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Ab initio simulations of molten Ni alloys

Convective instabilities responsible for misoriented grains in directionally solidified turbine airfoils are produced by variations in liquid–metal density with composition and temperature across the solidification zone. Here, fundamental properties of molten Ni-based alloys, required for modeling these instabilities, are calculated using ab initio molecular dynamics simulations. Equations of state are derived from constant number-volume-temperature ensembles at 1830 and 1750 K for elemental, binary (Ni–X, X=Al, W, Re, and Ta) and ternary (Ni–Al–X, X=W, Re, and Ta) Ni alloys. Calculated molar volumes agree to within 0.6%–1.8% of available measurements. Predictions are used to investigate the range of accuracy of a parameterization of molar volumes with composition and temperature based on measurements of binary alloys. Structural analysis reveals a pronounced tendency for icosahedral short-range order for Ni–W and Ni–Re alloys and the calculations provide estimates of diffusion rates and their dependence ...