Work

Electron-induced evolution of dislocation density and morphology in Mg-Y-Nd-Gd-Zr alloy at ultra-low temperature

Year: 2025

Type: article

Abstract: • Non-thermal dislocation annihilation: Electron-induced reduction of geometrically necessary dislocation density by 15.2 % in Mg-Y-Nd-Gd-Zr alloy at ultra-low temperatures (−150 °C to −196 °C), independent of Joule heating. • Multi-scale characterization: EBSD, XLPA, and TEM reveal inverse correlation between current intensity (6.67–15 A/mm²) and defect density, with direct visualization of dislocation cluster dissolution. • Charge-state-dependent vacancy dynamics: Localized charge accumulation reduces Mg vacancy formation energy by 2.8 %, lowering lattice resistance to dislocation glide (validated by first-principles calculations). • Mechanistic insight: Electron flow promotes dislocation annihilation via vacancy proliferation, establishing a charge-driven defect evolution pathway in hexagonal close-packed alloys. • Technological innovation: Proposes a cryogenic, non-oxidative method for rapid microstructural tuning of magnesium alloys, advancing electroplasticity applications. This study elucidates the non-thermal mechanism of dislocation density reduction in a Mg-Y-Nd-Gd-Zr alloy under continuous electropulsing (6.67–15 A/mm²) at ultra-low temperatures (−150 °C to −196 °C) through tripartite characterization and first-principles analysis. Electron backscatter diffraction (EBSD) reveals a 15.2 % decrease in geometrically necessary dislocation (GND) density with increasing current, while X-ray line profile analysis (XLPA) confirms the inverse correlation between current intensity and overall defect density. Transmission electron microscopy (TEM) directly visualizes the dissolution of entangled dislocation clusters into isolated lines under high-current treatment (15 A/mm²), corroborating the statistical trends. First-principles calculations demonstrate that localized charge accumulation at defect sites reduces Mg vacancy formation energy by up to 2.8 %, lowering lattice resistance to dislocation glide. This charge-state-dependent vacancy proliferation provides a mechanistic link between electron flow and dislocation annihilation. The reduction of vacancy formation energy is a significant factor in the electron-induced dislocation evolution effect at ultra-low temperatures. These findings provide direct evidence for electron-induced dislocation annihilation mechanisms independent of Joule heating, advancing the understanding of electroplasticity in hexagonal close-packed alloys, and providing a novel approach for rapid, non-oxidative microstructural and property tuning of magnesium alloys.

Source: Journal of Magnesium and Alloys

DOI: 10.1016/j.jma.2025.03.017