In-plane anisotropy and twin boundary effects in vanadium nitride under nanoindentation

Tao Fu,Xianghe Peng,Ning Hu,Henggao Xiang,Cheng Huang,Shayuan Weng,Zhongchang Wang

doi:10.1038/s41598-017-05062-0

Tao Fu, Xianghe Peng + Show 5 more

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https://doi.org/10.1038/s41598-017-05062-0

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Abstract

Twin boundaries (TBs) have been observed in and introduced into nonmetallic materials in recent years, which brought new concepts for the design of new structural materials. However, the roles of TB on the mechanical properties and strengthening/softening of transition metal nitrides remain unclear. To investigate the TB effects and the in-plane anisotropy, nanoindentations on VN (111) films with and without TB were simulated with molecular dynamics, in which a cylindrical indenter was used, and its longitudinal axis were assigned along <112> and <110>, respectively. We found that the effect of the indenter orientation is insignificant in the elastic stage, but significant in the following inelastic deformation. Different deformation mechanisms can be found for inelastic deformation, such as twinning and dislocation glide. The migration of TB can be observed, which may release the internal stress, resulting in softening; while the dislocation locking and pileup at TB can enhance the strength. We also found that the strengthening/softening induced by TB depends on the deformation mechanisms induced by indenter directions.

Highlights

Transition metal nitrides (TMNs), such as vanadium nitride (VN) and titanium nitride (TiN), have attracted increasing attention due to their excellent physical and mechanical properties, especially high hardness and wear resistance1–4
The modified embedded atom method (MEAM) potential developed by Baskes et al.28–30, which has been successfully applied to the tension31, deposition32, surface energy33, 34 and stacking energy35, 36, is chosen to express the interaction between the film atoms
Nanoindetations on VN (111) films with or without twin boundary were performed with molecular dynamics simulations, in which cylindrical indenters along directions and were used to investigate the in-plane anisotropy and the effects of Twin boundaries (TBs)

Summary

Introduction

Transition metal nitrides (TMNs), such as vanadium nitride (VN) and titanium nitride (TiN), have attracted increasing attention due to their excellent physical and mechanical properties, especially high hardness and wear resistance. Transition metal nitrides (TMNs), such as vanadium nitride (VN) and titanium nitride (TiN), have attracted increasing attention due to their excellent physical and mechanical properties, especially high hardness and wear resistance1–4 The testing of these mechanical properties usually involves plastic deformation. The in-plane anisotropy and the corresponding deformation mechanisms may exist under nanoindentation if a cylindrical indenter is used, because the (111) surface has a three-fold rotation symmetry about its normal direction. We first investigate the in-plane anisotropy of VN (111) under nanoindentation with a cylindrical indenter along different axial directions, and explore the effects of TB on the mechanical properties of VN

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