Scale-bridging dislocation plasticity in MgO at room temperature

TL;DR

This study investigates dislocation-mediated plasticity in MgO across different length scales and dislocation densities, revealing size effects, dislocation mechanisms, and improved ductility through experiments and simulations.

Contribution

It provides new insights into dislocation mechanics in MgO by systematically analyzing the effects of dislocation density and size, combining experiments and simulations.

Findings

Dislocation density influences yield strength and deformation mechanisms.

Size effects lead to higher strength in nano-/micro-pillars compared to bulk.

Dislocation activities and work hardening are qualitatively analyzed via 3D-DDD simulations.

Abstract

Dislocations in ceramics have recently gained renewed research interest, in contrast to the traditional belief that ceramics are inherently brittle. Understanding dislocation mechanics in representative oxides is beneficial for effective dislocation engineering. Here, we use MgO single crystals with mechanically seeded dislocation densities from about 10 to the power of 12 to about 10 to the power of 15 per square meter to investigate the mechanical behavior such as yield and fracture. Micro-pillar compression tests reveal a dislocation density dependent yield strength, mediated by the varying dominating dislocation mechanisms from nucleation to multiplication/motion. In situ TEM compression measurements highlight the dislocation-seeded samples can achieve a much-improved compressive plastic strain beyond about 70%, with a high yield strength of about 2.35 GPa (diameter of about 400 nm), indicating size effect. Complementary bulk compression tests, along with digital image correlation (DIC), demonstrate a consistent dislocation-mediated deformation and a notable size effect, with bulk samples exhibiting much reduced yield strength (about 120 MPa) compared to the nano-/micro-pillars. Using three-dimensional Discrete Dislocation Dynamics (3D-DDD) simulation, we further qualitatively analyze the collective dislocation activities (slip events) and work hardening during compression. This study provides new insights into dislocation-mediated plasticity in MgO, across different length scales, by systematically tuning dislocation density.