A modified indentor technique for generating cone cracks in diamond and new results obtained from the technique

The traditional Hertzian method of generating cone cracks in diamond by usi ng a spherical diamond indentor is costly in terms of preparation time of t he indentor and the fact that very few indents can be made before the inden tor fails. A new technique of indentor strength testing was developed which utilises a polycrystalline diamond (PCD) tip shaped into a flattened cone of included angle 120 degrees with a flat tip of diameter 90 mu m. To reduc e the stress intensifying-effect of asperities on the PCD tip, a 50 mu m th ick, 316 L annealed stainless steel shim was inserted between the indentor tip and the diamond sample. Atomic force microscopy and micro Raman spectro scopy of cone cracks on synthetic 1b {100} polished diamond surfaces have p rovided additional information on the deformation and fracture mechanisms o f diamond. Deformation of material near the inner edge of the ring crack ap pears to be larger due to friction along the crack interface preventing com plete relaxation of the indented cone. Depressions within the ring crack ar e believed to be evidence for the microplasticity of diamond at room temper ature without associated fracture. (C) 1999 Elsevier Science S.A. All right s reserved.