Model scratch corrosion studies for WC/Co hardmetals

WC/Co hardmetals are widely used in tool applications where resistance to abrasive wear is important. In corrosive environments the loss of material is amplified due to synergistic effects. This paper reports the results of model experiments using a micro-tribology test system and diamond indenters to examine the details of microstructural mechanisms of wear and damage that take place in abrasion of these materials. An important element of the experiments was to examine the differences in wear and damage that were generated when a corrosive fluid was present compared to the similar experiments when the corrosive fluid was not present. A sequence of scratches was made using the test system interspersed with examination of the scratch in a high resolution SEM at periodic intervals. A time history of damage was built up at the scale of the grain structure or finer in the materials. It was found that when no corrosive fluid was present, a layer of binder phase with embedded nano-sized fragments of WC was generated. There was also considerable evidence of plastic deformation of the WC grains leading to fracture of the grains. With corrosive fluid (HCl), no Co was left on the surface of the sample and considerable fracture of the surface had occurred leading to removal of WC grains from the surface. The results of this study are compared and contrasted with the results of other types of abrasive wear experiments on WC/Co hardmetals.