Deciphering the interactions between single arm dislocation sources and coherent twin boundary in nickel bi-crystal

Vahid Samaee,Helena Van Swygenhoven,Hosni Idrissi,Maxime Dupraz,Thomas Pardoen,Dominique Schryvers

doi:10.1038/s41467-021-21296-z

Abstract

The introduction of a well-controlled population of coherent twin boundaries (CTBs) is an attractive route to improve the strength ductility product in face centered cubic (FCC) metals. However, the elementary mechanisms controlling the interaction between single arm dislocation sources (SASs), often present in nanotwinned FCC metals, and CTB are still not well understood. Here, quantitative in-situ transmission electron microscopy (TEM) observations of these mechanisms under tensile loading are performed on submicron Ni bi-crystal. We report that the absorption of curved screw dislocations at the CTB leads to the formation of constriction nodes connecting pairs of twinning dislocations at the CTB plane in agreement with large scale 3D atomistic simulations. The coordinated motion of the twinning dislocation pairs due to the presence of the nodes leads to a unique CTB sliding mechanism, which plays an important role in initiating the fracture process at a CTB ledge. TEM observations of the interactions between non-screw dislocations and the CTB highlight the importance of the synergy between the repulsive force of the CTB and the back stress from SASs when the interactions occur in small volumes.

Highlights

The introduction of a well-controlled population of coherent twin boundaries (CTBs) is an attractive route to improve the strength ductility product in face centered cubic (FCC) metals
Micro-tension is generally used to overcome most of the experimental shortcomings of the micropillar compression approach such as the deformation of the substrate and the lateral constraint between the pillar top surface and the compression tip, quantitative in-situ transmission electron microscopy (TEM) tensile testing on focused ion beam (FIB) defect-free bi-crystal samples is still missing in the literature
Since the tensile axis is parallel to the CTB plane, the tensile direction in both grains is close to the 541 direction and the Schmid factors of the slip systems are similar in both grains

Summary

Introduction

The introduction of a well-controlled population of coherent twin boundaries (CTBs) is an attractive route to improve the strength ductility product in face centered cubic (FCC) metals. We perform on a pure Ni bi-crystal sample quantitative in-situ TEM observations under uniaxial tensile testing of the interaction mechanisms between curved screw dislocations with a single ∑3 {111}〈110〉 annealing CTB parallel to the tensile axis.

Results

Conclusion