Stepwise erosion as a method for determining the mechanisms of wear in gas borne particulate erosion

In erosion and abrasion, the detailed processes that cause material removal are still poorly understood. This means that with a few notable exceptions, good models for the prediction of materials behaviour are not still readily available. Stepwise testing is a new approach that has been recently developed as a way of providing information on the build up of damage in erosion. The technique uses a combination of exposing a test sample to repeated very low duration abrasion or erosion followed by accurate relocation in the SEM. This enables the real wear processes within a material to be followed in considerable detail, giving an excellent basis for developing new and improved models. In this preliminary study, the technique has been applied to the gas borne particulate erosion wear of a high speed steel and a WC/Co hardmetal. For the hardmetal, it was observed that in the initial stage of wear although gross damage to the structure of the material occurred over the localised area corresponding to the impact area of the particle, some damage occurred over a much wider area. This was thought to be due to immediate fragmentation of impacting particles followed by scouring of the surface near the impact site by fragments. Further damage was caused by a combination of further removal of the binder phase, build up of plastic deformation in single WC grains followed by fracture and fragmentation and removal, and intergranular fracture of the WC skeleton. Multi-grain cracking was not observed, suggesting that models based on indentation cracking are not realistic.