Dual phase patterning during a congruent grain boundary phase transition in elemental copper

TL;DR

This study reveals nanoscale patterning of grain boundary phases in elemental copper, showing a first-order, diffusionless transition and the role of phase junctions in stabilizing the pattern at room temperature.

Contribution

It provides the first atomic-scale observation and simulation of grain boundary phase transitions in elemental metals, highlighting pattern formation mechanisms.

Findings

Nanoscale patterning of grain boundary phases observed in copper.

First-order, diffusionless phase transition confirmed by simulations.

Grain boundary phase junctions influence pattern stability at low temperatures.

Abstract

The phase behavior of grain boundaries can have a strong influence on interfacial properties. Little is known about the emergence of grain boundary phases in elemental metal systems and how they transform. Here, we observe the nanoscale patterning of a grain boundary by two alternating grain boundary phases with distinct atomic structures in elemental copper by atomic resolution imaging. The same grain boundary phases are found by grain boundary structure search indicating a first-order transformation. Finite temperature atomistic simulations reveal a congruent, diffusionless transition between these phases under ambient pressure. The patterning of the grain boundary at room temperature is dominated by the grain boundary phase junctions separating the phase segments. Our analysis suggests that the reduced mobility of the phase junctions at low temperatures kinetically limits the transformation, but repulsive elastic interactions between them and disconnections could additionally stabilize the pattern formation.