Effects of twin thickness, strain rate, and temperature on the mechanical properties of nanotwinned diamond

Abstract

Nanotwinned (NT) diamond is a superior ceramic material known for its extreme hardness and strength. Both intrinsic and extrinsic factors strongly affect the mechanical properties of NT diamond. Here, we perform molecular dynamics (MD) simulations to study the mechanical properties of NT diamond under uniaxial tension, emphasizing the effects of twin thickness, strain rate, and temperature. The structural evolution, crack initiation and propagation, and scaling laws of strength and toughness are studied. Our findings reveal that a higher number of branching cracks enhance the mechanical properties of NT diamond, particularly when compared to single-crystal diamond. The presence of twin structures alters the orientation of diamond atoms, changing the direction of crack propagation and resulting in increased branching cracks upon fracture. Within constrained geometries, a “thinner is stronger” trend is observed concerning twin thickness. Our quantitative analysis further shows that mechanical properties decline with decreasing strain rates and increasing temperatures. This strain rate effect is attributed to the relaxation of residual stress, where the released energy compensates for the formation of new surfaces. We also provide a predictive model for the mechanical properties of NT diamond, offering valuable insights for the development of high-performance NT superhard materials.