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High strength-ductility synergy is difficult to achieve in Nb alloys. Although high strength has been achieved through severe plastic deformation (SPD) technology, led to low ductility in alloys. In this work, FSP technology was applied to treat Nb–5W–2Mo–1Zr-0.1C (Nb521) alloys in preparation of fine-grained (FG)/ultrafine-grained (UFG) Nb521 with excellent strength and ductility. The microstructure evolution and mechanical property improvement mechanism were systematically studied for Nb521 alloy through various characterization pathways. The research results indicated that UFG Nb521 alloy with a grain size of 0.63 ± 0.41 μm can be prepared using low shoulder plunge depth FSP (LPD-FSP), which is the first report of UFG Nb521 alloy. The main reason for the formation of onion rings structure in SZ is the periodic wear of the stirring tool, and the onion rings structure does not cause mechanical damage. The texture formed by Nb521 alloy under different processing parameters is off-axis shear texture, which matches the ideal shear texture of D2 (112‾)[111] after rotation. In addition, this study also elaborated on the refinement mechanism of the second phase particles (Nb, Zr) C in Nb521 alloy during FSP. This study also indicated that the increase in yield strength of FSP samples at room temperature is mainly determined by grain refinement. These findings provided new ideas for the development of high-performance niobium alloys.

Among the procedures developed for structure grain refinement, equal channel angular extrusion techniques experience a great popularity, owing to its proficiency to produce significant grain refinement in fully dense bulk-scale materials. It is essential to compromise between the design of die and processing parameters to estimate a homogeneous deformation, optimize the strain distribution, and load requirement. In this regard, numerical modelling has been done to comprehend the impact of temperature and friction on the newly developed plastic deformation technique known as "nonequal channel multi-angular extrusion" (NECMAE), which experienced a cross-sectional area reduction on the subsequent channel. Three friction coefficients were examined combined with heat generation analysis to evaluate the plastic strain homogeneity. The preliminary results obtained show that 30% reduction case with µ=0.1 has the most uniform strain distribution across the workpiece and improves strain homogeneity significantly by 6 times greater than the frictionless case. In general, the optimum strain distribution could be achieved by using the right combination of area reduction and frictional conditions. The analysis implies that plastic strain, temperature, and required load are significantly affected by localized plastic deformation zone and the incrementation of heat generated. Current study opens the opportunity to satisfy the workpiece hardening level due to different localizations of plastic deformation of the proposed die design.

Six cycles of ARB at three elevated temperatures (400, 450, and 500 °C) were applied on Al/Mg laminated metallic composites. Samples were studied by microscopy, spectroscopy, and x-ray diffraction to investigate the effect of temperature on microstructures, second phases, and preferred crystallographic orientations. Stoichiometry analysis indicated the formation of non-equilibrium intermetallic phases at the Al/Mg interface. The thickness of the intermetallic layer increased in consecutive passes and by increasing process temperature. Annealing moved the composition toward predicted thermodynamically stable phases by absorbing Al and rejecting excess Mg. EDS examination showed the formation of Al2Mg and Al30Mg23 phases in addition to the previously reported Al12Mg17 and Al3Mg2. XRD results indicated that the preferred crystallographic orientation of the Al layer deviates from the expected plain-strain rolling texture. At the same time, for the Mg layer, the hexagonal c-axis remained parallel to the applied rolling force direction. The most uniform crack-free structure has been formed at 450 °C. [ABSTRACT FROM AUTHOR]

Pure titanium is limited to be used in biomedical applications due to its lower mechanical strength compared to its alloy counterpart. To enhance its properties and improve medical implants feasibility, advancements in titanium processing technologies are necessary. One such technique is equal-channel angular pressing (ECAP) for its severe plastic deformation (SPD). This study aims to surface modify commercially pure titanium using micro-arc oxidation (MAO) or plasma electrolytic oxidation (PEO) technologies, and mineral solutions containing Ca and P. The composition, metallography, and shape of the changed surface were characterized using X-ray diffraction (XRD), digital optical microscopy (OM), and scanning electron microscope (SEM), respectively. A microhardness test is conducted to assess each sample's mechanical strength. The weight % of Ca and P in the coating was determined using energy dispersive spectroscopy (EDS), and the corrosion resistance was evaluated through potentiodynamic measurement. The behavior of human dental pulp cell and periodontal cell behavior was also studied through a biomedical experiment over a period of 1-, 3-, and 7-days using culture medium, and the cell death and viability can be inferred with the help of enzyme-linked immunosorbent assay (ELISA) since it can detect proteins or biomarkers secreted by cells undergoing apoptosis or necrosis. This study shows that the mechanical grain refinement method and surface modification might improve the mechanical and biomechanical properties of commercially pure (CP) titanium. According to the results of the corrosion loss measurements, 2PassMAO had the lowest corrosion rate, which is determined to be 0.495 mmpy. The electrode potentials for the 1-pass and 2-pass coated samples are 1.44 V and 1.47 V, respectively. This suggests that the coating is highly effective in reducing the corrosion rate of the metallic CP Ti sample. Changes in the grain size and the presence of a high number of grain boundaries have a significant impact on the corrosion resistance of CP Ti. For ECAPED and surface-modified titanium samples in a 3.6% NaCl electrolyte solution, electrochemical impedance spectroscopy (EIS) properties are similar to Nyquist and Bode plot fitting. In light of ISO 10993-5 guidelines for assessing in vitro cytotoxicity, this study contributes valuable insights into pulp and periodontal cell behavior, focusing specifically on material cytotoxicity, a critical factor determined by a 30% decrease in cell viability. [ABSTRACT FROM AUTHOR]

The presence of dislocations significantly modifies the mechanical properties of crystalline solids. Severe plastic deformation (SPD) and the most used SPD process – the Equal Channel Angular Pressing (ECAP), affect the multiplication and localized accumulation of dislocations. This research is related to the observation of dislocation pile-up and significant reduction of the crystalline grain size caused by severe deformations in the ECAP process of the widely used aluminium material (Al 99.5%). Because of its lightweight, the application of Al 99.5 % can pose a challenge for the aviation and space industry, especially since its mechanical properties limit its application. Improving these mechanical properties can extend its applicability in cases of demanding constructions as well as influence the final product cost. As a confirmation of SPD in-fluence on mechanical properties, material hardness has been examined and described. Dislocation monitoring is enabled using the light and electron microscopy and AFM (Atomic Force Microscope) device. A numerical simulation of the Equal Channel Angular Pressing process using the ABAQUS software package determined the representative area of the most severe deformation.

In this paper, the impact of the number of passes of equal channel angular pressing (ECAP) on mechanical properties and corrosion behavior of Al5085 alloys in an HNO3 solution is investigated. After a single pass of ECAP, the ultimate tensile strength (UTS) was increased noticeably from 275 MPa to 342 MPa. Also, the yield strength (YS) and microhardness were improved from 82 MPa to 118.5 MPa and 94 HV to 136 HV, respectively. After the second pass all UTS, YS, and microhardness increased by 13.5%, 17.8%, and 11.7% compared to the first pass. Meanwhile, the elongation to failure was reduced by 15% and 7.5% after one and two passes of the ECAP, respectively. According to scanning electron microscope (SEM) micrographs, unlike the unprocessed sample in which there is no evidence of pitting corrosion occurrence, after one pass ECAP, the pitting corrosion occurred through all the surfaces of the sample. Also, there is no evidence of pitting corrosion after two passes of ECAP. [ABSTRACT FROM AUTHOR]

The presence of dislocations significantly modifies the mechanical properties of crystalline solids. Severe plastic deformation (SPD) and the most used SPD process – the Equal Channel Angular Pressing (ECAP), affect the multiplication and localized accumulation of dislocations. This research is related to the observation of dislocation pile-up and significant reduction of the crystalline grain size caused by severe deformations in the ECAP process of the widely used aluminium material (Al 99.5%). Because of its lightweight, the application of Al 99.5 % can pose a challenge for the aviation and space industry, especially since its mechanical properties limit its application. Improving these mechanical properties can extend its applicability in cases of demanding constructions as well as influence the final product cost. As a confirmation of SPD in-fluence on mechanical properties, material hardness has been examined and described. Dislocation monitoring is enabled using the light and electron microscopy and AFM (Atomic Force Microscope) device. A numerical simulation of the Equal Channel Angular Pressing process using the ABAQUS software package determined the representative area of the most severe deformation. [ABSTRACT FROM AUTHOR]

Strengthening by grain refinement via the Hall–Petch mechanism and softening by nanograin formation via the inverse Hall–Petch mechanism have been the subject of argument for decades, particularly for ultrafine-grained materials. In this study, the Hall–Petch relationship is examined for ultrafine-grained magnesium, aluminum, copper, and iron produced by severe plastic deformation in the literature. Magnesium, aluminum, copper, and their alloys follow the Hall–Petch relationship with a low slope, but an up-break appears when the grain sizes are reduced below 500–1000 nm. This extra strengthening, which is mainly due to the enhanced contribution of dislocations, is followed by a down-break for grain sizes smaller than 70–150 nm due to the diminution of the dislocation contribution and an enhancement of thermally-activated phenomena. For pure iron with a lower dislocation mobility, the Hall–Petch breaks are not evident, but the strength at the nanometer grain size range is lower than the expected Hall–Petch trend in the submicrometer range. The strength of nanograined iron can be increased to the expected trend by stabilizing grain boundaries via impurity atoms. Detailed analyses of the data confirm that grain refinement to the nanometer level is not necessarily a solution to achieve extra strengthening, but other strategies such as microstructural stabilization by segregation or precipitation are required. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity. Abbreviations: ARB: Accumulative Roll-Bonding; BCC: Body-Centered Cubic; DAC: Diamond Anvil Cell; EBSD: Electron Backscatter Diffraction; ECAP: Equal-Channel Angular Pressing (Extrusion); FCC: Face-Centered Cubic; FEM: Finite Element Method; FSP: Friction Stir Processing; HCP: Hexagonal Close-Packed; HPT: High-Pressure Torsion; HPTT: High-Pressure Tube Twisting; MDF: Multi-Directional (-Axial) Forging; NanoSPD: Nanomaterials by Severe Plastic Deformation; SDAC: Shear (Rotational) Diamond Anvil Cell; SEM: Scanning Electron Microscopy; SMAT: Surface Mechanical Attrition Treatment; SPD: Severe Plastic Deformation; TE: Twist Extrusion; TEM: Transmission Electron Microscopy; UFG: Ultrafine Grained

Photoreforming is a sustainable photocatalytic process that degrades plastic waste while simultaneously producing hydrogen (H 2) from water. However, this process has received limited attention due to the scarcity of effective catalysts capable of both plastic degradation and H 2 production, such as titanium dioxide (TiO 2). In this study, an active catalyst is developed by stabilizing the high-pressure orthorhombic phase of TiO 2 , known as columbite, using a high-pressure torsion (HPT) method. This material effectively degrades polyethylene terephthalate (PET) plastic under light, converting it into valuable organic compounds such as formic acid, terephthalate, glycolic acid, and acetic acid. Additionally, it produces a significant amount of H 2. The findings show that the high-pressure orthorhombic phase, especially in the presence of oxygen vacancies, enhances catalytic H 2 production and microplastic degradation by increasing light absorption, reducing electron-hole recombination, and generating hydroxyl radicals. These results highlight the substantial potential of modified high-pressure TiO 2 photocatalysts in simultaneously addressing the plastic waste crisis and the demand for H 2 fuel. • The high-pressure orthorhombic TiO2 phase rich in oxygen vacancies is stabilized. • The phase is used for the photoreforming of polyethylene terephthalate (PET) plastic. • PET is converted into formic acid, terephthalate, glycolic acid and acetic acid. • Significant hydrogen and hydroxyl amounts are also produced during photoreforming. • The activity of the vacancy-rich high-pressure phase is higher than anatase. [ABSTRACT FROM AUTHOR]

Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO 2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life. [ABSTRACT FROM AUTHOR]

A Mg-based composite material has been produced by the consolidation at room temperature of a Mg-5wt.% Ni-2wt.% Nb2O5 powder mixture subjected to high-pressure torsion (HPT), one of the processing methods to induce severe plastic deformations. The microstructure, density, and microhardness of the consolidated disks were characterized after the application of up to 30 revolutions in torsion under compression stresses of 3 and 5 GPa. According to the density measurements, the composite was consolidated in full after the application of five revolutions, although disks subjected to only one revolution exhibited densities close to the maximum measured value. On the other hand, grain size and microhardness measurements showed that differences existed at locations near the center and the periphery of the HPT-processed disks. Under the stress of 5 GPa, the grain size in the central regions stabilized at about 0.35 μm after five revolutions, while at the peripherical regions it gradually decreased with an increasing number of revolutions down to about 0.15 μm after 30 revolutions. In turn, the microhardness measured along a diametral cross section steadily increased with the number of revolutions between 1 and 10 revolutions, maintaining a gradient from the center to the periphery in all cases. With the application of 20 and 30 revolutions, only the peripheral regions increased considerably in hardness. It was discovered that the magnesium particles in the initial powder mixture had formed an oxide—hydroxide surface layer, which changed the expected final density of the consolidated material by about 2 to 4.5%. This superficial contamination of the Mg powders did not prevent the material from achieving full consolidation. [ABSTRACT FROM AUTHOR]

Pure titanium is limited to be used in biomedical applications due to its lower mechanical strength compared to its alloy counterpart. To enhance its properties and improve medical implants feasibility, advancements in titanium processing technologies are necessary. One such technique is equal-channel angular pressing (ECAP) for its severe plastic deformation (SPD). This study aims to surface modify commercially pure titanium using micro-arc oxidation (MAO) or plasma electrolytic oxidation (PEO) technologies, and mineral solutions containing Ca and P. The composition, metallography, and shape of the changed surface were characterized using X-ray diffraction (XRD), digital optical microscopy (OM), and scanning electron microscope (SEM), respectively. A microhardness test is conducted to assess each sample’s mechanical strength. The weight % of Ca and P in the coating was determined using energy dispersive spectroscopy (EDS), and the corrosion resistance was evaluated through potentiodynamic measurement. The behavior of human dental pulp cell and periodontal cell behavior was also studied through a biomedical experiment over a period of 1-, 3-, and 7-days using culture medium, and the cell death and viability can be inferred with the help of enzyme-linked immunosorbent assay (ELISA) since it can detect proteins or biomarkers secreted by cells undergoing apoptosis or necrosis. This study shows that the mechanical grain refinement method and surface modification might improve the mechanical and biomechanical properties of commercially pure (CP) titanium. According to the results of the corrosion loss measurements, 2PassMAO had the lowest corrosion rate, which is determined to be 0.495 mmpy. The electrode potentials for the 1-pass and 2-pass coated samples are 1.44 V and 1.47 V, respectively. This suggests that the coating is highly effective in reducing the corrosion rate of the metallic CP Ti sample. Changes in the grain size and the presence of a high number of grain boundaries have a significant impact on the corrosion resistance of CP Ti. For ECAPED and surface-modified titanium samples in a 3.6% NaCl electrolyte solution, electrochemical impedance spectroscopy (EIS) properties are similar to Nyquist and Bode plot fitting. In light of ISO 10993-5 guidelines for assessing in vitro cytotoxicity, this study contributes valuable insights into pulp and periodontal cell behavior, focusing specifically on material cytotoxicity, a critical factor determined by a 30% decrease in cell viability.

The production of metal matrix composites (MMCs) through recycled materials is a cost-saving process. However, the improvement of the mechanical and physical properties is another challenge to be concerned. In this study, recycled aluminium 6061 (AA6061) chips reinforced with different volumetric fractions of boron carbide (B4C) were produced through hot equal channel angular processing (ECAP). Response surface methodology (RSM) was carried out to investigate the dependent response (compressive strength) with independent parameters such as different volumetric fractions (5-15%) of added contents of B4C and preheating temperature (450 – 550°C). Also, the number of passes were examined to check the effect on the mechanical and physical properties of the developed recycled AA6061/B4C composite. The results show that maximum compressive strength and hardness of recycled AA6061/B4C were 59.2 MPa and 69 HV respectively at 5% of B4C contents. Likewise, the density and number of pores increased, which were confirmed through scanning electron microscope (SEM) and atomic force microscopes (AFM) analysis. However, the number of passes enhanced the mechanical and physical properties of the recycled AA6061/B4C composite. Therefore, the maximum compressive strength and hardness achieved were 158 MPa and 74.95 HV for the 4th pass. Moreover, the physical properties of recycled AA6061/B4C composite become denser of 2.62 g/cm3 at the 1st pass and 2.67 g/cm3 for the 4th pass. Thus, it can be concluded that the B4C volumetric fraction and number of passes have a significant effect on recycled AA6061 chips.

Cyclic extrusion compression (CEC) is an effective fabrication process for producing fine, ultrafine grains with superior physical and mechanical properties.In the present work, CEC process was applied on Al alloy 6061 and its silicon carbide (SiCp) composite containing 5 and 10 wt. % SiCp. . The specimens were pressed at room temperature up to 6 cycles for Al alloy 6061, 5 cycles for Al 6061 5 wt. % and 4 cycles for Al 6061 10 wt. % SiC corresponding to plastic strains of 3.72, 3.1 and 2.48 respectively. The evolution of microstructure, hardness and dry sliding wear tests were conducted. The samples were investigated before and after the CEC process by optical microscope, and the worn surfaces were investigated by Scanning Electron Microscope (SEM) and (EDX) analysis. The CEC cycles reduced the grain size, porosity % and SiC particle size. These microstructural parameters were reflected on the increase in hardness and reduction in wear rate and a slight reduction in coefficient of friction. In general, this improvement in properties is associated with the following parameters; grain refining, reinforcement volume fraction, size and distribution of SiCp as well as the number of CEC cycles. Regarding the composite samples, a significant improvement in wear resistance was obtained and the Al 6061 10 wt. % SiC, showed the best performance. The wear mechanism was also affected by the CEC process.

The indentation of bearing raceways frequently contributes to bearing failures, as in gearboxes. The dents act as surface stress raisers through the Rolling Contact Fatigue (RCF) cycles, leading to crack initiation and spalling. The microstructural evolution mechanism occurring is not completely understood. Hence, to enhance bearing lifetime, it is crucial to identify microstructural parameters that influence crack initiation and propagation. Therefore, this study presents a multi-scale characterization of martensitic 100Cr6 bearings before and after RCF. It includes SEM, SEM/FIB, EBSD, TKD and ACOM-ASTAR observations. It showed that, before RCF, the bearing raceway features a 0.5 µm thick surface layer consisting in refined martensite and spread primary carbides, resulting from finishing operations. After RCF, no further grain refinement was observed along the raceway, except beneath the dent shoulder where a material plastic flow, nano-grains and ultra-fine grains of martensite, and sheared and spread primary carbides were detected up to 1.4 µm deep. Below and up to 3 µm deep, a fine grain layer is observed. The martensite morphology, size and disorientation suggest that it undergoes refinement through continuous Dynamic Recrystallisation and twinning. Crack initiation was preferentially observed in the nano-grains layer, at primary carbides/matrix interfaces. Above the crack, another refined region is observed resulting from high deformation and stresses through crack propagation. Finally, even in severely deformed areas, nanosized retained austenite islands were detected, indicating that it is not completely transformed. [Display omitted] [ABSTRACT FROM AUTHOR]

This study examines the corrosion resistance of ultrafine-grained Al 0.1 CoCrFeNi high-entropy alloy processed by high-pressure torsion (HPT), focusing on stored energy, diffusion, and the high-entropy effect. Microstructural analysis revealed a single-phase FCC structure with numerous defects and reduced crystallite size following the HPT process. Samples with higher HPT turns formed high - angle grain boundaries, equiaxed nanograins, and numerous nanotwins, contributing to a notable increase in Vickers microhardness from 159 Hv for the initial sample to 550 Hv after 5 turns of HPT. Corrosion behavior is found to be influenced by stored energy and chromium diffusion. Low HPT turns increased the corrosion rate due to sluggish diffusion of chromium and high stored energy in the form of dislocations. Conversely, corrosion resistance improved with increased HPT turns due to fast diffusion through non-equilibrium grain boundaries and the formation of nanotwins with lower stored energy. These findings suggest that a relatively low entropy plays a critical role in the chromium segregation from the solid solution for forming a passive film and enhancing corrosion resistance. • Corrosion resistance of Al 0.1 CoCrFeNi-HEA after HPT was examined. • Hardness increased from 159 to 550 Hv and corrosion resistance improves after 5 turns. • Low stored energy initially reduces corrosion rate due to limited chromium diffusion. • Corrosion resistance increases with the formation of films containing chromium. • Grain boundaries and low high-entropy effect lead to the enrichment of chromium. [ABSTRACT FROM AUTHOR]

This paper presents a study on the perspectives of structure refinement of aluminum and its alloys by reciprocating extrusion (cyclic extrusion compression—CEC). The study included Al99.5 and Al99.992 aluminum and AlMg5 and AlCu4Zr alloy. Aluminum and alloys were deformed by reciprocating extrusion (CEC) in the strain range ϕ = 0.42 (1 CEC cycle) to ϕ = 59.8 (67 CEC cycles). After deformation, the structure of the specimens was investigated by optical microscopy (OM) and transmission electron microscopy (TEM), which revealed that the primary mechanism of hardening, over the range of applied strains, was the result of the propagation of shear bands throughout the specimens. The intersection of shear bands was found to divide the volume of the specimens into nano and microvolumes with dimensions limited by the width of the microbands. Due to structure renewal processes such as polygonization and dynamic geometric recrystallization, the formed micro and nano volumes were transformed into nano and micrograins with large misorientation angles. In terms of the occurrence of grain microstructure, a sustained uniform level of hardening was found, which was defined as steady-state flow. The research has shown that the steady state of flow is a result of the competitive interaction between the processes of hardening and structure renewal. The higher the metal purity, the higher the intensity of the structure renewal processes was. The formation of new grains and their growth under dynamic and post-dynamic recrystallization was observed in Al99.992 aluminum, in which high purity of the metal and high strain accumulation caused the growth of new grains at room temperature. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity. Abbreviations: ARB: Accumulative Roll-Bonding; BCC: Body-Centered Cubic; DAC: Diamond Anvil Cell; EBSD: Electron Backscatter Diffraction; ECAP: Equal-Channel Angular Pressing (Extrusion); FCC: Face-Centered Cubic; FEM: Finite Element Method; FSP: Friction Stir Processing; HCP: Hexagonal Close-Packed; HPT: High-Pressure Torsion; HPTT: High-Pressure Tube Twisting; MDF: Multi-Directional (-Axial) Forging; NanoSPD: Nanomaterials by Severe Plastic Deformation; SDAC: Shear (Rotational) Diamond Anvil Cell; SEM: Scanning Electron Microscopy; SMAT: Surface Mechanical Attrition Treatment; SPD: Severe Plastic Deformation; TE: Twist Extrusion; TEM: Transmission Electron Microscopy; UFG: Ultrafine Grained This article comprehensively reviews recent advances on development of ultrafine-grained and nanostructured materials by severe plastic deformation and provides a brief history regarding the progress of this field. [ABSTRACT FROM AUTHOR]

In this study, a preparation route of Co–Cu alloys with soft magnetic properties by high-pressure torsion deformation is introduced. Nanocrystalline, supersaturated single-phase microstructures are obtained after deformation of Co–Cu alloys, which are prepared from an initial powder mixture with Co-contents above 70 wt.%. Isochronal annealing treatments up to 400 °C further reveal a remarkable microstructural stability. Only at 600 °C, the supersaturated phase decomposes into two fcc-phases. The coercivity, measured by SQUID as a function of annealing temperature, remains significantly below the value for bulk-Co in all states investigated. In order to understand the measured magnetic properties in detail, a quantitative analysis of the magnetic microstructure is carried out by magnetic force microscopy and correlated to the observed changes in coercivity. Our results show that the rising coercivity can be explained by a magnetic hardening effect occurring in context with spinodal decomposition.

In this study, evolution of intermetallic layer of the cold roll bonded bilayer of Aluminum-Steel sheets, during severe plastic deformation (SPD) followed by annealing has been investigated. The effect of such evolution on mechanical properties has been discussed. For this purpose, Constrained Groove Pressing (CGP) was used as a SPD process. Field emission scanning electron microscope equipped with energy dispersive spectroscopy and optical microscopy were used for examination of intermetallic compounds morphology and composition. Meanwhile, tensile properties of the bilayer sheets were evaluated. According to microstructural observations, continuous intermetallic layer was formed during rolling and annealing processes. This intermetallic layer was completely cracked into very fine particles after the first pass of CGP. Some of these intermetallic compounds were pushed into the base layers by the shear stress and some of them remained at the interface. Moreover, it was observed that during the CGP process, at the interface and between remaining intermetallic compounds and fresh surfaces of both Al and steel, new bonds were formed. After formation of such new bonds and during the second step of the CGP process, flattening process, mechanical interlocks were created. However, after the second CGP pass, no intermetallic compound was observed at the interface yet delamination was seen. Due to formation of intermetallic compounds at the bonding area and the vicinity of it, reinforced area, mechanical interlocks and higher dislocation density in that region, the ultimate tensile strength (UTS) increased after the first pass of CGP, but due to delamination, it decreased in second pass. The effect of evolution of bond structure on the tensile strength was measured by using bonding portion (BP) criterion defined as the difference in the UTS of the bonded versus non-bonded samples undergone similar deformation and annealing treatment. The BP values show similar trend to the UTS data, increased at the first pass and decreased at the second pass. In the following study, the CGPed samples have been annealed in order to recover the intermetallic layer. The CGPed samples were annealed at 350 °C, 400 °C and 450 °C for 30, 60 and 90 min. The optimum thickness of 2.6 μm was observed at the 450 °C in 30 min annealing treatment. The UTS, BP and elongation to break increased 7%, 32% and 60%, respectively, in comparison to those of the as-CGPed sample.

Strengthening by grain refinement via the Hall–Petch mechanism and softening by nanograin formation via the inverse Hall–Petch mechanism have been the subject of argument for decades, particularly for ultrafine-grained materials. In this study, the Hall–Petch relationship is examined for ultrafine-grained magnesium, aluminum, copper, and iron produced by severe plastic deformation in the literature. Magnesium, aluminum, copper, and their alloys follow the Hall–Petch relationship with a low slope, but an up-break appears when the grain sizes are reduced below 500–1000 nm. This extra strengthening, which is mainly due to the enhanced contribution of dislocations, is followed by a down-break for grain sizes smaller than 70–150 nm due to the diminution of the dislocation contribution and an enhancement of thermally-activated phenomena. For pure iron with a lower dislocation mobility, the Hall–Petch breaks are not evident, but the strength at the nanometer grain size range is lower than the expected Hall–Petch trend in the submicrometer range. The strength of nanograined iron can be increased to the expected trend by stabilizing grain boundaries via impurity atoms. Detailed analyses of the data confirm that grain refinement to the nanometer level is not necessarily a solution to achieve extra strengthening, but other strategies such as microstructural stabilization by segregation or precipitation are required.

A Mg-based composite material has been produced by the consolidation at room temperature of a Mg-5wt.% Ni-2wt.% Nb2O5 powder mixture subjected to high-pressure torsion (HPT), one of the processing methods to induce severe plastic deformations. The microstructure, density, and microhardness of the consolidated disks were characterized after the application of up to 30 revolutions in torsion under compression stresses of 3 and 5 GPa. According to the density measurements, the composite was consolidated in full after the application of five revolutions, although disks subjected to only one revolution exhibited densities close to the maximum measured value. On the other hand, grain size and microhardness measurements showed that differences existed at locations near the center and the periphery of the HPT-processed disks. Under the stress of 5 GPa, the grain size in the central regions stabilized at about 0.35 μm after five revolutions, while at the peripherical regions it gradually decreased with an increasing number of revolutions down to about 0.15 μm after 30 revolutions. In turn, the microhardness measured along a diametral cross section steadily increased with the number of revolutions between 1 and 10 revolutions, maintaining a gradient from the center to the periphery in all cases. With the application of 20 and 30 revolutions, only the peripheral regions increased considerably in hardness. It was discovered that the magnesium particles in the initial powder mixture had formed an oxide—hydroxide surface layer, which changed the expected final density of the consolidated material by about 2 to 4.5%. This superficial contamination of the Mg powders did not prevent the material from achieving full consolidation.

The production of metal matrix composites (MMCs) through recycled materials is a cost-saving process. However, the improvement of the mechanical and physical properties is another challenge to be concerned. In this study, recycled aluminium 6061 (AA6061) chips reinforced with different volumetric fractions of boron carbide (B4C) were produced through hot equal channel angular processing (ECAP). Response surface methodology (RSM) was carried out to investigate the dependent response (compressive strength) with independent parameters such as different volumetric fractions (5-15%) of added contents of B4C and preheating temperature (450 – 550°C). Also, the number of passes were examined to check the effect on the mechanical and physical properties of the developed recycled AA6061/B4C composite. The results show that maximum compressive strength and hardness of recycled AA6061/B4C were 59.2 MPa and 69 HV respectively at 5% of B4C contents. Likewise, the density and number of pores increased, which were confirmed through scanning electron microscope (SEM) and atomic force microscopes (AFM) analysis. However, the number of passes enhanced the mechanical and physical properties of the recycled AA6061/B4C composite. Therefore, the maximum compressive strength and hardness achieved were 158 MPa and 74.95 HV for the 4th pass. Moreover, the physical properties of recycled AA6061/B4C composite become denser of 2.62 g/cm3 at the 1st pass and 2.67 g/cm3 for the 4th pass. Thus, it can be concluded that the B4C volumetric fraction and number of passes have a significant effect on recycled AA6061 chips. [ABSTRACT FROM AUTHOR]

Electrocatalysis using renewable energy sources provides a clean technology to produce hydrogen from water. Titanium oxide is considered as a potential electrocatalyst not only for hydrogen production but also for CO2 conversion. In this study, to enhance the cathodic electrocatalytic activity of TiO2, the phase composition on TiO2 surface is modified by inclusion of high-pressure TiO2-II phase using high-pressure torsion (HPT) straining. Detailed spectroscopic studies revealed that the energy band gap is reduced and the valence band energy increased with increasing the TiO2-II fraction. The highest electrocatalytic activity for hydrogen production was achieved on an anatase-rich nanocomposite containing TiO2-II nanograins.

The emergence of shear inhomogeneity across grain boundaries during severe shear deformation in Cu at the micrometer length-scales is demonstrated through in situ imaging inside a scanning electron microscope. The deformation mechanics during machining is found to be orientation dependent. Microstructure refinement from severe plastic deformation in confined volumes is entirely suppressed in certain orientations but results in a characteristic ultrafine structure in others. Rampant ductile fracture is found to nucleate at some grain boundaries due to elevated dislocation densities, and this failure mechanism is imprinted on the freshly generated surface, which limits the precision of machining-based processes (e.g., diamond turning) in nanometrically-smooth roughness profiles.

High-pressure torsion (HPT) is widely used as a severe plastic deformation technique to create ultrafine-grained structures with promising mechanical and functional properties. Since 2007, the method has been employed to enhance the hydrogenation kinetics in different Mg-based hydrogen storage materials. Recent studies showed that the method is effective not only for increasing the hydrogenation kinetics but also for improving the hydrogenation activity, for enhancing the air resistivity and more importantly for synthesizing new nanostructured hydrogen storage materials with high densities of lattice defects. This manuscript reviews some major findings on the impact of HPT process on the hydrogen storage performance of different titanium-based and magnesium-based materials.

The capability of high-pressure torsion on the preparation of supersaturated solid solutions, consisting of Cu-14Fe (wt.%), is studied. From microstructural investigations a steady state is obtained with nanocrystalline grains. The as-deformed state is analyzed with atom probe tomography, revealing an enhanced solubility and the presence of Fe-rich particles. The DC-hysteresis loop shows suppressed long range interactions in the as-deformed state and evolves towards a typical bulk hysteresis loop when annealed at 500∘ C. AC-susceptometry measurements of the as-deformed state reveal the presence of a superparamagnetic blocking peak, as well as a magnetic frustrated phase, whereas the transition of the latter follows the Almeida-Thouless line, coinciding with the microstructural investigations by atom probe tomography. AC-susceptometry shows that the frustrated state vanishes for annealing at 250∘ C. [ABSTRACT FROM AUTHOR]

Oxynitrides are considered as new potential candidates for photocatalysis due to their lower bandgap compared with traditional oxide photocatalysts. However, the formation of native nitrogen monovacancies during the synthesis of oxynitrides reduces their photocatalytic activity due to the vacancy-induced electron/hole recombination. This study shows that a transition from the native nitrogen monovacancies to the nitrogen-based vacancy complexes in a GaN–ZnO oxynitride not only diminishes the recombination but also enhances the photocatalytic hydrogen production. Here, the vacancy complexes are introduced by mechanical straining via the high-pressure torsion (HPT) method and it is shown that the vacancy complexes reduce the bandgap and increase the over-potential for hydrogen production on the conduction band. The current results introduce a simple but effective approach to turn the nitrogen vacancies to favorable defects for photocatalysis. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Butterfly defects initiate from inclusions in the subsurface of steel bearing components subject to rolling contact. The white etching matter (WEM) microstructure is a characteristic of butterflies and is related to the dissolution of carbides and thus generally believed to be enriched with carbon, in supersaturated solid solution, relative to the parent microstructure. Here, several butterflies are investigated using wavelength dispersive spectroscopy (WDS), soft x-ray emission spectroscopy (SXES) and electron microscopy (EM). Contrary to established thinking, in all cases investigated the butterfly-neighbouring WEM was found to be depleted in carbon, relative to parent material, by around 27% (measured in counts). Furthermore, the carbon level was shown to be lower than the matrix itself, suggesting that solute carbon is also expelled from the WEM during its formation, possibly due to the low level of solubility of carbon in ferrite. This was observed in both AISI 52100 and 18NiCrMo14-6 bearing steels. In spite of this depletion, nano-indentation found that WEM in both alloys was ~17% harder than the parent material. This may explain the strings of micro-voids observed near the WEM-parent interface, which appear to play a role in the growth of the butterfly cracks. It is suggested that the increased hardness of the WEM is mainly due to microstructural changes, rather than changes in solute carbon concentration. Image, graphical abstract [ABSTRACT FROM AUTHOR]

TiO 2 and ZnO, two semiconductors with promising optical properties, are considered as potential candidates for solar and photocatalytic applications. Although chemical methods have been primarily used to enhance the optical properties of these oxides, the current authors recently reported enhanced photocatalytic performance of pure TiO 2 and ZnO by plastic straining due to the generation of high-pressure phases and oxygen vacancies. In this study, to improve the optical properties further, large fractions of ZnO/TiO 2 interphase boundaries are also introduced by application of high-pressure torsion (HPT) straining to a mixture of anatase-TiO 2 and wurtzite-ZnO powders. It was found that the amounts of oxygen vacancies and nanograined high-pressure TiO 2 -II and rocksalt-ZnO phases increase with increasing plastic strain. Moreover, due to the plastic strain effect, the rutile-TiO 2 phase is formed at room temperature, which is at least 600 K below the reported anatase-to-rutile transition temperature. These structural features, together with the formation of large fraction of interphase boundaries, lead to electron spin resonance, optical bandgap narrowing, diminishing of the band-to-band photoluminescence and thus, improvement of photocatalytic hydrogen generation. Despite improvements in the photocatalytic activity of TiO 2 -ZnO composites after large straining, photocatalytic activity becomes poor by processing at ultra-large strains due to the significant reduction in crystallinity. Image 1 • TiO2 and ZnO mixture is plastically stained by high-pressure torsion. • Fractions of high-pressure phases and oxygen vacancies increase with straining. • Large fractions of ZnO/TiO 2 interphases are formed by increasing plastic strain. • Optical bandgap increases and band-to-band photoluminescence decreases by straining. • Photocatalytic hydrogen production improves for samples with reasonable crystallinity. [ABSTRACT FROM AUTHOR]

The deformation structures formed in an Al-0.1Mg single-phase aluminium alloy have been studied during plane strain compression (PSC) down to liquid nitrogen temperature, following prior equal channel angular extrusion (ECAE) to a strain of ten. Under constant deformation conditions a steady state was approached irrespective of the temperature, where the rate of grain refinement stagnated and a minimum grain size was reached which could not be further reduced. A 98% reduction at 77 K (−196 °C) only transformed the ECAE processed submicron grain structure into a microstructure with thin ribbon grains, where a nanoscale high angle boundary (HAB) spacing was only approached in the sheet normal direction. It is shown that the minimum grain size achievable in severe deformation processing is controlled by a balance between the rate of compression of the HAB structure and dynamic recovery. The required boundary migration rate to maintain a constant boundary spacing is found far higher than can be justified from conventional diffusion-controlled grain growth and at low temperatures, a constant boundary spacing can only be maintained by invoking an athermal mechanism and is considered to be dominated by the operation of grain boundary dislocations.

High-pressure torsion (HPT) is widely used not only as a severe plastic deformation (SPD) method to produce ultrafine-grained metals but also as a mechanical alloying technique to synthesize different alloys. In recent years, there have been several attempts to synthesize functional high-entropy alloys using the HPT method. In this paper, the application of HPT to synthesize high-entropy materials including metallic alloys, hydrides, oxides and oxynitrides for enhanced mechanical and hydrogen storage properties, photocatalytic hydrogen production and high light absorbance is reviewed.

White etching cracks (WECs) initiate subsurface in bearings and can propagate to cause premature failure. These cracks are bordered by an altered microstructure known as white etching matter (WEM), which is thought to form via a crack-rubbing mechanism. However, WEM is often observed bordering a single side of a meandering crack. In search of a microstructural difference to justify the observed WEM asymmetry, regions of untransformed material, adjacent to cracking in a bearing inner ring, which had undergone hydrogen charging prior to testing, were studied using correlative electron microscopy (EM), electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA) and nano-indentation techniques. The investigations found no significant differences between the untransformed material neighbouring the cracks and the parent material; both were found to have similar: grain size and shape; crystallographic texture; carbon concentration; carbide population and hardness, which questions why only one rubbed surface of the crack has formed WEM. The initiation of WEM ahead of the crack is suggested, however more investigations are needed to build another WEM formation model. EPMA characterisation revealed evidence of carbide dissolution in the WEM. Despite this, significant variation in the carbon concentration of the WEM was found; ranging from +13% enrichment to 42% depletion (in counts), relative to the parent material. Image 1 [ABSTRACT FROM AUTHOR]

Electrocatalysis using renewable energy sources provides a clean technology to produce hydrogen from water. Titanium oxide is considered as a potential electrocatalyst not only for hydrogen production but also for CO2 conversion. In this study, to enhance the cathodic electrocatalytic activity of TiO2, the phase composition on TiO2 surface is modified by inclusion of high-pressure TiO2-II phase using high-pressure torsion (HPT) straining. Detailed spectroscopic studies revealed that the energy band gap is reduced and the valence band energy increased with increasing the TiO2-II fraction. The highest electrocatalytic activity for hydrogen production was achieved on an anatase-rich nanocomposite containing TiO2-II nanograins. The first application of high-pressure TiO2-II phase for electrocatalysis confirm that the inclusion of phase in anatase-based nanocomposites is effective to enhance the electrocatalytic hydrogen production on titanium oxide due to the modification of electronic structure. [ABSTRACT FROM AUTHOR]

Abstract For structural and aerodynamic reasons, curved profiles are widely used in the transport industry for manufacturing lightweight structures. In the present work, a curved AA1050 bar with fine grains and high strength was manufactured by a novel forming technique, differential velocity sideways extrusion (DVSE). The evolution of grain structure and micro-texture during DVSE and the mechanical properties of the formed bar were studied, and the grain refinement mechanism was revealed. Due to the severe strains arising in the process, (greater than that for conventional one pass equal channel angular extrusion), significant grain refinement in the curved bar (grain size ∼3 μm) was achieved from the original billet (grain size ∼357 μm) in one extrusion operation. Coarse band-like structures containing subgrains with low angle boundaries in the shearing zone gradually transformed into fine shear band-like structures containing equiaxed (sub)grains with a mixture of low and high angle boundaries. The fine shear band-like structures inclined approximately along the shear intersection planes. Severe plastic deformation induced a high dislocation density that initiated subgrain walls with low angle boundaries, which gradually transformed into grain boundaries with high misorientation, indicating that refinement of AA1050 grains in the DVSE process is due mainly to continuous dynamic recrystallization (cDRX). Due to the appearance of greater effective strain on the inner bend of the extruded bar, the grain refinement degree and high angle boundary fraction of the material on the inner bend are slightly greater than those of the material on the outside. DVSE resulted in a weak C-type shear-texture component which can be determined by a proper rotation of the negative simple shear texture. Compared with the billet, significant increase of the hardness, yield strength and ultimate tensile strength by 134.8%, 354.0% and 116.8% respectively was achieved in the formed curved bar, although the elongation to fracture was decreased by 60.0%. Graphical abstract Image 1 Highlights • A curved profile with fine grains and high strength is manufactured by a novel forming-bending-refining process. • Grains of the curved profile are refined to less than 1% of the original billet at room temperature. • Grain refinement mechanism is revealed where continuous dynamic recrystallization occurs due to severe plastic deformation. • Hardness, yield strength and ultimate tensile strength of the profile increase by 134.8%, 354.0% and 116.8% respectively. [ABSTRACT FROM AUTHOR]

Abstract Plastic deformation of oxides is generally difficult due to their hard and brittle nature resulting from their covalent or ionic bondings. In this study, severe plastic deformation was successfully introduced in SiO 2 glass and crystalline VO 2 by high-pressure torsion (HPT). SiO 2 glass transformed to a denser amorphous phase without showing any crystallization after processing in the temperature range of 300–723 K. Crystalline VO 2 transformed from the coarse-grained monoclinic phase to a nanograined triclinic phase with insulating electrical properties by plastic strain effect. These findings indicate the potential of HPT process in tuning the crystal structure of optical and electrical oxides. Graphical abstract Image 1 Highlights • Strain effect on phase transition of SiO 2 glass and crystalline VO 2 is studied. • High-pressure torsion is used to introduce plastic strain in both materials. • SiO 2 glass transformed to a denser amorphous phase without any crystallization. • VO 2 transformed to a nanograined triclinic phase with insulating electrical property. • Plastic strain appears to be so effective to control the crystal structure of oxides. [ABSTRACT FROM AUTHOR]

In the present study, the wear behavior of ultra-fine grained (UFG) Al-Mg alloys produced by a severe plastic deformation (SPD) method was assessed and compared against the annealed coarse-grained alloy. To this end, weight loss, wear resistance, friction coefficient, and morphology of the worn surfaces was investigated. Constrained groove pressing-cross route (CGP-CR) process, an SPD technique, was implemented at ambient temperature up to two passes to impose an equivalent plastic strain of about 4.64. Formation of a UFG structure with an average sub-grain size of ~ 350 nm with an enhanced tensile strength of up to ~ 225 MPa and indentation hardness of up to ~ 95 HV were achieved upon two passes of CGP-CR process. The pin-on-disk dry wear sliding testing was conducted up to a distance of 1000 m under normal loads of 5, 7, and 9 N at a constant sliding speed of 0.5 m/s. The trends measured for the evaluation of wear properties/mechanisms are discussed based on the microstructural features and mechanical property of UFGed alloys. The results showed that by employing the CGP-CR process and through the formation of UFG structure, the wear resistance was considerably increased. This was even beyond two times (~ 100%) larger depending on the normal loading with the lowest coefficient of friction around 0.6. Observation and study of the morphology of the worn surfaces under field emission-scanning electron microscopy (FE-SEM) revealed a change in the wear mechanism from sticking followed by formation of plastic deformation bands and delamination in the coarse-grained annealed alloy into a combined abrasive-adhesive behavior in the UFG material. [ABSTRACT FROM AUTHOR]

3D finite element method (3D FEM) simulations of equal channel angular pressing (ECAP) and high-pressure torsion (HPT) of Al6061-T6 alloy were carried out and analyzed. 3D FEM results were correlated and compared with those obtained experimentally and theoretically through different mathematical equations. Furthermore, the hardness was estimated using the FEM strain and theoretical strain. The simulations and experimental results were in high conformity with each other. The ECAP load−displacement curves, the HPT load-time curves, and peak loads of FEM and experimental results were close to each other. FEM simulations provided clear strain distribution maps in different planes that fully explain the plastic deformation characteristics and homogeneity in the ECAP and HPT processes. FEM effective strain results have high reliability with a slight deviation from those theoretically estimated through the mathematical equations. The hardness distribution and the strain contours maps were in good agreement, confirming the quality of the FEM results. Hardness values calculated based on FEM effective strain indicate a deviation range of 0.96%–8.8% from experimental results that support the reliability of the FEM results. Microstructure results support hardness increase because of the effect of the grain refinement after ECAP and HPT processing.

Laves phase high-entropy alloys are considered as good candidates for hydrogen storage applications. However, they usually suffer from poor first hydrogenation kinetics, the so-called activation process. In this paper, we attempt to solve the activation problem of the Ti 0.5 Zr 0.5(Mn 1- x Fe x)Cr 1 (x = 0, 0.2 and 0.4) by high-pressure torsion (HPT). The HPT process was carried out under 6 GPa pressure for 5 revolutions in air on samples synthesized by arc melting. The hydrogenation kinetics were measured using a Sievert's type apparatus at room temperature under 2 MPa of hydrogen pressure. While the as-cast alloys become totally inert to hydrogen after air exposure, the HPT-processed samples absorb 1.6–1.8 wt% of hydrogen at room temperature in a few seconds even after air exposure for 2 months. The easy activation of alloys processed by HPT is due to the formation of lattice defects that act as nucleation points. These results confirm that HPT processing is an effective strategy to develop active hydrogen storage materials. • The effect of high-pressure torsion over Ti0.5Zr0.5(Mn1-xFex)Cr1 (x = 0, 0.2 and 0.4) alloy was investigated. • High-pressure torsion alloys could be activated after long air exposure. • Induced microstructural changes improved adsorption kinetics. [ABSTRACT FROM AUTHOR]

Over the last two decades, many researchers have developed a variety of stainless steel-based medical implant types,taking full advantage of nanostructuring technologies. In this paper the application, fabrication and development of nanostructured stainless steel based materials with new composition for medical implants will be discussed. It is well established that application of severe plastic deformation (SPD) can decrease the grain size of metals and alloys significantly to the nanometer range. Among all the available SPD methods, equal channel angular pressing (ECAP) is very applicable. Stainless Steel became the raw structural material for the majority of the developed medical implants, and several techniques had to be studied and established in order to fabricate a feasible stainless steel-based neural probe. These nanostructured implants present a superior performance mechanically, biologically and electrically, when compared to the conventional implants. Finally, the effect of alloying elements on the bio-interaction of stainless steel will be explained.

Microstructural investigation of extremely strained samples, such as severely plastically deformed (SPD) materials, by using conventional transmission electron microscopy techniques is very challenging due to strong image contrast resulting from the high defect density. In this study, low angle annular dark field (LAADF) imaging mode of scanning transmission electron microscope (STEM) has been applied to study the microstructure of a Mg-3Zn-0.5Y (at%) alloy processed by high pressure torsion (HPT). LAADF imaging advantages for observation of twinning, grain fragmentation, nucleation of recrystallized grains and precipitation on second phase particles in the alloy processed by HPT are highlighted. By using STEM-LAADF imaging with a range of incident angles, various microstructural features have been imaged, such as nanoscale subgrain structure and recrystallization nucleation even from the thicker region of the highly strained matrix. It is shown that nucleation of recrystallized grains starts at a strain level of revolution $ N = 1/4 $ (earlier than detected by conventional bright field imaging). Occurrence of recrystallization of grains by nucleating heterogeneously on quasicrystalline particles is also confirmed. Minimizing all strain effects by LAADF imaging facilitated grain size measurement of $ 150\pm 25 $ nm in fully recrystallized HPT specimen after $ N = 5 $.

Single-phase, face-centered cubic (FCC) high-entropy alloys (HEA) are promising materials for future applications. In order to improve the mechanical properties, especially the tensile strength of these materials, this study focuses on the combination of spark plasma sintering (SPS) and equal-channel angular pressing (ECAP). The initial fine-grained microstructure produced by SPS is further refined by ECAP in a 90°-die. Optical microscopy and electron backscatter diffraction (EBSD) confirm this considerable grain refinement, leads to a grain size below 1 µm after 1 ECAP pass. An alternating arrangement of fine-grained areas and much coarser regions, aligned under an angle of approximately 27°, is found. Moreover, a first microstructural investigation of the twin structure is conducted. The mechanical behavior was investigated by hardness measurements and tensile testing. Both the hardness and tensile strength are remarkably increased after ECAP. In contrast, the uniform elongation and elongation at fracture are significantly reduced due to the strengthening mechanisms of strain hardening and grain refinement. It is concluded that the combination of SPS and ECAP is an attractive approach for designing (ultra)fine-grained HEAs with superior properties. The investigated techniques could be applied to understand the underlying microstructural mechanisms.

The effect of reverse straining on the microstructure, texture, and hardness of the pure Al during the single cycle of the simple shear extrusion (SSE) process is investigated. Electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are used for microstructural evaluations. Due to the nature of the SSE process, the direction of the shear is reversed in the second half channel. As a result, the mean misorientation angle, dislocation density, and hardness decrease. The grain size increases to some extent in the exit of the channel compared with that in the middle. The structural evolution during the single pass of SSE is described in terms of the dislocation cancelling, “untangling” of the cell walls and disintegration of the “forward” cell structure due to the reverse straining in the second half channel. Some simple shear components replace the first texture component in the middle of the channel. At the exit of the channel, the primary texture components appear somewhat confirming the strain reversal effect in the second half channel.

In this study, five MgZnCa alloys with low alloy content and high biocorrosion resistance were investigated during thermomechanical processing. As documented by microhardness and tensile tests, high pressure torsion (HPT)-processing and subsequent heat treatments led to strength increases of up to 250%; as much as about 1/3 of this increase was due to the heat treatment. Microstructural analyses by electron microscopy revealed a significant density of precipitates, but estimates of the Orowan strength exhibited values much smaller than the strength increases observed. Calculations using Kirchner’s model of vacancy hardening, however, showed that vacancy concentrations of 10−⁵ could have accounted for the extensive hardening observed, at least when they formed vacancy agglomerates with sizes around 50–100 nm. While such an effect has been suggested for a selected Mg-alloy already in a previous paper of the authors, in this study the effect was substantiated by combined quantitative evaluations from differential scanning calorimetry and X-ray line profile analysis. Those exhibited vacancy concentrations of up to about 10−3 with a marked percentage being part of vacancy agglomerates, which has been confirmed by evaluations of defect specific activation migration enthalpies. The variations of Young’s modulus during HPT-processing and during the subsequent thermal treatments were small. Additionally, the corrosion rate did not markedly change compared to that of the homogenized state.

This paper presents a state-of-the-art and a retrospective view of the critical stages in the evolution of equal-channel angular extrusion (ECAE) from the original idea to a cost-effective industrial technology. These stages include optimization of the structure modification and material processing, development of the special tools, process commercialization, and a large-scale validation of the semi-continuous ECAE at the industrial floor. All aspects are extensively summarized, based on the author’s experience in the field, which spans almost half of a century. Special attention is paid to the processing of large batch billets. Practical examples illustrate industrial applications of ECAE. The scope for future development is also discussed.

High-pressure torsion (HPT) is widely used as a severe plastic deformation technique to create ultrafine-grained structures with promising mechanical and functional properties. Since 2007, the method has been employed to enhance the hydrogenation kinetics in different Mg-based hydrogen storage materials. Recent studies showed that the method is effective not only for increasing the hydrogenation kinetics but also for improving the hydrogenation activity, for enhancing the air resistivity and more importantly for synthesizing new nanostructured hydrogen storage materials with high densities of lattice defects. This manuscript reviews some major findings on the impact of HPT process on the hydrogen storage performance of different titanium-based and magnesium-based materials. [ABSTRACT FROM AUTHOR]