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An aluminum silicon-based alloy Al-7wt%Si-2wt%Fe, was processed by severe plastic deformation technique in high-pressure torsion (HPT) at room temperature under a pressure of 6.0 GPa and rotational speed of 1.0 rpm with various numbers of turns up to five. Microstructure evolution, especially iron-containing intermetallic phases, was observed using an optical microscope and a scanning electron microscope (SEM). The microstructure results demonstrate that the large strains introduced by HPT at ambient temperature cause fragmentation of iron-intermetallic particles. The degree of fragmentation increases with increasing numbers of turns so that the intermetallic particles decreased in size with increasing imposed strain. In addition, the wear properties were evaluated using ball-on-disc dry sliding testing for both the as-cast material and the alloy processed by HPT using micro-tribometer UMT-2 (CETR Co., USA) following the ASTM G99-05 (2010) standard. The wear tests were conducted on the surface of the samples at 1.5 mm from the disc center under a normal load of 5 N with a rotational speed of 60 rpm and sliding time of 10 min. The friction coefficient and wear volume loss were examined to evaluate the effect of HPT on wear resistance. The results show that the samples processed by HPT have lower average values for the COF and wear volume loss than that of unprocessed samples.

The processing of bulk metals through the application of severe plastic deformation (SPD), using procedures such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), is now well established for the fabrication of materials with exceptionally small grain sizes, usually in the submicrometer range and often having grain sizes at the nanometer level. These grain sizes cannot be achieved using thermo-mechanical processing or any conventional processing techniques. Recently, these procedures have been further developed to process alternative advanced materials. For example, by stacking separate disks within the HPT facility for the synthesis of bulk nanocrystalline metastable alloys where it is possible to achieve exceptionally high hardness, or by pressing powders or metallic particles in order to obtain new and novel nanocomposites exhibiting unusual properties.

Superplasticity denotes the ability of a limited number of materials to achieve exceptionally high tensile elongations of at least 400%. Experiments show that the Al-Mg-Sc alloys provide excellent capabilities for achieving superplastic flow and also they can be formed easily in biaxial superplastic forming operations. It is important, therefore, to examine the superplastic flow mechanism when the alloy is prepared using different procedures. This report examines the superplastic characteristics of these alloys after preparation without subjecting to any severe plastic deformation (SPD), after processing using the two SPD procedures of equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) and after processing using the alternative procedure of friction stir processing (FSP). The results are compared using each technique and they are examined with reference to a theoretical model that was developed specifically for superplastic flow in conventional alloys.

Processing through the application of high-pressure torsion (HPT) provides significant grain refinement in bulk metals at room temperature. These ultrafine-grained (UFG) materials after HPT generally demonstrate exceptional mechanical properties. Recent reports demonstrated the bulk-state reactions for mechanical bonding of dissimilar lightweight metal disks to synthesize hybrid alloy systems by utilizing conventional HPT processing. Accordingly, the present report provides a comprehensive summary of the recent work on processing of several UFG hybrid alloy systems including Al-Mg and Al-Cu by HPT under 6.0 GPa at room temperature and a special emphasis was placed on understanding the evolution of hardness. This study demonstrates a significant opportunity for the application of HPT for a possible contribution to current enhancements in diffusion bonding, welding and mechanical joining technologies as well as to an introduction of hybrid engineering nanomaterials.

High-pressure torsion (HPT) was conducted under 6.0 GPa on commercial purity titanium up to 10 turns. An ultrafine-grained (UFG) pure Ti with an average grain size of ~96 nm was obtained. The thermal properties of these samples were studied by using differential scanning calorimeter (DSC) which allowed the quantitative determination of the evolution of stored energy, the recrystallization temperatures, the activation energy involved in the recrystallization of the material and the evolution of the recrystallized fraction with temperature. The results show that the stored energy increases, beyond which the stored energy seems to level off to a saturated value with increase of HPT up to 5 turns. An average activation energy of about 101 kJ/mol for the recrystallization of 5 turns samples was determined. Also, the thermal stability of the grains of the 5 turns samples with subsequent heat treatments were investigated by microstructural analysis and Vickers microhardness measurements. It is shown that the average grain size remains below 246 nm when the annealing temperature is below 500 °C, and the size of the grains increases significantly for samples at the annealing temperature of 600 °C.

An investigation was conducted to evaluate the effect of dynamic plastic deformation (DPD) and post-DPD annealing on the microstructural evolution and mechanical properties of a tempered low carbon-low alloy steel. The results showed that ultrafine-grained structures consisting of elongated martensitic laths and sub-grains are achieved after DPD processing. The amounts and sizes of carbides in the steels, identified as (Fe, Cr, Mn, Mo)3C, decreased markedly with DPD straining due to their fragmentation and dissolution but the strength increased and the plasticity showed a slight decrease with increasing DPD strain. A simultaneous improvement in the strength and plasticity was obtained at strains below ~0.8. This increase in strength by ~30-60% after DPD processing by comparison with the as-received state is attributed primarily to grain boundary strengthening and dislocation strengthening and the good plasticity is due to the occurrence of more active sliding systems and a reduction in the stress concentration during loading because of a decrease in the amounts of M3C distributed along the interfaces. After post-DPD annealing both the strength and the plasticity improved by comparison with the as-received steel in the tempered state. Strengths higher by ~15-35% than the as-received condition were attributed to a combination of grain boundary strengthening, dislocation strengthening and precipitation strengthening derived from a re-precipitation of fine and dispersed carbides. The dislocation recovery occurring during annealing led to a decrease in strength compared with the strength before annealing. The incremental increase in plasticity after annealing is ascribed to dislocation recovery and the inhibition in micro-crack propagation due to an even distribution of fine carbides within the matrix

The effect of the grain size on the mechanical properties of metallic materials has been a topic of significant interest for researchers and industry. For many decades a relationship defining the mechanical strength proportional to the inverse of the square root of the grain size has been widely accepted despite some reports of deviations from this behavior. Nevertheless, the initial explanations for this relationship, based mainly on the activation of slip systems by dislocation pile-ups at grain boundaries, have provided essentially no predictive capability. Here we show that a physically-based model for grain boundary sliding predicts, in excellent agreement with experimental data, the flow stress for plastic deformation for a broad range of materials using the fundamental properties of each material over a wide range of grain sizes and testing conditions. This mechanism also successfully predicts the reported enhanced strain rate sensitivity in ultrafine and nanocrystalline materials at different temperatures.

This study demonstrates an approach of utilizing high-pressure torsion (HPT) to fabricate a novel hybrid material by the direct bonding of Al and Ti disks at room temperature under a compressive pressure of 6.0 GPa and with increasing numbers of HPT turns up to 50. Detailed structural observations revealed the formation of a multi-layered nanostructure in the edge regions of the disks with a grain size of ~30 nm. X-ray diffraction (XRD) and selected area electron diffraction (SAED) confirmed the presence of three intermetallic compounds, AlTi, Al3Ti and Ti3Al, in the layered structures. Processing by HPT led to the formation of a hybrid nanocomposite with exceptional hardness (over 300 Hv) in the edge regions of the disks. Special emphasis was placed on understanding the evolution of hardness in the hybrid material. The investigation demonstrates a significant opportunity for using HPT processing to deepen the knowledge on diffusion bonding and mechanical joining technologies as well as for fabricating new and valuable hybrid nanomaterials.

Research was conducted on the microstructural evolution and ensuing mechanical response from high-pressure torsion (HPT) processing of Ti-6Al-4V alloy in the as-cast and β-forged conditions with and without 0.1 wt.% boron addition. The boron addition produces refinement of the prior β grains and the (α+β) colonies and introduces an additional TiB phase but this affects the deformation response and the microstructural evolution only at low strains of 0.5 to 5 rotations. In the initial condition the orientation of the (α+β) colonies significantly affects the deformation response and leads to differences in substructure formation in both the as-cast and β-forged conditions. This orientation dependence counts on the initial microstructural differences between the unmodified and the boron modified alloys. At higher strains, there is a similar deformation response and microstructure evolution all the alloys. The hardness variation with equivalent strain is similar for the unmodified and boron modified alloys in as-cast and β-forged conditions and represents various deformation regimes in HPT-processing. Strength modelling confirms a simultaneous contribution from microstructural refinement and increased dislocation density towards the hardness increment during HPT processing. Overall, the as-cast and β-forged Ti-6Al-4V-0.1B alloys possess identical deformation response to the β-forged unmodified Ti-6Al-4V alloy in the initial and intermediate stages. At high levels of straining, all alloys respond in an equivalent manner, thus ruling out any possible effects from additional TiB phase or microstructural refinement for the boron-modified alloys.

Experimental data show that the conventional Hall-Petch relationship cannot be maintained in its original form for metals having submicrometer structures. We now propose a dislocation model which modifies the Hall-Patch relationship to provide a uniform description of the grain size strengthening of submicron-structured face-centered cubic (f.c.c.) metals and solid solution alloys.

The high pressure torsion (HPT) process was performed on a Bi-Sn eutectic alloy up to 10 revolutions and the materials were stored at room temperature for durations up to 91 days in order to investigate the strain weakening and self-annealing behaviour of the alloy. The results show that HPT processing leads to significant grain refinement and enhanced superplasticity in the alloy. When the material is stored at room temperature, the grain size increases and the microhardness also increases producing a near linear relationship between grain size and microhardncess. This effect is attributed to the enhanced creep behaviour of the Bi-Sn alloy after HPT processing.

Experiments were conducted to investigate, within the framework of a multiscale approach, the mechanical enhancement, deformation and damage behavior of copper–silicon carbide composites (Cu–SiC) fabricated by spark plasma sintering (SPS) and the combination of SPS with high-pressure torsion (HPT). The mechanical properties of the metal–matrix composites were determined at three different length scales corresponding to the macroscopic, micro- and nanoscale. Small punch testing was employed to evaluate the strength of composites at the macroscopic scale. Detailed analysis of microstructure evolution related to SPS and HPT, sample deformation and failure of fractured specimens was conducted using scanning and transmission electron microscopy. A microstructural study revealed changes in the damage behavior for samples processed by HPT and an explanation for this behavior was provided by mechanical testing performed at the micro- and nanoscale. The strength of copper samples and the metal–ceramic interface was determined by microtensile testing and the hardness of each composite component, corresponding to the metal matrix, metal–ceramic interface, and ceramic reinforcement, was measured using nano-indentation. The results confirm the advantageous effect of large plastic deformation on the mechanical properties of Cu–SiC composites and demonstrate the impact on these separate components on the deformation and damage type.

A magnesium/aluminium composite was produced by room temperature consolidation through high-pressure torsion (HPT) processing. Half-discs of the pure metals were placed side-by-side and subjected to different numbers of turns. The initially reduced interface between the phases gradually increased with increasing rotation. The composite displayed a significant ductility even after 10 turns. The distribution of hardness in the HPT-processed discs was bi-modal in the early stages of processing. As the number of turns increased and the thickness of the phases decreased there was a noticeable increase in hardness. The hardness values of the composite further increased after thermal treatment due to the formation of intermetallics within the interface between the magnesium and aluminium-rich phases.

Experiments were conducted to study the compressive mechanical properties of an Al-Zn-Mg alloy after solid solution treatment and equal-channel angular pressing (SS-ECAP) using strain rates ranging from 1.0 × 10−3 to 3.0 × 103 s−1. The results show that SS-ECAP processing enhances the compressive strength due to the high dislocation density, large numbers of fine precipitates and grain refinement. The alloy in both the peak-aged (as-received) and the SS-ECAP states shows a strain rate strengthening effect such that the strain rate sensitivity increases with increasing strain rate. The high volume fraction of fine precipitates in the SS-ECAP alloy decreases the strain rate sensitivity. The coarse precipitates in the peak-aged alloy are fragmented while their sizes increase in the SS-ECAP alloy due to dynamic precipitation assisted by the high density of dislocations during compressive testing. With increasing strain rate, the size of the precipitates further increases for the SS-ECAP alloy and this is influenced by accelerated dislocation motion. During compression, the T (Al20Cu2Mn3) and E (Al18Mg3Cr2) phases evolve into a new tetragonal phase containing Mg, Mn, Cr and Zn with Al.

In general, the process of superplastic deformation is regarded as steady-state so that the flow stress is given as a function of the strain rate only, thereby emphasizing the significance of the strain rate sensitivity and its determining methods. In this work, in addition to the important role of the strain rate sensitivity, it is shown that it is necessary also to consider the stability criteria for real, stable superplastic deformation through other factors such as work hardening. A possible scenario is proposed to describe the process whereby the work hardening rate may stabilize the deformation process when a perturbation occurs in the cross-section of the sample. The assumption of a work hardening effect is confirmed by its application for interpretation of the systematic deviations observed between the strain rate sensitivities determined experimentally using different experimental methods.

Commercial purity titanium (CP-Ti) was processed by high-pressure torsion (HPT) with various numbers of turns (N = 1, 10 and 20). The hardness of the CP-Ti increased with an increasing number of HPT turns due to grain refinement. Tensile testing showed that the PT-processed 10 turns sample had low ductility and high strength but the ductility may be improved through post-HPT short-term annealing at carefully selected temperatures. Some HPT-processed samples were laser surface-treated with different laser powers and scanning speeds.The surface roughness of the laser-textured samples increased with increasing laser power and led to a lower contact angle which signifies an increased hydrophilicity. After a holding time of 13 days, the samples underwent a hydrophilic-to-hydrophobic transformation as the contact angle increasedto as much as 129 degree. It is concluded that laser surface texture processes are capable of controlling the hydrophilic / hydrophobic properties of ultra-fine grained CP-Ti.

High pressure torsion offers unique conditions for the consolidation of metallic particles at room temperature owing to the high hydrostatic compressive stresses combined with the high shear strain. A Mg-Al2O3 composite was produced by consolidation of machining chips of pure magnesium with 10% in volume of alumina particles. The consolidation process was investigated by optical and scanning electron microscopy and X-ray microtomography. It is shown that shear deformation concentrates along thick alumina particle layers in the initial stage of deformation. A significant fraction of the hard phase particles are pushed into the outflow in quasi-constrained HPT and a homogeneous composite is achieved after significant straining. The composite exhibits a refined microstructure, a higher hardness and improved resistance against room temperature creep compared to pure magnesium.

High-pressure torsion (HPT) processing was applied to an Fe-10Ni-7Mn (wt.%) martensitic steel at room temperature and the grain size was reduced from an initial value of ~5.5 μm to an ultrafine value of ~185 nm for the ferritic phase and around 30 nm for the austenitic phase after 20 HPT turns. The microstructure and mechanical properties of the as-processed material were evaluated using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), field emission scanning electron microscopy (FESEM), microhardness measurements and tensile testing. In addition, annealing of an as-processed specimen was analyzed by differential scanning calorimetry (DSC). The results show that HPT processing increases the hardness and ultimate tensile strength to ~690 Hv and ~2230 MPa, respectively, but the ductility is decreased from ~16.5% initially to ~6.4% and ~3.1% after 10 and 20 turns, respectively. The hardness distributions and EBSD images show that a reasonably homogeneous microstructure is formed when applying a sufficient level of pressure and torsional strain. The DSC results demonstrate that processing by HPT reduces the start and finish temperatures of the reverse transformation of martensite to austenite and there is continuous re-crystallization after the recovery process.

The effect of high-pressure torsion (HPT) on the textural components and microstructural evolution of an Fe-10Ni-7Mn steel was investigated. Six turns of HPT, with a rotation rate of 1rpm and with a pressure of 6.0 GPa, was applied to a solution annealed steel. Microstructural and textural evolution, including dislocation characteristics and grain size/misorientation measurements, were accomplished using Electron Backscatter Diffraction (EBSD). The resultsshowed that a fully martensitic structure, containing a high density of dislocations, was developed during the solution annealing and subsequently the application of six turns of HPT processing converted the low-angle grain boundaries (LAGBs) of the solution annealed condition into highangle grain boundaries (HAGBs). Thus, the sub-grain boundaries established in the solutionannealed condition were altered into very sharp HAGBs. The grain size decreased from ~25 µm in the solution annealed condition to ~210 nm in the severely deformed condition after six turns of HPT and the yield strength, tensile strength and ductility were increasd from 765 MPa, 840 MPa and 15.2 % to 1890 MPa, 2230 MPa and 6.1 % in the HPT-processed sample. Applying six turnsof HPT developed a predominantly {111}//ND texture but the overal texture intensity of the HPTprocessed sample was weakened to a value of about one-quarter of the as-quenched solution treated sample. This was related to dynamic recrystallization and grain subdivision as well as a dislocationdensity reduction in the HPT-processed sample. The texture components of strong Copper ({112}), S ({123}) and some avarage intesnsity Cube {100} were observed in the {100} pole figure in the solution annealed condition and γ-fiber (//ND) and β-fibre were seen in this condition. However, {110} fibres mostly developed in the six-turn sample with texture components of E1 {011̅} < 111 >, E2 {01̅1} < 111 >, J1{01̅1} < 2̅11 >,J2 + {11̅0} < 1̅1̅2 >, D2 {1̅1̅2} < 111 > , D1 {112̅} < 111 > and F {110} < 001 >. In addition, the Cu{112}〈111〉 component was significantly diminished. This weakened Cu{112}〈111〉 will enhance the mechanical properties, particularly the formability and toughness, as previously reported by the current authors. It was found that applying severe plastic deformation (SPD) in the form of HPT reduces the effect of martensitic texture in the solution treated steel.

It is a challenge in practice to cost-effectively fabricate copper matrix composites having high mechanical properties and outstanding electrical conductivity for electric power applications. This report describes a new and simple mass production strategy that was developed to construct Cu/Nb multilayer composites having an ultra-thin continuous laminated structure processed by accumulative roll bonding (ARB). Benefiting from the synergistic contributions from alternating heterogeneous lamellar structures, regular arrays of interfacial dislocations as well as efficient electron transport channels and a low electron scattering structure, the fabricated Cu/Nb multilayer composites exhibit ultrahigh tensile strengths of ~1.2 GPa while retaining their electrical conductivity, thereby negating the general trade-off between strength and electrical conductivity. This study illustrates that interface strengthening is broadly important to improve the strength of multilayer composites. The excellent performance of the Cu/Nb multilayer composites indicates that these composites, having alternating heterogeneous lamellar structures, are promising for future energy and power applications. More significantly, the proposed method provides a potentially novel process for the high-yield production of nanolaminated composites and thereby gives a robust strategy for the development of structural and multifunctional materials.

Oxygen-free copper of >99.95% purity was processed by equal-channel angular pressing at room temperature (RT) for up to 24 passes and then pulled to failure at RT using strain rates from 10−4 to 10−2 s−1. The results show that the microstrain increases with strain at the lower numbers of passes but decreases between 16 and 24 passes. Similar trends were found also for the dislocation density, the Vickers microhardness and the values of the measured yield stresses in tensile testing. X-ray diffraction measurements showed a minor increase in the crystallite size at the high strain imposed by processing through 24 passes. These results demonstrate the occurrence of dynamic recovery at the highest strain. In tensile testing at a strain rate of 10−3 s−1 the results gave a yield stress of ~391 MPa and an elongation to failure of 52% which is consistent with an earlier report using Cu of much higher purity but not consistent with an earlier report using Cu of the same purity.

The Pb-Sn alloy has a wide use in the electronic, energy storage and nuclear industries and a fine-grained Pb-Sn alloy may open up new possibilities for applications in these industries. In order to understand the behavior of grain refinement, a Pb-62% Sn eutectic alloy was processed by high-pressure torsion (HPT), stored at room temperature (RT) and then the microstructures of the alloy after HPT were repeatedly investigated during the course of self-annealing using electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is demonstrated that there is a large fraction of twin boundaries with a twin relationship of 62.8° in the microstructure of the initial as-cast condition. Due to the presence of the high imposed pressure, the mobility of Ʃ21 boundaries at 71° is greatly favoured during processing by HPT. After the high pressure is removed, the mobility of dislocation-twin boundaries near 62.8° is then favoured. Processing by HPT significantly increases the solubility of Sn in the Pb phase. The supersaturated state of Sn in Pb is not stable during self-annealing at RT and instead a decomposition of Sn from the Pb-rich phase is observed after storage for 16 days. The main mechanism for this decomposition is lattice diffusion.

Experiments were conducted to evaluate the evolution of the stored energy in grains with shear texture orientations 퐴1 ∗ {111}, 퐴2 ∗ {111}, A {111}, 퐴̅ {111}, B {112}, 퐵 ̅ {112} and C {100} for Cu-2.5Ni-0.6Si and Fe-36Ni (wt.%) alloys after high-pressure torsion (HPT) processing up to 10 turns at ambient temperature using a Kernel Average Misorientation (KAM) approach. A typical stable shear texture developed in the Cu-2.5Ni-0.6Si alloy immediately after 1 turn whereas there was a continuous transformation of texture in the Fe-36Ni alloy up to 10 turns. The results show that HPT processing produces similar stored energies of ~35 J/mol and ~24 J/mol but with the different shear texture components for the Cu-2.5Ni-0.6Si and the Fe-36Ni alloy, respectively. The stored energy in all shear components for the Cu-2.5Ni-0.6Si alloy increases with increasing HPT processing up to 1 turn and then slightly decreases through 10 turns. By contrast, the stored energy of the Fe-36Ni alloy continuously decreases with increasing numbers of HPT turns. These evolutions are examined with reference to the initial textures, dynamic recrystallization, grain refinement mechanisms and differences in the stacking fault energies.

The mechanical properties and structural stability of a high-pressure torsion (HPT)-induced bulk nanostructured metastable Al–Mg system were examined after natural aging at room temperature for 60 days. The sample demonstrated a high yield strength of 1.3–1.5 GPa with an excellent plasticity by achieving a high strain rate sensitivity of 0.036. The high hardness is attributed to the concurrent contributions of grain refinement and solid solution strengthening. An X-ray diffraction analysis revealed a high compositional microstrain of ~0.0202 due to the supersaturation of Mg in the Al matrix after processing. This microstrain increased to ~0.0274 after natural aging due to the heterogeneous distribution of supersaturated Mg solutes without any nucleation of a second phase, thereby demonstrating a reasonable structural stability.

Nanocomposites of Zr/Nb with exceptionally high hardness were fabricated successfully through the high-pressure torsion (HPT) processing of prepacked Nb/Zr/Nb sandwich samples at ambient temperature. The initial layers of Nb and Zr became fragmented during HPT processing with the formation of many fine-scale intermixed Zr/Nb layers. The intermixing of these Zr/Nb layers increased both with increasing HPT revolutions from 10 to 100 and with increasing radial positions on the disks. The Vickers microhardness, Hv, increased with increasing revolutions and with radial position reaching a maximum of ~700 Hv at the edge of the 100 turns sample. Exceptional grain refinement to the range of ~20–40 nm and the occurrence of twinning were associated with the HPT-processed Zr/Nb composites after 100 turns. These results suggest a potential route for fabricating high strength bulk Zr/Nb nanocomposites.

A supersaturated Al–Zn–Mg alloy was processed by dynamic plastic deformation (DPD) using a Split-Hopkinson pressure bar (SHPB) facility with strain range from 0.5 to 1.5 and then subjected to compressive testing at strain rates of 1 × 10−3–4 × 103 s−1. The results show that there is concurrent occurrence of grain refinement, increase in dislocation density and precipitation of fine precipitates in different morphologies during DPD at strain over 1. This enhances the yield strength of the Al alloy after DPD over the as-received material in peak-aging state (T6). Grains are refined through the formation of low angle grain boundaries (LAGBs) by rearrangement of dislocations which leads to the subdivision of original grains. Heterogeneous coarse precipitates mainly of T (Al20Cu2Mn3) and E (Al18Mg3Cr2) phases distribute along dislocations and grain boundaries after DPD. Dynamic precipitation of very fine η′ and η during DPD occurs where the volume fraction of precipitates increases with increasing the number of presses. The influence of precipitates on the strain rate sensitivity is also discussed.

The microstructure, texture and mechanical properties of a quasi-single-phase Zn-0.5Cu (wt. %) alloy processed by high-pressure torsion (HPT) for up to 10 turns were investigated using electron backscatter diffraction (EBSD), Vickers hardness measurements and uniaxial tensile tests. The results show that during torsional straining there is dynamic recrystallization, subgrain refinement, a dissolution of ε – Zn4Cu precipitates and solid-solution strengthening. Monotonic deformation develops a strong {0001}〈112ത0〉 local texture instead of the characteristic basal fiber texture. Sharp texture and misorientation angles for all grain boundaries of < 30° causes significantly higher yield stress and ultimate tensile stress compared to processing of the alloy by equal-channel angular pressing.

Oxygen-free copper was processed by equal-channel angular pressing (ECAP) at room temperature for 1, 4 and 8 passes and then the ECAP specimens were further deformed by dynamic testing at 298 K using a strain rate of 10 s−1. Experiments were conducted to investigate the influence of the initial microstructures induced by ECAP on the subsequent grain refinement and mechanical properties after dynamic testing. The results show the strength of copper increased with increasing numbers of ECAP passes and a significant additional grain refinement was produced in the ECAP specimens through the dynamic testing. Thus, the initial grain sizes after ECAP for 1, 4 and 8 passes were ~16, ~4.4 and ~2.9 μm, respectively, and these values were reduced to ~400, ~330 and ~300 nm by dynamic testing, The grains were refined by conventional dislocation processes in the 1-pass specimen but there was evidence for dynamic recrystallization in the specimen processed by 8 passes.

Superplastic Pb-Sn alloys were produced via tube high-pressure shearing (t-HPS), in a single step starting from elemental solid bulks. A Pb-40 wt% Sn alloy showed an exceptional superplastic elongation as high as ∼1870% at a strain rate of 1.0 × 10 −3 s −1 at room temperature, thereby elevating the optimum strain rate for maximum elongation under these conditions by more than one order of magnitude over conventional cast Pb-Sn alloys. This unprecedented room temperature superplasticity is attributed to the equiaxed grains having uniform sizes of the order of one micrometer, and in particular to the well-mixed domains of Pb and Sn in nearly equal proportions. This microstructure cannot be attained in cast eutectic or hypoeutectic alloys through conventional thermomechanical processing, but instead it is a direct outcome of t-HPS-generated compositional patterning at room temperature.

The high-pressure torsion processing technique was used to consolidate and process magnesium-based chips. Chips were prepared by machining commercially pure magnesium and a magnesium alloy AZ91 separately. Optical microscopy and microhardness measurements showed good consolidation of pure magnesium. The magnesium alloy continued to exhibit the boundaries between the chips even after 5 turns of HPT suggesting poor bonding. The results show that soft chips are easier to consolidate through HPT than harder alloys.

High-entropy alloys (HEAs) are currently attracting much interest because they offer unique properties and good ductility at low temperatures. These materials are of interest primarily because they contain five or more principal elements, with each element having a concentration between 5 and 35 at. %, and yet they have very simple structures based on solid solution phases. Superplasticity is defined formally as a tensile elongation without failure of at least 400% and very recent experiments have shown that the HEAs also have a potential for exhibiting superplastic ductilities when testing at elevated temperatures. Since superplasticity requires a very small grain size, typically

Bulk ultrafine-grained (UFG) materials usually show superior mechanical and physical properties. The development of micro-mechanical behavior is observed after significant changes in microstructure through high-pressure torsion (HPT) processing. This report summarizes recent results on the evolution of small-scale mechanical response examined by the nanoindentation technique on two UFG materials including a high-entropy alloy and an Al-Mg metal matrix nanocomposite processed by HPT. Special emphasis is placed on demonstrating the interrelationship of essential microstructural changes with increasing torsional strain and applying a post-deformation annealing treatment and the evolution of the micro-mechanical behavior in these UFG materials by estimating the strain rate sensitivity.

This report summarizes a recent study demonstrating simple and rapid synthesis of a new Al-Mg alloy system and ultimately synthesizing a metal matrix nanocomposite (MMNC) which was achieved by processing stacked disks of the two dissimilar metals by conventional high-pressure torsion (HPT) processing. The synthesized Al-Mg alloy system exhibits exceptionally high hardness through rapid diffusion bonding and simultaneous nucleation of intermetallic phases with increased numbers of HPT turns through 20 and improved plasticity was demonstrated by increasing strain rate sensitivity in the alloy system after post-deformation annealing. An additional experiment demonstrated that the alternate stacking of high numbers of dissimilar metal disks may produce a faster metal mixture during HPT. Metal combinations of Al-Cu, Al-Fe and Al-Ti were processed by the same HPT procedure from separate pure metals to examine the feasibility of the processing technique. The microstructural analysis confirmed the capability of HPT for the formation of heterostructures across the disk diameters in these processed alloy systems. The HPT processing demonstrates a considerable potential for the joining and bonding of dissimilar metals at room temperature and the expeditious fabrication of a wide range of new metal systems.

CrFe2NiMnV0.25C0.075 and CrFe2NiMnV0.25C0.125 high entropy alloys (HEA) were processed by high-pressure torsion (HPT) followed by post-deformation annealing (PDA) at 823 and 1273 K. This severe plastic deformation led to a significant microhardness increment (by a factor of ~2.5) up to ~435 Hv and the microstructures exhibited exceptional grain refinement with average grain sizes of ~30 nm in both HEAs. It was found that the hardness increased up to~555 Hv after annealing at 823 K due to precipitation of the σ phase but thereafter the hardness decreased to ~195 Hv after annealing at 1273 K which was very close to the value of the initial coarse-grained condition. This behavior is caused by a combination of grain coarsening and a dissolution of the precipitates. These results suggest that the nanocrystalline HEA facilitates theformation of precipitates owing to the large number of grain boundaries which serve both as fast diffusion pathways and as preferential nucleation sites for precipitate formation.

A CoCrFeNiMnTi0.1 high-entropy alloy (HEA) was processed by high-pressure torsion (HPT) followed by post-deformation annealing (PDA) at 200–900 °C. Microstructural evaluations revealed that the initial and HPT-processed microstructures consisted of a single fcc phase and there was no evidence for decomposition during severe plastic deformation. However, PDA at temperatures below 900 °C promoted the formation of a multi-phase microstructure containing new precipitates and significant grain coarsening occurred after PDA at > 800 °C due to a dissolution of the precipitates. PDA at 800 °C for 60 min led to very good mechanical properties with an ultimate tensile strength (UTS) and elongation to failure of > 1000 MPa and ~ 40%, respectively. The results demonstrate that the minor addition of Ti to the CoCrFeNiMn alloy has no direct effect on the strengthening mechanisms but nevertheless this addition significantly increases the thermal stability of the precipitates and these precipitates are effective in minimizing grain coarsening. Therefore, the Ti addition plays an important role in strengthening the HEA.

A CoCrFeNiMn high-entropy alloy (HEA) with an addition of 2 at% Ti was processed by high-pressure torsion to produce a grain size of ~30 nm and then tested in tension at elevated temperatures from 873 to 1073 K using strain rates from 1.0 × 10−3 to 1.0 × 10−1 s−1. The alloy exhibited excellent ductility at these elevated temperatures including superplastic elongations with a maximum elongation of 830% at a temperature of 973 K. It is shown that the Ti addition contributes to the formation of precipitates and, combined with the sluggish diffusion in the HEA, grain growth is inhibited to provide a reasonable stability in the fine-grained structure at elevated temperatures. By comparison with the conventional CoCrFeNiMn HEA, the results demonstrate that the addition of a minor amount of Ti produces a smaller grain size, a higher volume fraction of precipitates and a significant improvement in the superplastic properties.

An austenitic low-density steel was processed by dynamic plastic deformation (DPD) over the strain range from 0.25 to 0.75 followed by aging at 450°C and then it was subjected to compressive testing at strain rates of 1.0 × 10-3 − 2.0 × 103 s-1. The results show that fine grain structures with high density dislocations are achieved after DPD processing. After aging, the grain size increased slightly together and there was an additional marginal decrease in the dislocation density. κ-carbides only appeared in the samples after DPD processing at the strain of 0.75 and after subsequent aging. Submicron-sized (Nb, Mo)C particles existed in the matrix before DPD and there was no change in size and distribution during DPD processing and post-DPD aging. The yield strengths of the steels after DPD at different strain rates increased significantly by ~120-190% compared with the as-received sample, where this is mainly due to a combination of dislocation strengthening and grain boundary strengthening. For the steel processed by DPD at strain of 0.75, there was an additional precipitation strengthening of κ-carbides besides the dislocation strengthening and grain boundary strengthening, and this produced an increase of over ~900 MPa in yield strength by comparison with the as-received steel. After aging, the yield strength decreased slightly due to a reduction in the dislocation density and a slight coarsening of the grains, except for samples after DPD at a strain of 0.75 which showed a slight increase in strength due to further κ precipitation. The strain rate strengthening effect and strain hardening ability were also analyzed.

An Al-7075 aluminum alloy and a ZK60 magnesium alloy were processed by a combination of equal-channel angular pressing (ECAP) for 4 passes and high-pressure torsion (HPT) through total numbers of up to 20 turns. Processing by ECAP and HPT were performed at 473 K and room temperature, respectively. Mechanical testing showed an increase in the hardness value of the Al-7075 alloy after a combination of ECAP and HPT whereas in the ZK60 alloy the hardness was reduced. Microstructural images of the Al-7075 alloy revealed very significant grain refinement after a combination of ECAP + HPT compared to the individual processing techniques. By contrast, and consistent with the hardness measurements, the average grain size of the ZK60 alloy was larger after processing by the two-step SPD technique. These results are examined and an explanation is presented based on the available microstructural evidence.