Impact of W on structural evolution and diffusivity of Ni–W melts: an ab initio molecular dynamics study

Abstract: Effects of W on structural evolution and diffusivity of Ni–10W and Ni–20W (at.%) melts are studied via ab initio molecular dynamic simulations. The atomic local topology is characterized in terms of pair correlation functions, structure factors, bond pairs, and topological structures. It is observed that the Ni–20W melt is more closely packed than the Ni–10W, showing higher average coordination number and more Voronoi polyhedra with high coordination numbers. The tracer diffusion coefficients of Ni and W calculated by the mean-squared displacement are very close to each other in both Ni–W alloys. Comparing with their self-diffusion coefficients of pure Ni and pure W, the tracer diffusion coefficient of Ni in Ni–W melts decreases, while that of W increases. Nearly identical tracer diffusivities of Ni and W in Ni–W melts attribute to the formation of local solute-centered polyhedra with high deformation electron density severing as bridges between various atomic clusters and strengthening the atomic bonding, indicating the collective motion of Ni and W in those melts. Moreover, atomic bonds of Ni–W metallic melts characterized by the deformation electron density present the network among different atomic clusters, revealing the physical nature of the collective motions between W and Ni.

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