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

Abstract

a b s t r a c tThe 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.

Plastic Deformation of Single‐Crystal Diamond Nanopillars

“…Early reports suggested that improvements in nanodiamond strength can be achieved by a controlled introduction of nanotwinning . On the other hand, localized plastic deformation can be induced by mechanical indentation at very high temperatures . However, due to challenges in nanofabrication of diamond all earlier studies were done on bulk or microstructured diamond, and our understanding of mechanical properties of nanoscale single‐crystal diamond are poor.…”

Plastic Deformation and Strengthening Mechanisms of Nanopolycrystalline Diamond

“…All of these are characteristics of a dislocation-slip mechanism, which is fundamentally no different from that in diamond single crystals. The fact that PCDCs are weaker than single crystals may be attributed to the binder materials used, which preferentially reside along diamond grain boundaries, , weakening the bulk mechanical properties. Impurities and concentrations of point defects on or near the surface of diamond grains are also known to affect mechanical properties …”

“…Cell assembly used in these experiments was identical to that reported in an earlier report (Figure S2). Deformation was achieved by advancing the two differential rams, shortening the sample along the cylindrical axis. Since the differential rams can be adjusted independently from the main hydraulic ram, differential stress and sample axial strain were controlled essentially independently from hydrostatic pressure.…”

A Review of Binderless Polycrystalline Diamonds: Focus on the High-Pressure–High-Temperature Sintering Process

“…Plastic behavior of NPDs compared to conventional PDCs was studied at HP–HT using D-DIA press coupled with X-ray radiography and diffraction [ 190 , 191 , 192 ]. Deformation of PDCs was highly dependent on the binder content and resulted in strong work hardening.…”