In situ observation of the pseudoelasticity of twin boundary

Abstract

Twin boundary (TB) is a special and fundamental internal interface that plays a key role in altering the mechanical and physical properties of materials. However, the atomistic deformation mechanism of TB remains under debate, of which the most concerned aspect is how TB would affect the mechanical strength and plasticity of a material. Herein, we introduce our new discovery that the pseudoelastic strain of a TB can recover with decomposition and escape of pile-up dislocations, demonstrated by imposing a spontaneous pseudoelastic deformation with recoverable plastic bending strain up to 5.1% on a TB. We found that the steps on the curved TB gradually annihilated during the migration of the TB, which was induced by the slip of decomposition dislocations on the TB. The TB not only provides local strain hardening through interaction with dislocations during the loading stage but also acts as a channel for the fast movement of decomposition dislocations during the recovery stage. Beside, the TB can maintain excellent pseudoelasticity under a multicycle bending test, which may play an important role in improving the fatigue resistance of materials. These findings could open up a new avenue for optimizing the mechanical properties of materials by manipulating their twin boundaries at the nanoscale.