Mechanical behavior of diamond matrix composites with ceramic Ti3(Si,Ge)C2 bonding phase

Abstract

Polycrystalline diamond, PCD, compacts are usually produced by high pressure–high temperature (HP–HT) sintering. This technique always introduces strong internal stresses into the compacts, which may result in self-fragmentation or graphitization of diamond. This may be prevented by a bonding phase and Ti3(Si,Ge)C2 was so investigated. This layered ceramic was produced by Self Propagating High Temperature Synthesis and the product milled. The Ti3(Si,Ge)C2 milled powder was mechanically mixed, in the range 10 to 30wt.%, with 3–6μm diamond powder (MDA, De Beers) and compacted into disks 15mm in diameter and 5mm high. These were sintered at a pressure of 8.0GPa and temperature of 2235K in a Bridgman-type high pressure apparatus. The amount of the bonding phase affected the mechanical properties: Vickers hardness from 20.0 to 60.0GPa and Young's modulus from 200 to 500GPa, with their highest values recorded for 10wt.% Ti3(Si,Ge)C2. For this composite fracture toughness was 7.0MPam1/2, tensile strength 402MPa and friction coefficient 0.08. Scanning and transmission electron microscopy, X-ray and electron diffraction phase analysis were used to examine the composites.