The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the she...The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the shearing flow near the narrow face of mold, the entrapment caused by vortexes around the submerged entry nozzle （SEN）, and the entrapment caused by the Ar bubbling. Both the velocity of the surface flow and the level fluctuation of the liquids are enlarged with increasing the casting speed, reducing the submersion depth of SEN, decreasing the downward angles of the nozzle outlets, and increasing the Ar flowrate, all of which increase the tendency of mold powder entrapment. Among the four above-mentioned factors, casting speed has the largest effect.展开更多
Optimization of mathematical model of flow field in slab continuous casting mold was performed by means of industrial measurement and mathematical modeling.The rod deflection method was used to quantitatively measure ...Optimization of mathematical model of flow field in slab continuous casting mold was performed by means of industrial measurement and mathematical modeling.The rod deflection method was used to quantitatively measure the velocities near the mold surface at high temperature.The measurement results were compared with the simulation results of three mathematical models at different argon gas flow rates of 6,10 and 14 L min^(−1).The model 1 neglects the mold powder layer,thermal effect and solidified shell.The model 2 only considers the influence of mold powder layer.The model 3 considers the influence of mold powder layer,thermal effect and solidified shell on the flow field.In all three models,the diameter of argon bubbles obeys Rosin-Rammler distribution fitted according to the experimental data of others’previous work.With increasing the argon gas flow rate,the velocity of liquid steel near the mold surface decreases.The model 1 seriously underestimates the shear stress of liquid steel near the mold surface,and its calculation results show higher velocity near the mold surface,lower turbulent kinetic energy and wider distribution of argon gas bubbles in the mold.The simulation results of model 2 only considering the viscous resistance of the mold powder layer to liquid steel makes the velocity near the surface lower than the measurement results obviously.The calculated velocities near the mold surface with model 3 are in best agreement with the measured results,showing the reasonable spatial distribution range of argon bubbles in the mold and the moderate turbulent kinetic energy.In the present conditions,the best argon gas flow rate is 10 L min^(−1) due to the moderate velocity near the mold surface,the appropriate distribution of argon gas bubbles in the mold and the smallest fluctuation amplitude on the mold surface.展开更多
The No. 3 slab caster,which mainly provides slabs to the 5000 mm plate mill at Baosteel, was put into production in December,2004. The size of the biggest slab produced by this caster is 2300 mm in width and 300 mm in...The No. 3 slab caster,which mainly provides slabs to the 5000 mm plate mill at Baosteel, was put into production in December,2004. The size of the biggest slab produced by this caster is 2300 mm in width and 300 mm in thickness. The designed output of the caster is 2.3 Mt/a. Slab surface longitudinal crack defects,which were related to the heat flux of the mold, frequently occurred in the early stage of the startup of the caster. As mild cooling powder is beneficial to the uniformity of the shell of initial slabs ,the concentration of stress is reduced, and the longitudinal cracking on the surface is avoided. This study evaluates the performance of several kinds of powder, and the results show that mold powder of high basicity, high crystallization proportion and low heat flux is to the benefit of the reduction of the longitudinal cracks on the surface and the defects of slabs.展开更多
Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of...Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.展开更多
In this work,the formation mechanism of the droplet-to-granule was investigated in detail based on mold powder manufacturing.A specific mathematical model of two-stage spray drying was established to describe droplet ...In this work,the formation mechanism of the droplet-to-granule was investigated in detail based on mold powder manufacturing.A specific mathematical model of two-stage spray drying was established to describe droplet and granule motion,heat and mass transfer,and granule morphology during spray drying.Then,the relationships between spray drying parameters(inlet temperature,atomization pres-sure,slurry mass flow rate)and the properties of the drying tower(temperature and velocity fields)and mold powder granules(temperature,evaporation rates,moisture content,and diameter)were simulated and calculated using ANSYS/Fluent software.To ensure that the granule size of mold powder was controlled within the ideal range(0.2-0.6 mm)for producing granules with appropriate mechanical and metallurgical properties,the following optimum spray drying parameters were chosen based on the results of the numerical simulation:inlet temperatures,873 K;slurry atomization pressure,1.8 MPa;slurry mass flow rate,0.05 kg s-1.Among these parameters,the slurry mass flow rate has the most significant effect on granule size.展开更多
Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic mate...Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic materials containing F^(-)constituent such as HF and SiF4 leads to serious environmental pollution.Overall,six powder samples were made during this research to study the effects of such compounds as calcium fluoride(CaF_(2))and manganese oxide(MnO)on the crystallization of mold powder and compare with that of the original mold powder.Having considered the chemical compounds of these six samples,two were finally chosen:powder sample A and powder sample E.The former was a simulated sample of the original mold powder using CaF_(2),and the latter was a less-F^(-)sample in which MnO was used as a substitution for F^(-)in the compounds of the mold powder.In other words,the amount of F^(-)was cut in half comparing to that of the original mold powder.The thermal gravimetric analysis(TGA)was performed on the original mold powder,the simulated sample of the original mold powder and the less-F^(-)sample.The results of the TGA demonstrated the reduction of thermal loss in samples A and E comparing to the original mold powder.On the other hand,the results of differential thermal analysis(DTA)of these three samples,i.e.,original mold powder and samples A and E,demonstrated that melting and crystallization temperatures of the original mold powder were similar to those of samples A and E.Therefore,it can be concluded that samples A and E are potential laboratory-scale substitutions for the original mold powder.展开更多
An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. Th...An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere （10^-3 Pa）. The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.展开更多
High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this a...High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.展开更多
With miniaturization and complication of the shape of electronic devices in recent years,powder injection molding(PIM)seems to be a suitable process for fabricating the higher performance soft magnetic components.In t...With miniaturization and complication of the shape of electronic devices in recent years,powder injection molding(PIM)seems to be a suitable process for fabricating the higher performance soft magnetic components.In this paper,high quality Fe-50Ni soft magnetic alloy was fabricated by PIM with carbonyl iron and nickel,and the effect of sintering process on its microstructure and magnetic properties were investigated.The mechanical and magnetic properties can be obviously improved by increasing the sintering temperature or using the hydrogen atmosphere instead of high vacuum,which causes by the increase of grain size and the densification.At the optimum sintering conditions,the PIM Fe-50Ni soft magnetic alloy with high properties are obtained,whose relative density,tensile strength,B_(m),H_(c),μ_(m)are 97%,465 MPa,1.52 T,16.62 A·m^(-1),42.5 mH·m^(-1),respectively.展开更多
By optimizing formulation and fabrication methods, a new binder forplasticizing powder extrusion molding of hard metal, with excellent integrated properties anduniform distribution characters, has been developed. Ther...By optimizing formulation and fabrication methods, a new binder forplasticizing powder extrusion molding of hard metal, with excellent integrated properties anduniform distribution characters, has been developed. Thermal debonding mechanism and the extrudingtheological behaviours have been studied. The technology of fabrication of binder and thermaldebonding process have also been investigated. Using the novel binder, the hard-metalextrusion-molding rods with diameter up to 25mm, have been manufactured.展开更多
The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powde...The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis（SHS） and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax（PW）,35 wt.% polypropylene（PP）,and 5 wt.% stearic acid（SA）.After the removal of binder,specimens were sintered at 1850°С in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m^-1·K^-1 and 3.28 g·cm^-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W·m^-1·K^-1 and 3.23 g·cm^-3,respectively,and the secondary phase is YN.展开更多
The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 ...The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 （ wt% ） composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing （CIP） technology was used before or after debinding. Specimens were siutered by vacuum siutering and hot isostatic pressing （HIP）. The density, Rockwell A hardness, magnetic coercivity , and magnetic saturation induction of siutered specimen were measured. The microstructure of the green bodies and the siutered specimens was studied by scanning electron microscopy （SEM）. Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be siutered to 99.5% density of composite cemented carbide rods with an average grain size of about 200- 300 nm, magnetic coercivity of 30.4 KA / m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85% . Superfine WC- 10 Co cemented carbide rods with excellent properties were obtained.展开更多
Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full den...Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full density by metal injection molding approach. Compacts from the optimal powder binder mixture were studied for molding and sintering behaviors. Milling significantly increases the maximum powder loading and homogeneity of the feedstock, and enhances the sintering densification process. When solid state sintered at 1 350～1 450 ℃, the alloy shows very fine grains (～3 μm), high tensile strength (>1 130 MPa) and almost no distortion. [展开更多
The rheological behaviors of feedstocks for powder extrusion molding, in the temperature range of 40～80 ℃ and the Newton shear rate of 3～800 s -1 , were studied. The effects of feedstock constitution, shear rate an...The rheological behaviors of feedstocks for powder extrusion molding, in the temperature range of 40～80 ℃ and the Newton shear rate of 3～800 s -1 , were studied. The effects of feedstock constitution, shear rate and temperature on apparent viscosity, shear stress and active energy were investigated. The viscose flow active energy of PEM feedstocks is 15.89～90.77 kJ/mol. Based on this research, the PEM technical parameters have optimized. [展开更多
An improved wax based multi component binder and a new debinding method termed high pressure condensed solvent extraction were developed for powder injection molding of tungsten cemented carbide. The results indicate ...An improved wax based multi component binder and a new debinding method termed high pressure condensed solvent extraction were developed for powder injection molding of tungsten cemented carbide. The results indicate that a critical powder loading of 65% (volume fraction) and an ideal rheological properties were obtained by the feedstock based on the binder. High debinding rate and specimens with high strength were obtained by the debinding method. Moreover, by making high temperature holding time adjustable, it makes the subsequent thermal degradation process more flexible to debinding atmosphere and carbon content of the as debinded specimens controllable. The transverse rupture strength, hardness and density of the as sintered specimens made by an optimized PIM process are 2.48 GPa, HRA90 and 14.72 g/cm 3, respectively. Good shape retention and about 0.02% dimension deviation were achieved.展开更多
Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with ...Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.展开更多
Stainless steel samples were made by Powder injection Molding (PIM) process with-400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process incl...Stainless steel samples were made by Powder injection Molding (PIM) process with-400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process included mixing, injection molding, debin- ding and sintering. Neck growth model was used to analyze the sintering mechanism. The results show that lattice (volume) diffusion is the main mechanism in the sintering process, the products with higher density (>95%) and properties are obtained. At lower temperatures, grain boundary diffusion may play a role in the sintering densification.展开更多
The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）,...The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The results show that the compressive stress exists in the products and the bend strength reaches 300MPa. ZrO2 phase and stainless steel phase are uniform in samples. The toughness of ceramic increases with the increasing the content of stainless steel. Through TEM study of the interface, some crystalline orientation relationships are determined.展开更多
The polymer binder selection is one of the very important aspects for the powder injection molding. However,even nowadays the binder selection is still mainly performed by try and error method. Six commercial or inten...The polymer binder selection is one of the very important aspects for the powder injection molding. However,even nowadays the binder selection is still mainly performed by try and error method. Six commercial or intensive studied binder fo rmulas were analyzed according to state diagram and chemical characteristics of ingredients in each binder formula. In addition,the interactions between the bi nder components and additives were also taken into account. Based on the analysi s,the optimum binder formula was selected and some selection criterions were pu t forward for the binder and additives.展开更多
文摘The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the shearing flow near the narrow face of mold, the entrapment caused by vortexes around the submerged entry nozzle （SEN）, and the entrapment caused by the Ar bubbling. Both the velocity of the surface flow and the level fluctuation of the liquids are enlarged with increasing the casting speed, reducing the submersion depth of SEN, decreasing the downward angles of the nozzle outlets, and increasing the Ar flowrate, all of which increase the tendency of mold powder entrapment. Among the four above-mentioned factors, casting speed has the largest effect.
基金supported by the National Natural Science Foundation of China(U1960202)and HBIS Handan Iron and Steel Group Co.,Ltd.
文摘Optimization of mathematical model of flow field in slab continuous casting mold was performed by means of industrial measurement and mathematical modeling.The rod deflection method was used to quantitatively measure the velocities near the mold surface at high temperature.The measurement results were compared with the simulation results of three mathematical models at different argon gas flow rates of 6,10 and 14 L min^(−1).The model 1 neglects the mold powder layer,thermal effect and solidified shell.The model 2 only considers the influence of mold powder layer.The model 3 considers the influence of mold powder layer,thermal effect and solidified shell on the flow field.In all three models,the diameter of argon bubbles obeys Rosin-Rammler distribution fitted according to the experimental data of others’previous work.With increasing the argon gas flow rate,the velocity of liquid steel near the mold surface decreases.The model 1 seriously underestimates the shear stress of liquid steel near the mold surface,and its calculation results show higher velocity near the mold surface,lower turbulent kinetic energy and wider distribution of argon gas bubbles in the mold.The simulation results of model 2 only considering the viscous resistance of the mold powder layer to liquid steel makes the velocity near the surface lower than the measurement results obviously.The calculated velocities near the mold surface with model 3 are in best agreement with the measured results,showing the reasonable spatial distribution range of argon bubbles in the mold and the moderate turbulent kinetic energy.In the present conditions,the best argon gas flow rate is 10 L min^(−1) due to the moderate velocity near the mold surface,the appropriate distribution of argon gas bubbles in the mold and the smallest fluctuation amplitude on the mold surface.
文摘The No. 3 slab caster,which mainly provides slabs to the 5000 mm plate mill at Baosteel, was put into production in December,2004. The size of the biggest slab produced by this caster is 2300 mm in width and 300 mm in thickness. The designed output of the caster is 2.3 Mt/a. Slab surface longitudinal crack defects,which were related to the heat flux of the mold, frequently occurred in the early stage of the startup of the caster. As mild cooling powder is beneficial to the uniformity of the shell of initial slabs ,the concentration of stress is reduced, and the longitudinal cracking on the surface is avoided. This study evaluates the performance of several kinds of powder, and the results show that mold powder of high basicity, high crystallization proportion and low heat flux is to the benefit of the reduction of the longitudinal cracks on the surface and the defects of slabs.
文摘Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.
基金the financial support from the National Natural Science Foundation of China(grant No.52274319)the Youth Foundation of Guizhou Academy of Sciences,China(grant No.202147).
文摘In this work,the formation mechanism of the droplet-to-granule was investigated in detail based on mold powder manufacturing.A specific mathematical model of two-stage spray drying was established to describe droplet and granule motion,heat and mass transfer,and granule morphology during spray drying.Then,the relationships between spray drying parameters(inlet temperature,atomization pres-sure,slurry mass flow rate)and the properties of the drying tower(temperature and velocity fields)and mold powder granules(temperature,evaporation rates,moisture content,and diameter)were simulated and calculated using ANSYS/Fluent software.To ensure that the granule size of mold powder was controlled within the ideal range(0.2-0.6 mm)for producing granules with appropriate mechanical and metallurgical properties,the following optimum spray drying parameters were chosen based on the results of the numerical simulation:inlet temperatures,873 K;slurry atomization pressure,1.8 MPa;slurry mass flow rate,0.05 kg s-1.Among these parameters,the slurry mass flow rate has the most significant effect on granule size.
文摘Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic materials containing F^(-)constituent such as HF and SiF4 leads to serious environmental pollution.Overall,six powder samples were made during this research to study the effects of such compounds as calcium fluoride(CaF_(2))and manganese oxide(MnO)on the crystallization of mold powder and compare with that of the original mold powder.Having considered the chemical compounds of these six samples,two were finally chosen:powder sample A and powder sample E.The former was a simulated sample of the original mold powder using CaF_(2),and the latter was a less-F^(-)sample in which MnO was used as a substitution for F^(-)in the compounds of the mold powder.In other words,the amount of F^(-)was cut in half comparing to that of the original mold powder.The thermal gravimetric analysis(TGA)was performed on the original mold powder,the simulated sample of the original mold powder and the less-F^(-)sample.The results of the TGA demonstrated the reduction of thermal loss in samples A and E comparing to the original mold powder.On the other hand,the results of differential thermal analysis(DTA)of these three samples,i.e.,original mold powder and samples A and E,demonstrated that melting and crystallization temperatures of the original mold powder were similar to those of samples A and E.Therefore,it can be concluded that samples A and E are potential laboratory-scale substitutions for the original mold powder.
文摘An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere （10^-3 Pa）. The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.
文摘High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.
基金This work was financially supported by the National 863 Program(No.2001AA337075).
文摘With miniaturization and complication of the shape of electronic devices in recent years,powder injection molding(PIM)seems to be a suitable process for fabricating the higher performance soft magnetic components.In this paper,high quality Fe-50Ni soft magnetic alloy was fabricated by PIM with carbonyl iron and nickel,and the effect of sintering process on its microstructure and magnetic properties were investigated.The mechanical and magnetic properties can be obviously improved by increasing the sintering temperature or using the hydrogen atmosphere instead of high vacuum,which causes by the increase of grain size and the densification.At the optimum sintering conditions,the PIM Fe-50Ni soft magnetic alloy with high properties are obtained,whose relative density,tensile strength,B_(m),H_(c),μ_(m)are 97%,465 MPa,1.52 T,16.62 A·m^(-1),42.5 mH·m^(-1),respectively.
基金This project is financially supported by the National Natural Science Foundation of China (No. 5964120,69971007)
文摘By optimizing formulation and fabrication methods, a new binder forplasticizing powder extrusion molding of hard metal, with excellent integrated properties anduniform distribution characters, has been developed. Thermal debonding mechanism and the extrudingtheological behaviours have been studied. The technology of fabrication of binder and thermaldebonding process have also been investigated. Using the novel binder, the hard-metalextrusion-molding rods with diameter up to 25mm, have been manufactured.
基金supported by the National Natural Science Foundation of China(Nos.50025412 and 60576011)the National Key Basic Research and Development Program of China(No.TG2000067203).
文摘The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis（SHS） and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax（PW）,35 wt.% polypropylene（PP）,and 5 wt.% stearic acid（SA）.After the removal of binder,specimens were sintered at 1850°С in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m^-1·K^-1 and 3.28 g·cm^-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W·m^-1·K^-1 and 3.23 g·cm^-3,respectively,and the secondary phase is YN.
基金Funded by Open Foundation of State Key Laboratory of AdvancedTechnologyfor Materials Synthesis and Processing, Wuhan Universi-ty of Technology, the Post PhD Science Foundation of China(2003034504) andthe Foundation of Wuhan University of Technol-ogy(2003XJJ202)
文摘The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 （ wt% ） composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing （CIP） technology was used before or after debinding. Specimens were siutered by vacuum siutering and hot isostatic pressing （HIP）. The density, Rockwell A hardness, magnetic coercivity , and magnetic saturation induction of siutered specimen were measured. The microstructure of the green bodies and the siutered specimens was studied by scanning electron microscopy （SEM）. Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be siutered to 99.5% density of composite cemented carbide rods with an average grain size of about 200- 300 nm, magnetic coercivity of 30.4 KA / m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85% . Superfine WC- 10 Co cemented carbide rods with excellent properties were obtained.
文摘Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full density by metal injection molding approach. Compacts from the optimal powder binder mixture were studied for molding and sintering behaviors. Milling significantly increases the maximum powder loading and homogeneity of the feedstock, and enhances the sintering densification process. When solid state sintered at 1 350～1 450 ℃, the alloy shows very fine grains (～3 μm), high tensile strength (>1 130 MPa) and almost no distortion. [
文摘The rheological behaviors of feedstocks for powder extrusion molding, in the temperature range of 40～80 ℃ and the Newton shear rate of 3～800 s -1 , were studied. The effects of feedstock constitution, shear rate and temperature on apparent viscosity, shear stress and active energy were investigated. The viscose flow active energy of PEM feedstocks is 15.89～90.77 kJ/mol. Based on this research, the PEM technical parameters have optimized. [
文摘An improved wax based multi component binder and a new debinding method termed high pressure condensed solvent extraction were developed for powder injection molding of tungsten cemented carbide. The results indicate that a critical powder loading of 65% (volume fraction) and an ideal rheological properties were obtained by the feedstock based on the binder. High debinding rate and specimens with high strength were obtained by the debinding method. Moreover, by making high temperature holding time adjustable, it makes the subsequent thermal degradation process more flexible to debinding atmosphere and carbon content of the as debinded specimens controllable. The transverse rupture strength, hardness and density of the as sintered specimens made by an optimized PIM process are 2.48 GPa, HRA90 and 14.72 g/cm 3, respectively. Good shape retention and about 0.02% dimension deviation were achieved.
基金the National Natural Science Foundation of China (No. 51172018)the Kennametal, Inc. for the fnancial support
文摘Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.
文摘Stainless steel samples were made by Powder injection Molding (PIM) process with-400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process included mixing, injection molding, debin- ding and sintering. Neck growth model was used to analyze the sintering mechanism. The results show that lattice (volume) diffusion is the main mechanism in the sintering process, the products with higher density (>95%) and properties are obtained. At lower temperatures, grain boundary diffusion may play a role in the sintering densification.
文摘The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The results show that the compressive stress exists in the products and the bend strength reaches 300MPa. ZrO2 phase and stainless steel phase are uniform in samples. The toughness of ceramic increases with the increasing the content of stainless steel. Through TEM study of the interface, some crystalline orientation relationships are determined.
文摘The polymer binder selection is one of the very important aspects for the powder injection molding. However,even nowadays the binder selection is still mainly performed by try and error method. Six commercial or intensive studied binder fo rmulas were analyzed according to state diagram and chemical characteristics of ingredients in each binder formula. In addition,the interactions between the bi nder components and additives were also taken into account. Based on the analysi s,the optimum binder formula was selected and some selection criterions were pu t forward for the binder and additives.
