The wear of diamond

The wear of diamond when rubbing against materials softer than itself is investigated. It is shown that the rate of wear depends primarily on the hardness of the second member, varying as hardness to the power 3.5 for hardnesses above 200 V. p. n. When the hardness of the second member is high enough, the tensile stresses acting on the diamond reach the fracture stress, and the wear quickly becomes visible. Below this point, the rate of wear is small and there is an appreciable delay before its onset can be detected. For metals, such as copper, silver and gold, which are well below the critical hardness, the scale of the wear process becomes extremely small and the relation between wear rate and hardness changes. It is thought that in these conditions the rate of wear becomes affected by residual effects arising from the stressing of the surface during the initial processes of polishing.