Hot Isostatic Pressing of Cubic Boron Nitride with Alumina

Abstract

Hot isostatic pressing of cBN with Al₂O₃ was carried out in the thermodynamically metastable region of cBN in the phase diagram of BN. No hBN was yielded in the cBN-Al₂O₃ specimens HIP ped under 150MPa at 1200°C for 3hr. The specimen which had a large amount of cBN did not densify, because the pressure and temperature of the HIP condition were not so high as compared with those of the conventional very high pressure sintering condition of cBN. The specimens containing cBN up to 30vol%, however, densified to about 95% or more. The microhardness increased monotonously as cBN content increased from 0 to 30vol%. The HIP ped 30vol% cBN-70vol% Al₂O₃ had a vickers microhardness of above 2800 which is equal to 130% of that of sintered Al₂O₃. It is concluded that fabrication of high-density cBN-Al₂O₃ composites containing a relatively large amount of cBN, but not including hBN, is possible by HIP.