High-pressure, high-temperature plastic deformation of sintered diamonds

• Two polycrystalline diamond (PCD) samples were deformed jointly at high pressure and temperature.
• Their strength was retrieved in situ using synchrotron X-ray diffraction.
• Our data show that the samples were deformed in the dislocation creep regime.
• One of the samples presents fewer impurities and improved mechanical properties.

The strength of polycrystalline diamond (PCD) was investigated through a high pressure (P) and temperature (T) deformation experiment. Prior to the deformation experiment, two bulk samples were sintered back to back under identical conditions with two different precursors, which shared identical initial grain size distribution. Precursor of one sample (2E) had lower concentration of crystalline defects than that of the other sample (1S). In crushing strength tests, precursor of 2E exhibited an enhanced crushing strength compared to that of 1S. During the high P–T deformation experiment, the two samples were stacked back to back and deformed together. Their mechanical properties were investigated in situ using synchrotron X-ray diffraction and imaging in the deformation DIA apparatus. The strain data based on imaging showed that the two samples were deformed at identical strain rates (ca. 1.5 × 10− 5 s− 1) and analysis based on lattice plane distortions in the diffraction patterns showed that sample 2E exhibits marginally higher strength than that of sample 1S. The X-ray data indicate that, upon deformation, larger elastic lattice strain builds up within the grains in sample 2E, indicating greater strength at grain-to-grain level in this sample. In addition, lower micro-stress levels are evidenced upon hydrostatic loading of sample 2E, strongly indicating a better sintering state than that in sample 1S. We interpret these differences as due to a lower defect concentration, particularly on the grain surfaces of the precursor powder, that results in stronger diamond–diamond bonding. Altogether, these data suggest that the use of diamond grains with reduced defect concentration and cleaner surfaces as precursors will likely improve the wear resistance of the resulting PCD via stronger individual grains and better sintering.

Figure optionsDownload as PowerPoint slide