Molecular dynamics simulation for orientation dependence of deformations in monocrystalline AlN during nanoindentation
HG Xiang and HT Li and JJ Chen and S Sun and QB Li and B Yang and XH Peng, CERAMICS INTERNATIONAL, 44, 10376-10382 (2018).
Molecular dynamics simulations were performed for the nanoindentations using a virtual cylindrical indenter on monocrystalline aluminum nitride (AlN) with the indentation surface orientations of 0001, 10 (1) over bar0, (1) over bar2 (1) over bar0 and (1) over bar 01 (2) over bar, respectively, to investigate the orientation dependence of the material. Vashishta potential was used to model the interactions between Al-Al, N-N, and Al-N atoms in the specimens. Simulation results indicated that the deformation mechanism varies with surface orientations at the initial inelastic stage. In the specimens with the surface orientations of 0001 and 10 (1) over bar0 phase transformation plays a predominant part, in the case of (1) over bar2 (1) over bar0 dislocation slip dominates the inelastic deformation, whereas in the case of (1) over bar 01 (2) over bar both phase transformation and dislocation slip act a leading role. However, the phase transformation and dislocation slip occur in all the samples during the further indentation. We found two paths of B4 to B1 phase transitions. Path I includes two steps: Al and N atoms move along the 0001 axis by an anti-parallel vertical motion, followed by horizontal relative movement of the two types of atoms. Path II is similar to Path I, but the sequence of relative movement of Al and N atoms is different. Path I occurs in the cases of 0001 and (1) over bar 01 (2) over bar orientations, while Path II in the cases of the other two orientations.
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