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Based on the deforming technique of severe plastic deformation (SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion (RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 °C and decreasing by 10 °C for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent.

In this study, the microstructural evolution, mechanical properties and biocorrosion performance of a Mg–Zn–Ca–Mn alloy were investigated under different conditions of heat treatment, extrusion, one pass and two passes of half equal channel angular pressing (HECAP) process. The results showed significant grain refinement of the homogenized alloy after two passes of HECAP process from 345 µm to 2 µm. Field emission scanning electron microscopy (FESEM) revealed the presence of finer Mg6Zn3Ca2 phase as well as α-Mn phase after HECAP process. The results also showed that mechanical characteristics such as yield strength, ultimate tensile strength and elongation of the HECAPed samples improved by ∼208%, ∼144% and ∼100% compared to the homogenized one, respectively. Crystallographic texture analysis indicated that most of the grains at the surface were reoriented parallel to the (0001) basal plane after HECAP process. Electrochemical corrosion tests and immersion results indicated that the sample with two passes of HEACP had the highest biocorrosion resistance confirming that the basal planes had the lowest corrosion rate compared to the non-basal ones. The mechanical behavior and bio-corrosion evaluation demonstrated that the HECAPed Mg–Zn–Ca–Mn alloy has great potential for biomedical applications and a mechanism was proposed to explain the interrelations between the thermomechanical processing and bio-corrosion behavior.

Magnesium (Mg) based alloys are promising candidates for many applications, but their untreated surfaces usually have low strength and hardness. In this study, a single point diamond turning (SPDT) technique was applied to refine the grain size and improve the mechanical properties of the surface layers of Mg-Li alloys. By refining grains in the topmost layer to the nanometer scale (∼ 60 nm), the surface hardness was found to be enhanced by approximately 60%. The atomic plastic deformation process during the SPDT was then studied by the real-time atomistic molecular dynamics (MD) simulations. A series of MD simulations with different combinations of parameters, including rake angle, cutting speed and cutting depth, were conducted to understand their influences on the microstructural evolution and associated plastic deformation mechanisms on the surface layer of the workpieces. The MD simulation results suggest that using increased rake angle, cutting speed and cutting depth can help to achieve better grain refinement. These simulation results, which provide atomic-level details of the deformation mechanism, can assist the parameter design for the SPDT techniques to achieve the high-performance heterogeneous nanostructured materials.

The equal channel angular pressing (ECAP) of single-crystal aluminum was investigated using molecular dynamics to provide insights into the deformation behavior and polycrystal formation. Three samples with different initial crystallographic orientations were processed by an ECAP die with a curvature angle (Ψ) of 20° and a channel angle (Φ) of 90° at 300 K. The samples were oriented, such that [100], [110], and [111] directions were parallel to the extrusion direction (ED). The shear strain was the predominant mode of deformation during ECAP with the presence of normal strain before entering the deformation zone due to the high compression force. The sample with [100] direction oriented along the ED showed significant grain fragmentation, the highest lattice rotation but the lowest dislocation density and shear strain, whereas the sample with [111] orientation showed the opposite results. A correlation between the number of active slip systems, the magnitude of shear strain, and grain rotation angle was observed with most of the lattice rotation occurring around the transverse direction. Furthermore, the deformation and grain fragmentation processes occurring in the deformation zone were also investigated. Finally, the model could produce results similar to the results obtained experimentally in the literature.

The FCC structured CoCrFeMnNi high entropy alloy (HEA) has attracted great attention due to its excellent ductility and strain hardening ability, but the lowest yield strength is insufficient for structural applications. To achieve high strength and ductility, we developed a new strategy called harmonic structure (HS) consisting of soft coarse and hard fine grains via controlled mechanical milling time. The SEM and EBSD microscopic characterizations reveal that the formation of HS from surface to the interior of powder is due to a difference in the degree of plastic deformation. The hardness of HS HEAs increased with increasing distance from center to surface regions due to a reduction in grain size. Compared with the homogeneous HEA, the yield strength of HS HEAs increased from 370 MPa to 730 MPa and 760 MPa due to grain boundary strengthening, dislocation strengthening, and twin boundary strengthening effects. While HS HEAs exhibited enhanced strain hardening ability due to gradient structure with their mechanical incompatibility provide back stress strengthening. Furthermore, the compressive deformation behavior of homogeneous and HS HEAs was analyzed by microstructural evolution.

Powder processing by ball milling is an effective approach for materials engineering. Although various methods for material processing are available, only high-energy shaker/vibratory or planetary mills have been intensively utilized to develop mechanical milling or alloying routes for structural control of MgB2 superconducting materials. Herein, we have attempted structural modification by using a low-rotation shaker, which is categorized as a low-energy and economical mill in terms of industrial applications. The operation speed was kept constant at 40 rpm, which is much lower than typical conditions employed for planetary mills. Instead of adjusting the low rotational speed, the other processing parameters were controlled to enhance the energy transfer from the balls to powders. The applied milling conditions were ultimately found to cause severe plastic deformation of the raw powders. The shape and size changed drastically, depending on the processing time. The morphological variation of the processed powders as precursors for the MgB2 materials influenced the void structure and the composition including amorphous phases. By considering these results, we also elucidated the mechanism underlying the structural changes upon ball milling and their effects on the transport critical current performance. The present approach for powder processing offers potential as an effective milling route for structural modification of superconducting materials.

A new friction-based riveting technique, Rotating Hammer Riveting (RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a pre-heating operation. Due to preliminary twinning and followed by dynamic recrystallization, AZ31 Mg grains in the rivet head were refined during RHR, which enhance the formability of Mg rivets by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top AZ31 Mg sheet, which eliminates a significant pathway for corrosion.

An advanced and newly developed severe plastic deformation (SPD) method called accumulative fold-forging (AFF) was applied to produce layered nanostructured MgNi alloys exhibiting superior hydrogen storage capacity. Microstructural developments and storage properties were characterized in depth to correlate the structure and performance of this advanced material. The enhanced hydrogen storage performance of the magnesium-based layered composite material was investigated in comparison to the pristine state by conducting hydrogenation and dehydrogenation testing. It was also shown that the hydrogen uptake and release characteristics can be controlled by adjusting the layered structure or the Mg: Ni stoichiometry ratio. Refining the grain structure of the magnesium alloy down to the nano-scale range (∼400–900 nm) by applying high cycles AFF consolidation to promote creation of multi-million nanometric interfaces led to superior storage performance with a remarkable hydrogen absorption capacity of up to ∼1.425 wt%. X-ray diffraction (XRD) analysis of the hydrogenated products revealed the formation of MgH2 that indicates the dominance of the magnesium matrix for controlling the hydrogen storage behavior of the layered Mg/Ni composite material. Finally, the relationship between the directional hydrogen storage behavior and the induced structural features upon AFF treatment were also established using quantitative characterization and analytical tools.

The effect of shear deformation via torsion on tensile strain-hardening behavior of SCM415 low-alloy steel was investigated. Hot-rolled SCM415 rods were machined into round tensile-test specimens based on ASTM E8M. SCM415 round tensile specimens were subjected to shear deformation using a free-end torsion testing machine at a constant rotational speed of 0.1 rpm. The specimens were torsionally deformed at room temperature to four different angles: 0.314 rad, 0.628 rad, 1.256 rad, and 2.512 rad. Tensile tests of torsionally deformed specimens were then carried out. The engineering stress-strain curves indicated that yield strength and ultimate tensile strength increased while ductility decreased with a higher degree in shear deformation via torsion. From true stress-strain curves generated using engineering stress and strain values, it was found that the strain hardening rates were lower in specimens with a higher degree of shear deformation via torsion. A power law was applied to curve fit the true stress-strain data in the uniform plastic deformation region. The strength coefficient and strain hardening exponent were lower in specimens with a higher degree of shear deformation via torsion. The decrease in strain hardening exponent and work hardening capacity of specimens with a higher degree of shear deformation via torsion was presumably caused by a combination of high dislocation density and grain refinement after severe plastic deformation.

ZK60B (Mg-6% Zn-0.6% Zr) alloy joints fabricated by bobbin tool friction stir welding (BTFSW) with various traverse speeds were investigated. The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters. The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone (SZ) followed by evolution of a bimodal grain structure with distributed bands of 0.8–1.7 μm ultrafine grains and 4.1–7.1 μm equiaxed grains. Micro-hardness of SZ is substantially reduced in contrast to that of parent metal (PM) in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix. With the decrease in traverse speed, randomization degree of the plasticized metal flow increases, which is evidenced by the randomized arc line pattern at the low traverse speed. Among all defect-free joints, the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties, which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%, respectively, as compared to the PM. The randomized texture hinders the joint fracturing within SZ at low elongation. Therefore, a relatively high elongation of 10.8% was achieved, which corresponded to 72% of the PM value.

The present research was conducted to improve the mechanical properties of pure titanium, in which a composite reinforced with reduced graphene oxide (RGO) nanosheets was fabricated using spark plasma sintering (SPS) method and was subjected to severe plastic deformation (SPD) process at room temperature with simple shear extrusion (SSE). Its mechanical properties were investigated in terms of tensile and yield strengths applying tension and hardness tests. Moreover, characterizations were accomplished through field emission scanning electron microscopy (FE-SEM) equipped with EDS, light microscopy (LM), and X-ray diffraction (XRD). The obtained results revealed that the grain growth was observed for all the samples in the annealing step, yet the elongation in the highest percentage of RGO was severely limited. Following SSE, the grain size decreased in the severe plastic deformation and consequently, mechanical properties of composite improved. In this regard, the hardness improved from 373 HV after SPS to 536.5 HV after two passes of SSE for composite reinforced by 0.1% RGO; moreover, tensile strength enhanced up to 969 MPa. This nanocomposite might be utilized in diverse fields, particularly in bio applications.

In the present study, a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion (HPT) process under a pressure of 7.5 GPa up to 10 revolutions. Experimental results revealed that the microhardness of Ti6Al4V was increased remarkably by about ∼ 41% and saturated at about 432 Hv after the HPT process. A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about 52.7 nm was obtained eventually, and no obvious formation of metastable ω phase was detected by XRD analysis. For the first time, the tribological properties of the HPT processed Ti6Al4V alloy were investigated by a ball-on-disc test at room temperature under a dry condition. It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy. With increasing the number of HPT revolutions, both friction coefficient and specific wear rate were obviously decreased due to the reduction of abrasion and adhesion wears. After being deformed by 10 HPT revolutions, the friction coefficient was reduced from about 0.49 to 0.37, and the specific wear rate was reduced by about 48%. The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.

Gradient materials can achieve both external strengthening and internal toughening, which has great potential to break the strong plastic tradeoff. Titanium carbide (TiC) particle is conducive to form a wearable surface in biomedical Titanium (Ti) alloy. In this work, gradient TiC/Ti6Al4V composites were successfully prepared by friction stir processing (FSP). Microstructure, texture and mechanical properties of the material were systematically characterized. Scanning electron microscopy (SEM) showed that the equiaxed grains near the machined surface were transformed into elongated grains inside. The results of energy spectrum analysis (EDS) showed that there was element aggregation near TiC particles. X-ray diffraction (XRD) indicated martensitic transformation in the stir zone and in the transition zone. The results of nano indentation showed that the hardness of stir zone was higher. In order to promote recrystallization and improve the hardness of the transition zone, high temperature rapid heat treatment was carried out after FSP. When the sample was heated at 700°C and cooled in the furnace, the hardness increased to the maximum. In the process of rapid heating, the dissolution of elements near TiC particles also led to the increase of hardness. This study provides a new idea for surface modification of gradient titanium alloy by using FSP method to improve its mechanical properties.

The aim of this study was to investigate the effects of severe plastic deformation (SPD) and thermal treatment on the nanostructure and properties of the anodic oxide layer of AA6063. SPD was conducted using up to 6 passes of equal channel angular pressing (ECAP) which was followed by post-deformation aging treatment. Two-step anodization via hybrid pulse voltage was utilized to form highly ordered anodic coatings. Positive pulse and reverse pulse modes were used for the first and second steps of anodization, respectively. Nanostructure, uniformity, porosity, roughness, micro hardness and brightness of the anodic oxide layers were investigated. It was found that with increasing deformation, the size of intermetallic particles decreased which improved the order and uniformity of the Al2O3 layer. This was attributed to increasing micro- and nano-scale orders of anodic structure. The micro-scale order of anodic structure increases due to high density of grain boundaries after SPD. With increasing deformation, two-dimensional ordering in micro and nano-scales was observed. In addition, micro hardness and brightness of coatings were increased and the roughness and porosity were decreased. This may be due to the fact that a more uniform current can establish between anode and cathode during anodization of samples with more significant deformation which leads to uniform and highly ordered anodic layers. In addition, application of aging treatment leads to higher non-uniformity in established current and causes reduced ordering and uniformity of anodic layer in addition to enhanced roughness and porosity and reduction in brightness.

To have an insight into the occurrence of inverse Hall-Petch relationship in ultrafine-grained (UFG) aluminum alloys produced by severe plastic deformation (SPD), ultra-SPD (i.e. inducing several ten thousand shear strains via high-pressure torsion, HPT) followed by aging is applied to an Al-La-Ce alloy. Average nanograin sizes of 40 and 80 nm are successfully achieved together with strain-induced Lomer-Cottrell dislocation lock formation and aging-induced semi-coherent Al11(La,Ce)3 precipitation. Analysis of hardening mechanisms in this alloy compared to SPD-processed pure aluminum with micrometer grain sizes, SPD-processed Al-based alloys with submicrometer grain sizes and ultra-SPD-processed Al-Ca alloy with nanograin sizes reveals the presence of two breaks in the Hall-Petch relationship. First, a positive up-break appears when the grain sizes decrease from micrometer to submicrometer which is due to extra hardening by solute-dislocation interactions. Second, a negative down-break and softening occur by decreasing the grain sizes from submicrometer to nanometer which is caused by weakening the dislocation hardening mechanism with minor contribution of the inverse Hall-Petch mechanism. Detailed analyses confirm that nanograin formation is not necessarily a solution for extra hardening of Al-based alloys and other accompanying strategies such as grain-boundary segregation and precipitation are required to overcome such a down-break and softening.

Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes. This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments: pre-deformation artificial ageing or post- deformation natural ageing. For this purpose, microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement. Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing. For instance, the yield strength of the alloy increases to more than 400 MPa, about one-third greater than the counterpart amount after the usual T6 treatment. This superlative strength mainly occurs due to refinement of grains, an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing. Considering the applied models, it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.

Single-phase Al–Mg alloys processed by severe plastic deformation (SPD) usually suffer from unsatisfactory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening. In the present work, an Al–7Mg alloy prepared by equal-channel angular pressing (ECAP) possessed markedly enhanced thermal stability upon annealing at moderate to high temperatures (200–275 ℃), compared with those ultrafine-grained dilute Al–Mg alloys with a uniform microstructure. The enhanced thermal stability is due primarily to the multimodal grain structure consisting of nano-, ultrafine- and micron-sized grains, strong segregation and/or clusters of Mg solute along grain boundaries (GBs), and Al3Mg2 precipitates formed during annealing. First, extensive recovery predominates over recrystallization and consumes most of the stored energy in the ECAPed Al–7Mg alloy annealed at ≤ 275 ℃, leading to the recrystallization and growth of nano/ultrafine grains being retarded or postponed. Moreover, Mg solute segregation and/or clusters along GBs of nano/ultrafine grains could further suppress grain growth via diminishing GB energy and dragging GBs efficiently. In addition, Al3Mg2 precipitates formed with increasing annealing time could inhibit grain growth by pinning GBs. The present multimodal-grained Al–7Mg alloy with enhanced thermal stability is believed to be particularly attractive in potential engineering applications at moderate to high temperatures.

Severe plastic deformation is known to induce grain refinement and gradient structure on metals’ surfaces and improve their mechanical properties. However, the fundamental mechanisms behind the grain refinement and micromechanical properties of materials subjected to severe plastic deformation are not still well studied. Here, ultrasonic surface rolling process (USRP) was used to create a gradient microstructure, consisting of amorphous, equiaxed nano-grained, nano-laminated, ultrafine laminated and ultrafine grained structure on the surface of TB8 β titanium alloy. High energy and strain drove element co-segregation on sample surface leading to an amorphous structure during USRP processing. In situ transmission electron microscope compression tests were performed in the submicron sized pillar extracted from gradient structure and coarse grain, in order to reveal the micromechanics behavior of different grain morphologies. The ultrafine grained layer exhibited the lowest yield stress in comparison with single crystal and amorphous-nanocrystalline layers; the ultrafine grained layer and single crystal had an excellent strain hardening rate. The discrepancy among the grain sizes and activated dislocation sources led to the above mentioned different properties. Dislocation activities were observed in both compression test and microstructure evolution of USRP-treated TB8 alloy. An evolution of dislocation tangles and dislocation walls into low angle grain boundaries and subsequent high angle grain boundaries caused the grain refinement, where twinning could not be found and no phase transformation occurred.

Magnesium (Mg) alloys despite being the ideal candidate for structural applications, owing to their high specific strength and low density, are not widely used due to lack of active slip systems at room temperature in their hexagonal close-packed crystal structure, eliciting poor ductility and formability. Amongst the various series of Mg alloys, the AZ and ZK series alloys have been standouts, as they inherit better room temperature strength and flow characteristics through their solute elements. Grain refinement, as well as eliminating casting defects through metal processing techniques are vital for the commercial viability of these alloys since they play a key role in controlling the mechanical behaviour. As such, this review highlights the effect of different Bulk-deformation and Severe Plastic Deformation techniques on the crystal orientation and the corresponding mechanical behaviours of the AZ31 alloy. However, every process parameter surrounding these techniques must be well thought of, as they require specially designed tools. With the advent of finite element analysis, these processes could be computationally realized for different parameters and optimized in an economically viable manner. Hence, this article also covers the developments made in finite element methods towards these techniques.

The influence of particle size and morphology on grain refinement in low stacking fault energy (SFE) alloys was studied by comparing the grain structures in single- and multi-phase Al-bronze (AB) alloys following equal channel angular pressing (ECAP) between 350 and 500 °C. In particular, nickel aluminium bronze (NAB) was chosen as it contained both coarse and fine rounded particles, as well as a lamellar phase which evolved during ECAP. Grain refinement in the single-phase alloy was achieved through dynamic recrystallisation initiated at deformed twin boundaries. By contrast, different mechanisms were observed in the particle-containing NAB. Recrystallisation around the coarse κII particles (∼5 μm) was promoted through particle stimulated nucleation (PSN), whereas recrystallisation in the region of the fine κIV (∼0.4 μm) was delayed due to the activation of secondary slip. Grain refinement in areas of the lamellar κIII showed significant variation, depending on the lamellar orientation relative to the shear plane of ECAP. As the lamellae deformed, numerous high angle grain boundaries were generated between fragments and served as nucleation sites for recrystallisation, while PSN occurred around spheroidised lamellae. The spreading of the κIII particles by ECAP then enhanced the total area of recrystallised grains.

Friction self-piercing riveting (F-SPR) is an emerging technique for low ductility materials joining, which creates a mechanical and solid-state hybrid joint with a semi-hollow rivet. The severe plastic deformation of work materials and localized elevated temperatures during the F-SPR process yield complex and heterogeneous microstructures. The cut-off action of the work materials by the rivet further complicates the material flow during joint formation. This study employed the F-SPR process to join AA7075-T6 aluminum alloy sheets and systematically investigated the microstructural evolutions using electron backscatter diffraction (EBSD) techniques. The results suggested that as the base material approached the rivet, grains were deformed and recrystallized, forming two distinct fine grain zones (FGZs) surrounding the rivet and in the rivet cavity, respectively. Solid-state bonding of aluminum sheets occurred in the FGZs. The formation of FGZ outside the rivet is due to dynamic recrystallization (DRX) triggered by the sliding-to-sticking transition at the rivet/sheet interface. The FGZ in the rivet cavity was caused by the rotation of the trapped aluminum, which created a sticking affected zone at the trapped aluminum/lower sheet interface and led to DRX. Strain rate gradient in the trapped aluminum drove the further expansion of the sticking affected zone and resulted in grain refinement in a larger span.

Turning is a machining process extensively applied to produce revolution parts. Durability of these parts are known to depend on the turning process signature that is often referred as surface integrity. The surface integrity generated in a fillet radius has been barely studied in the literature so far, despite the well-known geometrical stress concentration factor of such singularities. Therefore this paper deals with the investigation of machining-induced surface integrity when turning a fillet radius in a 316L austenitic stainless steel. Different characterization methods are used for that purpose - SEM, EBSD, nanoindentation and X-Ray diffraction. It points out that the turning-induced consequences are not homogeneous along the machined profile. Residual stresses are strongly affected and microstructure is highly modified over a depth of 80 μm that leads to a mechanical properties gradient. It is evidenced that the average uncut chip thickness is the main governing parameter regarding surface integrity. It is also reported that deformation twins appear in the affected zone. It highlights that turning-induced microstructure evolution at a given depth is rather a consequence of severe plastic deformation at high strain rate than dynamic recrystallization.

Severe plastic deformation (SPD)-induced gradient nanostructured (GNS) metallic materials exhibit superior mechanical performance, especially the high strength and good ductility. In this study, a novel high-speed machining SPD technique, namely single point diamond turning (SPDT), was developed to produce effectively the GNS layer on the hexagonal close-packed (HCP) structural Mg alloy. The high-resolution transmission electron microscopy observations and atomistic molecular dynamics simulations were mainly performed to atomic-scale dissect the grain refinement process and corresponding plastic deformation mechanisms of the GNS layer. It was found that the grain refinement process for the formation of the GNS Mg alloy layer consists of elongated coarse grains, lamellar fine grains with deformation-induced-tension twins and contraction twins, ultrafine grains, and nanograins with the grain size of ∼70 nm along the direction from the inner matrix to surface. Specifically, experiment results and atomistic simulations reveal that these deformation twins are formed by gliding twinning partial dislocations that are dissociated from the lattice dislocations piled up at grain boundaries. The corresponding deformation mechanisms were evidenced to transit from the deformation twinning to dislocation slip when the grain size was below 2.45 μm. Moreover, the Hall-Petch relationship plot and the surface equivalent stress along the gradient direction estimated by finite element analysis for the SPDT process were incorporated to quantitatively elucidate the transition of deformation mechanisms during the grain refinement process. Our findings have implications for the development of the facile SPD technique to construct high strength-ductility heterogeneous GNS metals, especially for the HCP metals.

For the first time, the novel combination of multi-pass equal channel angular extrusion/pressing (ECAE/P) and selective laser melting (SLM) was investigated. Herein, four passes of ECAP via route Bc at 150 °C were applied as a severe plastic deformation (SPD) technique on the SLM as-built AlSi12 to promote superior mechanical properties. The microstructure and mechanical behavior of AlSi12 fabricated by SLM were studied before and after ECAP, applying several mechanical and microstructural characterization techniques. Results of the tensile experiments revealed that the yield point, the ultimate strength, and the ductility of the as-built sample were improved by 56%, 11%, and 55% after 4 passes of ECAP, respectively. This enhancement is attributed to the effective grain refinement and the persisting silicon phase network after SPD as evidenced by electron backscatter diffraction and elemental mapping results. Moreover, micro-computed tomography analysis disclosed that ECAP considerably reduces the remnant porosity of the post-treated SLM AlSi12 samples eventually further affecting the strength of the ultra-fine grained AlSi12 in a positive way. Findings presented herein indicate that it is viable to utilize ECAP as a post-AM processing tool for mechanical property improvement of laser powder bed fused microstructures with the virtue of enhanced densification. Even if geometrical restrictions exist in ECAP, results obtained herein are transferrable to other SPD techniques with suitable processing windows, which would pave the way to advanced properties of adequately post-treated conditions.

The constraint groove pressing (CGP) is a severe plastic deformation (SPD) method for producing ultra-fine grained sheet metals. Firstly, the present study reports the effect of CGP on mico-hardness, tensile strength, and grain size in the multi-pass CGP of aluminium and copper. The aluminium and copper sheets are processed up to two passes. The improvement in tensile strength and hardness after every pass due to grain size reduction is reported. Further, an empirical model that correlates residual stresses and grain size is established. The residual stresses were measured by X-ray diffraction (XRD) and layer removal technique along the thickness of the samples. Moreover, the effect of residual stress nature on mechanical properties is investigated. It is found that the micro-hardness of the sheet depends on the nature of residual stress. Finally, a finite element (FE) model is constituted to predict the stresses, deformation, and residual stresses after every pass. This FE model can be used for exploring possibilities of improving the process capability of CGP by examining conditions not evaluated during experiments. The residual stress, Von Mises stress, deformation were decreased with the decrease in grain size up to two passes.

New fields of application are coming along at an outstanding pace for cold spray deposition. More recently cold spray is being introduced as an additive manufacturing method that supersonically accelerates microparticles to induce bonding via severe plastic deformation. However, the thriving of cold spray as a widespread additive manufacturing technology with high production rates is still limited by inadequate geometrical control of the deposit shape. Thus, to establish cold spray in the additive manufacturing sector, substantial development is still required regarding digitalization and automatization of the process. To take a further step towards gaining control on the deposit geometry, present study reports the development of a 3D model able to simulate the cold spray deposit profile. The physical basis of the model is represented by a partial differential equation, which describes the deposit profile evolution as the number of passes grows. The model offers total freedom regarding the choice of the nozzle trajectory and the substrate geometry. The effects of the various process parameters, namely the number of scanning passes, spray angle, scanning speed and stand-off distance are implemented and realistically reflected in the model. More complex conditions like superimposed tracks with different spray angles, curved substrates, shadow effect and non-Gaussian profiles have been effectively simulated. The developed model has been validated with a wide range of experiments, demonstrating high accuracy and notable potential to promote the digitalization of cold spray additive manufacturing.

Capability of a novel severe plastic deformation (SPD) method of hydrostatic cyclic extrusion compression (HCEC) for processing of hcp metallic rods with high length to diameter ratios was investigated. The process was conducted in two consecutive cycles on the AZ91 magnesium alloy, and microstructural evolution, mechanical properties and corrosion behavior were investigated. The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods. Its ability in improving strength and ductility simultaneously was also shown. The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen, respectively. Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%. The potentials derived from the polarization curves were high and the currents were much low for the processed samples. Also, the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples. The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC. HCEC is a unique SPD method, which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.

Journal of materials research and technology 12, 1235 - 1242 (2021). doi:10.1016/j.jmrt.2021.03.073, Initial powder mixtures of Cu, Fe and Co are exposed to severe plastic deformation by high-pressure torsion to prepare solid solutions. A broad range of compositions is investigated, whereas this study aims at the synthesis of soft magnetic materials and therefore at the formation of a homogeneous and nanocrystalline microstructure. For intermediate ferromagnetic contents, high-pressure torsion at room temperature yields single-phase supersaturated solid solutions. For higher ferromagnetic contents, two consecutive steps of high-pressure torsion deformation at different temperatures yield the desired nanocrystalline microstructure. Depending on the Co-to-Fe-ratio, either a single-phase supersaturated solid solution or a nanocomposite forms. The composite exhibits an enhanced magnetic moment, indicating the formation of a (Fe,Co)-alloy upon severe plastic deformation. Soft magnetic properties are verified for large Co-to-Fe-ratios and this microstructure is found to remain stable up to 400 ��C., Published by Elsevier, Rio de Janeiro

An austenitic stainless steel was processed by high-pressure torsion, and formed a hierarchical nanostructure with ultrafine grains, ultrafine-precipitates, nano-twins and high densities of dislocations. As a result, the hierarchical nanostructure contributes collectively to the double hardness value of the austenitic stainless steel (514 ± 44 HV) in comparison to the coarse-grained counterpart (217 ± 11 HV). Both the nanostructural hierarchy and high hardness can be maintained at the temperatures up to ~600 °C. Annealing treatment at temperatures from 400 to 600 °C may induce recovery to the hierarchical nanostructure, resulting in a reduced microstructural heterogeneity and increased hardness for the high-pressure torsion processed steel.

A comparative study of the structure and mechanical behavior of an Al−5Mg−0.18Mn−0.2Sc−0.08Zr− 0.01Fe−0.01Si (wt.%) alloy ingot subjected to multidirectional isothermal forging (MIF) to a strain of 12 or equal-channel angular pressing (ECAP) to a strain of 10 at 325 °C, and subsequent warm and cold rolling (WR and CR) at 325 and 20 °C, was performed. The results showed that the MIF process of ultrafine-grained structure with a (sub)grain size dUFG=2 µm resulted in enhanced room-temperature ductility and superplastic elongation up to 2800%. Further grain refinement under WR as well as development of a heavily-deformed microstructure with high dislocation density by subsequent CR resulted in a yield/ultimate tensile strength increase from 235/360 MPa after MIF to 315/460 and 400/515 MPa after WR and CR, respectively. Simultaneously, WR led to improved superplastic elongation up to 4000%, while after CR the elongation remained sufficiently high (up to 1500%). Compared with MIF, ECAP resulted in more profound grain refinement (dUFG=1 µm), which promoted higher strength and superplastic properties. However, this effect smoothed down upon WR, ensuring equal properties of the processed sheets. CR of the ECAPed alloy, in contrast, led to higher strengthening and slightly better superplastic behavior than those after CR following MIF.

Ultrafine-grained alloys fabricated by severe plastic deformation (SPD) have high strength but often poor uniform ductility. SPD via high-ratio differential speed rolling (HRDSR) followed by an annealing treatment was applied to Al0.5CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be achieved. The optimized microstructure was composed of an ultrafine-grained FCC matrix (1.7–2 μm) with a high fraction of high-angle grain boundaries (61 %–66 %) and ultrafine BCC particles (with a size of 0.6–1 μm and a volume fraction of 8 %–9.3 %) distributed uniformly at the grain boundaries of the FCC matrix. In the severely plastically deformed microstructure, the nucleation kinetics of the BCC phase was accelerated. Continuous static recrystallization (CSRX) took place during the annealing process at 1273 K. Precipitation of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC grains . The precipitation of the hard and brittle σ phase was, however, suppressed. The annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14 %–20 %. These tensile properties are comparable to those of transformation-induced plasticity steel. Strengthening mechanisms of the severely plastically deformed alloy before and after annealing were identified, and each strengthening mechanism contribution was estimated. The calculated results matched well with the experimental results.

Peridynamics was originally developed to model spontaneously emerged discontinuities such as crack propagation and progressive failure. In this paper, contrary to typical peridynamic applications in the realm of modeling of discontinuities, a modeling approach is proposed in the framework of non-ordinary state-based peridynamics to simulate impact-driven solid-state welding processes that can effectively join a wide variety of similar and dissimilar combinations of materials. A scheme to model formations of metallurgical bonds resulting from severe plastic deformation due to high-velocity impact is developed in virtue of peridynamic bonds. The proposed model is of combined Lagrangian-Eulerian nature, given that nonlocal interactions are established on both reference and deformed configurations. Impact bonding processes of single- and bi-material joints are successfully simulated and validated. Distinctive morphological features of bonding interface are reproduced. Effectiveness and robustness of the proposed modeling approach are demonstrated by a numerical study of influences of processes variables on the morphology and stability of interface features.

A new severe plastic deformation (SPD) technique for improvement of the metallurgical properties of the magnesium alloys is presented. In this process, a cyclic extrusion compression angular pressing (CECAP) process is followed by an extrusion step in the outlet playing the role of additional back pressure. Therefore, more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing (ECAP). In order to evaluate the effectiveness and capabilities of this new method, an AM60 magnesium alloy was processed. Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method. In addition, ~110% increase in compressive stress was observed in new method compared to the conventional ECAP. Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refined β-phase along the boundaries. It may be concluded that the new process is very promising for future magnesium alloy products.

An equal channel reciprocating extrusion (ECRE) was proposed first to obtain a severe plastic deformation (SPD) of 7005 alloy. The microstructure and mechanical properties of one-pass ECREed (ECRE processed) 7005 alloy were investigated. The results show that SPD occurring in ECRE leads to a mixed microstructure. ECREed 7005 alloy exhibits a significant improvement of ultimate tensile strength (UTS) and elongation. Mechanical properties in the region undergoing a complete ECRE process are higher than those in the region undergoing an incomplete ECRE process due to larger dislocation strengthening effect. Yield strength (YS) and UTS first decrease and then increase with an increase of extrusion temperature. The YS of 359.2 MPa, UTS of 490 MPa and elongation of 17.7% are obtained after T6 treatment. Fine-grain strengthening, dislocation strengthening and precipitation strengthening in the T6-treated ECREed sample all play important roles in improving the mechanical properties.

The influence of severe plastic deformation by torsion in the Bridgman anvil on the lattice parameters of pure ferromagnetic metals Ni and Co is investigated by x-ray diffraction analysis. It is shown that torsion combined with strong compression leads to decrease in the lattice of these metals and to the change in the level of crystal lattice microstrains. The mechanisms of deformation influence on the lattice parameters are proposed.

Joining of dissimilar materials with different thicknesses in automobile and shipbuilding industries by conventional arc welding methods is a challenge due to unequal stress distribution during welding. The problem of imbalanced stress can be reduced or avoided in solid state welding methods. In the present work, aluminium alloys of dissimilar thickness are joined by Friction stir spot welding, FSSW. The feasible welding conditions were determined by Response surface methodology. The maximum strength of 6.204 kN was obtained at 1000 RPM, 0.02 mm/s plunge speed and thread pin profile. The rotational speed was identified as the vital parameter that influenced the joint strength by analysis of variance. The Artificial neural network was used to predict the mechanical strength of the weld joints. The microstructure analysis revealed that tool profile significantly influenced the hook shape. The microhardness survey revealed that the stir zone hardness was higher than the hardness at the heat-affected zone due to severe plastic deformation.

Equal channel angular pressing (ECAP), is a proven manufacturing technique that produces ultrafine-grained structure (UFG) accompanied by various property enhancements of the material such as coherent interface and high shear bonding. The exceptional feature that separates this process with other joining processes is the advantage of having isotropic microstructural grain distribution along with the joining layer of the two dissimilar metals, with that as a motive the focus was given to the bonding of MgAZ31B and AA6082 through ECAP but the process failed to meet the expected objectives. The reasons for failure were analyzed and recorded that the difference in material ductility caused the bonding failure of the two dissimilar metals. The second part of the article deals with the severe plastic deformation of Al 6061 as the ECAP specimen based on its mechanical properties and applications in industries. Al 6061 samples were processed up to two passes of ECAP in an acute angle die and were characterized. Route B produced maximum strength enhancement compared to Route A. Microstructural investigation was carried out to identify the reason for the difference in the results of both the routes.

Deformation-induced grain-growth in nanocrystalline materials is a widely-reported phenomenon that has been attributed to grain boundary (GB) processes. In this paper, we report on the opposite phenomenon, wherein a stable nanocrystalline (NC) Cu-Ta alloy undergoes a further refinement of the nano-grains during severe plastic deformation (SPD). SPD up to 250% results in a significant grain-size reduction despite the 350°C increase in temperature caused by the deformation process. Experiments and atomistic-simulations show that this unexpected grain-refinement is a direct result of well-dispersed Ta-nanoclusters throughout grain centers and along GBs acting as kinetic-pinning agents and suppressing GB processes that occur during recrystallization.

Severe Plastic Deformation (SPD) processes bring about phenomenal grain refinement, by imparting plastic strain onto the materials being processed, owing to which significant improvements in mechanical properties are brought about. While plenty of processes exist for processing bulk materials, the direct utilization of such materials is very limited. Tubular materials buy enlarge are some of the most widely used form of industrial products and this work reviews the SPD techniques that are available for processing tubular materials. Considering the extent to which tubular materials are used, the lack of wide range of SPD techniques to process them is very unfortunate. A systematic review of process methodology of these SPD techniques which process tubular materials and the impact of such processing on mechanical properties of the materials is made. The review is aimed at providing the readers with a design thinking that would enable the readers to adopt the SPD techniques that they are familiar with into something that would process tubular materials. SPD processed tubes, with strengthened walls, of course could have a reduced thickness amounting to materials savings. Such savings would not only result in cost savings but also would lead to sustainability.

Equal-channel angular pressing (ECAP) is one of the emerging Severe plastic deformation (SDP) technique that makes ultra-fine grains (UFG) microstructure to improve the properties of different materials and composites. The uniqueness of the ECAP technique is that it can refine the grain size without changing the cross-section. Many factors like processing temperature, number of ECAP passes, die channel angle and processing route affects the results obtained from ECAP technique. This review is mainly focused on the mechanical and microstructural properties of aluminium alloys generated after ECAP Process along with number of passes. It is observed as the number of passes increased the hardness and tensile strength of the alloy increase and ductility of the material is reduced. The maximum percentage of grain refining is obtained in the first two or three passes after that no significant changes were observed because the effect of temperature is more than the effect number of passes on the grain size.

The gas turbines are the components which are commonly affected by severe high-temperature erosion wear due to impingement of solid particles entrained in the stream of fluid. The present investigation focuses on the applicability of plasma sprayed coatings for turbines by improving the erosion resistance of the base material. The present work includes high-temperature solid particle erosion behaviour of [35%(WC-Co)/65%(Cr3C2NiCr), [70%NiCrAlY + 30%TiO2] & [70%NiCrAlY + 25%Cr2O3 + 5%YSZ] coatings deposited by atmospheric plasma spray (APS) process. All the coating materials are considered by weight (%). The effect of impact angle on erosion performance of uncoated and coated specimens were comparatively studied by using the air-jet erosion tester (ASTM G76-13). The eroded surface morphology was analysed by using a porosity tests, microhardness values, scanning electron microscopy & X-ray diffraction analysis. All Coatings exhibits the ductile erosive mechanism at the temperature of 700 °C with severe plastic deformation. The NiCrAlY + TiO2 coating is more protective than the other two coatings in high temperature and erosion environments due to its higher ductility, homogenous microstructure, and lesser porosity of the coatings. However, uncoated MDN 420 steel exhibits lesser wear loss when compared to the coated substrates. This may be due to the alumina particles' embedment onto the coated surface, which might present a shielding effect against further material loss to occur.

Equal-channel angular pressing (ECAP) is also known as Equal-channel angular extrusion (ECAE) process. ECAP is a Severe plastic deformation process which can produce ultrafine grains with superior mechanical properties. There is a very significant role of number of passes in the ECAP process, mechanical properties and grain refining is depending on it. This study is focused on the influence of the number of passes and processing routes on hardness, tensile strength and elongation of different alloys, so only mechanical properties are mentioned under this review. Among all the processing route of the ECAP process, BC route shows the maximum strength. Some limitations or disadvantages related to the ECAP process are also discussed in this study.

In comparison with normal monolithic materials, composite materials are having many advantages and are widely used in the present-day technologies for various applications. The current work is to prepare metal matrix composites of Si3N4 reinforced Al6061 by stir casting technique and subjecting the composites to Severe Plastic Deformation (SPD) through Equal Channel Angular Pressing (ECAP) for 3 passes and to study the tribological characteristics of Al6061-Si3N4 composites. By changing the reinforcement percentage from 0 to 4% in the increments of 1%, the Aluminium Metal Matrix composites (AMCs) are fabricated. As the reinforcement percentage and the number of passes increased, the deformation load also increases making the specimens to undergo more and more strain hardening. The wear test has been performed on the specimens for speeds 100, 200 and 300 rpm at 10 N, 20 N and 30 N loads. The specimen has exhibited an increase in both hardness and wear resistance.

The effect of ultrasonic surface rolling process (USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-centered cubic structure. Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base material, which was attributed to the presence of gradient structure surface layers. Five subsequent USRP passes resulted in the highest fatigue strength, due to the optimal surface properties including higher extent of grain refinement, larger compressive residual stresses, “smoother” surface morphology and increased micro-hardness. However, the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys (for example, Ti6Al4V), which was attributed to the notable surface residual stresses relaxation revealed from measurements on post-fatigued USRP samples. Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor. Small cracks were found to propagate into the core material in a mixed transgranular and intergranular mode. Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.

During the many years, severe plastic deformation study carried out based on processes appropriate for sheet and solid materials. However, the review to study the SPD methods suitable for nanostructure tube yet not done. So, efforts have been put to review and develop effective SPD processes suitable for producing cylindrical tubes. Severe plastic deformation is recognized to be the paramount technique for manufacturing bulk ultrafine-grained and nanostructured materials with high strength and hardness. The present study is about the state-of-the-art review on different SPD methods suitable to produce ultrafine-grained and multilayer nanostructured tubes. This study also reveals the impact of various tube SPD methods on the material properties of the tube. The comparison between them based on the advantages and disadvantages of SPD techniques are done based on the viewpoints of processing and properties. Also, find out the literature review gap for a more detail study on a multilayer nanostructured tube.

Cold gas dynamic spraying is a relatively new coating technology in which coatings are produced by spraying metal powders at high velocity. This generates particle–substfrate bonding through severe plastic deformation at temperatures, well below the melting point of the powders. In the present study corrosion resistant nickel coatings were produced on preheated mild steel substrates by cold spraying. The substrate deposition temperature was varied systematically and post fabrication annealing was introduced to reduce the deposition impact stress. Post deposition heat treatment, although improved the interfacial bonding, lead to increased corrosion due to increase in porosity of the samples. Coatings deposited at low temperatures (∼500°C) provide the best corrosion resistance as evidenced through their microstructure.

The current paper shows the various characteristic features of aluminum and its alloys that have an extensive use in material science and manufacturing processes. These aluminum based alloys possess numerous applications due to their mechanical and interfacial properties which include strength-to-weight ratio, fatigue, hardness, density, equivalent strain, and toughness. The adequate process of obtaining fine equiaxed grains in aluminum alloys is Multi-axial forging (MAF) or Multi-directional forging (MDF). This is one among the various severe plastic deformation (SPD) processes that is used to bring about grain refinement. In Multi-directional forging, each sample is initially forged in one direction and then it is rotated by 90°and forged in that direction, this constitutes a pass. Alternate forging of these alloys takes place in order to achieve bulk grain refinement. This paper carefully attempts to grab the attention of the viewer to Multi-directional forging technique and to bring about a review on the present findings and a research on the ongoing aspects of Multi-directional forging.

This review paper mainly focused on microstructural and mechanical properties ofultrafine grained nanocrystalline (Nc) Magnesium alloy fabricated by Severe Plastic Deformation(SPD) process. The influence of SPD over mechanical, microstructural, physical, optical, and corrosion properties of Nanocrystalline magnesium alloy are detailed and discussed. It has been observed that nanocrystalline (Nc) magnesium materials has shown superior properties over the bonding of grains while during the Extrusion, Annealing, quenching, Normalizing, Spark Plasma Sintering (SPS) processes. The outcome based by many researchers showed that nanocrystalline Magnesium alloy processed by Severe Plastic Deformation (SPD) showed an improved properties over the Hardness, Dislocation density, Compressive, Tensile and texture, and it’s found to be increased up to certain limit beyond that decrease of microstructural stability, micro hardness and dislocation density were seen to be observed. The Microstructural and Mechanical properties are well improved by Spark Plasma Sintering (SPS), Extrusion, Annealing, Equal channel angular pressing (ECAP), Accumulative Roll Bonding (ARB) and High-Pressure Torsion (HPT) processes. Grain growth Mechanism, Energies Activation during grain growth, Thermal stability, Relative density and stress corrosion rate were observed by previous Researchers during Fractography analysis over several nanocrystalline (Nc) Magnesium alloy specimens.

Friction stir welding (FSW) employs a tool that does not require any filler materials; frictional heat is produced and performs a solid-state joining method. Severe plastic deformation causes to join similar and dissimilar materials without melting the workpiece at the welding line. Friction stir welding is the most recent friction welded joining processes with the most surprising features when welding various metal alloys, including magnesium, aluminium, copper, and steel. FSW is victorious of all the other conventional welding methods implied in many industrial applications like automobile, aerospace, fabrication, shipping, marines and robotics. It gives high-quality welds, energy input, and distortion are lower, better retention of mechanical properties; it is eco-friendly and can be performed less operating cost. This research work aims at the FSW process in Al-Cu alloys, highlighting:(a) Optimizing the welding process parameters, welding feed rate, tool rotation speed, (b) Evaluation of Electrical Conductance properties of joints, (c) Mechanical properties and metallography characteristics of joints.