Amorphous phase crystallization-involved cooperative deformation mechanism in a crystalline-amorphous nanostructured compositionally complex alloy

Abstract

Crystalline-amorphous nanostructured metals, comprising extremely refined nanograins encapsulated by nanoscale amorphous phase acting as grain boundaries (GBs), exhibit exceptional mechanical properties with sustained strengthening, primarily due to unique dislocation-mediated cooperative deformation mechanisms. However, the atomic-scale understanding of dislocation activities, their interaction with nanograins and amorphous GBs, and the resulting microstructural change during plastic deformation remain elusive. In this work, a crystalline-amorphous nanostructured layer is fabricated on a Fe<inf>45</inf>Mn<inf>35</inf>Cr<inf>10</inf>Co<inf>10</inf> compositionally complex alloy via laser surface remelting. High-resolution transmission electron microscopy (HRTEM), complemented by atomistic molecular dynamics (MD) simulations, reveals the atomic-scale dynamic cooperative deformation behavior. The results show that partial dislocations initially nucleate at the nanograin/amorphous GB interfaces, forming faulted bands across nanograins. As deformation progresses, these dislocations accumulate and induce local atomic rearrangements within the amorphous zones. This activity promotes fragmentation of disordered regions, enabling further dislocation nucleation and initiating a disorder-to-order transition that drives progressive crystallization of the amorphous GBs. Such crystallization progressively thins the amorphous GBs, transforming them into conventional sharp boundaries. Continued dislocation movement in the GBs trigger slight rotations of adjacent nanograins, particularly those with small misorientations, facilitating grain coalescence for coarsening. These findings offer profound insights into the cooperative co-deformation mechanisms in crystalline-amorphous nanostructures which are beneficial for enhanced mechanical properties through microstructural optimization.