Thermodynamic modeling of Mo–Os, W–Os and Mo–Os–W systems

Abstract

Based on critical evaluation of the literature data, the Mo–Os and W–Os binary systems have been reviewed and assessed by means of the CALPHAD technique. The substitutional solution models are adopted to describe the liquid, bcc (βMo, βW) and hcp (αOs) phases, and the compound energy models with two sublattices are to describe the σ and Mo₃Os phases. The phase equilibrium data of the Mo–Os and W–Os systems are well produced by the present modeling. Using the obtained thermodynamic parameters of the sub-binary systems, the thermodynamic description has been extended to the Mo–Os–W ternary system, covering the whole composition and temperature ranges. There is no ternary compound in this system. The σ phase forms a continuous solid solution crossing the phase diagram. A set of self-consistent thermodynamic parameters for the Mo–Os–W system is systematically optimized to describe to the bcc, σ and Mo₃Os phases. Comprehensive comparisons between the calculated and reported phase diagram information show that the reliable information is satisfactorily accounted for by the present modeling. The liquidus projection and reaction scheme of the Mo–Os–W system are also generated by using the present thermodynamic parameters.