MECHANICAL-PROPERTIES OF POLYCRYSTALLINE TRANSLUCENT CUBIC BORON-NITRIDE AS CHARACTERIZED BY THE VICKERS INDENTATION METHOD

Mechanical properties of polycrystalline translucent cubic boron nitri de (cBN) were characterized by Vickers indentation measurement. The ca lculated hardness decreased from 54 to 49 GPa as the load increased to 39 N, and then remained constant for values above this load. Accordin g to the relationship between crack length and applied indentation loa d, the formation of the median/radial type of cracks seems to take pla ce at an applied load above 29 N. Assuming that the ratio of hardness and Young's modulus is constant in the polycrystalline cBN, the fractu re toughness, K-IC, of cBN was estimated to be 5.0 +/- 0.5 MPa . m(1/2 ).