Severe Plastic Deformation Techniques Research Articles

Cyclic Extrusion Compression Process for Achieving Ultrafine-Grained 5052 Aluminum Alloy with Eminent Strength and Wear Resistance

Previous studies have yet to show a consistent effect of severe plastic deformation (SPD) processing on the wear behavior of different metals and alloys. To fill this scientific gap, this study investigated the effect of the cyclic extrusion compression (CEC) process, as one of the prominent SPD techniques, on the wear behavior of AA5052. In addition, the microstructure evolution and mechanical properties of the sample before and after the process were experimentally examined and studied. It was found that the yield and ultimate tensile strength of the AA5052 improved significantly after the first pass, while the elongation-to-failure decreased considerably. Further, the subsequent passes mildly changed the trend of increasing strength and reducing elongation-to-failure. SEM morphology indicated that the ductile mode of the initial annealed alloy changed to a combination of ductile and brittle failure modes, in which the level of the brittle failure mode increased with the addition of passes. TEM observations showed that the grain refinement during the CEC process included the formation of dislocation cell structures, subgrain boundaries, and low-angle grain boundaries, with the subgrain boundaries initially evolving into low-angle grain boundaries and, eventually, due to the imposition of additional plastic strain, into high-angle grain boundaries. Furthermore, the CEC process and its increased number of passes led to a significant improvement in wear resistance due to the enhanced tensile strength achieved through grain refinement. In this regard, the wear mechanism of the initial alloy was a combination of adhesion and delamination, with the plastic deformation bands changing to plowing bands with decreased adhesive wear during the process. Eventually, oxidization was found to be a mechanism contributing to wear under all conditions.

High Strain Behaviour of Ultrafine‑grained Aluminium Alloys Processed Through the Severe Plastic Deformation Techniques: A Review

High Strain Behaviour of Ultrafine‑grained Aluminium Alloys Processed Through the Severe Plastic Deformation Techniques: A Review

Microstructural evolution during short heat treatment of constrained groove pressed Cu‐5%Zn alloy

Severe plastic deformation (SPD) is a widely used technique to obtain superior material properties specially mechanical properties. Constrained groove pressing (CGP) is found to be the most attractive SPD technique for the deformation of sheets and plates. However, this technique results in microstructural inhomogeneity during processing. The microstructural inhomogeneity can be alleviated by employing a thermal cycle, which assists in controlled recovery and recrystallisation. The current work focuses on, the microstructure evolution of one pass as-deform CGP sample followed by a short heat-treated (SHT). A correlative imaging technique of transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM) showed the presence of dislocation cell structure in an as-deformed condition. The short heat treatment resulted in the transformation of the dislocation cell wall to high-angle boundaries, with a further increase in heat-treatment time resulting in grain growth.

Experimental and numerical investigation of residual stress distribution in Al-6061 tubes under using tubular channel angular pressing process by new trapezoidal channel

Tubular channel angular pressing (TCAP) method is an appropriate severe plastic deformation (SPD) techniques for the generation of ultra-fine grained (UFG) and nanostructured (NS) tubes. In forming methods, the measurement of residual stresses is very important due to their significant effects on the processed samples. Therefore, determining the residual stresses created by the TCAP method in metals is of great importance. In this research, the distribution of residual stresses in Al-6061 tubes under the TCAP process, was studied experimentally and numerically. For this purpose, first the TCAP process was applied on Al-6061 tubes and after that the residual stresses generated in the TCAPed tubes were measured. Sachs method was used experimentally to measure the residual stresses. Sachs method is one of the destructive, convenient and efficient methods for measuring the residual stresses of axisymmetric cylindrical samples. Residual stresses measured by Sachs method in the processed samples showed that the tensile and compressive residual stresses were created on the external and internal tube surfaces, respectively. In addition, a good agreement was existed between the results of the numerical simulation and experimental methods for measuring the residual stress distribution.

Development of ultra-fine grain microstructures in a metastable-β titanium alloy via phase transformation assisted recrystallisation

Generally, in metallic alloys, attaining ultra-fine sub-micron grain sizes by recrystallisation requires severe plastic deformation (SPD), however SPD techniques are difficult to apply to large quantities of material. In this work, we explore a strategy to reach an ultra-fine grained microstructure in a metastable-β titanium Ti-20Nb-6Zr (at.%) by controlled recrystallisation after conventional rolling and annealing. The thermally stable sub-micronic dual phase microstructures are associated with the formation of strain-induced martensite during rolling and its subsequent reversion during annealing. Some specimens were cold-rolled to change most of the β microstructure to stress-induced martensite (SIM); others were “warm rolled” just above the critical temperature for formation of SIM (453 K). The role of SIM in grain refinement was isolated by comparing the microstructural evolution of the two sets of specimens during annealing treatments. The cold rolled specimens produced an effective ultrafine grain recrystallisation, which was identified to start from 723 K, and a final equiaxed alpha-beta microstructure of ~250 nm. In warm rolled specimens without SIM, no new beta grains were observed, only an array of intragranular acicular alpha precipitates of approximately 50 nm thickness.

Comparison of the effect of ECAP and SSE on microstructure, texture, and mechanical properties of magnesium

Microstructure, crystallographic texture, and mechanical properties of pure Mg, as a model hcp metal, were compared after processing by the two severe plastic deformation (SPD) techniques of equal channel angular pressing (ECAP) and simple shear extrusion (SSE). Both processes were performed on extruded bars at 250 °C for up to four passes, where the minimum grain sizes of 13.7 and 9.8 µm were achieved in the ECAP and SSE processes, respectively. The fraction of dynamically recrystallized (DRX) grains, high angle grain boundaries (HAGBs), and the evolution of dislocation density with equivalent strain experienced the same trend in both processes with higher values after ECAP. The textural evolutions were completely different during ECAP and SSE despite their similar deformation modes. A conventional shear texture was developed after ECAP, while after SSE basal planes were aligned parallel to the processing direction. In the ECAP-processed material, texture softening and lower dislocation density counterbalanced the strengthening effect of grain refinement, resulting in a decrease in shear yield stress (SYS) and ultimate shear strength (USS), while in SSE the shear strength increased constantly with increasing number of passes. It can be deduced from the experimental results that SSE was more effective in achieving a fine-grained homogenous microstructure with high shear strengths as compared to ECAP. • Compare microstructure, and strengths after simple shear extrusion (SSE) and equal channel angular pressing (ECAP) of Mg. • SSE was found more efficient in grain refinement compared to ECAP. • Higher fractions of DRX and high angle grain boundaries (HAGBs) were achieved in ECAP than in SSE. • Develop different shear texture components after ECAP and SSE despite having similar deformation modes. • In contrast to ECAP, the shear strengths after SSE increases by increasing the number of passes.

Microstructure-refinement–driven enhanced tensile properties of high-pressure die-cast A380 alloy through friction stir processing

This work employs friction stir processing (FSP), a well-known severe plastic deformation technique, to selectively modify the microstructure of thin-walled, high-pressure die-cast (HPDC) aluminum alloy A380, a major HPDC alloy fabricated in the die casting sector. FSP effectively breaks down Al dendrites and acicular Si particles, creating a homogenized distribution of equiaxed Si particles in the aluminum matrix. After FSP, the refined Si particles (~1.5 μm) are smaller than the eutectic Si particles (3–8 μm) in HPDC condition. In addition, interparticle distance has decreased almost 50% compared to dendritic arm spacing, and FSP has reduced the aspect ratio of Si particles to ~2. Furthermore, FSP eliminates porosity, and breaks down needle-like second-phase Fe-Mn and Cu-rich particles, yielding a refined, homogeneous distribution. The FSP-induced microstructural refinement and porosity reduction improve bulk yield strength and ductility by 23% and 66%. Tensile properties are enhanced beyond those of the die skin of the HPDC plate, and the alloy possesses lower defect density and a highly refined microstructure. This study establishes the viability of FSP as a tool for microstructure modification and mechanical property improvement for HPDC Al alloys for the light-weighting goal of the automotive industries.

Optimization of processing conditions in equal channel angular pressing for superior structure and properties

In the past 25 years, much interest has been paid to the production of ultrafine-grained (UFG) materials due to their superior structure and properties. Equal channel angular extrusion or pressing (ECAE or ECAP) is one of the severe plastic deformation (SPD) technique used to produce UFG materials. Compared to other SPD process, higher strain per pass and higher total productive strain after ‘n’ number of passes is possible in this technique. ECAP process is affected by various processing conditions or parameters. These processing conditions mainly affects the structure and properties produced through this technique. In this article, an effort has been made to provide the effect of each processing parameter on the structure and properties developed through this technique. Various processing conditions like- processing route, channel angle, outer arc of curvature, pressing speed, load and friction, processing temperature and application of back-pressure are critically discussed and effect of these parameters are summarized.

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.

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.

A Review of Ultrafine-Grained Magnetic Materials Prepared by Using High-Pressure Torsion Method.

High-pressure torsion (HPT) is a severe plastic deformation technique where a sample is subjected to torsional shear straining under a high hydrostatic pressure. The HPT method is usually employed to create ultrafine-grained nano-structures, making it widely used in processing many kinds of materials such as metals, glasses, biological materials, and organic compounds. Most of the published HPT results have been focused on the microstructural development of non-magnetic materials and their influence on the mechanical properties. The HPT processing of magnetic materials and its influence on the structural and magnetic properties have attracted increasing research interest recently. This review describes the application of HPT to magnetic materials and our recent experimental results on Mn3O4, Mn4N, and MnAl-based alloys. After HPT, most magnetic materials exhibit significantly reduced grain size and substantially enhanced coercivity.

Mechanical, stress corrosion cracking and crystallographic study on flat components processed by two combined severe plastic deformation techniques

Although the current field of application of Al–alloy 7075 (AA7075) is vast, it is still limited due to some drawbacks, especially due to its susceptibility to stress corrosion cracking (SCC). This work aims to evaluate the microstructural, mechanical, and stress corrosion cracking (SCC) behaviors on an AA7075 in flat format deformed by a combination of repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB) techniques. Four different deformation routes were applied, namely: ARB (A), RCS (R), RCS + ARB (RA) and ARB + RCS (AR). As expected, the efficiency for grain refinement depends on the applied route, in terms of average grain size regarding the initial condition IC): AR > A > RA > R. All conditions resulted in unimodal and widened grain size distributions of micro-, submicro- and nano-metric dimensions. The study of crystallographic orientations showed that route R did not generate any new texture, whereas different preferred orientations were obtained for routes A, RA, and AR. The hardness and three-point bending tests showed an improvement of mechanical strength in the following order: AR > RA > A > R. The cracks per cm2 obtained in the corrosion study indicated that the best SCC resistance was R > A > AR > RA. Based on the above, the best combination of microstructural, mechanical, and SCC properties until one deformation pass was obtained by the single route of the ARB process.

THE EFFECT OF PRECIPITATION ON MICROSTRUCTURE AND CORROSION BEHAVIOUR OF ZK60 SUBJECTED TO SEVERE PLASTIC DEFORMATION AS BIODEGRADABLE MATERIAL

Microstructure and corrosion behaviour of ZK60 subjected to severe plastic deformation (SPD) as biodegradable material has been investigated in terms of grain refinement process and precipitation formation. Equal channel angular pressing (ECAP) was one of the well-known SPD techniques due to their advantages to promote dislocation and grain fragmentation. ZK60 billet was cut to a 10 mm diameter cylindrical shape for biodegradable material application. ECAP process was carried out up to two passes by Route Bc at 423 K temperature process. Microhardness test was performed at ECAP processed sample, and the structure observation was carried by optical microscope and transmission electron microscope. The corrosion behaviour of the material was investigated by an anodic polarization curve. The ECAP process promotes dislocation accumulation efficiently and ultrafine-grained structure formation. It may improve the formability characteristic of ZK60. The hardness also showed significant increment during the ECAP process due to the high level of deformation. Corrosion behaviours and microstructure observation during the ECAP process showed a correlation that concluded that grain refinement and precipitation formation influenced the electrochemical properties. The alloying element such as Zn and Zr promoted the protective film for corrosion due to their ability for pitting protection. ECAP improved the precipitation formation for corrosion resistance, microstructure uniformity and material formability.

Annealing treatments to enhance thermal and mechanical stability of ultrafine-grained metals produced by severe plastic deformation

Abstract Ultrafine-grained (UFG) metals produced by techniques of severe plastic deformation, such as equal channel angular pressing (ECAP), exhibit extraordinary strength properties. However, in the as-ECAP-processed state, the heavily deformed microstructure of such UFG metals is rather unstable and is prone to undergo grain coarsening (recrystallization) at moderate temperatures. This microstructural instability is enhanced in the presence of modest mechanical stressing as, for example, in cyclic deformation. Thus, all measures to enhance the thermal stability are also considered as beneficial for the improvement of the mechanical stability. One main objective of the present work is to analyse the thermal and mechanical stability of ECAP-processed metals during specific annealing and cyclic deformation tests. As a by-product, some conclusions relating to the separate effects of dislocation density, grain size (in the UFG regime) and internal stresses on the (micro)yielding behaviour will be drawn. Another goal is to explore the potential of different annealing treatments with respect to the stabilization of the microstructure and the optimization of the mechanical properties of ECAP-processed UFG metals in terms of an optimal combination of strength and ductility. In order to demonstrate the potential and the limitations of this approach, experimental work performed on UFG copper, aluminium and α-brass produced by ECAP will be reported and discussed. The results presented indicate strongly that a heat treatment leading to a bimodal grain size distribution provides the best compromise between strength and ductility.

Hardness and Microstructure Homogeneity of Pure Copper and Iron-Chromium Alloy Processed by Severe Plastic Deformation

Hardness and microstructure homogeneity of pure copper and iron-chromium alloy processed by severe plastic deformation (SPD) were investigated in grain refinement. Equal channel angular pressing (ECAP) is one of the well-known techniques of the SPD technique due to their up-scale ability and other methods. SPD was applied to pure copper and iron-chromium alloy at comparable temperatures up to four passes. The microstructure and microhardness were observed and measured in the transverse plane for each billet. The homogeneity observation was carried out from the sub-surface until in the middle of the billet. The result showed that the deformed structure appeared adequately after the first pass and had a higher hardness level. The first pass showed a higher inhomogeneity factor than the fourth pass due to the homogeneity microstructure. The hardness also showed homogeneous value along the transverse plane, and it was concluded that ECAP could achieve complete homogeneity in grain refinement

Optimization of Al 6063 Button Head Rivet FEM Analysis Subjected to CRYO ECAP and RT ECAP

The severe plastic deformation technique that has attracted much attention from the material community in recent years is Equal Channel Angular Pressing (ECAP). By using this technique, ultrafine-grained microstructures can be produced without a significant change in the geometry of the material. In the present research, an aluminum 6063 sample was tensile tested after the ECAP process to know the properties of the material. ECAP is performed for two sets of specimens in which the channel angle is 108. One set of samples is at room temperature, and the other set is at -197oC, i.e., dipped in liquid nitrogen for 20 minutes. Tensile properties of the obtained samples are tested once more. The tensile test properties of samples, i.e., before processing and after Room Temperature (RT) and CRYO ECAP, are tabulated and saved for simulation. A rivet with American Society for Testing and Materials (ASTM) dimensions is designed using a design modeller in Analysis of Systems (ANSYS), and the properties obtained from the tensile tests are assigned to the rivet. One end of the rivet is constrained with a fixed support, and the other end is loaded with 35 kN in the downward direction. The process is repeated for three different sets of samples. The developed stresses in the three rivets are tabulated and correlated, and the results are drawn in the present investigation, which showed good correlation.

Experimental studies and optimization of process variables in multi-angular twist extrusion (MATE) of Cu-Cr-Zr alloy

Researchers have recently interested in devising integrated severe plastic deformation (SPD) techniques that can create ultra-fine grained (UFG) metal in one pass. This paper proposes a novel integrated severe plastic technique called multi-angular twist channel extrusion (MATE). This technique was created the aim of retaining strain uniformity while applying a significant strain in a single pass. The input parameters such as annealing temperature, type of lubricant and ram speed, were optimized in this study in relation to the Vickers hardness, hardness inhomogeneity and ultimate tensile strength of the extruded material. Experiments were carried out based on full factorial design, and the TOPSIS approach was used to find the best combination of input parameters. The analysis of variance is used to determine the amount of contribution of input parameters on the mechanical properties. Finite element analysis was performed with the identified optimum parameter of annealing temperature = 550 °C, type of lubricant = MoS2 and ram speed = 3 mm/sec. The average effective strain of 2.72 is obtained by in the MATE process. Experimental studies revealed that the strength and hardness of copper alloy was increased by 69.8 % and 80.5 % respectively. Scanning electron microscope image revealed the grain refinement by MATE process in the copper alloy.

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.

Commercially pure titanium modification to enhance corrosion behavior and osteoblast response by ECAP for biomedical applications

When it comes to using bio-metals, the chemical and biocompatibility properties of titanium led to its widespread use in biomedical implants. However, pure titanium possesses lower mechanical properties than Ti alloys containing cytotoxic elements. Severe plastic deformation (SPD) techniques were able to cause a significant strength increase, corrosion behavior improvement, and the release of the alloying elements. In this study, the ECAP process was performed on commercially pure titanium with a square cross-section at two and four passes, which resulted in a finer grain size and a more uniform microstructure. In order to improve cell behaviors, etch treatment was performed to produce nano-rough and nano-texture surfaces for all Ti samples. The effect of surface etching on corrosion, surface roughness, and cell behaviors on ECAP and untreated samples was also investigated. Optical/Field Emission Scanning Electron Microscopy, Atomic Force Microscopy, and X-Ray Diffraction were used to study the microstructural characterizations of samples. In addition, the impact of grain structure on the contact angle, electrochemical corrosion behavior, osteoblast response, and cell viability was investigated. The titanium that was ECAPed four times provided finer grains (200 nm) than the unprocessed sample (25 µm). The potentiodynamic polarization test revealed that corrosion resistance of ECAPed samples was enhanced, which was associated with grain refinement, affecting the passive film formation. Corrosion resistance and wettability experienced an apparent increase after each ECAP pass. In conclusion, improvement of grain size and surface roughness was due to the simultaneous effect of ECAP and etching treatment that led to the osteoblast response and cellular activity of samples.

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.