Non-uniform mechanical behaviour of uniaxially rolled Ti–6Al–4V with micro-texture regions

Abstract

Uniaxial strain rate controlled and creep behavior of a unidirectionally rolled Ti–6Al–4V with micro-texture regions (MTR) were studied. The presence of MTR was identified and characterized using polarized light microscopy (PLM) and correlated with electron back-scatter diffraction (EBSD). Uniaxial tests were carried out along the rolling (RD), transverse (TD) and normal (ND) directions. Uniaxial strain rate controlled tests at strain rates of 10−3, 10−4 and 10−5 s−1 showed noticeable strain rate sensitivity at both room temperature (RT) and 200 °C. The yield strength in RD and TD was higher than ND by 16% and 8%, respectively. Creep behavior was sensitive to the initial strain rate during loading. The creep strain was fitted to a Norton-Bailey power law, ε=Aσntα, where ε, σ and t are creep strain, stress and time, respectively and A, n and α are constants, and showed a primary stress exponent, n, of 15 at RT and 10.4 at 200 °C and a time exponent, α, of 0.31 at RT and 0.125 at 200°C. In a first-of-its-kind exercise, PLM-EBSD was augmented with DIC in uniaxial strain rate controlled and creep tests for precise strain measurement and microstructural correlation with the directionality of testing. It revealed a significant effect of MTR on strain localization which may explain the role of MTR in failure nucleation.