Severe Plastic Deformation Process Research Articles

High Temperature Deformation of Harmonic Structure Designed CrMnFeCoNi High Entropy Alloy

The Harmonic Structure (HS) is a recently introduced concept that paves the way for engineering metallic materials to achieve superior mechanical performance. They consist of soft, coarse-grained regions surrounded in three dimensions by an interconnected network of hard, ultra-fine grained regions. In addition, from a structural materials point of view, high entropy alloys have attracted attention due to their unique mechanical properties. In the present study, the HS design was applied to a high entropy CrMnFeCoNi alloy (also called "Cantor alloy"). The HS-designed Cantor alloy was successfully fabricated by mechanical milling, which is one of the surface severe plastic deformation processes, and the subsequent sintering process. The mechanical properties of these HS and homogeneous (Homo) Cantor alloy compacts were investigated by high-temperature compression tests in the temperature range of room temperature (RT) and 1173K, under initial strain rates of 0.01 s-1, 0.001 s-1, and 0.0001 s-1. The stress-strain curves of the HS compacts showed a large initial increase in stress and then a rapid decrease with strain, while that of the Homo compact showed a gentle increase and a gradual decrease. EBSD observation of the deformed compacts revealed that the HS compacts were probably deformed not only by dynamic recrystallization, but also by grain boundary sliding during deformation. The strain rate sensitivity value m of the HS compacts was 0.541 (true strain: 0.2) at 1173 K. In other words, the HS compacts exhibited pseudo-superplastic deformation at these temperatures.

Effect of Process Condition and Test Environment on Tensile Properties in Cold-Rolled Al-Cu-Mg Alloys

Severe plastic deformation processing and subsequent aging treatment have been known to be effective for achieving higher strength than the conventional aging treatment in aluminum alloys. This study prepared the Al-Cu-Mg-based alloy sample, Al-5.3Cu-2.8Mg (mass%). The alloys were solution treated at 480, 495 and 505°C, and cold-rolled by 90%. The effect of process condition and test environment on tensile properties in cold-rolled Al-Cu-Mg alloys was investigated. Results confirm that strength and ductility were improved with increasing the solution heat treatment temperature regardless of test environment. 0.2% proof stress and ultimate tensile strength were higher than aging treatment specimens, but elongation to failure was lower than aged one. Hydrogen embrittlement susceptibility increased with increasing solution treatment temperature. Ductile fracture with many dimples is observed in both cold-rolled and aged specimens. Second-phase particles were observed at the bottom of the dimples. There was no significant difference in fracture surface between the different test environments.

Crystallographic Textures of Al and Al-Mg Alloy Formed by Shot-Peening

Shot-peening (SP) is one of the severe surface plastic deformation (SSPD) processing techniques. Due to large plastic strain by the SP, the SP for metallic materials forms crystallographic texture on the peened surface. Since the crystallographic texture formed by the SP depends on the dislocation slip, it can be expected that this texture is affected by stacking fault energy (SFE) of the materials. However, effects of the SFE on the crystallographic texture formed on the peened surface by the SP is not clear. In this study, crystallographic textures of pure Al (higher SFE) and Al-10 mass%Mg alloy (lower SFE) formed by the SP are investigated. When the pure Al is SPed, {001}+{111} double fiber texture with the <001> and <111> directions parallel to the plane normal direction of the peened surface is obtained. On the other hand, in the case of Al-10 mass%Mg alloy with the SFE close to the pure Cu, {110} fiber texture is formed as well as the pure Cu. Therefore, it is found that the crystallographic texture formed by the SP is influenced by the SFE.

Constrained Constant Radius Pressing (CCRP) process to improve mechanical properties and microstructural homogeneity of pure copper sheet

Constrained groove pressing (CGP) is a well-known severe plastic deformation (SPD) process used to improve the mechanical properties of metallic sheets by forming the ultrafine grain (UFG) structure. The conventional CGP process employs 45° grooved dies to impart good amount of plastic strain on the specimen without altering the specimen's initial dimensions. The literature indicates that conventional CGP-processed sheets have inherent strain inhomogeneity. In the present investigation, an effort was made to minimize the inherent strain inhomogeneity by modifying conventional CGP dies into symmetric constrained constant radius pressing (CCRP) dies. Three distinct CCRP dies with varying radius of curvature and die parameters were designed to attain the optimal combination of mechanical properties. It was found that metal sheets processed by new modified dies (CCRP) exhibit improved ductility and significantly enhanced toughness, in contrast to the sheets processed by conventional CGP dies. The improvement in mechanical properties could be attributed primarily to homogeneous grain refinement. In addition, the finite element analysis (FEA) was used to simulate the influence of different die designs on the strain distribution across the sheet, and it showed that lower die angle of CCRP lead to more homogeneous distribution of strain across the arc of the CCRP die.

INVESTIGATION OF MICROSTRUCTURE OF AA7075 ALLOYS AFTER SEVERE PLASTIC DEFORMATION APPLICATION

The aim of this study is to investigate the change of microstructural properties of AA7075 alloys after severe plastic deformation. Severe Plastic Deformation is a process used to improve the properties of the material by creating intense plastic deformations on the material surface. Equal channel angular compression molding (ECAP) was used for the severe plastic deformation process in our study. AA7075 alloy samples were primarily prepared for severe plastic deformation treatment. Then, the microstructural properties of the samples were investigated using various imaging techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The research results showed that significant microstructural changes occurred in AA7075 alloys after the severe plastic deformation process. The SPD process improved the mechanical properties of the material by transforming the crystalline structures of the material into a fine-grained structure. In addition, it was observed that deformation lines and pits occurred on the surface of the samples after the SPD process. It is seen that the SPD treatment increases the mechanical properties of the material such as strength, hardness and durability. Therefore, this study is an important step towards the development of the alloy's use in various industries.

Microstructure and Mechanical Properties of 2024 Aluminum Alloy with and Without Rare-Earth and Thermomechanical Treatment After Multi-pass Stir Friction Processing

Friction stir processing (FSP) is the most effective severe plastic deformation process for creating materials with very fine grains and good properties. The target of the present research is to investigate the influence of FSP on the microstructure and mechanical properties of homogenized 2024 aluminum alloy with and without rare-earth (RE) and thermomechanically treated conditions (TMT). The rare-earth elements used were Ce and La in the form of a master alloy containing (50% Ce + 50% La). The casting of 2024 aluminum alloys, both with and without (Ce + La), was carried out using the conventional stir cast technique. Part of the obtained alloys was homogenized, whereas the other part was thermomechanically treated (TMT). The homogenized 2024 material was exposed to FSP with multiple passes (one, two, and three) to obtain the suitable pass number. After that, the best pass number was performed on the 2024 aluminum alloy refined with RE (Ce + La) and TMT materials. The microstructures in different conditions (homogenized and stir friction) were examined by optical and scan microscopes attached with EDS and Map analyzer. At the same time, a tensile test was conducted to assess the mechanical properties. The findings indicated that the microstructures were significantly refined after adding RE (Ce + La) or applying the TMT technique. Whereas, the microstructures were greatly improved after applying FSP to both conditions. Ultra-fine grains were observed for both TMT and RE-containing alloys after FSP. On the other hand, the results of mechanical properties were significantly increased after applying multiple passes of FSP. The optimum results were obtained when two passes of stir friction were applied to the TMT alloy condition.

Multi-physics Approach to Predict Fatigue Behavior of High Strength Aluminum Alloy Repaired via Additive Friction Stir Deposition

A smooth particle hydrodynamic (SPH) simulation of an additive friction stir deposition (AFSD) repair was used to inform a multi-physics approach to predict the fatigue life of a high strength aluminum alloy. The AFSD process is a solid-state layer-by-layer additive manufacturing approach in which a hollow tool containing feedstock is used to deposit material. While an understanding of the evolving microstructures is necessary to predict material performance, the elevated temperatures and strain rates associated with severe plastic deformation processes (SPDP) make accurate collection of experimental data within AFSD difficult. Without the ability to experimentally determine material history within the AFSD process, an SPH model was employed to predict the thermomechanical history. The SPH simulation of an AFSD repair was used to inform several microstructural models to predict material history during and after processing with AFSD and a post-processing heat treatment. These microstructure models are then used to inform a mechanistic microstructure and performance model to predict the fatigue life of an AFSD repair in AA7075.

Improvement of strength and performance properties of copper wire during severe plastic deformation and drawing process

The paper studies the evolution of microstructure and mechanical properties of copper wire during a new combined straining process. The main point of the technological process is to strain the wire in a rotating equal-channel step die and subsequent drawing. The die rotates around the wire axis and thereby creates tension due to equal-channel angular pulling and twisting in the die. Transmission electron microscopy and EBSD analysis, as well as tensile testing and microhardness determination investigated the strained copper wire. Ultra-fine grain gradient microstructure with a high component of high-angle grain boundaries was obtained as a result of straining. The tensile strength of the strained copper wire compared to the unstrained one increases more than twice from 302 to 635 MPa, and the yield strength increases from 196 to 406 MPa. The use of such hardened copper wire in construction will reduce the weight of the structure due to the reduction of diameter.

A novel strategy for fabricating phase transforming NiTi shape memory alloy via multiple processes of severe plastic deformation

NiTi shape memory alloy was successfully fabricated from Ni/Ti multilayers via an innovatively combinative route consisting of accumulative roll bonding (ARB), high-pressure torsion (HPT) and annealing. Due to the severe plastic deformation induced by ARB and HPT, the subsequent post annealing time was significantly reduced. Differential scanning calorimetry (DSC) analysis confirms the occurrence of austenitic and martensitic transformations during heating and cooling process, implying that the shape memory effect was obtained.

Microstructure and magnetic properties of binary Mn54-Al46 alloy particulates obtained by severe plastic deformation processing via end-milling and annealing

We utilize the plastic deformation process associated with the machining operation of end-milling for the preparation of ε-phase Mn-Al particulates with micron scale external dimensions and self-similar shapes from binary as-cast feedstock with composition 54 at.% Mn and 46 at.% Al. The structural evolution and development of magnetic properties in response to the single-pass plastic deformation processing by the end-milling and subsequent thermal annealing have been studied. Effects of end-milling process parameter combinations, primarily the rotational speed of the cutting tool, have been identified to permit genesis of morphological self-similar particulates of ε-phase characterized by cold-worked and sub-micron to nanometer scale refined microstructures. The end-milling derived particulates were suitable for preparation of τ-phase based MnAl particulates with enhanced permanent magnet properties via isothermal annealing. Discernibly higher rates for the exothermic ε-phase decomposition reactions in the end-milling derived particulates have been observed for isothermal annealing at temperatures in the range of 673 K ≤ T ≤ 723 K. The enhanced decomposition reaction kinetics have been attributed to reduced effective nucleation barriers for the respective product phases stemming primarily from reduced grain size. Large saturation magnetization and coercivity in combination with reasonable squareness ratios of the magnetization curves resulted in a (BH)max = 4.2 MGOe for the end-milling derived binary Mn54Al46 particulates obtained for the highest rotational tool speed of 4200 RPM used here after annealing for 20 min at 673 K. The ε-phase Mn-Al particulates derived by end-milling have potential as precursors for the fabrication of τ-phase Mn-Al based PM materials.

Nanostructured Ti-13Nb-13Zr alloy for implant application-material scientific, technological, and biological aspects.

In dentistry, the most commonly used implant materials are CP-Titanium Grade 4 and Ti-6Al-4V ELI, possessing comparably high Young's modulus (>100GPa). In the present study, the second-generation titanium alloy Ti-13Nb-13Zr is investigated with respect to the production of advanced dental implant systems. This should be achieved by the fabrication of long semi-finished bars with high strength and sufficient ductility to allow the automated production of small implants at low Young's modulus (<80GPa) to minimize stress shielding, bone resorption, and gap formation between the bone and implant. In addition, bacterial colonization is to be reduced, and bone adhesion is to be enhanced by adjusting the microstructure. To do so, a dedicated thermo-mechanical treatment for Ti-13Nb-13Zr has been developed. This includes the adaption of equal channel angular swaging, a modern process of severe plastic deformation to continuously manufacture nanostructured materials, to Ti-13Nb-13Zr and short-time recrystallization and ageing treatments. In particular, two-pass equal channel angular swaging at a deformation temperature of 150°C and a counterpressure of 8MPa has successfully been used to avoid shear band formation during deformation and to produce long Ti-13Nb-13Zr bars of 8mm diameter. During recrystallization treatment at 700°C for 10min followed by water quenching, a sub-micron-size primary α-phase in a matrix of α″-phase was developed. Subsequent ageing at 500°C for 1h leads to martensite decomposition and, thus, to a homogeneously nanostructured microstructure of α- and β-phase with substructures smaller than 200nm. The resulting mechanical properties, especially the ultimate tensile strength of more than 990MPa, fulfill the requirements of ASTM F1713 at Young's modulus of 73GPa. Biological investigations show promising results in reducing bacterial biofilm formation and increased cell proliferation of osteoblasts compared to CP-Titanium Grade 4 and Ti-6Al-4V ELI, especially, if etched surfaces are applied.

Potency of Severe Plastic Deformation Processes for Optimizing Combinations of Strength and Electrical Conductivity of Lightweight Al-Based Conductor Alloys

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.

Simulation of the Dynamics of Supersonic N-Crowdions in fcc Lead and Nickel

In the case where an interstitial atom is located in a close-packed atomic row of the crystal lattice, it is called a crowdion. Crowdions play an important role in the processes of mass and energy transfer resulting from irradiation, severe plastic deformation, ion implantation, plasma and laser processing, etc. In this work, supersonic N-crowdions (N=1, 2) in fcc lattices of lead and nickel are studied by the method of molecular dynamics. Modeling shows that the propagation distance of a supersonic 2-crowdion in lead at a high initial velocity is less than that of a supersonic 1-crowdion. In other fcc metals studied, including nickel, supersonic 2-crowdions have a longer propagation distance than 1-crowdions. The relatively short propagation distance of supersonic 2-crowdions in lead is due to their instability and rapid transformation into supersonic 1-crowdions. This feature of the dynamics of supersonic N-crowdions in lead explains its high radiation-shielding properties.

An Overview on the Corrosion Behavior of Steels Processed by Severe Plastic Deformation

Ultrafine grained (UFG) and nanostructured steels have gained attention in the last years because of the possibility of improving both strength and ductility, but also because of their potential for improving several properties in metal applications which allows replacing some conventional steels. The refinement of the microstructure obtained through Severe Plastic Deformation (SPD) has allowed for the improvement of mechanical properties and the performing of several studies related to corrosion control, mitigation, and protection. In this review, the corrosion behavior of ultra-fine grained (UFG) steels is presented regarding the existing literature and the microstructural changes produced through different SPD processes. A focus is placed on the importance of the processes for grain refinement and microstructural changes and, therefore, on the corrosion behavior.

Severe Plastic Deformation through High-Pressure Torsion for Preparation of Hydrogen Storage Materials -A Review

Severe plastic deformation (SPD) processes are excellent processing methods that can refine grains, introduce crystal defects and improve mechanical properties and functionality. Among them, high-pressure torsion (HPT) was used for the preparation of hydrogen storage materials in recent years owing to the fact that HPT can process powder materials and introduce greater plastic deformation. HPT technology is not only an effective method to prepare bulk samples from powders, but also a brilliant route to enhance the kinetics, activation, air resistivity and long-term stability of hydrogen storage materials. In addition, new alloys, intermetallics, composites, and hydrogen storage materials even in the immiscible Mg-based alloy systems can be successfully synthesized through the HPT process. In this review, different SPD methods and HPT technology applied for different hydrogen storage materials are carefully reviewed.

Overview: Using Severe Plastic Deformation in the Processing of Superplastic Materials

In tensile testing, polycrystalline materials generally fail at relatively low total elongations but under some limited conditions it is possible to achieve exceptionally high elongations of up to and exceeding 400%. This superplastic condition is important scientifically but also it has important uses through the industrial development of superplastic forming operations. This overview traces the historical development of this superplastic effect and it provides a summary of the main characteristics of the superplastic flow process. Conventional thermomechanical processing is not able to produce exceptionally small grain sizes within the submicrometer or nanometer range but this limitation was effectively overcome through processing using severe plastic deformation (SPD). The advantages of SPD processing are discussed and examples are presented. Finally it is demonstrated that the experimental data may be easily and effectively displayed through the construction of deformation mechanism maps based on combinations of stress, grain size and temperature.

Deformation mechanisms and mechanical properties of the high-strength and ductile Al-Zn-Mg-Cu alloys processed by repetitive continuous extrusion forming process with different heat treatments

Continuous severe plastic deformation (SPD) processes, which overcome the limitations of economic efficiency and sample size for classical SPD approaches, are promising industry technologies for manufacturing aluminum alloy products with refined microstructures and enhanced properties. In the present work, the repetitive continuous extrusion forming (R-Conform) process combined with auxiliary thermal treatments was implemented in Al-Zn-Mg-Cu alloys, which had poor workability. By combining microstructural observation, mechanical testing and finite element simulation, the influence of auxiliary heat treatments on the mechanisms of grain refinement and strengthening for Al-Zn-Mg-Cu alloys processed by R-Conform were systematically investigated. The results indicated that the grains of Al-Zn-Mg-Cu alloys were significantly refined by a continuous dynamic recrystallization (CDRX) during the R-Conform process with special thermomechanical conditions. The increased supersaturated solid solution concentration and constituent precipitate fraction caused by prehomogenization were found to accelerate CDRX for grain refinement through the pinning effect on dislocation motion. Due to the simultaneous effect of shear deformation and online solution, the R-Conformed alloys contained massive lattice distortions and high concentrations of solute atoms. As a result, the processed Al-Zn-Mg-Cu alloys combined with prehomogenization and direct aging treatments possibly possess a good combination of strength and ductility due to the integrated functions of fine grains, massive lattice distortion, and evenly distributed nanosized precipitates.

Machinability and surface integrity analysis of magnesium AZ31B alloy during laser assisted turning

Magnesium AZ31B alloys are promising materials for biomedical, aviation, and automotive industries. Severe plastic deformation processes such as machining processes have shown capabilities to improve the performance of magnesium AZ31B alloys. However, the usage of water and oil-based coolants during the machining of magnesium AZ31B alloys generates hydrogen and hazardous gases, which can explode and create a hazardous environment for nature and human beings. Therefore, machining without using any coolants has been preferred to machine magnesium AZ31B alloys. Moreover, laser assisted turning (LAT) has emerged as a hybrid machining process to machine various materials without using any coolants and in an eco-friendly manner. Hence, an attempt has been made to analyze the machining performance of magnesium AZ31B alloy during the LAT process. In this study, the machinability and surface integrity of magnesium AZ31B alloy was compared for LAT and conventional turning (CT) processes. With the usage of laser, a substantial decrement in machining forces, surface roughness, and tool wear was achieved during LAT than CT. Though, the machining temperature was obtained to be higher for LAT in comparison to CT. Long, continuous, and ductile chips were formed in LAT. Lesser scratches, cracks, and pits were observed on the machined surface during LAT than in CT. Coarse grain microstructure was observed for both CT and LAT. However, lower microhardness was obtained in LAT than in CT. Compressive residual stresses were achieved for LAT than tensile residual stresses in CT. Corrosion resistance was enhanced by up to 50 % for the LAT process than in the CT process.

Establishing Equal-Channel Angular Pressing (ECAP) for sheet metals by using backpressure: manufacturing of high-strength aluminum AA5083 sheets

Severe plastic deformation (SPD) processes offer the possibility of improving the mechanical properties of metallic materials by grain refinement. However, this great potential has so far mostly been applied on a laboratory scale or on small series. Equal-Channel Angular Pressing (ECAP) also enables to integrate the advantages in industrial processes with large output—so far, mainly for bars or thick plates. In this paper, we investigate the ECAP process for sheet metal. Preliminary investigations have shown that cracks form on the surface when aluminum AA5083 sheets are processed. To solve this problem, we determined the Johnson–Cook fracture criterion for the material and modeled the process numerically. The simulation was carried out with the superposition of a backpressure and subsequently implemented and validated experimentally. The semi-finished sheet metal products from the ECAP investigation were then mechanically characterized with microhardness measurements and tensile tests. In addition, the microstructure was investigated with Electron Back Scatter Diffraction (EBSD). Even comparatively small amounts of backpressure (10 MPa) already result in a significant suppression of the crack formation in the numerical and experimental investigations. The microhardness measurements indicate a more homogeneous strain distribution for a sufficient level of applied backpressure which enables the processing of crack-free sheets in multiple ECAP passes. As with ECAP of bulk materials, tensile tests on the processed sheets show a reduced elongation to failure (− 73%) but a significantly increased yield strength (+ 157%) compared to the initial condition of the material. Distinct substructures are found in the EBSD measurements and explain this behavior. The findings provide the basis for using ECAP on an application-oriented scale and demonstrate an advanced manufacturing method for the production of high-strength aluminum sheets.

Orthogonal cutting to develop a damage law for severe plastic deformation processes: application to friction stir welding

Orthogonal cutting to develop a damage law for severe plastic deformation processes: application to friction stir welding