Wear of bulk ceramics in micro-scale abrasion—The role of abrasive shape and hardness and its relevance to testing of ceramic coatings

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Abstract There is a wide body of literature wherein the micro-scale abrasion test has been employed to assess the behaviour of a range of vapour-deposited ceramic coatings. However, the fundamentals of the micro-scale abrasion process with ceramic materials in general (both in monolithic form and as coatings) are not well understood. In this work, the micro-scale abrasive wear behaviour of a range of brittle materials was examined as a function of abrasive particle type and applied load. The three types of abrasive particle slurries were alumina, silicon carbide and diamond, of similar size distributions and all suspended in water. It was shown that the relative wear rates of the materials depended strongly upon the abrasive type selected. When the abrasives were harder than the testpiece in question, the behaviour was dominated by the angularity and the particle size distribution of the abrasive. High angularity and wide size distributions, observed with alumina and silicon carbide abrasives, resulted in the applied load being carried by a small number of abrasive particles which resulted in lateral fracture and high rates of wear, whereas blocky abrasives (such as diamond) resulted in the load being carried by a larger number of particles and thus lateral fracture being restricted with correspondingly low rates of wear. However, when the abrasives were either softer or not significantly harder than the testpieces, the relative hardnesses dominated the operative wear mechanisms. In previous work, it has been shown that ball roughness in the micro-scale abrasion test promotes abrasive entrainment into the wear zone throughout the test. In this work, it has been shown that high testpiece roughness as developed in the wear scar (due to lateral fracture being the primary mechanism of material removal) hinders further abrasive particle entrainment, and that testpieces which wear with a smooth surface morphology (by plastic flow rather than by brittle fracture) exhibit enhanced particle entrainment under conditions (such as high applied load) where other materials are demonstrating limited entrainment.