Abstract

Over the past few years our work has focused on exploring fundamental deformation processes in Ti and its alloys. The work has two main strands: (i) extraction of single crystal mechanical properties, and (ii) characterising local stress and lattice rotation fields that develop during deformation. We have developed methods to extract single crystal elastic constants, and critical resolved shear stresses from polycrystalline samples. FIB is used to machine micro-cantilevers and/or micro-pillars within individual selected grains offering suitable orientations, and these are tested in bending or compression with a nanoindenter. For plastic deformation significant size effects are evident but we are able to extrapolate the data to bulk values. Data will be presented for Ti (α), Ti-6Al (α) and Ti-6Al-4V (α+β), and comparison made between different slip systems. We have also been using the high resolution EBSD method, developed in the group, to map local lattice rotations and elastic strain variations in deformed Ti alloys. The lattice curvatures (and elastic strain gradients) can be used to determine a lower bound estimate of the geometrically necessary dislocation density which allows the accumulation of dislocations within a microstructure to be studied. The presentation ill include application of the method to studying indents in single grains of Ti, the interaction of slip bands and twins with grain boundaries, and mapping of dislocation content in Ti-6Al-4V polycrystals deformed by rolling, tension and fatigue.