An examination of nickel doping effect on the mechanical strength of a tungsten grain boundary

Abstract

Grain boundary (GB) embrittlement in nanostructured metals intended for high temperature applications is considered an important detriment. In the present work, embrittlement in a nickel (Ni)-doped tungsten (W) 〈100〉–〈210〉 GB is examined using ab initio simulations based on Car Parrinello molecular dynamics (CPMDs) framework. The atomic fraction of substituted Ni atoms in the examined W GB and simulation temperature are varied in order to understand the strength of the W GB as a function of temperature. An increase in the Ni atomic fraction in the W GB from 12.5% to above 25% value leads to a peak in yield strength and reduction in the strain corresponding to the ultimate tensile strength which can be characterized as embrittlement. While the elastic modulus does not show a dependence on Ni atomic fraction variation and temperature, the yield strength, the ultimate tensile strength, and the fracture strength show an appreciable dependence. Addition of Ni atoms adds localized peaks in f-orbital electron density of states which is found to contribute to increase in the bond strength with increase in Ni atomic fraction. Based on analyses performed, a relation expressing tensile strength of the examined W GB as a function of W surface energy, Ni atomic fraction, and simulation temperature is derived. The relation is shown to predict temperature dependent strength of examined Ni-doped W GB that fits the simulation data.