Severe Plastic Deformation Research Articles

A profound study of damage behavior for Al 2024-T3 alloy worksheet produced by constrained groove pressing in the superior practical condition

Constrained groove pressing (CGP) process is one of the most efficient and novel methods of severe plastic deformation to manufacture ultra-fine sheet metal. The present research work is related to the study of CGP process of 2024-T3 Aluminum alloy sheet. The empirical and numerical simulation of CGPed- specimens have been examined at both room and elevated temperatures. In order to simulate the constrained groove pressing process in Abaqus software, the Johnson–Cook material model has been employed. The geometrical variables of the CGP process include the teeth number, teeth angle, and sheet thickness, and the criterion for the superiority of the numerical test is the maximum reduction of two equivalent strain and equivalent force factors, simultaneously. To determine the weight’s coefficients of the target factors and select the superior test, the Shannon’s Entropy and Simple Additive Weighting (SAW) methods have been used, respectively. After validating the numerical findings, the variation of damage parameter, stress triaxiality and the equivalent plastic strain distribution in the superior practical condition have been evaluated in detail. Based on the Entropy-SAW hybrid technique, the weight’s coefficients of equivalent strain and equivalent force target factors were computed to, in turn, 0.38 and 0.62. Also, the results revealed that the CGP process could not be performed at room temperature based on high damage evolution. But, at elevated temperature, the damage parameter (D) doesn't exceed 0.26. Also, the maximum stress triaxiality and equivalent plastic strain (PEEQ) at this process temperature reached to 0.5 and 0.1, respectively.

Synthesis of an Ultra-high Hardness Nanostructured AlSi10Mg Alloy via A Hybrid Laser Powder Bed Fusion/High-Pressure Torsion Approach

The hybrid combination of laser powder bed fusion (L-PBF) and high-pressure torsion, respectively an additive manufacturing (AM) and severe plastic deformation (SPD) has recently emerged as an important field of study due to the ability to produce novel nanostructured metals/alloys with simultaneous enhancements in mechanical (hardness, yield and tensile strengths) and functional (corrosion and wear) performances. Pioneering studies on the hybrid L-PBF/HPT approach was focused on 316L stainless steel (316L SS) and AlCuMg alloys due to their widespread engineering applications. AlSi10Mg, an alloy widely used in the automotive industry is expected to benefit from this hybrid combination but has not been investigated before. Thus, this study aims to investigate the microstructural features and hardness of the nanostructured AlSi10Mg attained by the hybrid L-PBF/HPT technique via transmission electron microscopy (TEM) and Vickers microhardness (HV) measurements, respectively. The results showed novel microstructures, including nano-scale grain sizes (< 200 nm), nano-sized Mg2Si precipitates (~200 nm), and dense dislocation networks. The average hardness value was determined as 230 ± 20 HV, homogeneously distributed throughout the disk surface as indicated by the low deviation (error bar). The microstructures of L-PBF/HPT-synthesised AlSi10Mg are different and significantly refined than conventionally cast AlSi10Mg, which contributed to the two- to four-fold hardness (typical HV values of as-cast AlSi10Mg ranges from 60 – 68 HV) increase via grain boundary and dislocation strengthening mechanisms.

On the fatigue crack growth behavior of nanocrystalline CrMnFeCoNi

The fatigue crack growth (FCG) behavior of the equimolar CrMnFeCoNi Cantor-alloy in the nanocrystalline grain size regime has been explored with special focus on the influence of specimen orientation and the effect of additional heat-treatments. For the synthesis severe plastic deformation using high-pressure torsion (HPT) was used. The results were critically discussed regarding the impact of grain size on the FCG-behavior and compared to a conventional 316L stainless steel in the nanocrystalline state: The reduction of grain size in the Cantor alloy from the micrometer to the nanometer regime invokes crack growth rates being about one order of magnitude higher paired with significantly lower threshold values. Furthermore, the sensitivity of thresholds and crack growth rates in the Paris regime on the applied load ratio in the NC material state is also profoundly reduced. This can be explained based on a diminishing contribution of crack closure effects, especially roughness induced closure. Even though the chemical composition differs distinctively, the crack growth rates and fatigue threshold values of the nanocrystalline Cantor alloy and the stainless steel are comparable with the latter being slightly lower for the CrMnFeCoNi alloy. Moreover, the extent of anisotropy is more pronounced than for 316L. Heat-treatment leading in the NC-Cantor alloy to an increasing hardness, has also an effect on the FCG-rate and depends on the specimen orientation. In addition, an unusual self-annealing behavior affecting the FCG behavior of the Cantor alloy was found.

Adapting Conductivity and Mechanical Properties through Layer Thickness Variation in Copper Niobium Laminated Metallic Composites

Cu/Nb laminated metallic composites (LMCs) exhibit extraordinary mechanical strength while electrical conductivity is maintained at a high level. In this research, Cu‐based LMCs with varying volume fraction of niobium are produced via accumulative roll bonding (ARB) and additionally cold‐rolled and heat‐treated to identify the role of these heterogeneous phase boundaries on the overall sheet properties. Deformation structures in these layered materials are studied through scanning transmission electron microscopy investigations. The existence of an interface‐affected zone at the phase boundaries and mechanical intermixing is attributed to decreasing electrical and increasing mechanical properties, especially in very thin layered LMCs. Atom probe tomography measurements show that mechanical alloying occurs due to severe plastic deformation during ARB processing of the laminates. An additional subsequent heat treatment leads to chemical demixing at the interfaces of the phase boundaries.

The synergistic effect of gradient nanostructure and residual stress induced by expansion deformation on the tension-tension fatigue performance of Ti6Al4V holes

A large number of titanium alloy structural components in aircraft are joined and assembled through holes. The complex service conditions pose high requirements for the fatigue performance of the holes. The study aims to use expansion deformation to induced gradient nanostructures and residual stress enhance the fatigue performance of Ti6Al4V holes. By studying the evolution process of the microstructure in titanium alloys, the formation mechanism of gradient nanostructures has been obtained, and their impact on various stages of fatigue fracture is analyzed. The results showed that the split sleeve cold expansion (CE) process caused severe plastic deformation on the surface of the hole, resulting in a large amount of LAB production and a transformation of the main texture components. Meanwhile, the gradient nanostructures are formed on the hole surface, which include nanocrystalline layer, superfine lath grain layer, lath grain layer and severe deformation layer. During the expansion deformation process, the slip of dislocations leads to the formation of high-density dislocation structures, which evolve into subgrain boundaries and then undergo dynamic recrystallization through subgrain rotation to achieve grain refinement. What's more, the degree of grain refinement, depth of gradient nanostructure, and residual stress increase as the expansion deformation intensifies. The depth of gradient nanostructure is 300 μm, and the maximum residual stress is −419 MPa, when the deformation is 5 %. The combined effect of gradient nanostructures and high residual compressive stress induced by expansion deformation has increased the total fatigue life and crack propagation life of CE-5 specimen by 2.9 and 3.4 times compared to NCE specimen. This work provides an effective method and theoretical analysis for improving the fatigue life of titanium alloy holes.

Effect of severe plastic deformation and magnetic field-assisted heat treatment on the magnetic properties of equiatomic FeNi alloy

Effect of severe plastic deformation and magnetic field-assisted heat treatment on the magnetic properties of equiatomic FeNi alloy

Temperature effect on the microstructural refinement of equiatomic CoCrNi medium entropy alloy via cyclically multi-directional impact

Severe plastic deformation can effectively refine alloy microstructure and improve the mechanical properties of alloys surprisingly. In this work, a new approach of severe plastic deformation was proposed based on split Hopkinson pressure bar, i.e., cyclically multi-directional impact. Using this newly developed technique for microstructural refinement at different temperatures (77 K, 293 K, and 1073 K), bulk equiatomic CoCrNi medium entropy alloys with refined microstructures were obtained, and the stress vs. strain relation of the equiatomic CoCrNi medium entropy alloy during the cyclically multi-directional impact can be in situ measured. The strain rate of the cyclically multi-directional impact was controlled at about 1500 /s. The hardnesses of the CoCrNi medium entropy alloy increase dramatically from 216 Hv to 460 Hv after the cyclically multi-directional impact at 77 K, 484 Hv after the cyclically multi-directional impact at 293 K, and 434 Hv after the cyclically multi-directional impact at 1073 K. The microstructural evolutions of the CoCrNi MEA after cyclically multi-directional impact at three temperatures were characterized and analyzed. This study aims to provide a new approach to microstructural refinement for bulk alloys.

Experimental investigation of abrasive potential and drilling efficiency at elevated temperatures via Cerchar rock scratching

To see if and how abrasive potential as well as drilling efficiency change due to rock heating, Cerchar scratch tests were performed on six types of rock at eight temperature levels. Results indicate that rock abrasivity is temperature-dependent. The change of rock abrasivity expressed by the Cerchar abrasivity index can be divided into two stages on either side of 500 °C. Meanwhile, the drilling efficiency expressed by the Cerchar abrasion ratio can significantly be enhanced, especially when the heating temperature exceeds 500 °C. The observation of damaged surfaces indicates that the material volume removed from the rock surface increase after rock heating. The worn steel surfaces (115CrV3 tool steel) shows the severe plastic deformation and fracturing associated with cracking, delamination, dislocation and chipping of the steel.

High-temperature tribological behavior of the Al/Mg/Cu multilayered composite produced by the severe plastic deformation

In the current research, the microstructure and wear behavior of Al/Mg/Cu multilayered composite at high temperatures were investigated. For this purpose, the Al/Mg/Cu composite was produced by the accumulative roll bonding (ARB) process and continued until the sixth pass at ambient temperature. The hot wear tests were performed at loads of 10, 20, and 40 N at 100, 150, and 250 °C for different passes. The findings demonstrated that with the increase of ARB passes, the wear rate decreased. So under 40 N at 100, 150, and 250 °C, the wear rate in the sixth pass decreased by 53 %, 65 %, and 76 %, respectively, compared to the first pass. The examination of the worn surfaces showed at 100 °C under high loads, fatigue wear was dominant. At 150 °C, oxidation was the main wear mechanism. The presence of oxidized grooves on the surface showed that the abrasive wear encouraged oxidation. At 250 °C under 40 N, inhomogeneous oxidation was the main wear mechanism of the samples. So that aluminum and magnesium regions were oxidized and copper areas remained un-oxidized like isolated islands.

Effect of High-Temperature Deformation Twinning on the Work Hardening Behavior of Fe-38Mn Alloy during Hot Shear-Compression Deformation.

The effect of high-temperature deformation twinning on the work hardening behaviors of Fe-38Mn alloy during hot shear-compression deformation was investigated. The discovery of micro-shear bands and deformation twinning is significant for continuous work hardening, and this represents an important step toward gaining a complete understanding of the effect of deformation twinning on work hardening behaviors. Deformation twinning is widely acknowledged to accommodate plastic strain under cold deformation, even under severe plastic deformation. At present, the equivalent stress vs. strain curves for hot shear-compression deformation of Fe-38Mn alloy exhibit the characteristics of continuous work hardening. In addition, continuous work hardening is classified into five stages when considering high-temperature deformation twinning.

Multiple Deformation Mechanisms in Adiabatic Shear Bands of a Titanium Alloy during High Strain Rate Deformation.

The occurrence of adiabatic shear bands, as an instability phenomenon, is viewed as a precursor to failure caused by instability at high strain rates. Metastable β titanium alloys are extensively utilized due to their excellent mechanical properties, which are often subjected to high strain rate loads in service conditions. Understanding and studying their adiabatic shear instability behavior is thus crucial for preventing catastrophic failure and enhancing material performance. In this study via detailed microstructural analyses in the adiabatic shear region of a Ti-10V-2Fe-3Al alloy subjected to high strain rates, it was observed that α″ martensitic transformation and nano-twinning plus β-to-α phase transformation with α″ martensite as an intermediate phase occurred, in addition to substantial fine grains. The grain refinement mechanisms were mainly related to dynamic recovery dominated by dislocation migration alongside severe plastic deformation.

Effect of shot peening on surface characteristics and high-temperature corrosion behaviour of super 13Cr martensitic stainless steel

Super 13Cr, as an economy stainless steel (SS) for oil country tubular goods, needs stable corrosion resistance in high-pressure and high-temperature (HPHT) downhole medium. Severe plastic deformation (SPD) are the surface modification technology to improve mechanical properties, fatigue behavior and corrosion resistance of metals, and shot peening (SP) has been the most widely used SPD process. However, there are quite limited studies about the microsutructure evolution, residual stress, and high-temperature corrosion behavior of SP-treated martensitic SS. In this study, super 13Cr martensitic SS was treated by SP with various air pressures and nozzle speeds. The surface characteristics and high-temperature corrosion behaviour in 3.17 mol/L K2HPO4 solution were investigated through finite element model analysis, characterization of residual stress and microstructure, as well as electrochemical and stress corrosion cracking (SCC) tests at 160 °C and 10 MPa. The results showed that SP-treated super 13Cr could generate high-level compressive residual stress and SPD microstucture, including nano-sized equiaxed grains, gradient lamellar structure and fragmented carbides. Increasing air pressure contributed to achieve uniform nanocrystalline, but tended to generate high dislocation density and surface defects. The improving effect of SP treatment at low air pressure of 0.15 MPa on passivation ability was limited, and high air pressure adversely impacted corrosion resistance. SP-treated specimens showed high SCC susceptibility, due to the introduction of more surface defects, high angle grain boundaries, and dislocations.

Nanostructured Titanium with Ultrafine‐Grained Structure as Advanced Engineering Material for Biomedical Application

Titanium and its alloys are popular materials for medical application, particularly in implant devices, where high mechanical properties and osseointegration are critical factors for successful implantation. In this work, the progress in the studies of nanostructured commercially pure Grade 4 titanium (nanoTi) is demonstrated, in which an ultrafine‐grained structure with nanoscale grain size is formed using severe plastic deformation processing. Nanostructured Grade 4 Ti has a very high strength, and its physical nature and strengthening mechanisms are analyzed herein. NanoTi proved also to have very high osseointegration during in vivo experiments. At the same time, the highest biofunctionality is demonstrated by the etched nanoTi samples with pronounced surface roughness, the latter being revealed from precise roughness measurements. The present study provided convincing evidence of accelerated bone formation on nanoTi, which is very promising for manufacture of dental and maxillofacial implants.

Nanostructuring and Hardness Evolution in a Medium‐Mn Steel Processed by High‐Pressure Torsion Technique

Severe plastic deformation (SPD) is performed on a newly developed medium‐Mn steel with the composition of Fe–7.66Mn–2Ni–1Si–0.23C–0.05Nb (wt%) to achieve a nanocrystalline microstructure. The SPD process utilizes the high‐pressure torsion (HPT) technique, resulting in a nominal shear strain of approximately 36 000% after processing the disk for 10 turns. In X‐Ray diffraction line profile analysis, an increase in dislocation density to around 230 × 1014 m−2 is observed. In addition, under high strains, a face‐centered cubic (fcc) secondary phase emerges within the body‐centered cubic (bcc) matrix. In analytical transmission electron microscopy, using energy‐dispersive X‐Ray spectroscopy, it is indicated that the secondary‐phase particles are enriched in Al, Mn, and Si. As the strain imposed during HPT increases, the simultaneous rise in dislocation density and nanostructuring lead to material hardening. However, the partial phase transformation from bcc to fcc contributes to material softening. As a result of these two opposite effects, the hardness exhibits a non‐monotonic variation with the shear strain, displaying, for 10 turns of HPT, a lower hardness compared to fewer turns, despite the continuous increase in dislocation density and decrease in crystallite size.

Numerical study of micro-dimple depth and stress distribution induced by laser shock waves in visco-elasto-plastic materials

Laser shock peening (LSP) is an advanced surface strengthening technology that uses laser shock waves (LSWs) to induce severe plastic deformation, considerable compressive residual stress, and grain refinement, and thereby improve the fatigue performance of metallic materials. Understanding the spatiotemporal distribution of the stress wave is important for precisely managing the strengthening effect of LSP. In this paper, the stress distribution of LSWs and the equation for LSW-induced residual strain in visco-elasto-plastic materials are presented. The formation of LSW-induced micro dimples on the surface is noteworthy. We derived an approximate equation for the maximum micro-dimple depth induced by LSWs. Finally, we measured the micro-dimple depths induced by LSWs at different peak pressures and verified the reliability of the theoretical calculation by comparing the calculated data with the experimental data. The micro-dimple depth can serve as an indicator of the effectiveness of LSP and improvement in fatigue performance. This characteristic can be utilized as a non-destructive testing method. This study has demonstrated the potential for promoting and applying of LSP in different industries.

Microstructural and material property changes in severely deformed Eurofer-97

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.

Tensile strength optimisation in AA2014 aluminum alloy joints via friction stir welding: a rivet-free approach examining materials flow behaviour

ABSTRACT Steel rivets are alternative materials for connecting materials for structural fabrication industry. The use of rivets may significantly increase the structure weight, impacting its overall performance. Additionally, there is a risk of inducing corrosion at the interface due to galvanic coupling. Therefore, careful consideration of material choices and potential consequences is necessary during the design and fabrication processes. When joining dissimilar alloys, manufacturers and designers face numerous challenges with conventional fusion welding techniques. Friction stir welding is effective at joining materials without reaching their melting points; instead, it relies on severe plastic deformation and recrystallization to create a welded joint. Proper selection of the tool and process parameters is crucial for achieving a sound weld result. The results from experimental investigations highlight the significance of plastic deformation, material flow, and recrystallization as influential factors on joint strength. This finding suggested that FSW is an ideal joining process for high-strength alloys. Although friction stir welding is a suitable alternative to permanent joints, such as rivets, notably, the experimental findings reveal that friction stir welding of both but and lap joints yields maximum load-carrying capabilities of 50.5 and 51.2 kN, respectively, emphasising the efficacy of the method in structural applications

Low-Temperature Superplasticity of Ultrafine-Grained Aluminum Alloys: Recent Discoveries and Innovative Potential.

The last two decades have witnessed significant progress in the development of severe plastic deformation techniques to produce ultrafine-grained materials with new and superior properties. This review examines works and achievements related to the low-temperature superplasticity of ultrafine-grained aluminum alloys. The examples are provided of the possibility to observe low-temperature superplasticity in aluminum alloys at temperatures less than 0.5 Tmelt and even at room temperature, and herein, we demonstrate the cases of achieving high ductility and high strength in aluminum alloys from processing utilizing severe plastic deformation. Special emphasis is placed on recent studies of the formation of segregations of alloying elements at grain boundaries in UFG Al alloys and their influence on the development of grain boundary sliding and manifestation of low-temperature superplasticity. In addition, the current status and innovative potential of low-temperature superplasticity in aluminum alloys are observed.

Saturation of Grain Fragmentation upon Severe Plastic Deformation: Fact or Fiction?

There has been general agreement that grain refinement upon severe plastic deformation (SPD) saturates at equivalent strains of 10–20, as a dynamic equilibrium between refinement and coarsening is established. Meanwhile, few reports question such steady state, but suggest another strain hardening regime might be entered for strains >1000. So far, neither an in‐depth analysis nor a general theory for such ultra‐SPD strain hardening has been established. The present work provides clear evidence for additional strain hardening at ultra‐severe strains. Although at this stage the strain hardening rate is awfully weak (≈0.03 MPa), it manifests in noticeable grain refinement and hardness increase. Texture and the existence of subgrains still support dislocation‐based plasticity. Specimens deformed to ultra‐severe strains possess improved thermal stability. Although an unambiguous conclusion regarding the origin of the ultra‐SPD strain hardening is currently not possible, the potential mechanisms are being discussed. While continuous impurity uptake from the anvils could explain the hardening and improved thermal stability, estimation of grain boundary migration rates suggests that a slight but continuous net refinement is also plausible. Together with structural transformations of grain boundaries, this offers an alternative, intrinsic source for ultra‐SPD hardening. It is hoped that this thought‐provoking conclusion stimulates further research into this subject.

Co‐Deformation in Severely Deformed Multiphase Crystalline Metallic Systems: Physical Mechanisms, Intrinsic Limitations, and Perspectives

The deformation of multiphase metallic alloys or metal matrix composites by forming processes such as rolling or drawing requires the co‐deformation of phases. Severe plastic deformation processes have extended possibilities with the ability to produce unique nanoscaled structures through the formation of strain‐induced super‐saturated solid solutions, the fragmentation of second‐phase particles, or ultimate co‐deformation down to the nanoscale. Based on various examples, the fundamental mechanisms of co‐deformation are addressed. Parameters that promote the extension of existing heterophase boundaries are discussed, and some possible atomic‐scale mechanisms involving dislocation activities based on geometrical and energetic considerations are proposed. Finally, the physical limits of co‐deformation are considered before suggesting research directions that might be followed to develop fundamental knowledge and applications in the field.