Application of Raman spectroscopy to determine stress in polycrystalline diamond tools as a function of tool geometry and temperature

Polycrystalline diamond (PCD) tools commonly consist of a PCD layer sintered onto a cobalt-tungsten carbide (Co-WC) substrate. These tools are used in diverse applications and both the magnitude and distribution of the stresses in the PCD layer affect tool behavior. These stresses in sample drill-bits were investigated by means of micro-Raman spectroscopy in which the properties of the diamond Raman peak reveal both the nature of the stress present (compressive or tensile) and its magnitude. It was found that the surface preparation techniques influenced the average stress present in the PCD surface layer which was in compression in all cases investigated. The largest stresses were encountered in the roughly lapped sample (1.4 GPa) with the stress values decreasing for fine lapping (0.8 GPa) and polishing (0.1 GPa). Small areas with low tensile stresses were found in some polished samples. Measurements of stress as a function of temperature for roughly lapped sample drill-bits indicated a linear trend of decreasing stress values with increasing temperature, although the stress remained compressive. Cyclic annealing of a sample drill-bit to 600 °C shows that the tool properties are retained after 5 cycles, while similar cycling to 800 °C resulting in a permanent degradation of the tool properties.

Research highlights
► Raman study of surface compressive stress in polycrystalline diamond toolbits.
► Study of dependence of surface stress state on lapping and polishing.
► Effect of high temperatures on compressive stress in PCD layer.