Comparison of the creep properties of single crystal and polycrystalline diamond cutting tool materials

This paper presents original work on the time dependent plastic deformation of a polycrystalline diamond (PCD) cutting tool material. The material, an aggregate of type Ib diamond and beta -SiC, with a room temperature Vickers hardness of 40 GPa, has been studied using the soft impressor method. To simulate working conditions more closely, impressions were made using a polycrystalline cubic boron nitride (PcBN) impressor, in the temperature range 800 degreesC-1250 degreesC and a normal load of 100 N. The pressure transmitted by the blunt impressor to type Ib diamond single crystal introduces macroscopic plastic how through multiple {111}(1 (1) over bar0) intersecting slip. Furthermore, direct phase detecting interferometry (DPDI) confirms that both the impression depth and the associated internal residual plastic strain increases proportionally with increased contact time. By comparison, there was no evidence to support time dependent plastic how in the PCD material as a result of the mean contact pressures developed by PcBN. However, an increase in both the diameter and the depth of Vickers indentations with increasing contact time was observed, suggesting that in this type of composite material, impression creep by dislocation controlled slip processes occurs at significantly higher pressures than in single crystal type Ib diamond. (C) 2001 Elsevier Science B.V. All rights reserved.