Reducing the Ideal Shear Strengths of ZrB2 by High Efficient Alloying Elements (Ag, Au, Pd and Pt)

Fu-Zhi Dai,Yanchun Zhou

doi:10.1038/srep43416

Abstract

Activating the plasticity of ZrB2 is a promising approach to improve its key properties for applications in hypersonic vehicles, including high temperature strength and thermal shock resistance. The present work demonstrates that ideal shear strength of ZrB2, which is a good indicator of the critical stress for dislocation nucleation, can be significantly reduced by dissolving of appropriate alloying elements. Analyzing on the bonding nature of ZrB2 reveals that choosing alloying elements with low energy valence electrons will prevent electron transferring from alloying element to the electron deficient B-B π orbits, which will reduce the local stability of the region surrounding the alloying element. Under the criterion, elements with d electrons tending to be full-filled (Ag, Au, Pd and Pt, the full-filled state is associated with low energy level) are selected as promising candidates with their prominent efficiency in reducing ideal shear strengths verified by first-principles calculations. The results provide useful guidelines for further designs of ZrB2 based materials, especially for improving their mechanical properties.

Highlights

ZrB2 based ultra-high temperature ceramics (UHTCs) exhibit unique combination of excellent properties, including high melting point, chemical inertness, effective wear and environment resistance, which makes them promising for applications as shape leading-edges and nose-tips in hypersonic vehicles[1,2]
To characterize the effects of alloy elements on the plasticity of ZrB2, the ideal shear strengths of ZrB2 with and without adding alloying elements were simulated by first-principles
Ideal strength can be defined as the stress necessary to induce permanent deformation in a material without prior imperfections[9,10], which is an important material characterization. It implies that the ideal shear strength can be taken as an indicator on the critical stress for dislocation nucleation, which has been broadly adopted in investigations[11,12,13,14]

Summary

Introduction

ZrB2 based ultra-high temperature ceramics (UHTCs) exhibit unique combination of excellent properties, including high melting point, chemical inertness, effective wear and environment resistance, which makes them promising for applications as shape leading-edges and nose-tips in hypersonic vehicles[1,2]. Evaluating the effect of alloying elements on the ideal shear strengths of ZrB2 is a promising guideline on the selection of elements that can improve the plasticity of ZrB2, since dislocation initiation is difficult for intrinsic brittle ceramics.

Results

Conclusion