Severe Plastic Deformation Process Research Articles

Using Severe Plastic Deformation to Produce Nanostructured Materials with Superior Properties

The past decade was marked by significant advances in the development of severe plastic deformation (SPD) techniques to achieve new and superior properties in various materials. This review examines the achievements in these areas of study and explores promising trends in further research and development. SPD processing provides strong grain refinement at the nanoscale and produces very high dislocation and point defect densities as well as unusual phase transformations associated with particle dissolution, precipitation, or amorphization. Such SPD-induced nanostructural features strongly influence deformation and transport mechanisms and can substantially enhance the performance of advanced materials. Exploiting this knowledge, we discuss the concept of nanostructural design of metals and alloys for multifunctional properties such as high strength and electrical conductivity, superplasticity, increased radiation, and corrosion tolerance. Special emphasis is placed on advanced metallic biomaterials that promote innovative applications in medicine.

Influence of Parallel Tubular Channel Angular Pressing (PTCAP) Processing on the Microstructure Evolution and Wear Characteristics of Copper and Brass Tubes.

The influence of the number of passes and the tube materials on the microstructural evolution, mechanical properties, and wear behavior of Cu and brass tubes after parallel tubular channel angular pressing (PTCAP) was investigated. The grain size decreased to final grain sizes of 138.6 nm and 142.7 nm, after PTCAP of the Cu and brass tubes was conducted in up to 4 and 2 passes, respectively. PTCAP contributes to obtaining an ultra-fine grain (UFG) microstructure, with a mixture of different grain sizes that conferred high hardness. The present results indicate the superior wear resistance of Cu and brass PTCAP tubes, relative to Cu and brass samples that were previously deformed by different severe plastic deformation (SPD) processes. The wear mechanism of the Cu tubes changed from delamination and cracks with a high degree of adhesive wear before PTCAP into a combination of adhesive and abrasive wear, with a decrease in the presence of oxygen content after the PTCAP procedure. The wear mechanism also changed from a combination of adhesive and abrasive mechanisms into abrasive ones with the absence of oxygen after the PTCAP of brass tubes.

Severe plastic deformation (SPD) of biodegradable magnesium alloys and composites: A review of developments and prospects

The use of magnesium in orthopedic and cardiovascular applications has been widely attracted by diminishing the risk of abnormal interaction of the implant with the body tissue and eliminating the second surgery to remove it from the body. Nevertheless, the fast degradation rate and generally inhomogeneous corrosion subsequently caused a decline in the mechanical strength of Mg during the healing period. Numerous researches have been conducted on the influences of various severe plastic deformation (SPD) processes on magnesium bio-alloys and biocomposites. This paper strives to summarize the various SPD techniques used to achieve magnesium with an ultrafine-grained (UFG) structure. Moreover, the effects of various severe plastic deformation methods on magnesium microstructure, mechanical properties, and corrosion behavior have been discussed. Overall, this review intends to clarify the different potentials of applying SPD processes to the magnesium alloys and composites to augment their usage in biomedical applications.

The formation mechanism, mechanical properties and thermal stability of the pure copper sheet with gradient structure processed by plastic flow machining

Plastic flow machining (PFM) is a novel severe plastic deformation (SPD) process. Ultrafine-grained metal sheets or strips with gradient structures are processed by PFM in a single step under the combined effects of cutting and pressing. In this paper, the formation mechanism, mechanical properties, and thermal stability of pure copper sheets with gradient structures for different extrusion thicknesses were studied. The results implied that there was a pronounced gradient in terms of strain, grain size, and hardness across the sheet thickness. As the extrusion thickness was varied from 1.0 to 1.6 mm, the increasing thickness of the deformed coarse-grained layer contributed to decreases in the yield strength (YS) and ultimate tensile strength (UTS) and an increase in the elongation after fracture. As a result, the distribution of the gradient structure across the sheet thickness was controllable. There were considerable improvements in hardness, YS, and UTS and only a small reduction in elongation after fracture. In addition, after annealing at 150 °C, the hardness and tensile properties of the sheets were slightly different than those of the untreated sheets, indicating that the sheets had good thermal stability below this annealing temperature. Thus, PFM is an efficient SPD process for preparing the gradient structure sheets with high strength and reasonable ductility. • The formation mechanism of the pure copper sheets with gradient structure processed by plastic flow machining was analyzed. • The variation of the gradient structure of the pure copper sheets with different processing conditions was analyzed. • Thermal stability of the pure copper sheets was analyzed.

Assessment of Severe Plastic Deformation Processes in Bulk and Nanostructured Metallic Glass

The metallic glasses are known as amorphous and metastable materials. These materials have superior mechanical properties over crystalline materials with the same chemistry. Continuous efforts were made to improve the properties of metallic glass. The severe plastic deformation (SPD) method is used to improve the ductility of the glass. SPD causes the deformation at the atomic level in the disordered structure of the glass. Many methods are reported, such as cryogenic cycling, high-pressure torsion, and equal channel angular pressing, which are used for the SPD. In recent works on nanostructured metallic glasses, it has been evidenced that some properties, for example, mechanical, thermal, and magnetic, have improved compared to the bulk metallic glass. This paper has reviewed the recent progress in the SPD of the bulk and nanostructured metallic glasses. Different methods for the SPD have been addressed here. The effect of SPD on the properties of metallic glass is deliberated in this paper. Moreover, the challenging tasks of deformation occurrence in the glass and its characterization were considered, trying to develop a sound understanding of SPD in bulk and nanostructured metallic glasses.

Strength and ductility enhancement of AZ61/Al2O3/SiC hybrid composite by ECAP processing

Magnesium is a low-density metal which is used in extensive structural applications such as load-bearing components in the automobile industry. To improve the strength and ductility of the magnesium alloys, method of production of metal matrix composites have been developed. In this study, AZ61 magnesium alloy was reinforced with hybrid particles (2 wt% Al2O3 and 1 wt% SiC) fabricated by the stir casting method. Then, the casted samples were homogenized at 410 °C for 24 h, aged at 200 °C for 10 h followed by severe plastic deformation (SPD) processing using equal channel angular pressing (ECAP). The obtained microstructure observation showed that the hybrid reinforcement particles were uniformly distributed in the metal matrix. After the ECAP process, the grain size was significantly reduced from 148.79 ± 79 µm to 12.2 ± 8 µm due to the dynamic recrystallization (DRX) mechanism during the plastic deformation. The mechanical properties of hardness, yield strength (YS), ultimate tensile strength (UTS), and elongation are effectively improved after each ECAP pass; the maximum values achieved were 61.2 ± 4.6 HV, 110.3 MPa, 250.1 MPa, and 19.3%, respectively on the AZ61/Al2O3/SiC hybrid composite subjected to two passes of ECAP. The enhancement of the mechanical properties of the AZ61 hybrid composites was mainly attributed to the Hall-Petch strengthening mechanism.

Fatigue Properties of Ti Alloys with an Ultrafine Grained Structure: Challenges and Achievements

Ultrafine-grained (UFG) structure formation in Ti alloys, by severe plastic deformation (SPD) processing and enhancement of their mechanical properties, including fatigue properties, has been demonstrated in numerous studies in the past 20 years. The present overview analyzes the fatigue properties achieved to date in Ti alloys subjected to SPD. Such aspects are examined as the effect of a UFG structure on the fatigue behavior of commercially pure (CP) Ti, two-phase Ti alloys, using the popular Ti-6Al-4V alloy as an example, as well as on the kinetics and mechanisms of fatigue failure. The prospects and problems of the practical application of UFG Ti materials in medicine and aircraft engine construction are discussed.

New Die Design for High-Pressure Torsion

A special design of the die was developed, which allows to implement the process of severe plastic deformation by high pressure torsion to deform ring blanks, which will be the starting material for creating high-strength piston rings. A special feature of the die design is the provision of torsion of the deforming tool with constant rectilinear movement of the press punch due to the composite deforming tool, which includes both displacement and rotation blocks. Using the obtained geometry, computer simulation of this process in the Deform program was performed in order to assess the possibility of a stable process flow. AISI-316 austenitic stainless steel was chosen as the material of the billet. The resulting strain force on the first two cycles was considered. On the first cycle, the force was equal to 464 kN, on the second cycle the force value was about 1200 kN. The obtained values are quite adequate, which indicates the possibility of multi-cycle deformation.

Investigation of the joinability of single- and multi-layered AA6014 sheets produced by accumulative roll bonding in the shear-clinching process

Accumulative roll bonding belongs to the severe plastic deformation processes and is suitable for producing multi-layered as well as high-strength sheets through repeated rolling. After four accumulative roll bonding-cycles, the strength of the investigated AA6014-T4 alloy is elevated due to strain and fine grain hardening by 170% in yield strength and by 37% in ultimate tensile strength. This is accompanied by a significant decrease in material ductility which is disadvantageous for joining processes based on forming operations. Shear-clinching, however, can be used to join high-strength and low-ductile materials on the die side. Thus, it is a promising method for the mechanical joining of accumulative roll bonding components. The multi-layered and more brittle material is located on the die side whereas the single-layered base material with higher ductility is positioned on the punch side. At present, there is no scientific knowledge how the multi-layered material behaves in the shear-clinching process. Since the material is cut in the process, delamination effects could occur at the interfaces produced via accumulative roll bonding. Additionally, the investigation aims at the influence of the accumulative roll bonding process on the properties of the joints. They are expected to depend on the number of process cycles and thus on the change of mechanical properties of the multi-layered material. The bond strength of the shear-clinched joints is determined by shear and tensile tests. The areas of material failure are analysed via metallographic methods. From the failure behaviour and load-bearing capacity it is determined which number of accumulative roll bonding cycles is ideal for joining multi-layered sheets via shear-clinching.

Mechanical properties and microstructural evolution of high-pressure torsion-processed Al7075 alloy at elevated temperatures

The severe plastic deformation of aluminum alloys can be advantageous for developing a unique microstructure by inducing dynamic recovery and dynamic precipitation. Because dynamic recovery and precipitation are related to temperature changes, an elevated temperature atmosphere during severe plastic deformation may accelerate microstructural changes in aluminum, resulting in different properties compared to that of the room-temperature processed sample. In the present work, the microstructural and mechanical properties of the elevated temperature high-pressure torsion-processed Al7075 alloy were investigated. Experimental results demonstrated that the elevated temperature during high-pressure torsion not only induces a dynamic recovery at a high shear strain regime but also yields coarse Mg, Zn, and Cu-rich precipitates in the aluminum matrix. Although the grain growth occurs from the shear strain of 7.8, evolved precipitates represents larger strength than matrix that result into continuous mechanical properties enhancement in the elevated temperature-processed sample. This result indicates that solute migration acceleration at an elevated temperature could be a suitable method to enhance the mechanical properties of aluminum alloys undergoing severe plastic deformation processing.

Significant Bauschinger effect and back stress strengthening in an ultrafine grained pure aluminum fabricated by severe plastic deformation process

Bauschinger test in uniaxial tension-compression mode was carried out for the first time on the pure Al specimens having homogeneous ultra-fine grained (UFG) microstructures fabricated by equal-channel angular pressing (ECAP) and subsequent annealing processes. Significant Bauschinger stress (transient softening), Bauschinger energy parameter and their strong dependences on the tensile plastic pre-strain at the very early stage of the tensile deformation were measured in the UFG specimens, in sharp contrast to their coarse-grained (CG) counterpart. The grain size dependence of the Bauschinger effect in pure Al was qualitatively discussed in terms of the back stress arising from the formation of dislocation pile-up against the grain boundary during plastic deformation.

Effects of ECAE process on the fatigue crack growth rate of copper metal

In this study, the effects of the number of passes performed by the Equal Channel Angular Extrusion as a severe plastic deformation process on copper metal's microstructure and mechanical properties, especially its resistance to fatigue crack growth, have been investigated. The experimental results show that as the number of processes passes increases, the copper metal grains become finer and as a result less stress is concentrated at the starting points of the fatigue fracture, which delays the fracture. For example, after performing 8 ECAE process passes, the threshold values of fatigue crack growth increases by 113.2% relative to the base metal. Moreover, as the grains become smaller, the number of grains and consequently the number of grain boundaries will increase and thus more obstacles will be placed in the way of crack growth. Also, the SEM images indicate that many fine and equiaxed dimples in processed copper become smaller as the number of passes increases. This shows that finer and more equiaxed grains will be obtained by repeating the ECAE process and thus repeating the occurrence of recrystallization. It was cleared that this process improves the mechanical properties of the copper other than the failure strain. However, by increasing the number of process passes, this problem can be significantly reduced. Highlights The fine grains considerably delay the fatigue fracture By ECAE process, the threshold value of fatigue crack growth increases by 113.2% All zones resulting from fatigue fracture are recognizable in fractured ECAE sample The SEM images indicate that a ductile failure has occurred in the tensile samples

Influence of Fly Ash and Emery based particulate reinforced AA7075 surface composite processed through friction stir processing

The novel friction stir technology is adopted in modern automotive industries to meet the desired properties like hardness, impact toughness and tribological behaviour over the conventional techniques like stir casting, compo casting, squeeze casting, electroplating and infiltration methods. AA7075 surface composites fabricated with different volume fractions of fly ash and emery particles is said to enhance the aforementioned properties. The composites are processed through friction stir process (rotational speed −1200 rpm, transverse speed – 56 mm/min, tool tilt angle – 2 °). During characterization, the Microstructural examination of surface composites depicts fine and homogenous distribution of reinforcements in the friction stir process region owing to severe plastic deformation and dynamic recrystallization process. Substantially, good interface is formed between the reinforcement particulates and base substrate. Inclusion of Fe3O4, Al2O3 and SiO2 constituents through fly ash and emery reinforcements associated with the homogenous dispersion strengthening mechanism favours for the superior hardness of surface hybrid composite specimen 50E50FA. Decremented grain size and load bearing capacity of the reinforcements is beneficial for the crack propagation resistance that enhances the impact toughness behaviour (17.4 J/cm2) of the same specimen. Wear rate of the specimens are evaluated through pin on disc tribometer. The decrease in the wear rate of hard specimen 50E50FA is observed due to the reduced contact area between its surface and counter disc. The morphology of worn specimens using SEM analysis shows the combined abrasive and adhesive wear as the worn mechanism.

Finite element analysis of copper tube to study the behavior of equivalent strength during the severe plastic deformation process

In this work, Finite Element Modeling is used to depict enhanced perception about the spd process. A 3-dimensional FE model was built to simulate the copper tube drawing process using Ansys2020R2 software. The severe plastic deformation (spd) process is used to manufacture high-precision tubes for different industrial applications. The finite element analysis for severe plastic deformation process suitable for sheet and solid is already done but numerical study to optimize the nanostructure tube yet not done. In this process, the tubes are drawn in a controlled fashion through a die to reduce their diameters and wall thickness. Modeling and simulation of metal forming processes are becoming increasingly popular, as the resulting models have shown to be useful tools for optimizing existing processes and developing new ones. In this paper, finite element analysis to depict the deformation, yield stress, ultimate tensile stress, and strain during the severe plastic deformation process is explained. In addition, the final dimension of a tube with very high precision is calculated after the first pass of the spd process. The von-mises stress observed is 381.31 Mpa. The tube thickness was reduced by 1.16 mm.

Nanostructural design of superstrong metallic materials by severe plastic deformation processing

Ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniques often exhibit significantly higher strengths than those calculated by the well-known Hall-Petch equation. These higher strengths result from the fact that SPD processing not only forms the UFG structure but also leads to the formation of other nanostructural features, including dislocation substructures, nanotwins and nanosized second-phase precipitations, which further contribute to the hardening. Moreover, the analysis of strengthening mechanisms in recent studies demonstrates an important contribution to the hardening due to phenomena related to the structure of grain boundaries as a non-equilibrium state and the presence of grain boundary segregations. Herein, the principles of the nanostructural design of metallic materials for superior strength using SPD processing are discussed.

Friction stir welding, FSW, of metal matrix composites, MMCs, with high reinforcement content

To a large extent, the promising expectations that were set in the 1980s in metal matrix composites, MMCs, have been diluted in recent decades. One reason for this frustration lies in the impossibility of joining these materials by conventional welding methods: these methods (involving fusion) destroy the homogeneous distribution of the reinforcement and give rise to reaction products detrimental to the properties of the joint. Friction stir welding, FSW, however, does not involve fusion, it occurs by a severe plastic deformation process, avoiding the drawbacks of traditional welding techniques. Therefore, recent years have witnessed a growing interest in the study of welds by this technique, not only of MMCs but also of dissimilar welds MMC-monolithic metal. joining MMCs by FSW is not simple, particularly if the reinforcement content is high,> 20 vol%. This paper discusses the most important difficulties facing this welding process and summarizes the recent results of CENIM-AIMEN studies on joints of MMCs with up to 40%vol. of reinforcement, and dissimilar joints. The most relevant correlations between the different mechanical stresses required under different advancing and rotational velocities are presented. This will allow an analysis of the energy balance of the work necessary to produce the deformation of the material and to heat it. In summary, it is emphasized the importance of measuring these efforts to deepen the severe plastic deformation process that takes place, always at high strain rates.

Severe plastic deformation by Constrained Backward Flowforming

The last decades have seen several attempts to develop Severe Plastic Deformation (SPD) processes to manufacture parts with Ultra-Fine Grained (UFG) microstructure without additional thermal processing. However, they remained mostly focused on producing small components, often in the micro-scale range, thus limiting the technological and environmental impact of SPD techniques. The paper introduces a new approach to produce large size UFG metal sheets which main innovation lies in a constrained flowforming process that allows obtaining large deformations under high hydrostatic pressure. Metal sheets with isotropic grain distribution and average grain size of 4 μm were manufactured by this process chain and their mechanical properties assessed.

Ударная вязкость титанового сплава ВТ6 с ультрамелкозернистой структурой, полученной методом равноканального углового прессования

The wide use of two-phase titanium alloys in aircraft engine building, as well as the intense development of this industry, stipulate more and more stringent requirements to structural materials and the enhancement of their reliability, strength and performance characteristics. The formation of an ultrafine-grained (UFG) state in metals and alloys using severe plastic deformation (SPD) processing enables achieving high strength properties. However, an important aspect of UFG materials is their structural and textural effects which may lead to a strong anisotropy of their properties. In this respect, the authors studied the effect of microstructural features on the mechanical properties and impact toughness of the VT6 alloy after equal-channel angular pressing (ECAP) and subsequent deformation by upsetting, imitating die forging. The study showed that the formation of a UFG structure in the VT6 titanium alloy with a grain size of about 0.4 µm allows increasing the ultimate tensile strength up to 1250 MPa. The additional upsetting of the UFG alloy at T=750 °C leads to grain growth up to 0.5–1 µm and a decline in strength to 1090 MPa as a result of the recovery and recrystallization processes. Impact toughness tests were conducted on specimens with a V-shaped stress raiser at room temperature, showing that the impact toughness of the UFG VT6 alloy was 0.41 MJ/m2. The tests revealed the anisotropy of impact toughness in the UFG VT6 alloy after equal-channel angular pressing and additional upsetting due to the metallographic and crystallographic texture formed as the result of deformation treatment. In test direction No. 1, the impact toughness value is the lowest and equals 0.31 MJ/m2.

Effect of the nanostructuring by high-pressure torsion process on the secondary phase precipitation in UNS S32750 Superduplex stainless steel

In this work, the precipitation and the morphology of secondary phases after severe plastic deformation (SPD) processing followed by an isothermal treatment was investigated. High-pressure torsion (HPT) was the SPD process carried out on superduplex 2507 (UNS S32750) stainless steel material under P = 6 GPa at room temperature. At this high strain levels (ε up to 170) samples have shown grain size decrease and strained microstructure with high dislocation density and nanostructure features. After a short isothermal treatment at 830 °C, the sigma phase and chromium nitrides were revealed as the main secondary phases identified by scanning and transmission electron microscopy and element analysis by energy dispersive spectroscopy. Scanning precession electron diffraction and automated crystal orientation mapping have been carried out in order to confirm the precipitation of the secondary phases. In fact, the results provide evidence that the precipitation of chromium nitrides seems to be the preferred nucleation site for sigma phase at higher deformation strain, in addition to the intergranular precipitation of sigma. Both the sigma phases nucleated integranularly and besides chromium nitrides are randomly orientated.

Strength-Ductility Synergy in High Entropy Alloys by Tuning the Thermo-Mechanical Process Parameters: A Comprehensive Review.

The strength–ductility trade-off is an eminent factor in deciding the mechanical performance of a material with regard to specific applications. The strength–ductility synergy is generally inadequate in as-synthesized high entropy alloys (HEAs); however, it can be tailored owing to its tunable microstructure and phase stability. Thermo-mechanical processing (TMP) allows the microstructure to be tailored to achieve desired strength–ductility combination. The additional attribute is evolution of texture, which also significantly influences the mechanical properties. This review presents a critical insight into the role of TMP to achieve superior strength–ductility symbiosis at room temperature in single-phase (FCC, BCC) and multiphase HEA. The role of overall processing strategy of HEAs encompassing rolling and subsequent annealing in relation to the evolution of microstructure and texture in have been discussed. Recently practiced severe plastic deformation processes have also shown promise in improving the strength–ductility combination. The relevance of these processes in the processing of HEAs has also been analysed. At the end, futuristic approaches have been elaborated to enable efficient as well as hassle-free process towards achieving the proficiency of strength–ductility in HEAs.