Search

High-pressure torsion (HPT) was used to investigate the synthesis of Zn-Mg hybrids by direct bonding of separate disks of Zn and Mg at room temperature under an applied pressure of 6.0 GPa after 1, 5, 15 and 30 turns. Microstructural characterisation of the HPT-processed disks showed the formation of a sub-micron multilayered structure embedded in a Zn-rich matrix with an average grain size of ∼ 600 nm at the disk periphery after 30 turns. XRD and TEM analysis revealed the presence of MgZn2 and Mg2Zn11 intermetallic compounds, which increased in volume fractions with increasing number of turns. The formation of these intermetallics, together with Hall-Petch strengthening, led to an exceptional increase of the hardness values after 15 turns. Electrochemical testing in simulated body fluid showed that the degree of plastic deformation had an impact on the corrosion resistance of the Zn-Mg hybrids, which would affect their implementation in the biomedical field for absorbable applications. This study confirmed that there is significant potential for using HPT in the joining of dissimilar metals at room temperature to form Zn-Mg hybrids containing ultrafine-grained metal-matrix heterostructures with enhanced hardness. [ABSTRACT FROM AUTHOR]

The tradeoff between strength and ductility has long been identified as the 'Achilles' heel' of the mechanical properties in engineering applications. Metal hybrids processed by severe plastic deformation (SPD) have gained significant attention in recent years, as they have shown potential for enhancing strength and ductility simultaneously through different heterostructured designs. Among SPD processes, high-pressure torsion (HPT) is considered the most effective in grain refinement and offers excellent versatility for synthesising new materials with a wide variety of experimental setups and processing parameters. This review article describes the current state-of-the-art of metal hybrids processed by HPT, characterised by heterogeneous microstructures (i.e. nanoscale and/or microscale), through a comprehensive study of their synthesis-microstructure-property relationships. The potential of HPT-processed hybrids is highlighted and discussed along with their limitations. Suggestions are provided with the aim to advance current research trends towards future application in high-impact technologies, including the biomedical and microelectronic industries. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) techniques have been used extensively over the past 40 years for producing strong metals and alloys. High-pressure torsion (HPT) is one of the most promising SPD techniques for achieving high strength through nanoscale grain refinement and phase transformation. In this research, a mixture of pure zinc (Zn) and magnesium (Mg) powders, Zn-3Mg (wt%), was HPT-processed under a pressure of 6 GPa for 1, 5, 10, 20, and 30 turns at room temperature to achieve a high strength biodegradable material. In order to understand the effects of pre-consolidation on the resulting microstructure and hardness, HPT processing was performed on loose powders placed in the die and also on a pre-compacted powder mixture and the resulting HPT disks were characterized by X-ray diffraction, scanning electron microscopy, atom probe tomography, and Vickers microhardness. In both cases, the HPT disk microstructures contained nanoscale grains, and stable and metastable strain-induced intermetallics, but an unusual softening appeared at large shear strains. Grain size, grain morphology, and the formation of different intermetallics were analyzed to explain the unusual hardness distribution, and it was found that an inverse Hall-Petch relationship between hardness and grain size exists. It is suggested that thermally-activated phenomena such as grain boundary sliding contributed to the strain-induced softening of this nano-structured biomaterial due to its low melting point. The current results are compared with those for HPT-processed cast alloys and hybrids of the same composition. • Microstructural evolution is compared between HPT-processed loose and compact powder disks. • HPT on Zn-3Mg (wt%) powder mixture resulted in the refinement of the Zn matrix grains. • The formation of Mg 2 Zn 11 , Mg 2 Zn 3 , and MgZn 2 intermetallics and ZnO were observed in the HPT disks. • Softening occurred at large equivalent strains in both the loose and compact powder HPT disks. • Immiscible intermetallic phases influenced the hardness distribution of HPT-processed disks. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) was used to investigate the potential of grain refinement and strengthening achievable for aluminum alloy 2139-T8. Discs of 20 mm diameter and approximately 0.9 mm thickness were HPT processed at room temperature under an applied pressure of 5 GPa after 1, 2, 4 and 8 revolutions. Microstructural characterization of the HPT-processed discs showed the formation of a sub-micron grain structure after one revolution. The HPT processing led to an exceptional increase of the hardness and tensile strength after only one revolution as well as a relatively homogenous microstructure containing refined grains. Some grain growth occurred with increasing number of revolutions. X-ray diffraction line profile analysis suggested dislocation arrangements consistent with the microstructural evolution and strengthening behavior. Overall, this study confirmed that there is a potential for using HPT for manufacturing Al 2139 with enhanced hardness and tensile strength. [ABSTRACT FROM AUTHOR]

Processing of metal hybrid nanocomposites have emerged in the recent years by means of solid-state reactions through severe plastic deformation techniques, resulting in heterogenous microstructures and mechanical properties. Despite the increased scientific interest in these unusual materials, little is known regarding their comparative attributes with respect to a homogeneous material having equivalent nominal composition. This work provides a direct comparison of the microstructure and the hardness evolution between a Zn–3Mg (wt.%) alloy and its hybrid counterpart, after high-pressure torsion (HPT) and after HPT followed by a post-deformation annealing (PDA) treatment. Experimental results indicate that both the alloy and the hybrid reach a similar level of grain refinement after HPT processing, however, grain growth follows different trends after PDA. The HPT-processed alloy exhibits clusters of Mg 2 Zn 11 nanocrystalline domains that coalesce into coarser grains maintaining a unimodal GS distribution after PDA. On the other hand, the hybrid after PDA displays a multimodal GS distribution consisting of ultrafine Mg-rich grains containing MgZn 2 and Mg 2 Zn 11 nanoscale intermetallics, in a matrix of coarser dislocation-free Zn grains. These observations were supported by kernel average misorientation (KAM) maps and pole figures obtained through electron backscattered diffraction (EBSD) analysis. • Microstructural evolution is compared between a HPT-processed alloy and its hybrid counterpart. • Heterostructured Zn–Mg hybrid is synthesized via HPT followed by post-deformation annealing (PDA). • Nanocrystalline domains coalesced into coarser grains in the HPT alloy upon PDA. • In-situ precipitation of Mg 2 Zn 11 and MgZn 2 intermetallics ocurred in the hybrid during HPT. • Hardness values and hardness heterogeneity increased after PDA in both the alloy and the hybrid. [ABSTRACT FROM AUTHOR]

Heterostructured metals have attracted increasing interest because of their unique capability to overcome the strength-ductility tradeoff typically observed in engineering materials. Here, a new strategy for synthesizing heterostructured Zn–Mg hybrids is proposed via high-pressure torsion (HPT) followed by post-deformation annealing (PDA). Experimental results indicate a transition from a relatively homogenous nanograined structure after HPT, to a heterogeneous microstructure, containing a distribution of Mg 2 Zn 11 and MgZn 2 intermetallic nanoprecipitates, upon subsequent PDA. This led to a simultaneous increase in hardness and strain rate sensitivity. The observed three-regime strain hardening behavior was suggested to be due to the activation of multiple strengthening mechanisms, including grain refinement, in-situ precipitation, and back-stress strengthening associated with geometrically necessary dislocations. Thus, the mechanical response of Zn–Mg hybrids may be tailored to obtain the desired response for task-specific applications. Image 1 [ABSTRACT FROM AUTHOR]