Nanoindentation and tribology of a (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide

Abstract

Abstract A (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide was prepared by ball milling and a two-step Spark Plasma Sintering process, achieving a single-phase ceramic sample with a high relative density of 99.4%. The wear resistance of the sample was measured by tribology and micro-scale mechanical behaviour was studied by nanoindentation on both the non-deformed and worn surfaces. Grains and the vicinity of grain boundaries exhibited high hardness values of 38.5\u2009±\u20090.5\u2009GPa and 35.5\u2009±\u20091.0\u2009GPa with similar Young’s moduli of 562\u2009±\u200911\u2009GPa and 547\u2009±\u200916\u2009GPa, respectively. The dominant wear mechanism was mechanical wear with limited grain pull-out and fracture, and with a localized and thin tribo-layer formation. The specific wear rate exhibited an increase with the increasing load from 2.53·10-6\u2009mm3/Nm at 5\u2009N to 9.03·10-6\u2009mm3/Nm at 50\u2009N. This was correlated to the decrease of nanohardness of the worn surfaces with increasing wear load, which is attributed to the increased number of microcracks.