Temperature dependency of slip and twinning in plane strain compressed magnesium single crystals

A crystal plasticity model for hexagonal close packed (HCP) crystals including twinning and de-twinning mechanisms

Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials.

Structural evolutions of metallic materials processed by severe plastic deformation

Influence of texture on Hall–Petch relationships in an Mg alloy

We present a single crystal plasticity model for pure Mg incorporating slip and deformation twinning. The model uses the basic framework of Kalidindi (1998), but proposes constitutive descriptions for the slip and twin evolution and their interactions that are motivated by experimental observations. Based on compelling experimental evidences, we distinguish between the constitutive descriptions of the tension and compression twinning to better represent their roles in the overall hardening of Mg single crystals. With these improved phenomenological descriptions, we first calibrate material parameters for the different slip and twin modes by performing threedimensional simulations mimicking the plane-strain compression experiments by Kelley and Hosford (1967, 1968) on single crystal pure Mg. In doing so, these computational responses are critically compared with their corresponding orientation-dependent microscopic (slip and twin activities) and macroscopic (stress–strain responses) experimental observations. Then, the calibrated parameters are used to predict several other experimental results on pure single- and poly-crystal Mg under different loading conditions. We also investigate the role of pre-existing heterogeneities such as initial twin population and stiff, elastic inclusions on the single crystal macroscopic and microscopic responses. Microstructural characteristics show that such heterogeneities strongly influence the local and global evolution of the slip and twin activities, and in some cases modulate the strength anisotropy that is commonly observed in monolithic single crystals. These results may provide useful indicators toward designing novel composite Mg microstructures.

Ryan Harris

Papers

Deformation twinning in AZ31: Influence on strain hardening and texture evolution