The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addr...The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addressed through the use of pulsed laser annealing,where a specific target layer is heated,preventing the overheating of other layers or the substrate.However,this method is only applicable to a very limited range of materials and requires very expensive,powerful pulsed laser sources.Herein,a novel approach for the selective local thermal treatment of thin films is proposed;in this method,short,powerful current pulses are applied to the target conductive layer.The application of two current pulses with a length of 1.5 s induced the crystallization of a 160-nm thick indium tin oxide(ITO)film,resulting in a sheet resistance of 8.68Ω·sq^(-1),an average visible light transmittance of 86.69%,and a figure of merit(FoM)of 293.61.This FoM is an order of magnitude higher than that of the as-prepared ITO film,and to the best of our knowledge,is among the highest reported values for the polycrystalline ITO films.Simulations have shown that even faster and more localized crystallization could be achieved by increasing the power of pulsed current.This novel annealing method is applicable to most semi-conductive or metallic thin films and requires only a relatively inexpensive pulsed current source,making it potentially more attractive than pulsed laser annealing.展开更多
The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-f...The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.展开更多
Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardnes...Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.展开更多
An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency...An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.展开更多
Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military v...Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.展开更多
The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors,...The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.展开更多
The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composit...The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composite rotatable design matrix is used to op- timize the number of experiments. The mathematical models have been developed by response surface method. The adequacy of the models is checked by analysis of vari- ance technique. By using the developed mathematical models, grain size and ultimate tensile strength of the joints can be predicted with 99% confidence level. Contour plots are drawn to study the interaction effect of pulsed current micro plasma arc welding parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 weld joints.展开更多
The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show th...The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show that PC strengthens the migration of boundaries,and then the twin grains,most of which distribute in the coarse grains,“spheroidize”to equiaxed grains,thus separating the coarse grains and refining the microstructure.This process homogenizes the initial microstructure and eliminate the typically lamellar twin grains.Moreover,PC also strengthens the dislocation annihilation.When the specimens were annealed by PC at 300℃for 4 min,the dislocation density was even lower than that annealed by furnaces at 400℃for 3 h before deformation.Furthermore,dislocation annihilation is enhanced with the increase of peak current density and the decrease of pulsed frequency.展开更多
Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by high-temper- ature confocal laser-scanning microscopy. In this way, the influences of pulsed current and pulsed magnetic f...Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by high-temper- ature confocal laser-scanning microscopy. In this way, the influences of pulsed current and pulsed magnetic field complex pretreatment on carbide precipitation and martensite transformation during continuous cooling have been studied. The results show that the electropulsing complex pretreatment promotes the precipitation of M7 C3-type car- bides at high temperature, increases the start and finish temperatures of martensite transformation, and extends the phase transformation time. Martensite prefers to nucleate in the austenite with less precipitation of carbides due to the chemically homogeneous distribution of solute atoms.展开更多
In this paper, Ta/[NiFe（15 nm）/FeMn（10 nm）]/Ta exchange-biased bilayers are fabricated by magnetron sputtering, and their static and dynamic magnetic properties before and after rapid annealing treatment with puls...In this paper, Ta/[NiFe（15 nm）/FeMn（10 nm）]/Ta exchange-biased bilayers are fabricated by magnetron sputtering, and their static and dynamic magnetic properties before and after rapid annealing treatment with pulsed current are charac- terized by using a vibrating sample magnetometer （VSM） and a vector network analyzer （VNA）, respectively. The exchange bias field He and static anisotropy field Hksta decrease from 118.45 Oe （10e = 79.5775 A.m-1） and 126.84 Oe at 0 V to 94.75 Oe and 102.31 Oe at 90 V, respectively, with increasing capacitor voltage, which supplies pulsed current to heat the sample. The effect of flash thermal annealing by pulsed current on the rotational anisotropy （Hrot）, the difference value between static and dynamic magnetic anisotropy, is investigated particularly. The highest Hrot is obtained in the sample annealing with 45-V capacitor （3300 μF） voltage. According to the anisotropic magnetoresistance measurements, it can be explained by the fact that the temperature of the sample is around the blocking temperature of the exchange bias system （Tb） at 45 V, the critical temperature where the formation of more unstable antiferromagnetic grains occurs.展开更多
To improve the plastic deformation performance of a 08AL carbon steel ultra-thin strip,a pulsed electric field was integrated into the plastic processing of the ultra-thin strip,and the effects of high-energy current ...To improve the plastic deformation performance of a 08AL carbon steel ultra-thin strip,a pulsed electric field was integrated into the plastic processing of the ultra-thin strip,and the effects of high-energy current on its deformation ability were investigated.Current-assisted tensile tests were employed,and the results clarified that the pulsed current could reduce the activation energy of faults and promoted dislocation slip within grains and at grain boundaries,leading to a decrease in the deformation resistance of the metal and an increase in its plastic properties.Under the current density of 2.0 A/mm2,the yield strength,tensile strength,and elongation of the rolled sample reached 425 MPa,467 MPa,and 12.5%,respectively.During the rolling process,it was found that the pulsed current promoted the dynamic recrystallization of the ultra-thin strip,reduced its dislocation density and deformation resistance,and promoted the coordinated deformation of the metal.展开更多
The annealing process is usually used to heat-treat cold-deformed 304 stainless steel to improve its microstructure and properties to a certain extent;however,it requires a high temperature and a long time.Because the...The annealing process is usually used to heat-treat cold-deformed 304 stainless steel to improve its microstructure and properties to a certain extent;however,it requires a high temperature and a long time.Because the thickness of the ultrathin strip reaches the micrometer level,it has only one or several layers of grains in the thickness direction,and the control of morphology and performance is complex.In this study,pulsed current loading was used to replace traditional annealing for treating ultrathin strips of cold-rolled 304 stainless steel.After loading a 25 W pulsed current treatment for 5 min on the cold-rolled sample,which had a thickness of 0.035 mm and width of 6 mm,complete recrystallization occurred,and the mechanical properties were significantly improved.At this point,the measured temperature was 540°C.When annealing was used to treat the sample with the same temperature and for the same duration,the microstructure was still dominated by deformed crystals,and the mechanical properties were poor.When annealing was used to obtain a microstructure and properties similar to those obtained via 25 W electrical treatment,the required annealing temperature and time were 810°C and 60 min,respectively.Pulsed current can increase the vacancy diffusion flux in the sample,accelerate the atomic movement,reduce the recrystallization activation energy,and make the cold-rolled 304 stainless steel ultrathin strip completely recrystallize at a lower temperature and in a shorter time.As the current power continued to increase,the recrystallized grains grew.When the pulsed current power was increased to 25 W,the recrystallized grains grew negligibly.Both recrystallization and grain growth have power thresholds.This study provides a novel approach for regulating the microstructure and mechanical properties of ultrathin cold-rolled 304 stainless steel strips.展开更多
The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amount...The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.展开更多
The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and no...The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.展开更多
The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is de...The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element（FE） model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope（OM） and scanning electron microscope（SEM）, and then the diameters of fusion zone and heat affected zone（HAZ） are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer（EDS）, scanning probe microscopy（SPM） and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extension of the crack is presented and can provide a reference for the compressor rotor blade remanufacturing.展开更多
Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,...Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,including bubble,electromagnetic stirring,filtration separation,fluid flow,and sedimentation,often struggle with the removal of fine inclusions.Apart from these known methods,pulsed electric current(PEC),as an emerging technology,has demonstrated immense potential and environmental advantages.PEC offers adjustable current parameters and simple equipment,making it an attractive alternative to traditional methods.Its green energy-saving features and excellent results in regulating inclusion morphology and migration,as well as inhibiting submerged entry nozzle(SEN)clogging,make it a promising technology.In comparison to continuous current technology,PEC has shown significant advantages in regulating inclusions,not only improving purification efficiency but also demonstrating outstanding performance in flow stability and energy consumption.The ability of PEC to efficiently reduce inclusion numbers enhances the purity and quality of molten steel,improving its mechanical properties.Currently,the theoretical basis for controlling the movement of inclusions by current is mainly composed of three major theories:the double electric layer theory,electromagnetic force reverse separation theory,and electric free energy drive theory.These theories together form an important framework for researchers to understand and optimize the behavior of impurity movement controlled by electric current.Looking ahead,PEC is expected to pave the way for new solutions in directional regulation of inclusion migration,efficient inclusion removal,SEN clogging prevention,and the purification of molten steel.展开更多
Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate at...Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate atomic diffusion to achieve ultra-fast spheroidization of carbides.However,the understanding of the mechanism by which different pulse current parameters regulate the dissolution behavior of carbides requires a large amount of experimental data to support,which limits the application of pulse current technology in the field of heat treatment.Based on this,quantify the obtained pulse current processing data to create an important dataset that could be applied to machine learning.Through machine learning,the mechanism of mutual influence between carbide regulation and various factors was elucidated,and the optimal spheroidization process parameters were determined.Compared to the 20 h required for traditional heat treatment,the application of pulsed electric current technology achieved ultra-fast spheroidization of GCr15 bearing steel within 90 min.展开更多
The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental resul...The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.展开更多
A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the allo...A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.展开更多
A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for w...A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.展开更多
基金supported by the National Key R&D Program of China(No.2021YFB2801600)the National Natural Science Foundation of China(Nos.52072060,52202164 and 52021001)the Natural Science Foundation of Sichuan(Nos.2023NSFSC1950 and 2022NSFSC1990).
文摘The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addressed through the use of pulsed laser annealing,where a specific target layer is heated,preventing the overheating of other layers or the substrate.However,this method is only applicable to a very limited range of materials and requires very expensive,powerful pulsed laser sources.Herein,a novel approach for the selective local thermal treatment of thin films is proposed;in this method,short,powerful current pulses are applied to the target conductive layer.The application of two current pulses with a length of 1.5 s induced the crystallization of a 160-nm thick indium tin oxide(ITO)film,resulting in a sheet resistance of 8.68Ω·sq^(-1),an average visible light transmittance of 86.69%,and a figure of merit(FoM)of 293.61.This FoM is an order of magnitude higher than that of the as-prepared ITO film,and to the best of our knowledge,is among the highest reported values for the polycrystalline ITO films.Simulations have shown that even faster and more localized crystallization could be achieved by increasing the power of pulsed current.This novel annealing method is applicable to most semi-conductive or metallic thin films and requires only a relatively inexpensive pulsed current source,making it potentially more attractive than pulsed laser annealing.
文摘The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.
文摘Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.
文摘An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.
文摘Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.
文摘The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.
文摘The paper focuses on developing mathematical models to predict grain size and ul- timate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy. Four factors, five levels, central composite rotatable design matrix is used to op- timize the number of experiments. The mathematical models have been developed by response surface method. The adequacy of the models is checked by analysis of vari- ance technique. By using the developed mathematical models, grain size and ultimate tensile strength of the joints can be predicted with 99% confidence level. Contour plots are drawn to study the interaction effect of pulsed current micro plasma arc welding parameters on fusion zone grain size and ultimate tensile strength of Inconel 625 weld joints.
基金Project(51635005)supported by the National Natural Science Foundation of China
文摘The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show that PC strengthens the migration of boundaries,and then the twin grains,most of which distribute in the coarse grains,“spheroidize”to equiaxed grains,thus separating the coarse grains and refining the microstructure.This process homogenizes the initial microstructure and eliminate the typically lamellar twin grains.Moreover,PC also strengthens the dislocation annihilation.When the specimens were annealed by PC at 300℃for 4 min,the dislocation density was even lower than that annealed by furnaces at 400℃for 3 h before deformation.Furthermore,dislocation annihilation is enhanced with the increase of peak current density and the decrease of pulsed frequency.
基金Item Sponsored by National Natural Science Foundation of China(51204092)Open Project of Shanghai Key Laboratory of Modern Metallurgy and Materials Processing of China(SELF-2012-02)
文摘Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by high-temper- ature confocal laser-scanning microscopy. In this way, the influences of pulsed current and pulsed magnetic field complex pretreatment on carbide precipitation and martensite transformation during continuous cooling have been studied. The results show that the electropulsing complex pretreatment promotes the precipitation of M7 C3-type car- bides at high temperature, increases the start and finish temperatures of martensite transformation, and extends the phase transformation time. Martensite prefers to nucleate in the austenite with less precipitation of carbides due to the chemically homogeneous distribution of solute atoms.
基金Project supported by the Young Science and Technology Innovation Team of Sichuan Province,China(Grant No.2017TD0020)
文摘In this paper, Ta/[NiFe（15 nm）/FeMn（10 nm）]/Ta exchange-biased bilayers are fabricated by magnetron sputtering, and their static and dynamic magnetic properties before and after rapid annealing treatment with pulsed current are charac- terized by using a vibrating sample magnetometer （VSM） and a vector network analyzer （VNA）, respectively. The exchange bias field He and static anisotropy field Hksta decrease from 118.45 Oe （10e = 79.5775 A.m-1） and 126.84 Oe at 0 V to 94.75 Oe and 102.31 Oe at 90 V, respectively, with increasing capacitor voltage, which supplies pulsed current to heat the sample. The effect of flash thermal annealing by pulsed current on the rotational anisotropy （Hrot）, the difference value between static and dynamic magnetic anisotropy, is investigated particularly. The highest Hrot is obtained in the sample annealing with 45-V capacitor （3300 μF） voltage. According to the anisotropic magnetoresistance measurements, it can be explained by the fact that the temperature of the sample is around the blocking temperature of the exchange bias system （Tb） at 45 V, the critical temperature where the formation of more unstable antiferromagnetic grains occurs.
基金supported by the National Natural Science Foundation of China(Nos.51974196,52275361,and 52105390)Open Research Fund from National Key Laboratory of Metal Forming Technology and Heavy Equipment(S2308100.W01)+1 种基金Natural Science Foundation of Shanxi Province(No.20210302124426)Special Funds for the Central Government to Guide Local Science and Technology Development(No.YDZX20191400002149).
文摘To improve the plastic deformation performance of a 08AL carbon steel ultra-thin strip,a pulsed electric field was integrated into the plastic processing of the ultra-thin strip,and the effects of high-energy current on its deformation ability were investigated.Current-assisted tensile tests were employed,and the results clarified that the pulsed current could reduce the activation energy of faults and promoted dislocation slip within grains and at grain boundaries,leading to a decrease in the deformation resistance of the metal and an increase in its plastic properties.Under the current density of 2.0 A/mm2,the yield strength,tensile strength,and elongation of the rolled sample reached 425 MPa,467 MPa,and 12.5%,respectively.During the rolling process,it was found that the pulsed current promoted the dynamic recrystallization of the ultra-thin strip,reduced its dislocation density and deformation resistance,and promoted the coordinated deformation of the metal.
基金Supported by National Natural Science Foundation of China(Grant Nos.51974196,51804215)China Postdoctoral Science Foundation(Grant No.2020T130463)+1 种基金Shanxi Provincial Key Research and Development Program(Grant No.201903D421047)Shanxi Provincial Science and Technology Major Projects(Grant No.20181102015)。
文摘The annealing process is usually used to heat-treat cold-deformed 304 stainless steel to improve its microstructure and properties to a certain extent;however,it requires a high temperature and a long time.Because the thickness of the ultrathin strip reaches the micrometer level,it has only one or several layers of grains in the thickness direction,and the control of morphology and performance is complex.In this study,pulsed current loading was used to replace traditional annealing for treating ultrathin strips of cold-rolled 304 stainless steel.After loading a 25 W pulsed current treatment for 5 min on the cold-rolled sample,which had a thickness of 0.035 mm and width of 6 mm,complete recrystallization occurred,and the mechanical properties were significantly improved.At this point,the measured temperature was 540°C.When annealing was used to treat the sample with the same temperature and for the same duration,the microstructure was still dominated by deformed crystals,and the mechanical properties were poor.When annealing was used to obtain a microstructure and properties similar to those obtained via 25 W electrical treatment,the required annealing temperature and time were 810°C and 60 min,respectively.Pulsed current can increase the vacancy diffusion flux in the sample,accelerate the atomic movement,reduce the recrystallization activation energy,and make the cold-rolled 304 stainless steel ultrathin strip completely recrystallize at a lower temperature and in a shorter time.As the current power continued to increase,the recrystallized grains grew.When the pulsed current power was increased to 25 W,the recrystallized grains grew negligibly.Both recrystallization and grain growth have power thresholds.This study provides a novel approach for regulating the microstructure and mechanical properties of ultrathin cold-rolled 304 stainless steel strips.
文摘The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.
文摘The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.
基金Supported by National Basic Research Program of China(973 Program,Grant No.2011CB013402)
文摘The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element（FE） model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope（OM） and scanning electron microscope（SEM）, and then the diameters of fusion zone and heat affected zone（HAZ） are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer（EDS）, scanning probe microscopy（SPM） and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extension of the crack is presented and can provide a reference for the compressor rotor blade remanufacturing.
基金supported by the Fundamental Research Funds for the Central Universities(No.FRF-BD-23-01).
文摘Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,including bubble,electromagnetic stirring,filtration separation,fluid flow,and sedimentation,often struggle with the removal of fine inclusions.Apart from these known methods,pulsed electric current(PEC),as an emerging technology,has demonstrated immense potential and environmental advantages.PEC offers adjustable current parameters and simple equipment,making it an attractive alternative to traditional methods.Its green energy-saving features and excellent results in regulating inclusion morphology and migration,as well as inhibiting submerged entry nozzle(SEN)clogging,make it a promising technology.In comparison to continuous current technology,PEC has shown significant advantages in regulating inclusions,not only improving purification efficiency but also demonstrating outstanding performance in flow stability and energy consumption.The ability of PEC to efficiently reduce inclusion numbers enhances the purity and quality of molten steel,improving its mechanical properties.Currently,the theoretical basis for controlling the movement of inclusions by current is mainly composed of three major theories:the double electric layer theory,electromagnetic force reverse separation theory,and electric free energy drive theory.These theories together form an important framework for researchers to understand and optimize the behavior of impurity movement controlled by electric current.Looking ahead,PEC is expected to pave the way for new solutions in directional regulation of inclusion migration,efficient inclusion removal,SEN clogging prevention,and the purification of molten steel.
基金supported by the National Key R&D Program of China(2020YFA0714900,2023YFB3709903)the National Natural Science Foundation of China(U21B2082,52474410)+6 种基金the Key R&D Program of Shandong Province,China(2023CXGC010406)the Scientific Research Special Project for First-Class Disciplines in Inner Mongolia Autonomous Region(YLXKZX-NKD-001)the International Science and Technology Cooperation Project of Higher Education Institutions in Inner Mongolia Autonomous Region(GHXM-002)the Natural Science Foundation of Inner Mongolia Autonomous Region of China(2024ZD06)the Technology Support Project for the Construction of Major Innovation Platforms in Inner Mongolia Autonomous Region(XM2024XTGXQ16)the Beijing Municipal Natural Science Foundation(2222065)the Fundamental Research Funds for the Central Universities(FRF-TP-22-02C2).
文摘Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate atomic diffusion to achieve ultra-fast spheroidization of carbides.However,the understanding of the mechanism by which different pulse current parameters regulate the dissolution behavior of carbides requires a large amount of experimental data to support,which limits the application of pulse current technology in the field of heat treatment.Based on this,quantify the obtained pulse current processing data to create an important dataset that could be applied to machine learning.Through machine learning,the mechanism of mutual influence between carbide regulation and various factors was elucidated,and the optimal spheroidization process parameters were determined.Compared to the 20 h required for traditional heat treatment,the application of pulsed electric current technology achieved ultra-fast spheroidization of GCr15 bearing steel within 90 min.
基金Projects(51074031,51271042,50874022)supported by the National Natural Science Foundation of ChinaProject(2013M530913)supported by the China Postdoctoral Science FoundationProject(DUT12RC(3)35)supported by the Fundamental Research Funds for the Central Universities of China
文摘The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.
基金Projects(51101177,51401040,51171146,51171216) supported by the National Natural Science Foundation of ChinaProject(CSTC2012JJA245) supported by the Natural Science Foundation of Chongqing,China
文摘A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.
文摘A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.
