Indentation size effect anisotropy in TaC and HfC ceramic grains

Abstract

The indentation size effect (ISE) anisotropy was investigated in grains of low-index orientations in TaC and HfC polycrystalline ultra-high temperature ceramics. The samples were prepared by spark plasma sintering from precursor carbides and were subjected to careful surface preparation. The crystallographic orientations of grains were determined by electron backscatter diffraction. ISE was studied on low-index {001}, {101}, and {111} crystal facets, which were subjected to nanoindentation using a Berkovich tip with a maximum penetration depth of 1000 nm. It was revealed that the Nix–Gao model adequately describes both materials above ∼170 nm, resulting in a more significant ISE for TaC compared to HfC. The analysis of model parameters inferred different slip activations reported in the literature. HfC exhibited a more brittle behavior due to the limited number of independent slip systems compared to TaC. The most intense cracking was observed on the {101} facets in both materials, and the anisotropic cracking was in agreement with the calculated maximum density of geometrically necessary dislocations.