Laser powder bed fusion(L-PBF)of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys.To clarify the modification roles of Sc/Zr elements,...Laser powder bed fusion(L-PBF)of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys.To clarify the modification roles of Sc/Zr elements,an Al–4.66Mg–0.48Mn–0.72Sc–0.33Zr(wt.%)alloy was processed using L-PBF.The effect of the local solidification condition of the molten pool on the precipitation behavior of primary Al_(3)(Sc,Zr)was analyzed based on time-dependent nucleation theory.It was found that primary Al_(3)(Sc,Zr)inevitably precipitated at the fusion boundary,while its precipitation could be effectively suppressed in the inner region of the molten pool.This subsequently induced the formation of a heterogeneousα-Al matrix.After direct aging,the heredity of solidification microstructure introduced heterogeneous secondary Al_(3)(Sc,Zr)precipitates withinα-Al matrix.Owing to the inverse relationship between grain boundary strengthening and precipitation strengthening,the direct-aged sample with dual heterogeneous structures exhibited reduced mechanical heterogeneity,resulting in lowered hetero-deformation-induced hardening.The low strain-hardening capability in the direct-aged sample promoted necking instability while inducing a large Lüders elongation,which effectively improved the tensile ductility.展开更多
Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent duc...Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent ductility has become a key focus in fields like aerospace and lowaltitude flight.The novel low-density steel presented here exhibits a yield strength of 1000 MPa,which is 2-3 times higher than conventional low-alloy high-strength steels,while maintaining an elongation of about 18.7%.By combining ex-situ experimental characterization with a phase mechanical response model based on the iso-work theory and the von Mises equivalent method,the role of heterogeneous deformation-induced strengthening was revealed.The calculated values align closely with experimental results.This exceptional performance is attributed to a multiphase heterogeneous microstructure,where fresh martensite,bainite/tempered martensite,and deformation-induced martensite act as hard regions.These regions release micro-stresses through inhomogeneous cooperative deformation with soft ferrite,enabling multiple plastic deformation mechanisms and stress concentration relief.This research offers new insights into optimizing microstructures through mechanical metallurgy,which is crucial for producing high-performance,lightweight components.展开更多
Microstructural evolution and dynamic recrystallization(DRX)mechanisms of a Ti-48Al-2Cr-2Nb(at.%)alloy prepared by selective electron beam melting(SEBM)during hot deformation at 1150℃and 0.1 s^(-1)were investigated b...Microstructural evolution and dynamic recrystallization(DRX)mechanisms of a Ti-48Al-2Cr-2Nb(at.%)alloy prepared by selective electron beam melting(SEBM)during hot deformation at 1150℃and 0.1 s^(-1)were investigated by hot compression tests,optical microscope(OM),scanning electron microscope(SEM),electron back-scattered diffraction(EBSD)and transmission electron microscope(TEM).The results show that the initial microstructure of the as-SEBMed alloy exhibits layers of coarseγgrains and fineγ+α_(2)+(α_(2)/γ)lamellar mixture grains alternately along the building direction.During the early stage of hot deformation,deformation twins tend to form within the coarse grains,facilitating subsequent deformation,and a small number of DRX grains appear in the fine-grained regions.With the increase of strain,extensive DRX grains are formed through different DRX mechanisms in both coarse and fine-grained regions,involving discontinuous dynamic recrystallization mechanism(DDRX)in the fine-grained regions and a coexistence of DDRX and continuous dynamic recrystallization(CDRX)in the coarsegrained regions.展开更多
The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entr...The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entropy alloy(AMEA)was prepared via the magnetron sputtering to investigate the microstructural thermostability and nanoindentation creep behavior.Thermal annealing below the glass transition temperature gave rise to the microstructural heterogeneity due to the positive mixing enthalpy in TaTiZr AMEA,which became increasingly enhanced with raising the annealing temperature.Correspondingly,there appeared a monotonic increase in hardness as well as the elastic/shear modulus,yet a reduction in strain-rate sensitivity m or an increment in shear transformation zone volume with annealing temperature.Meanwhile,the indentation morphology measured by atomic force microscope exhibited a significant transformation from pile-up to sink-in,demonstrating the degradation of plastic deformability with enhancing the microstructural heterogeneity.Based on the relaxation time spectra for Maxwell-Voigt model,the microstructural heterogeneity can restrain the activation of internal defects associated with the operation of flow units during creeping,further triggering the strain-strengthening behavior and improved creep resistance in the annealed samples.This work provides significant guidance for the structural design of high-performance amorphous alloys.展开更多
Type 2 diabetes markedly elevates fracture risk despite normal or high bone mineral density,a paradox reflecting qualitative skeletal deficits rather than loss of mass.Chronic hyperglycemia fosters the accumulation of...Type 2 diabetes markedly elevates fracture risk despite normal or high bone mineral density,a paradox reflecting qualitative skeletal deficits rather than loss of mass.Chronic hyperglycemia fosters the accumulation of advanced glycation end products in bone;their nonenzymatic crosslinks stiffen type I collagen,impair mineralization,and erode mechanical strength.By engaging the receptor for advanced glycation end products,these adducts activate nuclear factorκB and mitogen-activated protein kinase cascades,amplifying oxidative stress,inflammation,osteoblast dysfunction,and osteoclastogenesis.This review synthesizes epidemiological data from type 1 and type 2 diabetes,highlights the limits of densitybased skeletal assessment,and details the molecular pathology of the glycation-collagen axis.It also appraises antiglycation therapies,including formation inhibitors,crosslink breakers and receptor antagonists,with a particular focus on sodium-glucose cotransporter 2 inhibitors that couple glycemic control with modulation of the glycation pathway.By integrating recent basic and clinical advances,we propose a mechanistic framework for diabetic bone disease and outline strategies to mitigate glycationdriven skeletal fragility.展开更多
The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscop...The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.展开更多
Strength and plasticity of metallic structural materials are the fundamental indicators of the service reliability[1].However,as is well known,a general trade-offrelationship exists between strength and plasticity of ...Strength and plasticity of metallic structural materials are the fundamental indicators of the service reliability[1].However,as is well known,a general trade-offrelationship exists between strength and plasticity of metallic materials,making it difficult to improve both of them synchronously[2].At present,only few of the successful cases[3-8],achieved via nano-particles[7],heterogeneous microstructures[8],etc.are mostly limited to some specific materials or processes.展开更多
The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with...The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with outstanding mechanical performances.However,its creep mechanism has not been revealed yet.The present study systematically investigates and evaluates the high-temperature creep mechanism of LPBFed WE43 alloy under varying temperatures and applied stress conditions.In addition,it thoroughly elucidates the interactions and evolution mechanisms between precipitates and disloca-tions during the creep process.Subject to residual stresses and thermal cycling,theβphase is formed in the form of“precipitation chains”(PCs)within the grains.The metastable phasesβ″,β′,andβ_(1) in-situ precipitate between the PCs.The creep resistance of the(LPBFed)WE43 alloy is governed by the evolution of precipitates and their interactions with dislocations during the creep.Under creep condi-tions at 200℃,a large number of<c+a>anddislocations undergo climb and cross-slip behaviors within the grains.During the climb and cross-slip of dislocations,the Orowan strengthening effect ofβ″,the cutting mechanisms ofβ′andβ_(1) phases relative to dislocations,and the dislocation barriers formed by theβphase arrays collectively impart excellent creep resistance to the WE43 alloy.As creep time progresses,dislocations accumulate within the grains,and theβandβ_(1) phases promote the forma-tion of subgrain boundaries,further triggering discontinuous dynamic recrystallization behaviors during the creep process.Furthermore,influenced by the directional diffusion of elements,precipitates dynami-cally form around the grain boundaries of recrystallized grains,thereby enhancing the resistance to grain boundary sliding.When the creep temperature increases to 250℃ or 300℃,a large number of<c+a>dislocations,accompanied by the dissolution of metastable phases and elemental re-diffusion,transform during the creep process into stacking faults(SFs).SFs not only exhibit high thermal stability but also act as effective dislocation barriers at high temperatures through lattice mismatch mechanisms.However,under high-temperature conditions,thermal activation leads to the dissolution of unstable metastable phases,promoting rapid coarsening and transformation of precipitates into various morphologies ofβphases,thereby causing a catastrophic decline in creep performance.At the same time,high tempera-tures further exacerbate elemental diffusion,resulting in precipitate-free zones near grain boundaries,thereby inducing crack initiation.Therefore,the creep resistance of as-deposited alloys decreases signif-icantly at higher temperatures.Building on this,the future development trends of LPBFed WE43 alloys are envisioned,where homogenizing heterostructures or introducing high aspect ratio precipitates and high-density SFs prior to creep can be regarded as a promising approach for enhancing creep resistance in LPBFed WE43 alloys.展开更多
As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced usin...As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced using the laser powder bed fusion(LPBF)additive manufacturing(AM)process for the first time.The printability,microstructure characteristics,and post-heat treatment conditions of the GW63K alloy are systematically investigated.The as-built GW63K samples demonstrate high relative densities exceeding 99.6%and exhibit no macroscopic and microscopic cracking across a wide range of process parameters,indicating excellent printability.An exceptional heterogeneous microstructure is observed in the as-built GW63K alloy,comprising coarse columnar grains,fine equiaxed grains with an average grain size of 21.72μm,uniformly distributed nano-sized Mg_(24)(Gd,Y)_(5)secondary phase,and numerous dislocations.Consequently,the as-built GW63K alloy displays enhanced tensile strengths and ductility compared to the as-cast alloy,with yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)values of 218±4 MPa,284±5 MPa and 11.9±1.6%respectively.Additionally,due to the absence of coarse micron-sized secondary phase,a specific direct aging(T5)heat treatment regime at 200℃for 128 h is optimized for the as-built GW63K alloy to introduce dense and dispersedβ’aging precipitates.This T5 treatment surpasses the conventional solution plus aging(T6)heat treatment in enhancing mechanical properties.The LPBF-T5 GW63K alloy exhibits YS,UTS and EL values of 293±6 MPa,359±4 MPa and 2.9±0.7%,respectively.Notably,the YS of the LPBF-T5 alloy represents the highest value for the GW63K alloy,even surpassing that of the extrusion-T5 alloy.This study indicates that the GW63K alloy is a highly promising material for manufacturing near-net-shape high-strength Mg alloy components with intricate geometries using LPBF.展开更多
Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further impro...Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.展开更多
In this work,pure Cu with excellent strength and ductility(UTS of 271 MPa,elongation to fracture of 43.5%,uniform elongation of 30%)was prepared using cold spray additive manufacturing(CSAM),realizing a breakthrough i...In this work,pure Cu with excellent strength and ductility(UTS of 271 MPa,elongation to fracture of 43.5%,uniform elongation of 30%)was prepared using cold spray additive manufacturing(CSAM),realizing a breakthrough in the field.An in-depth investigation was conducted to reveal the microstructure evolution,strengthening and ductilization mechanisms of the CSAM Cu,as well as the single splats.The results show that the CSAM Cu possesses a unique heterogeneous microstructure with a bimodal grain structure and extensive infinitely circulating ring-mounted distribution of twinning.Based on the single splat observation,the entire copper particle forms a gradient nano-grained(GNG)structure after high-speed impact deposition.The GNG-structured single splat serves as a unit to build the heterogeneous microstructure with bimodal grain distribution during the successive deposition in CSAM.The results also show that CSAM can achieve synergistic strengthening and ductilization by controlling the grain refinement and dislocation density.This work provides potential for CSAM technique in manufacturing various metallic parts with the desired combination of high strength and good ductility without additional post-treatments.展开更多
Beta flecks are one of the most common defects occur in someα+βandβtitanium alloys.In this study,formation of beta flecks in Ti-17 alloy was investigated by directional solidification experiments.Samples were direc...Beta flecks are one of the most common defects occur in someα+βandβtitanium alloys.In this study,formation of beta flecks in Ti-17 alloy was investigated by directional solidification experiments.Samples were directionally solidified under a constant temperature gradient of 2×10^4 K/m and a wide range of withdrawal rates(R)from 3 mm/h to 150 mm/h.We find that macrostructure of the directionally solidified Ti-17 samples can be characterized by"four zones and two lines"after the heat treatment.Profile of the solid-liquid interface transits from planar to cellular to dendritic shape with solidification rate increasing from 3 mm/h to 150 mm/h.The critical rates for planar to cellular(Rc1)transition and cellular to dendritic(Rc2)transition can be well predicted based on the traditional solidification theory.Dark and light contrast areas in macrostructure are directly related to elemental segregation.Dark contrast areas are rich of Cr,Zr but lean of Mo,while no apparent segregation is found in light contrast areas and the mean level of Cr,Zr is lower and Mo is higher in this area than that in dark contrast areas.We conclude thatβ-flecks in Ti-17 titanium alloy are induced by segregation of alloying elements with k<1 and their shape and size are determined by solidification conditions.Based on the findings of the present article and other literatures,three types ofβ-flecks are proposed and their formation mechanisms are discussed.展开更多
Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous mi...Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite,resulting in a low yield ratio(YR)and high impact toughness in a high-strength low-alloy steel.The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing,in comparison to the steel with full martensitic microstructure.The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering.The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases,but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.展开更多
In order to simultaneously improve strength and formability,an analytical model for the concentration distribution of precipitates and solute elements is established and used to theoretically design and control the he...In order to simultaneously improve strength and formability,an analytical model for the concentration distribution of precipitates and solute elements is established and used to theoretically design and control the heterogeneous microstructure of Al−Zn−Mg−Cu alloys.The results show that the dissolution of precipitates is mainly affected by particle size and heat treatment temperature,the heterogeneous distribution level of solute elements diffused in the alloy matrix mainly depends on the grain size,while the heat treatment temperature only has an obvious effect on the concentration distribution in the larger grains,and the experimental results of Al−Zn−Mg−Cu alloy are in good agreement with the theoretical model predictions of precipitates and solute element concentration distribution.Controlling the concentration distribution of precipitates and solute elements in Al−Zn−Mg−Cu alloys is the premise of accurately constructing heterogeneous microstructure in micro-domains,which can be used to significantly improve the formability of Al−Zn−Mg−Cu alloys with a heterostructure.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
To overcome the dimension limits of immiscible alloys produced by traditional techniques and enhance their mechanical properties,bulk Cu-Fe-based immiscible alloy with abundant nanotwins and stacking faults was succes...To overcome the dimension limits of immiscible alloys produced by traditional techniques and enhance their mechanical properties,bulk Cu-Fe-based immiscible alloy with abundant nanotwins and stacking faults was successfully produced by selective laser melting(SLM).The SLM-produced bulk immiscible alloy displays a heterogeneous microstructure characterized by micro-scaledγ-Fe particles dispersed in fineε-Cu matrix with a high fraction(~92%)of high-angle grain boundaries.Interestingly,abundant nanotwins and stacking faults are generated in the interior of nano-scaledγ-Fe particles embedded withinε-Cu matrix.The heterogeneous interface of soft domains(ε-Cu)and hard domains(γ-Fe)not only induces the geometrically necessary dislocations(GNDs)but also affects the dislocation propagation during plastic deformation.Therefore,the bimodal heterogeneous interface,and the resistance of nanotwins and stacking faults to the propagation of partial dislocation make the bulk immiscible alloy exhibit an enhanced strength of~590 MPa and a good ductility of~8.9%.展开更多
Improving the plasticity of TiAl alloys at room temperature has been a longstanding challenge for the de-velopment of next-generation aerospace engines.By adopting the nacre-like architecture design strategy,we have o...Improving the plasticity of TiAl alloys at room temperature has been a longstanding challenge for the de-velopment of next-generation aerospace engines.By adopting the nacre-like architecture design strategy,we have obtained a novel heterogeneous lamellar Ti_(2)AlC/TiAl composite with superior strength-plasticity synergy,i.e.,compressive strength of∼2065 MPa and fracture strain of∼27%.A combination of micropil-lar compression and large-scale atomistic simulation has revealed that the superior strength-plasticity synergy is attributed to the collaboration of Ti_(2)AlC reinforcement,lamellar architecture and heteroge-neous interface.More specifically,multiple deformation modes in Ti_(2)AlC,i.e.,basal-plane dislocations,atomic-scale ripples and kink bands,could be activated during the compression,thus promoting the plas-tic deformation capability of composite.Meanwhile,the lamellar architecture could not only induce sig-nificant stress redistribution and crack deflection between Ti_(2)AlC and TiAl,but also generate high-density SFs and DTs interactions in TiAl,leading to an improved strength and strain hardening ability.In addi-tion,profuse unique Ti_(2)AlC(1¯10¯3)/TiAl(111)interfaces in the composite could dramatically contribute to the strength and plasticity due to the interface-mediated dislocation nucleation and obstruction mecha-nisms.These findings offer a promising paradigm for tailoring microstructure of TiAl matrix composites with extraordinary strength and plasticity at ambient temperature.展开更多
Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter...Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.展开更多
In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the form...In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.展开更多
Additive manufacturing of aluminum alloys has received significant attention in the aerospace industry;however,achieving sufficient high strength,especially at elevated temperatures,remains challenging.Here,a crack-fr...Additive manufacturing of aluminum alloys has received significant attention in the aerospace industry;however,achieving sufficient high strength,especially at elevated temperatures,remains challenging.Here,a crack-free and near-full dense Al-1Fe-0.6Cu-1.3Zr alloy was fabricated by the laser powder bed fusion(LPBF)technique.The Al-Fe-Cu-Zr alloy exhibits heterogeneous microstructures with two distinct zones.One is the so-called coarse-grain zones(CGZs)with an average grain size of 0.95μm,where(Al,Cu)Fe_(3) nanoparticles precipitate in the Al matrix and Fe and Cu cosegregate at the grain boundaries(GBs).The other is fine-grain zones(FGZs)with an average grain size of 0.45μm,where an Al 3 Zr nanoparti-cle precipitates in each of theα-Al grains(serves as the nuclei),and Fe-rich nanoprecipitates and Fe/Cu cosegregation appear at the GBs.As a result,the LPBF Al-Fe-Cu-Zr alloy,with these unique heteroge-neous structures,displays high strength at both room temperature and elevated temperatures,e.g.,with high yield strengths of 500 MPa at room temperature,and 163 MPa at 573 K,both are higher than those of additive manufactured Al-based alloys reported thus far.It is suggested that the high strength over a wide temperature range of the current LPBF Al alloy is mainly attributed to the combination of the precipitation strengthening mechanism and grain-boundary strengthening mechanism.展开更多
基金financially supported by the National Key Research and Development Program of China(Nos.2018YFB1106302 and 2016YFB1100104)the National Natural Science Foundation of China(No.52005411)。
文摘Laser powder bed fusion(L-PBF)of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys.To clarify the modification roles of Sc/Zr elements,an Al–4.66Mg–0.48Mn–0.72Sc–0.33Zr(wt.%)alloy was processed using L-PBF.The effect of the local solidification condition of the molten pool on the precipitation behavior of primary Al_(3)(Sc,Zr)was analyzed based on time-dependent nucleation theory.It was found that primary Al_(3)(Sc,Zr)inevitably precipitated at the fusion boundary,while its precipitation could be effectively suppressed in the inner region of the molten pool.This subsequently induced the formation of a heterogeneousα-Al matrix.After direct aging,the heredity of solidification microstructure introduced heterogeneous secondary Al_(3)(Sc,Zr)precipitates withinα-Al matrix.Owing to the inverse relationship between grain boundary strengthening and precipitation strengthening,the direct-aged sample with dual heterogeneous structures exhibited reduced mechanical heterogeneity,resulting in lowered hetero-deformation-induced hardening.The low strain-hardening capability in the direct-aged sample promoted necking instability while inducing a large Lüders elongation,which effectively improved the tensile ductility.
基金funded by the National Natural Science Foundation of China(No.51974134)the Innovation Ability Promotion Plan Project of Hebei Province,China(No.24461002D)。
文摘Under equivalent stiffness conditions,material substitution based on a thin-walled design is crucial for the lightweight of components.Developing high-performance steels with both high-yield strength and excellent ductility has become a key focus in fields like aerospace and lowaltitude flight.The novel low-density steel presented here exhibits a yield strength of 1000 MPa,which is 2-3 times higher than conventional low-alloy high-strength steels,while maintaining an elongation of about 18.7%.By combining ex-situ experimental characterization with a phase mechanical response model based on the iso-work theory and the von Mises equivalent method,the role of heterogeneous deformation-induced strengthening was revealed.The calculated values align closely with experimental results.This exceptional performance is attributed to a multiphase heterogeneous microstructure,where fresh martensite,bainite/tempered martensite,and deformation-induced martensite act as hard regions.These regions release micro-stresses through inhomogeneous cooperative deformation with soft ferrite,enabling multiple plastic deformation mechanisms and stress concentration relief.This research offers new insights into optimizing microstructures through mechanical metallurgy,which is crucial for producing high-performance,lightweight components.
基金the financial supports from the Shaanxi Province Key Research and Development Projects,China(No.2023KXJ-071)the National Natural Science Foundation of China(Nos.52274402,52174381)。
文摘Microstructural evolution and dynamic recrystallization(DRX)mechanisms of a Ti-48Al-2Cr-2Nb(at.%)alloy prepared by selective electron beam melting(SEBM)during hot deformation at 1150℃and 0.1 s^(-1)were investigated by hot compression tests,optical microscope(OM),scanning electron microscope(SEM),electron back-scattered diffraction(EBSD)and transmission electron microscope(TEM).The results show that the initial microstructure of the as-SEBMed alloy exhibits layers of coarseγgrains and fineγ+α_(2)+(α_(2)/γ)lamellar mixture grains alternately along the building direction.During the early stage of hot deformation,deformation twins tend to form within the coarse grains,facilitating subsequent deformation,and a small number of DRX grains appear in the fine-grained regions.With the increase of strain,extensive DRX grains are formed through different DRX mechanisms in both coarse and fine-grained regions,involving discontinuous dynamic recrystallization mechanism(DDRX)in the fine-grained regions and a coexistence of DDRX and continuous dynamic recrystallization(CDRX)in the coarsegrained regions.
基金financially supported by the National Natural Science Foundation of China(Nos.U2067219,52371118,92163201,U23A6013,92360301,and U2330203)Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58)the Fundamental Research Funds for the Central Universities(Nos.xtr042024014 and xtr062024006).
文摘The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entropy alloy(AMEA)was prepared via the magnetron sputtering to investigate the microstructural thermostability and nanoindentation creep behavior.Thermal annealing below the glass transition temperature gave rise to the microstructural heterogeneity due to the positive mixing enthalpy in TaTiZr AMEA,which became increasingly enhanced with raising the annealing temperature.Correspondingly,there appeared a monotonic increase in hardness as well as the elastic/shear modulus,yet a reduction in strain-rate sensitivity m or an increment in shear transformation zone volume with annealing temperature.Meanwhile,the indentation morphology measured by atomic force microscope exhibited a significant transformation from pile-up to sink-in,demonstrating the degradation of plastic deformability with enhancing the microstructural heterogeneity.Based on the relaxation time spectra for Maxwell-Voigt model,the microstructural heterogeneity can restrain the activation of internal defects associated with the operation of flow units during creeping,further triggering the strain-strengthening behavior and improved creep resistance in the annealed samples.This work provides significant guidance for the structural design of high-performance amorphous alloys.
基金Supported by Clinical Medical Research Fund of the Zhejiang Medical Association,No.2025ZYC-Z32Henan Provincial Key Research and Development Program,No.231111311000+1 种基金Henan Provincial Science and Technology Research Project,No.232102310411Clinical Medical Research Fund of the Zhejiang Medical Association,2024ZYC-Z30.
文摘Type 2 diabetes markedly elevates fracture risk despite normal or high bone mineral density,a paradox reflecting qualitative skeletal deficits rather than loss of mass.Chronic hyperglycemia fosters the accumulation of advanced glycation end products in bone;their nonenzymatic crosslinks stiffen type I collagen,impair mineralization,and erode mechanical strength.By engaging the receptor for advanced glycation end products,these adducts activate nuclear factorκB and mitogen-activated protein kinase cascades,amplifying oxidative stress,inflammation,osteoblast dysfunction,and osteoclastogenesis.This review synthesizes epidemiological data from type 1 and type 2 diabetes,highlights the limits of densitybased skeletal assessment,and details the molecular pathology of the glycation-collagen axis.It also appraises antiglycation therapies,including formation inhibitors,crosslink breakers and receptor antagonists,with a particular focus on sodium-glucose cotransporter 2 inhibitors that couple glycemic control with modulation of the glycation pathway.By integrating recent basic and clinical advances,we propose a mechanistic framework for diabetic bone disease and outline strategies to mitigate glycationdriven skeletal fragility.
基金supported by the National Natural Science Foundation of China(Nos.52301025,52371065,52301179)the Fundamental Research Program of Shanxi Province,China(Nos.202203021222039,202203021212124)。
文摘The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.
基金financially supported by the National Natural Science Foundation of China(NSFC)(Nos.52371084,52301177,52322105,52130002,and 52321001)the Youth Innovation Promotion Association CAS(No.2021192)+1 种基金the IMR Innovation Fund(No.2023-ZD01)the Fund of Science and Technology on Surface Physics and Chemistry Laboratory(No.XKFZ202303).
文摘Strength and plasticity of metallic structural materials are the fundamental indicators of the service reliability[1].However,as is well known,a general trade-offrelationship exists between strength and plasticity of metallic materials,making it difficult to improve both of them synchronously[2].At present,only few of the successful cases[3-8],achieved via nano-particles[7],heterogeneous microstructures[8],etc.are mostly limited to some specific materials or processes.
基金financially supported by the National Natu-ral Science Foundation of China(Nos.52201105 and 52475324)the National Key Research and Development Program of China(Nos.2023YFB3408003 and 2023YFB3308001)+4 种基金the Graduate Sci-entific Research and Innovation Foundation of Chongqing(No.CYB23018)the Innovation Support Program for Overseas Re-turnees in Chongqing(No.cx2023061)the Research Project from Chongqing Key Laboratory of High-performance Structural Additive Manufacturing(No.02090011044158)the Chengdu Key Research and Development Support Program(No.2023-YF11-00077-HZ)the Fundamental Research Foundation for the Central Universities in China(Nos.2024IAIS-QN012 and 2023CDJKYJH049)。
文摘The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with outstanding mechanical performances.However,its creep mechanism has not been revealed yet.The present study systematically investigates and evaluates the high-temperature creep mechanism of LPBFed WE43 alloy under varying temperatures and applied stress conditions.In addition,it thoroughly elucidates the interactions and evolution mechanisms between precipitates and disloca-tions during the creep process.Subject to residual stresses and thermal cycling,theβphase is formed in the form of“precipitation chains”(PCs)within the grains.The metastable phasesβ″,β′,andβ_(1) in-situ precipitate between the PCs.The creep resistance of the(LPBFed)WE43 alloy is governed by the evolution of precipitates and their interactions with dislocations during the creep.Under creep condi-tions at 200℃,a large number of<c+a>anddislocations undergo climb and cross-slip behaviors within the grains.During the climb and cross-slip of dislocations,the Orowan strengthening effect ofβ″,the cutting mechanisms ofβ′andβ_(1) phases relative to dislocations,and the dislocation barriers formed by theβphase arrays collectively impart excellent creep resistance to the WE43 alloy.As creep time progresses,dislocations accumulate within the grains,and theβandβ_(1) phases promote the forma-tion of subgrain boundaries,further triggering discontinuous dynamic recrystallization behaviors during the creep process.Furthermore,influenced by the directional diffusion of elements,precipitates dynami-cally form around the grain boundaries of recrystallized grains,thereby enhancing the resistance to grain boundary sliding.When the creep temperature increases to 250℃ or 300℃,a large number of<c+a>dislocations,accompanied by the dissolution of metastable phases and elemental re-diffusion,transform during the creep process into stacking faults(SFs).SFs not only exhibit high thermal stability but also act as effective dislocation barriers at high temperatures through lattice mismatch mechanisms.However,under high-temperature conditions,thermal activation leads to the dissolution of unstable metastable phases,promoting rapid coarsening and transformation of precipitates into various morphologies ofβphases,thereby causing a catastrophic decline in creep performance.At the same time,high tempera-tures further exacerbate elemental diffusion,resulting in precipitate-free zones near grain boundaries,thereby inducing crack initiation.Therefore,the creep resistance of as-deposited alloys decreases signif-icantly at higher temperatures.Building on this,the future development trends of LPBFed WE43 alloys are envisioned,where homogenizing heterostructures or introducing high aspect ratio precipitates and high-density SFs prior to creep can be regarded as a promising approach for enhancing creep resistance in LPBFed WE43 alloys.
基金supported by the National Key Research and Development Program of China (No.2021YFB3701000)the National Natural Science Foundation of China (Nos. U21A2047, 52201129, 51821001,U2037601)+1 种基金the support by the China Postdoctoral Science Foundation (No. 2023M742219)the Postdoctoral Fellowship Program (Grade B) of CPSF(No. GZB20240419)
文摘As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced using the laser powder bed fusion(LPBF)additive manufacturing(AM)process for the first time.The printability,microstructure characteristics,and post-heat treatment conditions of the GW63K alloy are systematically investigated.The as-built GW63K samples demonstrate high relative densities exceeding 99.6%and exhibit no macroscopic and microscopic cracking across a wide range of process parameters,indicating excellent printability.An exceptional heterogeneous microstructure is observed in the as-built GW63K alloy,comprising coarse columnar grains,fine equiaxed grains with an average grain size of 21.72μm,uniformly distributed nano-sized Mg_(24)(Gd,Y)_(5)secondary phase,and numerous dislocations.Consequently,the as-built GW63K alloy displays enhanced tensile strengths and ductility compared to the as-cast alloy,with yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)values of 218±4 MPa,284±5 MPa and 11.9±1.6%respectively.Additionally,due to the absence of coarse micron-sized secondary phase,a specific direct aging(T5)heat treatment regime at 200℃for 128 h is optimized for the as-built GW63K alloy to introduce dense and dispersedβ’aging precipitates.This T5 treatment surpasses the conventional solution plus aging(T6)heat treatment in enhancing mechanical properties.The LPBF-T5 GW63K alloy exhibits YS,UTS and EL values of 293±6 MPa,359±4 MPa and 2.9±0.7%,respectively.Notably,the YS of the LPBF-T5 alloy represents the highest value for the GW63K alloy,even surpassing that of the extrusion-T5 alloy.This study indicates that the GW63K alloy is a highly promising material for manufacturing near-net-shape high-strength Mg alloy components with intricate geometries using LPBF.
基金financially supported by the Natural Science Foundation of Guangdong Province(Nos.2021A151510042,2021A1515011728)the China Postdoctoral Science Foundation(2022M711190)+1 种基金the National Natural Science Foundation of China(No.51875211)the Key Area Research and Development Program of Guangdong Province(No.2020B010186002)。
文摘Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.
基金the National Natural Science Foundation of China(Nos.52001191,52001078,52061135101)the Shanghai Science and Technology Committee(No.20511107700)+5 种基金Shanghai“Shuguang Program”(No.20SG42)Shanghai Rising-Star Program(No.20QA1403800)Key-Area Research and Development Program of Guangdong Province of China(No.2020B0101330001)Guangzhou Science and Technology Program of China(No.202007020008)the Research Fund of the State Key Laboratory of Solidification Processing(NPU,China)(No.2022-TZ-01)the Guangdong Provincial Key Laboratory of Modern Surface Engineering Technology and the Institute of New Materials,Guangdong Academy of Sciences(No.2020B1212060049).
文摘In this work,pure Cu with excellent strength and ductility(UTS of 271 MPa,elongation to fracture of 43.5%,uniform elongation of 30%)was prepared using cold spray additive manufacturing(CSAM),realizing a breakthrough in the field.An in-depth investigation was conducted to reveal the microstructure evolution,strengthening and ductilization mechanisms of the CSAM Cu,as well as the single splats.The results show that the CSAM Cu possesses a unique heterogeneous microstructure with a bimodal grain structure and extensive infinitely circulating ring-mounted distribution of twinning.Based on the single splat observation,the entire copper particle forms a gradient nano-grained(GNG)structure after high-speed impact deposition.The GNG-structured single splat serves as a unit to build the heterogeneous microstructure with bimodal grain distribution during the successive deposition in CSAM.The results also show that CSAM can achieve synergistic strengthening and ductilization by controlling the grain refinement and dislocation density.This work provides potential for CSAM technique in manufacturing various metallic parts with the desired combination of high strength and good ductility without additional post-treatments.
文摘Beta flecks are one of the most common defects occur in someα+βandβtitanium alloys.In this study,formation of beta flecks in Ti-17 alloy was investigated by directional solidification experiments.Samples were directionally solidified under a constant temperature gradient of 2×10^4 K/m and a wide range of withdrawal rates(R)from 3 mm/h to 150 mm/h.We find that macrostructure of the directionally solidified Ti-17 samples can be characterized by"four zones and two lines"after the heat treatment.Profile of the solid-liquid interface transits from planar to cellular to dendritic shape with solidification rate increasing from 3 mm/h to 150 mm/h.The critical rates for planar to cellular(Rc1)transition and cellular to dendritic(Rc2)transition can be well predicted based on the traditional solidification theory.Dark and light contrast areas in macrostructure are directly related to elemental segregation.Dark contrast areas are rich of Cr,Zr but lean of Mo,while no apparent segregation is found in light contrast areas and the mean level of Cr,Zr is lower and Mo is higher in this area than that in dark contrast areas.We conclude thatβ-flecks in Ti-17 titanium alloy are induced by segregation of alloying elements with k<1 and their shape and size are determined by solidification conditions.Based on the findings of the present article and other literatures,three types ofβ-flecks are proposed and their formation mechanisms are discussed.
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFB 0304800)One of the authors,H.Guo,would like to express her gratitude for the financial support of China Scholarship Council(award for one year visiting at Northwestern University in the USA,No.201706465056).
文摘Here we present a novel approach of intercritical heat treatment for microstructure tailoring,in which intercritical annealing is introduced between conventional quenching and tempering.This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite,resulting in a low yield ratio(YR)and high impact toughness in a high-strength low-alloy steel.The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing,in comparison to the steel with full martensitic microstructure.The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering.The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases,but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.
基金financially supported by the National Key Research and Development Program of China (No. 2021YFE0115900)the National Natural Science Foundation of China (Nos. 51871029, 51571023, 51301016)+1 种基金the Government Guided Program-Intergovernmental Bilateral Innovation Cooperation Project, China (No. BZ2019019)the Opening Project of State Key Lab of Advanced Metals and Materials, China (No. 2020-ZD02)。
文摘In order to simultaneously improve strength and formability,an analytical model for the concentration distribution of precipitates and solute elements is established and used to theoretically design and control the heterogeneous microstructure of Al−Zn−Mg−Cu alloys.The results show that the dissolution of precipitates is mainly affected by particle size and heat treatment temperature,the heterogeneous distribution level of solute elements diffused in the alloy matrix mainly depends on the grain size,while the heat treatment temperature only has an obvious effect on the concentration distribution in the larger grains,and the experimental results of Al−Zn−Mg−Cu alloy are in good agreement with the theoretical model predictions of precipitates and solute element concentration distribution.Controlling the concentration distribution of precipitates and solute elements in Al−Zn−Mg−Cu alloys is the premise of accurately constructing heterogeneous microstructure in micro-domains,which can be used to significantly improve the formability of Al−Zn−Mg−Cu alloys with a heterostructure.
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financially supported by the Projects of MOE Key Lab of Disaster Forecast and Control in Engineering in Jinan University(No.20200904006)the Guangdong Basic and Applied Basic Research Foundation(No.2020B1515420004)。
文摘To overcome the dimension limits of immiscible alloys produced by traditional techniques and enhance their mechanical properties,bulk Cu-Fe-based immiscible alloy with abundant nanotwins and stacking faults was successfully produced by selective laser melting(SLM).The SLM-produced bulk immiscible alloy displays a heterogeneous microstructure characterized by micro-scaledγ-Fe particles dispersed in fineε-Cu matrix with a high fraction(~92%)of high-angle grain boundaries.Interestingly,abundant nanotwins and stacking faults are generated in the interior of nano-scaledγ-Fe particles embedded withinε-Cu matrix.The heterogeneous interface of soft domains(ε-Cu)and hard domains(γ-Fe)not only induces the geometrically necessary dislocations(GNDs)but also affects the dislocation propagation during plastic deformation.Therefore,the bimodal heterogeneous interface,and the resistance of nanotwins and stacking faults to the propagation of partial dislocation make the bulk immiscible alloy exhibit an enhanced strength of~590 MPa and a good ductility of~8.9%.
基金the National Natural Science Foundation of China(Grant No.52101174)the State Key Lab of Advanced Metals and Materials(No.2022-Z15).
文摘Improving the plasticity of TiAl alloys at room temperature has been a longstanding challenge for the de-velopment of next-generation aerospace engines.By adopting the nacre-like architecture design strategy,we have obtained a novel heterogeneous lamellar Ti_(2)AlC/TiAl composite with superior strength-plasticity synergy,i.e.,compressive strength of∼2065 MPa and fracture strain of∼27%.A combination of micropil-lar compression and large-scale atomistic simulation has revealed that the superior strength-plasticity synergy is attributed to the collaboration of Ti_(2)AlC reinforcement,lamellar architecture and heteroge-neous interface.More specifically,multiple deformation modes in Ti_(2)AlC,i.e.,basal-plane dislocations,atomic-scale ripples and kink bands,could be activated during the compression,thus promoting the plas-tic deformation capability of composite.Meanwhile,the lamellar architecture could not only induce sig-nificant stress redistribution and crack deflection between Ti_(2)AlC and TiAl,but also generate high-density SFs and DTs interactions in TiAl,leading to an improved strength and strain hardening ability.In addi-tion,profuse unique Ti_(2)AlC(1¯10¯3)/TiAl(111)interfaces in the composite could dramatically contribute to the strength and plasticity due to the interface-mediated dislocation nucleation and obstruction mecha-nisms.These findings offer a promising paradigm for tailoring microstructure of TiAl matrix composites with extraordinary strength and plasticity at ambient temperature.
基金the National Natural Science Foundation of China(Grant Nos.U20A20277,51861130361,51861145312,51850410522,5201101443,and 52011530180)the Newton Advanced Fellowship by Royal Society(Grant No.RP12G0414)+5 种基金the Royal Academy of Engineering(No.TSPC1070)the Special Fund for Key Program of Science and Technology of Liaoning Province(Grant No.2019JH1/101000014)the Research Fund for Central Universities(Grant Nos.N172502004 and N2025025)the Xingliao Talents Program(Nos.XLYC1807024 and XLYC1802024)the Regional Innovation Joint Fund of Liaoning Province(No.2020-YKLH-39)funded in part by the National Research Foundation of South Africa(No.BRICS171211293679)。
文摘Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.
基金supported by the Beijing Natural Science Foundation under Grant(2202005)the Natural Science Foundation of China(No.51331003,No.51931007)+2 种基金the General Program of Science and Technology Development Project of Beijing Municipal Education Commission of China under Grant(KM201710005006)the International S&T Cooperation Program of China under Grant2015DFG52020the Program of Top Disciplines Construction in Beijing under GrantPXM2019014204500031。
文摘In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52061160483 and 92166130)the Hubei Science Fund for Distinguished Young Scholars(No.2020CFA086).The authors are also grateful to the Analytical and Testing Center,Huazhong University of Science and Technology for technical assistance.
文摘Additive manufacturing of aluminum alloys has received significant attention in the aerospace industry;however,achieving sufficient high strength,especially at elevated temperatures,remains challenging.Here,a crack-free and near-full dense Al-1Fe-0.6Cu-1.3Zr alloy was fabricated by the laser powder bed fusion(LPBF)technique.The Al-Fe-Cu-Zr alloy exhibits heterogeneous microstructures with two distinct zones.One is the so-called coarse-grain zones(CGZs)with an average grain size of 0.95μm,where(Al,Cu)Fe_(3) nanoparticles precipitate in the Al matrix and Fe and Cu cosegregate at the grain boundaries(GBs).The other is fine-grain zones(FGZs)with an average grain size of 0.45μm,where an Al 3 Zr nanoparti-cle precipitates in each of theα-Al grains(serves as the nuclei),and Fe-rich nanoprecipitates and Fe/Cu cosegregation appear at the GBs.As a result,the LPBF Al-Fe-Cu-Zr alloy,with these unique heteroge-neous structures,displays high strength at both room temperature and elevated temperatures,e.g.,with high yield strengths of 500 MPa at room temperature,and 163 MPa at 573 K,both are higher than those of additive manufactured Al-based alloys reported thus far.It is suggested that the high strength over a wide temperature range of the current LPBF Al alloy is mainly attributed to the combination of the precipitation strengthening mechanism and grain-boundary strengthening mechanism.
