corresponding volume change of a martensitic phase transformation are key parameters that determine the formation of a self-accommodated martensitic microstructure and related functional properties. Based on experimentally determined lattice parameters of the cubic austenite β and of the hexagonal and orthorhombic martensites α′ and α″, the lattice strain and the volume change related to the β → α′/α″ martensitic transformations in TiNb alloys are analyzed in dependence of composition. The lattice strains of the transformation β → α″ increase with decreasing Nb content but those of β → α′ are not affected by the amount of Nb. Depending on the composition, both a volume dilatation and contraction is encountered. It is proposed that the volume change plays a decisive role in determining the lattice structure of the martensitic phase that evolves when the transformation is thermally induced.