Temperature-dependent hardness of diamond-structured covalent materials

TL;DR

This study develops a temperature-dependent hardness model for diamond-structured covalent materials, revealing how dislocation mechanisms and material properties influence hardness variation with temperature, aiding superhard material design.

Contribution

A novel hardness formula based on dislocation theory that accounts for temperature effects and dislocation mechanisms in diamond-structured covalent materials.

Findings

Hardness controlled by Poisson's ratio and shear modulus at low temperature.

Transition from shuffle-set to glide-set dislocation control with increasing temperature.

Model aligns well with experimental data and guides superhard material design.

Abstract

Understanding temperature-dependent hardness of covalent materials is not only of fundamental scientific interest, but also of crucial importance for technical applications. In this work, a temperature-dependent hardness formula for diamond-structured covalent materials is constructed on the basis of the dislocation theory. Our results show that, at low temperature, the Vickers hardness is mainly controlled by Poisson's ratio and shear modulus with the latter playing a dominant role. With increasing temperature, the plastic deformation mechanism undergoes a transition from shuffle-set dislocation control to glide-set dislocation control, leading to a steeper drop of hardness at high temperature. In addition, an intrinsic parameter, a3G, is revealed for diamond-structured covalent materials, which measures the resistance to soften at high temperature. Our hardness model shows remarkable agreement with experimental data. Current work not only sheds lights on the physical origin of hardness, but also provides a direct principle for superhard materials design.