The carbides and nitrides of transition metals are technologically very important materials due to their hardness and high melting points. In this paper we present the mechanical properties of these compounds of Ti and Zr in NaCl (B₁ phase) and CsCl type (B₂ phase ) structures. Using the calculated properties, we discuss the mechanical stability and brittle/ductile nature of these compounds. The elastic constants C₁₁, C₁₂ and C₄₄ are first calculated by applying various distortions to the original crystal structure and then elastic properties such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio are derived using these elastic constants in the standard relations. FPLAPW method has been used within the framework of density functional theory.

Keywords: Ab-initio, Mechanical stability, Elastic properties, Brittle, Ductile.