Effect of Strain Heterogeneities on Microstructure, Texture, Hardness, and H-Activation of High-Pressure Torsion Mg Consolidated from Different Powders

Abstract

Severe plastic deformation techniques, such as high-pressure torsion (HPT), have been increasingly applied on powder materials to consolidate bulk nanostructured materials. In this context, the aim of the present study is to compare the plastic deformation characteristics during HPT of two distinct Mg-based powder precursors: (i) atomized micro-sized powder and (ii) condensed and passivated nanopowder. Dynamic recrystallization could take place during HPT consolidation of the atomized powder particles while the oxide pinning of the grain boundaries restricted it for the condensed powder. Consequently, there have been substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of consolidated products. Different types of local strain heterogeneities were also revealed in the consolidated products. The associated diversity in microstructure within the same consolidated product has been demonstrated to have an effect on the hydrogen activation kinetics to form hydrides for these Mg-based materials that could be suitable for solid state H-storage applications.

In-situ transmission electron microscopy investigation of the influence of hydrogen on the oxidation mechanisms of fine grained magnesium

“…As shown on the STEM Bright Field (BF) image (Fig. 1), the material processed by severe plastic deformation exhibits a submicron grain size, in agreement with an earlier study [22,23]. The grain size is slightly finer than in bulk Mg processed by SPD [X2] due to a small fraction of nanoscaled oxide particles pinning boundaries.…”

The Effect of Ultragrain Refinement on the Strength and Strain Rate Sensitivity of a ZK60 Magnesium Alloy

“…[7] A breakdown in Hall-Petch behavior and inverse Hall-Petch relationship, or grain refinement softening, has been reported in pure Mg in bulk samples with grain sizes smaller than a few micrometers [8][9][10] although grain refinement hardening, at much smaller grain sizes, has been reported in samples of pure magnesium consolidated from powders. [11,12] Room-temperature annealing has been reported in pure Mg processed by high-pressure torsion (HPT), leading to an increase in strength, [13] which also supports the occurrence of grain refinement softening in this material. The grain refinement softening is usually associated with a remarkable increase in strain rate sensitivity and exceptional increase in formability in pure magnesium.…”

Hydrogen Storage in Mg and Mg-Based Alloys and Composites Processed by Severe Plastic Deformation

“…In another investigation, Panda et al 12) reported a more detailed study concerning the microstructural development during HPT using two different initial powders (atomized and condensed) and observed substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of products. Such differences resulted in a significant effect on the hydrogen activation kinetics to form hydrides.…”