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
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 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
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
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
The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(...The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.展开更多
Additively manufactured bimetallic structures combine the advantages of dissimilar materials and can achieve localized properties through a customized composition distribution.However,additively manufactured parts may...Additively manufactured bimetallic structures combine the advantages of dissimilar materials and can achieve localized properties through a customized composition distribution.However,additively manufactured parts may still lack the dimensional accuracy and surface integrity essential for precision mechanical assemblies that the post-machining process can address.Therefore,this study aims to systematically investigate the microstructure and machinability of 316L/CuSn10 bimetallic structures fabricated using laser powder bed fusion.The results show that the fusion zone of the bimetallic structure had refined grains of microscale size owing to the mixture of the primary elements of the bimetals,which resulted in the highest microhardness of 3.4 GPa.The difference in microstructure and microhardness between the single-material and fusion zones also causes significant differences in the cutting response during the ultraprecision process.The 316L stainless steel side exhibited the highest cutting force and more severe material accumulation in the chips.The cutting force drops when cutting through the fusion zone,with an observable fracture in the chips and separation of dissimilar materials on the machined grooves,indicating that the heterogeneous properties of additively manufactured 316L/CuSn10 bimetallic structures pose challenges to the improvement of surface quality.The simulation results also showed that stress accumulation occurred in the tool path through the fusion zone owing to the higher yield strength and hardness of stainless steel,indicating that lower cutting speeds and depths of cut are favorable for reducing cutting force and improving surface quality.This study provides deep insight into the microstructure evolution mechanism and a theoretical basis for improving the surface quality of additively manufactured bimetallic structures using an ultraprecision machining process.展开更多
High-entropy alloys(HEAs)consisting of CoCrFeNiAlTi systems,with a face-centered cubic(FCC)matrix reinforced by ordered L12 precipitates,have demonstrated exceptional strength-ductility combinations.However,the curren...High-entropy alloys(HEAs)consisting of CoCrFeNiAlTi systems,with a face-centered cubic(FCC)matrix reinforced by ordered L12 precipitates,have demonstrated exceptional strength-ductility combinations.However,the current compositional design of HEAs heavily relies on high Ni and Co contents,compro-mising the balance between properties and cost.Thus,it is crucial to optimize the cost-performance trade-offby fine-tuning the range of Fe,Co,and Ni,while maintaining excellent strength-ductility com-bination.In this study,we propose a novel Fe-based HEA with nanosized precipitates and a heteroge-neous grain distribution,achieving a strength-ductility combination comparable to state-of-the-art Ni-or Co-based HEAs.The alloy benefits from both precipitation hardening and hetero-deformation-induced strengthening attributed to the heterogeneous grain distribution,resulting in excellent yield strength of 1433 MPa,tensile strength of 1599 MPa,and ductility of 22%.The microstructural evolution and its in-fluence on mechanical properties are unraveled with respect to the observation of precipitate-dislocation interaction and hetero-deformation-induced stress(HDI stress)evaluation.This study suggests that the challenge of balancing properties and cost can be addressed through optimized compositional and mi-crostructural design.展开更多
A new metastable dual-phase Fe59 Cr13 Ni18 Al10 medium entropy alloy(MEA)with hierarchically heteroge-neous microstructure from micro-to nano-scale was designed in this work.Partially recrystallized FCC phase and lots...A new metastable dual-phase Fe59 Cr13 Ni18 Al10 medium entropy alloy(MEA)with hierarchically heteroge-neous microstructure from micro-to nano-scale was designed in this work.Partially recrystallized FCC phase and lots of NiAl-rich B2 precipitates are obtained by annealing and aging treatment.The yield strength of the MEA at room temperature(298 K)and liquid nitrogen temperature(77 K)increased from∼910 MPa and∼1250 MPa in the annealed state,respectively,to∼1145 MPa and∼1520 MPa in the aged state,while the uniform elongation maintained more than 15%.The excellent mechanical properties of the MEA both at 298 and 77 K are attributed to the co-activation of multiple strengthening mech-anisms,including fine grain,dislocation,precipitation,transformation-induced plasticity,stacking faults,and nano-twins.展开更多
In this study,an AlCu/AlMgSc bimetallic alloy is prepared using a dual-wire arc direct energy deposition method and a triple heterogeneous microstructure(fine/coarse equiaxed grains/columnar grains)is constructed.Addi...In this study,an AlCu/AlMgSc bimetallic alloy is prepared using a dual-wire arc direct energy deposition method and a triple heterogeneous microstructure(fine/coarse equiaxed grains/columnar grains)is constructed.Additionally,a quantitative comparative analysis of the deformation behavior of triple and dual heterogeneous microstructures during interrupted tensile testing is conducted,with emphasis on the effects of grain morphology and size on the tensile deformation mechanisms in the heterogeneous microstructure.Compared with the AlCu alloy with a double heterogeneous microstructure(equiaxed/columnar grain),the AlCu/AlMgSc bimetallic alloy exhibits a higher ultimate tensile strength of 301.4±7.9 MPa,a yield strength of 181.3±1.4 MPa,and an elongation of 9.7%±1.3%,which correspond to increases by 19.4%,21.2%,and 24.4%,respectively.Interrupted tensile testing is performed and a quasi-in-situ approach is employed to investigate the plastic deformation mechanisms of the triple heterogeneous microstructure during tensile deformation.The density of geometrically necessary dislocations(GNDs)in the fine equiaxed grains and the rate of GND accumulation during deformation,surpassed those observed in coarse equiaxed and columnar grains.Furthermore,in micrometer-sized equiaxed grains,the ability to accumulate GNDs decreases as the equiaxed grain size increases,and the equiaxed grains exhibit a higher capacity to accumulate GNDs compared with columnar grains.The triple heterogeneous microstructure provides a more favorable environment for trapping GNDs,thus resulting in enhanced strength and plastic deformation capabilities.This study offers guidance for the formulation and engineering application of heterogeneous microstructure alloys with diverse grain morphologies and multiple length scales.Additionally,novel approaches are introduced to enhance the strength and ductility of Al alloys.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 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
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
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
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
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
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
In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was inve...In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.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 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Projects(52001083,52171111,U2141207)supported by the National Natural Science Foundation of ChinaProject(LH2020E060)supported by the Natural Science Foundation of Heilongjiang,China。
文摘The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.
基金supported by Guangdong Basic and Applied Basic Research Foundation(Grant.Nos.2023A1515110594,2024A1515012049)GDA Project of Science and Technology De-velopment(Grant.Nos.2022GDASZH-2022010107,2022GDASZH-2022010108)the China Postdoctoral Science Foundation(Grant.No.2022M711807)。
文摘Additively manufactured bimetallic structures combine the advantages of dissimilar materials and can achieve localized properties through a customized composition distribution.However,additively manufactured parts may still lack the dimensional accuracy and surface integrity essential for precision mechanical assemblies that the post-machining process can address.Therefore,this study aims to systematically investigate the microstructure and machinability of 316L/CuSn10 bimetallic structures fabricated using laser powder bed fusion.The results show that the fusion zone of the bimetallic structure had refined grains of microscale size owing to the mixture of the primary elements of the bimetals,which resulted in the highest microhardness of 3.4 GPa.The difference in microstructure and microhardness between the single-material and fusion zones also causes significant differences in the cutting response during the ultraprecision process.The 316L stainless steel side exhibited the highest cutting force and more severe material accumulation in the chips.The cutting force drops when cutting through the fusion zone,with an observable fracture in the chips and separation of dissimilar materials on the machined grooves,indicating that the heterogeneous properties of additively manufactured 316L/CuSn10 bimetallic structures pose challenges to the improvement of surface quality.The simulation results also showed that stress accumulation occurred in the tool path through the fusion zone owing to the higher yield strength and hardness of stainless steel,indicating that lower cutting speeds and depths of cut are favorable for reducing cutting force and improving surface quality.This study provides deep insight into the microstructure evolution mechanism and a theoretical basis for improving the surface quality of additively manufactured bimetallic structures using an ultraprecision machining process.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(Nos.NRF-2022R1A5A1030054,NRF-2023M3H4A6A01058096).
文摘High-entropy alloys(HEAs)consisting of CoCrFeNiAlTi systems,with a face-centered cubic(FCC)matrix reinforced by ordered L12 precipitates,have demonstrated exceptional strength-ductility combinations.However,the current compositional design of HEAs heavily relies on high Ni and Co contents,compro-mising the balance between properties and cost.Thus,it is crucial to optimize the cost-performance trade-offby fine-tuning the range of Fe,Co,and Ni,while maintaining excellent strength-ductility com-bination.In this study,we propose a novel Fe-based HEA with nanosized precipitates and a heteroge-neous grain distribution,achieving a strength-ductility combination comparable to state-of-the-art Ni-or Co-based HEAs.The alloy benefits from both precipitation hardening and hetero-deformation-induced strengthening attributed to the heterogeneous grain distribution,resulting in excellent yield strength of 1433 MPa,tensile strength of 1599 MPa,and ductility of 22%.The microstructural evolution and its in-fluence on mechanical properties are unraveled with respect to the observation of precipitate-dislocation interaction and hetero-deformation-induced stress(HDI stress)evaluation.This study suggests that the challenge of balancing properties and cost can be addressed through optimized compositional and mi-crostructural design.
基金supported by the National Natural Science Foundation of China(Nos.52101053 and 52274399)the Henan Provincial Science and Technology Research Project(No.232102231025).
文摘A new metastable dual-phase Fe59 Cr13 Ni18 Al10 medium entropy alloy(MEA)with hierarchically heteroge-neous microstructure from micro-to nano-scale was designed in this work.Partially recrystallized FCC phase and lots of NiAl-rich B2 precipitates are obtained by annealing and aging treatment.The yield strength of the MEA at room temperature(298 K)and liquid nitrogen temperature(77 K)increased from∼910 MPa and∼1250 MPa in the annealed state,respectively,to∼1145 MPa and∼1520 MPa in the aged state,while the uniform elongation maintained more than 15%.The excellent mechanical properties of the MEA both at 298 and 77 K are attributed to the co-activation of multiple strengthening mech-anisms,including fine grain,dislocation,precipitation,transformation-induced plasticity,stacking faults,and nano-twins.
基金supported by the National Natu-ral Science Foundation of China(No.52205414)the Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001)+3 种基金the Advance Research Projects in the Field of Manned Spaceflight,China Manned Space Agency,China(No.040302)the Shang-hai Aerospace Science and Technology Innovation Fund Project,the Shanghai Academy of Spaceflight Technology,China(No.SAST2018-066)the 73rd batch of China Postdoctoral Science Foun-dation General Financial Support(No.2023MD734199)the Shaanxi Provincial Natural Science Basic Research Program(No.2023-JC-QN-0551).
文摘In this study,an AlCu/AlMgSc bimetallic alloy is prepared using a dual-wire arc direct energy deposition method and a triple heterogeneous microstructure(fine/coarse equiaxed grains/columnar grains)is constructed.Additionally,a quantitative comparative analysis of the deformation behavior of triple and dual heterogeneous microstructures during interrupted tensile testing is conducted,with emphasis on the effects of grain morphology and size on the tensile deformation mechanisms in the heterogeneous microstructure.Compared with the AlCu alloy with a double heterogeneous microstructure(equiaxed/columnar grain),the AlCu/AlMgSc bimetallic alloy exhibits a higher ultimate tensile strength of 301.4±7.9 MPa,a yield strength of 181.3±1.4 MPa,and an elongation of 9.7%±1.3%,which correspond to increases by 19.4%,21.2%,and 24.4%,respectively.Interrupted tensile testing is performed and a quasi-in-situ approach is employed to investigate the plastic deformation mechanisms of the triple heterogeneous microstructure during tensile deformation.The density of geometrically necessary dislocations(GNDs)in the fine equiaxed grains and the rate of GND accumulation during deformation,surpassed those observed in coarse equiaxed and columnar grains.Furthermore,in micrometer-sized equiaxed grains,the ability to accumulate GNDs decreases as the equiaxed grain size increases,and the equiaxed grains exhibit a higher capacity to accumulate GNDs compared with columnar grains.The triple heterogeneous microstructure provides a more favorable environment for trapping GNDs,thus resulting in enhanced strength and plastic deformation capabilities.This study offers guidance for the formulation and engineering application of heterogeneous microstructure alloys with diverse grain morphologies and multiple length scales.Additionally,novel approaches are introduced to enhance the strength and ductility of Al alloys.
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.
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.
基金supported by the National Natural Science Foundation of China(NSFC)(No.51265043 and 51265042)the Special Construction Project of Advanced Science and Technology Innovation Team of Jiangxi Province(No.20171BCB24007)
文摘In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.
