Use of Spherical Nanoindentation Protocols to Study the Anisotropic Mechanical Response of Alpha-Beta Single Colonies in Ti–6Al–4V Alloy

The recently developed spherical nanoindentation stress–strain protocols were employed in this study to investigate systematically the anisotropic elastic and yield response of the individual α-β colonies in a Ti–6Al–4V alloy. This was accomplished by indenting selected individual colonies with different lattice orientations of the secondary α in the colony (measured by electron back-scattered diffraction) in the polycrystalline sample. It is seen that the employed protocols can provide reliable and consistent information on the elastic-plastic anisotropy of the colonies in a high-throughput manner, compared to the other approaches being explored in current literature. Furthermore, the responses measured in this study have been compared against similar measurements on differently oriented grains of primary α in another Ti–6Al–4V sample. It was noted that the α-β colonies exhibit distinctly different elastic and plastic anisotropy compared to the primary α grains. Specifically, a significant dip in the indentation yield properties at 45 degrees declination angle (between c⃗ axis of colony α and the indentation direction) was observed, while the elastic response was found to be mostly isotropic. The experimental protocols presented in this work are broadly applicable to other grain-scale morphologies and alloys, and the results produced from these protocols will be invaluable to the further development and refinement of mesoscale material constitutive models.