Dominant Deformation Mode Research Articles

Annealing parameters effect on microstructure evolution, tensile properties and deformation behaviors of direct-cold-rolled UNS S32101 duplex stainless steel with heterogeneous layered structure

Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.

Twinning transfer in a near β-Ti alloy under high strain rate dynamic loading

The microstructure evolution of near β-Ti alloys with initially lamellar and equiaxed microstructures subjected to dynamic loading was investigated. Results showed that during high strain rate compression, shear failure is more likely to occur in equiaxed microstructure. Owing to temperature rise and stress concentration, the lamellar α phase in adiabatic shear band (ASB) zone was recrystallized and re-melted, while the equiaxed α phase transformed in strip-shaped following the propagating direction of adiabatic shear band. During high strain rate loading, the twinning transfer was observed between β matrix and α phase, which demonstrates that twinning is the dominant deformation mode to accommodate plastic deformation.

The annealing strengthening effects in a high-ductile ZG205 alloy sheet

A high-ductile Mg-1.70Zn-0.47Gd (wt.%) alloy sheet was pre-tensile strained to 0.2% and 4% (0.2S & 4S) in the transverse direction with an initial strain rate of 0.001s−1, followed by annealing at temperatures ranging from 100 to 250 °C. The effect of annealing temperature on yield strength (σys) was investigated. Generally, the σys increased up to 200 °C annealing temperature, and beyond this temperature annealing softening was observed. In pre-tensile strained specimens, the more the amount of strain, the higher was the σys. Thus, in 0.2S and 4S specimens, the maximum increase in σys by annealing strengthening alone was 5 and 18 MPa, respectively. After straining at room temperature, different variants of {101‾2} extension twins were observed, and dominant deformation mode was established in un-twinned and severely twinned grains separately by Schmid factor analysis considering the relative activity of slip and twinning. It was concluded that the annealing strengthening mechanism was precipitation strengthening, as revealed by the similar microstructural features in TEM micrographs of 0.2S and 4S specimens.

Microstructure Evolution and Deformation Behavior of Extruded Mg-5Al-0.6Sc Alloy during Room and Elevated Temperature Tension Revealed by Ex-Situ EBSD and VPSC.

In this study, the microstructure evolution and deformation behavior of the extruded Mg-5Al-0.6Sc (AS51) alloy during tensile testing at room temperature (RT) and 250 °C were investigated by electron backscattered diffraction (EBSD) characterization and Visco Plastic Self Consistent (VPSC) simulation. The results showed that a continuous hardening behavior of the alloy occurred during the deformation at RT, and a certain softening was caused by the occurrence of dynamic recovery (DRV) and dynamic recrystallization (DRX) in the late stage of deformation at 250 °C. The primary deformation mechanism at both RT and 250 °C was dislocation slip, with prismatic <a> slip being the dominant deformation mode, and no significant changes in grain size or texture type occurred. By identifying the activated twin variants, the results indicated that the selection of twin variants was closely related to the local stress concentration. The relatively low activation frequency of extension twinning at 250 °C is partly attributed to the fact that the consumption of dislocations by DRV and DRX can effectively relax the local stress concentration. Meanwhile, the DRX mechanism during the deformation of the alloy at 250 °C was mainly discontinuous dynamic recrystallization (DDRX), with a low recrystallization fraction.

Insight on the in vivo wear characteristics of goat artificial cervical disc implanted for 6 months

Since the prosthesis may suffer overload or extreme motion during the daily activities, some special failure modes may be found in service. In order to give an insight on the in vivo stability of artificial cervical disc, the wear characteristics of goat prosthesis were studied after implanted in goat animal for 6 months. The prosthesis was designed with a ball-on-socket structure under the material combination of PE-on-TC4. The X-ray examination was performed to monitor the in vivo wear process. The worn morphology and wear debris were analyzed in detail by EDX and SEM. The result indicated that goat prosthesis revealed good safety and effectiveness during 6-month in vivo wear test. The wear damage occurred only on nucleus pulposus component with the dominant failure mode of surface fatigue and deformation. The damage distribution and wear severity was seriously uneven with a trend that the closer to the edge, the more severe the wear. For example, slippage phenomenon caused a wide and curved severe ploughing damage on the edge. Three kinds of debris were found including bone debris, carbon-oxygen compound debris and PE wear debris. Both bone debris and carbon-oxygen compound debris came from superior endplate while PE wear debris came from nucleus pulposus. The debris proportion for endplate was 82% for bone debris, 15% for carbon-oxygen compound debris and 3% for PE debris while for nucleus pulposus it was 8% for carbon-oxygen compound debris and 92% for PE debris. The size range of PE debris for nucleus pulposus was 0.1–100 μm, with an average size of 9.58 ± 16.34 μm. For the bone debris of endplate components, the size range was 0.1–600 μm, with an average size of 49.18 ± 94.54 μm. After wear test, the equivalent elastic modulus of nucleus pulposus increased from 28.55 MPa to 38.25 MPa. The results of FT-IR spectrum showed that the functional groups on the surface of polyethylene have not changed significantly after wear test. The results indicated that there were some differences in wear characteristics of wear morphology and wear debris between in vivo wear and in vitro wear.

Strain transfer behavior and crystallographic mechanism of crack initiation during cyclic deformation in zirconium

Fully-reversed cyclic deformation of a pure Zr (a thickness of 17 mm) was conducted at two different strain amplitudes (0.4% and 0.8%) to investigate the deformation and crack initiation behaviors based on slip trace analysis. It was found that prismatic 〈a〉 slip with a higher Schmid Factor (m > 0.4) was the dominant deformation mode. The grains containing persistent slip bands (PSBs) tended to go towards [1¯21¯0] pole and the Schmid Factor had a critical value of 0.4 above which prismatic and pyramidal slip were dominant. Fatigue cracks were mainly initiated at PSBs and grain boundaries (GBs). It showed that 61.1% of the cracks were PSB cracks under a strain amplitude of 0.4%, while it decreased to 53.5% at a strain amplitude of 0.8%. PSB cracks were mainly parallel to prismatic 〈a〉 slip with higher Schmid Factor while some cracks tended to be initiated at GBs with higher misorientation angles. The interaction of PSBs with GBs would result in strain transferring to the neighboring grain. Strain transfer was more likely to occur at the condition of the higher geometrical compatibility factor m′, and lower residual Burgers vector Δb, which could reduce strain localization.

Effect of interface structure and layer thickness on the mechanical properties and deformation behavior of Cu/Ag nanolaminates

We performed molecular dynamics (MD) simulations to study the effect of interface structure and layer thickness on the mechanical properties of multilayered Cu/Ag composite with Cu{111}//{111}Ag and Cu{100}//{100}Ag interfaces. The results indicate that deformation twinning is the dominant plastic deformation mode in the multilayer with Cu{100}//{100}Ag interfaces and differs from the dislocation slip in the models containing Cu{111}//{111}Ag interfaces. The interfaces in the Cu{111}//{111}Ag multilayer are significantly roughened by dislocation transmission across interfaces. The Shockley partial dislocations are difficult to cross Cu{100}//{100}Ag interface until the interface is twisted by deformation twinning. The deformation twinning in the Ag channel induces twists of Cu{100}//{100}Ag interface, facilitating twinning in Cu channels and dislocation transmitting across the Cu/Ag interface within twin bands. The mechanism results in strong interface roughening. The Cu{110}//{110}Ag interface is formed after the deformation twinning in models containing Cu{100}//{100}Ag interfaces, which exhibits extremely high shear strength than the Cu{100}//{100}Ag interface and produces a weak blocking effect on gliding dislocations.

A high temperature manufacturability study of ultrafine grained Magnesium Rare-Earth alloy using processing map and constitutive analysis

The rare-earth (RE) contained ultrafine grained (UFG) Magnesium (Mg) alloys are excellent materials for aerospace and automobile industries due to their ultra-light weight, high strength, reduced tension to compression yield asymmetry, etc. Despite their excellent properties, the manufacturing potential of UFG Mg-RE alloys is yet to be realized. The present work is focused on engineering UFG microstructure in a Mg-Ag-Nd alloy (a Mg-RE alloy) and establishing the manufacturing potential of such engineered UFG Mg-RE alloy via processing map and constitutive analysis studies. The processing map is developed for a temperature range of 300 °C-450 °C and a strain rate range of 0.001 s−1-1 s−1, respectively. Three stability domains and one instability domain were identified. The governing mechanisms and scientific know-how of both types of domains are established via mechanical testing followed by detailed microstructural characterization, including Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) analysis. A unique unexplored grain boundary sliding (GBS) mechanism-based stability domain is found as a dominant mode of deformation in one of the stability domains in the engineered UFG Mg-RE alloys.

Electron Microscopy Study of Structural Defects Formed in Additively Manufactured AlSi10Mg Alloy Processed by Equal Channel Angular Pressing

This study focused on electron microscopy studies of microstructural defects formed in an additively manufactured (AM) AlSi10Mg alloy as a result of post-deformation by equal channel angular pressing (ECAP), with the aim of elucidating the fundamental deformation mechanisms that govern the plasticity of both the aluminium matrix and the silicon phase. This article focused on the process of grain refinement, metastable phase transformations, and microstructural defects such as stacking faults or amorphous areas that severely disrupt the face-centred cubic (FCC) crystal lattice symmetry. The findings presented in this study imply that deformation twinning, phase transformation, and amorphization are not mutually exclusive modes of Si phase deformation. Both can occur at an ECAP temperature of 150 °C. At a deformation temperature of 100 °C, amorphization is the dominant deformation mode of the Si phase. It was also discovered that dislocation slip was the predominant deformation mode of Al matrix at 150 °C, while at 100 °C, additionally stacking faults were formed within the Al matrix. The present findings provide not only a fundamental understanding of the deformation micro-mechanism of the SLMed AlSi10Mg alloy but also open a new horizon for the development of the next generation of structural materials.

A novel coherent particles-reinforced FCC-based high-entropy superalloy with superior high-temperature compressive properties

A novel κʹ-strengthened FCC-based Al0.5CoFeNiC0.1 high entropy superalloy (HESA) with minor B2 phase was prepared by arc melting. The FCC/κʹ dual-phase microstructure with thermal stability is similar to γ/γʹ microstructure of Ni-based superalloys. Surprisedly, the large volume fraction (nearly 50%), high density and nano-scale coherent κʹ particles with uniform distribution are easily accessible only by direct solidification, which gives rise to superior compressive yield strengths at both room and elevated temperatures, reaching 1130 MPa at 25 °C and 830 MPa at 700 °C, respectively. The sustained high-temperature yield strength is contributed to both the antiphase boundaries (APBs) and stacking faults (SFs) shearing κʹ particles. Further, optics and electron microscopy analyses revealed the changes (transition point about at 0.6 Tm, where Tm is melting temperature) of the dominant deformation and failure mechanisms, dependent on the temperature. The dominant deformation mode is planar slip and SFs at relatively low temperatures, while the cross slip and dislocation dissociation above 800 °C (0.6 Tm), coupled with the diffusion-controlled recovery mechanisms. The failure mechanism shows failure mode from shearing fracture to thermal softening. Our κʹ-strengthened FCC-based superalloy provides a route for elevated-temperature applications.

Numerical investigations on dynamic responses of subway segmental tunnel lining structures under internal blasts

Numerical simulation of segmental lining tunnel subjected to internal explosive loading is carried out in this paper based on the arbitrary-Lagrangian-Eulerian (ALE) and finite element (FE) coupled algorithms. A high-fidelity FE model considering assembled features of segmental lining structure is established, and the mapping technique is adopted to accurately simulate the explosion process. The calculated overpressure histories and failure modes of the lining structure fit well with field test results of full-scale specimens, indicating the applicability and accuracy of the numerical model. A more comprehensive numerical model considered the practical service state of segmental lining tunnel is further built based on the verified model. Influences of mechanical properties and pressure levels of surrounding soils on dynamic responses of tunnel structure under internal explosion are investigated. Numerical results show that dominated deformation modes of the segmental lining tunnel under the action of internal explosion include opening deformation at the segmental joints of the charged ring and shear deformation between the adjacent rings. The modest explosion caused by terrorist bombing attacks may severely harm the shield tunnel structure and impair its service performance, especially if the tunnel is buried in soft soil at a shallow depth

An interface nucleation rate limited sintering kinetic model applied to in situ sintering Al2O3-SmAlO3 composites

A nucleation rate limited sintering model was recently developed based on observations of bicrystal sintering. This work validates the applicability of this model for sintering of polycrystalline clusters of Al2O3-SmAlO3 at high temperature in the range of 1130–1610 ℃. The model fits the data well and agrees with trends observed during bicrystal sintering. A temperature dependence to the dominant sintering strain deformation modes is observed from in situ heating experiments performed in a transmission electron microscope (TEM). The observations provide insights into how temperature influences the early stages of sintering by affecting the pore size distribution through local de-sintering. This provides insights into the role heating rate and sintering schedule play in microstructural evolution that influences the grain size versus density trajectory.

Synergistic Strengthening of Dislocation and Heterodeformation Induced in Gradient Nanograined Copper Film: A Molecular Dynamics Study

Unlike conventional homogeneous nanograined (NG) materials, gradient structured materials combine high strength and ductility. The gradient nanograined (GNG) structures are divided into three zones by grain size: the small‐grained zone, the transition‐grained zone, and the large‐grained zone. Molecular dynamics (MD) simulation is performed to investigate the effect of the widths of zones on the strength of GNG structures with different grain sizes. The simulation results reveal the strengthening mechanism of GNG structures from the perspective of microstructure evolution. With the change in grain size, the dominant deformation mode changes from grain boundary (GB) activities in the mall‐grained zone to dislocation slip in the large one. The inverse Hall–Petch phenomenon is observed during plastic deformation. Synergistic strengthening of dislocation and heterodeformation induced (HDI) can be achieved in the structure by regulating the widths of zones with different grain sizes.

Microstructure optimization for higher strength of a new Fe–Ni-based superalloy

Tensile properties and deformation mechanisms of a Fe–Ni-based superalloy with different size of γ′ precipitates obtained through varied aging time are investigated at 700 °C. The γ′ phase size increases with aging time, the yield strength of the alloy increases first and then decreases, which is consistent with the change trend of critical resolved stress of deformation mechanism. The dominant deformation mode of the alloy with fine γ′ phase is weakly-coupled dislocation pairs with slip bands, and then changes to Orowan looping at a γ′ size of approximately 30 nm, resulting in the occurrence of peak value of strength. As the γ′ size is above 40 nm, the deformation mechanism is Orowan bowing along with stacking fault shearing, decreasing the yield strength of the alloy. When γ′ size is between 30 nm and 40 nm, the dominant deformation mechanism is Orowan looping with strongly-coupled dislocation pairs and the fracture mode is intergranular. Intermediate temperature brittleness occurs in the secondary aging treated alloy with a γ′ phase size of approximately 30 nm, which is attributed to the increase in critical resolved stress and strain localization caused by the transformation of tensile deformation mechanism, and stress concentration due to dislocation entanglement at grain boundary. The sub-aging state of the alloy used for advanced ultra-supercritical plants may be a good choice for obtaining simultaneously favorable strength and ductility.

Microstructural factors dictating the initial plastic deformation behavior of an ultrafine-grained Fe–22Mn-0.6C TWIP steel

While leading a great strain hardening capability, carbon-containing twinning-induced plasticity (TWIP) steels exhibit serrations on their stress-strain curves, resulting in barriers to commercial development. Although grain refinement is believed to suppress the serrations, how the grain size, particularly in the ultrafine-grained (UFG) range, and its orientation impacting on the serrations and plastic deformation mechanism are overlooked. Here, we compared the plastic deformation behavior in fine-grained (2 μm) and ultrafine-grained (0.86 μm) specimens, in both macroscopic and microscopic behavior, using digital image correlation (DIC) and scanning transmission and transmission electron microscopy (S/TEM) techniques. Our results showed that the dominant plastic deformation mode was changed from dislocation gliding and tangling to stacking faults and deformation twinning in the grains equal to or smaller than 1 μm (ultrafine grains). This alteration is also strongly influenced by the grain orientation, i.e., the maximum resolved shear stress for slip versus twinning. The enhancement of strain localization and the inhibition of the serrations in the UFG specimens are discussed.

The effect of grain size on deformation modes and deformation heterogeneity in a rolled Mg–Zn–Ca alloy

Grain refinement could promote the activation of non-basal slip and enhance the strength and ductility of Mg alloy simultaneously. In this work, the grain size effect on deformation modes and deformation heterogeneity and its relations to crystallographic orientation in a rolled Mg–1.58Zn–0.1Ca alloy sheet with a weakened transverse direction (TD) spread texture were investigated via intragranular misorientation axis (IGMA) and high resolution-digital image correlation (HR-DIC) measurement. The results indicate that a decrease of the grain size from 55 to 13 μm increased the yield strength (YS) by 56.9%, from 72 MPa to 113 MPa, for the TD samples, but only by 8% for the rolling direction (RD) samples, from 125.7 to 135.7 MPa. Moreover, grain refinement enhanced the elongation by 76.4% for the TD samples, from 11% to 19.1%, and merely by 26.5% for the RD samples, from 16.6% to 21%. The transition in dominant deformation modes due to grain size decreasing can be summarized as: for the RD samples: basal slip → prismatic slip; for the TD samples: basal slip + tension twinning → prismatic slip. The enhanced activity of prismatic slip in the fine-grained (FG)-TD and FG-RD samples can be ascribed to the reduced ratio of critical resolved shear stress (CRSS)prismatic/CRSSbasal. For both the RD and TD samples, grain refinement facilitated deformation homogeneity, which could be related to the enhanced activity of basal slip and non-basal slip, as well as the resulting improved deformation compatibility across grain boundary.

A general theory for the bending of multilayer van der Waals materials

Multilayer van der Waals (vdW) materials exhibit nontrivial out-of-plane responses and deformability due to their inherent atomic scale thickness coupled with weak interlayer vdW interactions, which call for a general mechanical framework to quantify such extraordinary characteristics given the structure and material properties. Here, we demonstrate that by considering the competing mechanisms between intralayer stretching, interlayer shearing, and monolayer bending, a general centerline-based theory for multilayered structures is developed to portray the bending landscape of multilayer vdW materials. Combined with large-scale molecular dynamics simulations of three-point bending, we find that when the slenderness ratio or the interlayer shear rigidity is smaller or the intralayer elasticity is higher, the multilayered structures exhibit pronounced nonplanar section deformation due to the interlayer shear capacity. To elucidate quantitative correlations between deformation distribution and structural dimensions and material properties, a critical criterion is proposed to depict the transformation from planar to nonplanar section deformation through a dimensionless characteristic parameter. The effective bending stiffness is then systematically explored in the space of characteristic geometries and material properties to reveal the underlying mechanism of the anomalous size effect. We identify that the effective bending stiffness follows a unified scaling law regarding the dimensionless characteristic parameter. More importantly, a series of deformation-mode phase diagrams are constructed using two universal characteristic lengths, intuitively illustrating the transition of dominated deformation modes and the synergism of geometries and inherent material properties on the bending responses. Validated by several typical vdW materials and novel semiconducting two-dimensional materials, the proposed diagrams not only deepen the understanding of bending in multilayer vdW materials but also provide guidelines for the design and optimization of vdW material-based devices.

Quaternary E-W Extension Uplifts Kythira Island and Segments the Hellenic Arc.

Several crustal and lithospheric mechanisms lead to deformation and vertical motion of the upper plate during subduction, but their relative contribution is often enigmatic. Multiple areas of the Hellenic Forearc have been uplifting since Plio-Quaternary times, yet spatiotemporal characteristics and sources of this uplift are poorly resolved. The remarkable geology and geomorphology of Kythira Island, in the southwestern Hellenic forearc, allow for a detailed tectonic reconstruction since the Late Miocene. We present a morphotectonic map of the island, together with new biostratigraphic dating and detailed analyses of active fault strikes and marine terraces. We find that the Tortonian-Pliocene stratigraphy in Kythira records ∼100m of subsidence, and a wide coastal rasa marks the ∼2.8-2.4Ma maximum transgression. Subsequent marine regression of ∼300-400m and minor E-W tilt are recorded in ∼12 marine terrace levels for which we estimate uplift rates of ∼0.2-0.4mm/yr. Guided by simple landscape evolution models, we interpret the coastal morphology as the result of initial stability or of slow, gradual sea-level drop since ∼2.8-2.4Ma, followed by faster uplift since ∼1.5-0.7Ma. Our findings on- and offshore suggest that E-W extension is the dominant mode of regional active upper crustal deformation, and N-S normal faults accommodate most, if not all of the uplift on Kythira. We interpret the initiation of E-W extension as the result of a change in plate boundary conditions, in response to either propagation of the North Anatolian Fault, incipient collision with the African plate, mantle dynamics or a combination thereof.

Unraveling hot deformation behavior and microstructure evolution of nanolamellar TiAl/Ti3Al composites

An in-depth understanding of the deformation behavior of a nanolamellar TiAl/Ti3Al composite is prerequisite to control the mechanical properties of this material. Nevertheless, to obtain the excellent performance, the role of microstructure evolution on the deformation mechanism maps at a wide temperature range is still required. To this end, the effect of temperature on the compressive response and deformation mechanism of a nanolamellar TiAl/Ti3Al composite is investigated using molecular dynamics simulations. The deformation-induced α2→γ phase transformation results in the softening, and the deformation twinning causes the strain hardening. The high temperature reduces the local shear strain along the interface, to enhance the deformation capacity of the γ phase. At a low strain, the dislocation slip on the single slip system is the dominant deformation mode; at a medium strain, the phase transformation controls the plastic deformation; at a high strain, the deformation twinning associated with the activation of the multi-slip systems is responsible for the late plastic stage. The phase interface bents towards the γ phase, and then the α2 phase grows up, resulting in the evolution of the dynamic complex microstructures. The origin of the nanoscale plasticity event depends upon the atomic-scale deformation gradient field and the atomic-scale microrotation field. The current temperature-dependent deformation mechanism maps provide an insight into the design and fabrication of the advanced nanolamellar TiAl/Ti3Al composites with outstanding strength and ductility.

Rediscovery of Hall-Petch strengthening in bulk ultrafine grained pure Mg at cryogenic temperature: A combined in-situ neutron diffraction and electron microscopy study

Grain refinement can lead to the strengthening of metallic materials according to the Hall-Petch relationship. However, our recent results suggested that grain boundary sliding is the dominant deformation mode in bulk ultrafine grained (UFG) pure Mg at room temperature, leading to softening. Here, for the first time, we report that the Hall-Petch strengthening can be regained in bulk UFG pure Mg at cryogenic temperature. At 77K, the UFG pure Mg with a mean grain size of 0.6 μm exhibited ultrahigh tensile yield strength and ultimate tensile strength of 309 MPa and 380 MPa, respectively. Combined in-situ neutron diffraction and electron microscopy investigation indicated that residual dislocation structures and deformation twins hardly formed in the UFG specimen during tensile test at 298K. In contrast, fast accumulation of lattice defects and remarkable reorientation were evident at 77K, suggesting that the grain-boundary-mediated process was suppressed and the plastic deformation was dominated by dislocation slip and deformation twinning. In addition, all the pure Mg specimens exhibited pronounced strain hardening at 77 K, which was mainly attributed to the suppressed grain boundary sliding and dynamic recovery. The mean dislocation density and relative fractions of dislocations with various Burgers vectors of the UFG specimen deformed at 77K were determined quantitatively from neutron diffraction data. Despite the strong strain hardening capacity, the UFG specimen fractured prematurely at an elongation of 5% at 77K. The significantly reduced ductility at 77K was possibly caused by its higher tensile strength, which generated high intergranular stress and resulted in intergranular fracture before reaching the point of plastic instability. Potential ways for improving the strength and ductility synergy of the UFG Mg at cryogenic temperature were proposed.