Severe Plastic Deformation Method Research Articles

Novel severe plastic deformation method for extrusion compression composite processing

The capability of a novel severe plastic deformation method for extrusion compression composite processing was investigated. Deform-3D software was used to study the effect of back pressure on the strain distribution of a workpiece by simulating the forming process with and without back pressure. The Mg-12.5Gd-4Y-2Zn-0.5Zr alloy was used to analyze the effect of strain on microstructure and mechanical properties. Results showed that back pressure led to the uniform strain distribution of the deformed workpiece and the decrease in the effective strain standard deviation from 0.73 to 0.68. With increasing strain, the grain size tended to decrease and then increase, contrary to the recrystallization rate trend. The tensile strength gradually increased with increasing strain, but the elongation change trend was changed due to the influence of the bimodal structure.

A new wavy cross-sectional torsion extrusion method with an application to improve the mechanical properties of an aluminum matrix composite

Torsion extrusion (TE) as a severe plastic deformation (SPD) method has shown promise in effectively improving the mechanical properties of metal matrix composites (MMCs) by means of extreme shear strain. However, the circumferential sliding between the rotating die and the material seriously degrades the shear effects during TE processing. In order to address this challenge, a modified torsion extrusion method, namely wavy cross-sectional TE (W-TE), was proposed to enhance the shear effect. The method applied a rotating die consisting of a deformation cavity followed by a bearing segment with a wavy cross-section. The material is extruded through the rotating die, and the wavy cross-section holds the deformed billet to rotate with the rotating die, so that the relative sliding is prevented. The method was applied to an in-situ TiB2 particle reinforced 2026 Al composite for dispersing the reinforcing particles and refining the microstructures. Numerical simulations indicated that the W-TE processed material undertook larger torsion deformation than the ones processed by the conventional TE, so the shear effect was enhanced. Experiments showed that, compared with the conventional TE, W-TE can efficiently disperse the reinforced particles and refine the microstructure of the extruded materials. Mechanical tests demonstrated that the samples processed by W-TE exhibits a simultaneously increase in the strength and ductility. Furthermore, with the aid of the enhanced shear effect, the extrusion force of W-TE was reduced greatly compared with conventional extrusion or other TEs, thus making the proposed W-TE an efficient way for improving mechanical properties of metal matrix composites.

Cyclic contraction-expansion extrusion (CCEE): An innovate severe plastic deformation method for tailoring the microstructure and mechanical properties of magnesium AZ91 alloy

In this study, the Cyclic Contraction-Expansion Extrusion (CCEE) process, a novel severe plastic deformation (SPD) technique, is applied to the AZ91 magnesium alloy to enhance its mechanical properties through microstructural refinement. The CCEE method combines cyclic expansion extrusion (CEE) and cyclic extrusion compression (CEC), integrating their advantages while overcoming drawbacks. The CCEE process is capable of inducing substantial plastic strain (3.38) within a single processing cycle, eliminating the need for secondary punches or a synchronized backpressure system. The process is conducted at a temperature of 300 °C, resulting in a bimodal microstructure through the dynamic recrystallization (DRX) mechanism. This microstructure consists of refined equiaxed α-Mg grains with an average size of 2.8 μm, surrounded by a network of newly nucleated α-Mg grains and Mg17Al12 particles with an average size of 500 nm in the two-pass processed sample. Results obtained from the tensile test technique indicate a significant enhancement in the ultimate tensile strength (UTS) of the AZ91 alloy, increasing from 139 MPa to 276 MPa and 290 MPa, and a notable improvement in elongation, increasing from 4% to 8% and 12% after two passes of the CCEE process. Macro-texture X-Ray diffraction (XRD) measurements reveal the formation of a pyramidal deformation texture in the one-pass sample, contributing to the UTS improvement. This texture weakens during the second pass, leading to an increase in elongation. Furthermore, microhardness measurements show an increase from HV 62 to HV 85 after the first pass of the CCEE and HV 73 after the second pass.

Fabrication of ultrafine-grained Cu-Mn alloy with uniform microstructure and high mechanical properties

Homogenization, random orientation, and high strength are the research goals of target materials. In this study, the bulk ultrafine-grained (UFG) Cu-5Mn alloy target materials were prepared by two typical severe plastic deformation methods, equal channel angular pressing (ECAP) and auxiliary-cooling multi-pass friction stir processing (MPFSP), and their structure-property relationships were comparatively investigated. Compared to the ECAP sample with extremely heterogeneous microstructure, the MPFSP sample exhibited finer and more uniform equiaxed microstructure with weaker texture and higher tensile strength of 614 MPa, which was consistent with the requirements of an ideal target material. This study provides a new perspective on the optimization of target materials.

Grain refinement effect on fatigue life of two grades of commercially pure titanium

The fatigue life and fatigue limit of commercially pure Ti grade 2 and 4 in coarse-grained and ultrafine-grained states were experimentally determined. Ultrafine structures were prepared by Conform severe plastic deformation method and by conventional Equal channel angular pressing, respectively. The differences in the improvement of fatigue life and the influence of both procedures on the fatigue limit based on 107 cycles to fracture are discussed in terms of grain refinement, microstructure, differences in fatigue damage mechanism and influence of surface roughness on the initiation of fatigue cracks. Improvement in fatigue life was observed for both materials, however, the improvement of the fatigue limit was found only for Ti grade 2.

Magnesium Alloys Processed by Severe Plastic Deformation (SPD) for Biomedical Applications: An Overview

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

A mini-review of surface severe plastic deformation methods and their effects on steel and stainless steel

Surface severe plastic deformation is an important technology for the preparation of bulk ultrafine grain or even nanocrystalline materials. Based on the technical achievements made in the field of surface severe plastic deformation at home and abroad, this article presents the basic principles of various kinds of surface severe plastic deformation techniques in detail. In addition, the effects of surface severe plastic deformation on the microstructure and mechanical properties of steel and stainless steel are reported. The current status of research on the effects of surface severe plastic deformation on fatigue properties and the tribological and biological properties of steel and stainless steel are summarized. The problems of the current surface severe plastic deformation technology for steel and stainless steel are pointed out, and the future development trend is foreseen.

Structure Refinement and Bauschinger Effect in fcc and hcp Metals

Although the Bauschinger effect has been investigated in some detail in various materials, the number of articles on the effect of grain size is extremely limited, and in current nanostructured materials it is practically absent. Since such materials are considered as promising for structural applications, it is important to understand their mechanical behavior under conditions of changing the direction of deformation, and, therefore, it is necessary to study the Bauschinger effect and its dependence on grain size. The Bauschinger effect was investigated by a single exemplary method for tensile compression of commercially pure hcp titanium and fcc copper, with different grain sizes in the range from hundreds of microns to hundreds of nanometers. The change in grain size was performed by structure refinement by the method of severe plastic deformation using equal-channel angular pressing and subsequent annealing. It has been established that, in both materials, the Bauschinger effect increases with a decrease in grain size, the degree of permanent strain and the duration of exposure between forward and reverse deformation. The signs of the Bauschinger parameter in copper and titanium are opposite. The relationship between the Bauschinger effect and the nature of strain hardening in titanium and softening in copper in the ultrafine-grained state is discussed.

Incremental Feeding High-Pressure Sliding (IF-HPS) Process for Upscaling Highly Strained Areas in Metallic Materials with Enhanced Mechanical Properties

This paper presents an overview of the recent development of incremental feeding high-pressure sliding (IF-HPS) process for grain refinement of metallic sheets with enlarged areas. The IF-HPS process is a method of severe plastic deformation (SPD) under high pressure without increasing the machine capacity. The IF-HPS process combines an incremental feeding technique with the high-pressure sliding (HPS) process so that a severely deformed area can be extended. Development of the IF-HPS process includes the use of flat-type anvils instead of groove-type anvils, which makes it easier to enlarge the SPD-processed areas. The development is also described in terms of the sliding mode and the feeding pattern, where the former is determined by the sliding distance and the numbers of the reciprocation of the sliding and the latter by the feeding distance and the feeding direction. The application of the IF-HPS process is made to metallic materials such as a Ni-based superalloy (Inconel 718), a Ti-6Al-7Nb alloy (F1295) and commercially available Al alloys (A1050, A3105, A5052 and A5182). It is shown that the grain refinement is successfully achieved so that superplastic elongation more than 400% is attained in the Ni- and Ti-based alloys, and the room-temperature tensile strength is well enhanced in the Al alloys. It is then demonstrated that the IF-HPS process is promising to extend the SPD-processed area without increasing the machine capacity. Furthermore, a new approach is suggested for material design, such as the hybrid materials composed of conventional and fine-grained materials and functionally graded materials.

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.

The Evolutions of Microstructure, Texture and Hardness of A1050 Deformed by HPT at the Transition Area.

High-pressure torsion (HPT) is an effective severe plastic deformation method to produce ultrafine-grained (UFG) and nanocrystalline (NC) materials. In the past, most studies have focused on the evolutions in the microstructure, texture and mechanical properties of HPT-deformed materials at peripheral regions. The corresponding evolutions at a special area were observed in this study to reveal the potential plastic deformation mechanism for face-centred cubic (FCC) material with high stacking fault energy. A decreasing trend was found in grain size, and the final grain size was less than 1 μm. However, close observation revealed that the general trend could be divided into different sub-stages, in which grain elongation and grain fragmentation were dominant, respectively. Additionally, microhardness demonstrated a non-linear increase with the development of plastic deformation. Finally, the microhardness reached a high level of ~64 HV. At the early stages of HPT, the C component was transformed into a cube component, suggesting the material flows around the shear plane normal (SPN) axis at these stages. However, finally they will be replaced by ideal simple shear orientations.

Microstructure development and mechanical behaviour of pure copper processed by the novel TWO-CAP procedure

AbstractIn this study, thin-walled open channel angular pressing (TWO-CAP) technique was applied to pure copper specimens as a novel severe plastic deformation (SPD) method. The TWO-CAP process was applied to the specimens up to four passes. After each pass, the microstructural and mechanical characterization of the material was investigated by tensile and hardness tests along with OM, SEM, EDS, TEM and XRD analyses. As a result, a highly increase in the mechanical properties was obtained, in addition satisfactory grain refinement was observed in microstructures. Strength and hardness values were positively affected from the minimizing the grain sizes after TWO-CAP process. Another reason of the improvements in mechanical properties can be explained as the increase in dislocation density. Furthermore, the effect of the TWO-CAP process on the dislocation density of the material has been demonstrated by XRD and TEM analyses in nanoscale. Moreover, the strain equation has been developed analytically and the effect of each pass on strain was calculated. Finally, the effect of the process on the stress-strain properties of the material was examined by the numerical analysis method and the study was verified.

The development of a W-shaped channel extrusion for fabricating magnesium alloy shells by combining high amplitude shear strain with a shorter process

This paper introduced a novel single-pass severe plastic deformation method, W-shaped channel extrusion (WCE), for the direct manufacturing of magnesium alloy shells. Based on a strategically installed mandrel and die with a sloping asymmetric step structure, the WCE constructed a narrow severe plastic deformation gap specially reinforced by a backpressure-shear structure and an asymmetric shear-extrusion section. Therefore, slender bar with large height-to-diameter ratio (i.e. small diameter, large height) could easily be extruded into larger diameter shell in narrow gap through only one pass, and an impressive average plastic strain of over 4.1 was concurrently achieved, evidenced by upper bound theory calculation. The WCE process was further experimentally conducted on AZ80 alloy at 340 °C, demonstrating remarkable improvements in yield strength, ultimate tensile strength, and elongation of the extruded part by factors of 2.4, 2.2, and 4.3 over the as-cast condition. The consecutive multi-stage shear and high hydrostatic pressure catalyzed extreme grain refinement, favored high matrix dislocations and concurrently facilitated the early dynamic conception of granular β-Mg17Al12 particles in subgrains stage, all of which served the superior performance. Moreover, no prominent anisotropy detected in the extruded part due to the development of a special bimodal basal texture under shear stress, where its synergistic effect with grain refinement evidently promoted the balance of strength and plasticity. Finally, the mechanism of bimodal texture formation associated with specific slip activations during WCE and anisotropic weakening was revealed in detail.

Finite element method simulation of metal flow during Tubular Channel Angular Pressing (TCAP) of aluminium 7075

ABSTRACT Tubular Channel Angular Pressing (TCAP) is among the upcoming and highly interesting, severe plastic deformation methods (SPD). This technique is reported to be appropriate for the deformation of very large strains in cylindrical tubes. The tube is pressed by a top die in a space between a mandrel and a die containing three shear zones while maintaining the same tube thickness and diameters. To investigate the SPD process in tubular samples, a commercially available pure aluminium alloy (AA7075) was used to evaluate the influence of die geometry, coefficient of friction, pressing speed, die temperature and tube thickness. The average grain size of about 500 nm was attained from 25 μm by extensive grain refinement. The results of Finite Element (FE) indicated that an effective strain of 3 was achieved by correctly choosing the input parameters. The thickness and length of the tube processed by TCAP also exhibited excellent strain homogeneity. The TCAP process can impose large strains because of having three deformation zones. Depending on input parameters selection, this SPD method, therefore, has two major advantages; (i) excellent strain homogeneity and (ii) high effective strain.

Development of microstructure of asymmetrically rolled AA3003 aluminium sheets with Zr addition

Asymmetric rolling is a method of severe plastic deformation, which can produce large volumes of deformed material and is easy to implement for industrial use. Asymmetric rolling with different circumferential velocities of rolls gives rise to intense plastic shear strains, resulting in grain refinement and improving mechanical properties. An aluminium alloy from AA3003 series enhanced by 0.16 wt% Zr was produced by twin-roll casting in industrial conditions. A part of specimens was annealed at 450∘C in order to precipitate fine dispersion of Al3Zr particles, which may enhance recrystallization resistance at elevated temperatures. Materials were subjected to cold rolling and to asymmetric rolling in several steps. Both methods result in a substantial elongation and fragmentation of grains. The grain refinement is more distinctive after asymmetric rolling. During isochronal annealing Vickers microhardness of materials decreases. The main drop occurs in the asymmetrically rolled material between 400 and 450∘C. In the annealed material the main drop connected with recrystallization is shifted by 50∘C to higher temperatures due to the presence of Al3Zr particles. Recrystallization occurs in the cold-rolled material between 450 and 500∘C. The imposed deformation by rolling is lower in this specimen and hence the driving force for recrystallization is also lower than in the asymmetrically rolled material. After recrystallization, the grain size of both cold-rolled and asymmetrically rolled materials is comparable. However, grains are still elongated in the rolling direction.

Simple shear extrusion versus equal channel angular pressing: A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation (SPD) techniques of simple shear extrusion (SSE) and equal channel angular pressing (ECAP) were employed to process an extruded Mg−6Gd−3Y−1.5Ag (wt%) alloy at 553 K for 1, 2, 4 and 6 passes. The microstructural evolutions were studied by electron back scattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). The initial grain size of 7.5 μm in the extruded alloy was reduced to about 1.3 μm after 6 SPD passes. Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP, with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation. The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization (DRX), so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries (HAGBs). It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods, where dissimilar basal plane texture components were obtained. The compression tests, performed along extrusion direction (ED), indicated that the compressive yield stress (CYS) and ultimate compressive strength (UCS) of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes. ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE. This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction (ED) of each SPD technique.

Finite Element Simulation and Experimental Investigation of Nanostructuring Burnishing AISI 52100 Steel Using an Inclined Flat Cylindrical Tool

This article is devoted to the development of a sliding burnishing scheme using a flat cylindrical indenter. The previously established patterns of nanostructured state formation in the AISI 52100 steel subsurface layer showed a need to create a special tool with a variable tilt angle of the indenter and with force regulation. A new tool with a cubic boron nitride indenter opens wide possibilities for nanostructuring burnishing of hardened bearing steel. Firstly, a flat cylindrical indenter has high durability due to repeated rotation around its axis. Secondly, the change of the tilt angle to the treated surface allows controlling the contact compression pressure and plastic shear deformation, which determines the formation of a nanostructured state of the material by the method of severe plastic deformation (SPD). The purpose of the work is to determine the optimal parameters of the process and tool in order to form a nanostructure and significantly increase surface layer microhardness. The goal was achieved by the methods of finite element modeling (FEM) and experimental studies of burnishing when the indenter tilt angle changes from 0.5° to 2.5° under dry processing conditions. Numerical simulation of the process made it possible to establish optimal values of the indenter tilt angle of 2° and the burnishing force 250 N according to the criteria of maximum contact pressure and cumulative deformation. The experimental studies of cumulative deformations and the coefficient of friction by the method of burnishing a split disc and dynamometry of the process confirmed the FEM results. The transmission microscopy, durometry, and 3D surface profilometry showed the sensitivity of nanocrystallite sizes, microhardness, and roughness to an indenter tilt angle and confirmed the optimality of the established tilt angle value.

Modeling of Severe Plastic Deformation by HSHPT of As-Cast Ti-Nb-Zr-Ta-Fe-O Gum Alloy for Orthopedic Implant.

The High Speed High Pressure Torsion (HSHPT) is the severe plastic deformation method (SPD) designed for the grain refinement of hard-to-deform alloys, and it is able to produce large, rotationally complex shells. In this paper, the new bulk nanostructured Ti-Nb-Zr-Ta-Fe-O Gum metal was investigated using HSHPT. The biomaterial in the as-cast state was simultaneously compressed up to 1 GPa and torsion was applied with friction at a temperature that rose as a pulse in less than 15 s. The interaction between the compression, the torsion, and the intense friction that generates heat requires accurate 3D finite element simulation. Simufact Forming was employed to simulate severe plastic deformation of a shell blank for orthopedic implants using the advancing Patran Tetra elements and adaptable global meshing. The simulation was conducted by applying to the lower anvil a displacement of 4.2 mm in the z-direction and applying a rotational speed of 900 rpm to the upper anvil. The calculations show that the HSHPT accumulated a large plastic deformation strain in a very short time, leading to the desired shape and grain refinement.

Correction to: A novel severe plastic deformation method for manufacturing AZ31 magnesium alloy tube

Correction to: A novel severe plastic deformation method for manufacturing AZ31 magnesium alloy tube

Effects of multi-pass friction stir processing on mechanical and tribological properties of Mg–Zn–Zr alloys

Owing to high strength and good biocompatibility, Mg–Zn binary alloys have attracted significant attention as a potential candidate for producing human implants. However due to the formation casting defects and dendritic structure, these alloys show poor mechanical and wear performances. Alloying and applying severe plastic deformation methods are suggested as two techniques for modifying and improving the above properties. In this study, dry-sliding wear and friction behaviors of the Mg–0.5Zn (MZ) alloy were enhanced by micro-alloying with Zr (0.25 wt%) and applying multi-pass friction stir processing (FSP) technique. Adding Zr reduced the average grain size (AGS) from 1.5 ± 0.3 mm in the MZ sample to about 510 ± 50 μm through the formation of evenly distributed Zr-rich particles with the chemical composition of Mg: 8.84, Zn: 0.75, and Zr: 90.41 A% in the structure. Furthermore, the attendance of thermostable Zr particles stimulated the dynamic recrystallization (DRX) during FSP and reduced the AGS to less than ≈2 μm after the 3rd FSP pass. This substantial grain refinement along with the casting defects reduction, and the fragmentation and redistribution of Zr particles enhanced the hardness and tensile properties of the substrate. Thus, the improved substrate in the FSPed samples, increased the stability of the formed tribolayer on the worn surfaces and changed the wear mechanisms from severe adhesive/delamination in the MZ alloy to mild abrasive/adhesive in the FSPed Zr-modified samples. Therefore, in the optimal condition (3-pass FSPed Mg–0.5Zn–0.25Zr sample), the hardness and total elongation percentage (EL%) increased by 55% and 648% while the mass loss and average friction coefficient (AFC) were reduced by 54% and 39%, respectively, compared to the as-cast Mg–0.5Zn alloy (under a load of 30 N).