High brilliance synchrotron sources of high energy x-rays have recently provided researchers with a new class of 4D (in-situ and in-operando) techniques for assessing the evolution of strain and crystal orientation within individual grains of a polycrystal. Researchers can now measure the single-crystal elastic stiffness coefficients within alloys for which single crystals are unavailable. In many metallic alloy systems, the elastic properties are considered insensitive to details of alloy composition and heat treatment. Beta (BCC) Ti alloys are an exception, in which the Young’s modulus can vary by 50% with heat treatment. In fact, limited experimental assessments of their single crystal stiffness coefficients of exist within the literature. Means of computing the grain-level elastic anisotropy will be presented, and the results will be used to compute the stress tensor within each grain. In turn, the stress tensor and grain orientation can be used to assess the resolved stresses on dislocation slip systems of interest. Through a calibrated crystal plasticity model, the shear rates on individual slip systems can, thus, be estimated. Finally, the broadening of the diffraction peaks originating from individual grains can be used to assess the dislocation content within the grains. Given that dislocation densities are a favored internal state variable within the most sophisticated crystal plasticity models, high energy x-ray diffraction appears poised to provide unprecedented model validation.
2021-04-07 08:00:00
