C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated ...C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.展开更多
In order to obtain fine-microstructure magnesium alloys with superior mechanical properties, AZ61 alloy was processed by friction stir processing(FSP) combined with rapid heat sink. It is found that ultrafine-grained ...In order to obtain fine-microstructure magnesium alloys with superior mechanical properties, AZ61 alloy was processed by friction stir processing(FSP) combined with rapid heat sink. It is found that ultrafine-grained microstructure with average size less than 300 nm is observed in the resultant AZ61 alloy. The mean microhardness of the ultra-fine region reaches Hv120-130, two times higher than that of AZ61 substrate. All these results demonstrate clearly that under a cooling rate high enough, ultra-fine structure inAZ61 alloy with superior mechanical properties can be produced by one pass FSP via dynamic recrystallization.展开更多
A new thermomechanical process consisting of heavy cold rolling(HCR)and short-time heat treatment(STH)is developed to fabricate fine-grained martensite microstructure in a low-cost plain low-carbon steel.To achieve th...A new thermomechanical process consisting of heavy cold rolling(HCR)and short-time heat treatment(STH)is developed to fabricate fine-grained martensite microstructure in a low-cost plain low-carbon steel.To achieve the optimal mechanical properties after STH,three different ferrite-pearlite(F-P)dual-phase microstructures are prepared via hot rolling(HR),HR and austenitizing,and HR and HCR.The microstructure evolution and the comprehensive mechanical properties of the alloy during STH are then investigated.We find that the volume fractions of transformed martensite after STH increase with decreasing grain sizes of the pre-STH F-P dual phases.The rapid heating and short-time holding of STH promote grain nucleation and inhibit grain growth,resulting in microstructure refinement.The formation of martensites with different morphologies and different carbon concentrations in the HR and HCR+STH alloy is identified,owing to the inhomogeneous carbon distribution by STH.Tensile experiments demonstrate that STH greatly improves the comprehension mechanical properties of the alloy.Excellent mechanical properties,with a yield strength of 1224 MPa,a tensile strength of 1583 MPa,a uniform elongation of 4.0%and a total elongation of 7.3%are achieved in the HR and HCR+STH alloy.These excellent mechanical properties are principally attributed to the microstructure refinement and martensite formation induced by STH,with a yield strength improvement of 134%and a tensile strength improvement of 150%relative to the HR alloy.展开更多
The fine-grained microstructure of TA15 titanium alloy was prepared through two-step forging technology combined with high and low temperatures, and a transnormal superplastic elongation of more than 2000% was obtaine...The fine-grained microstructure of TA15 titanium alloy was prepared through two-step forging technology combined with high and low temperatures, and a transnormal superplastic elongation of more than 2000% was obtained. The superplastic behaviour and microstructure evolution were systematically researched at different temperatures and strain rates through superplastic tensile test. The results indicate that the fine-grained TA15 alloy exhibits superplasticity at temperatures of 760-980°C and initial strain rates from 1.1 × 10^-2 to 5.5 × 10^-5 s^-1. The optimal superplastic conditions are 940°C and 3.3 × 10^-4 s^-1, in which the average elongation is 2526% and the maximum elongation is 2743%. During superplastic deformation, dynamic recovery and recrystallization occur obviously, and the corporate effect of strain hardening and recrystallization softening decides the superplastic ability directly.展开更多
Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co...Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its x -ε, phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine- grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.展开更多
Channel die compression and initial textures are used to activate different deformation mechanisms in a fine-grained magnesium alloy AZ31. The σ-ε curves, microstructures and, particularly, textures are analyzed to ...Channel die compression and initial textures are used to activate different deformation mechanisms in a fine-grained magnesium alloy AZ31. The σ-ε curves, microstructures and, particularly, textures are analyzed to reveal different deformation mechanisms and to compare with those of coarse grained samples. Dominant double-prismatic slip, {1012} twinning and basal slip are detected in three types of samples, respectively, which is similar to those of coarse grained samples. The detrimental effect of shear band formation or {1011} twinning is limited in fine grained microstructure. In addition to the higher flow stress at low temperature an early decrease in flow stress at higher temperature is also found in fine-grained samples in comparison with their coarse-grained counterparts. This softening is ascribed to the early dynamic recrystallization or grain boundary glide.展开更多
The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission ele...The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and welding thermal simulation test.It is found that serious embrittlement occurs in the FGHAZ with an 81.37% decrease of toughness,compared with that of the base metal.Microstructure analysis reveals that the FGHAZ is mainly composed of acicular,equiaxed ferrite,granular ferrite,martensite,and martensite-austenite（M-A） constituent.The FGHAZ embrittlement is mainly induced by granular ferrite because of carbides located at its boundaries and sub-boundaries.Meanwhile,the existence of martensite and M-A constituent,which distribute in a discontinuous network,is also detrimental to the mechanical properties.展开更多
Mechanical properties of Mg-3Gd(wt.%)samples with average grain sizes ranging from 3 to 45μm were characterized by room temperature tensile test.A reversal of the trade-off,i.e.,high yield strength and large tensile ...Mechanical properties of Mg-3Gd(wt.%)samples with average grain sizes ranging from 3 to 45μm were characterized by room temperature tensile test.A reversal of the trade-off,i.e.,high yield strength and large tensile elongation,was simultaneously observed in the fine-grained samples.The microstructures and hardening response were analyzed in terms of the viewpoint of strain evolution,including local strain evolution by tensile digital image correlation strain measurement,and lattice strain by using synchrotronbased in-situ high energy X-ray diffraction technique.The dislocation-based deformation mechanisms were investigated to underpin the microstructural origin of the yield point phenomenon and enhancement in work-hardening.The occurrence of the yield point phenomenon represented by a yield drop and propagation of the Lüders band is related to the absence of mobile dislocations at an early stage and to the slip transmission between the adjacent grain.The extraordinary work-hardening enhancement over an extended range can be ascribed mainly to the increases in dislocation multiplication and accumulation capabilities by the activation and interaction of multiple slip systems includingand<c+a>types.These results contribute to the design of strong and ductile Mg alloys.展开更多
Surface microstructure and microhardness of （ferrite＋ cementite） microduplex structure of the ultrafine- grained high carbon steel after laser shock processing （LSP） with different impact times were investigated ...Surface microstructure and microhardness of （ferrite＋ cementite） microduplex structure of the ultrafine- grained high carbon steel after laser shock processing （LSP） with different impact times were investigated by means of scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and microhardness measurements. Equiaxed ferrite grains were refined from 400 to 150 nm, and the cementite lamellae were fully spheroidized, with a decrease of the particle diameter from 150 to 100 nm as the impact times increased. The cementite dissolution was enhanced significantly. Correspondingly, the lattice parameter of α-Fe and microhard- hess increased with the impact times.展开更多
An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properti...An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.展开更多
Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties.In the recent work,the Mg-2Zn-0.46Y-0.5Nd,as materials for degradable stents,was applied ...Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties.In the recent work,the Mg-2Zn-0.46Y-0.5Nd,as materials for degradable stents,was applied to produce as-extruded micro-tube with an outer diameter of 3.0mm and a wall thickness of 0.35mm by hot extrusion with an extrusion ratio of 105:1 at 653K and rapid cooling.The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled,resulting in more excellent mechanical properties relative to air-cooled micro-tube.The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism.During the hot extrusion process,the activation of the non-basal slip system,especially the pyramidal(c+a)slip,could significantly weaken the texture strength,and the as-extruded micro-tube exhibits weak"RE"texture components(011^(-)1)||ED and(1^(-)21^(-)1)||ED.Hence,the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture,which is favorable for further process and governance.展开更多
In the pursuit of manufacturing intricate components for the nuclear industry,we developed a novel Zr_(63.2)Cu_(36.8)(wt.%)alloy via vacuum melting for brazing applications involving equiatomic high-entropy alloys(HEA...In the pursuit of manufacturing intricate components for the nuclear industry,we developed a novel Zr_(63.2)Cu_(36.8)(wt.%)alloy via vacuum melting for brazing applications involving equiatomic high-entropy alloys(HEA)of CoCrFeMnNi and zircaloy(Zr-3).We systematically investigated the influence of various brazing parameters on microstructure evolution and shear properties.Furthermore,we established a com-prehensive understanding of the relationship between the lattice structure of interfacial products,residual stress,and fracture behavior in HEA/Zr-Cu/Zr-3 joints.Our findings revealed that under specific conditions(1010℃for 10 min),the reaction products in HEA/Zr-Cu/Zr-3 joints consisted of lamellar HEAP/lamellar Zr(Cr,Mn)_(2),granular(Zr,Cu)/Zr_(2)(Cu,Ni,Co,Fe),bulk Zr(Cr,Mn)_(2),and Zrss.With increasing temperature and prolonged holding time,the layered HEAP and Zr(Cr,Mn)_(2)phases adjacent to the HEA substrates thick-ened,while the relative amounts of Zr_(2)(Cu,Ni,Co,Fe)decreased,with a remarkable increase in ductile Zrss.Growth kinetics analysis of the reaction layer and EBSD analysis indicated that the HEAP phases exhibited a lower growth rate compared to the Zr(Cr,Mn)_(2)layer during brazing,and both phases exhibited random grain orientations.Particularly noteworthy was the precipitation of(Zr,Cu)within the layered Zr(Cr,Mn)_(2),which increased and coarsened with higher temperatures and extended durations.Finite element analysis and TEM analysis revealed higher residual stresses at the non-coherent Zr(Cr,Mn)_(2)/HEAP interface with a lattice mismatch of 40.6%.The body-centered cubic(BCC)structural HEAP,composed of fine grains,effectively mitigated the concentrated residual stresses due to its superior plasticity.Moreover,micro-nanoscale close-packed hexagonal(HCP)precipitates(Zr,Cu)were distributed within the brittle Zr(Cr,Mn)_(2)phases,contributing to the overall strength improvement of the joints.Consequently,high-quality HEA/Zr-3 joints were achieved,featuring a maximum strength of 172.1 MPa,equivalent to approximately 62.6%of the yield strength of Zr-3.These results highlight the potential of Zr_(63.2)Cu_(36.8)(wt.%)alloys in advanced brazing applications.展开更多
Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based met...Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based metal AM method(refer to“SoftTouch”depositionin thefiledpatent)thatis suitablefor making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures.The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties.Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment,avoiding pricy powders and costly inert or vacuum conditions.The resulting multi-layer de-posited 6061 aluminum alloys yield strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment.The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites,adding novel features to existing parts,repairing damaged metal parts,and welding advanced metals for supporting sustainable manufac-turing,in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.展开更多
Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this stu...Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this study,the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion.The hot deformation behavior,microstructure evolution and dynamic recrystallization(DRX)mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction(EBSD).The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s^(-1).The strain compensated power law equation was established to describe the hot deformation behavior of the composites.The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol,respectively,suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep.The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement.The grain size increases with the decrease in Zener-Hollomn(Z)parameter,which can be well fitted by power-law relationship.With the increase in grain size and decrease in Z parameter,the geometrically necessary dislocation density decreases,which shows the approximately power-law relationship.A random and weak texture was formed after hot compression.The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s^(-1) and 573 K/0.001 s^(-1),respectively.展开更多
The aim of this paper was to address the effect of laser shock processing (LSP) on the microstructure of ultrafine-grained commercially pure aluminium which was produced through severe cold rolling and annealing. The ...The aim of this paper was to address the effect of laser shock processing (LSP) on the microstructure of ultrafine-grained commercially pure aluminium which was produced through severe cold rolling and annealing. The microstructure characteristics of ultrafine-grained commercially pure aluminium were experimentally investigated by TEM during ultra-high strain rate loading. The results show that microstructure was obviously refined due to ultra-high plastic strain induced by a single pass LSP impacts. The grain sizes decrease from 0.6 μm after severe cold rolling and annealing to 0.3 μm at the center of the laser shock wave after a single pass LSP. There is a distinct increase in the dislocation density at the edge of the laser shock wave. These experiments have guide meaning to the practical engineering applications of LSP technique.展开更多
Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then strain- ing at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmissi...Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then strain- ing at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6μm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3 μm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.展开更多
Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of...Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of about 1.3 μm. The microstructure is characterized by nearly uniform ultrafine equiaxed microstructure without twins. The evolution of the misorientation distribution during ARB was measured by EBSD. Grain refinement can be contributed to the grain subdivision induced by severe accumulated strain, the accumulated strain enhanced concurrent dynamic recovery and recrystallization as well as the complicated distribution of interface and shear strain during ARB.展开更多
We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research resu...We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.展开更多
In-situ formed high Mn steel coating reinforced by carbides was formed by laser surface alloying(LSA).Laser alloyed layers on 1Cr18Ni9Ti steel with Mn+W_(2)C(specimen A),Mn+NiWC(specimen B)and Mn+SiC(specimen C)powder...In-situ formed high Mn steel coating reinforced by carbides was formed by laser surface alloying(LSA).Laser alloyed layers on 1Cr18Ni9Ti steel with Mn+W_(2)C(specimen A),Mn+NiWC(specimen B)and Mn+SiC(specimen C)powders were fabricated to improve the wear and corrosion behavior of 1Cr18Ni9Ti steel blades in high speed mixers.Microstructure evolution,phases,element distribution,microhardness,wear and corrosion behavior of the laser alloyed layers were investigated.Results indicated that high Mn steel matrix composites with undissolved W_(2)C,WC and other in-situ formed carbides were formed by LSA with Mn+W_(2)C and Mn+NiWC while SiC totally dissolved into the high Mn matrix when adding Mn+SiC.Ni as the binding phase in Ni-WC powder decreased the crack sensitivity of the alloyed layer as compared with the addition of W_(2)C powder.An improvement in average microhardness was achieved in the matrix in specimen A,B and C,with the value of 615,602 and 277 HV_(0.5),while that of the substrate was 212 HV_(0.5).The increase of microhardness,wear and corrosion resistance is highly corelated to microstructure,formed phases,type and content of carbides,micro-hardness and toughness of the alloyed layers.展开更多
The microstructures and mechanical properties of Al-8.3Zn-3.3Cu-2.2Mg alloys prepared via hot extrusion and liquid forging methods were investigated.Results show that based on DEFORM simulation analysis,the optimal ho...The microstructures and mechanical properties of Al-8.3Zn-3.3Cu-2.2Mg alloys prepared via hot extrusion and liquid forging methods were investigated.Results show that based on DEFORM simulation analysis,the optimal hot extrusion parameters are determined as ingot initial temperature of 380°C and extrusion speed of 3 mm/s.The hot-extruded aluminum alloy after T6 heat treatment presents superior mechanical properties with yield strength of 519.6 MPa,ultimate tensile strength of 582.1 MPa,and elongation of 11.0%.Compared with the properties of gravity-cast and liquid-forged alloys,the yield strength of hot-extruded alloy increases by 30.8%and 4.9%,and the ultimate tensile strength improves by 43.5%and 10.2%,respectively.The significant improvement in tensile strength of the hot-extruded alloys is attributed to the elimination of casting defects and the refinement of matrix grain and eutectic phases.In addition,the hot-extruded alloy demonstrates superior plasticity compared with the liquid-forged alloy.This is because severe plastic deformation occurs during hot extrusion,which effectively breaks and disperses the eutectic phases,facilitating the dissolution and precipitation of the second phases and inhibiting the microcrack initiation.展开更多
文摘C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.
基金Project(50771067) supported by the National Natural Science Foundation of China
文摘In order to obtain fine-microstructure magnesium alloys with superior mechanical properties, AZ61 alloy was processed by friction stir processing(FSP) combined with rapid heat sink. It is found that ultrafine-grained microstructure with average size less than 300 nm is observed in the resultant AZ61 alloy. The mean microhardness of the ultra-fine region reaches Hv120-130, two times higher than that of AZ61 substrate. All these results demonstrate clearly that under a cooling rate high enough, ultra-fine structure inAZ61 alloy with superior mechanical properties can be produced by one pass FSP via dynamic recrystallization.
基金funded by the National Natural Science Foundation of China(No.52071212).
文摘A new thermomechanical process consisting of heavy cold rolling(HCR)and short-time heat treatment(STH)is developed to fabricate fine-grained martensite microstructure in a low-cost plain low-carbon steel.To achieve the optimal mechanical properties after STH,three different ferrite-pearlite(F-P)dual-phase microstructures are prepared via hot rolling(HR),HR and austenitizing,and HR and HCR.The microstructure evolution and the comprehensive mechanical properties of the alloy during STH are then investigated.We find that the volume fractions of transformed martensite after STH increase with decreasing grain sizes of the pre-STH F-P dual phases.The rapid heating and short-time holding of STH promote grain nucleation and inhibit grain growth,resulting in microstructure refinement.The formation of martensites with different morphologies and different carbon concentrations in the HR and HCR+STH alloy is identified,owing to the inhomogeneous carbon distribution by STH.Tensile experiments demonstrate that STH greatly improves the comprehension mechanical properties of the alloy.Excellent mechanical properties,with a yield strength of 1224 MPa,a tensile strength of 1583 MPa,a uniform elongation of 4.0%and a total elongation of 7.3%are achieved in the HR and HCR+STH alloy.These excellent mechanical properties are principally attributed to the microstructure refinement and martensite formation induced by STH,with a yield strength improvement of 134%and a tensile strength improvement of 150%relative to the HR alloy.
文摘The fine-grained microstructure of TA15 titanium alloy was prepared through two-step forging technology combined with high and low temperatures, and a transnormal superplastic elongation of more than 2000% was obtained. The superplastic behaviour and microstructure evolution were systematically researched at different temperatures and strain rates through superplastic tensile test. The results indicate that the fine-grained TA15 alloy exhibits superplasticity at temperatures of 760-980°C and initial strain rates from 1.1 × 10^-2 to 5.5 × 10^-5 s^-1. The optimal superplastic conditions are 940°C and 3.3 × 10^-4 s^-1, in which the average elongation is 2526% and the maximum elongation is 2743%. During superplastic deformation, dynamic recovery and recrystallization occur obviously, and the corporate effect of strain hardening and recrystallization softening decides the superplastic ability directly.
基金financially supported by the Major Special Project,Ministry of Industry and Information Technology,China (No.2012ZX04003061)
文摘Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its x -ε, phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine- grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.
基金This work was supported by the National Natural Sci-ence Foundation of China under grant No.50171009the National 863 Program of China(No.2002A A305501)Part work was performed at IMM RWTH A achen,Germany.
文摘Channel die compression and initial textures are used to activate different deformation mechanisms in a fine-grained magnesium alloy AZ31. The σ-ε curves, microstructures and, particularly, textures are analyzed to reveal different deformation mechanisms and to compare with those of coarse grained samples. Dominant double-prismatic slip, {1012} twinning and basal slip are detected in three types of samples, respectively, which is similar to those of coarse grained samples. The detrimental effect of shear band formation or {1011} twinning is limited in fine grained microstructure. In addition to the higher flow stress at low temperature an early decrease in flow stress at higher temperature is also found in fine-grained samples in comparison with their coarse-grained counterparts. This softening is ascribed to the early dynamic recrystallization or grain boundary glide.
基金supported by the National High-Tech Research and Development Program of China (No.2006AA09A103-6)
文摘The mechanical properties and microstructure features of the fine-grained heat-affected zone（FGHAZ） of ASTM4130 steel was investigated by optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and welding thermal simulation test.It is found that serious embrittlement occurs in the FGHAZ with an 81.37% decrease of toughness,compared with that of the base metal.Microstructure analysis reveals that the FGHAZ is mainly composed of acicular,equiaxed ferrite,granular ferrite,martensite,and martensite-austenite（M-A） constituent.The FGHAZ embrittlement is mainly induced by granular ferrite because of carbides located at its boundaries and sub-boundaries.Meanwhile,the existence of martensite and M-A constituent,which distribute in a discontinuous network,is also detrimental to the mechanical properties.
基金financially supported by the National Key Research and Develop-ment Program(No.2023YFB3712702)the National Natural Science Foundation of China(Nos.52071038,52071039,and 52301156)the Natural Science Foundation of Jiangsu Province(Nos.BK20232025 and BK20243005)。
文摘Mechanical properties of Mg-3Gd(wt.%)samples with average grain sizes ranging from 3 to 45μm were characterized by room temperature tensile test.A reversal of the trade-off,i.e.,high yield strength and large tensile elongation,was simultaneously observed in the fine-grained samples.The microstructures and hardening response were analyzed in terms of the viewpoint of strain evolution,including local strain evolution by tensile digital image correlation strain measurement,and lattice strain by using synchrotronbased in-situ high energy X-ray diffraction technique.The dislocation-based deformation mechanisms were investigated to underpin the microstructural origin of the yield point phenomenon and enhancement in work-hardening.The occurrence of the yield point phenomenon represented by a yield drop and propagation of the Lüders band is related to the absence of mobile dislocations at an early stage and to the slip transmission between the adjacent grain.The extraordinary work-hardening enhancement over an extended range can be ascribed mainly to the increases in dislocation multiplication and accumulation capabilities by the activation and interaction of multiple slip systems includingand<c+a>types.These results contribute to the design of strong and ductile Mg alloys.
基金Sponsored by National Natural Science Foundation of China(50801021,51201061)Program for Young Key Teachers in Henan Province of China(2011GGJS-070)Program for Henan Province for Science and Technology Innovation Excellent Talents of China(144200510001)
文摘Surface microstructure and microhardness of （ferrite＋ cementite） microduplex structure of the ultrafine- grained high carbon steel after laser shock processing （LSP） with different impact times were investigated by means of scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and microhardness measurements. Equiaxed ferrite grains were refined from 400 to 150 nm, and the cementite lamellae were fully spheroidized, with a decrease of the particle diameter from 150 to 100 nm as the impact times increased. The cementite dissolution was enhanced significantly. Correspondingly, the lattice parameter of α-Fe and microhard- hess increased with the impact times.
基金financially supported by the National Major Science and Technology Project of China (No. 2014ZX07214-002)
文摘An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.
基金The authors are grateful for the financial support of Key Projects of the Joint Fund of the National Natural Science Foundation of China(U1804251)the National Key Research and Development Program of China(2018YFC1106703,2017YFB0702504 and 2016YFC1102403).
文摘Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties.In the recent work,the Mg-2Zn-0.46Y-0.5Nd,as materials for degradable stents,was applied to produce as-extruded micro-tube with an outer diameter of 3.0mm and a wall thickness of 0.35mm by hot extrusion with an extrusion ratio of 105:1 at 653K and rapid cooling.The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled,resulting in more excellent mechanical properties relative to air-cooled micro-tube.The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism.During the hot extrusion process,the activation of the non-basal slip system,especially the pyramidal(c+a)slip,could significantly weaken the texture strength,and the as-extruded micro-tube exhibits weak"RE"texture components(011^(-)1)||ED and(1^(-)21^(-)1)||ED.Hence,the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture,which is favorable for further process and governance.
基金supported by the National Natural Science Foundation of China(Nos.52275321 and 52205348)the Shandong Natural Science Foundation(No.ZR2023JQ021)+3 种基金the Taishan Scholars Foundation of Shandong Province(No.tsqn201812128)the Innovation Scientists and Technicians Troop Projects of Henan Province(No.204200510031)the Heilongjiang Touyan Innovation Team Program(No.HITTY-20190013)supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIP)(Nos.NRF-2021R1A2C3006662 and NRF-2022R1A5A1030054).
文摘In the pursuit of manufacturing intricate components for the nuclear industry,we developed a novel Zr_(63.2)Cu_(36.8)(wt.%)alloy via vacuum melting for brazing applications involving equiatomic high-entropy alloys(HEA)of CoCrFeMnNi and zircaloy(Zr-3).We systematically investigated the influence of various brazing parameters on microstructure evolution and shear properties.Furthermore,we established a com-prehensive understanding of the relationship between the lattice structure of interfacial products,residual stress,and fracture behavior in HEA/Zr-Cu/Zr-3 joints.Our findings revealed that under specific conditions(1010℃for 10 min),the reaction products in HEA/Zr-Cu/Zr-3 joints consisted of lamellar HEAP/lamellar Zr(Cr,Mn)_(2),granular(Zr,Cu)/Zr_(2)(Cu,Ni,Co,Fe),bulk Zr(Cr,Mn)_(2),and Zrss.With increasing temperature and prolonged holding time,the layered HEAP and Zr(Cr,Mn)_(2)phases adjacent to the HEA substrates thick-ened,while the relative amounts of Zr_(2)(Cu,Ni,Co,Fe)decreased,with a remarkable increase in ductile Zrss.Growth kinetics analysis of the reaction layer and EBSD analysis indicated that the HEAP phases exhibited a lower growth rate compared to the Zr(Cr,Mn)_(2)layer during brazing,and both phases exhibited random grain orientations.Particularly noteworthy was the precipitation of(Zr,Cu)within the layered Zr(Cr,Mn)_(2),which increased and coarsened with higher temperatures and extended durations.Finite element analysis and TEM analysis revealed higher residual stresses at the non-coherent Zr(Cr,Mn)_(2)/HEAP interface with a lattice mismatch of 40.6%.The body-centered cubic(BCC)structural HEAP,composed of fine grains,effectively mitigated the concentrated residual stresses due to its superior plasticity.Moreover,micro-nanoscale close-packed hexagonal(HCP)precipitates(Zr,Cu)were distributed within the brittle Zr(Cr,Mn)_(2)phases,contributing to the overall strength improvement of the joints.Consequently,high-quality HEA/Zr-3 joints were achieved,featuring a maximum strength of 172.1 MPa,equivalent to approximately 62.6%of the yield strength of Zr-3.These results highlight the potential of Zr_(63.2)Cu_(36.8)(wt.%)alloys in advanced brazing applications.
基金This work was financially supported by the University of Michi-gan College of Engineering startup grant and FL and PD acknowl-edge the technical support from the Michigan Center for Materials Characterization(MC^(2)).
文摘Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based metal AM method(refer to“SoftTouch”depositionin thefiledpatent)thatis suitablefor making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures.The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties.Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment,avoiding pricy powders and costly inert or vacuum conditions.The resulting multi-layer de-posited 6061 aluminum alloys yield strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment.The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites,adding novel features to existing parts,repairing damaged metal parts,and welding advanced metals for supporting sustainable manufac-turing,in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.
基金supported by the Qinghai Provincial Science and Technology Program (No.2020-ZJ-707)the Financial supports from the Natural Science Foundation of China (No.52261016).
文摘Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this study,the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion.The hot deformation behavior,microstructure evolution and dynamic recrystallization(DRX)mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction(EBSD).The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s^(-1).The strain compensated power law equation was established to describe the hot deformation behavior of the composites.The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol,respectively,suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep.The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement.The grain size increases with the decrease in Zener-Hollomn(Z)parameter,which can be well fitted by power-law relationship.With the increase in grain size and decrease in Z parameter,the geometrically necessary dislocation density decreases,which shows the approximately power-law relationship.A random and weak texture was formed after hot compression.The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s^(-1) and 573 K/0.001 s^(-1),respectively.
基金National Nature Science Foundation of China (50801021)
文摘The aim of this paper was to address the effect of laser shock processing (LSP) on the microstructure of ultrafine-grained commercially pure aluminium which was produced through severe cold rolling and annealing. The microstructure characteristics of ultrafine-grained commercially pure aluminium were experimentally investigated by TEM during ultra-high strain rate loading. The results show that microstructure was obviously refined due to ultra-high plastic strain induced by a single pass LSP impacts. The grain sizes decrease from 0.6 μm after severe cold rolling and annealing to 0.3 μm at the center of the laser shock wave after a single pass LSP. There is a distinct increase in the dislocation density at the edge of the laser shock wave. These experiments have guide meaning to the practical engineering applications of LSP technique.
基金support from the National Natural Science Foundation of China (No. 50801021)
文摘Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then strain- ing at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6μm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3 μm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.
基金Project (50801027) supported by the National Natural Science Foundation of ChinaProject(2007001) supported by the Public Foundation of Guangdong Key Laboratory for Advanced Metallic Materials Processing,South China University of Technology,China
文摘Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of about 1.3 μm. The microstructure is characterized by nearly uniform ultrafine equiaxed microstructure without twins. The evolution of the misorientation distribution during ARB was measured by EBSD. Grain refinement can be contributed to the grain subdivision induced by severe accumulated strain, the accumulated strain enhanced concurrent dynamic recovery and recrystallization as well as the complicated distribution of interface and shear strain during ARB.
基金Funded by the National Natural Science Foundation of China(Nos.U23A20672,52171270,51879168)the PI Project of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML20240001,GML2024009)。
文摘We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.
文摘In-situ formed high Mn steel coating reinforced by carbides was formed by laser surface alloying(LSA).Laser alloyed layers on 1Cr18Ni9Ti steel with Mn+W_(2)C(specimen A),Mn+NiWC(specimen B)and Mn+SiC(specimen C)powders were fabricated to improve the wear and corrosion behavior of 1Cr18Ni9Ti steel blades in high speed mixers.Microstructure evolution,phases,element distribution,microhardness,wear and corrosion behavior of the laser alloyed layers were investigated.Results indicated that high Mn steel matrix composites with undissolved W_(2)C,WC and other in-situ formed carbides were formed by LSA with Mn+W_(2)C and Mn+NiWC while SiC totally dissolved into the high Mn matrix when adding Mn+SiC.Ni as the binding phase in Ni-WC powder decreased the crack sensitivity of the alloyed layer as compared with the addition of W_(2)C powder.An improvement in average microhardness was achieved in the matrix in specimen A,B and C,with the value of 615,602 and 277 HV_(0.5),while that of the substrate was 212 HV_(0.5).The increase of microhardness,wear and corrosion resistance is highly corelated to microstructure,formed phases,type and content of carbides,micro-hardness and toughness of the alloyed layers.
基金Natural Science Foundation of Shandong Province of China(ZR2023QE193)。
文摘The microstructures and mechanical properties of Al-8.3Zn-3.3Cu-2.2Mg alloys prepared via hot extrusion and liquid forging methods were investigated.Results show that based on DEFORM simulation analysis,the optimal hot extrusion parameters are determined as ingot initial temperature of 380°C and extrusion speed of 3 mm/s.The hot-extruded aluminum alloy after T6 heat treatment presents superior mechanical properties with yield strength of 519.6 MPa,ultimate tensile strength of 582.1 MPa,and elongation of 11.0%.Compared with the properties of gravity-cast and liquid-forged alloys,the yield strength of hot-extruded alloy increases by 30.8%and 4.9%,and the ultimate tensile strength improves by 43.5%and 10.2%,respectively.The significant improvement in tensile strength of the hot-extruded alloys is attributed to the elimination of casting defects and the refinement of matrix grain and eutectic phases.In addition,the hot-extruded alloy demonstrates superior plasticity compared with the liquid-forged alloy.This is because severe plastic deformation occurs during hot extrusion,which effectively breaks and disperses the eutectic phases,facilitating the dissolution and precipitation of the second phases and inhibiting the microcrack initiation.
