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A series of three-dimensional molecular dynamics (MD) simulations was performed to investigate the effect of temperature on the nanoscale deformation behaviour and mechanical properties of c -plane monocrystalline gallium nitride (GaN) under nanoindentation. Simulation results showed that the atomic displacement and strain increased with increasing temperature. Thus, the nucleation and propagation of dislocations in the main slip systems were promoted to intensify the plastic deformation of GaN crystal. Increasing the temperature also contributed to the increase in local phase transition from the wurtzite crystal structure (B4-GaN) to the zinc-blende crystal structure (B3-GaN) and a very evident amorphization of GaN in the indentation zone. Based on the analysis of the load-depth curves, it was found that both the hardness and Young's modulus decreased as the temperature increased. This work can enrich the atomic-level understanding of the effect of temperature on the mechanical response of monocrystalline GaN when subjected to the external loads. [ABSTRACT FROM AUTHOR]

Mechanical activation in mechanical removal of GaN using diamond tip and mechanochemical removal using Al 2 O 3 tip are described by the Archard equation and mechanically assisted Arrhenius-type kinetic model, respectively. Evident material-removal under elastic contact occurs with the assistance of interfacial mechanochemical reactions. By analyzing the mechanochemical reactions with Arrhenius-type kinetic model and Hertzian contact mechanics, the critical activation volume and activation barrier are determined semiquantitatively. The mechanical activation originating from the chemically active counter-surface facilitates the mechanochemical atomic attrition by altering the energy barrier of the reaction kinetics. This work can provide deep insights into the mechanochemical-removal mechanism of GaN. • Linear dependence between load and GaN removal against diamond obeys Archard's equation. • Evident mechanochemical removal of GaN against Al 2 O 3 occurs under purely elastic contact. • Mechanochemical removal of GaN using Al 2 O 3 is described by the modified Arrhenius-type model. • Mechanical activation reduces the energy barrier of mechanochemical reaction kinetics. • Synergic effect of counter-surface chemistry and mechanical energy is elucidated. [ABSTRACT FROM AUTHOR]

• Texturing effects on nanotribological properties and subsurface damage are studied. • Nanoscale friction and wear behaviour of GaN can be regulated by texture parameter. • Nano-texture can alleviate dislocation development and reduce subsurface damage. • The m -GaN exhibits lower wear and thicker damage layer compared with the c -GaN. Surface nanotribological properties and subsurface damage of flat and textured gallium nitride (GaN) substrates during both linear and circular nanoscratching processes are investigated using molecular dynamics simulation. Results show that the surface texture can remarkably reduce not only the surface friction and wear but also the scratching-induced subsurface damage regardless of the tip radius and penetration depth. Tangential force and friction coefficient decreased with an increase in groove width or depth primarily due to the reduced contact area. The effect of texturing on stress distribution can affect the development of dislocation to alleviate the nanoscale material deformation and removal and thereby reduce surface wear and subsurface damage. Increasing tip radius can reduce the friction coefficient and surface wear, but it promotes subsurface damage. By contrast, increasing tip penetration depth can increase the friction, wear, and subsurface damage for flat and textured GaN substrates. Compared with the c -plane, the m -plane GaN substrate exhibits higher friction but lower material wear, and it has a considerably thicker subsurface damage layer due to the difference in their dislocation networks. This work can provide useful insights into the design of GaN-based material with antifriction and wear properties through the surface texturing treatments. [ABSTRACT FROM AUTHOR]

• Nano abrasive machining of monocrystalline GaN is studied by molecular dynamics simulations. • Deformation of monocrystalline GaN is associated with both the propagation of dislocation and the contact of workpiece/tool. • Dislocation and phase transition are identified in the deformation layer after nano abrasive machining. • Pile-up and elastic recovery of monocrystalline GaN are affected by the stagnation region and slip system. • Effects of cutting velocity, depth of cut and abrasive shape on deformation are systematically investigated. Molecular dynamics simulations are carried out to investigate the nano abrasive machining of monocrystalline gallium nitride (GaN). Effects of the cutting velocity, depth of cut (DOC) and abrasive shape on the atomic strain, stress, temperature, cutting forces, and deformation layer are systematically investigated, aiming at understanding the deformation behaviour of monocrystalline GaN during nano abrasive machining. The results show that the strain, stress and temperature were increased by using the higher cutting velocity, the larger DOC or cub-octahedral abrasive. Being affected by both the average stress and the elasto-plastic deformation zone right ahead the diamond particle, the cutting forces increase with the increase in DOC but decrease under a larger cutting velocity, or when using a cub-octahedral abrasive. The deformation layer in the subsurface is insensitive to the cutting velocity, while impressively shrinks under a larger DOC or cub-octahedral abrasive used. As the stress and temperature rise, the use of higher cutting velocity, larger DOC or cub-octahedral abrasive would facilitate the nucleation of dislocation, phase transition and the development of pile-up. This work can enrich the understanding on the nanoscale deformation mechanism of monocrystalline GaN material during the ultra-precision machining process. [ABSTRACT FROM AUTHOR]