Molecular Dynamics Simulation of Zener Pinning by Differently Shaped and Oriented Particles

Yi Li,Jian Zhou,Runjie Li,Qingyu Zhang

doi:10.3389/fmats.2021.682422

Abstract

Zener pinning between a curved Cu grain boundary (GB) and a differently shaped and oriented Ag particle has been simulated via molecular dynamics. The computed magnitudes of the maximum pinning force agreed with theoretical predictions only when the force was small. As the force increased, discrepancy became obvious. Through careful inspection of the structures of the Cu–Ag interfaces, detailed interaction processes, and variation of the Cu GB during the interaction, the discrepancy is found to correlate with GB faceting, which very likely reduces the maximum pinning force and facilitates boundary passage. GB anisotropy and/or interface characteristics are also found to slightly contribute to the discrepancy. These findings suggest that the assumption of an isotropic GB with constant energy utilized in previous theoretical studies for deriving the maximum pinning force might be inappropriate and that an accurate maximum pinning force could not be predicted without knowing the effects of GB evolution together with detailed properties of both GBs and interfaces.

Highlights

Zener pinning (Smith, 1948; Zener, 1949), i.e., grain boundary (GB) migration hindered by secondphase particles, has been widely exploited for refining grain sizes (Gladman et al, 1999; Cao et al, 2005; St John et al, 2005), as well as stabilizing nanostructures (Koch et al, 2013)
Commonly assumed that, during GB– particle interaction, (I) equilibrium between the surface tensions is maintained at intersection position; for an incoherent particle, a GB meets a particle at 90◦; (II) a GB is isotropic and assumes constant energy/mobility; and (III) the intersection line is of a rather regular shape, e.g., a spherical particle makes a planar hole on an initially flat GB
The results eventually demonstrated that these assumptions, in some cases, are inappropriate and that boundary faceting, GB anisotropy, and interface characteristics had been considered for rationalizing the evaluated F values

Summary

Introduction

Zener pinning (Smith, 1948; Zener, 1949), i.e., grain boundary (GB) migration hindered by secondphase particles, has been widely exploited for refining grain sizes (Gladman et al, 1999; Cao et al, 2005; St John et al, 2005), as well as stabilizing nanostructures (Koch et al, 2013). The maximum pinning force of one particle acting on one moving GB was derived as the first key step in obtaining Equation 1. This derivation step was performed based on either GB energy/shape evolution (Gladman, 1966; Hellman and Hillert, 1975) or mechanics of surface tensions with respect to the GB and the GB–particle interface (Smith, 1948; Ashby et al, 1969; Ryum et al, 1983; Nes et al, 1985; Ringer et al, 1989; Li and Easterling, 1990). Commonly assumed that, during GB– particle interaction, (I) equilibrium between the surface tensions is maintained at intersection position; for an incoherent particle, a GB meets a particle at 90◦; (II) a GB is isotropic and assumes constant energy/mobility; and (III) the intersection line is of a rather regular shape, e.g., a spherical particle makes a planar hole on an initially flat GB

Methods

Results

Conclusion