Indentation fracture and soft impresser fatigue in sapphire and polycrystalline alumina

• Published in: International journal of refractory metals & hard materials 1998-03, Vol.16 (406), p.323-329
• Main Authors: Hooper, R M, Guillou, M-O, Henshall, J L
• Format: Article
• Language: English
• ISSN: 0263-4368

The soft impresser technique has many advantages compared with conventional diamond pyramid indentation for studying the deformation and fracture of materials that would normally be considered "brittle". In particular, as utilised in this study, it can be used to study the evolution of deformation and crack initiation and propagation under contact fatigue conditions. Alumina, both in its sintered polycrystalline form and as single crystals (sapphire), has been investigated because of its many uses in engineering load-bearing applications. Initially conical tool steel impressers were used to subject the flat ceramic surfaces to mean pressures of 5.2plus/minus2.4 GPa for up to 7.5x10 exp 6 cycles. Plastic deformation in the polycrystalline alumina was observed after only 10 exp 3 loadings, followed by cracking at the edge of the contact zone and subsequent crack interlinking and radial extension. The sapphire showed no signs of deformation or cracking under these conditions, but did deform and crack after only one cycle when a harder WC/Co impresser was used.