Processing ultrafine-grained (UFG) and nanostructured (NS) materials in industrial size with simultaneous strength and ductility are the main challenges in severe plastic deformation (SPD) approaches. Hydrostatic SPD methods are a modified version of conventional SPD and forming methods with the difference of conducting fluid between the die and the sample to reduce surface contact or metal-to-metal contact. Recent studies show that hydrostatic SPD methods could process relatively long samples, making them usable in industrial applications. Also, a good combination of high strength and low ductility loss and more homogeneous properties could be achieved due to higher hydrostatic pressure. This article reviews hydrostatic SPD methods, their unique properties, and their capabilities.

In the last years, nanostructured metals prepared by severe plastic deformation (SPD) techniques have emerged as a promising class of advanced biomaterials for load-bearing applications such as orthopedic implants. This is mainly because of the simultaneous improvements in mechanical and biocompatibility properties during the creation of nanostructures. This article provides a brief overview of the effects of SPD techniques in producing nano/ultrafine-grained structures in advanced biomaterials for implant applications. The role of microstructure refinement achieved by SPD and its effect on mechanical properties and biocompatibility, together with processing challenges are reviewed. As advanced biomaterials, pure titanium, and Ti-based alloys which possess a broad range of applications in the biomedical industry are initially discussed. Further, the recent results on high-entropy alloys and metal-protein composites obtained by means of SPD for biomedical purposes are reviewed. The results discussed here clearly demonstrate the beneficial effects of SPD techniques in designing and producing nanostructured advanced biomaterials with exceptional mechanical and functional properties desired for implants.

This report is aimed at giving an overview of the significance of the novel and innovative microstructural and microscopic characterization techniques for bulk nanostructured metals processed by severe plastic deformation, specifically high-pressure torsion (HPT). In practice, the microstructural relaxation behavior upon heating of nanostructured 316L stainless steel and CoCrFeNi high-entropy alloy was characterized by in-situ heating neutron diffraction measurements; the heterogeneous phase distribution of an HPT-bonded hetero-nanostructured Al–Mg alloy was examined using synchrotron high-energy X-ray diffraction; and the microstructural evolution upon heating of a nanostructured CoCrFeNiMn high-entropy alloy was examined by laser-scanning confocal microscopy. These novel techniques are complementary to each other and any other in- or ex-situ testing methods, especially when nanocrystalline metals are transforming microstructurally and compositionally with temperature and time in a hierarchical manner. The outcomes of the studies emphasize the importance of the methodologies and the development of characterization techniques for further in-depth exploration in the research field of severe plastic deformation.

Various techniques enabling surface severe plastic deformation (SSPD) have been developed or optimised over the past years. This manuscript presents a broad overview of recent developments in the field of SSPD and its application that take advantages of having a deformed gradient surface with both (i) higher strength and (ii) an improved “reactivity”. First, the principle and technological advantages/disadvantages of several SSPD technologies, involving either guided or non-directional mechanical impacts, are recalled. Then, after a short recall on the nature of the structure the modified surface formed under SSPD, the effects of the processing parameters and temperature of deformation on the surface roughness and subsurface microstructure modifications are illustrated with a particular emphasis on the surface mechanical attrition treatment (SMAT) and ultrasonic shot peening (USP) techniques deriving from the traditional pre-strain shot peening. The effect of these surface and sub-surface modifications on the mechanical properties, and in particular the fatigue response, are recalled with a special emphasis on the surface integrity and potential over shot peening. Then, the manuscript concentrates on the effect of the surface enhanced diffusion of chemical species induced by the presence of structural defects to modify the corrosion behaviour and enhance the potential assisted SSPD + thermo-chemically “duplex” treatments. In these cases, in addition to induce grain refinement and dislocations, the importance of controlling some potential surface contamination is stressed. Finally, the manuscript terminates by illustrating some new research studies on potential applications for the challenges in the hydrogen sector for its solid-state storage and the protection of mechanical infrastructures as well as for bio-medical applications with biocompatible Ti-based alloys and biodegradable Mg-based ones.

Ultra-fine grained and even nanostructured magnesium alloys obtained by processing with methods of severe plastic deformation (SPD) are promising biomaterials for absorbable orthopaedic implants due to their enhanced mechanical properties, adequate corrosion resistance and biocompatibility. This paper presents an overview of the impact of the most important SPD methods – equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) – on microstructure refinement and improvement of the mechanical properties of magnesium alloys intended for medical implants. Several selected groups of magnesium alloys which have the potential for use as bioabsorbable implants are discussed. The presented results of many years of research indicate the beneficial effect of SPD methods on obtaining ultra-fine and even nanostructures of magnesium alloys with improved mechanical and better functional properties, which are necessary for bioabsorbable implants.

Low-temperature superplasticity (LTS) is crucial to reduce manufacturing cost and to enhance the applications of superplastic forming. It is well known that grain refinement is the key point to decrease the temperature at which superplasticity is attained. Therefore, ultrafine-grained (UFG) materials have become attractive for achieving LTS. Severe plastic deformation (SPD) techniques provide abnormal grain refinement, and thus they have been used to achieve LTS in metallic materials. This paper overviews and examines the reports of LTS in the severely-deformed metallic materials. It provides fundamentals of grain refinement via different SPD techniques in various classes of metallic materials including Al-, Mg-, and Ti-based alloys. It also gives a brief summary about the effect of microstructural requirements on LTS with an emphasis on grain size, type and chemical composition of grain boundaries and microstructural alteration during the superplastic deformation. In the last section of the manuscript, the main deformation mechanism of LTS were also explained.

This paper gives an overview about some mechanical properties of materials processed by surface severe plastic deformation (SSPD) techniques. SSPD processed materials are classified in terms of characteristics, and main generated parameters that determine the output properties of materials are presented. The influences of SSPD on mechanical properties of materials are then reviewed. Furthermore, the roles played by some parameters such as gradient microstructure, nanostructured layer, compressive residual stress (CRS) and surface integrity are highlighted by discussing their contributions. Finally, some conclusions are drawn and possible prospects for future research are underlined.

In recent years, the severe plastic deformation community has developed an interest for metallic materials with high strength and high electrical conductivity, with special focus in Cu- and Al-based alloys, including composite materials. Several processing and metallurgical strategies have been applied to control the influence of microstructure features such as grain refinement, grain boundary condition, defect structures and segregation of secondary phases, over the electrical and mechanical properties. This work summarizes an important body of literature where several strengthening mechanisms and methods to restore the electrical conductivity have been applied to produce ultrafine-grained or nanostructured Cu and Al alloys, mainly by intense imposed strain. A wide variety of alloy systems were studied for their industrial applications in the electrical and electronic market. It can be concluded that the balanced combination of alloying element selection and processing route (mainly attainable under high hydrostatic conditions) could provide high strength with high conductivity and thermal stability materials.

An overview of the severe plastic deformation (SPD) of high entropy alloys (HEAs) is given with a focus on microstructure and texture evolution, phase transformation, strength and ductility, superplasticity, and thermal stability. It combines the now well-established research area of SPD with that of a recently discovered new class of advanced materials. The peculiarities of HEAs in relation to SPD are shown, such as phase decomposition and reduced grain growth. This offers the possibility of producing ultra-hard HEA materials by SPD processes or by post-annealing and enables extremely high superplasticity at high strain rates. The effect of SPD on changing properties is demonstrated mainly for the prototypes fcc Cantor and bcc Senkov HEA, but few examples of more complex HEAs indicate the high research potential of these advanced materials in the field of nanoSPD.

Ti–6Al–7Nb alloys have been widely used in the medical field, particularly in artificial hip joints, spinal fixators, and dental implants, owing to their light weight, low toxicity, and superior corrosion resistance. Grain refinement through a severe plastic deformation process under high pressure, such as high-pressure torsion (HPT) or high-pressure sliding, is widely employed for strengthening metallic materials. This overview presents the recent advances in the effect of HPT on the mechanical properties of the Ti–6Al–7Nb alloy. This alloy was grain-refined through HPT under applied pressures of 2 and 6 GPa, and the results revealed that the alloy subjected to HPT processing at 6 GPa exhibited a higher strength. To inhibit the decrease in the total elongation of the alloy, the number of revolutions in the HPT process was set to moderate. The tensile properties achieved after HPT processing were found to be dependent on the initial microstructure before the HPT treatment. Furthermore, an alloy with a bimodal equiaxed and acicular structure was subjected to grain refinement via the HPT process. The results revealed that fragmentation of the acicular structure during HPT further increased the strength. Moreover, the HPT-processed Ti–6Al–7Nb alloy exhibited superplasticity. It was thus confirmed that grain refinement by HPT is an effective method for strengthening the Ti–6Al–7Nb alloy, which is advantageous for medical applications.

This overview article discusses the Equal Channel Angular Pressing (ECAP) processing of different metallic materials. Particular emphasis is given to the microstructural evolution from the coarse grain (CG) to the ultrafine-grained (UFG) states throughout the electron backscattering diffraction (EBSD) technique. Iron-based alloys, such as duplex and 1020 low-carbon steels reached higher hardening with a lower deformation and lower non-ultrafine average grain sizes than the ultrafine pure iron condition due to fast grain fragmentation, i.e., more geometrically necessary dislocation (GND) grouping. Moreover, due to the magnesium adhesion, copper alloys reached superior mechanical properties compared to pure copper even when the initial grain size for as-cast alloys was over 1000 µm. On the other hand, low melting temperature (T_MP) materials processed at 250°C, like the ZK60 magnesium and AA6082 aluminum alloys (i.e., homologous temperatures (T_H) of 0.38T_MP and 0.37T_MP, respectively), showed grain refinement without reaching the ultrafine regime and mechanical softening due to the static and dynamic recrystallization phenomena. CP titanium also displayed heterogeneous grain sizes with average values of above 1 µm after four ECAP passes for temperatures ranging between 150°C and 400°C (T_H between 0.09T_MP − 0.24T_MP). The evolution of the GNDs suggested that the initial deformation stages of severe plastic deformation (SPD) by ECAP produced the most notorious density increments from 10¹² m⁻² to 10¹⁴ m⁻², which level up at high deformations (more than four ECAP passes) around 10¹⁴–10¹⁵ m⁻², explaining the fast and slow grain size reduction rates, respectively. The ECAP processing on different metallic material systems showed a larger grain fragmentation capacity in high melting points and alloyed materials, giving rise to steep yield strength increases and low ductility. The low ductility and grain size saturation correspond to a low capacity to create new grain boundaries manifested by the GNDs saturation in the UFG range.

Based on the experimental results obtained mainly by the authors, the effect of decreasing the temperature to 77 K using various methods of cryogenic severe plastic deformation (cryo-SPD), such as equal-channel angular pressing, high-pressure torsion, as well as large deformations in the form of cryorolling, on the mechanical properties and mechanisms of plastic deformation is investigated. The results are presented for deformation of a number of metals (titanium, zirconium, cobalt), Ni–18.75%Fe alloy and high-entropy alloys (HEA) Al_0.5CoCrCuFeNi, CrMnFeCoNi₂Cu, CoCrFeNiMn over a wide range of low temperatures. The efficiency of using cryo-SPD methods to increase their strength is demonstrated. The reasons for the paradoxical effect of cryo-SPD on the mechanical characteristics of some HEAs, which contradict the thermally-activated nature of plastic deformation, are analyzed. It is shown that the use of the thermal activation analysis method makes it possible to establish the most probable physical mechanisms that determine the plasticity of a wide class of materials in the coarse-grained and nanostructured states. The features of plastic deformation of various metals and alloys in the coarse-grained and nanostructured states in the ultralow temperature range (4.2–0.5 K) are described.

The high pressure torsion (HPT) of various binary Ti alloys with β-stabilizers (Fe, Co, Ni, Mo, Nb) was studied. Before HPT, the samples were annealed and contained (i) pure β-phase, (ii) α+β mixture with different portion of phases, (iii) α′ or α′′ martensites, (iv) the mixture of α-Ti and respective intermetallic phase. The microstructure of Ti alloys before and after HPT was studied by scanning and transmission electron microscopy (also high resolution one), X-rays diffraction (including the high-temperature in situ one), differential scanning calorimetry, atomic probe tomography, synchrotron irradiation. During HPT the (usual) strong grain refinement took place. Also, it was observed that HPT can lead to various phase transitions in the Ti alloys. In particular, the metastable high-pressure ω-phase and α′ martensite can form. The composition of phases (similar to their grain size) reached the steady-state value after about 1.5 plunger revolutions. In some cases, the equifinality of the HPT-driven phase transitions was observed. Equifinality means that the composition and portion of phases after HPT do not depend on the composition and portion of phases before HPT.

The HPT-driven phase transitions can be martensitic (i.e. without or almost without mass transfer) or diffusional (i.e. with mass transfer). In case of martensitic β-to-ω or α-to-ω phase transitions, the certain orientation relations between β and ω or α and ω phases were observed. The thermal stability of the ω-phase obtained by HPT has been studied by the in-situ X-rays diffraction at high temperatures. The ω-phase in the HPT-treated Ti alloys with β-stabilizers can remain in the samples up to 500–600°C. It is much higher than in pure titanium (∼180°C). Thus, the HPT-driven phase transitions open the new way for tailoring of grain size and phase composition of Ti-based alloys. In turn, it gives the new instrument in hands of engineers to improvement of the technologically important properties of Ti-based alloys. It is especially important for the medical application like the teeth or bone prosthesis.

This paper presents an overview of fundamentals and potential applications of ultrafine-grained Al-based conductors developed with the help of severe plastic deformation (SPD) techniques. Based on deliberate formation of nanoscale features (such as nanoprecipitates, segregation of solutes along crystallographic defects and so on) within ultrafine grains, it is possible to optimise their mechanical and functional performance enhancing the combination of strength and electrical conductivity to produce advanced lightweight conductors required by modern industries. Guidelines related to SPD-driven development of Al alloys with properties superior to those exhibited by traditionally processed conductors are discussed.

In the last three decades, several severe plastic deformation (SPD) procedures have been developed and applied in materials science to create bulk, ultrafine-grained (UFG) structures. As a consequence of the SPD, not only submicron and even nanometer grain sizes can be obtained, but also new grain boundaries with non-equilibrium structures in a material may be formed. Therefore, both the strength and ductility of the UFG materials can change significantly compared to the coarse-grained counterparts. This review is focused on unusual mechanical behaviors of UFG Al and Al alloys, associated with grain boundary structure and segregations which are responsible for the modification of the Hall-Petch relationship and the so-called size-effect for UFG structure. Unusually high strain rate sensitivity, intensive grain boundary sliding and superplasticity at low temperature are described and surveyed. In addition, innovation potential of these phenomena is also briefly considered.

This overview highlights some salient features of one of the most popular severe plastic deformation techniques: high-pressure torsion (HPT). It focuses on the unresolved challenging problems of HPT. The problems selected touch upon some fundamental questions of mechanics of plasticity, fracture, and friction that are at the core of the HPT process. The scientific significance of these problems and the proposed pathways to resolving them are discussed. The article is meant to promote the use of HPT as a potent tool for studying plasticity at large strains theoretically and also as a practical method enabling novel micromanufacturing routes.

Severe plastic deformations (SPD) under high pressure, mostly by high-pressure torsion, are employed for producing nanostructured materials and stable or metastable high-pressure phases. However, they were studied postmortem after pressure release. Here, we review recent in situ experimental and theoretical studies of coupled SPD, strain-induced phase transformations (PTs), and microstructure evolution under high pressure obtained under compression in diamond anvil cell or compression and torsion in rotational diamond anvil cell. The utilization of x-ray diffraction with synchrotron radiation allows one to determine the radial distribution of volume fraction of phases, pressure, dislocation density, and crystallite size in each phase and find the main laws of their evolution and interaction. Coupling with the finite element simulations of the sample behavior allows the determination of fields of all components of the stress and plastic strain tensors and volume fraction of high-pressure phase and provides a better understanding of ways to control occurring processes. Atomistic, nanoscale and scale-free phase-field simulations allow elucidation of the main physical mechanisms of the plastic strain-induced drastic reduction in phase transformation pressure (by one to two orders of magnitude), the appearance of new phases, and strain-controlled PT kinetics in comparison with hydrostatic loading. Combining in situ experiments with multiscale theory potentially leads to the formulation of methods to control strain-induced PT and microstructure evolution and designing economic synthetic paths for the defect-induced synthesis of desired high-pressure phases, nanostructures, and nanocomposites.

In this paper we review the use of cold rolling for the enhancement of magnesium-based alloys. After a short description of the technique, we discuss the main systems that have been investigated in the recent years. Namely pure magnesium and it’s hydride, Mg–Pd, Mg–Al, Mg–Cu, Mg–Fe, and Mg–Ni.

The study of metal forging over long period of time has made it possible to establish the major basic principles up to the most recent, those of Severe Plastic Deformation (SPD). Thus the fundamental characteristics resulting from the stresses and deformations applied have led to the definition and modelling of microstructural variations in grain size and shape, density of dislocations, slip bands and twins, all factors to be considered during the transformation of the micro/nanostructure by SPD. For this purpose, SPD techniques such as ECAP, HPT, ARB have produced invaluable results namely in views of solid state hydrogen storage. So the present report focuses on magnesium-based materials with the aim of generating a deformed structure that will react quickly to allow massive and reversible hydrogen storage. However, all here above mentioned methods are rather difficult to scale up to mass production because they are either too time-consuming or too energy and labor intensive. Furthermore, it is revealed that at extreme, fast forging (FF) can introduce high densities of vacancies, voids and finally cracks in addition to grain refinement down to the ultrafine and nano-scale sizes. This leads in the FF worked material exhibiting excellent hydrogen reactivity as shown on a few examples.

Friction stir processing (FSP) has been performed on 2024 aluminum alloy sheets. The process was carried out using two different cooling rate i.e., Air Cooling (FSP-AC) and cooling using the liquid nitrogen (FSP-NC). In the current research, the effect of different cooling rates on microstructures and relating precipitates has been investigated. The results have been shown that the average grain size in the stirred zone (SZ) has been decreased significantly in the FSP-NC (1.75 µm) condition, with respect to the FSP-AC (3.3 µm). The misorientation angle of grain boundaries created the special structure. The grain boundaries were facet in FSP-AC and FSP-NC and the rough boundaries was observed in FSP-AC specimen.

TEM and EBSD analysis have been indicated the dissolution of Ω-Al₂Cu precipitates in the SZ in the FSP-NC specimen, while FSP-AC caused formation of supersaturated copper solid solution with Ω-Al₂Cu precipitates in the grain boundaries. Furthermore, in the both FS-processed specimens (FSP-AC and FSP-NC) fine and dispersed Al₂₀Cu₂Mn₃ precipitates have been observed.

This study presents that A1050 commercial-purity aluminum increases the tensile strength and ductility using the processes of accumulative roll bonding (ARB) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 240 MPa after processing by ARB for 10 cycles and by HPS for the sliding distance of 15 mm, respectively. The stress-strain behavior is evaluated through microstructure observations and measurements of strain hardening rates. Significant grain refinement with well-defined grain boundaries is responsible for the strength increase. The grain refinement also leads to an increase in strain hardening rate and thus an increase in the ductility.

A high-pressure torsion (HPT) processed Fe–21Cr–5Ni–2Mo (mass%) two-phase stainless steel was used to study the morphology and crystallographic features of austenite (γ) precipitated from ferrite (α) during aging in the (α + γ) two-phase region. The starting material was a gas-atomized powder with a completely ferritic structure. The HPT process was carried out to produce a fully dense compact under 6 GPa for 5 revolutions. The compact was given an equivalent strain of about 130. After the HPT process, the matrix ferrite formed a pancake–like nanograined structure with a strong texture, i.e. ND (Normal Direction) // {110} α. By annealing at 1173 K for 3.6 ks, an ultrafine (α + γ) microduplex structure with high-angle grain boundaries was formed. In addition, the strong texture formation of {110} α/{111} γ/ND plane was formed in the α and the γ grain duplex structure. The α and γ phases had average grain sizes of 2.1 µm and 1.6 µm, respectively. The area fraction of the γ phase was 37.2%, which exceeded that of a cold-pressed compact, 6.7%. Both ultrafine grain refinement and γ precipitation were accelerated by the HPT process. In other words, the application of the HPT process to the two-phase alloys enables the formation of the ultrafine microduplex structure. The Kurdjumov-Sachs (K-S) orientation relationship between α and γ phases is usually observed in the alloy, however, the K-S orientation relationship was not dominant except for the close packing plane parallel orientation relationship, {110} α/{111} γ, in the HPT-processed material.

A titanium–iron intermetallic with minor addition of manganese (TiFe_0.7Mn_0.3) was processed by severe plastic deformation through high-pressure sliding (HPS). A rectangular strip sample was embedded in stainless steel and strained under a pressure of 4 GPa at room temperature. The hydrogen storage kinetics and activation of the HPS-processed sample were significantly enhanced in comparison with the as-received ingot without the HPS processing.

In this work, microstructure and magnetic properties of sintered Nd_16.5Fe₇₇B_6.5 magnets with intergranular addition of Dy₃₀Nd₁₇Pr₃Al₄₀Cu₁₀ were investigated. The additional particles with size in the range of 1–2 µm were homogeneously mixed into micrometer Nd_16.5Fe₇₇B_6.5 master powder with different weight fractions. The investigation shows that coercivity H_c of the added magnets significantly increases, while their remanence B_r decreases with increasing Dy₃₀Nd₁₇Pr₃Al₄₀Cu₁₀ additional fraction. The coercivity of the magnets increases from 14.5 kOe to 31.5 kOe with increasing the additional fraction from 0 to 9 wt.%. By adding Dy₃₀Nd₁₇Pr₃Al₄₀Cu₁₀ compound to grain boundary, the Dy concentration can be reduced by 60 wt.% in comparison with the conventional method.

Nanoclusters formed in Al–Mg–Si alloys affect the aging behavior of the alloys depending on the formation temperature. In the present study, first-principles calculations were carried out to evaluate the two- and three-body interactions between Mg, Si atoms and vacancies in the Al matrix and estimate the effect of local bonding on the formation of nanoclusters. Monte Carlo simulations were subsequently performed to investigate the stable structure of the nanocluster formed in Al–0.95 mass pct Mg–0.81 mass pct Si alloy. We found that the Mg–Si and Si–Vac pairs are stable in the Al matrix. The result shows that the solute atoms easily aggregate with different types of solute atoms and that the Si atom has a strong attractive interaction with a vacancy. Furthermore, Mg–Si–vacancy triplets are more stable than Mg–Si and Si–vacancy pairs in the Al matrix. The nanoclusters in the Al matrix were thermally stabilized by the stable configurations between solute atoms and vacancy. Thus, the electronic structure calculations suggested that the local bondings within a nanocluster play a significant role in not only the thermal stability but also the formation and growth behavior of nanoclusters during aging at low temperatures.

This Paper was Originally Published in Japanese in J. JILM 72 (2022) 47–53. The abstract, the captions of Figs. 1, 2, 3, 4 and the caption of Table 3 are slightly modified.

Large amounts of solid waste-spent cathode carbon (SCC) was produced in aluminum electrolysis process. At present, landfill and storage methods are widely used, which will not only cause great harm to the environment, but also cause a lot of waste of resources. Nickel and iron were recovered from laterite nickel ore by reduction roasting-magnetic separation using SCC as reducing agent. The fluorine in SCC was fixed in roasted ore by adding CaO. The feasibility of the method was verified by thermodynamic analysis and experiments, and the optimum conditions for CaO addition were determined. The recovery of nickel and iron reached 91.23% and 89.63% respectively when the addition of SCC was 14 wt.% and CaO was 8 wt.%. Adding 8 wt.% CaO under the condition of SCC as reducing agent can change the viscosity of roasted ore and promote the aggregation of ferronickel particles. The concentration of soluble F⁻ in roasted ore was reduced and fixed in roasted ore in the form of insoluble calcium fluoride. Under the condition of adding 8 wt.% CaO, the fluorine fixation rate was 95.99%, and the concentration of F⁻ in roasted ore was only 31 mg·L⁻¹.

Binder jetting (BJT) holds enormous promise as an additive manufacturing technique due to its high throughput and low-cost equipment. The ability to fabricate geometrically complex parts from aluminum alloy via BJT would have a significant impact on the development of high-performance machine components and heat-dissipation devices. However, processing printed objects by sintering of aluminum alloy is difficult due to the surface oxide layer that covers the powder particles, which prevents the final parts from reaching a sufficiently high density. In order to investigate the sintering mechanism for controlling the quality of sintered parts, we directly observed the sintering behavior of pure Al and Al–10%Si–0.4%Mg (mass%) alloy using an in situ scanning electron microscopy system equipped with a heating stage. It is found that the surface roughness of the powder particles is reduced above their melting or solidus temperature. Subsequently, the liquid ruptures the oxide layer and forms necks between the particles.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 68 (2021) 311–316.

In order to understand the influence of dislocation substructures on the size-dependent strength (smaller is stronger) of micron-sized metals, we have fabricated single-crystal cylindrical micropillars with various diameters approximately ranging from 1 to 10 µm, which were prepared on the surface of the fully annealed sample and the subsequently cold-rolled samples of high-purity aluminum (Al). The annealed micropillars exhibited a size dependence of the resolved shear stress required for slip. The shear stress (τ_i) normalized by shear modulus (G) and the specimen diameter (d) normalized by Burgers vector (b) followed the correlation of τ_i/G = 0.33(d/b)^−0.63. The size-dependent strength was reduced by cold-rolling, resulting in lower power-law exponents (0.26∼0.31) for the correlation in the cold-rolled specimens. The fine dislocation substructures introduced by the cold-rolling could be associated with the reduced size-dependent strength, which can be rationalized using the stochastic model of the dislocation source length in an assumption of homogenously distributed dislocations existing in the experimental micropillars. The inhomogeneous dislocation substructure with various dislocation cell sizes would contribute to a variation in the measured strength depending on the location, likely due to the probability of exiting the dislocation cell walls (local variation in dislocation density) in the micropillars fabricated on the cold-rolled Al samples.

Nanoindentation tests were conducted near the grain boundary (GB) of the Al–Mg–Si alloy, and the influence of GB character on the aging precipitation behavior and the mechanical properties was confirmed. After obtaining the GB characters by electron back scattered diffraction (EBSD) analysis and nanoindentation tests were carried out on under-aged, peak-aged, and over-aged samples. And then, the indentation areas were observed by back scattered electrons imaging (BSE) in order to identify indentation positions to the GB. In this study, for the GB character, focusing on the rotation angle, the high-angle GB (HAGB) and the low-angle GB (LAGB) were selected. In addition, coincidence site lattice GBs (CSL) were selected as the special GB. In the 180°C under-aged sample, the nano-hardness near GB is higher than that far from GB, while 180°C peak-aged and 250°C aged samples, the nano-hardness is lower than that far from GB. Then the amount of change in hardness of HAGB was larger than that of the LAGB. This suggests that the GB character affects the aging precipitation behavior and mechanical properties.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 7–16.

Copper alloy suspension wires are used in the optical pickups and image stabilization mechanisms of mobile cameras. The durability of suspension wires used in mobile cameras is greatly affected by the increase in the weight of the lens assembly as makers improve the image quality of the camera. Therefore, the durability of the wire needs improvement. In this study, the stress reduction effect of twisted suspension wires was investigated using finite element method (FEM) analysis. In addition, a practical equation was obtained to facilitate the structural design. From this study, the following conclusions were obtained. In contrast to the conventional single-wire structure, the twisted wire structure enables a significant reduction in the stress generated while maintaining the stiffness. A simple formula that approximates the results of many FEM analyses was developed to enable rapid product design.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 61 (2022) 339–343.

The relationship between the crystal phase and absorbed hydrogen in cobalt electrodeposited from a LiCl-based highly concentrated (HC) aqueous solution was investigated using X-ray diffraction and thermal desorption spectroscopy. We expected that the use of an HC solution would enable the electrodeposition of cobalt without hydrogen evolution and the concomitant hydrogen absorption. The current efficiency of cobalt deposition was more than 99% at potentials above −0.8 V vs. Ag/AgCl, indicating that hydrogen evolution is really suppressed, but the electrodeposited cobalt accompanied the fcc phase irrespective of the deposition temperature. Moreover, electrodeposited cobalt contained a large amount of hydrogen despite the high current efficiency. The hydrogen content of cobalt obtained at 100°C was approximately 10% of that obtained at room temperature; however, the fcc phase was still co-deposited, suggesting that factors other than hydrogen could be responsible for fcc-Co formation. The reason for hydrogen inclusion from the HC solution is discussed in terms of the hydrogen reduction mechanism.

Solidification microstructure in Fe-based Fe–X-based metallic glasses (X = Cu, Ag, Au, Pd, Pt, Rh, Ir, Ru, Os, Re, Hg) (X is a noble metallic element) with liquid phase separation (LPS) was categorized. Only Fe–Cu-based and Fe–Ag-based metallic glasses with liquid phase separation were reported among Fe–X-based alloys. Fe–P–C–Ag immiscible metallic glasses which showed liquid-phase separation were designed using the alloy parameters of mixing enthalpy, the ground state diagrams constructed by the Materials Project, and Calculation of Phase Diagrams (CALPHAD). Macroscopically separated ribbons composed of FCC-Ag entangled ribbons and Fe–P–C metallic glass ribbons were obtained by a melt-spinning method. The formation mechanism of the macroscopically separated ribbons in Fe–P–C–Ag immiscible metallic glasses is described with LPS behavior and melt-spinning process in this study.

This Paper was Originally Published in Japanese in J. Japan Soc. Powder Powder Metallurgy 69 (2022) 185–194. Errata in Japanese were reported in J. Japan Soc. Powder Powder Metallurgy 70 (2023) 173 and 312. Minor corrections to the paper were made in the text body.

The structural characterization, and the electronic, magnetic and magnetocaloric properties of polycrystalline samples of La_0.7Ca_0.3Mn_1−xCu_xO₃ (x = 0, 0.04, 0.06, 0.08) have been investigated. X-ray powder diffraction analysis indicates all samples having an orthorhombic structure, belonging to the Pbnm space group. X-ray absorption fine structure spectra reveal that Mn is in the mixed state of Mn³⁺ and Mn⁴⁺ while Cu has divalent state (Cu²⁺). With the substitution of Cu²⁺ for Mn, the Curie temperature, T_C, decreases monotonically from 248 K for x = 0 to 156 K for x = 0.08, which is due to weakened exchange interactions. The downturn in the temperature dependencies of the inverse magnetic susceptibility, χ⁻¹(T), curves observed above T_C for x = 0 and 0.08 is characteristic of the Griffiths-like phase. The analysis of isothermal magnetization data M(T, H) based on the Banerjee’s criteria has indicated x = 0, 0.04, and 0.06 samples undergoing a first-order magnetic phase transition. However, the x = 0.08 sample, the coexistences of second-order magnetic phase transition at low magnetic fields below 8 kOe and first-order magnetic phase transition at high magnetic fields were observed. The maximum magnetic entropy change measured at a magnetic field span of 50 kOe occurring near the T_C decreases from 10.3 to 4.8 J/kg.K with increasing x from 0 to 0.08. However, the relative cooling power (RCP) tends to increase, in which a maximum RCP of 360 J/kg for x = 0.08 that is about 1.3 times greater than that observed for the parent sample (x = 0).

Heavily and simply cold-rolled Cu alloys with ultra-low stacking fault energy exhibit superior strength/ductility balance. The excellent mechanical properties are attained by the formation of a heterogeneous-nano (HN) structure consisting of twin domains, shear bands, and lamellar grains. In this study, using a Cu–Zn system alloy, two specimens with different initial textures were subjected to cold rolling. One has a strong 〈001〉 texture along the normal direction (ND) of the rolling surface, and the other has a 〈111〉 texture. Then, the effects of the initial texture of specimens on the formation of deformation twins in the early stage of cold rolling were precisely investigated. Also, the microstructure and mechanical properties of the alloys with finally developed HN structure after 90%-cold-rolling were examined. At the early stage of rolling, the mechanical twinning occurred more frequently in the specimen with 〈001〉 texture than in the 〈111〉 one. The difference in the twinning frequency can be reasonably explained by the significant difference in the ratio of the Schmid factor for twinning partial to the one for the perfect dislocation. On the 90% cold rolling, the 〈001〉 specimen exhibited better strength/ductility balance than that of the 〈111〉 specimen since the 〈001〉 one has a higher volume fraction of the deformation twin domains. It can be concluded that the initial texture of the specimen before the cold rolling plays an important role in the mechanical properties of HN structured materials via the formation of the twin domains.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 61 (2022) 62–67.

The eight papers were selected for the best paper award in 2021 to 2022 from Materials Transactions. Here, the awarded papers are briefly summarized as current trends in research of Materials Transactions. Among the eight best papers, four were specially selected for young scientists whose ages are 35 or below. An important trend in the year of 2021 is that three best papers are from a special issue with the title of “Materials Science on Hypermaterials”, which is based on an ongoing national research project, Grant-in-Aid for Scientific Research on Innovative Areas.

The partial substitution of Cu for Co was found to be effective in improving the magnetostrictive properties of CoFe₂O₄. The magnetic field dependence of the strain for the Cu_xCo_1−xFe₂O₄ samples with a cubic spinel structure showed a larger strain magnitude at lower magnetic fields as x increased to 0.6. As a result, the sample with x = 0.6 demonstrated the strain of approximately 511 ppm by changing the direction of 1 T magnetic field. This value was approximately 1.6 times larger than that of Galfenol, a commercial magnetostrictive material without rare-earth elements. Such superior magnetostrictive properties were not obtained in the samples with x ≥ 0.7 containing a tetragonal structure. Therefore, the cubic spinel Cu_xCo_1−xFe₂O₄ system is a promising candidate for rare-earth-free magnetostrictive materials.

Neutron scattering experiments were conducted to reveal the origin of diffuse scattering in a medium-entropy alloy (MnCoNi). Results showed that a time-temperature-dependent short- and long-range structural transformation from a face-centered cubic to a primitive tetragonal structure occurs. In the MnCoNi alloy, the long-range ordered phase with a relatively small c/a ratio of 3.7(1)% can only be grown in a limited temperature range, whereas short-range structural transformation with a short correlation length of 1–4 nm can be formed in a wide temperature range. On the contrary, no sign of short-/long-range staggered atomic rearrangement, such as L1₀ and L1₂ structures, was observed in the CrCoNi alloy at least at room temperature. The difference in the forming ability of short-/long-range ordering between the MnCoNi and CrCoNi alloys was discussed.

We have found that, during in-situ scanning transmission electron microscopy observations, heating of a Mg₉₇Zn₁Gd₂ (at%) alloy at 623 K leads to dynamic precipitations of face-centered-cubic (fcc)-based Gd nanoparticles. With the aid of density-functional theory (DFT) calculations, the observed lattice constant of 5.32 Å, which is larger than that expected for pure fcc-Gd of 5.06 Å, is likely to be due to oxygen atoms inserted at tetrahedral interstitial sites with essentially a fractional occupation. Systematic DFT calculations show that the fcc-base GdO_x can be stable configurations in a wide composition range, where the O atoms behave like a solute up to x ∼ 1.5 to provide continuously the non-stoichiometric GdO_x solid-solution phase.