A synchrotron X-ray and electron backscatter diffraction based investigation on deformation and failure micro-mechanisms of monotonic and cyclic loading in titanium

Abstract

Synchrotron X-ray diffraction technique has been used to estimate defect structure in terms of dislocation density, crystallite size and micro-strain in commercially pure titanium subjected to tension and cyclic deformation in stress and strain control mode. Statistical analysis of micro-texture data collected from electron backscatter diffraction approximately from the same region as that of synchrotron X-ray has been used to correlate orientation dependent micro-strain and dislocation density with deformation microstructure and micro-texture. Two different orientations, namely, A with prismatic-pyramidal and B with basal orientation along the loading axis has been considered. Weak initial texture yet significant anisotropy in hardening/softening response and failure mode for monotonic tension and cyclic loading paths has been observed. Higher strain hardening response of orientation A during monotonic tensile deformation can be attributed to the evolution of lower micro-strain on basal orientation grains i.e, 〈0002〉ǁND along with extensive multi-variant twinning that also restricts crack propagation and delays failure in stress control mode. On the other hand, in strain control mode, orientation B shows higher fatigue life due to the generation of lower micro-strain in the basal orientation grains and single variant twinning that can undergo detwinning easily is responsible for delayed crack nucleation and subsequent failure.