The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification pro...The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.展开更多
A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed gr...A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.展开更多
The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxi...The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxidized AgMgNi alloys,which were internally oxidized at 800℃ for 8 h under an oxy-gen atmosphere.We found that Mg-O clusters contributed to the hardening(138 HV)and strengthening(376.9 MPa)of the AgMg alloy through solid solution strengthening effects,albeit at the expense of duc-tility.To address this limitation,we introduced Ni nanoparticles into the AgMg alloy,resulting in signifi-cant grain refinement within its microstructure.Specifically,the grain size decreased from 67.2μm in the oxidized AgMg alloy to below 6.0μm in the oxidized AgMgNi alloy containing 0.3 wt%Ni.Consequently,the toughness increased significantly,rising from toughness value of 2177.9 MJ m^(-3) in the oxidized AgMg alloy to 6186.1 MJ m^(-3) in the oxidized AgMgNi alloy,representing a remarkable 2.8-fold enhancement.Furthermore,the internally oxidized AgMgNi alloy attained a strength of up to 387.6 MPa,comparable to that of the internally oxidized AgMg alloy,thereby demonstrating the successful realization of concurrent strengthening and toughening.These results collectively offer a novel approach for the design of high-performance alloys through the synergistic combination of cluster strengthening and grain refinement toughening.展开更多
This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl sol...This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl solution.The results demonstrate that grain refinement significantly impacts the adsorption and inhibition performance of BTAH on carbon steels.Ultra-refinement of steel grains to 0.6μm improves the maximum inhibition efficiency of BTAH to 90.0%within 168 h of immersion,which was much higher than that of the steels with 24.5μm(73.6%)and 4.3μm grain sizes(81.7%).Notably,grain sizes of 4.3 and 0.6μm facilitate a combination of physisorption and chemisorption of BTAH after 120 h of immersion,as evidenced by the X-ray photoelectron spectroscopy(XPS)results and Langmuir adsorption isotherms,while BTAH adsorbed on carbon steels with a grain size of 24.5μm through physisorption during the 168 h of immersion.Ultra-refinement of grains has beneficial impacts on promoting the formation of a stable and dense corrosion inhibitor film,leading to improved corrosion resistance and the mitigation of non-uniform corrosion.These advantageous effects can be attributed to the higher adsorption energy at grain boundaries(approximately-3.12 eV)compared to grain interiors(ranging from-0.79 to 2.47 eV),promoting both the physisorption and chemisorption of organic corrosion inhibitors.The investigation comprehensively illustrates,for the first time,the effects of grain size on the adsorption mechanism,film formation process,and inhibition performance of organic corrosion inhibitors on carbon steels.This study demonstrates a promising approach to enhancing corrosion inhibition performance through microstructural design.展开更多
Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can res...Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.展开更多
A newly developed P-doped CrCoNi medium-entropy alloy(MEA)provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA,even superior tensile ductility to the other-element-doped C...A newly developed P-doped CrCoNi medium-entropy alloy(MEA)provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA,even superior tensile ductility to the other-element-doped CrCoNi MEAs at similar yield strength levels.P segregation at grain boundaries(GBs)and dissolution inside grain interiors,together with the related lower stacking fault energy(SFE)are found in the P-doped CrCoNi MEA.Higher hetero-deformation-induced(HDI)hardening rate is observed in the P-doped CrCoNi MEA due to the grain-to-grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls(SFWs).The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid-solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs.During the tensile deformation,the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults(SFs)between them,rather than deformation twins,are observed to induce dynamic structural refinement for forming par-allelepiped domains in the P-doped CoCrNi MEA,due to the lower SFE and even lower atomically-local SFE.These nano-sized domains with domain boundary spacing at tens of nanometers can block disloca-tion movement for strengthening on one hand,and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand.展开更多
Titanium alloys,usually known as non-corrodible material,are susceptible to microbiologically influenced corrosion(MIC)in marine environment.While titanium-zirconium(TiZr)alloys have been extensively studied in medica...Titanium alloys,usually known as non-corrodible material,are susceptible to microbiologically influenced corrosion(MIC)in marine environment.While titanium-zirconium(TiZr)alloys have been extensively studied in medical applications,the influence of microorganisms,especially marine microorganisms,on their corrosion behavior has not been explored.In this work,a TiZrCu alloy with a combination of excel-lent mechanical,anti-corrosion,and antibacterial properties was developed by optimizing the Cu content and grain refinement.Its MIC and antibacterial mechanisms against Pseudomonas aeruginosa,a represen-tative marine microorganism,were systematically investigated.5.5 wt%was determined as the optimal copper content.The fine-grained Ti-15Zr-5.5Cu(TZC-5.5FG)alloy maintained high MIC resistance,exhibit-ing a corrosion current of 5.7±0.1 nA/cm^(2) and an antibacterial rate of 91.8% against P.aeruginosa.The mechanism of improved corrosion resistance was attributed to the denser passive film with high TiO2 content and the lower surface potential differenceΔE.The release of Cu^(2+)ions,ΔE,and the generation of ROS are three major factors that contribute to the antibacterial performance of TiZrCu alloys.Com-pared to other available marine metals,TZC-5.5FG alloy exhibited superior comprehensive performance,including excellent mechanical properties and anti-MIC capacity,which make it a promising material for load-bearing applications in marine environment.展开更多
To investigate the effect of microstructure evolution on corrosion behavior and strengthening mechanism of Mg-1Zn-1Ca(wt.%)alloys,as-cast Mg-1Zn-1Ca alloys were performed by equal channel angular pressing(ECAP)with 1 ...To investigate the effect of microstructure evolution on corrosion behavior and strengthening mechanism of Mg-1Zn-1Ca(wt.%)alloys,as-cast Mg-1Zn-1Ca alloys were performed by equal channel angular pressing(ECAP)with 1 and 4 passes.The corrosion behavior and mechanical properties of alloys were investigated by optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),electrochemical tests,immersion tests and tensile tests.The results showed that mechanical properties improved after ECAP 1 pass;however,the corrosion resistance deteriorated due to high-density dislocations and fragmented secondary phases by ECAP.In contrast,synchronous improvement in the mechanical properties and corrosion resistance was achieved though grain refinement after ECAP 4 passes;fine grains led to a significant improvement in the yield strength,ultimate tensile strength,elongation,and corrosion rate of 103 MPa,223 MPa,30.5%,and 1.5843 mm/a,respectively.The enhanced corrosion resistance was attributed to the formation of dense corrosion product films by finer grains and the barrier effect by high-density grain boundaries.These results indicated that Mg-1Zn-1Ca alloy has a promising potential for application in biomedical materials.展开更多
Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain...Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.展开更多
Recrystallization stands as an essential process that influences the microstructure and properties of magnesium(Mg)alloys,yet its mechanisms remain complex and multifaceted.This review explores the key factors affecti...Recrystallization stands as an essential process that influences the microstructure and properties of magnesium(Mg)alloys,yet its mechanisms remain complex and multifaceted.This review explores the key factors affecting the recrystallization behavior of Mg alloys,emphasizing how their unique structural characteristics impact the driving forces and dynamics of recrystallization.Unlike conventional alloys,Mg alloys exhibit distinctive recrystallization kinetics,which is significantly affected by deformation conditions,such as strain rate,temperature,and processing methods(e.g.,rolling,forging,and extrusion).The process is also influenced by material characteristics,including initial grain size,texture,dislocation density,solute clustering,and stacking fault energy.Additionally,uneven strain distribution,stress concentrations,and stored energy play crucial roles in shaping the formation of recrystallized grains,particularly near grain boundaries.Notably,recrystallization is driven by dislocation accumulation and the availability of slip systems,with new strain-free grains typically forming in regions of high dislocation density.This paper synthesizes the existing literature to provide a comprehensive understanding of the mechanisms and kinetics of recrystallization in Mg alloys,highlighting the influence of microstructural features such as second-phase particles and grain boundary characteristics.It also identifies key challenges and suggests promising directions for future research,including optimizing material compositions and the interaction between deformation conditions via machine learning.展开更多
Grain boundary hardening is an important mechanism for improving the strength and ductility of metal materials.However,the industrial fabrication of fine-grained FeCrAl alloys was limited by the interaction between th...Grain boundary hardening is an important mechanism for improving the strength and ductility of metal materials.However,the industrial fabrication of fine-grained FeCrAl alloys was limited by the interaction between the recrystallization and precipitation.Here,we report the facile mass production of fine-grained FeCrAl alloys by Si alloying and manipulation of the recrystallization process through introducing heterogeneous Si-rich Laves precipitates.The pre-precipitation of heterogeneous Laves phase not only promotes subsequent recrystallization grain nucleation by the PSN(Particles simultaneous nucleation)and SIBM(Strain-induced grain boundary migration)mechanisms,but also provides resistance to grain growth by the Zener pinning mechanism.Moreover,continuous grain refinement can be achieved by intensifying the heterogeneous Laves precipitates through decreasing their formation energy.This approach enables the preparation of a fully recrystallized fine-grain structure with a grain size of 4.6μm without the introduction of segregated boundaries.Consequently,an unprecedented synergy enhancement of strength(σ_(y)=625 MPa,σ_(uts)=867 MPa,)and ductility(ε_(u)=13.8%)is achieved in the fine-grain structured FeCrAl alloys compared with the coarse grain counterpart.The experimental results prove that the proposed strategy is appropriate for developing high strength and ductility FeCrAl alloys,and further boosting its potential applications as accident-tolerant-fuel cladding in nuclear reactors.In addition,this grainrefinement strategy should be extendable to other alloy systems,where there is a significant difference between precipitation and recrystallization temperatures.展开更多
The remodeling of macrophages mediated by biomaterials is an important step in osseointegration.The biointerfacial characteristics shaped by implants and the bioenergetic state derived from macrophages are considered ...The remodeling of macrophages mediated by biomaterials is an important step in osseointegration.The biointerfacial characteristics shaped by implants and the bioenergetic state derived from macrophages are considered the key to macrophage reprogramming.In this study,the integrated Ti/Zn composites with optimized morphology and bioactive phase were prepared by friction stir processing,which could meet the multi-biofunctional requirements in the application of narrow-diameter implants.The severe plastic deformation and the hindrance of Zn particles to grain growth promote grain refinement,resulting in enhanced mechanical properties.The cell interfacial adhesion mediated by the grain boundary collaborated the energy metabolism reprogramming induced by the released Zn ion,promoting jointly anti-inflammatory cascade in macrophages and favorable osteogenesis in bone marrow mesenchymal stem cells(BMSCs).This study provides a new simultaneous approach of morphology and composition modification for titanium implants,and reveals the important role of grain size and bioactive element in the reversion of macrophage fate as well.展开更多
The Fe–Mn damping alloys possess considerable damping capacity,but their yield strength is rather low.The 800 MPa Fe–Mn alloy with expected damping capacity was designed by the combination of grain refinement and ε...The Fe–Mn damping alloys possess considerable damping capacity,but their yield strength is rather low.The 800 MPa Fe–Mn alloy with expected damping capacity was designed by the combination of grain refinement and ε-martensite introduction.The yield strength can be greatly raised to around 700 MPa by refining grain size from 88.4 to 1.8μm.Although there exist numerous stacking faults in the fine-grained alloy,the damping capacity is strongly deteriorated due to the suppression of thermally activated ε-martensite.We demonstrate that the stacking faults cannot provide effective contribution to damping capacity and hence introduce a considerable volume fraction of stress/strain-induced ε-martensite to raise damping sources,including ε-martensite and γ/ε interfaces,etc.,by a small pre-strain.From this,the damping capacity can be improved,and the yield strength can be further enhanced from nearly 700 MPa to around 800 MPa.Thus,the combination of high yield strength and good damping capacity is realized.展开更多
The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused ...The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused by strengthening,the strengthening energy is limited and the ideal strengthening effect cannot be obtained.This work aims to propose a novel approach to address this issue effectively.The surface layer with high-density dislocations was obtained by a low-energy surface strengthening method(shot peening)at first.Then the surface strengthening mechanism changes from dislocation strengthen-ing to grain boundary strengthening after electropulsing treatment(EPT).The evolution of residual stress and microstructure was analyzed using multi-scale characterization techniques.The results demonstrate that EPT followed by surface strengthening makes a remarkable 304%increase in fatigue life of TC11 titanium alloy.The enhancement of fatigue life can be attributed to the grain refinement accompanied by the formation of nanotwins and sub-grains in the surface-strengthened layer,as well as the reduction in dislocation density within the substrate after EPT.This study demonstrates the significant potential of EPT in further enhancing the fatigue life of surface pre-strengthened thin-walled components.展开更多
This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined wi...This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.展开更多
The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increas...The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increasing the Cu content,the effect of Cu on the evolution of the microstructure and morphology of the Cu-Ni alloy during undercooling was studied.The mechanism of grain refinement at different degrees of undercooling and the effect of Cu content on its solidification behaviour were investigated.The solidification behaviour of Cu55Ni45 and Cu60Ni40 alloys was investigated using infrared thermometry and high-speed photography.The results indicate that both Cu55Ni45 and Cu60Ni40 alloy melts undergo only one recalescence during rapid solidification.The degree of recalescence increases approximately linearly with increasing undercooling.The solidification front of the alloy melts undergoes a transition process from a small-angle plane to a sharp front and then to a smooth arc.However,the growth of the subcooled melt is constrained to a narrow range,facilitating the formation of a coarse dendritic crystal morphology in the Cu-Ni alloy.At large undercooling,the stress breakdown of the directionally growing dendrites is primarily caused by thermal diffusion.The strain remaining in the dendritic fragments provides the driving force for recrystallisation of the tissue to occur,which in turn refines the tissue.展开更多
By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in ...By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in both alloys across both large and small undercooling ranges.High-speed photography was used to analyze the relationship between solidification front morphology and undercooling,showing that dendrite remelting and fragmentation caused grain refinement under small undercooling,while stress-induced recrystallization is responsible under large undercooling.Microhardness testing further demonstrates a sudden drop in microhardness near the critical undercooling point,providing evidence for grain refinement due to recrystallization in large undercooling tissues.展开更多
Ti6Al4V alloy has been widely used in dental applications,such as orthodontic mini-implants.However,it has been reported that fluoride ions could obviously accelerate the corrosion of implant materials and affect thei...Ti6Al4V alloy has been widely used in dental applications,such as orthodontic mini-implants.However,it has been reported that fluoride ions could obviously accelerate the corrosion of implant materials and affect their performance.This work aimed to improve the F^(−)erosion resistance of Ti6Al4V alloy through the strategy of both Cu addition and grain refinement.As contrasted with Ti6Al4V alloy,both the coarse-and ultrafine-grained Ti6Al4V-5Cu alloys effectively mitigated the acceleration of the fluoride ions to the anode process,because Cu substituents blocked the continuous damage of F·_(O) doped in the passive film.Furthermore,grain refinement enhanced the protective ability of the passive film,more oxides and less adsorption amount of fluorides presented in the passive film of ultrafine-grained Ti6Al4V-5Cu alloy than those of coarse-grained Ti6Al4V-5Cu alloy.Under the combination of Cu alloying and grain refinement,the ultrafine-grained Ti6Al4V-5Cu alloy is greatly appropriate for the fabrication of orthodontic devices.展开更多
The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were i...The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.展开更多
The effects of forward extrusion as well as extrusion combined with reversible torsion(KoBo extrusion),followed by additional deformation via the MaxStrain module of the Gleeble thermomechanical simulator,on the micro...The effects of forward extrusion as well as extrusion combined with reversible torsion(KoBo extrusion),followed by additional deformation via the MaxStrain module of the Gleeble thermomechanical simulator,on the microstructure,mechanical properties,and electrical conductivity of a Cu−0.7Mg(wt.%)alloy,were investigated.The simulation results highlighted the critical influence of processing history on determining the equivalent strain distribution.The sample subjected to forward extrusion at 400℃and subsequent MaxStrain processing(FM sample),possessed 76%lower grain size compared to the sample processed solely with MaxStrain(AM sample).Likewise,the KoBo-extruded and MaxStrain-processed sample(KM sample)exhibited 66%smaller grain size compared to the AM sample.Tensile test results revealed that the AM,FM,and KM samples,respectively,possessed 251%,288%,and 360%higher yield strength,and 95%,121%,and 169%higher tensile strength compared to the initial annealed alloy,as a result of grain refinement as well as deformation strengthening.Finally,the electrical conductivity measurements revealed that AM,FM,and KM samples,respectively,possessed electrical conductivity values of 37.9,35.6,and 32.0 MS/m,which,by considering their mechanical properties,makes them eligible to be categorized as high-strength and high-conductivity copper alloys.展开更多
基金Project supported by the Natural Science Foundation of Hunan Province(2024JJ4056)the Key Project of Guangxi Zhuang Autonomous Region(AB22080089)the Government of Chongzuo,Guangxi Zhuang Autonomous Region(FA20210716)。
文摘The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52074254,51874271,and 52174349)the Key Projects of International Cooperation(No.122111KYSB20200034)+3 种基金the Project of Key Laboratory of Science and Technology on Par-ticle Materials(No.CXJJ-22S043)the CAS Project for Young Scientists in Basic Research(No.YSBR-025)This work was finan-cially supported by the Selection of Best Candidates to Undertake Key Research Projects(No.211110230200)This research work was also financially supported by the OU Master Plan Implementation Project promoted under Osaka University.
文摘A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.
基金supported by the National Natural Science Foundation of China(Nos.51977027 and 51967008)the Scientific and Technological Project of Yunnan Precious Metals Lab-oratory(Nos.YPML-2023050250 and YPML-2022050206).
文摘The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxidized AgMgNi alloys,which were internally oxidized at 800℃ for 8 h under an oxy-gen atmosphere.We found that Mg-O clusters contributed to the hardening(138 HV)and strengthening(376.9 MPa)of the AgMg alloy through solid solution strengthening effects,albeit at the expense of duc-tility.To address this limitation,we introduced Ni nanoparticles into the AgMg alloy,resulting in signifi-cant grain refinement within its microstructure.Specifically,the grain size decreased from 67.2μm in the oxidized AgMg alloy to below 6.0μm in the oxidized AgMgNi alloy containing 0.3 wt%Ni.Consequently,the toughness increased significantly,rising from toughness value of 2177.9 MJ m^(-3) in the oxidized AgMg alloy to 6186.1 MJ m^(-3) in the oxidized AgMgNi alloy,representing a remarkable 2.8-fold enhancement.Furthermore,the internally oxidized AgMgNi alloy attained a strength of up to 387.6 MPa,comparable to that of the internally oxidized AgMg alloy,thereby demonstrating the successful realization of concurrent strengthening and toughening.These results collectively offer a novel approach for the design of high-performance alloys through the synergistic combination of cluster strengthening and grain refinement toughening.
基金support of the National Natural Science Foundation of China(Nos.52171063,52274362,and 52371049)the Key R&D projects of Henan Province(No.221111230800)+1 种基金the Doctoral Fund of Henan University of Technology(No.2023BS047)the Natural science Project of Zhengzhou Science and Technology Bureau(No.22ZZRDZX04)。
文摘This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl solution.The results demonstrate that grain refinement significantly impacts the adsorption and inhibition performance of BTAH on carbon steels.Ultra-refinement of steel grains to 0.6μm improves the maximum inhibition efficiency of BTAH to 90.0%within 168 h of immersion,which was much higher than that of the steels with 24.5μm(73.6%)and 4.3μm grain sizes(81.7%).Notably,grain sizes of 4.3 and 0.6μm facilitate a combination of physisorption and chemisorption of BTAH after 120 h of immersion,as evidenced by the X-ray photoelectron spectroscopy(XPS)results and Langmuir adsorption isotherms,while BTAH adsorbed on carbon steels with a grain size of 24.5μm through physisorption during the 168 h of immersion.Ultra-refinement of grains has beneficial impacts on promoting the formation of a stable and dense corrosion inhibitor film,leading to improved corrosion resistance and the mitigation of non-uniform corrosion.These advantageous effects can be attributed to the higher adsorption energy at grain boundaries(approximately-3.12 eV)compared to grain interiors(ranging from-0.79 to 2.47 eV),promoting both the physisorption and chemisorption of organic corrosion inhibitors.The investigation comprehensively illustrates,for the first time,the effects of grain size on the adsorption mechanism,film formation process,and inhibition performance of organic corrosion inhibitors on carbon steels.This study demonstrates a promising approach to enhancing corrosion inhibition performance through microstructural design.
基金supported by the National Natural Science Foundation of China(No.51871155).
文摘Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.
基金supported by the National Key R&D Program of China(No.2019YFA0209902)the Natural Science Foundation of China(Nos.52071326,52192593,51601204)+1 种基金the NSFC Basic Science Center Program for Multiscale Problems in Nonlinear Mechanics(No.11988102)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB22040503).
文摘A newly developed P-doped CrCoNi medium-entropy alloy(MEA)provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA,even superior tensile ductility to the other-element-doped CrCoNi MEAs at similar yield strength levels.P segregation at grain boundaries(GBs)and dissolution inside grain interiors,together with the related lower stacking fault energy(SFE)are found in the P-doped CrCoNi MEA.Higher hetero-deformation-induced(HDI)hardening rate is observed in the P-doped CrCoNi MEA due to the grain-to-grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls(SFWs).The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid-solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs.During the tensile deformation,the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults(SFs)between them,rather than deformation twins,are observed to induce dynamic structural refinement for forming par-allelepiped domains in the P-doped CoCrNi MEA,due to the lower SFE and even lower atomically-local SFE.These nano-sized domains with domain boundary spacing at tens of nanometers can block disloca-tion movement for strengthening on one hand,and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand.
基金supported by the National Key Research and Development Program of China(No.2022YFB3808800)the National Natural Science Foundation of China(No.52425112 and 52401178)+1 种基金the IMR Innovation Fund(No.2024-PY06)the CAS-WEGO Research and Development Plan Project.
文摘Titanium alloys,usually known as non-corrodible material,are susceptible to microbiologically influenced corrosion(MIC)in marine environment.While titanium-zirconium(TiZr)alloys have been extensively studied in medical applications,the influence of microorganisms,especially marine microorganisms,on their corrosion behavior has not been explored.In this work,a TiZrCu alloy with a combination of excel-lent mechanical,anti-corrosion,and antibacterial properties was developed by optimizing the Cu content and grain refinement.Its MIC and antibacterial mechanisms against Pseudomonas aeruginosa,a represen-tative marine microorganism,were systematically investigated.5.5 wt%was determined as the optimal copper content.The fine-grained Ti-15Zr-5.5Cu(TZC-5.5FG)alloy maintained high MIC resistance,exhibit-ing a corrosion current of 5.7±0.1 nA/cm^(2) and an antibacterial rate of 91.8% against P.aeruginosa.The mechanism of improved corrosion resistance was attributed to the denser passive film with high TiO2 content and the lower surface potential differenceΔE.The release of Cu^(2+)ions,ΔE,and the generation of ROS are three major factors that contribute to the antibacterial performance of TiZrCu alloys.Com-pared to other available marine metals,TZC-5.5FG alloy exhibited superior comprehensive performance,including excellent mechanical properties and anti-MIC capacity,which make it a promising material for load-bearing applications in marine environment.
基金financially supported by the National Natural Science Foundation of China(No.52374395)the Natural Science Foundation of Shanxi Province,China(Nos.20210302123135,202303021221143)+5 种基金the Scientific and Technological Achievements Transformation Guidance Special Project of Shanxi Province,China(Nos.202104021301022,202204021301009)the Central Government Guided Local Science and Technology Development Projects,China(No.YDZJSX20231B003)the Ministry of Science and Higher Education of the Russian Federation for financial support under the Megagrant(No.075-15-2022-1133)the National Research Foundation(NRF)grant funded by the Ministry of Science and ICT of Korea through the Research Institute of Advanced Materials(No.2015R1A2A1A01006795)the China Postdoctoral Science Foundation(No.2022M710541)the Research Project supported by Shanxi Scholarship Council of China(No.2022-038)。
文摘To investigate the effect of microstructure evolution on corrosion behavior and strengthening mechanism of Mg-1Zn-1Ca(wt.%)alloys,as-cast Mg-1Zn-1Ca alloys were performed by equal channel angular pressing(ECAP)with 1 and 4 passes.The corrosion behavior and mechanical properties of alloys were investigated by optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),electrochemical tests,immersion tests and tensile tests.The results showed that mechanical properties improved after ECAP 1 pass;however,the corrosion resistance deteriorated due to high-density dislocations and fragmented secondary phases by ECAP.In contrast,synchronous improvement in the mechanical properties and corrosion resistance was achieved though grain refinement after ECAP 4 passes;fine grains led to a significant improvement in the yield strength,ultimate tensile strength,elongation,and corrosion rate of 103 MPa,223 MPa,30.5%,and 1.5843 mm/a,respectively.The enhanced corrosion resistance was attributed to the formation of dense corrosion product films by finer grains and the barrier effect by high-density grain boundaries.These results indicated that Mg-1Zn-1Ca alloy has a promising potential for application in biomedical materials.
基金Key Research and Development Program of Shandong Province(2021CXGC010310)Shandong Province Science and Technology Small and Medium Sized Enterprise Innovation Ability Enhancement Project(2023TSGC0287,2024TSGC0519)+1 种基金Shandong Provincial Natural Science Foundation(ZR2022ME222)National Natural Science Foundation of China(51702187)。
文摘Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.
基金funding by the National Natural Science Foundation of China(Grant number U22A20187)(Grant No.52271147,No.52471175)China Postdoctoral Science Foundation(grant number 2024M751172)。
文摘Recrystallization stands as an essential process that influences the microstructure and properties of magnesium(Mg)alloys,yet its mechanisms remain complex and multifaceted.This review explores the key factors affecting the recrystallization behavior of Mg alloys,emphasizing how their unique structural characteristics impact the driving forces and dynamics of recrystallization.Unlike conventional alloys,Mg alloys exhibit distinctive recrystallization kinetics,which is significantly affected by deformation conditions,such as strain rate,temperature,and processing methods(e.g.,rolling,forging,and extrusion).The process is also influenced by material characteristics,including initial grain size,texture,dislocation density,solute clustering,and stacking fault energy.Additionally,uneven strain distribution,stress concentrations,and stored energy play crucial roles in shaping the formation of recrystallized grains,particularly near grain boundaries.Notably,recrystallization is driven by dislocation accumulation and the availability of slip systems,with new strain-free grains typically forming in regions of high dislocation density.This paper synthesizes the existing literature to provide a comprehensive understanding of the mechanisms and kinetics of recrystallization in Mg alloys,highlighting the influence of microstructural features such as second-phase particles and grain boundary characteristics.It also identifies key challenges and suggests promising directions for future research,including optimizing material compositions and the interaction between deformation conditions via machine learning.
基金supported by the National Natural Science Foun-dation of China(No.52122103)the Shaanxi Province Youth In-novation Team Project(No.22JP042)+1 种基金Shaanxi Province Innova-tion Team Project(Nos.2024RS-CXTD-58 and2023-CXTD-50)Shaanxi International Science and Technology Cooperation Base(No.2020GHJD-10).
文摘Grain boundary hardening is an important mechanism for improving the strength and ductility of metal materials.However,the industrial fabrication of fine-grained FeCrAl alloys was limited by the interaction between the recrystallization and precipitation.Here,we report the facile mass production of fine-grained FeCrAl alloys by Si alloying and manipulation of the recrystallization process through introducing heterogeneous Si-rich Laves precipitates.The pre-precipitation of heterogeneous Laves phase not only promotes subsequent recrystallization grain nucleation by the PSN(Particles simultaneous nucleation)and SIBM(Strain-induced grain boundary migration)mechanisms,but also provides resistance to grain growth by the Zener pinning mechanism.Moreover,continuous grain refinement can be achieved by intensifying the heterogeneous Laves precipitates through decreasing their formation energy.This approach enables the preparation of a fully recrystallized fine-grain structure with a grain size of 4.6μm without the introduction of segregated boundaries.Consequently,an unprecedented synergy enhancement of strength(σ_(y)=625 MPa,σ_(uts)=867 MPa,)and ductility(ε_(u)=13.8%)is achieved in the fine-grain structured FeCrAl alloys compared with the coarse grain counterpart.The experimental results prove that the proposed strategy is appropriate for developing high strength and ductility FeCrAl alloys,and further boosting its potential applications as accident-tolerant-fuel cladding in nuclear reactors.In addition,this grainrefinement strategy should be extendable to other alloy systems,where there is a significant difference between precipitation and recrystallization temperatures.
基金the National Natural Science Foundation of China(Nos.31971246&52274387)the Fundamental Research Funds for the Central Universities(No.YG2023QNA21)the Shanghai Science and Technology Commission(No.20S31900100)for their financial and project support.
文摘The remodeling of macrophages mediated by biomaterials is an important step in osseointegration.The biointerfacial characteristics shaped by implants and the bioenergetic state derived from macrophages are considered the key to macrophage reprogramming.In this study,the integrated Ti/Zn composites with optimized morphology and bioactive phase were prepared by friction stir processing,which could meet the multi-biofunctional requirements in the application of narrow-diameter implants.The severe plastic deformation and the hindrance of Zn particles to grain growth promote grain refinement,resulting in enhanced mechanical properties.The cell interfacial adhesion mediated by the grain boundary collaborated the energy metabolism reprogramming induced by the released Zn ion,promoting jointly anti-inflammatory cascade in macrophages and favorable osteogenesis in bone marrow mesenchymal stem cells(BMSCs).This study provides a new simultaneous approach of morphology and composition modification for titanium implants,and reveals the important role of grain size and bioactive element in the reversion of macrophage fate as well.
基金supported by Fundamental Research Funds for Central Universities(Grant No.N2107009)Reviving-Liaoning Excellence Plan(Grant No.XLYC2203186).
文摘The Fe–Mn damping alloys possess considerable damping capacity,but their yield strength is rather low.The 800 MPa Fe–Mn alloy with expected damping capacity was designed by the combination of grain refinement and ε-martensite introduction.The yield strength can be greatly raised to around 700 MPa by refining grain size from 88.4 to 1.8μm.Although there exist numerous stacking faults in the fine-grained alloy,the damping capacity is strongly deteriorated due to the suppression of thermally activated ε-martensite.We demonstrate that the stacking faults cannot provide effective contribution to damping capacity and hence introduce a considerable volume fraction of stress/strain-induced ε-martensite to raise damping sources,including ε-martensite and γ/ε interfaces,etc.,by a small pre-strain.From this,the damping capacity can be improved,and the yield strength can be further enhanced from nearly 700 MPa to around 800 MPa.Thus,the combination of high yield strength and good damping capacity is realized.
基金supported by the National Nature Science Foun-dation of China(Grant No.50875061).
文摘The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused by strengthening,the strengthening energy is limited and the ideal strengthening effect cannot be obtained.This work aims to propose a novel approach to address this issue effectively.The surface layer with high-density dislocations was obtained by a low-energy surface strengthening method(shot peening)at first.Then the surface strengthening mechanism changes from dislocation strengthen-ing to grain boundary strengthening after electropulsing treatment(EPT).The evolution of residual stress and microstructure was analyzed using multi-scale characterization techniques.The results demonstrate that EPT followed by surface strengthening makes a remarkable 304%increase in fatigue life of TC11 titanium alloy.The enhancement of fatigue life can be attributed to the grain refinement accompanied by the formation of nanotwins and sub-grains in the surface-strengthened layer,as well as the reduction in dislocation density within the substrate after EPT.This study demonstrates the significant potential of EPT in further enhancing the fatigue life of surface pre-strengthened thin-walled components.
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.20210302124220)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.
基金Funded by the Basic Research Project in Shanxi Province(No.202103021224183)the 2024 Science and Technology PlanProject of Jiaozuo City,Henan Province(No.2024410001)。
文摘The evolution of the microstructure and morphology of Cu55Ni45 and Cu60Ni40 alloys under varying degrees of undercooling was investigated through molten glass purification and cyclic superheating technology.By increasing the Cu content,the effect of Cu on the evolution of the microstructure and morphology of the Cu-Ni alloy during undercooling was studied.The mechanism of grain refinement at different degrees of undercooling and the effect of Cu content on its solidification behaviour were investigated.The solidification behaviour of Cu55Ni45 and Cu60Ni40 alloys was investigated using infrared thermometry and high-speed photography.The results indicate that both Cu55Ni45 and Cu60Ni40 alloy melts undergo only one recalescence during rapid solidification.The degree of recalescence increases approximately linearly with increasing undercooling.The solidification front of the alloy melts undergoes a transition process from a small-angle plane to a sharp front and then to a smooth arc.However,the growth of the subcooled melt is constrained to a narrow range,facilitating the formation of a coarse dendritic crystal morphology in the Cu-Ni alloy.At large undercooling,the stress breakdown of the directionally growing dendrites is primarily caused by thermal diffusion.The strain remaining in the dendritic fragments provides the driving force for recrystallisation of the tissue to occur,which in turn refines the tissue.
基金Funded by the Basic Research Project in Shanxi Province(No.202103021224183)the 2024 Science and Technology Plan Project of Jiaozuo City,Henan Province(No.2024410001)。
文摘By applying the rapid solidification technique of deep undercooling,Cu65Ni35 and Cu60Ni40 alloys achieved maximum undercoolings of 284 and 222 K,respectively.Microstructural images captured reveal grain refinement in both alloys across both large and small undercooling ranges.High-speed photography was used to analyze the relationship between solidification front morphology and undercooling,showing that dendrite remelting and fragmentation caused grain refinement under small undercooling,while stress-induced recrystallization is responsible under large undercooling.Microhardness testing further demonstrates a sudden drop in microhardness near the critical undercooling point,providing evidence for grain refinement due to recrystallization in large undercooling tissues.
基金supported by the Liaoning Provincial Science and Technology Program-Excellent Youth Fund Program(2023JH3/10200002)National Key Research and Development Program of China(2022YFC2406000)+1 种基金National Natural Science Foundation of China(52301308)IMR Innovation fund(2023-PY15).
文摘Ti6Al4V alloy has been widely used in dental applications,such as orthodontic mini-implants.However,it has been reported that fluoride ions could obviously accelerate the corrosion of implant materials and affect their performance.This work aimed to improve the F^(−)erosion resistance of Ti6Al4V alloy through the strategy of both Cu addition and grain refinement.As contrasted with Ti6Al4V alloy,both the coarse-and ultrafine-grained Ti6Al4V-5Cu alloys effectively mitigated the acceleration of the fluoride ions to the anode process,because Cu substituents blocked the continuous damage of F·_(O) doped in the passive film.Furthermore,grain refinement enhanced the protective ability of the passive film,more oxides and less adsorption amount of fluorides presented in the passive film of ultrafine-grained Ti6Al4V-5Cu alloy than those of coarse-grained Ti6Al4V-5Cu alloy.Under the combination of Cu alloying and grain refinement,the ultrafine-grained Ti6Al4V-5Cu alloy is greatly appropriate for the fabrication of orthodontic devices.
基金financially supported by the Major Projects in Aviation Engines and Gas Turbines (Grant No.2019-VI-0020-0136)the National Key Research and Development Program of China (Grant Nos.2022YFB3705101&2022YFB3705102)+1 种基金the National Natural Science Foundation of China (Grant No.U1708253)the Fundamental Research Funds for the Central Universities,China (Grant No.N2302005)。
文摘The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.
基金financially supported by Silesian University of Technology,Poland(No.11/030/BK_23/1127)V?B–Technical University of Ostrava Czech Republic(No.CZ.02.1.01/0.0/0.0/17_049/0008399)。
文摘The effects of forward extrusion as well as extrusion combined with reversible torsion(KoBo extrusion),followed by additional deformation via the MaxStrain module of the Gleeble thermomechanical simulator,on the microstructure,mechanical properties,and electrical conductivity of a Cu−0.7Mg(wt.%)alloy,were investigated.The simulation results highlighted the critical influence of processing history on determining the equivalent strain distribution.The sample subjected to forward extrusion at 400℃and subsequent MaxStrain processing(FM sample),possessed 76%lower grain size compared to the sample processed solely with MaxStrain(AM sample).Likewise,the KoBo-extruded and MaxStrain-processed sample(KM sample)exhibited 66%smaller grain size compared to the AM sample.Tensile test results revealed that the AM,FM,and KM samples,respectively,possessed 251%,288%,and 360%higher yield strength,and 95%,121%,and 169%higher tensile strength compared to the initial annealed alloy,as a result of grain refinement as well as deformation strengthening.Finally,the electrical conductivity measurements revealed that AM,FM,and KM samples,respectively,possessed electrical conductivity values of 37.9,35.6,and 32.0 MS/m,which,by considering their mechanical properties,makes them eligible to be categorized as high-strength and high-conductivity copper alloys.
