Severe Plastic Deformation Process Research Articles

Nanostructured Titanium with Ultrafine‐Grained Structure as Advanced Engineering Material for Biomedical Application

Titanium and its alloys are popular materials for medical application, particularly in implant devices, where high mechanical properties and osseointegration are critical factors for successful implantation. In this work, the progress in the studies of nanostructured commercially pure Grade 4 titanium (nanoTi) is demonstrated, in which an ultrafine‐grained structure with nanoscale grain size is formed using severe plastic deformation processing. Nanostructured Grade 4 Ti has a very high strength, and its physical nature and strengthening mechanisms are analyzed herein. NanoTi proved also to have very high osseointegration during in vivo experiments. At the same time, the highest biofunctionality is demonstrated by the etched nanoTi samples with pronounced surface roughness, the latter being revealed from precise roughness measurements. The present study provided convincing evidence of accelerated bone formation on nanoTi, which is very promising for manufacture of dental and maxillofacial implants.

Effect of shot peening on surface characteristics and high-temperature corrosion behaviour of super 13Cr martensitic stainless steel

Super 13Cr, as an economy stainless steel (SS) for oil country tubular goods, needs stable corrosion resistance in high-pressure and high-temperature (HPHT) downhole medium. Severe plastic deformation (SPD) are the surface modification technology to improve mechanical properties, fatigue behavior and corrosion resistance of metals, and shot peening (SP) has been the most widely used SPD process. However, there are quite limited studies about the microsutructure evolution, residual stress, and high-temperature corrosion behavior of SP treated martensitic SS. In this study, super 13Cr martensitic SS was treated by shot peening with various air pressures and nozzle speeds. The surface characteristics and high-temperature corrosion behaviour in 3.17 mol/L K2HPO4 solution was investigated through finite element model analysis, characterization of residual stress and microstructure, as well as electrochemical and stress corrosion cracking (SCC) tests at 160 °C and 10 MPa. The results showed that SP treated super 13Cr could generate high-level compressive residual stress and SPD microstucture, including nano-sized equiaxed grains, gradient lamellar structure and fragmented carbides. Increasing air pressure contributed to achieve uniform nanocrystalline, but tended to generate high dislocation density and surface defects. The improving effect of SP treatment at low air pressure of 0.15 MPa on passivation ability was limited, and high air pressure adversely impacted corrosion resistance. SP treated specimens showed high SCC susceptibility, due to the introduction of more surface defects, high angle grain boundaries, and dislocations.

Nanostructuring and Hardness Evolution in a Medium‐Mn Steel Processed by High‐Pressure Torsion Technique

Severe plastic deformation (SPD) is performed on a newly developed medium‐Mn steel with the composition of Fe–7.66Mn–2Ni–1Si–0.23C–0.05Nb (wt%) to achieve a nanocrystalline microstructure. The SPD process utilizes the high‐pressure torsion (HPT) technique, resulting in a nominal shear strain of approximately 36 000% after processing the disk for 10 turns. In X‐Ray diffraction line profile analysis, an increase in dislocation density to around 230 × 1014 m−2 is observed. In addition, under high strains, a face‐centered cubic (fcc) secondary phase emerges within the body‐centered cubic (bcc) matrix. In analytical transmission electron microscopy, using energy‐dispersive X‐Ray spectroscopy, it is indicated that the secondary‐phase particles are enriched in Al, Mn, and Si. As the strain imposed during HPT increases, the simultaneous rise in dislocation density and nanostructuring lead to material hardening. However, the partial phase transformation from bcc to fcc contributes to material softening. As a result of these two opposite effects, the hardness exhibits a non‐monotonic variation with the shear strain, displaying, for 10 turns of HPT, a lower hardness compared to fewer turns, despite the continuous increase in dislocation density and decrease in crystallite size.

Co‐Deformation in Severely Deformed Multiphase Crystalline Metallic Systems: Physical Mechanisms, Intrinsic Limitations, and Perspectives

The deformation of multiphase metallic alloys or metal matrix composites by forming processes such as rolling or drawing requires the co‐deformation of phases. Severe plastic deformation processes have extended possibilities with the ability to produce unique nanoscaled structures through the formation of strain‐induced super‐saturated solid solutions, the fragmentation of second‐phase particles, or ultimate co‐deformation down to the nanoscale. Based on various examples, the fundamental mechanisms of co‐deformation are addressed. Parameters that promote the extension of existing heterophase boundaries are discussed, and some possible atomic‐scale mechanisms involving dislocation activities based on geometrical and energetic considerations are proposed. Finally, the physical limits of co‐deformation are considered before suggesting research directions that might be followed to develop fundamental knowledge and applications in the field.

Evolution of Microstructure of Copper and Its Alloys during Severe Plastic Deformation Process

Evolution of Microstructure of Copper and Its Alloys during Severe Plastic Deformation Process

On Dynamic Recrystallization during the Friction Stir Processing of Commercially Pure Ti and Its Influence on the Microstructure and Mechanical Properties

Friction stir processing (FSP), a severe plastic deformation process, was applied on commercially pure Ti to obtain an improved microstructure. The process yielded a refined microstructure and higher mechanical properties at room temperature (RT). Yet the microstructure was found to contain bright bands demonstrating high hardness values of about 500 HV. High-resolution scanning electron microscopy (HRSEM) as well as electron backscattering diffraction (EBSD) analysis indicated that these bands were composed of extra-fine equiaxed α-Ti grains with an average radius of 1–2 microns. In addition, a retained β phase was detected at the boundaries of these α-Ti grains, together with a small quantity of separate β grains. The results of a fractography study conducted on broken tensile specimens showed that the material that underwent FSP was free of defects and that the fracture started at these bands. It is proposed that these bright bands are due to excessive deformation occurring during the processing stage, leading to an accelerated dynamic recrystallization (DRX) process. In turn, these heavy deformation regions act as a strengthening constituent, making the material superior to the parent material as far as its mechanical RT properties are concerned. Consequently, this means that the FSP of CP-Ti has the potential to serve as an industrial means of improving the mechanical properties of the material.

Microstructure, aging behavior, and friction and wear properties of ultrafine-grained 7050 aluminum alloy produced by cryogenic temperature extrusion machining

Cryogenic temperature extrusion machining (CT-EM), as a novel cryogenic temperature severe plastic deformation (CT-SPD) process, is an effective method to produce ultrafine-grained (UFG) materials. In this paper, the microstructure, microhardness, friction and wear properties of the UFG chips prepared by CT-EM and room temperature extrusion machining (RT-EM) were analyzed. The results show that CT-EM has a better grain refinement effect. The grain size of the CT-EM samples is smaller, the dislocation density is larger, and the microhardness is higher. After aging treatment, a large number of small secondary precipitates (η '/η) appear in the microstructure of the samples, which further improves the microhardness. This is the result of a synergistic effect of fine grain, dislocation, and precipitation strengthening. Cryogenic treatment can increase the precipitation kinetics of the secondary phase and shorten the time for the samples to reach peak hardness. The CT-EM samples have a lower friction coefficient and wear mass. With the increase of the machining velocity, the wear mechanism of the samples changes from abrasion wear to oxidation, adhesion, and fatigue wear.

Strength and formability improvement of ECARed aluminum alloy 6061 sheets using the artificial aging heat treatment

In the current research, the experimental investigation of the mechanical characteristics of 6061 aluminum alloy, which was subjected to Equal Channel Angular Rolling (ECAR) – A Severe Plastic Deformation Process – and artificial aging heat treatment, has been discussed. By performing the ECAR, the strength of the material increases, but the formability will be reduced. Consequently, the usage of this alloy has been limited. The artificial aging heat treatment process has been proposed after the ECAR operation, and the strength, hardness, and formability of the material have been investigated. In this regard, remarkable results were obtained. By controlling the aging time and temperature on the ECAR piece, not only the strength increased but also the ductility increased. Moreover, an artificial neural network was used to find the optimal aging time and temperature. Finally, the best aging time and temperature ranges to achieve the most desirable mechanical properties were provided using the neural network. The result show 150% increase in strength and 50% in formability by performing controlled-artificial aging heat treatment with ECAR process.

Influence of Equal Channel Angular Pressing Technique on Mechanical Properties, Corrosion Resistance, and Microstructural Behavior of Al-Alloy 5083

Introduction: During severe plastic deformation (SPD) processing, aluminum alloys exhibit moderate strength and ductility. Nevertheless, the materials' ductility, as determined by tensile testing, does not accurately represent their capacity for plastic deformation. After the tensile test, its material, aluminum alloy 5083, was observed to be super ductile. Method: The results of a more thorough plasticity analysis—applied for the first time to material following SPD processing—are presented in this paper. The aluminum alloy 5083 is examined in the patent both before and after equal channel angular pressing (ECAP). A highly effective aluminum alloy 5083 specimen preparation was suggested. Under heated temperatures, the process involves severe plastic deformation. Optical microscopy and scanning electron microscopy (SEM) were used for micro-structural research in order to look at the distribution of second-phase particles and the evolution of grain structure. Furthermore, Vickers micro-hardness testing was utilized to assess the mechanical characteristics of the alloy after processing. The outcomes showed that after ECAP processing, there was a significant decrease in grain size and an increase in micro-hardness. Result: Additionally, the production of a finer microstructure with a more uniform distribution of strengthening precipitates was clarified by electron microscopy (SEM). The micro-structural evolution and mechanical behavior of aluminum alloy 5083 under ECAP are well-explained in this patent, which may lead to improved performance in structural applications. This method can be used to forecast fractures in plastic deformation processes and estimate the final plasticity of the materials for various stress-strain states after ECAP processing, as well as the mechanical properties discussed. Conclusion: Due to its unique mechanical qualities, aluminum alloy 5083 shows great potential in a variety of structural applications. The effects of Equal Channel Angular Pressing (ECAP) on the hardness and microstructure of aluminum alloy 5083 were examined in this patent work. result: The specimen's mechanical characteristics are at their finest following a single deformation when the temperature reaches 300°C. Compared to the original specimen, the tensile strength observed enhanced after the fourth pass, and breaking elongation (28.3%) was improved. Through second-phase strengthening and fine-tuning, the recrystallized grains and second-phase particles increase the material's strength.

Quantitative study of solid-state mechanical mixing by high-pressure torsion based on image processing

Mechanical alloying through the process of severe plastic deformation can significantly enhance the mechanical properties of dissimilar metals. However, uneven mixing of these materials can adversely affect their mechanical performance and may even lead to material failure. To quantitatively assess the degree of mixing between dissimilar materials, a mechanical mixing efficiency index (η) has been introduced. This index is calculated accurately by combining an improved Non-dominated Sorting Genetic Algorithm II (NSGA-II) with computer image processing techniques. The study focuses on the Al-Zn mechanical mixture, establishing a parametric correlation between the mechanical mixing efficiency index and the microstructural evolution of mechanical mixing. The findings indicate that when the η value falls below 0.27865, the material transitions from the mechanical mixing stage to the chemical fusion stage. This research facilitates the controllable preparation of mechanical alloying, providing theoretical support and practical evidence for the process.

Processing of high-strength thermal-resistant Al-2.2% cerium-1.3% lanthanum alloy rods with high electric conductivity by High Pressure Torsion Extrusion

A novel severe plastic deformation (SPD) process of High Pressure Torsion Extrusion (HPTE) was applied to the rods of the Al-2.2 wt.% Ce-1.3 wt.% La (Al–3.5RE) alloy. The microstructure, microhardness, the mechanical strength, thermal stability, and electrical conductivity of the alloy after HPTE and subsequent annealing have been investigated. It was demonstrated that HPTE processing can simultaneously increase yield strength from 127 to 225 MPa and electrical conductivity from 54.7% IACS to 55.7% IACS in this alloy. Such a remarkable combination of properties was achieved thanks to significant refinement of microstructure constituents: grain size of Al matrix was reduced down to 0.9 µm and initially continuous network of Al11RE3 phase was broken to micrometer- and nanometer-sized particles. Furthermore, the yield strength of the HPTE-processed Al–3.5 RE alloy remains stable at 230 °C for 1 h due to micrometer- and nanometer-sized particles that pin the grain boundaries. Therefore, HPTE processing of Al–RE alloys has a high application potential in the electric power industry.Graphical abstract

Friction welding of UFG copper using the W2Mi prototype machine

Friction welding of UFG copper using the W2Mi prototype machine

Microstructure, mechanical properties, and strengthening mechanisms of ultra-high strength Al-Zn-Mg-Cu alloy prepared by continuous extrusion forming process

In recent years, the strategy of obtaining ultra-high strength bulk Al-Zn-Mg-Cu alloys materials through implementing severe plastic deformation (SPD) has emerged as the prominent trend in structural lightweight development in aerospace and transportation fields. However, the inherent poor formability makes the SPD process of high-alloying Al-Zn-Mg-Cu alloys a great challenge. In the present work, a continuous SPD process named the Conform, utilizing a rotational speed of 4 rpm and a mold preheating temperature of 300 °C, was performed on the high-alloying 7055 Al alloy and prepared rod materials with excellent mechanical properties. The results indicated that violent shear deformation accompanied by rapid temperature rise contributes to the specific grain refinement mechanism of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The grain configuration formed by this cooperative mechanism is advantageous for the alloy's compatible deformation capability. As a result, a synergistic improvement in the strength and ductility of the Conformed 7055 Al alloy was obtained. Additionally, the strengthening mechanisms induced by the Conform process were quantitatively calculated, revealing that solid solution strengthening and dislocation strengthening were the primary reasons for the enhanced strength of processed alloys.

Superior strength-ductility synergy in a near-α titanium alloy fabricated by severe plastic deformation at lower temperatures

This study demonstrates the crucial trade-off between strength and ductility in titanium alloys. High strength-ductility synergy is achieved through severe plastic deformation (SPD) at a relatively lower temperature, resulting in ultrafine grains and well-dispersed (Ti, Zr)6Si3 nano-precipitates. The samples SPD-processed at 800 °C demonstrate excellent room-temperature properties with a tensile strength of 1558.9 MPa and 7.2 % ductility. The findings highlight the impact of SPD temperature and alloying elements on silicide precipitation, revealing two different precipitation mechanisms depending on the SPD processing temperature: single diffusion-controlled nucleation at a higher SPD temperature while a coupled diffusion and dislocation-assisted nucleation at a lower SPD temperature. Lower-temperature SPD is critical to achieving superior strength-ductility synergy.

The deformation behavior of aluminum alloy in a novel severe plastic deformation process known as combined SSE-FE process

In this study, a novel method for severe plastic deformation (SPD) was introduced, entitled as Combined SSE-FE (CSSE-FE). The process was investigated experimentally and numerically on AA1050 alloy. After this process, due to the unique design of the die channel, the sample significantly fills the die outlet channel. Also, the CSSE-FE process can produce large strains without repeating the cycle. Therefore, this parameter was increased by around 53.16 % in comparison to simple shear extrusion (SSE) process after the first pass. Also, microhardness was increased by about 87.93 % in comparison to annealed sample.

Long term hydrogen storage properties of ZK60 Mg-alloy as processed by different methods of SPD

Hydrogen storage characteristics is studied in the Mg-alloy ZK60 after processing by different SPD (Severe Plastic Deformation) methods such as High Pressure Torsion (HPT) and Friction Stir Processing (FSP), applying various deformation extents and rates. The capacity and kinetics of hydrogen storage was investigated and analysed, up to 100 storage cycles. While the degree of SPD deformation is less important for the storage capacity, the SPD processing method itself matters, yielding about ~ 30% more capacity in FSP than in HPT. As shown by DSC and XRD analyses, it is the density of SPD-induced vacancy agglomerates which is significantly higher in FSP than in HPT (~ 10–3 instead of ~ 10–4) because of the enhanced dislocation slip activity. Thanks to their stabilization through Mg(Zn,Zr) precipitates, the vacancy agglomerates survive numerous cycles of hydrogen storage in spite of the high storage temperature of 350 °C, and can act as thermally stable heterogeneous nuclei for the hydrogenation. This latter mechanism was found in all SPD methods applied irrespective of the deformation extent, on the basis of Johnson–Mehl–Avrami-Kolmogorov analysis providing the Avrami exponent n = 1, already from the second up to the highest hydrogen storage cycles.

Enhancement of the Microstructure and Fatigue Crack Growth Performance of Additive Manufactured Titanium Alloy Parts by Laser-Assisted Ultrasonic Vibration Processing

AbstractPost-processing techniques can efficiently improve the surface quality, address microstructural defects, and optimize mechanical properties in additively manufactured parts. Surface severe plastic deformation processes such as ultrasonic nanocrystal surface modification (UNSM) integrated with localized laser heating were explored to enhance the surface properties, microstructure as well as the fatigue crack growth properties (FCG) in both directions of built. We successfully induced greater plasticity flow and achieved beneficial refinement of the surface grain structure by precisely controlling the heat and impact energies during surface treatment process. The LA-UNSM process, with the parameters utilized in this study considerably decreased the FCG rates of treated samples, when compared to samples without surface treatment. Improved fatigue crack growth properties along vertical and horizontal orientations after the post-process treatment were attributed to the induced-microstructural changes, improved surface quality, induced compressive residual stresses through gradient structure deformation layer that was prepared on the surface of the material. The fractographic analysis revealed that the cracks mostly originated from the pores in the as-produced state. This observation shows a clear correlation between the surface treatment performed and a substantial improvement in fatigue crack growth resistance.

Enhanced Microhardness and Corrosion Performance of Additively Manufactured Inconel 718 Specimens through Nanostructuring by Severe Plastic Deformation

Severe plastic deformation (SPD) processes, particularly high-pressure torsion (HPT) have been increasingly applied to metallic specimens fabricated by laser powder bed fusion (L-PBF) additive manufacturing (AM) for enhancing their mechanical and functional properties through nanoscale grain refinement (≤ 100 nm). In this study. L-PBF AM-fabricated Inconel 718 (IN 718) specimens are initially subjected to 10 HPT revolutions to produce nanosized grains. Subsequently, microstructural characterisation, as well as hardness and electrochemical tests are conducted to evaluate the evolution of microstructures, hardness, and corrosion performance of the as-received and HPT-processed specimens by using various microscopy, Vickers microhardness (HV) measurements, and corrosion performance, respectively. The results reveal an average grain size of ~ 46 nm, dense dislocation networks, and nanotwins after 10 HPT processing, which contribute to the two-fold hardness increase compared to the as-received condition. Such microstructures also contributed to the overall improved corrosion performance after 10 HPT processing, as quantified by the 83% and 73% reduction in corrosion rate and pitting potential, respectively.

Atomistic modeling of idealized equal channel angular pressing process

Severe plastic deformation (SPD) processes are forming techniques that impose large plastic strains to achieve ultra-fine grained and nanocrystalline microstructures. The refined microstructure results in a significant increase in strength and in many cases without a considerable loss in ductility. Despite their long existence, a comprehensive understanding of the deformation and grain refinement mechanisms during SPD is still lacking. Atomistic simulations that are regularly used to obtain insights into material behavior have rarely been used to study SPD processes. In this work, we use large scale atomistic simulations of the molecular statics/dynamics kind to model the equal channel angular pressing (ECAP) process, a specific SPD process. Three different materials—Al, Ni and Cu—are used to model high, medium and low stacking fault energy materials. Large simulation cells are used to facilitate grain refinement at the nanoscale. The simulations are carefully analyzed in terms of stress–strain behavior, dislocation activity and grain refinement. All samples show the formation of deformation twins at the nanoscale, which generally detwin at increased strains via dislocation twin interactions. A significant number of stair-rod dislocations form via dislocation–dislocation interactions and are present at low angle grain boundaries in the early stages of deformation. Such stair-rod dislocations also result in the formation of stacking fault tetrahedra which are present in significant numbers in all samples. Finally, difficulties in studying grain refinement at very large strains in atomistic simulations are discussed.

Magnetic Shape Memory Nanocomposites Assembled with High Speed High Pressure Torsion.

When a severe plastic deformation (SPD) process is performed at high temperatures, it becomes more versatile. Designed originally for the bulk nanoconstruction of hard-to-deform alloys, high-speed high-pressure torsion (HSHPT) is an SPD method used in this research for assembling multiple layers of shape memory nanocomposites. Three hard-to-deform magnetic alloys in the cast state were used. Soft magnetic shape memory alloys, NiFeGa and FePdMn, and a potentially hard magnetic alloy, CoZr, were assembled in various composites. Both grain refinement and strong layer bonding were achieved in ZrCo/FePdMn and ZrCo/NiFeGa composites in seconds. The very short SPD time is specific to HSHPT because of the intense friction that occurs under high pressures, which generates huge amounts of heat. After SPD, the temperature rises in bulk material like a pulse, being dissipated mostly through heat conduction. The SPD parameters were carefully controlled with an advanced automation system using a programmable logic controller. Nevertheless, the major drawbacks of high-pressure torsion were overcome, and large SPD discs were obtained. Various investigation techniques (optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy) show well-defined interfaces as well as a fine and ultrafine structure.