Effect of indenter radius on mechanical properties of B3-GaN in nanoindentation based on molecular dynamics

Abstract

Molecular dynamics (MD) simulation of nanoindentation was conducted to study the indentation of sphalerite gallium nitride (B3-GaN) according to different radius spherical indenters. The effect of indenter radius on the evolution of dislocations, atomic displacements, Von Mises stresses, and phase transition of B3-GaN was primarily analyzed. The outcomes of the study indicate that the plastic deformation of B3-GaN crystals may be attributed to the propagation of dislocations and amorphization. The pop-in events of load in the load-depth curve is related to dislocation nucleation, amorphization, and phase transition. As the indenter radius increases, the critical load during the elastic-plastic transformation increases, and the hardness decreases gradually. The Burgers vector of dislocations during indentation is almost all 1/2 <110>, and the main slip directions were along the <110> crystallographic direction family. The magnitude and distribution range of atomic displacements and Von Mises stresses increase with the indenter radius, and this further promotes the nucleation and propagation of dislocations in the slip system, thus intensifying the plastic deformation of B3-GaN crystals. The elastic deformation of B3-GaN crystals may be attributed to amorphization and phase transition. During the elastic deformation phase, increasing the indenter radius promotes the phase transition of B3-GaN to fibrillated gallium nitride (B4-GaN) and enhances the amorphization of B3-GaN in the deformation layer. In addition, the increase in the indenter radius delays the generation of amorphous phases and phase transition. The outcomes of the study help us understand the mechanical properties of B3-GaN along with its potential for use in precision finishing.