Adhesion and wear of diamond: formation of nanocracks and adhesive craters of torn out material

Abstract

Mechanical transformation of rough diamonds into brilliant ones is usually achieved by polishing using microsized abrasive diamond particles. It is shown that in addition to formation of periodic pattern of ‘partial’ Hertzian cone cracks on the diamond surface, nano-sized domains (50–150 nm in diameter) of crumbled material are observed. Because these domains are located in the centres of the regions (250–500 nm in diameter) partially surrounded by the Hertzian cone cracks, where the stresses are close to the stress field of hydrostatic compression, the material removal cannot be explained by creation of tensile or shear cracks. It is argued that the creation of these domains of crumbled material is due to adhesive interactions between sliding diamond particles and the diamond surface. Employing a two-term law of friction, the scheme of ultimate equilibrium between the particle and the surface is presented. The distributions of contact stresses are calculated for two approaches: (i) the extended Johnson–Kendall–Roberts model and (ii) the ‘soft’ model of adhesive contact. Thus, adhesion between the sliding diamond particle and the surface leads to creation of periodic pattern of the crumbling domains with the steps 500–1000 nm and adhesive tearing out of the material from the domains. This article is part of the theme issue ‘Nanocracks in nature and industry’.

Nanocracks in nature and industry

“…The first paper in this volume [ 19 ] describes experiments and theory that add to the original JKR concept by considering very small contacts in which the circular crack has nano-dimensions. This is followed by three papers [ 20 – 22 ] that investigate such JKR nanocracks in various circumstances, including adhesion of biofilm cells, elastic properties of cancer cells and the influence of shear forces that change the behaviour of the JKR cracks as sliding begins to occur.…”