Impact fatigue fracture of polycrystalline diamond compact (PDC) cutters and the effect of microstructure

The fatigue behaviour and failure of polycrystalline diamond compact (PDC) cutting tools under cyclic impact loading is investigated. These tools are composed of a polycrystalline diamond layer in-situ bonded onto a tungsten carbide substrate via a high temperature and high pressure sintering route. Their main application is in oil and gas drilling and non-ferrous machining. The tools were subjected to repeated impact loading until catastrophic failure occurred or up to 5000 impacts. Results show typical fatigue fractures, with cracks initiated and intermittently grown with each successive impact. Impact force or stress (S) was varied and the number of impacts (N) to crack initiation, growth and catastrophic failure recorded in order to generate S–N fatigue curves. PDC cutters with a coarser grain microstructure exhibited up to 70% better impact fracture resistance than their fine grain counterparts. Their fatigue endurance limit was also about 10–15% higher. The frequency at which impact loads occurred did tseem to affect the fatigue behaviour.