Abstract
Diamond/alumina composites were tried to sinter by both routes of hot pressing (HPing) and hot isostatic pressing (HIPing), in which both sintering conditions are thermodynamically unstable for diamond. When the composites were sintered by the HIPing under 150 MPa at 1423-1473 K for 10.8 ks and by the HPing under 36 MPa at 1673 K for 10.8 ks, the transformation of the diamond into graphite in the composites was not detected by an XRD analysis. Adding of a little magnesia and titania as sintering additives was very effective for the densification and hardening of the composites. Dispersing diamond was effective to restrain the alumina grain growth during the sintering. The Vickers hardness of the composites containing 10 vol.% diamond processed with the sintering additives was slightly increased as compared with that of the alumina with no diamond. It was revealed that the diamond/alumina composites could be successfully sintered by both hot isostatic pressing and hot pressing under thermodynamically unstable conditions for diamond.
