PNNL

Abstract

Solid-phase processing (SPP) often drives materials undergoing different states, not achievable via thermal processing alone, leading to the generation of rich palette of defects (thermal equilibrium and non-equilibrium defects) and defect substructure, such as dislocation network. It is essential to understand the mechanisms of deformation and defect structure formation to guide SPP towards achieving desired microstructures and material properties. In this study, large-scale molecular dynamics simulations are used to investigate the evolution of defect structures under severe shear deformation in a quasi-two-dimensional polycrystalline Al. The nucleation and reaction of defects are analyzed. The results reveal that a strong geometric constraint suppresses the nucleation and slide of low energy dislocation 1/2{111} but promotes the nucleation and slide of high energy dislocations such as [11 ¯0](001) and 1/2[11 ¯2 ¯ ](11 ¯1). A rough contact surface causes an inhomogeneous stress field which leads to a spatial dependence of activated slip systems and inhomogeneous defect substructures within a large grain. The results indicate that both geometric constraint and inhomogeneous stress affect dislocation response and defect substructure evolution which should be considered in modeling plastic deformation and grain refinement during SPP.