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This study investigates the influence of extrusion and deformation temperatures on the mechanical properties of the AZ61 Mg alloy. Increasing the extrusion temperature from 300 to 400 °C led to larger grain size and higher basal texture intensity. At 400 °C, the AZ61 alloy exhibited more Al–Mn phases and fewer Mg17Al12 phases, indicating enhanced dissolution of Mg17Al12 in the α-Mg matrix. Uniaxial tensile tests were conducted at room temperature (RT) and cryogenic temperature (CT, −150 °C). Despite grain growth, a higher yield strength (YS) was achieved at higher extrusion temperatures due to the texture-strengthening mechanism. However, during deformation at CT, the higher YS was primarily attributed to the formation of multiple twinning within individual grains, causing twinning interactions. These twin-interacting boundaries create additional barriers to dislocation movement. Notably, the AZ61 sample extruded at 400 °C demonstrated the formation of stacking faults during deformation at CT, with dislocations accumulating around the faults. This contributed to the best strength without compromising ductility in this sample.

The introduction of twin lamellae and dislocation interaction through Multi-directional forging (MDF) at room temperature (RT) has been reported to significantly improve the mechanical properties of Mg alloys. However, the Mg alloys typically exhibited poor plasticity at RT, making it highly susceptible to cracking. This study further enhanced the deformation capacity of AZ80 Mg alloy by adding a pre-cryogenic step before MDF. Compared to direct MDF at RT, MDF at cryogenic temperature (CT, −196 °C) further increased the alloy's deformation capacity from 0.72 (4P) to 1.08 (6P), with the tensile yield strength (TYS) and ultimate tensile strength (UTS) increasing to ∼420 MPa and ∼512 MPa. The alloy subjected to cryogenic MDF exhibited denser twin lamellae and a higher proportion of {10–12}-{10–12} twin interactions. The more frequent twin interactions under CT inhibited excessive twin growth and further increased the dislocation density of the matrix, facilitating the nucleation of new twins. Additionally, with increasing deformation passes, the texture of the RT specimens became more single, while the CT specimen showed a trend toward texture dispersion. The study elucidated that poor forgeability of the alloy under MDF at RT was hindered by unfavorable texture and limited twin activation. However, this issue was mitigated under CT, where the activation of more atypical twins with low Schmid factors (SFs) significantly enhanced the deformation coordination ability. Furthermore, the activation of atypical twins and extensive twin interactions promoted texture dispersion in CT specimens, which facilitated the activation of various slips/twins and suppressed excessive twinning-induced hardening, thereby improving forgeability.

CrMnFeCoNi high-entropy alloy (HEA) manufactured by laser powder bed fusion has been demonstrated to possess a superior trade-off of tensile strength and ductility due to unique microstructures during the printed process. However, the improvement of mechanical properties of 3D printed-CrMnFeCoNi HEA through the addition of nano-scaled ceramic particles instead of in-situ precipitated particles is poorly studied. In this work, the effects of WC additions on the microstructure evolution and strengthening mechanism of additive-manufactured HEA samples at both room temperature (298 K) and cryogenic temperature (77 K) were systematically investigated. Except for the representative hierarchical microstructure characteristics of 3D printed- HEA samples, WC particles are dissolved completely in the CrMnFeCoNi matrix without obvious element segregation. The mechanical tests at room temperature (RT) revealed an excellent comprehensive mechanical property (tensile strength of 925 MPa and ductility of 38%) of the HEA sample with 5 wt% WC addition, which is mainly attributed to the solid solution strengthening induced by WC dissolution. In addition, the strength and ductility of the HEA sample synchronously increase when the testing temperature decreases from 298 K to 77 K, due to the reaction between dislocation and high-density deformation twins (DTs). The tensile strength (∼1420 MPa) of HEA-5 wt% WC sample at 77 K is higher than that of traditional CrMnFeCoNi HEA, because of contribution to strengthening from dislocation pile-up, entanglement and wavy dislocation slide.

This paper presents new technology for stainless steel wire processing. This technology consists of using cryogenic cooling immediately after the wire leaves the drawing die. Results of a laboratory experiment show that use of cryogenic processing after wire drawing improves mechanical properties compared with traditional drawing. Metallographic analysis proves that deformation conditions during cryogenic drawing are an additional factor for realization of structural resources to optimize steel wire physical and mechanical properties. [ABSTRACT FROM AUTHOR]

This study investigates the influence of CaO (0.5, 1 (wt.%)) alloying on the microstructural evolution, texture development and deformation behavior of AZ61 magnesium alloy. The uniaxial tension tests at room (RT) and cryogenic (CT, -150 °C) temperature were performed to investigate the twinability and dislocation behavior and its consequent effect on flow stress, ductility and strain hardening rate. The results showed that the AZ61-1CaO exhibited superior strength/ductility synergy at RT with a yield strength (YS) of 223 MPa and a ductility of 23% as compared to AZ61 (178 MPa, 18.5%) and AZ61-0.5CaO (198 MPa, 21%). Similar trend was witnessed for all the samples during CT deformation, where increase in the YS and decrease in ductility were observed. The Mtex tools based in-grain misorientation axis (IGMA) analysis of RT deformed samples revealed the higher activities of prismatic slip in AZ61-CaO, which led to superior ductility. Moreover, subsequent EBSD analysis of CT deformed samples showed the increased fraction of fine {10-12} tension twins and nucleation of multiple {10-12} twin variants caused by higher local stress concentration at the grain boundaries, which imposed the strengthening by twin-twin interaction. Lastly, the detailed investigations on strengthening contributors showed that the dislocation strengthening has the highest contribution towards strength in all samples.

We demonstrate that cryogenic rolling can simultaneously achieve ultrahigh strength and significant ductility in 316L steel, thereby overcoming the existing limits of its tensile properties. The cryogenic-rolled 316L steel exhibited a 1.1 GPa yield strength (YS) at 298 K. Typically, deformed materials exhibit strain softening immediately after yielding with poor uniform ductility. However, during tensile straining, the cryogenic-rolled 316L steel underwent significant strain hardening despite being severely deformed, thus demonstrating exceptional uniform ductility. Consequently, the cryogenic-rolled 316L steel showed a significantly superior strength–ductility combination, impossible with typical cold rolling. The significantly increased YS of the cryogenic-rolled 316L steel resulted from the combined effect of the presence of the hard martensite phase and the refined austenite grains formed by high-density deformation bands. The significant strain hardening in the cryogenic-rolled 316L steel was possible because the low density of dislocations in the austenite matrix enabled the generation of substantial back stress when newly formed dislocations accumulated at obstacles such as grain boundaries during tensile deformation. Partial dislocations in the cryogenic-rolled 316L steel also contributed to considerable strain hardening by suppressing cross-slip during tensile deformation at 298 K—a well-known major mechanism that weakens strain hardening by facilitating dynamic recovery in metallic materials. Our findings suggest a new microstructural strategy for developing commercial steels with superior tensile properties. [ABSTRACT FROM AUTHOR]

• Room and cryogenic deformation behavior of AZ61 and AZ61-CaO alloys was investigated. • IGMA analysis showed the higher prismatic slip activity in AZ61-CaO alloys. • Numerus twins and twin-twin interactions lead to significant hardening at CT. • Dislocation strengthening was found to be major strengthening mechanisms. This study investigates the influence of CaO (0.5, 1 (wt.%)) alloying on the microstructural evolution, texture development and deformation behavior of AZ61 magnesium alloy. The uniaxial tension tests at room (RT) and cryogenic (CT, -150 °C) temperature were performed to investigate the twinability and dislocation behavior and its consequent effect on flow stress, ductility and strain hardening rate. The results showed that the AZ61-1CaO exhibited superior strength/ductility synergy at RT with a yield strength (YS) of 223 MPa and a ductility of 23% as compared to AZ61 (178 MPa, 18.5%) and AZ61-0.5CaO (198 MPa, 21%). Similar trend was witnessed for all the samples during CT deformation, where increase in the YS and decrease in ductility were observed. The Mtex tools based in-grain misorientation axis (IGMA) analysis of RT deformed samples revealed the higher activities of prismatic slip in AZ61-CaO, which led to superior ductility. Moreover, subsequent EBSD analysis of CT deformed samples showed the increased fraction of fine {10-12} tension twins and nucleation of multiple {10-12} twin variants caused by higher local stress concentration at the grain boundaries, which imposed the strengthening by twin-twin interaction. Lastly, the detailed investigations on strengthening contributors showed that the dislocation strengthening has the highest contribution towards strength in all samples. [Display omitted] [ABSTRACT FROM AUTHOR]

The data of a comparative analysis of the structure and hardness of pure metals with a face-centered cubic lattice – aluminum, nickel and copper, subjected to complex thermomechanical treatment (TMT), including isothermal cryogenic rolling at liquid nitrogen temperature and subsequent high-density electropulse treatment (EPT) were presented. The main stages, features and advantages of TMT, which first ensure strong work hardening of the processed material due to deformation at low temperatures and then its ultra-fast contact electropulse heating up to a specified temperature, were considered. A multi-level analysis of the metals structure evolution due to TMT was carried out using modern methods of scanning electron microscopy and X-ray diffractometry, recording a wide range of its linear and angular parameters. The kinetics and nature of the processes of the metals structure evolution under cryogenic rolling and EPT, their driving forces and controlling factors, as well as general patterns and temperature intervals of activation of the deformation structure recovery and recrystallization influenced by an electric pulse are identified and discussed. Based on the results of the analysis of the structural and mechanical behaviour of metals, it was concluded that the combination of severe plastic cryogenic deformation and a single-step treatment with ultrashort alternating current pulses is an effective way to obtain semi-finished products with controlled parameters of their structure and properties, including high-strength ultrafine-grain rolled products. At that the phenomenology and nature of the strengthening/softening of metals during cryogenic rolling and subsequent electropulsing are similar to those observed under cold rolling and furnace annealing.

The development of robust alloys capable of maintaining high strength and ductility at cryogenic temperatures has been a long-sought goal, particularly for load-bearing applications in extremely low-temperature environments. In this study, we reported a newly developed face-centered-cubic (FCC) metastable (Ni0·3Co0·4Cr0.3)94Mo6 medium-entropy alloy (Mo-MEA) with an excellent synergy of strength and ductility at 77 K, surpassing the toughest equiatomic NiCoCr MEA. Compared to the equiatomic NiCoCr MEA, the Mo-MEA exhibited a substantial increase in yield strength by 68 % (from 407 to 685 MPa) and a decent enhancement of the ultimate tensile strength by 10 % (from 1289 to 1415 MPa), along with a marginal increase in elongation from 75 % to 78.45 %. Electron backscatter diffraction and transmission electron microscopy revealed the activation of multimodal deformation mechanisms, including dislocations, stacking faults, twinning, and FCC-to-hexagonal-close-packed phase transformation, during the tensile deformation at 77 K.

Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure, and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength (ultimate tensile strength: 321 MPa, ductility: 21%) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components.

The tensile strain-hardening behavior of pure Ti at 100 K was investigated using X-ray diffraction line-profile analysis and plasticity simulation. The strain hardening was significantly increased at 100 K, compared with that observed at 298 K. Thus, at 100 K, necking was suppressed during tensile testing, which greatly increased material ductility. The remarkable increase in strain hardening at 100 K was attributed to the dominant activation of prismatic slip and the exceptionally increased rate of its activation stress with tensile strain at 100 K. This finding significantly advances the understanding of the strain-hardening behavior of pure Ti at low temperatures, and it can also guide the development of texture-engineering strategies to increase the low-temperature ductility of pure Ti.

Compression tests were conducted at room and cryogenic temperatures to investigate the low-temperature plasticity in Mg–3Al–1Zn alloy. The strain to failure and fracture strength in Mg–3Al–1Zn alloy increase by 21.4% and 51.6% from room to cryogenic temperature. Using a quasi-in-situ EBSD method, it is found that {10 1¯ 2} tension twins dominate at room temperature, while abundant (10 1¯ 2)-(01 1¯ 2) twin-twin interactions are observed at cryogenic temperature. Multiple slips, including pyramidal and basal slips, occur in twin-twin interactions, enhancing the strain to failure and flow stress at cryogenic temperature. The high dislocation density near twin-twin interactions boundaries would contribute to the high hardening rate and flow stress at cryogenic temperature. This work would provide a novel way to enhance plasticity in magnesium alloys and gain an in-depth understanding of twin-twin interactions.

• The ductility and strength of Mg alloys were significantly enhanced with the cryogenic-hot deformation process. • The effective grain refinement and texture weakening were achieved with the cryogenic-hot deformation process. • Abundant twin-twin interactions in cryogenically pre-deformed samples are recrystallization sites during the hot deformation. • Main recrystallization sites in the direct-hot deformed samples are deformation bands. Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure, and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength (ultimate tensile strength: 321 MPa, ductility: 21%) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components. [ABSTRACT FROM AUTHOR]

A novel treatment process that involves solution treatment, cryogenic pre-stretching, and artificial aging was applied to strengthen Al-Cu-Li alloy without ductility sacrificing in this work. The influence of pre-stretching deformation at ambient (RT, 25 °C) and cryogenic (CT, −196 °C) temperatures on dislocation configuration, precipitation behaviour, and after-aging mechanical properties of AA2195 was systematically investigated. Compared with conventional RT-stretched sample, the after-aging yield strength (YS) of CT-stretched sample was increased from 618 MPa to 655 MPa with ductility of 11.6%. The increased strength resulted from the combination of strain hardening and precipitation strengthening. The activated immovable dislocations on {100}Al during CT-stretching obstructed the subsequent slip of following dislocations to grain boundaries, prevented the dislocations piling-up at grain boundaries, and facilitated the dislocation accumulation at grain interior. The increased dislocations density within grains not only provided higher strain hardening to the alloy but also promoted the nucleation of T1 phase in the matrix, which significantly increased the yield strength. Additionally, the reduction of grain boundary dislocations suppressed the precipitation of T1 at grain boundaries, which prevented the formation of precipitate-free zones (PFZs) and the stress concentration at grain boundary during deformation, enhancing the alloy ductility.

Subsurface deformation and wear behavior of 15% SiCp/2009Al aluminum alloy matrix composites induced by sliding wear at room and cryogenic temperature were investigated in the present work. An external cryogenic device was designed to produce a steady cryogenic environment in the course of experiments. Microstructure evolution in the subsurface layer and wear mechanism on the worn surface were analyzed by various characterization methods. The results showed that sliding at cryogenic temperature caused greater plastic deformation in the subsurface layer than that at room temperature. This can be attributed to the increased plasticity of aluminum alloy matrix and increased brittleness of SiC particles at cryogenic temperature, which can reduce the block effect of SiC particles on the deformation of aluminum alloy matrix. Wear rate of the composite material was significantly reduced after cryogenic sliding, whose decrement was much higher under higher applied load. Worn surface presented a lower surface roughness and higher surface evenness after sliding at cryogenic temperature. Wear mechanism was found to be transformed from severe oxidative, adhesive and delamination wear at room temperature, to slight delamination wear and cracking feature under cryogenic sliding. Deformation layer after cryogenic sliding played a role of nanocrystalline work-hardening layer, as the work-hardening rate and dislocation density were increased at cryogenic temperature. This is responsible for suppressing the generation of cracks and correspondingly improving the wear performance of material. This work also offers a new strategy for designing high surface-performance aluminum matrix composites via the method of self-adaptively forming nano hardening layer in cryogenic temperature environment. [ABSTRACT FROM AUTHOR]

Two different types of shear bands generate in ultrafine-grained (UFG) CoCrFeMnNi high-entropy alloys deformed at 77 K, i.e. commonly-observed low angle grain boundary (LAGB) type and unusual twin-coupled type. Twin-coupled shear bands exhibit a misorientation of 56–67° with the matrix, in contrast to the LAGB shear band with a misorientation of 6–12°. Both annealing twins and deformation twins can act as precursor for twin-coupled shear bands, where dislocation accumulation along twin boundaries can tune the orientation of twin lamella. These observations suggest that twin-coupled shear bands can act as an important plastic carrier in materials deformed under extreme conditions.

Heterostructured materials (HSMs) has been shown to improve the strength-ductility trade-off of conventional alloys but their cryogenic performance has not been studied during real-time deformation. We investigated heterostructured CrCoNi medium-entropy alloy by in-situ neutron diffraction at cryogenic (77 K) and room (293 K) temperatures. The significant mechanical mismatch at interfaces between fine and coarse grains, due to pronounced grain size disparity, resulted in exceptional yield strength of 918 MPa at 293 K. The yield strength further increased to 1244 MPa at 77 K with an excellent uniform elongation of 34 %. The exceptional strength–ductility combination at 77 K can be attributed to enhanced geometrically necessary dislocation pile-up density boosted from high-mechanical mismatch interfaces, as well as higher planar faults, and martensitic phase transformation. Comparison with homogenous counterparts demonstrates the potential of HSMs as a new strategy to improve the mechanical performance of different materials, including medium-/high-entropy alloys for cryogenic applications. • In-situ neutron diffraction reveals defect evolution during cryogenic deformation. • Achieved a yield strength of 1244 MPa and 39 % ductility at cryogenic temperatures. • Description of synergistic and sequential deformation mechanisms. • Superior strength‒ductility trade-off boost for cryogenic environment applications. [ABSTRACT FROM AUTHOR]

• The strength-plasticity trade-off relationship is weakened at cryogenic temperature. • The physical mechanism of the grain size dependent cryo-deformation is revealed. • Modelling the grain size dependence of dislocation evolution in cryo-deformation. • The cryo-deformation of heterogeneous sheets is tracked in situ for the first time. • The dislocation evolution is quantitatively analyzed based on the developed model. In this paper, a physical-based constitutive model for cryogenic deformation was established by introducing internal variables related to temperature, T and grain size, d. Uniaxial tensile tests and microstructure observations were carried out to reveal macroscopic deformation behavior and corresponding microscopic deformation mechanism. The classical Kocks–Mecking model was modified by distinguishing the significant differences in the dislocation evolution in the grain interior and in the vicinity of the grain boundary. The parameters of the constitutive model were optimized by genetic algorithm (GA). The developed constitutive model was comprehensively validated, including the stress-strain curves and formability indexes at the macro level and the evolution of dislocation density at the micro level by using in-situ digital image correlation (DIC) tests and quasi-in-situ electron backscattered diffraction (EBSD) characterization. The coupling effects of grain size and cryogenic temperature (CT) on the evolution of dislocation are quantitatively analyzed and discussed based on the established constitutive model. The studies show that the constitutive model can effectively address the coupling effects of grain size and CT on the deformation behavior of pure aluminum, and accurately describe the deformation characteristics of heterogeneous sheets with gradient grain size at different temperatures. In addition, parametric analysis shows that the predominant dislocation annihilation in ultra-fine grained (UFG) pure aluminum gradually transitions from the vicinity of the grain boundary to the grain interior with the decrease in temperature, resulting in the significant weakening of the strength-plasticity trade-off relationship at cryogenic temperature. These results deepen the understanding of the grain size-dependent cryo-deformation and inspire a promising idea for the direct manufacture of heterogeneous components with grain size gradients. [Display omitted] [ABSTRACT FROM AUTHOR]

This study conducts a comprehensive examination of the microstructural and dislocation dynamics of AlSi10Mg alloys under various thermal conditions, utilizing quasi in-situ Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) analyses. The research focuses on comparing the microstructural response of as-built and T6 heat-treated samples to mechanical stress at both ambient (298 K) and cryogenic (77 K) temperatures. EBSD analysis underscores the grain stability under applied strain, while TEM investigations expose notable variations in dislocation mobility influenced by temperature, with a particular emphasis on the interaction between dislocations and silicon particles at cryogenic temperatures. An observed increase in Geometrically Necessary Dislocation (GND) density at 77 K points to enhanced resistance to plastic deformation, suggesting mechanisms of cryogenic strengthening. The findings illuminate the impact of heat treatment in augmenting the mechanical properties of the alloy, shedding light on its potential applications in aerospace and cryogenic environments. • Enhanced mechanical properties in SLM AlSi10Mg alloys at cryogenic temperatures, showing significant differences in strength and ductility. • Cryogenic conditions led to an increase in yield and tensile strengths for both as-built and heat-treated samples, with notable distinctions in ductility. • Quasi-in situ EBSD and TEM analyses revealed higher dislocation density and the activation of multiple slip systems at 77 K. • T6 heat treatment improved ductility and showed the interaction between dislocations and Si particles in TEM. [ABSTRACT FROM AUTHOR]

The microstructure and texture of many Mg alloys prepared by friction stir welding (FSW) have been investigated with associated to mechanical properties. However, the microstructure evolution and its correlation with mechanical properties are rarely studied in cryogenic temperature and high strain rate loading. In this work, the microstructure and mechanical behavior of Mg alloy joints, AZ31B, were investigated. The findings unveiled that the decrease of loading temperature promoted the compress twin activation, accompanied by an increase in ultimate strength and a slightly decrease in plasticity. The enhanced of ultimate tensile strength (about 60 MPa) from 25°C to −50°C is ascribed to twin-twin interactions and increased amount of compression twin({10-11}and{10-13}). The decrease of plasticity (about 4.5%) is associated to the stress concentration, due to the dislocation thermal activation is suppressed. [ABSTRACT FROM AUTHOR]

Two different types of shear bands generate in ultrafine-grained (UFG) CoCrFeMnNi high-entropy alloys deformed at 77 K, i.e. commonly-observed low angle grain boundary (LAGB) type and unusual twin-coupled type. Twin-coupled shear bands exhibit a misorientation of 56–67° with the matrix, in contrast to the LAGB shear band with a misorientation of 6–12°. Both annealing twins and deformation twins can act as precursor for twin-coupled shear bands, where dislocation accumulation along twin boundaries can tune the orientation of twin lamella. These observations suggest that twin-coupled shear bands can act as an important plastic carrier in materials deformed under extreme conditions. Atomic structure of twin-coupled shear band is unveiled in an UFG CoCrFeMnNi HEA deformed at 77 K, which involves in dislocation-twin boundary coupled mechanism, based on delicate structural characterization via high resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Serrated plastic deformation is an intense phenomenon in CoCrFeMnNi at and below 35 K with stress amplitudes in excess of 100 MPa. While previous publications have linked serrated deformation to dislocation pile ups at Lomer–Cottrell (LC) locks, there exist two alternate models on how the transition from continuous to serrated deformation occurs. One model correlates the transition to an exponential LC lock density–temperature variation. The second model attributes the transition to a decrease in cross-slip propensity based on temperature and dislocation density. In order to evaluate the validity of the models, a unique tensile deformation procedure with multiple temperature changes was carried out, analyzing stress amplitudes subsequent to temperature changes. The analysis provides evidence that the apparent density of LC locks does not massively change with temperature. Instead, the serrated plastic deformation is likely related to cross-slip propensity. [ABSTRACT FROM AUTHOR]

Abstract The effect of temperature was investigated on the consolidation of blended elemental powders of aluminum and copper by equal channel angular pressing (ECAP). Aluminum and Copper powders (1:1% vol.) were blended and consolidated in a 90° ECAP die at room (RT) and cryogenic temperatures (CT - ~77 K). ECAP samples were pressed until 4 passes at room temperature in route Bc. As a reference, a sample was obtained by conventional uniaxial pressing. The obtained results indicated a much denser (>99.5%) and harder structure by cryogenic ECAP. The hardness after one pass at CT was comparable with 4 passes at room temperature. Tensile tests performed at CT for materials with similar chemical composition showed a simultaneous increase in strength and ductility at CT, corroborating the results obtained by ECAP. The partial suppression of dynamic recovery and the activation and the transition between deformation mechanisms at CT, as well as stacking fault energies (SFE) of such metals, played an important role in these results. Copper presented a much higher capability of strain hardening than aluminum, due to its lower SFE and much lower homologous temperature. X-ray diffraction indicated a strong correlation between the variation of average microstrain and the variation of hardness on both metals. The results of this study demonstrated the great potential of the application of very low temperatures for the obtaining of deformation metal-metal composites.

This study rigorously examines the AA1060 aluminum alloy's mechanical properties across different thermal conditions (298K–77K) and orientations (RD-ND and TD-ND). Through annealing at 350 °C for 50 min followed by extensive mechanical testing at ambient and cryogenic temperatures, the study delves into the microstructural evolution and deformation mechanisms utilizing Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Findings indicate a pronounced increase in yield strength, tensile strength, and ductility with decreasing temperature. Notably, RD-ND oriented samples demonstrated enhanced mechanical strength over TD-ND oriented samples under both temperature regimes, underscoring the alloy's pronounced anisotropy. This comprehensive study illuminates the AA1060 alloy's temperature-dependent mechanical enhancements and anisotropic behavior, emphasizing the significant impact of microstructural orientation on its mechanical properties. The insights gained illuminate the AA1060 alloy's temperature-dependent and anisotropic behaviors, highlighting microstructural orientation's important role in its mechanical properties, with profound implications for aluminum alloy application across varying temperature and stress conditions. [ABSTRACT FROM AUTHOR]

2219 Al–Cu alloy transition rings are widely used in launch vehicles. However, the coarse and agglomerated second-phase Al2Cu particles significantly deteriorate the mechanical properties and ductility of 2219 Al–Cu alloy rings manufactured by traditional thermal deformation processes. In this study, cryogenic deformation (− 190 °C) is applied for the manufacturing of 2219 Al–Cu alloy rings to alleviate this problem. The effects on the evolution of second-phase Al2Cu particles and the mechanical properties of the T8-aged samples were examined in comparison with the results of room-temperature (25 °C) and conventional thermal deformation at 480 °C. The results indicate that cryogenic deformation can effectively produce high-density dislocations and strongly crush coarse particles, promoting the dissolution of Al2Cu particles and improving their distribution in the Al matrix when combined with subsequent solution treatment and rolling processes. As the deformation temperature was decreased from 480 to −190 °C, the area fraction of the coarse particles was decreased from 1.55 to 0.47%, while their mean size was decreased from 11.8 to 8.3 μm. Correspondingly, the uniformity and density of the precipitates after T8 aging were improved. Thus, the mechanical properties of the T8-aged samples were improved with decreasing deformation temperatures; the average ultimate tensile strength, yield strength, and elongation were increased by 20 MPa, 22 MPa, and 3.1% at room temperature. [ABSTRACT FROM AUTHOR]

Serrated plastic deformation is an intense phenomenon in CoCrFeMnNi at and below 35 K with stress amplitudes in excess of 100 MPa. While previous publications have linked serrated deformation to dislocation pile ups at Lomer–Cottrell (LC) locks, there exist two alternate models on how the transition from continuous to serrated deformation occurs. One model correlates the transition to an exponential LC lock density–temperature variation. The second model attributes the transition to a decrease in cross-slip propensity based on temperature and dislocation density. In order to evaluate the validity of the models, a unique tensile deformation procedure with multiple temperature changes was carried out, analyzing stress amplitudes subsequent to temperature changes. The analysis provides evidence that the apparent density of LC locks does not massively change with temperature. Instead, the serrated plastic deformation is likely related to cross-slip propensity.

Deformation mechanisms of high entropy alloys (HEAs) at cryogenic temperatures have attracted extensive research interest. We used in situ neutron diffraction to study the tensile behavior of a face-centered-cubic HEA at 77 and 15 K and compared its stacking fault energy (SFE) at ambient and cryogenic temperatures. The SFE dropped from 28 mJm−2 at 293 K to 11 mJm−2 at 15 K, leading to the transition of deformation mechanism from deformation-induced twinning to martensite phase transformation. As a result, excellent balance of strength and ductility was achieved at both temperatures. This finding highlights the importance of SFE for cryogenic alloy design. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We controlled the twin structure in pure Ti by deforming it at cryogenic temperature (∼77 K). Numerous thin individual twins were formed in the grains, thereby enabling strong twinning-induced grain refinement. The processed material had an ultrafine-grained microstructure, which greatly increased its strength. Notably, the ductility did not decrease significantly, despite the considerable strengthening, leading to superior tensile properties. This remarkable phenomenon occurred because the twin structure and the relatively small number of dislocations in the processed material enabled high resistance to necking instability. Our finding offers a new microstructural engineering method to achieve excellent tensile properties in pure Ti. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The flow behavior and deformation mechanism of solution quenched Al 7075 alloys at different cryogenic temperatures and strain rates are systematically investigated in the present work. Uniaxial tensile experiments were conducted at five different temperatures (room temperature (RT), −80 °C, −120 °C, −160 °C, −190 °C) and three different strain rates (0.00025 s−1, 0.001 s−1, 0.01 s−1). Deformation characteristics and microstructure of the sample were studied by optical microscope (OM), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that the deformation behavior of solid solution quenched 7075 aluminum alloy is synergistically affected by the deformation temperature and strain rate. The strength and plasticity of the sample are simultaneously elevated at −190 °C and −160 °C compared to that at RT with strain rates of 0.00025 s−1 and 0.001 s−1, respectively. The critical temperatures for plastic enhancement are −160 °C, −120 °C and −80 °C with strain rates of 0.00025s−1, 0.001s−1 and 0.01s−1, respectively. The proportion of increase in tensile strength and plasticity at −190 °C is more significant with the increase of strain rate. Different strain rates can lead to different Portevin-Le Chatelier (PLC) types of stress-strain curves. The PLC effect exhibits serrated fluctuations of type C, type B and type A at RT with strain rates of 0.00025s−1, 0.001s−1 and 0.01s−1, respectively. When the strain rates are 0.001s−1 and 0.01s−1, the PLC effect is completely suppressed at cryogenic temperatures. Interestingly, the PLC effect reappears at −160 °C and −190 °C with a strain rate of 0.00025s−1. The pinning effect of clusters formed by solute atom diffusion on dislocations as well as the grid-like entanglement formed by dislocations can result in the unstable plastic flow of aluminum alloy. In summary, the tensile properties and the PLC type of the 7075 aluminum alloys are determined by the combination of deformation temperature and strain rate. [ABSTRACT FROM AUTHOR]

This study presents a FCC crystal structure medium entropy alloy (MEA) with a nominal composition of Fe–25Mn–5Co-12.5Cr–5Ni-2.5Si (in at. %). The MEA deformed at room temperature exhibits superior mechanical performance compared to benchmark CoCrFeMnNi high entropy alloys (HEA). The empirical Hall-Petch equation was calculated with a high intrinsic strengthening coefficient of 335 MPa and a grain boundary strengthening coefficient of 634 MPa ∙ μ m − 1 / 2 . The deformed microstructure is comprised of planar and wavy dislocations and deformation twins. Cryogenic deformation results in an increase in mechanical strength, brought about by the complex deformed microstructure involving deformation twins and ε martensite laths. Addition of silicon to the alloy system increases the atomic misfit of the MEA and decreases the alloy's stacking fault energy (SFE) value, thereby activating the deformation mechanism of FCC-to-HCP martensitic phase transformation. Overall, the study concludes that MEA has the potential to be a more cost-effective alternative to expensive high entropy alloys. • A novel Fe–25Mn–5Co-12.5Cr–5Ni-2.5Si medium entropy alloy improved mechanical strength and cost-effectiveness simultaneously. • The Hall-Petch equation of the MEA displays superb intrinsic and grain boundary coefficients. • Cryogenic strengthening is evident in the alloy, and cryogenic deformation enhances its mechanical strength and elongation. • The Silicon addition in this MEA is proven to enhance the mechanical performance compared to the Si-free MEA. [ABSTRACT FROM AUTHOR]

Developing structural alloys for critical cryogenic applications is a challenging yet essential task, primarily due to the ductile-brittle transition phenomenon. To address this issue, we developed a twinning-aided coherent precipitation-containing Co 45 Cr 15 Ni 30 Al 5 Ti 5 high entropy alloy (HEA) with remarkable cryogenic properties. The activation threshold for twinning was successfully reduced via the disordering behavior of the L1 2 phase. In the present work, distinct temperature-dependent deformation behavior was observed. The dominant room-temperature strain accommodation mechanism was found to be the dislocation slip coupled with architectured stacking faults (SFs) and immobile Lomer-Cottrell (L-C) locks. Whereas, deformation twins were readily formed under cryogenic tensile loading, leading to significantly increased yield strength and ultimate tensile strength, approaching 1.5 GPa and 1.9 GPa, respectively. The remarkable cryogenic work hardening behavior contributes to persistent elongation of up to 31 % and the super-high ultimate tensile strength. The presence of SFs, deformation twins, and their interactions provide significant strain-hardening capability. • A twinning-aided L1 2 /FCC HEA with remarkable cryogenic properties was prepared. • Deformation was accommodated by dislocations, SFs networks and L-C locks at 298 K. • Deformation was accommodated by twinning, SFs, and their interactions at 77 K. • Twinning was promoted by reduced phase coherency and disordering of the L1 2 phase. [ABSTRACT FROM AUTHOR]

This study explored the influence of pre-stretching temperature on the microstructural characteristics and deformation behavior of AZ61 magnesium alloy and its implications on grain growth during subsequent annealing. AZ61 alloy was stretched to 5% plastic strain along rolling (RD) and transverse direction (TD) at room (RT) and cryogenic temperature (−150 °C, CT) followed by annealing at 320 °C for 1 h to investigate the twinning and dislocation evolution and its consequent effect on the flow stress, plastic strain and strain hardening rate. Compared to RT-stretched samples, significant improvement in yield stress, strain hardening rate and moderate reduction in elongation to failure were witnessed for CT-stretched samples along RD and TD. The subsequent EBSD analysis revealed the increased fraction of fine {10−12} twins and nucleation of multiple {10−12} twin variants caused by higher local stress concentration at the grain boundaries in CT-stretched samples as manifested by the kernel average misorientation. This higher twin fraction and twin-twin interaction imposed the strengthening by restricting the mean free path of dislocations leading to higher flow stress and strain hardening rate. During annealing of the RT/CT-stretched samples, the residual strain energy and twin boundaries were decreased due to static recovery leading to a coarse-grained twin-free microstructure. Strain induced boundary migration (SIBM) was found to be the predominant mechanism governing the grain growth during annealing via movement of high angle grain boundaries. • Effect of pre-stretching at room and cryogenic temperature was investigated. • Annealing treatment was carried out to witness the grain growth mechanism in stretched samples. • CT-stretched samples displayed significant improvement in yield strength. • Strain induced boundary migration was found to be the predominant mechanism governing the grain growth. [ABSTRACT FROM AUTHOR]

The effect of cryogenic rolling and intermediate aging on the microstructure and properties of the Cu-10Fe-1Nb composites were investigated. After aging for 1800 min, the microhardness, tensile strength and elongation of the Cu-10Fe-1Nb samples reached 158 HV, 623 MPa and 22%, respectively. The microstructure results showed that the fibrous Fe-rich phases and the matrix of the Cu-10Fe-1Nb samples were refined significantly after cryogenic rolling. It could be attributed to the increasing shear strain between the Fe-rich phases and matrix with dislocation density of the matrix, which inhibited the dynamic recovery recrystallization of the matrix. The intermediate aging promoted the dissolved Fe to precipitate obviously, and these precipitates effectively impeded the recrystallization of the matrix during the subsequent aging process. The improvement of mechanical properties was mainly attributed to the Orowan strengthening, refinement strengthening and work hardening resulted from the numerous precipitates, fine grains and high-density dislocation in the matrix, respectively. • Combining cryogenic rolling with intermediate aging was implemented to improve the comprehensive properties of the Cu-Fe-Nb composites. • The tensile strength, elongation and electrical conductivity of the Cu-Fe-Nb samples reached 623 MPa, 22% and 51%IACS, respectively. • Cryogenic rolling significantly increased the work-hardening by inducing more dislocations. • The Rule of Mixtures method was used to reveal the contribution of different strengthening mechanisms. [ABSTRACT FROM AUTHOR]

The sheet formability of cold-rolled pure titanium (Ti) was remarkably recovered after being slightly rolled at 77 K, i.e., subjected to cryogenic-deformation treatment (CDT). This recovery occurred because CDT increased the thinning capability of the cold-rolled pure Ti, thereby suppressing cracking by restraining local strain concentration during subsequent sheet forming. The thinning capability was high because CDT formed twins, and slip in their orientations was favorable to accommodate thinning deformation. In addition, twinning during deformation contributed to high thinning capability. The twinning was possible because during deformation, the preformed twins by CDT acted as twin nuclei, enabling growth-dominant twinning without requiring a substantial activation stress for twin nucleation. CDT also increased the strength of cold-rolled pure Ti by twinning-induced grain refinement and dislocation accumulation. These abilities of CDT are noteworthy because sheet formability and strength are typically mutually exclusive. Thus, CDT achieved a superior combination of sheet formability and strength, which cannot be achieved by cold rolling alone, overcoming the trade-off between these two properties in pure Ti. [ABSTRACT FROM AUTHOR]

Aluminum, copper and silver samples, all of them face-centered cubic (FCC) metals, were rolled at room and cryogenic temperatures until equivalent strains (ε) were between 3.23 and 4.13. The cryogenic temperature (CT) and room temperature (RT) rolled samples were evaluated by hardness tests and X-ray diffraction (XRD), which indicate influence of stacking fault energy (SFE) on process. Lower SFE metals tend to exhibit dislocation densities significantly increased and as consequence, hardness too. It was also noted that after sometime exposed to RT, the materials rolled at CT present hardness decrease.

In the present work, an ultrafine grained (UFG) aluminium matrix nano composite (UFANC) was prepared through a cryogenic deformation based manufacturing route. The influence of annealing on the microstructural evolution, mechanical properties and the crystallographic texture of the developed UFANC material was studied and compared with the unreinforced ultrafine grained counterpart (UFG). The presence of nano particles during deformation led to an increased generation of dislocations in the matrix. At low annealing temperatures high density dislocations provided a higher driving force for recrystallization in the UFANC. At high temperatures the grain growth in the UFANC was restricted by the pinning action of the nano reinforcement. This resulted in a higher activation energy for grain growth compared to the UFG counterpart. As a result, the UFANC retained high strength and possessed a fine microstructure even at annealing temperatures of up to 250 °C. The evolution of the texture during annealing was influenced due to the deformation at cryogenic environment. The presence of nano particles led to a more random texture in the UFANC compared to the UFG counterpart during annealing. Unlabelled Image • Ultrafine grained Al nano composite was annealed at different temperatures. • The effect of nano particle addition on the mechanical properties was evaluated. • The fracture behavior of the annealed material was analyzed. • The evolution of the crystallographic texture during annealing was investigated. [ABSTRACT FROM AUTHOR]

The present study concerns the cryogenic processing of metals with simultaneous analysis of x-ray diffraction in a synchrotron ring. The mechanical properties improvement related to cryogenic processing of metals is attributed to the partial suppression of dynamic recovery. Thus, commercially pure metals with different stacking fault energies (silver, copper and aluminum) were deformed by uniaxial tensile tests and characterized by in situ x-ray diffraction, at room (293 K) and cryogenic (77 K) temperatures. The cryogenic processing allows a simultaneous improvement in ductility and strength for silver and copper and an improvement in strength for aluminum. This difference in mechanical properties was investigated by means of variations in crystallite size, microstrain and also the amount and size of dimples on the fracture surface. The microstructural refinement at cryogenic temperatures shows a tendency related to the stacking fault energies. [ABSTRACT FROM AUTHOR]

The microstructure-mechanical property relationships of a non-equiatomic FeMnCoCr high entropy alloy (HEA), which shows a single face-centered cubic (fcc) structure in the undeformed state, have been systematically investigated at room and cryogenic temperatures. Both strength and ductility increase significantly when reducing the probing temperature from 293 K to 77 K. During tensile deformation at 293 K, dislocation slip and mechanical twinning prevail. At 173 K deformation-driven athermal transformation from the fcc phase to the hexagonal close-packed (hcp) martensite is the dominant mechanism while mechanical twinning occurs in grains with high Schmid factors. At 77 K athermal martensitic transformation continues to prevail in addition to dislocation slip and twinning. The reduction in the mean free path for dislocation slip through the fine martensite bundles and deformation twins leads to the further increased strength. The joint activation of transformation and twinning under cryogenic conditions is attributed to the decreased stacking fault energy and the enhanced flow stress of the fcc matrix with decreasing temperature. These mechanisms lead to an elevated strain hardening capacity and an enhanced strength-ductility combination. The temperature-dependent synergy effects of martensite formation, twinning and dislocation plasticity originate from the metastability alloy design concept. This is realized by relaxing the equiatomic HEA constraints towards reduced Ni and increased Mn contents, enabling a non-equiatomic material with low stacking fault energy. These insights are important for designing strong and ductile Ni-saving alloys for cryogenic applications. [ABSTRACT FROM AUTHOR]

A single FCC phase 40Fe-25Ni-15Cr-10Co-10V high-entropy alloy was designed, fabricated, and evaluated for potential cryogenic applications. The alloy forms a single FCC phase and exhibits higher yield strength, tensile strength, and elongation at cryogenic temperature (77 K) than at room temperature (298 K). The superior tensile properties at cryogenic temperature are discussed based on the formation of deformation twins during the tensile test at cryogenic temperature. In addition, a constitutive model reflecting the cryogenic deformation mechanism (i.e., twinning-induced plasticity) was implemented into the finite element method to analyze this behavior. Experimental results and the finite element analysis suggest that the increase in plastic deformation capacity at cryogenic temperature contributes to the formation of deformation twins. [ABSTRACT FROM AUTHOR]

Abstract The influence of alloy concentration with different stacking fault energy (SFE) on tensile properties of Cu and Cu-Al alloys processed by high pressure torsion (HPT) at room temperature (RT) and liquid nitrogen temperature (LNT) was investigated. With decreasing SFE, the twinning capability, the dislocation density and grain refinement were enhanced at LNT, however, tensile strength and uniform elongation were not simultaneously improved. The enhanced tensile properties are explained in terms of the twinning capability, the grain size and the dislocation density independent of the short range order (SRO). Graphical abstract Image 1 Highlights • Cu-Al alloys were processed by HPT at liquid nitrogen temperature. • Decreasing SFE enhances the twinning capability and the grain refinement. • A decrease of deformation temperature and SFE improves tensile strength. • Tensile strength and uniform elongation in Cu-Al alloys by HPT at LNT are not simultaneously improved. [ABSTRACT FROM AUTHOR]

In this study, a systematic investigation on the twin-induced dynamic recrystallization (DRX) of commercially pure titanium (CP-Ti) was carried out under uniaxial compression at room (RT) and cryogenic temperature (CT, −150 °C). The compression tests were intentionally interrupted at 0.02, 0.05 and 0.1 strain levels at both deformation temperatures and a detailed post-mortem analysis was performed via electron backscattered diffraction (EBSD) to examine the progressive evolution of microstructure. The results revealed that two major types of twins i.e. {10−12} extension twin (ETW) and {11−22} compression twin (CTW) were effectively activated at both deformation temperatures. During RT deformation, increased strain levels resulted in the higher evolution of ETWs and CTWs, where numerous twin lamellas, lateral twin thickening and twin-twin interactions (ETW-ETW, ETW-CTW) were observed. On the other hand, CT deformation led to significant grain refinement with the average grain size reduced by 94% (3.7 μm for CT-10 sample as compared to 63 μm of initial material). The recrystallization kinetics were understood with respect to three region of interests (ROIs). The DRX mechanism was identified as tDRX, where intersectional {10–12} ETWs and {11–22} CTWs network provided the preferential sites for the nucleation of DRXed grains due to high strain energy from the dislocation pile-ups at the TBs. • DRX of CP-Ti was carried out under compression at RT and CT(−150 °C). • RT deformation led to numerous twin lamellas, twin growth and twin interaction. • CT deformation led to significant grain refinement where grain size reduced by 90%. • DRX mechanism was identified as tDRX. [ABSTRACT FROM AUTHOR]

Abstract We compared deformation twinning activity and twin structure development of pure Ti at cryogenic temperature and room temperature by conducting unidirectional rolling at 77 K and 293 K. Twinning activity was significantly higher in rolling at 77 K than in rolling at 293 K. This was because lowering the deformation temperature increased the necessity for twinning operation to compensate for reduced accommodation of strain along the c -axis of the crystal structure, caused by inhibition of < c + a > slips. Twin structure was also entirely different between the two rolling temperatures. Compared to the case of rolling at 293 K, rolling at 77 K generated thin and numerous individual twins in the twinned grains, thereby giving rise to the development of a totally different twin structure. The differences in twin structure were caused by the combined effect of significant local stress concentration at grain boundaries and a reduction in stacking fault energy by rolling at 77 K. The twin structure strongly contributed to severe twinning-induced grain refinement that occurs at cryogenic temperature. [ABSTRACT FROM AUTHOR]

Abstract Asymmetric rolling combines direct compression and shear strain imposed by working rolls with different diameters or different rotations speeds. Processing at cryogenic temperatures may partially suppress dynamic recovery mechanisms, modifying the work-hardening rate and increasing the amount of accumulated strain. In this work, samples of AA6061 Al alloy were processed by asymmetric and conventional rolling, at room and cryogenic temperatures. The effects of asymmetric cryorolling were analyzed in terms of strain distribution, grain refinement, hardness, tensile strength and crystallographic texture after post-deformation heat treatments. Artificial aging after conventional rolling at room temperature proved to be more effective in increasing hardness and tensile strength, while the same heat treatment after asymmetric rolling at cryogenic temperature increased uniform elongation and reduced texture intensity. This behavior was associated with recovery and recrystallization phenomena after aging, which cause small dislocation-free grains to be generated inside deformation bands. This was observed directly by TEM and indirectly by texture analysis. [ABSTRACT FROM AUTHOR]

Annealing of the submicrocrystalline (SMC) structure of niobium obtained by high pressure torsion to e = 7 at the temperature of liquid nitrogen was carried out. The influence of the annealing temperature in the range of 100-1100°C on the recrystallization of the SMC structure and the formation of texture was investigated. This paper discusses the role of static recovery and thermoactivated formation of recrystallization nuclei. The submicrograined recrystallized structure characterized by an average grain size of 0.8 μm, by a high homogeneity, and by the lack of the texture has been obtained. The sharpest recrystallization texture is formed as a result of annealing at 900°C; the average grain size is 10 μm in this case. [ABSTRACT FROM AUTHOR]

A pre-cold-deformation process was applied for commercially pure titanium at cryogenic temperature to activate high-density deformation twins, and subsequent hot-deformation was used to induce dynamic recrystallization (DRX). Three major types of twins were effectively activated during cryogenic deformation, including { 11 2 ¯ 2 } contraction twins, { 11 2 ¯ 1 } extension twins, and { 10 1 ¯ 2 } extension twins. A special type of slipped { 11 2 ¯ 1 } “twins” was also activated by a sequential effect of twinning and slip. Selection of twinning variants followed Schmid's law well, where only the twinning systems with a Schmid factor of m  ≥ 0.4 could be activated. The pre-activated twinning led to a remarkably stable flow stress at 500 °C up to a true strain of 1.0, due to the attainment of dynamic equilibrium between strain hardening and high-temperature softening. Two DRX stages occurred: (1) twin-active DRX stage, and (2) discontinuous dynamic recrystallization (DDRX) stage. The DRX mechanisms identified were twinning-induced DRX (or TDRX) and DDRX. While the low-temperature slip alone had little influence on DRX, the pre-activated { 11 2 ¯ 2 } twins, { 11 2 ¯ 1 } twins, { 10 1 ¯ 2 } twins and slipped { 11 2 ¯ 1 } “twins” contributed effectively to DRX in the form of spheroidization of twin lamellae due to twin-dislocation interactions, leading to a substantial grain refinement from ∼41 to ∼1 μm during subsequent hot-deformation. [ABSTRACT FROM AUTHOR]

The deformation responses at 77 and 293 K of a FeCoNiCr high-entropy alloy, produced by a powder metallurgy route, are investigated using in situ neutron diffraction and correlative transmission electron microscopy. The strength and ductility of the alloy are significant improved at cryogenic temperatures. The true ultimate tensile strength and total elongation increased from 980 MPa to 45% at 293 K to 1725 MPa and 55% at 77 K, respectively. The evolutions of lattice strain, stacking fault probability, and dislocation density were determined via quantifying the in situ neutron diffraction measurements. The results demonstrate that the alloy has a much higher tendency to form stacking faults and mechanical twins as the deformation temperature drops, which is due to the decrease of stacking fault energy (estimated to be 32.5 mJ/m 2 and 13 mJ/m 2 at 293 and 77 K, respectively). The increased volume faction of nano-twins and twin-twin intersections, formed during cryogenic temperature deformation, has been confirmed by transmission electron microscopy analysis. The enhanced strength and ductility at cryogenic temperatures can be attributed to the increased density of dislocations and nano-twins. The findings provide a fundamental understanding of underlying governing mechanistic mechanisms for the twinning induced plasticity in high entropy alloys, paving the way for the development of new alloys with superb resistance to cryogenic environments. [ABSTRACT FROM AUTHOR]

Commercially pure titanium specimens were processed via three-directional compression at cryogenic temperature to activate homogeneous high-density deformation twins, and subsequent hot compression at 500 °C was applied to induce homogeneous grain refinement. Thus, homogenous and refined grains with an average grain size of 1.6 µm were achieved. During three-directional compression, four type of twins were activated, namely, parallel { 11 2 ¯ 2 } twins, parallel { 10 1 ¯ 2 } twins, intersectional { 10 1 ¯ 2 } twins and parallel { 11 2 ¯ 1 } twins. In the first pass, { 10 1 ¯ 2 } , { 11 2 ¯ 1 } and { 11 2 ¯ 2 } twins were activated; in the second pass, { 10 1 ¯ 2 } and { 11 2 ¯ 2 } twins were activated; and in the third pass, { 10 1 ¯ 2 } twins were activated. During hot compression, the dynamic recrystallization (DRX) process was divided into twin-active DRX stage and continuous DRX (CDRX) stage. In the first stage, the DRX mechanisms were twinning induced CDRX (TCDRX) and twinning induce DDRX (TDDRX) in parallel { 11 2 ¯ 2 } twins, TCDRX and TDDRX in parallel { 10 1 ¯ 2 } twins, TCDRX and intersectional twins induced DRX (ITDRX) in intersectional { 10 1 ¯ 2 } twins and TCDRX in parallel { 11 2 ¯ 1 } twins. Nine types of new texture components formed in this stage. In the last stage, the DRX mechanism was CDRX. The < a > basal slip, < a > pyramidal slip and 1st < c  +  a > pyramidal slip were the major deformation mechanisms during hot deformation. [ABSTRACT FROM AUTHOR]

Cryogenic deformation was introduced in thermomechanical processing to restrict dislocation mobility and tailor the initial dislocation distribution at the deformation stage, subsequently followed by annealing treatment to alter the grain boundary characteristic distribution with a view to the feasibility of grain boundary engineering in Incoloy 925. The microstructural evolution deformed at cryogenic (77 K) and room temperature (298 K) under various rolling reductions and annealing conditions was systematically studied to optimize the grain boundary network, which is evaluated using multi-source quantitative statistics of the twin related domains. The results showed that cryogenic deformation can adjust the dislocation accumulation mode and plastic deformation mechanism. Geometrically dislocation distributions, reconstructed by HR-EBSD device, with fishbone-like, ribbon-like or lamellar characteristics can be observed for the deformed specimens. During the subsequent annealing, the samples with 5% and 15% pre-strain are incapable of producing the ideal twin related domains, while the sample annealed at 1075°C with 10% pre-strain show the optimization of GBCD with the highest Σ3 n (n = 1, 2, and 3) boundary fraction being 69.67%. Compared with the room temperature pre-deformation, cryogenic deformation can effectively reduce the critical temperature of GBE, and also leads to the Σ3 n grain boundaries proportion increasing from 31.47% to 67.46% in 10%/1050°C sample. Meanwhile, with the appropriate strain, cryogenic deformation is more conducive to optimizing the GBCD than room-temperature deformation. • Cryogenic deformation was applied in TMP to tailor dislocation accumulation and GBCD. • GNDs with fishbone-like, ribbon-like, and lamellar are observed after cryogenic deformation. • Modified GBCD is realized by cryogenic deformation under appropriate strain. [ABSTRACT FROM AUTHOR]