Evolution of intergranular stresses in titanium studied using grazing incident X-ray diffraction and self-consistent model

Abstract

One of the important causes for the formation of residual stresses in polycrystalline materials is the anisotropy of the plastic deformation process. Different slip systems activity leads to different plastic deformations of polycrystalline grains. The resulting mismatch (incompatibility) between adjacent grains is a source of the second order incompatibility stresses. These stresses cannot be easily measured directly, but can be predicted by elastoplastic deformation models. In the present work, stresses in deformed titanium alloy are studied. The grazing incidence X-ray diffraction measurements carried out during an "in situ" tensile test and a novel method of interpreting the experimental data allowed us to determine the evolution of macroscopic stresses and second order stresses during elastic-plastic deformation. This work shows that second order stresses, related to microstructure of material, are generated during plastic deformation and remain in the material. It was shown that the distribution of second order stresses in the Euler space correlates with the distribution of the Schmid factor for the non-basal crystallographic systems, especially Pyramidal system P1 <c+a>. This confirms that these systems play a key role in generating intergranular stresses. Comparison of the experimental data with the predictions of the self-consistent model also allowed the determination of the critical resolved shear stresses for slip systems activated during plastic deformation.