Achieving Extraordinary Fatigue Resistance of Pure Mg by Introducing 〈C+A〉 Dislocations Via Dislocation Transmutation

Abstract

This study presents a novel approach to enhance the high-cycle fatigue (HCF) performance of pure magnesium (Mg) by introducing substantial ⟨c+a⟩ dislocations through dislocation transmutation, and a remarkable improvement in fatigue strength, increasing from 30 MPa to 60 MPa, is thus achieved. The introduction of a high density of ⟨c+a⟩ dislocations lead to a transformation in fatigue damage modes, shifting from intergranular cracking to persistent slip band (PSB) induced cracking. In the annealed sample, dislocations primarily pile up near grain boundaries (GBs), and no significant substructure formation is observed during fatigue. In contrast, after inducing abundant ⟨c+a⟩ dislocations, the pre-processed sample exhibits extensive dislocation substructures during fatigue, evolving sequentially from ring-like dislocation arrangements to dislocation walls, cell structures, and eventually sub-grains. These substructures effectively hinder long-range dislocation glide, reduce dislocation pile-ups at GBs, mitigate intergranular fracture, and suppress crack propagation. Furthermore, the formation of substructures delays the onset of surface roughness, thereby enhancing fatigue resistance. This study highlights the pivotal role of ⟨c+a⟩ dislocations in improving the fatigue behavior of pure Mg, offering new insights into fatigue optimization strategies.

Keywords: Magnesium, Fatigue strength, Dislocation configuration, Substructure, 〈c+a〉 dislocation