Damage processes in ceramics resulting from diamond tool indentation and scratching in various environments

• Published in: Wear 1995-03, Vol.181-183 (II), p.551-562
• Main Author: Ruff, A
• Format: Article
• Language: English
• ISSN: 0043-1648
• DOI: 10.1016/0043-1648(94)07104-7

Studies have been carried out to determine the influence of different chemical environments and tool shapes on damage produced during diamond tool scatching and indenting of two advanced ceramics: chemical-vapor-deposited silicon carbide and a composite aluminum oxide-titanium carbide. A nonindentation/scratching apparatus was used in a controlled-load mode for the studies. Two diamond tool shapes were used: a wedge with -45 deg rake and 0.5 mm radius curved edge, and a Vickers pyramid. The environments studied were: air, water, mineral oil, mineral oil+stearic acid and two commercial water-based fluids. It was of interest to identify damage mechanisms, critical loads for initiation of severe damage, specific scratching energies and the effect on damage of the different tool shapes. It was found that chemico-mechanical interactions during scratching in the different environments led to significant differences in such parameters as damage threshold load, maximum tool penetration depth and specific scratching energy. In some cases surface chemical films appeared to form and control the scratching process, especially at low loads. At higher loads significant chemical influences on the mechanical damage processes also were found. Damage morphology involved discrete surface cracking, spalling, grain pull-out and plastic deformation. In many cases considerable plastic response of the relatively brittle ceramics was observed. The proportions of cracking and plasticity varied substantially with tool shape, environment and material. Discontinuous surface cracking damage was observed in some cases, suggesting that a sub-surface process of damage or strain energy accumulation was involved.