Grain growth phenomenon during pressure-induced phase transformations at room temperature

TL;DR

This paper proposes a multistep mechanism explaining rapid grain growth during pressure-induced phase transformations at room temperature, supported by experimental evidence, challenging existing theories about nanocrystal stability.

Contribution

It introduces a new multistep kinetic model for grain growth during phase transformations, emphasizing the role of phase interfaces, grain boundaries, and nonhydrostatic stresses.

Findings

Grain growth occurs rapidly during high-pressure phase transformations at room temperature.

In situ experiments confirm the proposed multistep growth mechanism.

Nonhydrostatic stresses promote continuous grain growth rather than nucleation.

Abstract

Significant grain growth is observed during the high-pressure phase transformations (PTs) at room temperature within an hour for various materials. However, no existing theory explains this phenomenon since nanocrystals do not grow at room temperature even over a time span of several years because of slow diffusion. Here, we suggest a multistep mechanism for the grain growth during $\alpha\rightarrow\omega$ PT in Zr. Phase interfaces and grain boundaries (GBs) coincide and move together under the action of a combined thermodynamic driving forces. Several intermediate steps for such motion are suggested and justified kinetically. Nonhydrostatic stresses due to volume reduction in the growing $\omega$ grain promote continuous growth of the existing $\omega$ grain instead of a new nucleation at other GBs. In situ synchrotron Laue diffraction experiments confirm the main predictions of the theory. The suggested mechanism provides a new insight into synergistic interaction between PTs and microstructure evolution.