Elastic properties of translucent polycrystalline cubic boron nitride as characterized by the dynamic resonance method

Cubic boron nitride (cBN) is second only to diamond in a number of extreme material properties, and its performance exceeds diamond in many applications involving contact with ferrous alloys and/or high temperatures. However, its properties are less well understood. We have sintered cBN powder (2-4 mu m or 8-12 mu m particle size) into pure, translucent, polycrystalline compacts by pressing at a pressure of 7.7 GPa and temperatures from 2100 to 2350 degrees C without any sintering agent. We have determined the Young's modulus E, shear modulus G, and Poisson's ratio v of a number of translucent polycrystalline cBN compacts, in the form of free-standing disks, using the dynamic resonance method. The measured values for E, G, and v lay in the ranges of 665-895 GPa, 295-405 GPa, and 0.11-0.15, respectively, depending on the grain size of the cBN starting material and the sintering temperature. These values may be compared with the theoretical values of E, G, and v for pure, equiaxed, cBN of 909 GPa, 405 GPa, and 0.12, respectively. Combining the Young's modulus with previous Vickers hardness measurements, the fracture toughness K-IC of well-sintered translucent PCBN is evaluated as 6.8 MPa m(1/2). The dependence of the elastic properties on the synthesis conditions is discussed in the context of the microstructure and of related material properties. (C) 1999 Elsevier Science S.A. All rights reserved.