Deformation behaviors of dislocation cellular structures in alloys produced by additive manufacturing

Abstract

The dislocation cellular structure is a typical microstructural feature in additively manufactured alloys. A persistent debate surrounds how dislocation cellular structures strengthen materials. This study, utilizing in-situ tensile straining transmission electron microscopy, unveils the presence of two distinct types of cell walls, differentiated by the presence or absence of discernible crystallographic misorientations across the cell walls. Cell walls with misorientations act as dislocation sinks and absorb dislocations, whereas cell walls without misorientation hamper dislocation motion by forest dislocation entanglement. These contrasting cell wall–dislocation interaction mechanisms lead to different structural stabilities of cell walls. Cell walls with misorientations tend to maintain their structural integrity during deformation, while cell walls without misorientation are prone to dissolution under high strain. These deformation behaviors suggest that the dislocation cellular structure enforces both dislocation hardening and boundary hardening mechanisms, contingent on the type of dislocation cell walls. This study further demonstrates that by varying additive manufacturing parameters, the fractions of different types of cell walls can be adjusted, thereby enhancing the overall mechanical properties.