主講人： Prof. David Srolovitz (Dept. of Mechanical Engineering, The University of Hong Kong)
題目：Atom Size Dispersion Effects in the Thermodynamics of High Entropy Alloys
High entropy alloys (HEAs) (solid-solution, nearly equi-atomic, multicomponent alloys) are stabilised by the configurational entropy associated with randomly distributing the elemental constituents amongst lattice sites. In this talk, I will examine the role of differing atomic size on stabilising these alloys and controlling their structural, mechanical and thermodynamic properties. This is done through statistical mechanics analysis and molecular dynamics simulations of simple 1D and 2D systems and a 3D crystal in a model where all bonds are harmonic and atomic sizes vary. This approach rigorously captures the effects of this atomic size dispersion and temperature on universal thermodynamic, structural, and elastic features through a single, effective temperature. Atomic size disorder greatly stabilises HEAs by raising the effective temperature; this increases the stability of a solid solution relative to phase separation or ordering. Atomic size disorder can also be manipulated in HEAs to create a material with a zero coefficient of thermal expansion (the Invar effect). We quantify these effects by application to a wide range of high entropy alloys.