Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-d...Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-dimensional transition metal dichalcogenide MoSe_(2) is a particularly promising material for twisted multilayers,capable of sustaining moiréexcitons.Here,we report on a rational bottomup synthesis approach for twisted MoSe_(2) flakes by chemical vapor transport(CVT).Screw dislocation-driven growth was forced by surface-fused SiO_(2)nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition.Thus,crystal growth by in-situ CVT under addition of MoCl_(5) leads to bulk 2H-MoSe_(2) in a temperature gradient from 900 to 820℃ with a dwell time of 96 h.Hexagonally shaped 2H-MoSe_(2) flakes were grown from 710 to 685℃ with a dwell time of 30 min on SiO_(2)@Al_(2)O_(3)(0001)substrates.Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe_(2) with individual step heights between 0.9 and 2.9 nm on SiO_(2)@Si(100)under the same conditions.Finally,twisted MoSe_(2) flakes exhibiting a twist angle of 19°with respect to the[010]zone axis could be synthesized.展开更多
Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450...Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.展开更多
This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a co...This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.展开更多
Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity ca...Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.展开更多
The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined th...The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined the temperature-dependent Peierls stress for 30°and 90°partial dislocations in cadmium telluride(CdTe),using a combination of molecular statics and molecular dynamics simulations with a machine-learning force field,as well as density functional theory simulations.Our findings reveal that the 0 K Peierls stresses for these partial dislocations in CdTe are relatively low,ranging from 0.52 GPa to 1.46 GPa,due to its significant ionic bonding characteristics.Notably,in the CdTe system containing either a 30°Cd-core or 90°Te-core partial dislocation,a phase transition from the zinc-blende phase to theβ-Sn-like phase is favored over dislocation motion.This suggests a competitive relationship between these two mechanisms,driven by the bonding characteristics within the dislocation core and the relatively low phase transition stress of∼1.00 GPa.Furthermore,we observed a general trend wherein the Peierls stress for partial dislocations in CdTe exhibits a temperature dependence,which decreases with increasing temperature,becoming lower than the phase transition stress at elevated temperatures.Consequently,the dominant deformation mechanism in CdTe shifts from solid-state phase transition at low temperatures to dislocation motion at high temperatures.This investigation uncovers a compelling interplay between dislocation motion and phase transition in the plastic deformation of CdTe,offering profound insights into the mechanical behavior and electronic performance of CdTe and other II-VI semiconductors.展开更多
Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dyna...Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.展开更多
Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors rep...Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors report a case of this lesion in a 7-year-old child managed nonoperatively.展开更多
BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we descri...BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we describe a case of an elderly patient who pre sented with a type 2 dislocation after a fall.The mechanisms of inferior patella dislocation,their classification,key imaging features and treatment options are discussed.CASE SUMMARY A 75-year-old woman presented with a right knee fixed flexion deformity after a fall.Preoperative imaging confirmed a vertical intra-articular patella dislocation with a femoral trochlear osteochondral defect and lax though grossly intact patella tendon.Closed reduction was performed under general anaesthesia.Knee arthroscopy confirmed the presence of a femoral trochlear osteochondral defect whose edges were subsequently smoothed and there was debridement of scant debris with thorough irrigation of the joint.Postoperative imaging demonstrated anatomical alignment,however,there was a new nondisplaced medial femoral trochlear.The patient however was able to mobilise well in a range of motion brace set at 0-30 degrees and was discharged 1-day post operatively.CONCLUSION Inferior patella dislocation is rare and this article highlights its types and imaging features which determine the most appropriate management.展开更多
Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. Thi...Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. This is done by examining the acetabular placement in instances of hip dislocation after total hip arthroplasty (THA). Methodology: The authors searched 2653 patient records from 2015 to 2022 looking for patients who had total hip arthroplasty at our facility. For the analysis, 23 patients were culled from 64 individuals who exhibited post-THA dislocations, employing a stringent exclusion criterion, and the resultant acetabular angulation and anteversion were quantified utilizing PEEKMED software (Peek Health S.A., Portugal) upon radiographic evidence. Results: Within the operational timeframe, from the cohort of 2653 subjects, 64 presented with at least a singular incident of displacement. Post-exclusion criterion enforcement, 23 patients were eligible for inclusion. Of these, 10 patients conformed to the safe zone demarcated by Lewinnek for both inclination and anteversion angles, while 13 exhibited deviations from the prescribed anteversion and/or inclination benchmarks. Conclusion: Analysis of the 23 patients reveals that 13 did not confirm to be in the safe zone parameters for anteversion and/or inclination, whereas 10 were within the safe zone as per Lewinnek’s guidelines. This investigative review, corroborated by extant literature, suggests that the isolated consideration of the Lewinnek safe zone does not suffice as a solitary protective factor. It further posits that additional variables are equally critical as acetabular positioning and mandate individual assessment.展开更多
Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying cera...Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying ceramic-like brittle behavior once below a critical temperature.For decades,the dominant mechanism driving the ductile-to-brittle transition of metals-whether dislocation nucleation or dislocation slip-has been a topic of ongoing debate.A new concept of dislocation source efficiency,however,suggests that both processes are complementary and essential for overall ductile deformation.The relative mobility of screw versus edge dislocations dictates the efficiency of dislocation sources,which in turn governs dislocation multiplication and ultimately the material’s ability to plastic deformation.Furthermore,we developed a new model that incorporates factors affecting dislocation activities,such as the initial dislocation density and the number of dislocation sources,offering promising toughening strategies for both metallic structural alloys and ceramics.展开更多
Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms...Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.展开更多
Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading t...Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.展开更多
There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this ...There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.展开更多
Ensuring a harmonious coexistence between man and nature is crucial for China’s economic and social development.However,with increasing industrialization and urbanization,there is a growing mismatch between China’s ...Ensuring a harmonious coexistence between man and nature is crucial for China’s economic and social development.However,with increasing industrialization and urbanization,there is a growing mismatch between China’s ecological resilience(ER)and economic level(EL)of development,which poses a notable social threat.Currently,the link between ER and EL in China remains unclear,especially in terms of spatial dislocation(SD),referring to the disconnect between the locations where environmental impacts occur and those where economic benefits or activities are concentrated.Therefore,this paper aims to provide theoretical support and an empirical basis for policy-based solutions to address this gap.Based on the SD theory,this study systematically discusses the temporal changes,spatial patterns,and SD characteristics of China’s ER and EL using spatial auto-correlation and barycentric analysis to analyze data from 30 provinces covering the period 2011-2021.The key results are as follows.China’s ER shows a general trend of growth;however,its distribution is uneven.The spatial pattern generally decreases from the southeastern coastal provinces to the northwest.Moreover,a gradually increasing positive correlation is observed between the ER and EL,but this correlation varies by region,with some showing regional linkages and others developing independently.Finally,the dislocation index of ER and EL presents divergent results based on region-the eastern and central regions primarily show a high level of dislocation,whereas the western and northeastern regions show a low level of dislocation.The results provide a comprehensive overview of the spatiotemporal patterns in the association between ER and EL in China.The results emphasize that to balance sustainable regional development and ecological governance,a region-specific approach must be employed,prioritizing innovation-driven strategies for high ER in more developed regions and market-oriented strategies in less developed regions.展开更多
Pyramidal dislocations are important for ductility enhancement of magnesium alloys.In this work,molecular dynamics simulations were employed to study the gliding behavior of pyramidal(c+a)dislocations under c-axis com...Pyramidal dislocations are important for ductility enhancement of magnesium alloys.In this work,molecular dynamics simulations were employed to study the gliding behavior of pyramidal(c+a)dislocations under c-axis compressive loading and tensile loading.The Peierls stress of Py-Ⅰ dislocation shows strong tension-compression asymmetry.However,no tension-compression asymmetry is seen on the Py-Ⅱ dislocation and basal dislocation.The tension-compression asymmetry origins from the asymmetry of partial dislocations of Py-Ⅰ dislocation,which leads to the dislocation core contracted under c-axis compressive loading and expanded under tensile loading.By analyzing the forces acting on the partial dislocations,we defined a neutral direction,which deviates from the full dislocation Burgers vector by 70.3°.The neutral direction is dependent on the ratio of lattice stresses of partial dislocations.If the shear stress is applied along the neutral direction,tension-compression asymmetry is eliminated and the dislocation core is un-contracted/un-expanded.The neutral direction of symmetrical dislocations(Py-Ⅱ dislocation and basal dislocation)is just the full dislocation Burgers vector.The tension-compression asymmetry and dislocation core contraction/expansion have an important influence on the dislocation behaviors,such as cross-slip,decomposition,basaltransition and mobility,which can be used to explain the mechanical behaviors of Mg single-crystals compressed along c-axis.展开更多
High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN fi...High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN films on 17 nm AlN/sapphire tem-plates using metal-organic chemical vapor deposition(MOCVD).Comprehensive characterization reveals significant advance-ments in crystal quality and uniformity.Atomic force microscopy(AFM)shows progressive surface roughness reduction during early growth stages,achieving stabilization at a root mean square(RMS)roughness of 0.216 nm within 3 min,confirming suc-cessful 2D growth mode.X-ray rocking curve(XRC)analysis indicates a marked reduction in the(0002)reflection full width at half maximum(FWHM),from 445 to 96 arcsec,evidencing effective dislocation annihilation.Transmission electron microscopy(TEM)demonstrates the elimination of edge dislocations near the AlN template interface.Stress analysis highlights the role of a highly compressive 17 nm AlN template(5.11 GPa)in facilitating threading dislocation bending and annihilation,yielding a final dislocation density of~1.5×10^(7) cm^(-2).Raman spectroscopy and XRC mapping confirm excellent uniformity of stress and crystal quality across the wafer.These findings demonstrate the feasibility of this method for producing high-quality,large-area,atomically flat AlN films,advancing applications in optoelectronics and power electronics.展开更多
The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stres...The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stress, while the other view suggests growth on habit planes parallel to the applied stress. In this study, stress-aged Al-4 wt.%Cu single crystal was sampled from three different <100>Al zone axes to observe the distribution of θʹ precipitates. A hybrid Monte-Carlo/ molecular dynamics simulations were used to investigate the orientation effect of θʹ precipitates. The simulation results are consistent with experimental observations and indicate that θʹ precipitates prefer to grow on the habit planes that are parallel to the direction of the applied compressive stress, not along the planes perpendicular to it. It is also found that 1/2<110> perfect dislocations are generated as θʹ precipitates plates grow thicker, and the reaction of 1/2<110> perfect dislocations decomposing into 1/6<112> Shockley dislocations lead to an increase in the length of θʹ precipitates. The former does not enhance the orientation effect, whereas the latter leads to a more significant orientation effect. Additionally, the degree of the orientation effect of θʹ precipitates is determined by the reduction of 1/2<110> dislocations with a positive correlation between them.展开更多
A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplifie...A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplified representative of the 7xxx series Al alloys,and four distinct equal-channel angular pressing(ECAP)passes of 4,8,12,and 16 were used to adjust the Zn phase and dislocation distribution in the alloy.The corrosion behavior and mechanical properties of the alloy were evaluated by performing electrochemical and tensile tests as well as optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results indicate that the Al−5Zn alloy exhibits the highest polarization resistance value and the lowest corrosion current density after 16 ECAP passes.Additionally,its overall mechanical properties with ultimate tensile strength of 224 MPa,yield strength of 199 MPa,and elongation of 21.3%are excellent.The fragmentation and uniform distribution of the Zn phase as well as the even distribution of dislocations contribute to exceptional corrosion resistance and mechanical properties.展开更多
Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum a...Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum alloy largely pre-deformed(LPD)by 80%have been systematically investigated.The stress relaxation ratio of the LPD alloy reaches approximately 94%regardless of the initial stress(50–350 MPa)after ageing for 12 h at 140°C.This relaxation ratio is about 2.9 and 1.8 times that in the T4 tempered alloy(27.6%under 50 MPa and 31.5%under 150 MPa)and T3 tempered alloy(37.6%under 50 MPa and 51.2%under 150 MPa),respectively.The microstructures,comprised of GP zones/θ'precipitates plus dislocation tangles,and tensile properties in the stress-relaxation-aged LPD alloys remain basically invariant with different initial stresses,as is vital importance for property consistency at different locations of the formed part.Under the same SRA condition,the LPD alloy has an increase of 150–230 MPa in yield strength relative to T3/T4 tempered alloy and obtains a uniform elongation of about 8%.A simple dislocation-based constitutive model accurately describing stress relaxation enhanced by the high dislocation density is established and embedded in the finite element package through a user subroutine.Simulations and experimental verifications show the LPD alloy sheet parts exhibit a nearly zero springback(<5%)after unloading in contrast to the springback larger than 65%in the T3/T4 alloy sheet parts under the same condition.Our findings demonstrate the high-dislocation-density-enhanced SRA response enables a high-performance springback-free age forming of Al alloy sheet.展开更多
In recent years,(0001)twist grain boundaries(BTGBs)located in primary α grain clusters were identified as fatigue crack nucleation sites in different Ti alloys.In the present study,crack initiation was investigated i...In recent years,(0001)twist grain boundaries(BTGBs)located in primary α grain clusters were identified as fatigue crack nucleation sites in different Ti alloys.In the present study,crack initiation was investigated in a bimodal Ti-5Al-4 V alloy subjected to low-cycle fatigue and dwell-fatigue loadings at room temperature.The low fraction of primary α grains was not associated with a lack of sensitivity to BTGB cracking.Transmission electron microscopy and electron back-scattered diffraction were used to characterize BTGBs in the initial microstructure.The fatigue mechanisms were then analyzed with a focus on dislocation activity.α_(p) grains adjacent to cracked BTGBs contained a high dislocation density.It was primarily composed of planar slip bands of dislocations.In addition,<c+a>dislocations were noticed in the vicinity of cracked BTGBs.They supposedly pertain to crack tip plasticity during growth,and no evidence of a role of an incoming slip event in crack nucleation was obtained.Also,basal slip bands extending across adjacent grains were found to emerge from BTGBs.This feature provides an easier path for crack extension when growth along the grain boundary becomes difficult owing to a deviation from the basal plane.Atom probe tomography analyses evidenced V and Fe segregation at a grain boundary with a significant deviation from the BTGB configuration.This suggests a possible contribution of local solute segregation to the high cracking resistance of general α_(p)/α_(p) grain boundaries.This work provides new insights into the mechanisms involved in cracking of BTGB in Ti alloys subjected to cyclic loadings.展开更多
基金funding from SFB 1415 subproject B04(Deutsche Forschungsgemeinschaft,No.417590517)supported by the Deutsche Forschungsgemeinschaft through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter-ct.qmat(EXC 2147,No.390858490)the support provided by the DRESDEN-concept alliance of research institutions.
文摘Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-dimensional transition metal dichalcogenide MoSe_(2) is a particularly promising material for twisted multilayers,capable of sustaining moiréexcitons.Here,we report on a rational bottomup synthesis approach for twisted MoSe_(2) flakes by chemical vapor transport(CVT).Screw dislocation-driven growth was forced by surface-fused SiO_(2)nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition.Thus,crystal growth by in-situ CVT under addition of MoCl_(5) leads to bulk 2H-MoSe_(2) in a temperature gradient from 900 to 820℃ with a dwell time of 96 h.Hexagonally shaped 2H-MoSe_(2) flakes were grown from 710 to 685℃ with a dwell time of 30 min on SiO_(2)@Al_(2)O_(3)(0001)substrates.Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe_(2) with individual step heights between 0.9 and 2.9 nm on SiO_(2)@Si(100)under the same conditions.Finally,twisted MoSe_(2) flakes exhibiting a twist angle of 19°with respect to the[010]zone axis could be synthesized.
基金Supported by National Key Research and Development Program of China(2021YFB3601403)National Natural Science Foundation of China(62105181)Taishan Scholar of Shandong Province(tsqn202306014)。
文摘Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.
基金supported by the National Research Foundation of Singapore,Rolls-Royce Singapore Pte.Ltd.,and Nanyang Technological University through grants#002123-00009 and #002124-00009.
文摘This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.
基金support from the National Natural Science Foundation of China(No:52061040)China Postdoctoral Science Foundation(No:2021M692512)+1 种基金Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan Province(No:2023CL01)Open Projects of Key Laboratory of Advanced Technologies of Materials,Ministry of Education China,Southwest Jiaotong University(No:KLATM202003).
文摘Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.
基金supported by the National Science Foundation(No.CMMI-2019459).
文摘The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined the temperature-dependent Peierls stress for 30°and 90°partial dislocations in cadmium telluride(CdTe),using a combination of molecular statics and molecular dynamics simulations with a machine-learning force field,as well as density functional theory simulations.Our findings reveal that the 0 K Peierls stresses for these partial dislocations in CdTe are relatively low,ranging from 0.52 GPa to 1.46 GPa,due to its significant ionic bonding characteristics.Notably,in the CdTe system containing either a 30°Cd-core or 90°Te-core partial dislocation,a phase transition from the zinc-blende phase to theβ-Sn-like phase is favored over dislocation motion.This suggests a competitive relationship between these two mechanisms,driven by the bonding characteristics within the dislocation core and the relatively low phase transition stress of∼1.00 GPa.Furthermore,we observed a general trend wherein the Peierls stress for partial dislocations in CdTe exhibits a temperature dependence,which decreases with increasing temperature,becoming lower than the phase transition stress at elevated temperatures.Consequently,the dominant deformation mechanism in CdTe shifts from solid-state phase transition at low temperatures to dislocation motion at high temperatures.This investigation uncovers a compelling interplay between dislocation motion and phase transition in the plastic deformation of CdTe,offering profound insights into the mechanical behavior and electronic performance of CdTe and other II-VI semiconductors.
基金Financial supports from the National Natural Science Foundation of China(Nos.52171116,U22A20109,52334010 and T2325013)are greatly acknowledgedPartial financial support came from The Program for the Central University Youth Innovation Team,and the Fundamental Research Funds for the Central Universities,JLU.
文摘Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.
文摘Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors report a case of this lesion in a 7-year-old child managed nonoperatively.
文摘BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we describe a case of an elderly patient who pre sented with a type 2 dislocation after a fall.The mechanisms of inferior patella dislocation,their classification,key imaging features and treatment options are discussed.CASE SUMMARY A 75-year-old woman presented with a right knee fixed flexion deformity after a fall.Preoperative imaging confirmed a vertical intra-articular patella dislocation with a femoral trochlear osteochondral defect and lax though grossly intact patella tendon.Closed reduction was performed under general anaesthesia.Knee arthroscopy confirmed the presence of a femoral trochlear osteochondral defect whose edges were subsequently smoothed and there was debridement of scant debris with thorough irrigation of the joint.Postoperative imaging demonstrated anatomical alignment,however,there was a new nondisplaced medial femoral trochlear.The patient however was able to mobilise well in a range of motion brace set at 0-30 degrees and was discharged 1-day post operatively.CONCLUSION Inferior patella dislocation is rare and this article highlights its types and imaging features which determine the most appropriate management.
文摘Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. This is done by examining the acetabular placement in instances of hip dislocation after total hip arthroplasty (THA). Methodology: The authors searched 2653 patient records from 2015 to 2022 looking for patients who had total hip arthroplasty at our facility. For the analysis, 23 patients were culled from 64 individuals who exhibited post-THA dislocations, employing a stringent exclusion criterion, and the resultant acetabular angulation and anteversion were quantified utilizing PEEKMED software (Peek Health S.A., Portugal) upon radiographic evidence. Results: Within the operational timeframe, from the cohort of 2653 subjects, 64 presented with at least a singular incident of displacement. Post-exclusion criterion enforcement, 23 patients were eligible for inclusion. Of these, 10 patients conformed to the safe zone demarcated by Lewinnek for both inclination and anteversion angles, while 13 exhibited deviations from the prescribed anteversion and/or inclination benchmarks. Conclusion: Analysis of the 23 patients reveals that 13 did not confirm to be in the safe zone parameters for anteversion and/or inclination, whereas 10 were within the safe zone as per Lewinnek’s guidelines. This investigative review, corroborated by extant literature, suggests that the isolated consideration of the Lewinnek safe zone does not suffice as a solitary protective factor. It further posits that additional variables are equally critical as acetabular positioning and mandate individual assessment.
基金supported by the National Natural Science Foundation of China(Grant Nos.51971170 and 51922082)。
文摘Metallic materials,although composed of metallic bonds,exhibit a wide range of mechanical properties:some are ductile and deformable,while others undergo a pronounced ductile-to-brittle transition(DBT),displaying ceramic-like brittle behavior once below a critical temperature.For decades,the dominant mechanism driving the ductile-to-brittle transition of metals-whether dislocation nucleation or dislocation slip-has been a topic of ongoing debate.A new concept of dislocation source efficiency,however,suggests that both processes are complementary and essential for overall ductile deformation.The relative mobility of screw versus edge dislocations dictates the efficiency of dislocation sources,which in turn governs dislocation multiplication and ultimately the material’s ability to plastic deformation.Furthermore,we developed a new model that incorporates factors affecting dislocation activities,such as the initial dislocation density and the number of dislocation sources,offering promising toughening strategies for both metallic structural alloys and ceramics.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171013 and 52130110)the Key Research and Development Program of Shaanxi(Grant No.2025CY-YBXM-127)+1 种基金the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0369)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)China(Grant No.2023-QZ-03)。
文摘Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.
文摘Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.
基金Supported by National Natural Science Foundation of China(Grant No.U1910212)the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.
基金funded by the National Natural Science Foundation of China[Grant No.71963030]a subproject of China’s third comprehensive scientific expedition to Xinjiang[Grant No.SQ2021xjkk01800]+1 种基金a major science and technology project in the Xinjiang Uygur Autonomous Region[Grant No.2022A01003]a scientific research innovation project for excellent doctoral students of Xinjiang University[Grant No.XJU2022BS010].
文摘Ensuring a harmonious coexistence between man and nature is crucial for China’s economic and social development.However,with increasing industrialization and urbanization,there is a growing mismatch between China’s ecological resilience(ER)and economic level(EL)of development,which poses a notable social threat.Currently,the link between ER and EL in China remains unclear,especially in terms of spatial dislocation(SD),referring to the disconnect between the locations where environmental impacts occur and those where economic benefits or activities are concentrated.Therefore,this paper aims to provide theoretical support and an empirical basis for policy-based solutions to address this gap.Based on the SD theory,this study systematically discusses the temporal changes,spatial patterns,and SD characteristics of China’s ER and EL using spatial auto-correlation and barycentric analysis to analyze data from 30 provinces covering the period 2011-2021.The key results are as follows.China’s ER shows a general trend of growth;however,its distribution is uneven.The spatial pattern generally decreases from the southeastern coastal provinces to the northwest.Moreover,a gradually increasing positive correlation is observed between the ER and EL,but this correlation varies by region,with some showing regional linkages and others developing independently.Finally,the dislocation index of ER and EL presents divergent results based on region-the eastern and central regions primarily show a high level of dislocation,whereas the western and northeastern regions show a low level of dislocation.The results provide a comprehensive overview of the spatiotemporal patterns in the association between ER and EL in China.The results emphasize that to balance sustainable regional development and ecological governance,a region-specific approach must be employed,prioritizing innovation-driven strategies for high ER in more developed regions and market-oriented strategies in less developed regions.
基金financially supported by National Natural Science Foundation of China(12072211,12232008)Foundation of Key laboratory(2022JCJQLB05703)Sichuan Province Science and Technology Project(2023NSFSC0914)。
文摘Pyramidal dislocations are important for ductility enhancement of magnesium alloys.In this work,molecular dynamics simulations were employed to study the gliding behavior of pyramidal(c+a)dislocations under c-axis compressive loading and tensile loading.The Peierls stress of Py-Ⅰ dislocation shows strong tension-compression asymmetry.However,no tension-compression asymmetry is seen on the Py-Ⅱ dislocation and basal dislocation.The tension-compression asymmetry origins from the asymmetry of partial dislocations of Py-Ⅰ dislocation,which leads to the dislocation core contracted under c-axis compressive loading and expanded under tensile loading.By analyzing the forces acting on the partial dislocations,we defined a neutral direction,which deviates from the full dislocation Burgers vector by 70.3°.The neutral direction is dependent on the ratio of lattice stresses of partial dislocations.If the shear stress is applied along the neutral direction,tension-compression asymmetry is eliminated and the dislocation core is un-contracted/un-expanded.The neutral direction of symmetrical dislocations(Py-Ⅱ dislocation and basal dislocation)is just the full dislocation Burgers vector.The tension-compression asymmetry and dislocation core contraction/expansion have an important influence on the dislocation behaviors,such as cross-slip,decomposition,basaltransition and mobility,which can be used to explain the mechanical behaviors of Mg single-crystals compressed along c-axis.
基金supported by National Key R&D Program of China(2022YFB3605100)the National Science Fund for Distinguished Young Scholars of China(62425408)+5 种基金the National Natural Science Foundation of China(62204241,U22A2084,and 62121005)Key Research and Development Projects of Jilin Provincial Science and Technology Development Plan(20240302027GX)the Natural Science Foundation of Jilin Province(20230101345JC,20230101360JC,20230101107JC)the Youth Innovation Promotion Association of CAS(2023223)the Young Elite Scientist Sponsorship Program By CAST(YESS20200182)the CAS Talents Program.
文摘High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN films on 17 nm AlN/sapphire tem-plates using metal-organic chemical vapor deposition(MOCVD).Comprehensive characterization reveals significant advance-ments in crystal quality and uniformity.Atomic force microscopy(AFM)shows progressive surface roughness reduction during early growth stages,achieving stabilization at a root mean square(RMS)roughness of 0.216 nm within 3 min,confirming suc-cessful 2D growth mode.X-ray rocking curve(XRC)analysis indicates a marked reduction in the(0002)reflection full width at half maximum(FWHM),from 445 to 96 arcsec,evidencing effective dislocation annihilation.Transmission electron microscopy(TEM)demonstrates the elimination of edge dislocations near the AlN template interface.Stress analysis highlights the role of a highly compressive 17 nm AlN template(5.11 GPa)in facilitating threading dislocation bending and annihilation,yielding a final dislocation density of~1.5×10^(7) cm^(-2).Raman spectroscopy and XRC mapping confirm excellent uniformity of stress and crystal quality across the wafer.These findings demonstrate the feasibility of this method for producing high-quality,large-area,atomically flat AlN films,advancing applications in optoelectronics and power electronics.
基金Project(2023YFB3710503) supported by the National Key R&D Program of ChinaProject(52305439) supported by the National Natural Science Foundation of China。
文摘The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stress, while the other view suggests growth on habit planes parallel to the applied stress. In this study, stress-aged Al-4 wt.%Cu single crystal was sampled from three different <100>Al zone axes to observe the distribution of θʹ precipitates. A hybrid Monte-Carlo/ molecular dynamics simulations were used to investigate the orientation effect of θʹ precipitates. The simulation results are consistent with experimental observations and indicate that θʹ precipitates prefer to grow on the habit planes that are parallel to the direction of the applied compressive stress, not along the planes perpendicular to it. It is also found that 1/2<110> perfect dislocations are generated as θʹ precipitates plates grow thicker, and the reaction of 1/2<110> perfect dislocations decomposing into 1/6<112> Shockley dislocations lead to an increase in the length of θʹ precipitates. The former does not enhance the orientation effect, whereas the latter leads to a more significant orientation effect. Additionally, the degree of the orientation effect of θʹ precipitates is determined by the reduction of 1/2<110> dislocations with a positive correlation between them.
基金the National Natural Science Foundation of China(No.52303390),the Natural Science Foundation of Jiangsu Province,China(No.BK20230963)the Jiangsu Provincial Key Research and Development Program,China(No.BE2021027)+2 种基金the Nanjing Major Science and Technology Project,China(No.202309015)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology,China(No.ASMA202305)the Suzhou Science and Technology Project,China(Nos.SJC2023005,SZS2023023).
文摘A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplified representative of the 7xxx series Al alloys,and four distinct equal-channel angular pressing(ECAP)passes of 4,8,12,and 16 were used to adjust the Zn phase and dislocation distribution in the alloy.The corrosion behavior and mechanical properties of the alloy were evaluated by performing electrochemical and tensile tests as well as optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results indicate that the Al−5Zn alloy exhibits the highest polarization resistance value and the lowest corrosion current density after 16 ECAP passes.Additionally,its overall mechanical properties with ultimate tensile strength of 224 MPa,yield strength of 199 MPa,and elongation of 21.3%are excellent.The fragmentation and uniform distribution of the Zn phase as well as the even distribution of dislocations contribute to exceptional corrosion resistance and mechanical properties.
基金financially supported by the National Natural Science Foundation of China(Nos.52274404,52305441,and U22A20190)the Natural Science Foundation of Hunan province(Nos.2022JJ20065 and 2023JJ40739)+1 种基金the Science and Technology Innovation Program of Hunan Province(No.2022RC1001)the National Key R&D Program of China(No.2021YFB3400903).
文摘Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum alloy largely pre-deformed(LPD)by 80%have been systematically investigated.The stress relaxation ratio of the LPD alloy reaches approximately 94%regardless of the initial stress(50–350 MPa)after ageing for 12 h at 140°C.This relaxation ratio is about 2.9 and 1.8 times that in the T4 tempered alloy(27.6%under 50 MPa and 31.5%under 150 MPa)and T3 tempered alloy(37.6%under 50 MPa and 51.2%under 150 MPa),respectively.The microstructures,comprised of GP zones/θ'precipitates plus dislocation tangles,and tensile properties in the stress-relaxation-aged LPD alloys remain basically invariant with different initial stresses,as is vital importance for property consistency at different locations of the formed part.Under the same SRA condition,the LPD alloy has an increase of 150–230 MPa in yield strength relative to T3/T4 tempered alloy and obtains a uniform elongation of about 8%.A simple dislocation-based constitutive model accurately describing stress relaxation enhanced by the high dislocation density is established and embedded in the finite element package through a user subroutine.Simulations and experimental verifications show the LPD alloy sheet parts exhibit a nearly zero springback(<5%)after unloading in contrast to the springback larger than 65%in the T3/T4 alloy sheet parts under the same condition.Our findings demonstrate the high-dislocation-density-enhanced SRA response enables a high-performance springback-free age forming of Al alloy sheet.
基金financially supported by the National Natural Science Foundation of China(No.U21A2050)support of the Chinese Scholarship Council(No.202006290165).
文摘In recent years,(0001)twist grain boundaries(BTGBs)located in primary α grain clusters were identified as fatigue crack nucleation sites in different Ti alloys.In the present study,crack initiation was investigated in a bimodal Ti-5Al-4 V alloy subjected to low-cycle fatigue and dwell-fatigue loadings at room temperature.The low fraction of primary α grains was not associated with a lack of sensitivity to BTGB cracking.Transmission electron microscopy and electron back-scattered diffraction were used to characterize BTGBs in the initial microstructure.The fatigue mechanisms were then analyzed with a focus on dislocation activity.α_(p) grains adjacent to cracked BTGBs contained a high dislocation density.It was primarily composed of planar slip bands of dislocations.In addition,<c+a>dislocations were noticed in the vicinity of cracked BTGBs.They supposedly pertain to crack tip plasticity during growth,and no evidence of a role of an incoming slip event in crack nucleation was obtained.Also,basal slip bands extending across adjacent grains were found to emerge from BTGBs.This feature provides an easier path for crack extension when growth along the grain boundary becomes difficult owing to a deviation from the basal plane.Atom probe tomography analyses evidenced V and Fe segregation at a grain boundary with a significant deviation from the BTGB configuration.This suggests a possible contribution of local solute segregation to the high cracking resistance of general α_(p)/α_(p) grain boundaries.This work provides new insights into the mechanisms involved in cracking of BTGB in Ti alloys subjected to cyclic loadings.
