C. Kumar; F. Hakanen; S. Bhusare; J.S. Szabó; T. Csanádi; J. Lagerbom; E. Huttunen-Saarivirta; G. Mohanty
SSRN 6929033 (2026)
High-entropy carbides (HECs) are emerging as promising ultra-high temperature ceramics for extreme environments; however, their micro-scale deformation mechanisms remain poorly understood. In this study, the orientation-dependent mechanical response and grain boundary effects in a Hf-free (V–Nb–Mo–Ta–W)C HEC were systematically investigated using nanoindentation and micropillar compression investigations. Continuous stiffness nanoindentation performed on grains oriented close to (100), (101), and (111) revealed clear crystallographic anisotropy, with hardness following the order (111) > (101) > (100), while all orientations exhibited a comparable indentation size effect. Micropillar compression along the same orientations yielded high strengths (~12 GPa) with relatively weak orientation dependence. Schmid factor analysis and slip trace measurements suggested that plastic deformation was predominantly associated with {111}⟨110⟩ slip. Despite significant differences in geometric Schmid factors, the measured yield stresses showed minimal variations, suggesting that deformation is controlled by a high intrinsic lattice resistance associated with the HEC structure. Deviations from ideal Schmid behaviour further imply contributions from non-glide stress components. To elucidate grain boundary effects, micropillars containing controlled boundary locations were fabricated. Grain boundaries acted as preferential sites for localized decohesion, chipping, and stress drop under the present test conditions, whereas single-crystal regions exhibited measurable slip plasticity without catastrophic failure. The combined results establish the interplay between crystallographic orientation, intrinsic lattice resistance, and grain boundary stability in governing deformation of HECs, providing critical insight for microstructural design of ultra-high temperature ceramic systems.