Relationship between Si concentration and mechanical properties of Nb-Si compounds: A first-principles study

The effect of chemical bonding on the mechanical properties of high-temperature materials remains a big challenge. In this paper, the relationship between Si concentration and mechanical properties for Nb-Si compounds was investigated by first-principles calculations. One previously unreported crystal structure of Nb2Si with Ta2Si-type structure was predicted. The elastic properties, hardness and chemical bonding of Nb-Si compounds were calculated in detail. The calculated formation enthalpy shows that Nb5Si3 is more stable than that of other NbSi compounds at the ground state. The obtained shear modulus, Young's modulus and hardness of Nb-Si compounds increase with increasing Si concentration. NbSi2 exhibits the strongest shear deformation resistance and the biggest hardness among these Nb-Si compounds. It thus can be concluded that the variation of elastic properties depends not only on the Si concentration but also on the chemical bonding. With increasing Si concentration, Nb-Nb metallic bond is disappeared and Si-Si covalent bond is formed. (C) 2015 Elsevier Ltd. All rights reserved.