The surface of AZ91 D magnesium alloy was remelted by plasma beam. The microstructure, composition, hardness, wear and corrosion resistance of the plasma remelted layer（PRL） were characterized. The results show that...The surface of AZ91 D magnesium alloy was remelted by plasma beam. The microstructure, composition, hardness, wear and corrosion resistance of the plasma remelted layer（PRL） were characterized. The results show that there is extremely fine and dendrite structure in the PRL at low magnification observation, which is still composed of α-Mg and β-Mg17Al12 phases. But at high magnification observation, the microstructure of the PRL is equiaxial crystalline grains with size of 3-5 μm. And also the content of α-Mg phase decreases while that of β-Mg17Al12 increases and distributes more uniformly in α-Mg matrix compared with the substrate. The hardness of the PRL is much higher than that of the substrate. There are plastic deformation, grains uprooting and tearing evidence with tiny even dimples in the tensile fracture of the PRL, which are different from the substrate. Furthermore, the surface wear and corrosion resistance of AZ91 D are improved significantly after plasma remelting.展开更多
The sliding wear behavior of a grey cast iron surface remelted by tungsten inert gas （TIG） was studied and compared with the unremelted one in the current work. To evaluate the wear behavior a Pin-on-Disk wear test ...The sliding wear behavior of a grey cast iron surface remelted by tungsten inert gas （TIG） was studied and compared with the unremelted one in the current work. To evaluate the wear behavior a Pin-on-Disk wear test machine was used. Pins which were prepared from the samples with the remelted layers of different thicknesses of 1.2, 1.8, 2.5 and 3 turn were worn on an AISID3 steel counterface having a hardness of 63HRC under the applied loads of 54, 76 and gg N at a constant sliding velocity of 0.45 m/s. Scanning electron microscopy （SEM） equipped with energy dispersive X-ray analysis （EDS） and X-ray diffraction （XRD） techniques were used to characterize worn surface and subsurface and also wear debris obtained from the wear tests under different test conditions. Results showed that surface remelted grey cast iron have better wear properties for all applied normal loads in comparison with unremelted ones. Microscopic studies on the worn surfaces and subsurfaces of samples revealed that dominant wear mechanism for surface remelted samples was mild oxidative, while it was severe for unremelted samples. Increasing remelted layer thickness and then forming grosser microstructure lead to a decline of wear properties, whereas lower thickness of remelted layer with finer microstructure due to having higher cooling rate through remelting process can withstand better against wear.展开更多
For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Rece...For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Recent-ly, a commercially produced foundry ingot,the Duralcan composite of A356 Al alloy +20展开更多
The hardness and wear resistance of sprayed FeBSi coating after laser remelting were much improved by addition of 8 wt-% CeO_2.Microstructural observation on the FeBSi+CeO_2 coating revealed that the formation of mart...The hardness and wear resistance of sprayed FeBSi coating after laser remelting were much improved by addition of 8 wt-% CeO_2.Microstructural observation on the FeBSi+CeO_2 coating revealed that the formation of martensite occurs,as well as the refined grains and the more eutectic and compounds with regular morphology are dis- tributed.While the FeBSi coating free from CeO_2 is a sharp constrast in microstructure.展开更多
The microstructural variation in the non dendritic AlSi 7Mg samples remelted in the semi solid state has been investigated. It is proposed that the primary α Al phases are mainly coarsened by connecting the secondary...The microstructural variation in the non dendritic AlSi 7Mg samples remelted in the semi solid state has been investigated. It is proposed that the primary α Al phases are mainly coarsened by connecting the secondary arms or fine primary α Al phases together at the stage of a small quantity of liquid and slowly coarsened through diffusion at the stage of a great quantity of liquid. The dynamical coarsening equation controlled by diffusion is in good agreement with the equation of d 3- d 3 0= kt and the effect of the starting microstructures on the coarsening of primary α Al phases is gradually decreased when the soaking time is long enough.展开更多
The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experime...The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experimental results show that the solid particles obtained with self-inoculation method are in smaller grain size and globular shape after partial remelting, compared with those prepared with other casting methods. In the optimized process conditions, the average size of solid particles of partially remelted billet is 65 μm, and the shape factor is 1.12. The process parameters, i.e. pouting temperature, addition amount of self-inoculants, and the slope angle of multi-stream mixing cooling chalmel have influence on the microstructure of partially remelted billet. The optimized temperature is from 680 ℃ to 700 ℃, addition amount of self-inoculants is between 5% and 7% （mass fraction）, slope angle of multi-stream mixing cooling channel is between 30° and 45°, with which the dendritic microstructure of as-cast billet can be avoided, and the size of solid particles ofremelted billet is reduced.展开更多
Laser surface remelting of steels with different Cr contents has been performed by using a CO_2 laser. The results of oxidation tests showed that the effects of laser remelting on the oxidation resistance of Cr-contai...Laser surface remelting of steels with different Cr contents has been performed by using a CO_2 laser. The results of oxidation tests showed that the effects of laser remelting on the oxidation resistance of Cr-containing steels have close relation to the Cr contents and microstructures of the steels. The re- sistance to high temperature oxidation of 18-8 and HK40 at 1273 K can be obviously improved by laser remelting, whereas laser remelting showed little effect on the oxidation resistance of Fe-6Cr and Cr30 at 1173-1273 K.展开更多
The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a m...The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a magnetically controlled spin-vibration induced by the interaction of the ASMFs and the remelting current exists at the consumable electrode tip,resulting in thinner liquid melt film and smaller droplets.With the increase in magnetic flux density,the optimization effect of ASMFs on electroslag remelting process increases and reaches the peak with a 40 mT ASMF,then decreases.The cleanliness of the ingots was improved,and the count of inclusions larger than 5μm was reduced.The microstructure of the ingots processed with a 40 mT ASMF was significantly refined.The depth of the metallic molten pool was reduced from 45.2 to 17.5 mm with the application of 40 mT ASMF.The tensile strength,impact toughness,and Rockwell hardness of the ingots obtained under the 40 mT ASMF were significantly improved.The mechanisms of the spin-vibration occurring at the electrode tip end were interpreted in detail to elucidate the effect of ASMFs.展开更多
A numerical model of the VAR process has been developed in close collaboration with titanium and zirconium producers.The model is based on the solution of the coupled heat,mass and momentum transport equations in the ...A numerical model of the VAR process has been developed in close collaboration with titanium and zirconium producers.The model is based on the solution of the coupled heat,mass and momentum transport equations in the whole ingot(liquid pool,mushy zone and solidified part)using a finite volume method.It accounts for electromagnetic stirring, buoyancy flows and turbulence effects.Solidification mechanisms implemented in the model include a full coupling between energy and solute transport in the mushy zone.The numerical model has been applied to simulate the remelting of Ti6-4.The influence of the applied magnetic field on the fluid flow and segregation behaviour,for a number of different stirring practices,is presented and discussed.Also,the macrosegregation in Zy4 ingots is investigated.The comparison between the predicted segregation and the experimental results shows the importance of accounting for both the stirring and thermosolutal convection to forecast properly the segregation in remelted ingots.展开更多
The microstructure,eutectic carbides and intermetallic compounds in as-cast ingots with varying Nb contents produced by electroslag remelting were studied.The solidification behavior,microsegregation of alloying eleme...The microstructure,eutectic carbides and intermetallic compounds in as-cast ingots with varying Nb contents produced by electroslag remelting were studied.The solidification behavior,microsegregation of alloying elements and its influence on precipitates were analyzed.The increase in Nb content from 0.64 to 1.40 wt.%has no effect on the dendrite morphology and secondary dendrite arm spacing.The total area fraction of eutectic NbC and Laves phase in as-cast ingots increases with the increase in Nb content.The eutectic precipitates in the ingot with 0.64 wt.%Nb are mainly NbC,and the others are Fe_(2)Nb-type Laves phase.Increasing the Nb content of the steel significantly promotes the precipitation of Laves phases and lowers the precipitation temperature of NbC eutectic carbides.Eutectic carbide M_(2)C is precipitated only in the ingot with 1.4 wt.%Nb.The average concentration of Nb in both interdendritic and intragranular regions increases with the increase in Nb content of the steel,leading to a change in the morphology of Fe_(2)Nb-type Laves phase from honeycomb to blocky.Increasing the Nb content exerts little effect on the microsegregation degrees of Si,Mo,Cr and Ni in the steel.展开更多
The corrosion behavior of High-Velocity Oxygen Fuel (HVOF) sprayed MCrAlY coatings obtained from CoNiCrAlY particles (wt. 8% Al) mechanically doped with Al2O3 nanopowder was investigated before and after laser remelti...The corrosion behavior of High-Velocity Oxygen Fuel (HVOF) sprayed MCrAlY coatings obtained from CoNiCrAlY particles (wt. 8% Al) mechanically doped with Al2O3 nanopowder was investigated before and after laser remelting. The latter process was applied in order to achieve a homogeneous structure as well as better mechanical properties for the coating (reduced brittleness offered by the presence of the Al2O3 nanoparticles). Another important task of the laboratory investigations was the investigation of the corrosion behavior of the modified coatings. The results obtained from the potentiodynamic polarization measurements carried out in a chloride environment revealed an enhanced corrosion resistance of the laser remelted coatings comprising a refined microstructure. Microhardness measurements of the modified coatings revealed lower values in comparison with that of the samples in as-sprayed status. This observation leads to the assumption that a concomitant improvement of coatings ductility occurred as well.展开更多
Electroslag remelting(ESR) is an important metallurgical process for producing high-purity materials with homogeneous compositions and sound microstructures,and its typical products are ingots or simple castings.The c...Electroslag remelting(ESR) is an important metallurgical process for producing high-purity materials with homogeneous compositions and sound microstructures,and its typical products are ingots or simple castings.The core principle involves the resistive melting of a consumable electrode within a slag pool,followed by the refining of molten metal droplets as they traverse the slag,and subsequent sequential solidification in a water-cooled mold.However,conventional ESR processes face limitations in producing large or complex-shaped components,enhancing production efficiency,achieving highly specialized microstructures,and meeting ultra-high purity demands for advanced applications.Advanced composite ESR technologies have been developed to overcome these limitations by innovatively modifying key process aspects.For instance,electrode systems are improved using vibration,rotation,or multiple electrodes.Enhanced mold design and solidification control are achieved through techniques including conductive molds,mold rotation,and ingot withdrawal.Precise control of the process is realized through the use of protective gas,vacuum,or elevated pressure,as well as the application of external fields such as magnetic fields or ultrasonic vibration.This review comprehensively summarizes these advanced techniques,examining their principles and characteristics,and discussing their specific advantages and challenges.展开更多
Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back ...Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back scattering diffraction(EBSD)observations showed that the grains in melted zone(MZ)transformed into equiaxial grains with an average size of 1.31μm,and the grains in heat affected zone(HAZ)were refined.Moreover,the texture intensity dropped significantly from 13.86 to 6.35 in MZ and 10.79 in HAZ.The temperature gradient(G)to solidification rate(R)ratio decreased when the laser scanning speed slowed down to a certain extent in the LR process,which effectively improved the highly preferred orientation and filled the hole defects in the surface of LPBF-Ti6Al4V.Furthermore,the hardness,wear resistance and corrosion resistance of the surface of the LPBF samples were improved by LR treatment.展开更多
The hot deformation behavior and microstructure evolution of industrial grade American Iron and Steel Institute(AISI)M35 high-speed steel produced by electroslag remelting at different parameters were investigated.The...The hot deformation behavior and microstructure evolution of industrial grade American Iron and Steel Institute(AISI)M35 high-speed steel produced by electroslag remelting at different parameters were investigated.The results indicated that grains coarsening and M2C carbides decomposing appeared in the steel at 1150℃for 5 min,and the network carbides were broken and deformed radially after the hot deformation.A constitutive equation was determined based on the corrected flow stress-strain curves considering the effects of friction and temperature,and a constitutive model with strain-compensated was established.The dynamic recrystallization(DRX)characteristic values were calculated based on the Cingara-McQueen model,and the grain distribution under different conditions was observed and analyzed.Significantly,the action mechanisms of carbides on the DRX were illuminated.It was found from a functional relation between average grain size and Z parameter that grain size increased with increasing temperature and decreasing strain rate.Optimal parameters for the hot deformation were determined as 980-1005℃~0.01-0.015 s^(−1)and 1095-1110℃~0.01-0.037 s^(−1)at the strain ranging from 0.05 to 0.8.Increasing the strain rate appropriately during deformation process was suggested to obtain fine and uniformly distributed carbides.Besides,an industrial grade forging deformation had also verified practicability of the above parameters.展开更多
Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spot...Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.展开更多
In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled ...In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled transfer,which has the limitations of high cost,a large amount of calculating data and high computing power requirements.A novel network based on physics-informed neural network(PINN)was designed to realize the fast and high-fidelity prediction of the distribution of electromagnetic field and temperature field in ESR process.The physical laws were combined with the deep learning network through PINN,and physical constraints were embedded to achieve effective solution of partial differential equations(PDEs).PINN was used to minimize the loss function consisting of data error,physical information error and boundary condition error.The physical laws and boundary condition constraints in the ESR process were considered to maintain high PDE solution accuracy under different spatial and temporal resolutions.Automatic differentiation(Autodiff)technique and gradient descent algorithm were used to optimize the network parameters.The experimental results show that compared with the mechanistic models,PINN can effectively replace thermal experiments to realize the physical field simulation of ESR process with only a few experimental data,which can avoid the disadvantages of pure data-driven network simulation that requires a large amount of training data.Moreover,the solution of PINN has good physical interpretability and reliability of simulation results.For simulating electromagnetic field and temperature field distribution,the training time of the network is only 140 and 203 s,and the regression indicators of root mean square error can reach 12.65 and 13.76,respectively.展开更多
TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si de...TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si decreases from 65.8μm in the base metal(BM)to 7.1μm in RZ.The grain size of the RZ is refined to be approximately one-seventh that of the BM.The cellular microstructure in the RZ is characterised by theα(Al)in the centre and intermetallics preferentially located at the cellular boundaries.The results of the mechanical properties demonstrate that the average hardness value of RZ increases by 39%compared to that of BM.For the transverse samples,the ultimate tensile strength increases by~24.5%,which can be attributed to the solution strengthening of Si inα(Al).The average fracture toughness values are 15.0 and 12.7 MPa·m^(1/2)forα(Al)in BM and RZ,respectively.展开更多
To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal...To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal,and flow fields.Numerical simulation was performed to analyze the dynamic evolution of varying-mass electrode fragments during the vacuum arc remelting(VAR)of a∅508-mm TC2 titanium alloy in-got.The results indicate that Mn segregation caused by 15-kg electrode fragmentation during the VAR process of a TC2 titanium alloy ingot corresponds to the segregation observed in the TC2 titanium alloy bar.The numerical simulation of the VAR process provides effective result prediction and technical support for solving practical problems in smelting.展开更多
The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary ...The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy.Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction.Solute elements segregation was analyzed using an electron probe microanalyzer.FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism.Compared to traditional VAR,magnetic-controlled VAR generates a horizontal circulation,which makes a shallower and flatter molten pool and a more even temperature distribution.In the time dimension,the local solidification time is shortened,and the concentration of solute elements will be alleviated.In the spatial dimension,the secondary dendrite arm spacing decreases,alleviating the degree of inter-dendritic segregation.Consequently,the possibility of forming a segregation diminishes.Both aspects promote the even distribution of solute atoms,resulting in less segregation and hindering the development of primary carbide.This leads to the refinement of primary carbide size and its uniform distribution.The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot,causing it to expand more axially along the ingot,but also refines primary carbides and improves tensile and wear-resistant mechanical properties.展开更多
A novel process that combines squeeze casting with partial remelting to obtain AZ61 magnesium alloy with semi-solid microstructures was proposed. In this route, the squeeze casting was used to predeform the magnesium ...A novel process that combines squeeze casting with partial remelting to obtain AZ61 magnesium alloy with semi-solid microstructures was proposed. In this route, the squeeze casting was used to predeform the magnesium alloy billets to obtain small dendritic structures. During subsequent partial remelting, small dendritic structures transform into globular grains surrounded by liquid films. The results show that the squeeze casting AZ61 alloy after partial remelting produces more ideal, finer semi-solid microstructure compared with as-cast AZ61 alloy treated by the same isothermal holding conditions. Moreover, the mechanical properties of the thixoformed AZ61 alloy prepared by squeeze casting plus partial remelting are better than those of the thixoformed alloy prepared by conventional casting plus partial remelting.展开更多
基金Projects(51072104,51272141)supported by the National Natural Science Foundation of ChinaProject(ts20110828)supported by the Taishan Scholars Project of Shandong Province,ChinaProject(2015AA034404)supported by the Ministry of Science and Technology of China
文摘The surface of AZ91 D magnesium alloy was remelted by plasma beam. The microstructure, composition, hardness, wear and corrosion resistance of the plasma remelted layer（PRL） were characterized. The results show that there is extremely fine and dendrite structure in the PRL at low magnification observation, which is still composed of α-Mg and β-Mg17Al12 phases. But at high magnification observation, the microstructure of the PRL is equiaxial crystalline grains with size of 3-5 μm. And also the content of α-Mg phase decreases while that of β-Mg17Al12 increases and distributes more uniformly in α-Mg matrix compared with the substrate. The hardness of the PRL is much higher than that of the substrate. There are plastic deformation, grains uprooting and tearing evidence with tiny even dimples in the tensile fracture of the PRL, which are different from the substrate. Furthermore, the surface wear and corrosion resistance of AZ91 D are improved significantly after plasma remelting.
文摘The sliding wear behavior of a grey cast iron surface remelted by tungsten inert gas （TIG） was studied and compared with the unremelted one in the current work. To evaluate the wear behavior a Pin-on-Disk wear test machine was used. Pins which were prepared from the samples with the remelted layers of different thicknesses of 1.2, 1.8, 2.5 and 3 turn were worn on an AISID3 steel counterface having a hardness of 63HRC under the applied loads of 54, 76 and gg N at a constant sliding velocity of 0.45 m/s. Scanning electron microscopy （SEM） equipped with energy dispersive X-ray analysis （EDS） and X-ray diffraction （XRD） techniques were used to characterize worn surface and subsurface and also wear debris obtained from the wear tests under different test conditions. Results showed that surface remelted grey cast iron have better wear properties for all applied normal loads in comparison with unremelted ones. Microscopic studies on the worn surfaces and subsurfaces of samples revealed that dominant wear mechanism for surface remelted samples was mild oxidative, while it was severe for unremelted samples. Increasing remelted layer thickness and then forming grosser microstructure lead to a decline of wear properties, whereas lower thickness of remelted layer with finer microstructure due to having higher cooling rate through remelting process can withstand better against wear.
文摘For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Recent-ly, a commercially produced foundry ingot,the Duralcan composite of A356 Al alloy +20
文摘The hardness and wear resistance of sprayed FeBSi coating after laser remelting were much improved by addition of 8 wt-% CeO_2.Microstructural observation on the FeBSi+CeO_2 coating revealed that the formation of martensite occurs,as well as the refined grains and the more eutectic and compounds with regular morphology are dis- tributed.While the FeBSi coating free from CeO_2 is a sharp constrast in microstructure.
文摘The microstructural variation in the non dendritic AlSi 7Mg samples remelted in the semi solid state has been investigated. It is proposed that the primary α Al phases are mainly coarsened by connecting the secondary arms or fine primary α Al phases together at the stage of a small quantity of liquid and slowly coarsened through diffusion at the stage of a great quantity of liquid. The dynamical coarsening equation controlled by diffusion is in good agreement with the equation of d 3- d 3 0= kt and the effect of the starting microstructures on the coarsening of primary α Al phases is gradually decreased when the soaking time is long enough.
基金Project(2007CB613700) supported by the National Basic Research Program of ChinaProject(50964010) supported by the National Natural Science Foundation of ChinaProject(090WCGA894) supported by the International S&T Cooperation Program of Gansu Province,China
文摘The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experimental results show that the solid particles obtained with self-inoculation method are in smaller grain size and globular shape after partial remelting, compared with those prepared with other casting methods. In the optimized process conditions, the average size of solid particles of partially remelted billet is 65 μm, and the shape factor is 1.12. The process parameters, i.e. pouting temperature, addition amount of self-inoculants, and the slope angle of multi-stream mixing cooling chalmel have influence on the microstructure of partially remelted billet. The optimized temperature is from 680 ℃ to 700 ℃, addition amount of self-inoculants is between 5% and 7% （mass fraction）, slope angle of multi-stream mixing cooling channel is between 30° and 45°, with which the dendritic microstructure of as-cast billet can be avoided, and the size of solid particles ofremelted billet is reduced.
文摘Laser surface remelting of steels with different Cr contents has been performed by using a CO_2 laser. The results of oxidation tests showed that the effects of laser remelting on the oxidation resistance of Cr-containing steels have close relation to the Cr contents and microstructures of the steels. The re- sistance to high temperature oxidation of 18-8 and HK40 at 1273 K can be obviously improved by laser remelting, whereas laser remelting showed little effect on the oxidation resistance of Fe-6Cr and Cr30 at 1173-1273 K.
基金This work is supported by the National Key Research and Development Program of China under Grant numbers of 2016YFB0300401,2018YFF0109404,and 2016YFB0301401the National Natural Science Foundation of China under Grant numbers of U1860202,U1732276,50134010,51704193,51904184,and 52004156the Users with Excellence Program of Hefei Science Center CAS under Grant number of 2019HSC-UE010,and the Changjiang Scholar Program of Chinese Ministry of Education.
文摘The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a magnetically controlled spin-vibration induced by the interaction of the ASMFs and the remelting current exists at the consumable electrode tip,resulting in thinner liquid melt film and smaller droplets.With the increase in magnetic flux density,the optimization effect of ASMFs on electroslag remelting process increases and reaches the peak with a 40 mT ASMF,then decreases.The cleanliness of the ingots was improved,and the count of inclusions larger than 5μm was reduced.The microstructure of the ingots processed with a 40 mT ASMF was significantly refined.The depth of the metallic molten pool was reduced from 45.2 to 17.5 mm with the application of 40 mT ASMF.The tensile strength,impact toughness,and Rockwell hardness of the ingots obtained under the 40 mT ASMF were significantly improved.The mechanisms of the spin-vibration occurring at the electrode tip end were interpreted in detail to elucidate the effect of ASMFs.
基金Item Sponsored as a part of the OPERAS (Optimizing Processes based on Electrode Remelting with Arc or Slag) Project by the French National Research Agency (ANR-08-MAPR-0006-04)
文摘A numerical model of the VAR process has been developed in close collaboration with titanium and zirconium producers.The model is based on the solution of the coupled heat,mass and momentum transport equations in the whole ingot(liquid pool,mushy zone and solidified part)using a finite volume method.It accounts for electromagnetic stirring, buoyancy flows and turbulence effects.Solidification mechanisms implemented in the model include a full coupling between energy and solute transport in the mushy zone.The numerical model has been applied to simulate the remelting of Ti6-4.The influence of the applied magnetic field on the fluid flow and segregation behaviour,for a number of different stirring practices,is presented and discussed.Also,the macrosegregation in Zy4 ingots is investigated.The comparison between the predicted segregation and the experimental results shows the importance of accounting for both the stirring and thermosolutal convection to forecast properly the segregation in remelted ingots.
基金support by the National Natural Science Foundation of China(Grant Nos.51874026 and 52074027)the financial support from the State Key Laboratory of Advanced Metallurgy(Grant No.41621024).
文摘The microstructure,eutectic carbides and intermetallic compounds in as-cast ingots with varying Nb contents produced by electroslag remelting were studied.The solidification behavior,microsegregation of alloying elements and its influence on precipitates were analyzed.The increase in Nb content from 0.64 to 1.40 wt.%has no effect on the dendrite morphology and secondary dendrite arm spacing.The total area fraction of eutectic NbC and Laves phase in as-cast ingots increases with the increase in Nb content.The eutectic precipitates in the ingot with 0.64 wt.%Nb are mainly NbC,and the others are Fe_(2)Nb-type Laves phase.Increasing the Nb content of the steel significantly promotes the precipitation of Laves phases and lowers the precipitation temperature of NbC eutectic carbides.Eutectic carbide M_(2)C is precipitated only in the ingot with 1.4 wt.%Nb.The average concentration of Nb in both interdendritic and intragranular regions increases with the increase in Nb content of the steel,leading to a change in the morphology of Fe_(2)Nb-type Laves phase from honeycomb to blocky.Increasing the Nb content exerts little effect on the microsegregation degrees of Si,Mo,Cr and Ni in the steel.
文摘The corrosion behavior of High-Velocity Oxygen Fuel (HVOF) sprayed MCrAlY coatings obtained from CoNiCrAlY particles (wt. 8% Al) mechanically doped with Al2O3 nanopowder was investigated before and after laser remelting. The latter process was applied in order to achieve a homogeneous structure as well as better mechanical properties for the coating (reduced brittleness offered by the presence of the Al2O3 nanoparticles). Another important task of the laboratory investigations was the investigation of the corrosion behavior of the modified coatings. The results obtained from the potentiodynamic polarization measurements carried out in a chloride environment revealed an enhanced corrosion resistance of the laser remelted coatings comprising a refined microstructure. Microhardness measurements of the modified coatings revealed lower values in comparison with that of the samples in as-sprayed status. This observation leads to the assumption that a concomitant improvement of coatings ductility occurred as well.
基金supported by the National Natural Science Foundation of China (NSFC 52175352)。
文摘Electroslag remelting(ESR) is an important metallurgical process for producing high-purity materials with homogeneous compositions and sound microstructures,and its typical products are ingots or simple castings.The core principle involves the resistive melting of a consumable electrode within a slag pool,followed by the refining of molten metal droplets as they traverse the slag,and subsequent sequential solidification in a water-cooled mold.However,conventional ESR processes face limitations in producing large or complex-shaped components,enhancing production efficiency,achieving highly specialized microstructures,and meeting ultra-high purity demands for advanced applications.Advanced composite ESR technologies have been developed to overcome these limitations by innovatively modifying key process aspects.For instance,electrode systems are improved using vibration,rotation,or multiple electrodes.Enhanced mold design and solidification control are achieved through techniques including conductive molds,mold rotation,and ingot withdrawal.Precise control of the process is realized through the use of protective gas,vacuum,or elevated pressure,as well as the application of external fields such as magnetic fields or ultrasonic vibration.This review comprehensively summarizes these advanced techniques,examining their principles and characteristics,and discussing their specific advantages and challenges.
基金supported by the National Natural Science Foundation of China(No.51871243)the National Key Laboratory of Strength and Structural Integrity,China(No.ASSIKFJJ202304001)+3 种基金the State Key Laboratory of Precision Blasting and Hubei Key Laboratory of Blasting Engineering,China(No.PBSKL2022C01)the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology,China(No.HT-CSNS-DG-CD-0092/2021)the Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province,China(No.22kfgk06)the Hubei Longzhong Laboratory,China(No.2022KF-08)。
文摘Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back scattering diffraction(EBSD)observations showed that the grains in melted zone(MZ)transformed into equiaxial grains with an average size of 1.31μm,and the grains in heat affected zone(HAZ)were refined.Moreover,the texture intensity dropped significantly from 13.86 to 6.35 in MZ and 10.79 in HAZ.The temperature gradient(G)to solidification rate(R)ratio decreased when the laser scanning speed slowed down to a certain extent in the LR process,which effectively improved the highly preferred orientation and filled the hole defects in the surface of LPBF-Ti6Al4V.Furthermore,the hardness,wear resistance and corrosion resistance of the surface of the LPBF samples were improved by LR treatment.
基金support from Open Project of State Key Laboratory of Advanced Metallurgy,University of Science and Technology Beijing(No.41622030)Danyang Coinch New Material Technology Co.,Ltd.
文摘The hot deformation behavior and microstructure evolution of industrial grade American Iron and Steel Institute(AISI)M35 high-speed steel produced by electroslag remelting at different parameters were investigated.The results indicated that grains coarsening and M2C carbides decomposing appeared in the steel at 1150℃for 5 min,and the network carbides were broken and deformed radially after the hot deformation.A constitutive equation was determined based on the corrected flow stress-strain curves considering the effects of friction and temperature,and a constitutive model with strain-compensated was established.The dynamic recrystallization(DRX)characteristic values were calculated based on the Cingara-McQueen model,and the grain distribution under different conditions was observed and analyzed.Significantly,the action mechanisms of carbides on the DRX were illuminated.It was found from a functional relation between average grain size and Z parameter that grain size increased with increasing temperature and decreasing strain rate.Optimal parameters for the hot deformation were determined as 980-1005℃~0.01-0.015 s^(−1)and 1095-1110℃~0.01-0.037 s^(−1)at the strain ranging from 0.05 to 0.8.Increasing the strain rate appropriately during deformation process was suggested to obtain fine and uniformly distributed carbides.Besides,an industrial grade forging deformation had also verified practicability of the above parameters.
基金financially supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064).
文摘Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.
基金supported by National Natural Science Foundation of China(52274323 and 524743495)the Postdoctoral Fellowship Program of CPSF under Grant Number GZC20240231.
文摘In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled transfer,which has the limitations of high cost,a large amount of calculating data and high computing power requirements.A novel network based on physics-informed neural network(PINN)was designed to realize the fast and high-fidelity prediction of the distribution of electromagnetic field and temperature field in ESR process.The physical laws were combined with the deep learning network through PINN,and physical constraints were embedded to achieve effective solution of partial differential equations(PDEs).PINN was used to minimize the loss function consisting of data error,physical information error and boundary condition error.The physical laws and boundary condition constraints in the ESR process were considered to maintain high PDE solution accuracy under different spatial and temporal resolutions.Automatic differentiation(Autodiff)technique and gradient descent algorithm were used to optimize the network parameters.The experimental results show that compared with the mechanistic models,PINN can effectively replace thermal experiments to realize the physical field simulation of ESR process with only a few experimental data,which can avoid the disadvantages of pure data-driven network simulation that requires a large amount of training data.Moreover,the solution of PINN has good physical interpretability and reliability of simulation results.For simulating electromagnetic field and temperature field distribution,the training time of the network is only 140 and 203 s,and the regression indicators of root mean square error can reach 12.65 and 13.76,respectively.
基金the financial support of the National Natural Science Foundation of China(Nos.52205394,12202251,52305432),ChinaPostdoctoral Science Foundation(No.2021M702024)+3 种基金Ministry of Education Industry-School Cooperative Education Project,China(No.220606517023742)Natural Science Foundation of Shandong Province,China(No.ZR2022QE122)the Open Projects Fund of State Key Laboratory of Mechanical System and Vibration,China(No.MSV202215)Shanghai Key Laboratory of Digital Manufacture of Thin-walled Structure,China(No.202302).
文摘TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si decreases from 65.8μm in the base metal(BM)to 7.1μm in RZ.The grain size of the RZ is refined to be approximately one-seventh that of the BM.The cellular microstructure in the RZ is characterised by theα(Al)in the centre and intermetallics preferentially located at the cellular boundaries.The results of the mechanical properties demonstrate that the average hardness value of RZ increases by 39%compared to that of BM.For the transverse samples,the ultimate tensile strength increases by~24.5%,which can be attributed to the solution strengthening of Si inα(Al).The average fracture toughness values are 15.0 and 12.7 MPa·m^(1/2)forα(Al)in BM and RZ,respectively.
文摘To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal,and flow fields.Numerical simulation was performed to analyze the dynamic evolution of varying-mass electrode fragments during the vacuum arc remelting(VAR)of a∅508-mm TC2 titanium alloy in-got.The results indicate that Mn segregation caused by 15-kg electrode fragmentation during the VAR process of a TC2 titanium alloy ingot corresponds to the segregation observed in the TC2 titanium alloy bar.The numerical simulation of the VAR process provides effective result prediction and technical support for solving practical problems in smelting.
基金supported by the National Natural Science Foundation of China(Grant numbers 52204347,52274385,52004156,51904184,and 52204392)the National Key Research and Development Program of China(Grant number 2022YFC2904900)+1 种基金the Science and Technology Commission of Shanghai Municipality(13JC14025000,15520711000)the Shi Changxu Innovation Center for Advanced Materials(SCXKFJJ202204).
文摘The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy.Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction.Solute elements segregation was analyzed using an electron probe microanalyzer.FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism.Compared to traditional VAR,magnetic-controlled VAR generates a horizontal circulation,which makes a shallower and flatter molten pool and a more even temperature distribution.In the time dimension,the local solidification time is shortened,and the concentration of solute elements will be alleviated.In the spatial dimension,the secondary dendrite arm spacing decreases,alleviating the degree of inter-dendritic segregation.Consequently,the possibility of forming a segregation diminishes.Both aspects promote the even distribution of solute atoms,resulting in less segregation and hindering the development of primary carbide.This leads to the refinement of primary carbide size and its uniform distribution.The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot,causing it to expand more axially along the ingot,but also refines primary carbides and improves tensile and wear-resistant mechanical properties.
基金Project(51405466)supported by the National Natural Science Foundation of ChinaProject(Y32Z010F10)supported by the Western Light Program of the Chinese Academy of Sciences+1 种基金Project(cstc2014jcyj A50009)supported by Chongqing Research of Application Foundation and Advanced Technology,ChinaProject(cstc2014jcyj A50037)supported by Chongqing Research of Application Foundation and Advanced Technology,China
文摘A novel process that combines squeeze casting with partial remelting to obtain AZ61 magnesium alloy with semi-solid microstructures was proposed. In this route, the squeeze casting was used to predeform the magnesium alloy billets to obtain small dendritic structures. During subsequent partial remelting, small dendritic structures transform into globular grains surrounded by liquid films. The results show that the squeeze casting AZ61 alloy after partial remelting produces more ideal, finer semi-solid microstructure compared with as-cast AZ61 alloy treated by the same isothermal holding conditions. Moreover, the mechanical properties of the thixoformed AZ61 alloy prepared by squeeze casting plus partial remelting are better than those of the thixoformed alloy prepared by conventional casting plus partial remelting.
