Bulk nanopolycrystalline diamond (NPD) samples have been deformed plastically throughout the diamond stability discipline as much as 14 GPa and above 1473 Okay. Macroscopic differential stress Δσ was decided on the idea of the distortion of the 111 Debye ring utilizing synchrotron X-ray diffraction. As much as ∼5(2)% pressure, Debye ring distortion could be satisfactorily described by lattice pressure theories as an ellipse. Past ∼5(2)% pressure, lattice spacing d111 alongside the Δσ path turns into saturated and stays fixed with additional deformation. Transmission electron microscopy on as-synthesized NPD exhibits well-bonded grain boundaries with no free dislocations throughout the grains. Deformed samples additionally include only a few free dislocations, whereas density of 111 twins will increase with plastic pressure. Particular person grains show complicated distinction, exhibiting rising misorientation with deformation in accordance electron diffraction. Thus, NPD doesn’t deform by dislocation slip, which is the dominated mechanism in typical polycrystalline diamond composites (PCDCs, grain dimension >1 μm). The nonelliptical Debye ring distortion is modeled by nucleating dislocations or their dissociated partials gliding within the 111 planes to provide deformation twinning. With rising pressure as much as ∼5(2)%, power will increase quickly to ∼20(1) GPa, the place d111 reaches saturation. Energy past the saturation exhibits a weak dependence on pressure, reaching ∼22(1) GPa at >10% pressure. General, the power is ∼2–three instances that of typical PCDCs. Mixed with molecular dynamics simulations and lattice rotation concept, we conclude that the speedy rise of power with pressure is because of defect-source strengthening, whereas additional deformation is dominated by nanotwinning and lattice rotation.