Atomistic computer simulation analysis of nanocrystalline nickel-tungsten alloys

Abstract

Nanocrystalline nickel-tungsten alloys are harder, stronger, more resistant to degradation, and safer to electrodeposit than chromium. Atomistic computer simulations have previously met with success in replicating the energetic and atomic conditions of physical systems with 2-4nm grain diameters. Here, a new model subjects a vertically thin unique volume containing 3nm or 10nm FCC grains with aligned z axes to a Monte Carlo-type minimization to investigate the segregation and ordering behavior of W atoms. Short-range order is also tracked with the Warren-Cowley parameter, and energetic results are explored as well. It was found that the Ni-W system has a very strong tendency toward SRO. The 10nm models exhibited more robust order at low concentrations, but ordering in the 3nm model was generally more pronounced. At the dilute limit atoms are driven to the grain boundaries, but as the boundaries are saturated intragranular ordered formations increase and may even perpetuate over low-angle grain boundaries. Ordering was also observed within the grain boundaries at all concentrations for both diameters. The 10nm models were saturated at lower concentration, and grain boundary energy was reduced by up to 93%. W atoms preferred to associate with each other as third-nearest neighbors, but at very high concentrations formations with W atoms as second nearest neighbors were also observed.