Tubular channel angular pressing (TCAP) as a novel severe plastic deformation method for cylindrical tubes

A severe plastic deformation (SPD) technique based on tubular channel angular pressing (TCAP) is proposed suitable for deforming cylindrical tubes to extremely large strains without changing their dimensions. The tube constrained by inner and outer dies is pressed by a hollow cylindrical punch into a tubular angular channel with three shear zones. This technique was applied to a commercial AZ91 magnesium alloy and a significant grain refinement was achieved even after single cycle TCAP. Microhardness of the tube increased to 78 Hv from an initial value of 51 Hv. This new SPD process is promising for future industrial applications.     

Development of a novel severe plastic deformation method for tubular materials: Tube Channel Pressing (TCP)

A new severe plastic deformation (SPD) method entitled Tube Channel Pressing (TCP) is proposed. In this study, the ability of TCP on strength improvement and grain refinement is assessed. This method is based on pressing a tube through a tubular channel die with a neck zone. Utilization of a mandrel fitted inside the tube prevents the crumpling of tube and preserves its initial dimension. Due to the symmetric design, after one pass, the die is rotated upside down and the second pass is applied by pressing the tube in inverse direction. Ultimate strength of a commercial purity aluminum tube after 5 successful passes is improved to 2 times of the initial strength. Analytical calculations and simulation of this process accompanied by commercial finite element code ABAQUS/Explicit demonstrate that the total average equivalent strain of 1.2 is imposed in each pass. Furthermore, hardness distribution through tube thickness is assessed. Then, ability of TCP in grain refinement of tubular samples after each pass is determined.     

A novel severe plastic deformation method for fabricating ultrafine grained pure copper

A novel severe plastic deformation (SPD) method entitled elliptical cross-section spiral equal-channel extrusion (ECSEE) was proposed to fabricate ultrafine grained (UFG) pure copper. The principle of ECSEE process was adopted to accumulate shear stress within the workpiece without any cross-section area change. In order to primarily demonstrate the deformation characteristic and refinement ability of ECSEE method, the simulated and experimental investigations were both done. In the case of simulation, the ECSEE-ed workpiece containing scribed grids was analyzed for the flow net change. Simulated results indicated the trend of effective strain distribution decreased from the circumferential area to the central area on the cross-section of ECSEE-ed workpiece. In experimental investigations of a single-pass of ECSEE, a significant grain refinement from 10–50 μm to 1–10 μm was mainly in the circumferential area of the cross-section for processed workpieces. During the ECSEE deformation, shear strain as an essential role conduced the grain refinement. Besides, a significant increase of hardness, from ∼40 Hv to ∼85 Hv, was examined. The distribution characteristic of refinement and hardness were both consistent with that of simulated effective strain.     

Development of a new integrated severe plastic deformation method

ABSTRACT

A novel one-pass integrated severe plastic deformation method, entitled extrusion compression angular pressing forward extrusion (ECAP-FE), was designed and used for fabricating a fine-grained as-cast AZ31 Mg alloy. Subsequently, mechanical (room temperature compression, tensile and microhardness) and microstructural properties of the processed sample were investigated in detail. In addition, a finite element simulation of the proposed method was carried out for evaluating the equivalent plastic strain and strain rate distribution. The results showed that the ECAP-FE method is a powerful method for processing the ultrafine-grained as-cast AZ31 Mg alloy in a single pass to achieve a uniform and fine microstructure with enhanced mechanical properties. Therefore, it appears that the proposed method has a great potential to a wide range of industrial applications.     

Review of principles and methods of severe plastic deformation for producing ultrafine-grained tubes

Severe plastic deformation (SPD) is known to be the best method for producing bulk ultrafine-grained and nanostructured materials with excellent properties. Different SPD methods were developed that are suitable for sheet and bulk solid materials. During the past decade, efforts have been made to create effective SPD processes suitable for producing cylindrical tubes. In this paper, we review SPD processes intended to produce ultrafine-grained and nanostructured tubes, and their effects on material properties. The paper will focus on introduction of the tube SPD processes, and then comparison of them based on their advantages and disadvantages from the viewpoints of processing and properties.     

Deformation behavior in Simple Shear Extrusion (SSE) as a new severe plastic deformation technique

A new method for severe plastic deformation is proposed herein, entitled as Simple Shear Extrusion (SSE) due to the manner in which specimen's cross-section shape changes. This method is based on pressing material through a specially designed direct extrusion die. The process was investigated experimentally on commercially pure aluminum. Additionally, simulation of the process was also carried out, using the commercial finite element code ABAQUS/Explicit. Moreover, effect of back-pressure on the results was studied. Results show that SSE method is capable of imposing high strain values via strain accumulation during repeating the process, which is of great importance in producing ultrafine-grained or nanostructured materials.     

Interface sheet-constrained groove pressing as a modified severe plastic deformation process

In this paper, a new severe plastic deformation (SPD) process entitled interface sheet-constrained groove pressing (ISCGP) as a new variant of conventional CGP has been developed for producing ultrafine-grained metallic materials. In this process, repetitive shear deformation is imposed into the sheet material by utilising symmetrically grooved die along with two interface sheet on both sides. To study the applicability, mild steel sheets were processed by both ISCGP and CGP processes, and mechanical and microstructural properties of the processed samples were investigated. The results show a considerable improvement in mechanical properties including hardness, yield strength, and ultimate tensile strength, though the ductility sacrifice was reduced. Comparing ISCGP and conventional CGP revealed interesting results, which are shown that ISCGP can result in better surface quality and ductility.     

Novel severe plastic deformation technique—accumulated extrusion (AccumEx)

Accumulated extrusion, a novel severe plastic deformation technique based on conventional extrusion process, is proposed and has been validated on commercial pure aluminium sheets. Four sheets were extruded together at 75% reduction, and this product was recut into four pieces and reextruded up to eight passes to a strain of 13.2. The tensile strength increased up to 200?MPa after six passes. The elongation to failure was 21% after one pass and 6% after six passes. Ultrafine grains with average grain size of 600?nm were observed after eight passes. The refinement process was monitored along all three directions. Texture evolution played an influential role on the misorientation profile and high angle grain boundary fraction.     

Processing of AZ31 magnesium alloy by a new noble severe plastic deformation method

In the present investigation a wrought magnesium alloy (AZ31) has been processed applying the accumulative back extrusion (ABE) method. This was performed through different thermomechanical processing routes (different ABE deformation passes at temperatures of 80-380 °C). The results indicate that AZ31 alloy may successfully be deformed through ABE processing even at temperatures as low as 80 °C. Following the ABE processing a sophisticated microhardness testing was conducted and thorough microstructural observations were undertaken using optical microscopy. The results show that the equiaxed submicron size grains have been achieved. As the number of passes was increased, a more homogeneous microstructure with finer mean grain size was obtained. It was also found that increasing the temperature resulted in larger mean grain size and also higher microstructural homogeneity.     

Microstructure and properties of magnesium alloy processed by a new severe plastic deformation method

A new severe plastic deformation (SPD) method called C shape equal channel reciprocating extrusion (CECRE) was developed to fabricate fine grained AZ31 Mg alloys. The results show that homogeneous microstructure with mean grain size of 3.6 μm is obtained as the accumulated true strain is increased to 11. Strain localization leading to dynamic recrystallizaion (DRX) occurring is the main reason for grain refinement during CECRE process. At the same time, the hardness of AZ31 alloy increases from 62.6 of as-extruded to 74.6 of CECRE 4 passes.     

Modeling of plastic deformation in a cylindrical specimen under edge compression

The authors have elaborated mathematical models and information technologies for the experimental-analytical determination of stress-strain state and ultimate accumulated strain in a material on a barreled side surface of a cylindrical specimen under edge compression. A model that allows one to predict the ultimate accumulated plastic strain has been introduced in the form of an analytic relationship between plastic strain components which represents the specified nonstationary deformation conditions.     

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4 V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4 V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4 V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4 V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4 V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4 V alloy as the material base for mini-implants.     

Free volume simulation for severe plastic deformation of metallic glasses

Evolution of internal parameters of metallic glasses subjected to high pressure torsion was simulated using a free volume based thermo-mechanical model. Steady state has been predicted in the whole, plastically sheared volume for large strains irrespectively from the applied revolution rate. Based on the simplification of the model equations in steady state, simple methods were obtained to determine the in situ temperature increase and stress distribution from external torque measurements.     

Nanostructuring of metals by severe plastic deformation for advanced properties

Despite rosy prospects, the use of nanostructured metals and alloys as advanced structural and functional materials has remained controversial until recently. Only in recent years has a breakthrough been outlined in this area, associated both with development of new routes for the fabrication of bulk nanostructured materials and with investigation of the fundamental mechanisms that lead to the new properties of these materials. Although a deep understanding of these mechanisms is still a topic of basic research, pilot commercial products for medicine and microdevices are coming within reach of the market. This progress article discusses new concepts and principles of using severe plastic deformation (SPD) to fabricate bulk nanostructured metals with advanced properties. Special emphasis is laid on the relationship between microstructural features and properties, as well as the first applications of SPD-produced nanomaterials.     

On the capability of severe plastic deformation of twining induced plasticity (TWIP) steel

There are few reports showing that severe plastic deformation of relatively high strength materials such as steels is difficult due to the segmented flow. In the present paper, it is shown that twining induced plasticity (TWIP) steel can be processed successfully by simple shear extrusion without segmentation. Two simple shear extrusion dies with the maximum distortion angle of 30° and 45° are considered. For comparison, TWIP steel is also processed by equal channel angular pressing at two strain rates. Results show that equal channel angular pressing leads to the segmented flow due to flow localization while simple shear extrusion has the capability of processing TWIP steel without cracking. The microstructure after one pass of simple shear extrusion consists of many deformation twins due to imposing large plastic strains into the material.     

Decomposition process in a FeAuPd alloy nanostructured by severe plastic deformation

The decomposition process mechanisms have been investigated in a Fe50Au25Pd25 (at.%) alloy processed by severe plastic deformation. Phases were characterized by X-ray diffraction (XRD) and microstructures were observed using transmission electron microscopy (TEM). In the coarse grain alloy homogenized and aged at 450 °C, the bcc α-Fe and fcc AuPd phases nucleate in the fcc supersaturated solid solution and grow by a discontinuous precipitation process resulting in a typical lamellar structure. The grain size of the homogenized FeAuPd alloy was reduced in a range of 50–100 nm by high pressure torsion (HPT). Aging at 450 °C this nanostructure leads to the decomposition of the solid solution into an equi-axed microstructure. The grain growth is very limited during aging and the grain size remains under 100 nm. The combination of two phases with different crystallographic structures (bcc α-Fe and fcc AuPd) and of the nanoscaled grain size gives rise to a significant hardening of the alloy.     

Microstructures and mechanical deformation behaviors of ultrafine-grained commercial pure (grade 3) Ti processed by two-step severe plastic deformation

Ultrafine-grained (UFG) commercial pure (CP, grade 3) Ti was produced using two-step severe plastic deformation, eight passes equal channel angular extrusion (ECAE) and cold rolling (CR) at liquid nitrogen temperature (LNT). Microstructural evolution and mechanical behaviors of UFG CP-Ti have been systematically investigated. After eight passes ECAE, the grain size was refined to sub-micron scale, smaller than 0.5 μm. Subsequent CR at LNT or RT for both UFG and coarse-grained (CG) specimens led to further refinement of structure, dramatically intensifying (0 0 0 2) peak, and the preferred orientation along the (0 0 0 2) crystal plane is formed at the expense of other crystal plane. After eight passes ECAE and CR at LNT, the ultimate tensile strength of UFG CP-Ti (grade 3) is 1218 MPa, and an elongation of 12.6%. Strain hardening behaviors of UFG CP-Ti (grade 3) during tensile deformation at RT have been analyzed.