Surface Thermal Stability in Extremely Fine-Grained Metals: Surface Grain Boundary Reconstruction and its Initiating Destabilization

Abstract

The Schwarz crystal embodies a pioneering metastable polycrystalline structure distinguished by its extremely fine grains (<10 nm), stabilized via minimal curved grain boundaries (GBs) that are geometrically constrained by coherent twin boundaries (CTBs). This unique configuration bestows upon it exceptional thermal stability remaining stable even as temperatures near the melting point, and synergistically achieving unparalleled strength. Capitalizing on these remarkable attributes, the most promising application in the near future lies in surface Schwarzation, a technique poised to elevate the properties of metal crystal surfaces. However, a major challenge in this respect arises from the surface thermal stability of Schwarz crystals: Unlike their counterparts in the bulk, which possess well-defined minimal curved GBs and thus lacks a driving force for GB migration, the continuity of GBs at the surface is disrupted, leading to uncertainty in their thermal stability. Through atomistic simulations, we demonstrate the high surface thermal stability of Schwarz crystals, reveal both surface GB reconstruction and its initiating destalization. This study not only enhances our fundamental understanding of surface thermal stability in Schwarz crystals, but also establish the theoretical basis for the application of surface Schwarzation.

Keywords: Schwarz Crystals, Surface Thermal Stability, Quadruple junction lines, Surface energy dependence, Detwinning, Band-shaped Destabilization