The effects of surface-layer grain size and texture on deformation-induced surface roughening in polycrystalline titanium hardened by ultrasonic impact treatment

The ultrasonic impact treatment (UIT) of titanium specimens leads to the grain refinement and formation of a strong basal texture in the surface layer, affecting the mechanical properties of the UIT titanium parts. In this paper, we aim at investigating numerically the effects which the UIT-modified microstructure has on the micro- and mesoscale deformation behavior of titanium specimens subjected to uniaxial tension. For this purpose, three-dimensional polycrystalline models taking an explicit account of the grain morphology and crystallographic orientations of the base material and UIT modified surface layer are generated by the method of step-by-step packing and implemented in the finite-element calculations. The constitutive models describing the nonlinear behavior of individual grains are implemented in terms of anisotropic elasticity and crystal plasticity theories. The boundary value problem is solved within a dynamic approach using the ABAQUS/Explicit package. This study allows distinguishing between the grain size and texture effects and drawing conclusions on their roles in the stress-strain evolution, plastic strain localization and deformation-induced surface roughening in UIT titanium specimens under loading.