Fragmentation and stress diversification in diamond powder under high pressure

Studying the fragmentation and refinement of diamond powder as well as the diversification in the intergranular stress is crucial to produce a high-quality polycrystalline diamond. In this paper, using different micron-size diamond powders as the initial materials, the samples were compressed under different pressures at ambient temperature. The fragmentation behavior of the diamond powder was investigated by scanning electron microscopy and with a laser particle size analyzer. The results show that the fragmentation of diamond comprises three stages with increasing pressure: (i) fracturing of edges and corners, (ii) cracking of the crystal plane, and (iii) refinement of particle disorder; the particle deformation tends to become relatively stable after a certain pressure. In situ high-pressure synchrotron X-ray diffraction was used to study the intergranular stress distribution under non-hydrostatic compression to 35.1 GPa. A heterogeneous stress distribution was found in compressed diamond bulk, in which under the highest load, the maximum stress reached 69.5 GPa, whereas the minimum stress was only 18.8 GPa.