Hardness of hexagonal AlB2-like diborides of s, p and d metals from semi-empirical estimations

The high-level ab initio calculations of elastic moduli of materials now become a routine procedure, and the renewed attention is paid to the semi-empirical macroscopic models, providing the correlations between the Vickers hardness H-V and some elastic moduli. Such correlations, building up a bridge between Vickers hardness and elastic parameters, seem a helpful way to semi-quantitative estimations of hardness and to theoretical search of novel hard materials, based on the calculations of their elastic properties. Here, using the results of our calculations of elastic parameters of 14 hexagonal AlB2-like diborides of s, p and d metals MB2 (where M=Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W), we have probed six recently proposed correlations between Hv and bulk (B), shear (G), Young's moduli (E), as well as Poisson's ratio (v), and the parameter k (the G/B ratio), and we compare the obtained results with the available experimental data. Our analysis reveals that for this family of related materials the correlations H-V similar to G, and H-V similar to E will be the most suitable approximations which enable us to roughly evaluate the Vickers hardness of diborides numerically. (C) 2012 Elsevier Ltd. All rights reserved.