Temperature-induced tunable surface roughness in polycrystalline diamond

Abstract

Polycrystalline diamond (PCD) exhibits ultra-high hardness, fracture toughness and thermal conductivity, which is suitable for service at extreme temperatures. However, the correlation mechanism between temperature and surface roughness in PCD is still unclear, resulting in the inability to obtain atomic-scale surface. Therefore, the surface roughness of PCD at different temperatures was measured using an atomic force microscope, confirming that grain thermal expansion due to temperature has a significant impact on the surface roughness of PCD. Molecular dynamics simulation shows that the coefficient of thermal expansion of PCD decreases with a gradual increase in its average grain size. When the temperature changes, the model with a smaller average grain size exhibits more pronounced expansion compared to the model with a larger average grain size. This expansion inhomogeneity directly contributes to the variation in PCD surface roughness as a function of temperature. Inspired by the above, retaining an appropriate inverse height difference between grains on the surface of PCD based on the mapping relationship between service temperature and surface grain deformation at room temperature. So then, when PCD is raised from room temperature to service temperature, the different grains will be expanded to an approximate height level to obtain an ultra-smooth surface.