Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear tran...Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone （STZ） models, we first discuss in this article our recently proposed ＇core-shell＇ model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass （BMG）. With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.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
A multi-phase heterogeneous FeCoNi-based high-entropy alloy is developed to overcome the trade-off between strength and ductility.By alloying with a small amount of Cu and employing a rapid recrystalliza-tion process,...A multi-phase heterogeneous FeCoNi-based high-entropy alloy is developed to overcome the trade-off between strength and ductility.By alloying with a small amount of Cu and employing a rapid recrystalliza-tion process,it exhibits a good combination of yield strength(roughly 1300 MPa)and ductility(approach-ing 20%).Firstly,a multi-phase heterogeneous structure is tailored ranging from nano to micron.Cu is efficiently precipitated as nanoscale clusters(4.2 nm),high-density cuboidal L1_(2) particles(20-40 nm)and L2_(1) particles(500-800 nm)are found to be embedded in the matrix and a bimodal heterogeneous grain structure(1-40μm)is constructed.Secondly,the introduction of Cu effectively suppresses the pre-cipitation of coarse L21 phase at grain boundaries,reducing its volume fraction by 80%and replaced by smaller-scale continuous precipitations within the grains.Thirdly,the high mixing enthalpy gap of Cu and the matrix leads to the formation of local chemical fluctuation and the consequential rugged topog-raphy in the matrix,which result in retarded dislocation motion and promotes dislocation plugging and interlocking during strain,enhancing yield stress and work hardening rate.This study provides a valuable perspective to enhance strength and ductility via enlarged local chemical fluctuation-tailored multi-phase heterogeneous structures.展开更多
Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstra...Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.展开更多
In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing tre...In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing treatment.Instead of a distinct interface between the primaryα_(p)hase(α_(p))andβ_(t)ransformation microstructure(β_(t))in the equiaxed microstructure(EM),allα_(p)/β_(t)interfaces are eliminated in the HS,and the largeα_(p)phases are replaced by coarseαlamella.Compared to the EM alloy,the heterostruc-tured alloy exhibits a superior strength-ductility combination.The enhanced strength is predominantly attributed to the increased interfaces ofα/βplates and hetero-deformation induced(HDI)strengthening caused by back stress.Meanwhile,good ductility is ascribed to its uniform distribution of coarse and fineαlamella,which effectively inhibits strain localization and generates an extra HDI hardening.This can be evidenced by the accumulated geometrically necessary dislocations(GNDs)induced by strain partitioning of the heterostructure.Significantly,the HDI causes extra<c+a>dislocations piling up in the coarseαlamella,which generates an extra strain hardening to further improve the ductility.Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium al-loys with excellent mechanical properties.展开更多
In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal i...In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal insurance contract when maxing the insured’s expected utility of his/her remaining wealth under the smooth ambiguity model and the heterogeneous belief form satisfying the MHR condition. We calculate the insurance premium by using generalized Wang’s premium and also introduce a series of stochastic orders proposed by [1] to describe the relationships among the insurable risk, background risk and ambiguity parameter. We obtain the deductible insurance is the optimal insurance while they meet specific dependence structures.展开更多
The development of high-performance structural and functional materials is vital in many industrial fields.High-and medium-entropy alloys(H/MEAs)with superior comprehensive properties owing to their specific microstru...The development of high-performance structural and functional materials is vital in many industrial fields.High-and medium-entropy alloys(H/MEAs)with superior comprehensive properties owing to their specific microstructures are promising candidates for structural materials.More importantly,multitudinous efforts have been made to regulate the microstructures and the properties of H/MEAs to further expand their industrial applications.The various heterostructures have enormous potential for the development of H/MEAs with outstanding performance.Herein,multiple heterogeneous structures with single and hierarchical heterogeneities were discussed in detail.Moreover,preparation methods for compositional inhomogeneity,bimodal structures,dualphase structures,lamella/layered structures,harmonic structures(core-shell),multiscale precipitates and heterostructures coupled with specific microstructures in H/MEAs were also systematically reviewed.The deformation mechanisms induced by the different heterostructures were thoroughly discussed to explore the relationship between the heterostructures and the optimized properties of H/MEAs.The contributions of the heterostructures and advanced microstructures to the H/MEAs were comprehensively elucidated to further improve the properties of the alloys.Finally,this review discussed the future challenges of high-performance H/MEAs for industrial applications and provides feasible methods for optimizing heterostructures to enhance the comprehensive properties of H/MEAs.展开更多
The Eurasian beaver(Castor fiber Linnaeus,1758)can be considered a hydrological ecosystem engineer as it shapes environmental characteristics through its building activities and feeding behaviour.Even if several studi...The Eurasian beaver(Castor fiber Linnaeus,1758)can be considered a hydrological ecosystem engineer as it shapes environmental characteristics through its building activities and feeding behaviour.Even if several studies have so far reported beaver impact on multi-taxon biodiversity and forest regeneration,there is a lack of research on forest stand structure evolution following beaver direct activity on trees.This represents a pivotal topic for predicting restoration outcomes and reccommending sound silvicultural and management practices to maintain specific forest conditions.Specifically,the study aims at investigating forest stand structure and tree species diversity changes considering river variability,distance from the riverbank and beaver's gnawing activity intensity.The Eurasian beaver is only recently recolonising the three analysed Mediterranean rivers,but stand structure seems to be already significantly impacted by the species.The number of trees was reduced,increasing mean diameter at breast height at stand level,as most of the youngest and/or smaller trees are entirely cut down.Strongest structural variations can be detected in intensively impacted stands and in the forest portions closer to the riverbank.The absence of a significant effect on most of the diversity indices is likely due to the initially homogeneous composition of the tree layer in each stand and to the limited variety of beaver's diet within the sites.Future resprouting of secondary tree shoots,as well as beaver gnawing activity changes in intensity over time and space,can further produce variations in structural parameters and woody species diversity in the medium-and long-term period.Therefore,it will be crucial to further monitor the long-term effects,as structural shifts can produce significant effects on riparian ecosystem functions.展开更多
Metastable β titanium alloy is an ideal material for lightweight and high strength due to its excellent comprehensive mechanical properties.However,overcoming the trade-off relation between strength and ductility rem...Metastable β titanium alloy is an ideal material for lightweight and high strength due to its excellent comprehensive mechanical properties.However,overcoming the trade-off relation between strength and ductility remains a significant challenge.In this study,the mechanical properties of Ti-38644 alloy were optimized by introducing a heterogeneous bi-grain bi-lamella(BG-BL)structure through a well-designed combination of rolling,drawing and heat treatment.The results demonstrate that the present BG-BL Ti-38644 alloy shows a tensile strength of~1500 MPa and a total elongation of 18%.In particular,the high strength-elongation combination of the BG-BL Ti-38644 alloy breakthroughs the trade-off relation in all the titanium alloys available.The recrystallized grains with low dislocation enhance the ductility of the Ti-38644 alloy,while the highly distorted elongated grains mainly contribute to the high strength.The present study provides a new principle for designing Ti alloys with superior strength and ductility.展开更多
1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain bounda...1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain boundaries(GBs),which restricts local plastic flow dur-ing the plastic deformation and leads to stress concentration[3,4].Recently,the development of concepts aimed at achieving hetero-geneous grain has emerged as a promising approach for enhanc-ing comprehensive mechanical properties[5,6].展开更多
Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and p...Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and poor heat resistance limit their application scope.Recent advances have highlighted that the combination of extensional flow and thermal fields can achieve toughness–stiffness balance,high transparency,and good heat resistance.However,the effect of extensional flow on the post-non-isothermal crystallization of PLLA during heating and the resulting crystalline texture remains unclear.In this study,PLLA with a heterogeneous amorphous structure and oriented polymorph was prepared by extensional flow.The effect of heterogeneous amorphous structures on non-isothermal crystallization kinetics during the heating process was studied by thermal analysis,polarized optical microscopy,infrared spectroscopy,and ex situ/in situ X-ray characterization.These results clearly illustrate that extensional flow enhances the formation of oriented crystalline structures,accelerates non-isothermal crystallization,and modulates the polymorphic composition of PLLA.Moreover,an unexpected dual cold-crystallization behavior is identified in ordered PLLA samples upon extensional flow,which is from the extensional flow-induced heterogeneous amorphous phase into α' phase(low-temperature peak)and the pristine amorphous phase intoαphase(high-temperature peak).The extensional flow primarily promotes the formation of the more perfectαandα'phases,but has a negative effect on the final content ofαphase formed after cold crystallization andα'-to-αphase transformation.The findings of this work advance the understanding of PLLA non-isothermal crystallization after extensional flow and offer valuable guidance for high-performance PLLA upon heat treatment in practical processing.展开更多
1060/7050 Al/Al laminated metal composites(LMCs)with heterogeneous lamellar structures were prepared by accumulative roll bonding(ARB),cold rolling and subsequent annealing treatment.The strengthening mechanism was in...1060/7050 Al/Al laminated metal composites(LMCs)with heterogeneous lamellar structures were prepared by accumulative roll bonding(ARB),cold rolling and subsequent annealing treatment.The strengthening mechanism was investigated by microstructural characterization,mechanical property tests and in-situ fracture morphology observations.The results show that microstructural differences between the constituent layers are present in the Al/Al LMCs after various numbers of ARB cycles.Compared with rolled 2560-layered Al/Al LMCs with 37.5%and 50.0%rolling reductions,those with 62.5%rolling reductions allow for more effective improvements in the mechanical properties after annealing treatment due to their relatively high mechanical incompatibility across the interface.During tensile deformation,with the increased magnitude of incompatibility in the 2560-layered Al/Al LMC with a heterogeneous lamellar structure,the densities of the geometrically necessary dislocations(GNDs)increase to accommodate the relatively large strain gradient,resulting in considerable back stress strengthening and improved mechanical properties.展开更多
Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresol...Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.展开更多
In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing...In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing them to maintain high strength while offering superior ductility.Magnesium(Mg)alloys,renowned for their low density,high specific strength,exceptional vibration damping,and electromagnetic shielding properties,exhibit tremendous potential as lightweight and functional materials.Despite their advantageous properties,high-strength Mg alloys often suffer from limited ductility.However,the emergence of heterogeneous materials provides a fresh perspective for the development of Mg alloys with both high strength and ductility.This article provided a fundamental overview of heterostructured materials and systematically reviewed the recent research progress in the design of Mg alloys with strength-ductility balance based on heterostructure principles.The review encompassed various aspects,including preparation methods,formation mechanisms of diverse heterostructures,and mechanical properties,both within domestic and international contexts.On this basis,the article discussed the challenges encountered in the design and fabrication of heterostructured Mg alloys,as well as the urgent issues that require attention and resolution in the future.展开更多
The application of single-phase face-centered cubic(FCC)medium entropy alloys(MEAs)in the engi-neering industry is often hindered by the challenge of insufficient strength.In this study,a novel non-equiatomic ratio Ni...The application of single-phase face-centered cubic(FCC)medium entropy alloys(MEAs)in the engi-neering industry is often hindered by the challenge of insufficient strength.In this study,a novel non-equiatomic ratio Ni_(40)Co_(30)Cr_(20)Al_(5)Ti_(5)MEA was successfully fabricated.Through the well-designed mechan-ical heat treatment processing,we introduced a heterogeneous grain structure comprising 67.4%fine grain and 32.6%coarse grain.Additionally,heterogeneous size L12 phases consisting of 18.7%submicron precip-itates and 11.7%nano-sized precipitates,were incorporated into the alloy.Tensile tests conducted at room temperature revealed that the double heterogeneous structure alloy demonstrated remarkable strength–ductility synergy.It exhibited a yield strength of 1200 MPa,an ultimate tensile strength of 1560 MPa and a total elongation of 33.6%.The exceptional strength of the alloy can be primarily attributed to heteroge-neous deformation induced strengthening,grain boundary strengthening and precipitation strengthening.The excellent ductility is mainly attributed to the high-density stacking faults and Lomer–Cottrell locks.This study not only contributes to the clarification of the strengthening and deformation mechanism of double heterogeneous structure alloys but also provides an effective strategy for the development of high-performance alloys with high strength and ductility.展开更多
Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achiev...Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achieving HS in aluminum alloy can be quite challenging.In this study,7000 series alu-minum alloys are investigated by incorporating rare earth element Y to develop a dual-phase structure containing Al_(8)Cu_(4)Y and Al_(3)(Y,Zr)phases.And a heterogeneous lamella structure(HLS)is formed through the synergistic effect of Al_(8)Cu_(4)Y which includes dynamic recrystallization nucleation during deformation,and Al_(3)(Y,Zr)which hinders the growth of recrystallized grain by means of pinning dislocations and sub-grain boundaries.Substructures such as precipitates and nanocrystals are incorporated during the fabri-cation of HS,allowing for precise control over the volume fraction of fine grains by adjusting the ratio of two-scale second phases.When Y content reaches 0.3%,the 7Y55-2/heterogeneous lamella structure(HLS)samples exhibit a fine grain volume fraction of 76.5 vol.%,a tensile strength of 695 MPa,and an elon-gation of 16.6%.The alloy contains a large number of dislocations that preferentially induce the growth ofη’phases along specific directions,thereby promoting their development.The multi-coupling effect and composite strengthening mechanisms in the“heterostructure-dislocation-precipitate”microstructure contribute to the intrinsic excellent strength and plasticity of the alloy.This study tackles the challenge of inverted strength and plasticity observed in Al-Zn-Mg-Cu-Zr alloys,offering novel insights that pave the way for further applications of heterogeneous materials.展开更多
Compared with cold rolling,warm rolling can significantly reduce or completely eliminate microstruc-ture damage to regulate the microstructure of the material,which is an effective method to improve the mechanical pro...Compared with cold rolling,warm rolling can significantly reduce or completely eliminate microstruc-ture damage to regulate the microstructure of the material,which is an effective method to improve the mechanical properties of the material.However,the effect of warm rolling on refractory complex concen-trated alloys(RCCAs)has rarely been reported.This research examines how warm rolling influences the microstructure,texture,and mechanical properties of the Zr_(45)Ti_(15)Nb_(30)Ta_(10)RCCA.The RCCA was warm-rolled to a 75%reduction in thickness at 650℃(two-phase zone)and then annealed at 1000°C for 1 h.To highlight the advantages of warm rolling,a comparison was conducted with similarly deformed and annealed cold-rolled RCCA.The warm-rolled RCCA exhibits a layered heterogeneous structure and induces the precipitation of the(Nb,Ta)-enriched bcc2 phase.The deformation texture of warm-rolled RCCA is weaker than that of cold-rolled RCCA,which is attributed to localized deformation inhomogene-ity.After annealing,warm rolling resulted in a remarkable increase in the yield strength of the RCCA,i.e.,from 861 MPa to 1071 MPa;meanwhile,moreover,the tensile plasticity was almost identical.Warm rolling leads to a change in plastic deformation of the RCCA from dislocation cross-slip to one dominated by the interaction of dislocations with subgrain boundaries as well as the bcc2 phase.The back tress gen-erated by the heterogeneous structure induced by warm rolling is also effective in increasing the yield strength of the RCCA.The remarkably layered heterogeneous structure,subgrain boundaries and textures result in warm-rolled RCCA with optimal strength-ductility combination.Our results provide an effective processing approach for tailoring the microstructure and mechanical properties of RCCAs.展开更多
In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical p...In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.展开更多
Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In ...Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In this work,we successfully achieved RT plasticization in a brittle(TaMoTi)_(92)Al_(8)RHEA via in situ forming heterogeneous structure(HS)with the doping of Zr.Different from the mainstream design con-cept of“soft solid solution matrices with hard intermetallic phases”proposed in the literature,the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetal-lic B2 matrix.Such an HS leads to the remarkable strength-plasticity synergy in this alloy at RT,showing a large plasticity of>20%,associated with a high strength of>2380 MPa.It was found that solid solu-tion strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength,while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy,thus enabling the high strength and good RT plasticity.In short,the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT me-chanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs.展开更多
The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experi...The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.展开更多
基金support provided by City University of Hong Kong (CityU) through the start-up grant for newly recruited faculty members (Project No. 7200303)the research of C.T. Liu is also supported by CityU (Project No. CityU117612)
文摘Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone （STZ） models, we first discuss in this article our recently proposed ＇core-shell＇ model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass （BMG）. With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.
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financial support from the National Natural Science Foundation of China(Nos.52104306,52274301,52334009)the Aeronautical Science Foundation of China(No.2023Z0530S6005)+3 种基金the National Key Research and Development Program of China(No.2023YFB3712401)the Science and Technology Commission of Shanghai Municipality(No.21DZ1208900)the Academician Workstation of Kunming University of Science and Technology(2024),the Ningbo Yongjiang Talent-Introduction Programme(No.2022A-023-C)the Zhejiang Phenomenological Materials Technology Co.,Ltd.,China.
文摘A multi-phase heterogeneous FeCoNi-based high-entropy alloy is developed to overcome the trade-off between strength and ductility.By alloying with a small amount of Cu and employing a rapid recrystalliza-tion process,it exhibits a good combination of yield strength(roughly 1300 MPa)and ductility(approach-ing 20%).Firstly,a multi-phase heterogeneous structure is tailored ranging from nano to micron.Cu is efficiently precipitated as nanoscale clusters(4.2 nm),high-density cuboidal L1_(2) particles(20-40 nm)and L2_(1) particles(500-800 nm)are found to be embedded in the matrix and a bimodal heterogeneous grain structure(1-40μm)is constructed.Secondly,the introduction of Cu effectively suppresses the pre-cipitation of coarse L21 phase at grain boundaries,reducing its volume fraction by 80%and replaced by smaller-scale continuous precipitations within the grains.Thirdly,the high mixing enthalpy gap of Cu and the matrix leads to the formation of local chemical fluctuation and the consequential rugged topog-raphy in the matrix,which result in retarded dislocation motion and promotes dislocation plugging and interlocking during strain,enhancing yield stress and work hardening rate.This study provides a valuable perspective to enhance strength and ductility via enlarged local chemical fluctuation-tailored multi-phase heterogeneous structures.
基金supported by the Tianjin Science and Technology Plan Project(No.22JCQNJC01280)the Central Funds Guiding the Local Science and Technology Development of Hebei Province(Nos.226Z1001G and 226Z1012G)+1 种基金the National Natural Science Foundation of China(No.52002109,52071124)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.
基金financially supported by the National Natural Science Foundation of China(Nos.52161019 and 52271054)the Science and Technology Project of Guizhou Province,China(No.[2023]047)+1 种基金the GuiZhou DIIT Innovation Project(No.[2023]153)the One Hundred Person Project of Guizhou Province,China(No.[2020]6006).
文摘In this work,a heterogeneous structure(HS)with an alternating distribution of coarse and fineαlamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heat-ing treatment.Instead of a distinct interface between the primaryα_(p)hase(α_(p))andβ_(t)ransformation microstructure(β_(t))in the equiaxed microstructure(EM),allα_(p)/β_(t)interfaces are eliminated in the HS,and the largeα_(p)phases are replaced by coarseαlamella.Compared to the EM alloy,the heterostruc-tured alloy exhibits a superior strength-ductility combination.The enhanced strength is predominantly attributed to the increased interfaces ofα/βplates and hetero-deformation induced(HDI)strengthening caused by back stress.Meanwhile,good ductility is ascribed to its uniform distribution of coarse and fineαlamella,which effectively inhibits strain localization and generates an extra HDI hardening.This can be evidenced by the accumulated geometrically necessary dislocations(GNDs)induced by strain partitioning of the heterostructure.Significantly,the HDI causes extra<c+a>dislocations piling up in the coarseαlamella,which generates an extra strain hardening to further improve the ductility.Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium al-loys with excellent mechanical properties.
文摘In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal insurance contract when maxing the insured’s expected utility of his/her remaining wealth under the smooth ambiguity model and the heterogeneous belief form satisfying the MHR condition. We calculate the insurance premium by using generalized Wang’s premium and also introduce a series of stochastic orders proposed by [1] to describe the relationships among the insurable risk, background risk and ambiguity parameter. We obtain the deductible insurance is the optimal insurance while they meet specific dependence structures.
基金National Natural Science Foundation of China(52261032,51861021,51661016)Science and Technology Plan of Gansu Province(21YF5GA074)+2 种基金Public Welfare Project of Zhejiang Natural Science Foundation(LGG22E010008)Wenzhou Basic Public Welfare Scientific Research Project(G2023020)Incubation Program of Excellent Doctoral Dissertation-Lanzhou University of Technology。
文摘The development of high-performance structural and functional materials is vital in many industrial fields.High-and medium-entropy alloys(H/MEAs)with superior comprehensive properties owing to their specific microstructures are promising candidates for structural materials.More importantly,multitudinous efforts have been made to regulate the microstructures and the properties of H/MEAs to further expand their industrial applications.The various heterostructures have enormous potential for the development of H/MEAs with outstanding performance.Herein,multiple heterogeneous structures with single and hierarchical heterogeneities were discussed in detail.Moreover,preparation methods for compositional inhomogeneity,bimodal structures,dualphase structures,lamella/layered structures,harmonic structures(core-shell),multiscale precipitates and heterostructures coupled with specific microstructures in H/MEAs were also systematically reviewed.The deformation mechanisms induced by the different heterostructures were thoroughly discussed to explore the relationship between the heterostructures and the optimized properties of H/MEAs.The contributions of the heterostructures and advanced microstructures to the H/MEAs were comprehensively elucidated to further improve the properties of the alloys.Finally,this review discussed the future challenges of high-performance H/MEAs for industrial applications and provides feasible methods for optimizing heterostructures to enhance the comprehensive properties of H/MEAs.
基金support of the National Biodiversity Future Center (NBFC) to the University of Padova,the Research Centre for Plant ProtectionCertification (CREA),and the National Research Council (CNR),funded under the National Recovery and Resilience Plan (NRRP)+2 种基金Mission 4 Component 2 Investment 1.4-Call for tender No.3138 of 16 December 2021,rectified by Decree n.3175 of 18 December 2021 of Italian Ministry of University and Research funded by the European Union–NextGenerationEUProject code CN_00000033,Concession Decree No.1034 of 17 June 2022adopted by the Italian Ministry of University and Research,CUP:C93C22002810006,CUP:B83D21014060006,CUP:B83C22002930006,Project title“National Biodiversity Future CenterNBFC”support by Beaver Trust,grant number:1185451
文摘The Eurasian beaver(Castor fiber Linnaeus,1758)can be considered a hydrological ecosystem engineer as it shapes environmental characteristics through its building activities and feeding behaviour.Even if several studies have so far reported beaver impact on multi-taxon biodiversity and forest regeneration,there is a lack of research on forest stand structure evolution following beaver direct activity on trees.This represents a pivotal topic for predicting restoration outcomes and reccommending sound silvicultural and management practices to maintain specific forest conditions.Specifically,the study aims at investigating forest stand structure and tree species diversity changes considering river variability,distance from the riverbank and beaver's gnawing activity intensity.The Eurasian beaver is only recently recolonising the three analysed Mediterranean rivers,but stand structure seems to be already significantly impacted by the species.The number of trees was reduced,increasing mean diameter at breast height at stand level,as most of the youngest and/or smaller trees are entirely cut down.Strongest structural variations can be detected in intensively impacted stands and in the forest portions closer to the riverbank.The absence of a significant effect on most of the diversity indices is likely due to the initially homogeneous composition of the tree layer in each stand and to the limited variety of beaver's diet within the sites.Future resprouting of secondary tree shoots,as well as beaver gnawing activity changes in intensity over time and space,can further produce variations in structural parameters and woody species diversity in the medium-and long-term period.Therefore,it will be crucial to further monitor the long-term effects,as structural shifts can produce significant effects on riparian ecosystem functions.
基金financially supported by the National Natural Science Foundation of China(Nos.52321001,52322105,52130002,U2241245,52261135634 and 52371084)the Youth Innovation Promotion Association(CAS,No.2021192)the IMR Innovation Fund(No.2023-ZD01).
文摘Metastable β titanium alloy is an ideal material for lightweight and high strength due to its excellent comprehensive mechanical properties.However,overcoming the trade-off relation between strength and ductility remains a significant challenge.In this study,the mechanical properties of Ti-38644 alloy were optimized by introducing a heterogeneous bi-grain bi-lamella(BG-BL)structure through a well-designed combination of rolling,drawing and heat treatment.The results demonstrate that the present BG-BL Ti-38644 alloy shows a tensile strength of~1500 MPa and a total elongation of 18%.In particular,the high strength-elongation combination of the BG-BL Ti-38644 alloy breakthroughs the trade-off relation in all the titanium alloys available.The recrystallized grains with low dislocation enhance the ductility of the Ti-38644 alloy,while the highly distorted elongated grains mainly contribute to the high strength.The present study provides a new principle for designing Ti alloys with superior strength and ductility.
基金support by the National Natural Science Foundation of China(Grant Nos.U23A20546 and 52271010)the Chinese National Natural Science Fund for Distinguished Young Scholars(Grant No.52025015)the Natural Science Foundation of Tianjin City(No.21JCZDJC00510).
文摘1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain boundaries(GBs),which restricts local plastic flow dur-ing the plastic deformation and leads to stress concentration[3,4].Recently,the development of concepts aimed at achieving hetero-geneous grain has emerged as a promising approach for enhanc-ing comprehensive mechanical properties[5,6].
基金supported by the National Natural Science Foundation of China(Nos.U23A20583,52033005,U21A2090,and 52173040)Department of Science and Technology of Sichuan Province(No.2024NSFTD0003)。
文摘Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and poor heat resistance limit their application scope.Recent advances have highlighted that the combination of extensional flow and thermal fields can achieve toughness–stiffness balance,high transparency,and good heat resistance.However,the effect of extensional flow on the post-non-isothermal crystallization of PLLA during heating and the resulting crystalline texture remains unclear.In this study,PLLA with a heterogeneous amorphous structure and oriented polymorph was prepared by extensional flow.The effect of heterogeneous amorphous structures on non-isothermal crystallization kinetics during the heating process was studied by thermal analysis,polarized optical microscopy,infrared spectroscopy,and ex situ/in situ X-ray characterization.These results clearly illustrate that extensional flow enhances the formation of oriented crystalline structures,accelerates non-isothermal crystallization,and modulates the polymorphic composition of PLLA.Moreover,an unexpected dual cold-crystallization behavior is identified in ordered PLLA samples upon extensional flow,which is from the extensional flow-induced heterogeneous amorphous phase into α' phase(low-temperature peak)and the pristine amorphous phase intoαphase(high-temperature peak).The extensional flow primarily promotes the formation of the more perfectαandα'phases,but has a negative effect on the final content ofαphase formed after cold crystallization andα'-to-αphase transformation.The findings of this work advance the understanding of PLLA non-isothermal crystallization after extensional flow and offer valuable guidance for high-performance PLLA upon heat treatment in practical processing.
基金financial support from the Special Fund for Special Posts of Guizhou University,China(No.[2022]06)the Guizhou Provincial Basic Research Program(Natural Science),China(No.ZK[2023]78)+1 种基金the National Natural Science Foundation of China(No.52365020)the Open Fund Project of Key Laboratory of Advanced Manufacturing Technology,China(No.GZUAMT2022KF[04]).
文摘1060/7050 Al/Al laminated metal composites(LMCs)with heterogeneous lamellar structures were prepared by accumulative roll bonding(ARB),cold rolling and subsequent annealing treatment.The strengthening mechanism was investigated by microstructural characterization,mechanical property tests and in-situ fracture morphology observations.The results show that microstructural differences between the constituent layers are present in the Al/Al LMCs after various numbers of ARB cycles.Compared with rolled 2560-layered Al/Al LMCs with 37.5%and 50.0%rolling reductions,those with 62.5%rolling reductions allow for more effective improvements in the mechanical properties after annealing treatment due to their relatively high mechanical incompatibility across the interface.During tensile deformation,with the increased magnitude of incompatibility in the 2560-layered Al/Al LMC with a heterogeneous lamellar structure,the densities of the geometrically necessary dislocations(GNDs)increase to accommodate the relatively large strain gradient,resulting in considerable back stress strengthening and improved mechanical properties.
基金financially supported by the National Natural Science Foundation of China (Nos. 51971061 and 52231005)the Natural Science Foundation of Jiangsu Province (No. BK20221474)。
文摘Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.
基金supported by Yunnan Fundamental Research Projects(No.202201BE070001-014)Doctoral Scientific Research Foundation of Hubei University of Automotive Technology(No.BK202336)+4 种基金National Natural Science Foundation of China(No.52071035)Program for Science and Technology Innovation Team in Colleges of Hubei Province(No.T2021012)Outstanding Young Scientific&Technological Innovation Team Plan of Colleges and Universities in Hubei Province(No.T201518 and No.T201811)Major Science and Technology Project of Hubei Province(No.2022AAA001)Key R&D Project of Hubei Province(No.2021BAB019)。
文摘In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing them to maintain high strength while offering superior ductility.Magnesium(Mg)alloys,renowned for their low density,high specific strength,exceptional vibration damping,and electromagnetic shielding properties,exhibit tremendous potential as lightweight and functional materials.Despite their advantageous properties,high-strength Mg alloys often suffer from limited ductility.However,the emergence of heterogeneous materials provides a fresh perspective for the development of Mg alloys with both high strength and ductility.This article provided a fundamental overview of heterostructured materials and systematically reviewed the recent research progress in the design of Mg alloys with strength-ductility balance based on heterostructure principles.The review encompassed various aspects,including preparation methods,formation mechanisms of diverse heterostructures,and mechanical properties,both within domestic and international contexts.On this basis,the article discussed the challenges encountered in the design and fabrication of heterostructured Mg alloys,as well as the urgent issues that require attention and resolution in the future.
基金supported by the National Key R&D Program of China(No.2022YFA1603800)the National Natural Science Foundation of China(No.12274362)the Central Guidance on Local Science and Technology Development Fund of Hebei Province(No.216Z1012G)。
文摘The application of single-phase face-centered cubic(FCC)medium entropy alloys(MEAs)in the engi-neering industry is often hindered by the challenge of insufficient strength.In this study,a novel non-equiatomic ratio Ni_(40)Co_(30)Cr_(20)Al_(5)Ti_(5)MEA was successfully fabricated.Through the well-designed mechan-ical heat treatment processing,we introduced a heterogeneous grain structure comprising 67.4%fine grain and 32.6%coarse grain.Additionally,heterogeneous size L12 phases consisting of 18.7%submicron precip-itates and 11.7%nano-sized precipitates,were incorporated into the alloy.Tensile tests conducted at room temperature revealed that the double heterogeneous structure alloy demonstrated remarkable strength–ductility synergy.It exhibited a yield strength of 1200 MPa,an ultimate tensile strength of 1560 MPa and a total elongation of 33.6%.The exceptional strength of the alloy can be primarily attributed to heteroge-neous deformation induced strengthening,grain boundary strengthening and precipitation strengthening.The excellent ductility is mainly attributed to the high-density stacking faults and Lomer–Cottrell locks.This study not only contributes to the clarification of the strengthening and deformation mechanism of double heterogeneous structure alloys but also provides an effective strategy for the development of high-performance alloys with high strength and ductility.
基金supported by the National Key Research and Development Program of China(No.2023YFB3406800)the National Natural Science Foundation of China(Nos.52271036 and 51971237).
文摘Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achieving HS in aluminum alloy can be quite challenging.In this study,7000 series alu-minum alloys are investigated by incorporating rare earth element Y to develop a dual-phase structure containing Al_(8)Cu_(4)Y and Al_(3)(Y,Zr)phases.And a heterogeneous lamella structure(HLS)is formed through the synergistic effect of Al_(8)Cu_(4)Y which includes dynamic recrystallization nucleation during deformation,and Al_(3)(Y,Zr)which hinders the growth of recrystallized grain by means of pinning dislocations and sub-grain boundaries.Substructures such as precipitates and nanocrystals are incorporated during the fabri-cation of HS,allowing for precise control over the volume fraction of fine grains by adjusting the ratio of two-scale second phases.When Y content reaches 0.3%,the 7Y55-2/heterogeneous lamella structure(HLS)samples exhibit a fine grain volume fraction of 76.5 vol.%,a tensile strength of 695 MPa,and an elon-gation of 16.6%.The alloy contains a large number of dislocations that preferentially induce the growth ofη’phases along specific directions,thereby promoting their development.The multi-coupling effect and composite strengthening mechanisms in the“heterostructure-dislocation-precipitate”microstructure contribute to the intrinsic excellent strength and plasticity of the alloy.This study tackles the challenge of inverted strength and plasticity observed in Al-Zn-Mg-Cu-Zr alloys,offering novel insights that pave the way for further applications of heterogeneous materials.
基金This work was financially supported by the National Natu-ral Science Foundation of China(No.52074257)the Chinese Academy of Sciences(No.ZDBS-LY-JSC023).
文摘Compared with cold rolling,warm rolling can significantly reduce or completely eliminate microstruc-ture damage to regulate the microstructure of the material,which is an effective method to improve the mechanical properties of the material.However,the effect of warm rolling on refractory complex concen-trated alloys(RCCAs)has rarely been reported.This research examines how warm rolling influences the microstructure,texture,and mechanical properties of the Zr_(45)Ti_(15)Nb_(30)Ta_(10)RCCA.The RCCA was warm-rolled to a 75%reduction in thickness at 650℃(two-phase zone)and then annealed at 1000°C for 1 h.To highlight the advantages of warm rolling,a comparison was conducted with similarly deformed and annealed cold-rolled RCCA.The warm-rolled RCCA exhibits a layered heterogeneous structure and induces the precipitation of the(Nb,Ta)-enriched bcc2 phase.The deformation texture of warm-rolled RCCA is weaker than that of cold-rolled RCCA,which is attributed to localized deformation inhomogene-ity.After annealing,warm rolling resulted in a remarkable increase in the yield strength of the RCCA,i.e.,from 861 MPa to 1071 MPa;meanwhile,moreover,the tensile plasticity was almost identical.Warm rolling leads to a change in plastic deformation of the RCCA from dislocation cross-slip to one dominated by the interaction of dislocations with subgrain boundaries as well as the bcc2 phase.The back tress gen-erated by the heterogeneous structure induced by warm rolling is also effective in increasing the yield strength of the RCCA.The remarkably layered heterogeneous structure,subgrain boundaries and textures result in warm-rolled RCCA with optimal strength-ductility combination.Our results provide an effective processing approach for tailoring the microstructure and mechanical properties of RCCAs.
基金support from China Scholarship Council(No.202107000038)the Na-tional Natural Science Foundation of China(52004227).
文摘In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.
基金supported by the National Key Research&De-velopment Program of China(No.2022YFF0609002)the National Natural Science Foundation of China(Nos.U1908219,52171163,and 52271157)+4 种基金the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-2-2)the key Research&Devel-opment Plan of Jiangxi Province(No.20192ACB80001)the Natu-ral Science Foundation of Liaoning Province(No.2022-BS-001)the China Postdoctoral Science Foundation(No.2022M713210)the Shenyang National Laboratory for Materials Science.
文摘Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In this work,we successfully achieved RT plasticization in a brittle(TaMoTi)_(92)Al_(8)RHEA via in situ forming heterogeneous structure(HS)with the doping of Zr.Different from the mainstream design con-cept of“soft solid solution matrices with hard intermetallic phases”proposed in the literature,the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetal-lic B2 matrix.Such an HS leads to the remarkable strength-plasticity synergy in this alloy at RT,showing a large plasticity of>20%,associated with a high strength of>2380 MPa.It was found that solid solu-tion strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength,while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy,thus enabling the high strength and good RT plasticity.In short,the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT me-chanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs.
基金financially supported by the funding from Guangdong Province Basic and Applied Research Key Projects (No.2020B0301030001)National Key R&D Programme,Ministry of Science and Technology of China (Nos. 2018YFB1105200 and 2019YFA0209904)the National Natural Science Foundation of China (Nos.52371106 and 52371025)。
文摘The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.
