Effects of transition metal (TM = Zr, Hf, Nb, Ta, Mo, W) elements on the shear properties of TMB2s: A first-principles investigation

Transition metal diborides (TMB(2)s) exhibit unique combination of excellent properties makes them promising candidates for extreme environmental applications. It is believed that activation of dislocation plasticity is beneficial to retain fracture strength of TMB(2)s based materials at high temperature, since plastic deformation can release elastic energy accumulated in the material and then fracture is suppressed. In this paper, shear properties of TMB(2)s (TM = Zr, Hf, Nb, Ta, Mo, W) for both (0001)[(2) over bar 110]/3 and (01<(1)overbar>0)[(2) over bar 110]/3 shear modes are evaluated by first-principles and the dependence of shear properties on TM elements is discussed by electron redistribution during the deformation. The results show that properties of the (0001)[(2) over bar 110]/3 shear are solely determined by TM-B bond and exhibit substantial dependence on TM elements, while the (01<(1)overbar>0)[(2) over bar 110]/3 shear are controlled by both TM-B bond and B-B sigma bond, which makes the dependence of shear properties on TM elements not that obvious. The simulated ideal shear strengths demonstrate that dislocation nucleation become easier in an order of ZrB2 (approximate to HfB2), NbB2, TaB2, MoB2, WB2, which reasonably explains some experimental observations and provides useful information for the design of TMB2 based materials by alloying. (C) 2016 Elsevier B.V. All rights reserved.