Effect of zirconium doping on the mechanical properties of W1-xZrxB2 on the basis of first-principles calculations and magnetron sputtered films

Abstract

Potentially superhard W1-xZrxB2 polymorphs, hP6-P63/mmc-WB2 and hP3-P6/mmm-WB2, were thoroughly analyzed with zirconium doping in the range of x=0-25%, within the framework of the first-principles density functional theory, from both a structural and a mechanical point of view. The obtained results were subsequently compared with the properties of material deposited by the magnetron sputtering method. All predicted structures are mechanically and thermodynamically stable. Theoretical calculations suggest a decrease in hardness Hv and fracture toughness KIC of the hP6 phase with zirconium doping but no such effect on the hP3 phase. It was observed that an additional defect in the analyzed structure significantly weakens the hP6 phase but strengthens the hP3 phase. The deposited films are characterized by greater hardness but lower fracture toughness. The results of experiments show that not only is solid solution hardening responsible for strengthening the predicted new material but also the change in microstructure, the Hall–Petch effect and vacancies.