Molecular dynamics study on the nanofriction and wear mechanism of transverse grain boundaries in nickel-based alloys

Abstract

Context

This study employs molecular dynamics simulations to investigate the nanoscale tribological behavior of a single transverse grain boundary in a nickel-based polycrystalline alloy. A series of simulations were conducted using a repetitive rotational friction method to explore the mechanisms by which different grain boundary positions influence variations in wear depth, friction force, friction coefficient, dislocation, stress, and internal damage during repeated friction processes. The results reveal that the grain boundary structure enhances the strength of the nanoscale nickel-based polycrystalline alloy. When the friction surface is far from the transverse grain boundary, the grain boundary’s obstructive effect is weaker, leading to larger ranges of atomic displacement and migration of internal defects. This results in smaller fluctuations in friction force and coefficient, along with the formation of numerous densely packed downward defect bundles. At the grain boundary, two grains undergo relative slip along the grain boundary interface, while atoms below the grain boundary remain largely unaffected. When the grain boundary is closer to the friction surface, more wear debris atoms accumulate in front of and on the sides of the friction grinding ball, increasing the friction force during the process. If the friction grinding ball breaches the grain boundary layer, its supporting and strengthening effects are diminished, leading to a significantly greater wear depth compared to when the grain boundary remains intact.

Methods

In this paper, nanoscale modeling was performed in the large-scale atomic/molecular parallel simulator simulation environment (LAMMPS). Three potential functions, namely EAM potential, Morse potential, and Tersoff potential, are used to simulate the interaction between atoms during the processing. The model was visualized and analyzed in three dimensions by Open Visualization Tool (OVITO).