Thermodynamic analysis and modeling of Pd-Ni-S bulk metallic glass-forming system

Abstract

This study explores both experimental and computational aspects of the thermophysical properties of the novel ternary BMG-forming Pd-Ni-S system. Unlike more complex quinary BMG-formers, this ternary system's simplicity allows for applying the CALPHAD approach to model the underlying thermodynamics governing glass formation. Experimental investigations include quantifying specific heat capacity and studying crystallization across various compositions critical for generating essential input data. Using a two-state approach, initial modeling of the undercooled liquid and glass is conducted for individual elements and extended to the ternary system. Model predictions are validated against experimental findings and iteratively optimized. Using the parallel tangent method, the Gibbs free energy of crystalline and liquid phases at different compositions are calculated, providing a more accurate estimation of the nucleation driving force of the first forming phase compared to the conventional thermodynamic approach. These calculated driving forces are then used to model the isothermal Time-Temperature-Transformation (TTT) diagrams, and finally for the estimation of the interfacial energy between liquid and crystal during primary crystallization, which plays an important role in the glass-forming ability of this system. The experimental and calculated results are found to be compatible for near-eutectic compositions.