This study aims to achieve a synergy of strength and ductility in magnesium-based nanocomposite materials through the design of a dual-heterostructure. Utilizing ball milling and hot extrusion, a nano-TiC/AZ61 composi...This study aims to achieve a synergy of strength and ductility in magnesium-based nanocomposite materials through the design of a dual-heterostructure. Utilizing ball milling and hot extrusion, a nano-TiC/AZ61 composite featuring particle-rare coarse grain (CG) and particle-rich fine grain (FG) zones was successfully fabricated. Experimental results demonstrated that compared with the homogeneous structure, the dual-heterostructure composite achieved a significant increase in elongation by 116 % and a remarkable 165 % improvement in the strength-ductility product (SDP), while maintaining a high ultimate tensile strength (UTS) of 417±4 MPa. This substantial performance enhancement is primarily attributed to the additional strain hardening induced by hetero-deformation-induced (HDI) strain hardening and crack-blunting capabilities, as elucidated by microstructural characterization and crystal plasticity finite element modeling (CPFEM). Notably, the strain hardening contribution from the CG zones at the early stage of deformation (≤ 45 % of total plastic deformation amount) is minimal but increases significantly during the subsequent deformation stages. The dislocation increment rate in CG zones (219 %) is observed to be more than double that in FG zones (95 %), attributed to the large grain size and low dislocation density in CG zones, which provide more space for dislocation storage. In addition, the aggravated deformation inhomogeneity as deformation progresses leads to an increase in geometrically necessary dislocations (GNDs) generation near the heterogeneous interface, thereby enhancing HDI hardening. Fracture mechanism analysis indicated that the cracks mainly initiate in the FG region and are effectively blunted upon their propagation to the CG region, necessitating increased energy consumption and indicating higher fracture toughness for the dual-heterostructure composites. This study validates the effectiveness of the dual-heterostructure design in magnesium-based composites, providing a novel understanding of the deformation mechanism through both experimental analysis and CPFEM, paving the way for the development of high-performance, lightweight structural materials.展开更多
The application of machine learning in alloy design is increasingly widespread,yet traditional models still face challenges when dealing with limited datasets and complex nonlinear relationships.This work proposes an ...The application of machine learning in alloy design is increasingly widespread,yet traditional models still face challenges when dealing with limited datasets and complex nonlinear relationships.This work proposes an interpretable machine learning method based on data augmentation and reconstruction,excavating high-performance low-alloyed magnesium(Mg)alloys.The data augmentation technique expands the original dataset through Gaussian noise.The data reconstruction method reorganizes and transforms the original data to extract more representative features,significantly improving the model's generalization ability and prediction accuracy,with a coefficient of determination(R^(2))of 95.9%for the ultimate tensile strength(UTS)model and a R^(2)of 95.3%for the elongation-to-failure(EL)model.The correlation coefficient assisted screening(CCAS)method is proposed to filter low-alloyed target alloys.A new Mg-2.2Mn-0.4Zn-0.2Al-0.2Ca(MZAX2000,wt%)alloy is designed and extruded into bar at given processing parameters,achieving room-temperature strength-ductility synergy showing an excellent UTS of 395 MPa and a high EL of 17.9%.This is closely related to its hetero-structured characteristic in the as-extruded MZAX2000 alloy consisting of coarse grains(16%),fine grains(75%),and fiber regions(9%).Therefore,this work offers new insights into optimizing alloy compositions and processing parameters for attaining new high strong and ductile low-alloyed Mg alloys.展开更多
A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hard...A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.展开更多
Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restr...Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restricting widespread use.In this study,ultra-fine-grained and homogeneous Mg alloys were fabricated using double-sided friction stir processing(DS-FSP)with liquid CO_(2) rapid cooling,leading to a significant enhancement in the strength-ductility synergy of the stirred zone.The results demonstrate that DS-FSP samples exhibit simultaneous improvements in ultimate tensile strength(UTS)and elongation,reaching 334.1±15 MPa and 28.2±7.3%,respectively.Compared to the non-uniform fine-grained microstructure obtained through single-sided friction stir processing,DS-FSP generates a uniform ultra-fine-grained structure,fundamentally altering the fracture behavior and mechanisms of Mg alloys.The DS-FSP samples exhibit irregular fracture patterns due to variations in basal slip system activation among different grains.In contrast,single-sided friction stir processing samples,characterized by a fine-grained yet heterogeneous microstructure,display flat shear fractures dominated by high-density dislocation initiation induced by twin formation,with fracture propagation dictated by the non-uniform texture.By achieving an ultra-fine grain size and homogeneous texture,DS-FSP effectively modifies the fracture mechanisms,thereby enhancing the strength-ductility balance of bio-magnesium alloys.展开更多
Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a...Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a new strategy based onβ-subgrains-mediated hierarchicalα-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe(wt.%)alloy through a unique combination of hot rolling,short-term solid solution,and aging treatment,i.e.,RSST+A.Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of∼1581 MPa and decent ductility of∼8.4%,surpassing∼1060 MPa and∼2.7%of the corresponding RSST counterparts without final aging treatment.This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting ofβ-subgrains-mediated hierarchicalαprecipitates as a result of our specific processing approach.The designed short-term solution introduces abundantβsubgrains that are transformed from the retained intensive dislocations during hot rolling.Theβsubgrain boundaries subsequently promote a dramatic precipitation ofαallotriomorphs(αGB)and Widmanstätten side-plates(αWGB),which effectively subdividesβgrains into numerous tiny independent deformation units.Consequently,plastic strain is uniformly partitioned into a large number of small agedβsubgrains during tension,which strongly impedes strain localization that would typically occur across multipleβsubgrains in the fashion of long straight slip bands in the case of the RSST samples.Furthermore,the hierarchicalαstructure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining.These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing highstrength titanium alloys in the precipitation-hardening state.展开更多
In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructu...In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructural evolution during deposition and subsequent heat treatment was explained through multi-scale microstructural characterization techniques,and the impact of heat treatment on the strengthductility synergy of the deposited alloy was systematically compared.The results showed that the microstructure of the deposited sample was mainly composed of fine equiaxedα-Mg grains and Mg_(24)(Gd,Y)_(5) phase.The optimized solution heat treatment(450℃×2 h)had little effect on the grain size,but can effectively reduce the Mg_(24)(Gd,Y)_(5) eutectic phase on the grain boundary,resulting in a significant increase in elongation from 13.7% to 26.6%.After peak-aging treatment,the strength of the GW63K alloy increased to 370 MPa,which was significantly higher than the as-built state(267 MPa).The superior strength in this study is attributed to the refinement strengthening imparted by the fine microstructure inherited in the as-built GW63K alloy,as well as the precipitation strengthening due to the formation of dense β’precipitates with a pronounced plate-like aspect ratio.展开更多
Ti-xNb alloys produced by laser powder bed fusion(LPBF)from mixed powder usually exhibit an inhomogeneous elemental distribution,leading to a deterioration in mechanical properties.To address this issue,we proposed a ...Ti-xNb alloys produced by laser powder bed fusion(LPBF)from mixed powder usually exhibit an inhomogeneous elemental distribution,leading to a deterioration in mechanical properties.To address this issue,we proposed a strategy to achieve heterostructure in laser powder bed fused Ti-xNb alloys from mixed powders through precipitation ofωwithinβ.Moreover,the effect of Nb content on the micro structure and mechanical behavior of Ti-xNb alloys was studied.The results indicated that in-situ laser re-melting can realize the homogeneous elemental distribution in Ti-xNb alloys.When the Nb content increases from 30 wt%,35 wt%to40 wt%,Ti-xNb alloys experience a transformation from β+α' to β+ω and monolithic β.Specifically,ωnano-precipitates in Ti-35Nb alloy are only distributed in some β grains,forming a heterostructure with“softβ”and“hard β+ω”grains.As a result,LPBF-produced Ti-35Nb alloy demonstrates excellent mechanical properties,with yield strength of ^(792±6)MPa,tensile strength of ^(806±7)MPa,Young's modulus of ^(68±6)GPa,and uniform elongation of ^(18.0±1.1)%.The Frank-Read mechanism induces dislocation proliferation and dislocation cross-slip,and the geometrically necessary dislocations(GNDs)are induced at the heterogeneous interface of“softβ”and“hard β+ω”grains,resulting in an enhancement in the strength-ductility synergy of Ti-35Nb alloy produced by LPBF.This work provides an innovative strategy to improve the strength-ductility synergy of LPBF-produced Ti-xNb alloys from mixed powders by tailoring ω nano-precipitates.展开更多
The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the mate...The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the material’s high product of strength and elongation(PSE)and a moderate yield-to-strength ratio(YTS).This study presents an innovative approach using torsion deformation combined with shortterm aging treatment to create a gradient structure.This structure integrates gradients in plastic strain,dislocations,precipitated phases,and grain size,forming an in-situ core-shell configuration characterized by a“soft core and hard shell”.As a result,the yield strength,ultimate tensile strength,elongation,YTS,and PSE increased by 4.07%,5.72%,66.59%,−1.52%,and 76.12%,respectively,compared to the asreceived material.Its strengthening effect is significantly better than traditional T6 treatment.Notably,the formation of a gradient structure through this novel thermomechanical processing technique optimized YTS by 11.51%compared to traditional heat treatments.The significant increase in PSE is attributed to the marked improvement in elongation indicating an effective enhancement in the strength-ductility balance.This provides a promising strategy for designing and manufacturing high-performance components.展开更多
Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti...Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti_(11.7)B_(2.5)(at%)with a unique microstructure was developed in this work.The microstructure,which includes 17.8%nanosized L12 precipitates and 26.6%micron-sized annealing twins distributed within~8μm fine FCC grains,was achieved through cryogenic rolling and subsequent annealing.The alloy exhibits a yield strength(YS)of 1063 MPa,ultimate tensile strength(UTS)of 1696 MPa,and excellent elongation of~26%.The L1_(2) precipitates and high-density grain boundaries act as a barrier to the dislocation movement,resulting in a substantial strengthening effect.In addition,the dislocations can cut through the L1_(2) precipitates that are coherent with the FCC matrix,whereas the twin boundaries can effectively absorb and store dislocations,leading to a high work-hardening rate.Furthermore,the stacking faults,Lomer-Cottrell locks,and 9-layer rhombohedral stacking sequence(9R)structures formed during tensile deformation significantly enhance strain hardening by blocking dislocation movement and accumulating dislocations,resulting in excellent comprehensive tensile properties.Theoretical calculations reveal that the grain boundaries,L1_(2)precipitates,and twin boundaries contribute the strengths of 263.8,412.6,and 68.7 MPa,respectively,accounting for 71.9%of the YS.This study introduces a promising strategy for developing multicomponent alloys with significant strength-ductility synergies.展开更多
In this study,a novel strategy for breaking the strength-ductility dilemma of Mg-1.5Zn-0.6Gd(wt%)alloy via solute segregation was reported.The hot extruded alloy sheet was subjected to rolling deformation,and then hea...In this study,a novel strategy for breaking the strength-ductility dilemma of Mg-1.5Zn-0.6Gd(wt%)alloy via solute segregation was reported.The hot extruded alloy sheet was subjected to rolling deformation,and then heat-treated at 200℃.The high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)reveals a remarkable segregation of solute Zn atoms along both high and lowangle grain boundaries(GBs).As compared with as-rolled plate,the yield strength,ultimate tensile strength,and the elongation of annealed sample is increased by 15.6%,14%,and 8.4%,respectively,acquiring an obvious strength-ductility synergy effect.The solute segregation endows the rolled plate with excellent grain size stability and provides a prominent extra solute cluster strengthening,which completely resists the other softening effects including dislocation annihilation and grain coarsening.Meanwhile,the directional migration of Zn atoms and the annihilation of dislocations provide a"clear"space within the grain,which is beneficial for the moving and accumulating of subsequent dislocations.This work sheds light on the solute partitioning behavior and realizes a good application of GB segregation in improving the comprehensive mechanical properties of Mg alloys.展开更多
Zinc(Zn)is considered a promising biodegradable metal for implant applications due to its appropriate degradability and favorable osteogenesis properties.In this work,laser powder bed fusion(LPBF)additive manufacturin...Zinc(Zn)is considered a promising biodegradable metal for implant applications due to its appropriate degradability and favorable osteogenesis properties.In this work,laser powder bed fusion(LPBF)additive manufacturing was employed to fabricate pure Zn with a heterogeneous microstructure and exceptional strength-ductility synergy.An optimized processing window of LPBF was established for printing Zn samples with relative densities greater than 99%using a laser power range of 80∼90 W and a scanning speed of 900 mm s−1.The Zn sample printed with a power of 80 W at a speed of 900 mm s−1 exhibited a hierarchical heterogeneous microstructure consisting of millimeter-scale molten pool boundaries,micrometer-scale bimodal grains,and nanometer-scale pre-existing dislocations,due to rapid cooling rates and significant thermal gradients formed in the molten pools.The printed sample exhibited the highest ductility of∼12.1%among all reported LPBF-printed pure Zn to date with appreciable ultimate tensile strength(∼128.7 MPa).Such superior strength-ductility synergy can be attributed to the presence of multiple deformation mechanisms that are primarily governed by heterogeneous deformation-induced hardening resulting from the alternative arrangement of bimodal Zn grains with pre-existing dislocations.Additionally,continuous strain hardening was facilitated through the interactions between deformation twins,grains and dislocations as strain accumulated,further contributing to the superior strength-ductility synergy.These findings provide valuable insights into the deformation behavior and mechanisms underlying exceptional mechanical properties of LPBF-printed Zn and its alloys for implant applications.展开更多
Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior per...Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior performance due to internal defects and inherent columnar grains.Herein,external ultrasound fields with different powers were successfully introduced into the wire-arc DED of AZ31 Mg alloy.The microstructure,defects,and mechanical properties of the fabricated components were carefully charac-terized and compared.The results show that the external ultrasound fields lead to decreased porosity,complete columnar to equiaxed transition(CET),and enhanced performance.Consequently,the UA90 samples exhibited a remarkable increase of~30%,~45%,and~189%in yield strength,ultimate tensile strength,and elongation,respectively.The dominant mechanisms of enhanced strength-ductility synergy were analyzed in detail.This study thus sheds new light on wire-arc DED of Mg alloy components with excellent performance via external ultrasound fields.展开更多
The strength and ductility cannot achieve a good tradeoff for some superalloy(e.g.GH3536)prepared by selective laser melting(SLM),which seriously restricts their industrial applications.This work examined the effect o...The strength and ductility cannot achieve a good tradeoff for some superalloy(e.g.GH3536)prepared by selective laser melting(SLM),which seriously restricts their industrial applications.This work examined the effect of post-heat treatment(HT)on the microstructure and mechanical properties of GH3536 produced by SLM.In particular,the influence of carbide precipitate morphology and distribution on strength and ductility of the alloy after heat treatment was discussed.After aging at 650°C(denoted as HT1),the Cr23C6 carbides were distributed in chains.The ductility increased by approximately 31%,while the strength slightly decreased.After aging at 745°C(denoted as HT2),the Cr23C6 carbides were distributed in chains.However,the HT2 samples showed an increase in ductility of~58%and no reduction in strength.As the dislocation density of HT2 sample was higher than that of the HT1 sample,the chain carbides could be pinned to the grain boundaries,consequently improving the ductility but no loss in strength as compared with the as-deposited samples.When the aging temperature was increased to 900°C(denoted as HT3),the carbides were distributed in a discontinuous granular form.As a result,the HT3 samples presented the lowest dislocation density which reduced the strength.展开更多
Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneo...Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distributions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation tem peratures.The results reveal that the grain refinement process under mediumlow temperature deformation conditions(≤350℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultrafine sub-grains,and randomly orientated quasi-micron grains.Different deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal slip.The deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance ability.Analysis in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different tem peratures.By summarizing the tensile test results,the sample forged at 350℃exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2%with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8%.展开更多
A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 ...A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 MPa and 8.5%,respectively.This alloy has two types of a-Mg grains:coarse a_(1)-Mg((46±18)μm)and fine a_(2)-Mg((9.2±2.3)μm)grains,and various Al-GS(GS=Gd and Sm)particles located at grain boundaries while clear solute-atom segregation near grain boundaries with limited or free intermetallic particles.Characterizations using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)indicate the crystal structures of Al-GS phases.After aging,denseβ'precipitates and chain-shapedβ''-like structures precipitated near grain boundaries while a high density of ultrafineβ''-(Mg,Al)3Sm precipitates and Al-GS clusters formed in grain center.Relatively fine grains,Al-GS primary particles,solute-atom segregation near grain boundaries,and/or multiple precipitates contribute to the high strength of the studied alloy,while the multi-scale a-Mg grains,variety of intermetallic particles but discontinuous skeleton,and the multi-typed precipitated lead to its satisfactory ductility.展开更多
Laser powder bed fusion(LPBF)is a promising method for manufacturing functional and structural integrated Cu-Cr-Zr components.However,the LPBF-processed Cu-Cr-Zr alloys still suffer from the strength-ductility trade-o...Laser powder bed fusion(LPBF)is a promising method for manufacturing functional and structural integrated Cu-Cr-Zr components.However,the LPBF-processed Cu-Cr-Zr alloys still suffer from the strength-ductility trade-offdilemma,while maintaining high conductivity.Here,LPBF-processed Cu-Cr-Zr alloy with a hierarchical structure was obtained by increasing the Cr and Zr content simultaneously.After aging treatment,the hierarchical structure was composed of melt tracks at the macroscale,coarse grains(31.9±0.1μm)and fine grains(5.6±0.2μm)at the microscale,high-density of dislocations and dual precipitates at the nanoscale.The direct aged sample exhibited an excellent combination of strength and ductility(tensile strength was enhanced to 626±1 MPa and uniform elongation of 16.2%±1.1%),which is superior to the traditionally wrought and LPBF-processed Cu-Cr-Zr alloys reported previously.Meantime,a good electrical conductivity of 71.1%±0.3%IACS was also achieved.In addition,the heterogeneous deformation-induced stress caused by the hierarchical structure not only led to a large increase in yield strength but also promoted tensile ductility.展开更多
Eutectic high-entropy alloys(EHEAs)that combine the advantages of HEAs and eutectic alloys are promising materials for high-temperature environments.However,the mechanical properties of currently developed EHEAs still...Eutectic high-entropy alloys(EHEAs)that combine the advantages of HEAs and eutectic alloys are promising materials for high-temperature environments.However,the mechanical properties of currently developed EHEAs still cannot meet the servicing requirements.Here,we propose a strategy to optimize the tensile properties in a Al_(21)Co_(19.5)Fe_(9.5)Ni_(50)EHEA by regulating the phase transformation and precipitation features.The results showed that the as-cast Al_(21)Co_(19.5)Fe_(9.5)Ni_(50)EHEA mainly consists of face-centered cubic(FCC)and B2 phases showing a lamellar morphology,and the FCC and B2 phases keep a stable K-S orientation relationship.Solution treatment at 900 and 1100°C followed by furnace cooling to room temperature leads to a significant precipitation of L1_(2)phases within the FCC phases.In the subsequent tensile deformation process,dispersed L1_(2)phases and the transformation from B2 to L1_(0)phases can significantly enhance the yield strength of the designed EHEA.Furthermore,solution treatment at the same temperature,followed by rapid water quenching,results in the appearance of numerous L1_(0)phases within the B2 phases.The transformation from L1_(0)to B2 phases during subsequent tensile deformation can make the B2 and FCC phases return to a K-S orientation relationship.This,in turn,reduces the tendency for dislocation pile-ups at the phase interfaces and improves the ductility.We believe that this work will provide some new references for designing EHEAs with excellent mechanical properties.展开更多
Heterostructures of alloyed composites,comprising heterogeneous domains with dramatically different constitutive properties,hold remarkable potential to expand the realm of material design systems and resolve the trad...Heterostructures of alloyed composites,comprising heterogeneous domains with dramatically different constitutive properties,hold remarkable potential to expand the realm of material design systems and resolve the tradeoffbetween strength and ductility.This study introduces an innovative materials design method for synthesizing gradient pseudo-precipitates heterostructure(GPHS)in non-heat-treatable Al-2.5%Mg alloys.Utilizing cost-effective mild steel as both the diffusion source and protective layer,this heterostructure is achieved through pin-less friction stir-assisted cyclic localized deformation process.Exogenous Fe atoms diffuse across the interface by friction stir-induced heat conduction,forming Fe-Al second-phase particles in the Al alloy matrix.A rapid inter-diffusion mechanism is activated in conjunction with dense dislocation walls,grain boundaries,and sub-structures,resulting in the formation of pseudo-precipitates.These pseudo-precipitates are ultimately dispersed in a gradient distribution throughout the entire thickness of the Al alloy matrix induced by localized incremental deformation.The GPHSed Al-2.5%Mg alloy exhibits an enhanced synergy of strength and ductility,with a uniform elongation increase from 11%to 21.2%,while maintaining the strength.Multiple strengthening and hardening mechanisms,such as solid solution strengthening,dislocation hardening,and second phase strengthening,work synergistically to promote mechanical performance.Notably,the hetero-deformation between hard pseudo-precipitates and soft Al alloy matrix induces additional strain hardening,leading to high ductility.This work provides a fresh perspective on the design and fabrication of high-performance alloys with advanced heterostructures,especially for non-heat-treatable alloys.展开更多
Alloying is an effective strategy to tailor microstructure and mechanical properties of metallic materials to overcome the strength-ductility trade-off dilemma.In this work,we combined a novel alloy design principle,i...Alloying is an effective strategy to tailor microstructure and mechanical properties of metallic materials to overcome the strength-ductility trade-off dilemma.In this work,we combined a novel alloy design principle,i.e.harvesting pronounced solid solution hardening(SSH)based on the misfit volumes engineering,and simultaneously,architecting the ductile matrix based on the valence electron concentrations(VEC)criterion,to fulfill an excellent strength-ductility synergy for the newly emerging high/medium-entropy alloys(HEAs/MEAs).Based on this strategy,Al/Ta co-doping within NiCoCr MEA leads to an efficient synthetic approach,that is minor Al/Ta co-doping not only renders significantly enhanced strength with notable SSH effect and ultrahigh strain-hardening capability,but also sharply refines grains and induces abnormal twinning behaviors of(NiCoCr)_(92)Al_(6)Ta_(2) MEA.Compared with the partially twinned NiCoCr MEA,the yield strength(σy)and ultimate tensile strength(σUTS)of fully twinned Al/Ta-containing MEA were increased by~102%to~600 MPa and~35%to~1000 MPa,respectively,along with good ductility beyond 50%.Different from the NiCoCr MEA with deformation twins(DTs)/stacking faults(SFs)dominated plasticity,the extraordinary strain-hardening capability of the solute-hardened(NiCoCr)_(92)Al_(6)Ta_(2) MEA,deactivated deformation twinning,originates from the high density of dislocation walls,microbands and abundance of SFs.The abnormal twinning behaviors,i.e.,prevalence of annealing twins(ATs)but absence of DTs in(NiCoCr)_(92)Al_(6)Ta_(2) MEA,are explained in terms of the relaxation of grain boundaries(for ATs)and the twinning mechanism transition(for DTs),respectively.展开更多
The strength-ductility trade-offdilemma is hard to be evaded in high-strength Mg alloys at sub-zero temperatures,especially in the Mg alloys containing a high volume fraction of precipitates.In this paper,we report an...The strength-ductility trade-offdilemma is hard to be evaded in high-strength Mg alloys at sub-zero temperatures,especially in the Mg alloys containing a high volume fraction of precipitates.In this paper,we report an enhanced strength-ductility synergy at sub-zero temperatures in an aged Mg-7.37Gd-3.1Y-0.27Zr alloy.The tensile stress-strain curves at room temperature(RT),−70℃ and−196℃ show that the strength increases monotonically with decreasing temperature,but the elongation increases first from RT to−70℃ then declines from−70℃ to−196℃.After systematic investigation of the microstructure evolutions at different deformation temperatures via synchrotron X-ray diffraction,electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM),it is found that a high dislocation density with sufficient<c+a>dislocations promotes good tensile ductility at−70℃,which is attributed to the minimized critical resolved shear stress(CRSS)ratio of non-basal<c+a>to basaldislocations.In ad-dition,more shearable precipitates can further improve the ductility via lengthening the mean free path of dislocation glide.The present work demonstrates that an excellent strength-ductility synergy at sub-zero temperatures can be achieved by introducing a high dislocation density and shearable precipitates in high-strength Mg alloys.展开更多
基金support from the China Scholarship Council(No.202107000038)support from the National Natural Science Foundation of China(Nos.52004227,52061040,and 12222209)the China Postdoctoral Science Foundation(No:2021M692512).
文摘This study aims to achieve a synergy of strength and ductility in magnesium-based nanocomposite materials through the design of a dual-heterostructure. Utilizing ball milling and hot extrusion, a nano-TiC/AZ61 composite featuring particle-rare coarse grain (CG) and particle-rich fine grain (FG) zones was successfully fabricated. Experimental results demonstrated that compared with the homogeneous structure, the dual-heterostructure composite achieved a significant increase in elongation by 116 % and a remarkable 165 % improvement in the strength-ductility product (SDP), while maintaining a high ultimate tensile strength (UTS) of 417±4 MPa. This substantial performance enhancement is primarily attributed to the additional strain hardening induced by hetero-deformation-induced (HDI) strain hardening and crack-blunting capabilities, as elucidated by microstructural characterization and crystal plasticity finite element modeling (CPFEM). Notably, the strain hardening contribution from the CG zones at the early stage of deformation (≤ 45 % of total plastic deformation amount) is minimal but increases significantly during the subsequent deformation stages. The dislocation increment rate in CG zones (219 %) is observed to be more than double that in FG zones (95 %), attributed to the large grain size and low dislocation density in CG zones, which provide more space for dislocation storage. In addition, the aggravated deformation inhomogeneity as deformation progresses leads to an increase in geometrically necessary dislocations (GNDs) generation near the heterogeneous interface, thereby enhancing HDI hardening. Fracture mechanism analysis indicated that the cracks mainly initiate in the FG region and are effectively blunted upon their propagation to the CG region, necessitating increased energy consumption and indicating higher fracture toughness for the dual-heterostructure composites. This study validates the effectiveness of the dual-heterostructure design in magnesium-based composites, providing a novel understanding of the deformation mechanism through both experimental analysis and CPFEM, paving the way for the development of high-performance, lightweight structural materials.
基金funded by the National Natural Science Foundation of China(No.52204407)the Natural Science Foundation of Jiangsu Province(No.BK20220595)+1 种基金the China Postdoctoral Science Foundation(No.2022M723689)the Industrial Collaborative Innovation Project of Shanghai(No.XTCX-KJ-2022-2-11)。
文摘The application of machine learning in alloy design is increasingly widespread,yet traditional models still face challenges when dealing with limited datasets and complex nonlinear relationships.This work proposes an interpretable machine learning method based on data augmentation and reconstruction,excavating high-performance low-alloyed magnesium(Mg)alloys.The data augmentation technique expands the original dataset through Gaussian noise.The data reconstruction method reorganizes and transforms the original data to extract more representative features,significantly improving the model's generalization ability and prediction accuracy,with a coefficient of determination(R^(2))of 95.9%for the ultimate tensile strength(UTS)model and a R^(2)of 95.3%for the elongation-to-failure(EL)model.The correlation coefficient assisted screening(CCAS)method is proposed to filter low-alloyed target alloys.A new Mg-2.2Mn-0.4Zn-0.2Al-0.2Ca(MZAX2000,wt%)alloy is designed and extruded into bar at given processing parameters,achieving room-temperature strength-ductility synergy showing an excellent UTS of 395 MPa and a high EL of 17.9%.This is closely related to its hetero-structured characteristic in the as-extruded MZAX2000 alloy consisting of coarse grains(16%),fine grains(75%),and fiber regions(9%).Therefore,this work offers new insights into optimizing alloy compositions and processing parameters for attaining new high strong and ductile low-alloyed Mg alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.92263201,51927801,and 52001160)the National Key Research and Development Program of China(Grant No.2020YFA0405900).
文摘A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.
基金financial support from the National Key Research and Development Program of China(2021YFC2400703)Zhengzhou City Major Special Project for Collaborative InnovationChina Scholarship Council。
文摘Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restricting widespread use.In this study,ultra-fine-grained and homogeneous Mg alloys were fabricated using double-sided friction stir processing(DS-FSP)with liquid CO_(2) rapid cooling,leading to a significant enhancement in the strength-ductility synergy of the stirred zone.The results demonstrate that DS-FSP samples exhibit simultaneous improvements in ultimate tensile strength(UTS)and elongation,reaching 334.1±15 MPa and 28.2±7.3%,respectively.Compared to the non-uniform fine-grained microstructure obtained through single-sided friction stir processing,DS-FSP generates a uniform ultra-fine-grained structure,fundamentally altering the fracture behavior and mechanisms of Mg alloys.The DS-FSP samples exhibit irregular fracture patterns due to variations in basal slip system activation among different grains.In contrast,single-sided friction stir processing samples,characterized by a fine-grained yet heterogeneous microstructure,display flat shear fractures dominated by high-density dislocation initiation induced by twin formation,with fracture propagation dictated by the non-uniform texture.By achieving an ultra-fine grain size and homogeneous texture,DS-FSP effectively modifies the fracture mechanisms,thereby enhancing the strength-ductility balance of bio-magnesium alloys.
基金financially supported by the National Natural Science Foundation of China(Nos.52271113 and 92163201)the Key programme of National Natural Science Foundation of China(Nos.52431001 and 52431006)+1 种基金Jinyu Zhang is grateful for the Shaanxi Province Youth Innovation Team(No.22JP042)the Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58).
文摘Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a new strategy based onβ-subgrains-mediated hierarchicalα-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe(wt.%)alloy through a unique combination of hot rolling,short-term solid solution,and aging treatment,i.e.,RSST+A.Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of∼1581 MPa and decent ductility of∼8.4%,surpassing∼1060 MPa and∼2.7%of the corresponding RSST counterparts without final aging treatment.This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting ofβ-subgrains-mediated hierarchicalαprecipitates as a result of our specific processing approach.The designed short-term solution introduces abundantβsubgrains that are transformed from the retained intensive dislocations during hot rolling.Theβsubgrain boundaries subsequently promote a dramatic precipitation ofαallotriomorphs(αGB)and Widmanstätten side-plates(αWGB),which effectively subdividesβgrains into numerous tiny independent deformation units.Consequently,plastic strain is uniformly partitioned into a large number of small agedβsubgrains during tension,which strongly impedes strain localization that would typically occur across multipleβsubgrains in the fashion of long straight slip bands in the case of the RSST samples.Furthermore,the hierarchicalαstructure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining.These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing highstrength titanium alloys in the precipitation-hardening state.
基金Supported by the Industrial Collaborative Innovation Project of Shanghai(Grant No XTCX-KJ-2022-2-11)the National Natural Science Foundation of China(Grant No52073176)。
文摘In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructural evolution during deposition and subsequent heat treatment was explained through multi-scale microstructural characterization techniques,and the impact of heat treatment on the strengthductility synergy of the deposited alloy was systematically compared.The results showed that the microstructure of the deposited sample was mainly composed of fine equiaxedα-Mg grains and Mg_(24)(Gd,Y)_(5) phase.The optimized solution heat treatment(450℃×2 h)had little effect on the grain size,but can effectively reduce the Mg_(24)(Gd,Y)_(5) eutectic phase on the grain boundary,resulting in a significant increase in elongation from 13.7% to 26.6%.After peak-aging treatment,the strength of the GW63K alloy increased to 370 MPa,which was significantly higher than the as-built state(267 MPa).The superior strength in this study is attributed to the refinement strengthening imparted by the fine microstructure inherited in the as-built GW63K alloy,as well as the precipitation strengthening due to the formation of dense β’precipitates with a pronounced plate-like aspect ratio.
基金supported by the National Natural Science Foundation of China(Grant Nos.92166112,52373236 and 52271132)the Natural Science Foundation of Guangdong Province(Grant No.2024A1515010658)+6 种基金the Guangdong Province International Science and Technology Cooperation Project(Grant No.2023A0505050103)the Guangxi Key Laboratory of Information Materials(Grant No.231033-K)the Open Project Program of Wuhan National Laboratory for Optoelectronics(Grant No.2021WNLOKF010)Guangzhou Science and Technology Planning Project(2024A04J9966)Guangdong Provincial Science and Technology Plan Project(2022A0505050043)The financial support from the ECU industrial grant(No.G1006320)ECU DVC strategic research fund(project number 23965)。
文摘Ti-xNb alloys produced by laser powder bed fusion(LPBF)from mixed powder usually exhibit an inhomogeneous elemental distribution,leading to a deterioration in mechanical properties.To address this issue,we proposed a strategy to achieve heterostructure in laser powder bed fused Ti-xNb alloys from mixed powders through precipitation ofωwithinβ.Moreover,the effect of Nb content on the micro structure and mechanical behavior of Ti-xNb alloys was studied.The results indicated that in-situ laser re-melting can realize the homogeneous elemental distribution in Ti-xNb alloys.When the Nb content increases from 30 wt%,35 wt%to40 wt%,Ti-xNb alloys experience a transformation from β+α' to β+ω and monolithic β.Specifically,ωnano-precipitates in Ti-35Nb alloy are only distributed in some β grains,forming a heterostructure with“softβ”and“hard β+ω”grains.As a result,LPBF-produced Ti-35Nb alloy demonstrates excellent mechanical properties,with yield strength of ^(792±6)MPa,tensile strength of ^(806±7)MPa,Young's modulus of ^(68±6)GPa,and uniform elongation of ^(18.0±1.1)%.The Frank-Read mechanism induces dislocation proliferation and dislocation cross-slip,and the geometrically necessary dislocations(GNDs)are induced at the heterogeneous interface of“softβ”and“hard β+ω”grains,resulting in an enhancement in the strength-ductility synergy of Ti-35Nb alloy produced by LPBF.This work provides an innovative strategy to improve the strength-ductility synergy of LPBF-produced Ti-xNb alloys from mixed powders by tailoring ω nano-precipitates.
基金support received from the National Key Research and Development Program of China(Grant No.2021YFB3400902)the National Natural Science Foundation of China(Grant No.51275414,52205418)+1 种基金the Fundamental Research Funds for the Central Universities with Grant No.3102015BJ(Ⅱ)ZS007the Key Research and Development Program of Shaanxi Province(No.2020ZDLGY12-07).
文摘The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the material’s high product of strength and elongation(PSE)and a moderate yield-to-strength ratio(YTS).This study presents an innovative approach using torsion deformation combined with shortterm aging treatment to create a gradient structure.This structure integrates gradients in plastic strain,dislocations,precipitated phases,and grain size,forming an in-situ core-shell configuration characterized by a“soft core and hard shell”.As a result,the yield strength,ultimate tensile strength,elongation,YTS,and PSE increased by 4.07%,5.72%,66.59%,−1.52%,and 76.12%,respectively,compared to the asreceived material.Its strengthening effect is significantly better than traditional T6 treatment.Notably,the formation of a gradient structure through this novel thermomechanical processing technique optimized YTS by 11.51%compared to traditional heat treatments.The significant increase in PSE is attributed to the marked improvement in elongation indicating an effective enhancement in the strength-ductility balance.This provides a promising strategy for designing and manufacturing high-performance components.
基金supported by the Major Science and Technology Project of Gansu Province(Nos.23ZDGA010 and 22ZD6GA008)the National Natural Science Foundation of China(No.51564035).
文摘Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti_(11.7)B_(2.5)(at%)with a unique microstructure was developed in this work.The microstructure,which includes 17.8%nanosized L12 precipitates and 26.6%micron-sized annealing twins distributed within~8μm fine FCC grains,was achieved through cryogenic rolling and subsequent annealing.The alloy exhibits a yield strength(YS)of 1063 MPa,ultimate tensile strength(UTS)of 1696 MPa,and excellent elongation of~26%.The L1_(2) precipitates and high-density grain boundaries act as a barrier to the dislocation movement,resulting in a substantial strengthening effect.In addition,the dislocations can cut through the L1_(2) precipitates that are coherent with the FCC matrix,whereas the twin boundaries can effectively absorb and store dislocations,leading to a high work-hardening rate.Furthermore,the stacking faults,Lomer-Cottrell locks,and 9-layer rhombohedral stacking sequence(9R)structures formed during tensile deformation significantly enhance strain hardening by blocking dislocation movement and accumulating dislocations,resulting in excellent comprehensive tensile properties.Theoretical calculations reveal that the grain boundaries,L1_(2)precipitates,and twin boundaries contribute the strengths of 263.8,412.6,and 68.7 MPa,respectively,accounting for 71.9%of the YS.This study introduces a promising strategy for developing multicomponent alloys with significant strength-ductility synergies.
基金Project supported by the National Natural Science Foundation of China(52301041)Guizhou Provincial Science and Technology Projects(Qingnian No.2024-123)the Special Fund for Special Posts of Guizhou University(2023-26,2023-53)。
文摘In this study,a novel strategy for breaking the strength-ductility dilemma of Mg-1.5Zn-0.6Gd(wt%)alloy via solute segregation was reported.The hot extruded alloy sheet was subjected to rolling deformation,and then heat-treated at 200℃.The high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)reveals a remarkable segregation of solute Zn atoms along both high and lowangle grain boundaries(GBs).As compared with as-rolled plate,the yield strength,ultimate tensile strength,and the elongation of annealed sample is increased by 15.6%,14%,and 8.4%,respectively,acquiring an obvious strength-ductility synergy effect.The solute segregation endows the rolled plate with excellent grain size stability and provides a prominent extra solute cluster strengthening,which completely resists the other softening effects including dislocation annihilation and grain coarsening.Meanwhile,the directional migration of Zn atoms and the annihilation of dislocations provide a"clear"space within the grain,which is beneficial for the moving and accumulating of subsequent dislocations.This work sheds light on the solute partitioning behavior and realizes a good application of GB segregation in improving the comprehensive mechanical properties of Mg alloys.
基金National Natural Science Foundation of China (52305358)the Fundamental Research Funds for the Central Universities (2023ZYGXZR061)+3 种基金Guangdong Basic and Applied Basic Research Foundation (2022A1515010304)Science and Technology Program of Guangzhou (202201010362)Young Elite Scientists Sponsorship Program by CAST . (2023QNRC001)Young Talent Support Project of Guangzhou (QT-2023-001)
文摘Zinc(Zn)is considered a promising biodegradable metal for implant applications due to its appropriate degradability and favorable osteogenesis properties.In this work,laser powder bed fusion(LPBF)additive manufacturing was employed to fabricate pure Zn with a heterogeneous microstructure and exceptional strength-ductility synergy.An optimized processing window of LPBF was established for printing Zn samples with relative densities greater than 99%using a laser power range of 80∼90 W and a scanning speed of 900 mm s−1.The Zn sample printed with a power of 80 W at a speed of 900 mm s−1 exhibited a hierarchical heterogeneous microstructure consisting of millimeter-scale molten pool boundaries,micrometer-scale bimodal grains,and nanometer-scale pre-existing dislocations,due to rapid cooling rates and significant thermal gradients formed in the molten pools.The printed sample exhibited the highest ductility of∼12.1%among all reported LPBF-printed pure Zn to date with appreciable ultimate tensile strength(∼128.7 MPa).Such superior strength-ductility synergy can be attributed to the presence of multiple deformation mechanisms that are primarily governed by heterogeneous deformation-induced hardening resulting from the alternative arrangement of bimodal Zn grains with pre-existing dislocations.Additionally,continuous strain hardening was facilitated through the interactions between deformation twins,grains and dislocations as strain accumulated,further contributing to the superior strength-ductility synergy.These findings provide valuable insights into the deformation behavior and mechanisms underlying exceptional mechanical properties of LPBF-printed Zn and its alloys for implant applications.
基金National Natural Science Foun-dation of China(Nos.52275374,52205414)Xiaomi Founda-tion through the Xiaomi Young Scholar Program,the Key Research and Development Projects of Shaanxi Province(No.2023-YBGY-361)+2 种基金as well as the Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001)State Key Laboratory for Mechan-ical Behavior of Materials(NO.20212311)as well as the Xi’an Jiaotong University Basic Research Funds for Freedom of Explo-ration and Innovation-Student Programs(NO.xzy022023066).
文摘Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior performance due to internal defects and inherent columnar grains.Herein,external ultrasound fields with different powers were successfully introduced into the wire-arc DED of AZ31 Mg alloy.The microstructure,defects,and mechanical properties of the fabricated components were carefully charac-terized and compared.The results show that the external ultrasound fields lead to decreased porosity,complete columnar to equiaxed transition(CET),and enhanced performance.Consequently,the UA90 samples exhibited a remarkable increase of~30%,~45%,and~189%in yield strength,ultimate tensile strength,and elongation,respectively.The dominant mechanisms of enhanced strength-ductility synergy were analyzed in detail.This study thus sheds new light on wire-arc DED of Mg alloy components with excellent performance via external ultrasound fields.
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515120028)the National Natural Science Foundation of China(Grant Nos.52130204,52174376,52202070)+6 种基金the TQ Innovation Foundation(Grant No.23-TQ09-02-ZT-01-005)the Aeronautical Science Foundation of China(Grant No.20220042053001)the Key R&D Project of Shaanxi Province(Grant Nos.2024GXYBXM-220,2024GX-YBXM-400,2024GX-ZDCYL-03-03)the Science and Technology Innovation Team Plan of Shann Xi Province(Grant No.2021TD-17)the Thousands Person Plan of Jiangxi Province(Grant No.JXSQ2020102131)the Fundamental Research Funds for the Central Universities(Grant Nos.D5000230348,D5000220057)the China Scholarship Council(Grant No.202206290133).
文摘The strength and ductility cannot achieve a good tradeoff for some superalloy(e.g.GH3536)prepared by selective laser melting(SLM),which seriously restricts their industrial applications.This work examined the effect of post-heat treatment(HT)on the microstructure and mechanical properties of GH3536 produced by SLM.In particular,the influence of carbide precipitate morphology and distribution on strength and ductility of the alloy after heat treatment was discussed.After aging at 650°C(denoted as HT1),the Cr23C6 carbides were distributed in chains.The ductility increased by approximately 31%,while the strength slightly decreased.After aging at 745°C(denoted as HT2),the Cr23C6 carbides were distributed in chains.However,the HT2 samples showed an increase in ductility of~58%and no reduction in strength.As the dislocation density of HT2 sample was higher than that of the HT1 sample,the chain carbides could be pinned to the grain boundaries,consequently improving the ductility but no loss in strength as compared with the as-deposited samples.When the aging temperature was increased to 900°C(denoted as HT3),the carbides were distributed in a discontinuous granular form.As a result,the HT3 samples presented the lowest dislocation density which reduced the strength.
基金the financial support of the National Natural Science Foundation of China(Nos.U1910213 and 52205400)the China Postdoctoral Science Foundation(No.2021M692626)+2 种基金the Fundamental Research Program of Shanxi Province(No.202203021212321)Technological Innovation Talent Team Special Plan of Shanxi Province(No.202204051002002)the Doctoral Starting up Foundation of Taiyuan University of Science and Technology(No.20222046).
文摘Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distributions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation tem peratures.The results reveal that the grain refinement process under mediumlow temperature deformation conditions(≤350℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultrafine sub-grains,and randomly orientated quasi-micron grains.Different deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal slip.The deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance ability.Analysis in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different tem peratures.By summarizing the tensile test results,the sample forged at 350℃exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2%with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8%.
基金Project supported by the Scientific and Technological Developing Scheme of Jilin Province(20220101239JC,YDZJ202301ZYTS538)the Chinese Academy of Sciences Youth Innovation Promotion Association(2023234)。
文摘A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 MPa and 8.5%,respectively.This alloy has two types of a-Mg grains:coarse a_(1)-Mg((46±18)μm)and fine a_(2)-Mg((9.2±2.3)μm)grains,and various Al-GS(GS=Gd and Sm)particles located at grain boundaries while clear solute-atom segregation near grain boundaries with limited or free intermetallic particles.Characterizations using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)indicate the crystal structures of Al-GS phases.After aging,denseβ'precipitates and chain-shapedβ''-like structures precipitated near grain boundaries while a high density of ultrafineβ''-(Mg,Al)3Sm precipitates and Al-GS clusters formed in grain center.Relatively fine grains,Al-GS primary particles,solute-atom segregation near grain boundaries,and/or multiple precipitates contribute to the high strength of the studied alloy,while the multi-scale a-Mg grains,variety of intermetallic particles but discontinuous skeleton,and the multi-typed precipitated lead to its satisfactory ductility.
基金supported by the National Natural Science Foundation of China(Nos.52127802 and 51834009)the Science and Technology Project of Xi’an(No.2021SFGX0004).
文摘Laser powder bed fusion(LPBF)is a promising method for manufacturing functional and structural integrated Cu-Cr-Zr components.However,the LPBF-processed Cu-Cr-Zr alloys still suffer from the strength-ductility trade-offdilemma,while maintaining high conductivity.Here,LPBF-processed Cu-Cr-Zr alloy with a hierarchical structure was obtained by increasing the Cr and Zr content simultaneously.After aging treatment,the hierarchical structure was composed of melt tracks at the macroscale,coarse grains(31.9±0.1μm)and fine grains(5.6±0.2μm)at the microscale,high-density of dislocations and dual precipitates at the nanoscale.The direct aged sample exhibited an excellent combination of strength and ductility(tensile strength was enhanced to 626±1 MPa and uniform elongation of 16.2%±1.1%),which is superior to the traditionally wrought and LPBF-processed Cu-Cr-Zr alloys reported previously.Meantime,a good electrical conductivity of 71.1%±0.3%IACS was also achieved.In addition,the heterogeneous deformation-induced stress caused by the hierarchical structure not only led to a large increase in yield strength but also promoted tensile ductility.
基金supported by the funds of the Shanghai Sailing Program,the National Natural Science Foundation of China(No.52104386)the Xi’an Association for Science and Technology Young Talents Lifting Program,and the State Key Laboratory of Solidification Processing(NPU),China(No.2022-TS-08).
文摘Eutectic high-entropy alloys(EHEAs)that combine the advantages of HEAs and eutectic alloys are promising materials for high-temperature environments.However,the mechanical properties of currently developed EHEAs still cannot meet the servicing requirements.Here,we propose a strategy to optimize the tensile properties in a Al_(21)Co_(19.5)Fe_(9.5)Ni_(50)EHEA by regulating the phase transformation and precipitation features.The results showed that the as-cast Al_(21)Co_(19.5)Fe_(9.5)Ni_(50)EHEA mainly consists of face-centered cubic(FCC)and B2 phases showing a lamellar morphology,and the FCC and B2 phases keep a stable K-S orientation relationship.Solution treatment at 900 and 1100°C followed by furnace cooling to room temperature leads to a significant precipitation of L1_(2)phases within the FCC phases.In the subsequent tensile deformation process,dispersed L1_(2)phases and the transformation from B2 to L1_(0)phases can significantly enhance the yield strength of the designed EHEA.Furthermore,solution treatment at the same temperature,followed by rapid water quenching,results in the appearance of numerous L1_(0)phases within the B2 phases.The transformation from L1_(0)to B2 phases during subsequent tensile deformation can make the B2 and FCC phases return to a K-S orientation relationship.This,in turn,reduces the tendency for dislocation pile-ups at the phase interfaces and improves the ductility.We believe that this work will provide some new references for designing EHEAs with excellent mechanical properties.
基金financial support from the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIP)(Nos.NRF-2021R1A2C3006662 and NRF-2022R1A5A1030054)supported by Brain Pool Program through the National Research Foundation of Korea(NRF-RS202300263999).
文摘Heterostructures of alloyed composites,comprising heterogeneous domains with dramatically different constitutive properties,hold remarkable potential to expand the realm of material design systems and resolve the tradeoffbetween strength and ductility.This study introduces an innovative materials design method for synthesizing gradient pseudo-precipitates heterostructure(GPHS)in non-heat-treatable Al-2.5%Mg alloys.Utilizing cost-effective mild steel as both the diffusion source and protective layer,this heterostructure is achieved through pin-less friction stir-assisted cyclic localized deformation process.Exogenous Fe atoms diffuse across the interface by friction stir-induced heat conduction,forming Fe-Al second-phase particles in the Al alloy matrix.A rapid inter-diffusion mechanism is activated in conjunction with dense dislocation walls,grain boundaries,and sub-structures,resulting in the formation of pseudo-precipitates.These pseudo-precipitates are ultimately dispersed in a gradient distribution throughout the entire thickness of the Al alloy matrix induced by localized incremental deformation.The GPHSed Al-2.5%Mg alloy exhibits an enhanced synergy of strength and ductility,with a uniform elongation increase from 11%to 21.2%,while maintaining the strength.Multiple strengthening and hardening mechanisms,such as solid solution strengthening,dislocation hardening,and second phase strengthening,work synergistically to promote mechanical performance.Notably,the hetero-deformation between hard pseudo-precipitates and soft Al alloy matrix induces additional strain hardening,leading to high ductility.This work provides a fresh perspective on the design and fabrication of high-performance alloys with advanced heterostructures,especially for non-heat-treatable alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.51722104,51790482,51621063 and 51625103)the 111 Project 2.0 of China(PB2018008)+1 种基金the National Key Research and Development Program of China(2017YFA0700701)the Fundamental Research Funds for the Central Universities for part of financial support(xtr022019004)。
文摘Alloying is an effective strategy to tailor microstructure and mechanical properties of metallic materials to overcome the strength-ductility trade-off dilemma.In this work,we combined a novel alloy design principle,i.e.harvesting pronounced solid solution hardening(SSH)based on the misfit volumes engineering,and simultaneously,architecting the ductile matrix based on the valence electron concentrations(VEC)criterion,to fulfill an excellent strength-ductility synergy for the newly emerging high/medium-entropy alloys(HEAs/MEAs).Based on this strategy,Al/Ta co-doping within NiCoCr MEA leads to an efficient synthetic approach,that is minor Al/Ta co-doping not only renders significantly enhanced strength with notable SSH effect and ultrahigh strain-hardening capability,but also sharply refines grains and induces abnormal twinning behaviors of(NiCoCr)_(92)Al_(6)Ta_(2) MEA.Compared with the partially twinned NiCoCr MEA,the yield strength(σy)and ultimate tensile strength(σUTS)of fully twinned Al/Ta-containing MEA were increased by~102%to~600 MPa and~35%to~1000 MPa,respectively,along with good ductility beyond 50%.Different from the NiCoCr MEA with deformation twins(DTs)/stacking faults(SFs)dominated plasticity,the extraordinary strain-hardening capability of the solute-hardened(NiCoCr)_(92)Al_(6)Ta_(2) MEA,deactivated deformation twinning,originates from the high density of dislocation walls,microbands and abundance of SFs.The abnormal twinning behaviors,i.e.,prevalence of annealing twins(ATs)but absence of DTs in(NiCoCr)_(92)Al_(6)Ta_(2) MEA,are explained in terms of the relaxation of grain boundaries(for ATs)and the twinning mechanism transition(for DTs),respectively.
基金We acknowledge Prof.Jian Wang from the University of Nebraska-Lincoln for insightful discussion.This work is financially supported by the National Key R&D Program of China(No.2021YFB3501005)the Space Utilization System of China Manned Space Engineering(No.KJZ-YY-WCL04)+1 种基金the Natural Science Foundation of Shanghai(No.23ZR1431100)the National Natural Science Foundation of China(No.51825101).Shanghai Syn-chrotron Radiation Facility is acknowledged for supporting the syn-chrotron high energy X-ray diffraction experiments at Beam Line No.BL14B1.
文摘The strength-ductility trade-offdilemma is hard to be evaded in high-strength Mg alloys at sub-zero temperatures,especially in the Mg alloys containing a high volume fraction of precipitates.In this paper,we report an enhanced strength-ductility synergy at sub-zero temperatures in an aged Mg-7.37Gd-3.1Y-0.27Zr alloy.The tensile stress-strain curves at room temperature(RT),−70℃ and−196℃ show that the strength increases monotonically with decreasing temperature,but the elongation increases first from RT to−70℃ then declines from−70℃ to−196℃.After systematic investigation of the microstructure evolutions at different deformation temperatures via synchrotron X-ray diffraction,electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM),it is found that a high dislocation density with sufficient<c+a>dislocations promotes good tensile ductility at−70℃,which is attributed to the minimized critical resolved shear stress(CRSS)ratio of non-basal<c+a>to basaldislocations.In ad-dition,more shearable precipitates can further improve the ductility via lengthening the mean free path of dislocation glide.The present work demonstrates that an excellent strength-ductility synergy at sub-zero temperatures can be achieved by introducing a high dislocation density and shearable precipitates in high-strength Mg alloys.
