Experimental study and crystal plasticity finite element simulations of nano-indentation-induced lattice rotation and the underlying mechanism in TC6 single α-grain

A Berkovich indentation test was performed in a single primary α-phase grain of an equiaxed TC6 titanium alloy, to reveal the complex local lattice-rotation process under nano-indentation loading. Numerical simulations using an in-house-developed crystal plasticity finite element method code were also conducted. A high-resolution inverse pole figure of a slice across the nano-indention was obtained via the focused ion beam technique coupled with precession electron diffraction. The simulation results corresponded closely to the experimental observations. In the slice, the region beneath the indentation inner-edge and the region beneath the indentation facet underwent the greatest degree and the second-greatest degree of lattice rotation, respectively. In contrast, for the region directly below the indentation center, the lattice rotated first, but the orientation changed only slightly during the entire process. The bright field transmission electron microscopy and the geometrically necessary dislocation densities provided experimental confirmation of such orientation features. Furthermore, the nucleation and continuous growth process of subgrains was numerically predicted by virtually tracking the misorientation angle (>10°) map at different indentation depths in three-dimensional space. Thereafter, the evolution of each slip system type was captured at typical local regions of the indentation, leading to an in-depth understanding of the underlying mechanism.