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The present paper deals with twinning-induced plasticity (TWIP) steels with the microstructure refined by severe plastic deformation via equal channel angular pressing and explores the mechanical behavior of steel with qualitatively different microstructures formed in the temperature range 400–900°C. Mechanical characteristics of the steel in different structural states are studied in static tensile tests, biaxial and dynamic tests. Structural changes in the material during severe deformation at different temperatures are discussed, and their effect on the mechanical parameters of TWIP steel is considered. High temperatures of equal channel angular pressing allow for more homogeneous recrystallized structures, which ensure the best combination of the yield stress, formability, plasticity, and crack resistance. These findings can be important in developing high-performance steels for the automotive and hydrogen industries. [ABSTRACT FROM AUTHOR]

X-ray diffraction studies were conducted to examine changes in the structural-phase state and dislocation density of Ti49.8Ni50.2 alloy depending on the isochronal annealing temperature after severe plastic deformation by abc pressing at 573 K. The total true strain achieved in the alloy specimens during abc pressing was e = 9.55. Isochronal annealing was carried out for 1 h at 573, 673, 773, 873 and 973 K. Analysis of all studied specimens at room temperature revealed the coexistence of R and B19′ phases, whose relative fractions varied with annealing temperature. The high-temperature B2 phase was not detected. It was found that the most rapid decrease in the dislocation density, which was measured at 393 K (in the B2 state), occurred after annealing at 673 and 773 K. Specimens annealed at 773 K had the minimum dislocation density, which is more than an order of magnitude lower than the dislocation density immediately after abc pressing. In the same temperature range, there is a significant decrease in the root-mean-square B2 lattice microdistortions <ε2>1/2 and a slight increase in the average size of coherently diffracting domains (crystallities). After abc pressing and isochronal annealing, the main contribution to the intrinsic X-ray line broadening is made by B2 lattice microdistortions, while the contribution from crystallite size is insignificant. The obtained results show that intense recrystallization in Ti49.8Ni50.2 alloy after abc pressing at 573 K begins at T ≥ 773 K. [ABSTRACT FROM AUTHOR]

• Superplasticity of fine-grained Mg-10Li alloy was studied. • Severe plastic deformation was used to achieve the fine grains. • Its deformation mechanisms for superplastic flow were analyzed. • Deformation mechanism maps were constructed in 2D and 3D. The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy (LAZ1011) with a grain size of 3.2 µm, primarily composed of the BCC β phase and a small amount of the HCP α phase, were examined in a temperature range of 473 K to 623 K. The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling. The best superplasticity was achieved at 523 K and at strain rates of 10−4 -5 × 10−4 s−1, where tensile elongations of 550–600% were obtained. During the heating and holding stage of the tensile samples prior to tensile loading, a significant increase in grain size was observed at temperatures above 573 K. Therefore, it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms. In the investigated strain rate range, the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding, while at high strain rates, lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism. It was concluded that solute drag creep is unlikely to occur. During the late stages of deformation at 523 K, it was observed that grain boundary sliding led to the agglomeration of the α phase, resulting in significant strain hardening. Deformation mechanism maps were constructed for β-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate, stress, temperature, and grain size, using the constitutive equations for various deformation mechanisms derived based on the data of the current tests. [ABSTRACT FROM AUTHOR]

This paper discusses the formation of ultrafine-grained (UFG) structure and nanosized second-phase precipitates in commercially pure Grade 4 titanium subjected to severe plastic deformation by high pressure torsion at room temperature with subsequent heat treatment. It was found that the combined processing of Grade 4 titanium provides very high tensile strength (σB ≈ 1500 MPa), which significantly exceeds the previous results for this material. Analysis of the strengthening mechanisms showed that the superstrength of commercially pure titanium is due to several factors: UFG structure formation, dispersion strengthening from second-phase nanoparticles, high dislocation density, and grain boundary segregation. The contribution of these strengthening mechanisms is evaluated and compared with experimental data. [ABSTRACT FROM AUTHOR]

Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegradability, biocompatibility, low density and adequate mechanical properties. Nevertheless, there is a need to further improve these properties either by alloying or through the use of appropriate processing. Among the different biodegradable Mg alloys now in use, the Mg‒Zn series are of special interest and have been the subject of many research investigations. This is primarily because Zn is an essential element for the human body in addition to its positive effects in improving the mechanical strength and lowering the degradation rate of the implant. The properties of Mg‒Zn alloys may be further improved both through the addition of third and fourth alloying elements such as Ca, Ag, Sn or Sr and/or by thermo-mechanical processing where the latter is more environmentally and economically favorable. In practice, procedures based on the application of severe plastic deformation (SPD) are especially suited to produce fine-grained microstructures with improved mechanical, degradation and cell behavior. Equal-channel angular pressing (ECAP) is a popular SPD technique that has the capability of producing bulk materials that are sufficiently large for use as typical implants. Accordingly, this review is designed to provide a comprehensive summary of the research that has been undertaken on ECAP-processed biodegradable Mg‒Zn alloys. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite (SiC np /AZ91D) processed by cyclic extrusion and compression (CEC). It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy. Although there would be dynamic precipitation of the Mg 17 Al 12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries. The results also showed that the damping capacity of 1%SiC np /AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature. Considering the first derivative of the tanδ–T curve, the dominant damping mechanism based on test temperature can be divided into three regions. These three regions are as follows (i) dislocation vibration of the weak pinning points (≤T cr), (ii) dislocation vibration of the strong pinning points (T cr ∼T V), and (iii) grain boundary/interface sliding (≥T V). [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys have several advantages, such as low density, high specific strength and biocompatibility. However, they also suffer weak points, such as high corrosion, low formability and easy ignition, which makes their applications limited. Many studies have been conducted to overcome these disadvantages and further improve the advantages of Mg alloys. Severe plastic deformation (SPD) is one of the most important techniques and has great effects on the microstructure refinement of Mg alloys and improvements in their strength and formability. Several researchers have studied the corrosion behavior of SPD-processed Mg alloys in recent decades. However, these studies have reported some controversial effects of SPD on the corrosion of Mg alloys, which makes the research roadmap ambiguous. Therefore, it is important to review the literature related to the corrosion properties of Mg alloys prepared by SPD and understand the mechanisms controlling their corrosion behavior. Effective grain refinement by SPD improves the corrosion properties of pure Mg and Mg alloys, but control of the processing conditions is a key factor for achieving this goal because texture, dislocation density, size and morphology of secondary phase also importantly affects the corrosion properties of Mg alloys. Reduced grain size in the fine grain-size range can decrease the corrosion rate due to the increased barrier effect of grain boundaries against corrosion and the formation of a stable passivation layer on the surface of fine grains. Basal texture reduces the corrosion rate because basal planes with the highest atomic planar density are more corrosion resistant than other planes. Increased dislocation density after SPD deteriorates the corrosion resistance of the interior grains and thus proper annealing after SPD is important. The fine and uniform distribution of secondary phase particles during SPD is important to minimize the micro-galvanic corrosion effect and retain small grains during annealing treatment for removing dislocations. [ABSTRACT FROM AUTHOR]

It has been shown recently that hydrogen embrittlement in severely deformed low alloy steel results in the formation of specific tearing morphology on the fracture surface. The origin of such a fracture surface has not yet been fully understood. This paper reports the results of fractographic examination combined with electron backscatter diffraction study of the microstructure underlying the fracture surface in ultrafine-grained low alloy steel 09G2S produced by equal channel angular pressing. Tensile tests are carried out on hydrogen-free and cathodically hydrogen-charged specimens. It is found that all hydrogen-charged specimens exhibit tearing fracture morphology and numerous secondary cracks. The metallographic images obtained by scanning electron microscopy and electron backscatter diffraction clearly show that both hydrogen-induced cracking and hydrogen-assisted cracking in the ultrafine-grained steel occur primarily along hydrogen-embrittled high- and low-angle ultrafine grain boundaries and dislocation cell walls, resulting in the formation of tearing morphology on the fracture surface. The mechanism governing the formation of specific morphological elements on the fracture surface is proposed and discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Innovative grease chemistries and additives are continuously developed to meet challenging applications such as wind energy bearings and offshore/underwater applications. The non-equilibrium and transient structures within interfacial tribofilms play an influential role in the service life of a component. Atom probe tomography and transmission electron microscopy studies were performed to investigate the tribofilms formed by lithium complex and calcium sulfonate grease thickeners. The study reveals that morphology, amorphicity, nanostructure, and atomic layering play an influential role in the exceptional wear and corrosion performance of calcium sulfonate thickeners. [ABSTRACT FROM AUTHOR]

In this research, the feasibility of making aluminum–copper bimetallic bar by twist extrusion followed by forward extrusion is addressed. In this consecutive process, twist extrusion was used in several passes and its effect was investigated on the bond strength between aluminum and copper as well as the mechanical properties of the produced bimetallic bars. When forward extrusion was the only applied process, the compressive yield and shear bond strength of produced bimetallic bars were 184 MPa and 5.4 MPa, respectively. Applying four twist extrusion passes followed by one forward extrusion pass increased these values such that the compressive yield and shear bond strength were increased by about 64% and 200%, respectively. The hardness was also significantly increased by the utilization of this procedure. Microstructures of copper and aluminum in the produced bars showed that by applying and repetition of the twist extrusion, the grain size was reduced. The Mechanical locking was the main factor in bond formation. Reducing the gap between the metal plates at the interface and increasing the joint fraction improved the shear bond strength. [ABSTRACT FROM AUTHOR]

A multilevel mathematical model is proposed for studying the technological processing of metals and alloys by severe plastic deformation. The model is based on crystal elasto-viscoplasticity and can describe the evolving structure as well as predict crystallographic texture formation. A geometrically nonlinear nonstationary boundary value problem of quasi-static elasto-viscoplastic deformation of macroscopic polycrystalline samples is formulated in rate form, including systems of equations describing physical mechanisms at various structural scale levels. A distinctive feature of the proposed formulation is that it takes into account variable contact conditions on the material surface specified for each moment of the loading process. As a basic constitutive model, a two-level model of a polycrystal is used in which the characteristics of a macroscopic representative volume are calculated by consistent statistical averaging over the values of similar quantities for the contained mesoscopic elements (crystallites). Within the approach used, information on crystallographic textures in different parts of the workpiece is provided in the form of samples of crystal lattice orientations. The associated output data of numerical calculations are reproduced in a reduced form using cluster analysis methods. The developed apparatus is applied to study the drawing of a solid copper cylinder. [ABSTRACT FROM AUTHOR]

This paper investigates the characteristics and the formation of white layers and dark layers induced by hard turning of through-hardened AISI 52,100 steel. The investigation showed that different types of white layers exist e.g., formed predominantly through excessive thermal or mechanical energy loading. The thermally induced white layer is formed when the cutting temperature is above the critical austenitisation temperature for the material. The nano-sized microstructure is initiated through dynamic recovery, which transitions to dynamic recrystallisation when the temperature rises above the onset temperature for dynamic recrystallisation. The corresponding white layer is characterised by a higher retained austenite content compared to the unaffected material, and the presence of a dark layer beneath the white layer. The white layer and the adjacent dark layer are found to be ∼12% harder and 14% softer, respectively, compared to the unaffected material. On the other hand, the mechanically induced white layer is formed through severe plastic deformation, where the formation is controlled by dynamic recovery and results in an elongated and broken-down substructure. Neither austenite nor an adjacent dark layer could be found for such white layers. The mechanically induced white layer is ∼26% harder than the unaffected material. For both types of white layer, (Fe, Cr) 3 C carbides are found in the microstructure. The investigation shows that the heating rate, cooling rate, pressure, and duration of contact between the cutting tool and workpiece surface should also be considered to understand the underlying formation mechanisms. The characteristics of the examined white layers and the cutting conditions are summarised in a descriptive phenomenological model in order to create a systematic approach for the definition of the different types of white layers. [ABSTRACT FROM AUTHOR]

The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed (ECAPed) Mg–9Al–1Zn (AZ91) alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupled with high resolution techniques such as scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). During ECAP, dynamic recrystallization (DRX) and strain-induced dynamic precipitation (SIDP) simultaneously occurred, resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grains with a large volume fraction of β-Mg 17 Al 12 precipitates. Corrosion preferentially initiates and propagates in the DRXed grains, owing to the greater microchemistry difference between the β-Mg 17 Al 12 precipitates formed at the DRXed grain boundaries and the adjacent α-Mg matrix, which induces a strong microgalvanic coupling between these phases. Additionally, the weaker basal texture of the DRXed grains also makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains. The influence of dynamic recrystallization and dynamic precipitation was also studied in ECAPed alloys with different levels of deformation strain through corrosion and electrochemical techniques. Increasing the strain level led to a more uniform corrosion with a shallow penetration depth, lower corrosion rate values, and higher protective ability of the oxide film. Furthermore, higher levels of strain resulted in greater hardness values of the ECAPed alloys. The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination of smaller DRXed grain size, higher DRX ratio, and higher volume fraction of uniformly distributed fine β-Mg 17 Al 12 precipitates. [ABSTRACT FROM AUTHOR]

In this work, the Friction Stir Back Extrusion (FSBE) process of seamless Mg AZ31B tubes is investigated using numerical modeling and experiments. A Coupled Eulerian Lagrangian thermomechanical model is developed to simulate the FSBE process. Material flow, strains, strain rates, grain size, and temperature histories during the FSBE process were investigated. FSBE experiments were conducted to validate the model. It is shown that the measured reactive body force in the principal loading direction and the temperature histories at different locations of the die agree well with the modeling results. The numerical results show that a maximum strain rate of 90 s−1 was attained at the inner surface of the tube. The maximum temperature in the workpiece reaches 599 °C. The optical microscopy and numerical results show that fine grains were formed at the inner surface of the tube with diminishing refinement effects as the outer surface is approached. It is revealed that the material in the central region of the workpiece rotates around the tube centerline in a behavior similar to that seen in the rotation zone in friction stir welding. The material near the outer surface of the workpiece moves upward with slight rotation about the tube centerline. [ABSTRACT FROM AUTHOR]

The paper analyzes how the elastic properties of titanium and its alloys vary as their structure is transformed from coarse- to ultrafine-grained under severe plastic deformation. The analysis includes acoustic measurements of the elastic modulus of Ti materials with a piezoelectric composite oscillator over a wide amplitude range, a detailed examination of their microstructure by electron microscopy and electron backscatter diffraction, and estimations of their nanoporosity by small-angle X-ray scattering and their density by precision weighing before and after applying a high hydrostatic pressure (1.5 GPa). The results of the analysis show that such structural transformations can cause a noticeable change in the elastic properties of Ti materials due to dislocations, nanoporosity, high internal stress, and initial grain structure. [ABSTRACT FROM AUTHOR]

The paper analyzes the structure and mechanical properties of sheet-rolled Al 1560 alloy after four cycles of groove pressing. The analysis shows that under quasi-static uniaxial tension at a strain rate of 1 s-1, the offset yield strength of the groove-pressed alloy and its ultimate strength are respectively 1.4 and 1.5 times higher than their values in the as-received state. The ultimate tensile strain of the alloy after pressing is 17% against 21% in the as-received state, and its microhardness is 2.7 times higher. According to an electron backscatter diffraction analysis, the groove-pressed alloy has a bimodal structure composed of elongated coarse grains and agglomerates of equiaxed grains of micron and submicron sizes. When pressed, the alloy increases the density of its grain boundaries with a misorientation angle of less than 15° and changes its texture from rolling to upsetting whose volume during pressing grows. Part of the grain orientations in both states corresponds to recrystallization. The research data suggest that groove pressing provides grain structure refinement via plastic distortion in Al 15 60 alloy and a considerable increase in its strength properties. [ABSTRACT FROM AUTHOR]

Abstract Severe plastic deformation (SPD) was carried out on AZ80 alloy by high-pass multi-directional forging (MDF). Results showed that AZ80 alloy was effectively refined through MDF, and average grain size was refined to 0.73 µm after 24 passes of forging. Its tensile strength, yield strength and elongation reached 333.8 MPa, 233.7 MPa and 17.8%, respectively, which were 1.22 times, 1.35 times and 2.54 times of those before the forging. When the MDF was less than 6 passes, the coarse grains were mechanically divided and refined, and a small amount of recrystallized grains appeared in the deformation band and its cross zone. When the MDF was more than 6 passes, grain division, recrystallization nucleation and grain growth occurred simultaneously, the microstructure refinement was slowed, and the uniformity was improved continuously. The heating between forging passes mainly caused restoration in the early forging, and the static recrystallization refinement in the middle of forging. In the later stage of forging, the grain growth caused by static recrystallization and the grain refinement caused by the deformation canceled out, and the microstructure no longer continued to refine with the increase of the forging pass. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) has long been known to confer superior mechanical properties for many metals and alloys. In the general field of biomedical devices, and dental implants in particular, the superior strength of SPD-processed commercially pure (CP) titanium, that may surpass that of the stronger Ti6Al4V alloy, has been associated with a superior fatigue resistance. Such a property would make those materials both biocompatible and strong alternatives to the currently used titanium alloy. However, the fatigue characterization reported so far in the literature relies on a very small sample size, thereby precluding any meaningful statistical analysis. This paper reports and compares systematic fatigue testing of various grades as-received and SPD processed Grade 4 CP-Ti using the recently developed random spectrum loading approach, in both air and 0.9% saline solution. The results of this study do not support the claim that the SPD process, albeit causing noticeable strengthening, confers any advantage to Grade 4 CP-Ti in terms of fatigue response. [ABSTRACT FROM AUTHOR]

Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties. However for some of these applications, high plastic deformability is required to achieve desired component shapes and configurations; unfortunately, Mg and its alloys have low formability. Scientifically, the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems. But basically, the HCP crystal structure coupled with low stacking fault energies (SFE) are largely linked to the poor ductility exhibited by Mg alloys. These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys. Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability – mediated engineering use have been reported and still ongoing. This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour, specifically, plasticity characteristics. It also concisely presents various processing routes (Alloying, Traditional Forming and Severe Plastic Deformation (SPD)) which have been explored to enhance plastic deformability in Mg and its alloys. Grain refinement and homogenising of phases, reducing CRSS between slip modes, twinning suppression to activate non-basal slip, and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes. While identifying the limitations of these strategies, further areas to be explored for enhancing plasticity of Mg alloys are highlighted. [ABSTRACT FROM AUTHOR]

High Pressure Torsion (HPT) is historically the first and is currently most common process of the severe plastic deformation (SPD). HPT is used for producing nanocrystalline structures in metals and alloys, as well as for cold welding of powders. The result of the HPT treatment is determined by the flow kinematics and the stress state of a material under deformation. P. Bridgman proposed a simple model for the initial assessment of shear strain in the sample during HPT. A number of recent investigations show that the true plastic flow during HPT can differ significantly from the simple model. We present in our report results of the FEM investigation of different types of flow during HPT. We propose a hypothesis that the vortex formation during the SPD process is caused by the local blocking of simple shear in a material under deformation. [ABSTRACT FROM AUTHOR]

Processes based on severe plastic deformation (SPD) that are capable of producing microstructures with sizes on the order of nanometres are gaining importance these days. Their typical limitation is the small volume of the material processed. One of available ways to enhancing the productivity is to combine the CONFORM continuous extrusion process with the ECAP method. In the present study, commercially pure Grade 4 titanium was processed using the CONFORM SPD machine. The process was carried out at 220 °C. In total, three passes through the CONFORM SPD equipment were completed. The first pass through the CONFORM SPD machine led to a considerable reduction in grain size: from 12500 nm to 300–400 nm. Subsequent passes did not refine the grain any further. Instead, equiaxed grains were obtained. The mean grain size even increased after the third pass to values in the range of 400–450 nm. The first pass resulted in a marked increase in ultimate strength from 650 MPa to 750 MPa. Subsequent passes led to smaller increments that corresponded with the grain sizes attained. After the third pass, the ultimate strength reached 773 MPa. The present study highlights the potential of the continuous production of UFG materials by application of large deformation, and describes the dependence of materials characteristics on technological aspects of the process. [ABSTRACT FROM AUTHOR]

Shear strain and accumulated strain plays a critical role in the grain refinement of aluminium alloys processed by asymmetric rolling, when circumferential speeds of the top and bottom rolls are different. Asymmetric rolling induces larger grain refinement in the mode of severe plastic deformation, when accumulated strain with dominant shear strain is more than 3. Searching the optimal process parameters which provide such extremely high deformation characteristics is very important. This paper presents the distributions of the accumulated strain through strip thickness of Al-6.2Mg-0.7Mn alloy processed by a single-pass asymmetric warm rolling. Effects of thickness reduction per pass (10…60%), rolls speed ratio (1…60%), diameters of the rolls (50…500 mm), contact friction coefficient (0.1…0.4), initial strip thickness (1…8 mm) and ratio of contact arc length to average thickness of strip were investigated by the rigid-plastic finite-element analysis with taking into account the heat generation due to work of plastic deformation and friction. The non-linear effect of rolls speed ratio on the deformation characteristics during asymmetric warm rolling was found. Extremely high shear strain and accumulated strain up to e=3.8...4.8 were reached during a single-pass asymmetric warm rolling. Finite element analysis of the deformation characteristics, presented in this study, can be used for optimization of the asymmetric rolling process as a method of severe plastic deformation. [ABSTRACT FROM AUTHOR]

In this work, the effect of fine grain sizes on the mechanical and bio-corrosion properties of AZ31 magnesium alloy was studied. Bio-corrosion refers to the accelerated degradation of metal within the human body. Fine-grained (~1.5 µm) AZ31 was obtained through Severe Plastic Deformation (SPD) via three cycles of Constrained Groove-Pressing (CGP) under elevated temperature. The effects of CGP and post-annealing (at 473 K for 15 and 30 min) on bio-corrosion were preliminarily investigated by potentiodynamic polarization measurements and constant immersion tests. Results obtained show that the as-processed samples with annealing exhibited improvements in yield strength and ductility while the bio-corrosion rate in Hank’s solution remains fairly similar during the early stage. [ABSTRACT FROM AUTHOR]

NiTiNb shape memory alloy (SMA) has been widely used for pipe coupling because it possesses the wider phase transformation hysteresis. In the present study, Ni 47 Ti 44 Nb 9 (at.%) SMA, which is composed of B2 austenite phase and β-Nb phase, was subjected to local canning compression at the deformation degrees of 25%, 50% and 75%, respectively. Local canning compression causes Ni 47 Ti 44 Nb 9 SMA to be in a three-dimensional compressive stress state, which contributes to severe plastic deformation of the involved alloy. Severe plastic deformation leads to nanocrystallization and amorphization of Ni 47 Ti 44 Nb 9 SMA. Dislocation slip plays a dominant role in plastic deformation of Ni 47 Ti 44 Nb 9 SMA. Physical mechanisms for nanocrystallization and amorphization of Ni 47 Ti 44 Nb 9 SMA were revealed on the basis of statistically stored dislocation (SSD) and geometrically necessary dislocation (GND). As a soft phase, β-Nb phase is subjected to plastic yield more easily than B2 austenite phase. However, nanocrystalline phase and amorphous phase are more easily induced in B2 austenite phase than in β-Nb phase. The dislocations emitted from β-Nb phase move toward the interface between β-Nb phase and B2 austenite phase and consequently pile up at the corresponding interface, which plays a significant role in nanocrystallization and amorphization of Ni 47 Ti 44 Nb 9 SMA subjected to severe plastic deformation. The formation of nanocrystalline phase deals with the transformation from low angle grain boundary to high angle grain boundary. Nanocrystalline phase can be viewed as a transition from coarse grain to amorphous phase. The occurrence of amorphous phase is attributed to the fact that a high density of dislocations are induced during severe plastic deformation of Ni 47 Ti 44 Nb 9 SMA. [ABSTRACT FROM AUTHOR]

Based on equal channel angular extrusion (ECAE), NiTiFe shape memory alloy (SMA) was subjected to severe plastic deformation in order to obtain the refined microstructures. Finite element method (FEM), electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM) were used to investigate plastic deformation mechanisms of NiTiFe SMA subjected to ECAE. According to finite element simulation, equivalent stress and equivalent strain fields were obtained during ECAE of NiTiFe SMA, where larger shear stress at channel corner contributes to the refinement of the microstructures. Based on EBSD experiment and TEM observation, the grain refinement and even nanocrystlline grains were found in the NiTiFe SMA subjected to ECAE, and the mechanisms of grain refinement was revealed. It can be concluded that dislocation slip plays a significant role in plastic deformation of NiTiFe SMA subjected to ECAE. The sizes of the refined grains are related to the density of dislocations, so the refined grains possess various sizes due to the inhomogeneity of plastic deformation. The nanocrystalline grains are induced in the region with extremely high dislocation density. [ABSTRACT FROM AUTHOR]

Asymmetric sheet rolling process is one of the methods of severe plastic deformation which can be used to improve the microstructure and mechanical properties of metallic materials. The mechanism of severe plastic deformation during asymmetric rolling comes from synergistic combination of compressive strain and very significant shear strain. Laboratory simulation of stress-strain state and microstructure evolution, which are similar to that occurring during asymmetric sheet rolling process, is very important for design of technologies of producing fine grained materials. Shear-compression testing of materials is complicated by the fact that a state of large equivalent strain with dominant shear strain is not easily achievable. This paper presents the novel technique of laboratory simulation of asymmetric sheet rolling process by multicycle shear-compression testing at room temperature with equivalent strain e=1…5. The specimen consisted of a parallelepiped having an inclined gauge section created by two diametrically opposed semi-circular slots which were machined at 45°. Height of the specimen was 50 mm, section dimensions were 25×25 mm, gauge thickness was 5.0 mm and gauge width was 6.0 mm. The specimen provided dominant shear strain in an inclined gauge-section. The level of shear strain and equivalent strain was controlled through adjustment of the height reduction of the specimen, load application direction and number of cycles of shear-compression. Aluminium alloy Al-6.2Mg-0.7Mn was used as a material for specimen. FE simulation and analysis of the stress-strain state were performed. The microstructure of the specimen after multicycle shear-compression testing with equivalent strain e=1…5 was examined by optical and scanning electron microscope. The results of investigation can be used to optimize the asymmetric rolling process to improve microstructure and mechanical properties of aluminium sheets. [ABSTRACT FROM AUTHOR]

Nickel-titanium (NiTi) shape memory alloys are widely used for medical components, as they can accommodate large strains in their superelastic state. In order to further improve the mechanical properties of NiTi, grain refinement by severe plastic deformation is applied to generate an ultrafine-grained microstructure with increased strength. In this work comprehensive fracture and fatigue crack growth experiments were performed on ultrafine-grained NiTi to assess its damage tolerance, which is essential for the safe use of this material in medical applications. It was found, that equal channel angular pressing of NiTi for 8 passes route B C increases the transformation stress by a factor of 1.5 and the yield stress of the martensite by a factor of 2.6, without significantly deteriorating its fracture and fatigue crack growth behavior. The fatigue crack growth behavior at high mean stresses is even improved, with lower fatigue crack growth rates and higher threshold stress intensity factor ranges, however, beneficial contributions from crack closure are slightly reduced. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) is known to be the best method for producing bulk ultrafinegrained 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. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) has recently been advanced as the main process for fabricating bulk ultrafine grained or nanocrystalline metallic materials, which present much higher strength and better bio-compatibility than coarse-grained counterparts. Medical devices, such as aneurysm clips and dental implants, require high mechanical and biological performance (e.g., stiffness, yield strength, fatigue resistance, and bio-compatibility). These requirements match well the characteristics of SPD-processed materials. Typical aneurysm clips are made of a commercial Ti-6Al-4V alloy, which has higher yield strength than Ti. In this work, Ti and Ti-6Al-4V workpieces were processed by high-pressure torsion (HPT) to enhance their mechanical properties. Tensile tests and hardness tests were performed to evaluate their mechanical properties, and their microstructure was investigated. The hardness and yield stress of the HPT-processed Ti are comparable to those of the initial Ti-6Al-4V due to significantly refined microstructure. Finite element analyses for evaluating the opening performance of a specific geometry of the YASARGIL aneurysm clip were carried out using mechanical properties of the initial and HPT-processed Ti and Ti-6Al-4V. These results indicate that SPD-processed Ti could be a good candidate to substitute for Ti-6Al-4V in aneurysm clips. [ABSTRACT FROM AUTHOR]

The equal channel angular rolling process was successfully performed on commercial pure copper. After 4 passes of this process, grains with a diameter of about 70-500 nm were formed. The fatigue test results showed that the ultra-fine grained copper represents a longer lifetime under stress-controlled fatigue. To clarify the formation process of surface damage, morphological changes in the fractured surface were monitored by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

In this work, a Cellular Automaton (CA) model is for the first time developed to predict material microstructure evolution during cutting processes. Prior to the CA simulation, the dynamic thermomechanical loadings of work material, Aluminum Alloy 1100, induced by various orthogonal cutting conditions are simulated by finite element-based cutting models. Evolution of dislocation density is modeled using the CA model in MATLAB for the work material subjected to these loading conditions. Multiple mechanisms of microstructure evolution are coupled in the CA model including severe plastic deformation, dynamic recovery, dynamic recrystallization, and thermally-driven grain growth. [ABSTRACT FROM AUTHOR]

Tungsten was subjected to severe plastic deformation at 440 °C using high pressure torsion (HPT) with an improved die-set. Microhardness measurements suggest an appreciable ductility level in tungsten after HPT with Vickers microhardness HV as high as ∼11 500 MPa. Differential scanning calorimetry (DSC) analyses show that samples with less strain have a higher recrystallisation temperature (greater than 1450 °C) than samples with more strain (∼800 °C). X-ray diffraction analyses indicate increases in lattice strain up to 0.35%, lattice parameter up to 0.3177 nm and dislocation density up to 2.4 × 10 15 m −2 . The current study introduces the improved HPT process as an effective route for the production of ultrahigh strength W with significant ductility and specified thermostability [ABSTRACT FROM AUTHOR]

Nanostructured metallic materials are increasingly investigated for numerous biomedical implant applications. They offer benefits of high strength with enough ductility and often possess superior biocompatibility. Several materials processing routes involving severe plastic deformation of candidate materials lead to bulk nanostructured and surface nanostructured metals. Literature is replete with studies claiming their superior mechanical behaviour and biocompatibility in terms of wettability, cell adhesion and proliferation. In spite of their metallic properties, permanent metallic implants with an expected life span of 15 years or more, often break down prematurely and corrosion of some form is a common cause or trigger. Therefore, in order to ensure reliable performance of newly developed nanostructured metal implants in service, it is necessary to understand their electrochemical degradation behaviour. Concerns stem from adverse reactions from corrosion products, desired longevity of long term implants, and biodegradability of temporary implants. Present review covers the developments in this domain. [ABSTRACT FROM PUBLISHER]

Ti-based materials are one of the most important materials used in biomedical engineering. Recently, commercially pure (CP) Ti has attracted significant attention of research community due to its full biocompatibility with human body, and there is an ongoing demand to improve its mechanical properties without sacrificing other beneficial properties. A possible approach to achieving this aim is to use the method of severe plastic deformation (SPD) to obtain an ultra-fine grained (UFG) microstructure. Significant grain refinement by SPD processing leads to an improvement in mechanical and functional properties. This paper gives an overview of a range of the properties that can be achieved in the UFG CP Ti including microstructural features, mechanical properties, corrosion performance and biocompatibility. Attention is paid to the main SPD processing techniques developed for the fabrication of UFG CP Ti. Current and potential applications of UFG CP Ti in biomedical engineering are also considered. [ABSTRACT FROM PUBLISHER]

Biocompatible β Ti–45Nb (wt%) alloys were subjected to different methods of severe plastic deformation (SPD) in order to increase the mechanical strength without increasing the low Young׳s modulus thus avoiding the stress shielding effect. The mechanical properties, microstructural changes and texture evolution were investigated, by means of tensile, microhardness and nanoindentation tests, as well as TEM and XRD. Significant increases of hardness and ultimate tensile strength up to a factor 1.6 and 2, respectively, could be achieved depending on the SPD method applied (hydrostatic extrusion – HE, high pressure torsion – HPT, and rolling and folding – R&F), while maintaining the considerable ductility. Due to the high content of β-stabilizing Nb, the initial lattice structure turned out to be stable upon all of the SPD methods applied. This explains why with all SPD methods the apparent Young׳s modulus measured by nanoindentation did not exceed that of the non-processed material. For its variations below that level, they could be quantitatively related to changes in the SPD-induced texture, by means of calculations of the Young׳s modulus on basis of the texture data which were carefully measured for all different SPD techniques and strains. This is especially true for the significant decrease of Young׳s modulus for increasing R&F processing which is thus identified as a texture effect. Considering the mechanical biocompatibility (percentage of hardness over Young׳s modulus), a value of 3–4% is achieved with all the SPD routes applied which recommends them for enhancing β Ti-alloys for biomedical applications. [ABSTRACT FROM AUTHOR]

Forming by gradation extrusion enables severe plastic deformation with a large gradient of plastic strain resulting in a correlating gradient of the microstructure. Materials with tailored properties can thus be provided. Controlling the gradation of the microstructure also requires knowledge of the interaction of forming process and a special die geometry. Based on an analytical calculation approach, different geometry variants are characterized. Additionally, selected geometrical variants are studied more comprehensively by numerical simulation. The mechanisms of the interaction and possibilities of influencing the deformation process by die design and process parameter optimization are presented and analyzed. [ABSTRACT FROM AUTHOR]