Unstable twin in body-centered cubic tungsten nanocrystals

Xiang Wang,Li Zhong,Jiangwei Wang,Chongmin Wang,Scott X Mao,Yang He

doi:10.1038/s41467-020-16349-8

Abstract

Twinning is commonly activated in plastic deformation of low stacking-fault face-centered cubic (Fcc) metals but rarely found in body-centered cubic (Bcc) metals under room temperature and slow strain rates. Here, by conducting in situ transmission electron microscopy (TEM) at atomic scale, we discover that, in stark contrast to those in most Fcc metals, a majority of deformation twins in Bcc metals are unstable and undergo spontaneously detwinning upon unloading. Such unexpected instability of Bcc twins is found to be closely related to the prevalence of the inclined twin boundaries—a peculiar structure where twin boundaries are not parallel to the twinning plane, and the degree of instability is in direct proportion to the fraction of the inclined twin boundary. This work provides significant insights into the structure and stability of deformation twins in Bcc metals.

Highlights

Twinning is commonly activated in plastic deformation of low stacking-fault face-centered cubic (Fcc) metals but rarely found in body-centered cubic (Bcc) metals under room temperature and slow strain rates
There should exist an inclined twin boundary, which is nonparallel to the twinning plane between the twin and matrix in the overlapped region. This inclined twin boundary is fundamentally different from the traditional twin boundary–coherent twin boundary (CTB) and the Moiré fringes (MF) region should coincide with the projection of this inclined twin boundary in the current viewing direction
molecular dynamics (MD) simulation indicated that high-energy interfaces rather than coherent twin boundaries could induce the detwinning in Bcc nanowires during unloading[17], consistent with our experimental observation

Summary

Introduction

Twinning is commonly activated in plastic deformation of low stacking-fault face-centered cubic (Fcc) metals but rarely found in body-centered cubic (Bcc) metals under room temperature and slow strain rates. By conducting in situ transmission electron microscopy (TEM) at atomic scale, we discover that, in stark contrast to those in most Fcc metals, a majority of deformation twins in Bcc metals are unstable and undergo spontaneously detwinning upon unloading. Such unexpected instability of Bcc twins is found to be closely related to the prevalence of the inclined twin boundaries—a peculiar structure where twin boundaries are not parallel to the twinning plane, and the degree of instability is in direct proportion to the fraction of the inclined twin boundary. The spontaneous detwinning associated with the unstable twin brings possibilities to develop advanced materials with prominent pseudoelasticity and self-healing effect

Methods

Results

Conclusion