Hardness and Indentation Size Effect in Cubic Boron Nitride Materials (BL and BH Groups)

This paper investigates the hardness and indentation size effect (ISE) in cubic boron nitride (cBN) materials, specifically focusing on two groups: BL (below 70 vol.% cBN) and BH (more than 70 vol.% cBN). The study examines the load dependence of hardness in both groups, determining the load at which hardness becomes constant. Fracture toughness, (by the length of the crack) around indentations, is also evaluated for load dependence. The materials were synthesized using different additive combinations (Al, TiC, TiN, Mo) and sintered under high pressure and temperature. Hardness was measured using a Vickers indenter, and the ISE was analyzed using Meyer's law and the proportional sample resistance (PSR) model. Fracture toughness was calculated using the Niihara equation. Results show a significant ISE in BL materials, while BH materials exhibit less “load-hardness” dependence.