Plastic Deformation and Strengthening Mechanisms of Nanopolycrystalline Diamond

Abstract

Bulk nanopolycrystalline diamond (NPD) samples were deformed plastically within the diamond stability field up to 14 GPa and above 1473 K. Macroscopic differential stress Δσ was determined on the basis of the distortion of the 111 Debye ring using synchrotron X-ray diffraction. Up to ∼5(2)% strain, Debye ring distortion can be satisfactorily described by lattice strain theories as an ellipse. Beyond ∼5(2)% strain, lattice spacing d 111 along the Δσ direction becomes saturated and remains constant with further deformation. Transmission electron microscopy on as-synthesized NPD shows well-bonded grain boundaries with no free dislocations within the grains. Deformed samples also contain very few free dislocations, while density of {111} twins increases with plastic strain. Individual grains display complex contrast, exhibiting increasing misorientation with deformation according electron diffraction. Thus, NPD does not deform by dislocation slip, which is the dominated mechanism in conventional polycrystalline diamond composites (PCDCs, grain size >1 μm). The nonelliptical Debye ring distortion is modeled by nucleating dislocations or their dissociated partials gliding in the {111} planes to produce deformation twinning. With increasing strain up to ∼5(2)%, strength increases rapidly to ∼20(1) GPa, where d 111 reaches saturation. Strength beyond the saturation shows a weak dependence on strain, reaching ∼22(1) GPa at >10% strain. Overall, the strength is ∼2–3 times that of conventional PCDCs. Combined with molecular dynamics simulations and lattice rotation theory, we conclude that the rapid rise of strength with strain is due to defect-source strengthening, whereas further deformation is dominated by nanotwinning and lattice rotation.

Rational design of diamond through microstructure engineering: From synthesis to applications

“…Reproduced with permission: Copyright 2021, American Chemical Society. 257 et al 255 claimed that graphitization is the mechanism of plastic deformation through MD simulating nanoindentation experiments on {100} crystal plane of SCD (Figure 11D). The C-C bond fracture and recombination of neighboring C atoms result in the transformation from sp 3 into sp 2 carbon.…”

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

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“…1,2 With the advance of synthetic diamond technology, diamond's applications have attracted widespread attention, being recognized as an "extreme functional material" that ensures high performance in products across various fields, including aerospace, microelectromechanical systems, biomedicine, and nuclear energy. 3,4 Despite being the hardest known material, diamond is not capable of withstanding high friction against ferrous metals, including Fe, Mn, Cr, and Ti, and their alloys, such as alloy steel, the most important metal alloy in the world. 5,6 This is due to the strong affinity of diamond's sp 3 hybrid carbon for these ferrous metals.…”