Influence of load and speed on rolling micro-abrasion of CVD diamond and other hard coatings

Abstract

Micro-abrasion tests have been performed on CVD diamond coated tungsten substrates under a range of test conditions to evaluate those which result in uniform and repeatable three-body rolling abrasion generating near perfect wear scars. The optimum test conditions for CVD diamond were established to be 0.3 N normal load, 75 rpm (0.1 m/s) ball rotation speed and at a SiC slurry concentration of 0.5 g/ml. Under these conditions steady state three-body rolling abrasion of CVD diamond occurs through brittle micro-chipping of the diamond grains. Tests at higher loads and ball rotation speeds are accompanied by a transition from this steady state abrasion to a more severe non-uniform wear pattern where complete coating removal from the substrate at localised regions is observed and grooving and wear tracks are present on the wear crater surface. Regions of smooth black non-diamond carbon (graphitic type) deposits are also observed showing some wear occurs through a graphitic transformation step. The results show that the diamond coatings exhibited a steady state specific wear rate of approximately 2–3×10 −14 m 3/N m from the optimised test conditions which is an order of magnitude lower than CVD B 13C 2 and PVD TiN–TiC which were also tested.