Fracture toughness and thermal resistance of polycrystalline diamond compacts

Abstract

Polycrystalline diamond compacts (PCD) are being used increasingly for oil and gas drilling and in machining of ceramics and hard non-ferrous materials. Average diamond grain size and its distribution are used as one of the means to tailor properties of PCD compacts. The diamond sintering process requires use of a tungsten carbide cobalt disc placed onto diamond powder followed by high pressure and high temperature conditions. During this process pseudo-eutectic, WC-Co liquid from the tungsten carbide disc is infiltrated into diamond powder providing a liquid phase to facilitate inter-grain diamond bonding. The amount and chemical composition with respect to carbon content of the liquid phase are dependent on average diamond grain size and its distribution. Finer diamond sizes tend to have higher sintered density than coarser sizes indicating a higher volume fraction of metallic content. The role of residual metallic content of the diamond layer in conjunction with average grain size on fracture toughness of the diamond layer was investigated. The fracture toughness was determined using a diametral compression test. Larger grain PCD compacts having lower amounts of matallic content were found to have a higher toughness than fine grained materials with higher amounts of residual metallic phase. PCD compacts of different starting diameter grain sizes were subjected to elevated temperatures under different gas environments and examined for their thermal resistance. The results are explained in terms of total metal content of the diamond layer in conjunction with the development of inter-grain diamond bonding.