CN1915625B - Method for preparing gradient material of strong magnetism and weak magnetism through pressure filtration molding in pulse magnetism - Google Patents
Method for preparing gradient material of strong magnetism and weak magnetism through pressure filtration molding in pulse magnetism Download PDFInfo
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- CN1915625B CN1915625B CN200610053248XA CN200610053248A CN1915625B CN 1915625 B CN1915625 B CN 1915625B CN 200610053248X A CN200610053248X A CN 200610053248XA CN 200610053248 A CN200610053248 A CN 200610053248A CN 1915625 B CN1915625 B CN 1915625B
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Abstract
A press filter process for preparing strong magnetic-weak magnetic gradient material in pulse magnetic field includes such steps as preparing porous mould, proportionally mixing ceramic powder, strong magnetic metal powder and deionized water, ball grinding, pouring in mould, press filtering, baking, and sintering.
Description
Technical field
The present invention relates to strong magnetic-weak magnetic gradient material pressure filtration molding preparation method in a kind of pulsed magnetic field.
Background technology
The ceramic of powder stock preparation generally includes powder preparation, powder processing, powder compacting, sintering densification several steps.Each step all might be introduced defective.Some will be eliminated the defective of introducing in each step before the sintering in next step technical process, and have some will be retained to last or along with the propelling of technical process changes new defective into.The defective that finally causes material damage originates from the base substrate mostly, that is is formed at forming process.These defectives origin comprises: soft-agglomerated, hard aggregation, organic being mingled with, inorganic being mingled with and big crystal grain.These major defect kinds can be eliminated or reduce mostly by pressure filtration molding.
Filter-pressing process is a kind of forming ceramic parts technology that develops and cause extensive concern in recent years rapidly, its cardinal principle is under the impressed pressure effect, the slurry that is dispersed with the solid phase ceramic particle under certain condition in liquid medium is entered in the model cavity by stock line, and leach the operative liquid medium by the porous filtering layer, thereby closely being arranged, ceramic particle is solidified into ceramic body with definite shape.
Pressure filtration molding is the effective technology that improves the CERAMIC MATERIAL ENGINEERING reliability.Especially for the ceramic of preparation large-size cross section and complicated shape, pressure filtration molding more demonstrates its superiority.Because pressure filtration molding adopts the organic additive of minute quantity, the compact density height, and do not get rid of organic difficulty, and therefore be suitable for moulding heavy in section goods, also can eliminate organic substance and be mingled with the defective that is caused.Pressure filtration molding adopts liquid phase medium to prepare slurry directly-forming, can adopt method such as precipitate and separate to remove aggregate, the bulky grain in the powder and be mingled with body.And avoided the formation of new aggregate, thereby can improve the micro-uniformity of molding blank without the dry run straight forming.When the preparation ceramic matric composite, pressure filtration molding can also avoid destroying fibrous compound phase, and can effectively it be uniformly distributed in the matrix.
Functionally Graded Materials (FGM) is under the condition at high temperature, thermal cycle and big temperature fall, operate as normal and the class new material developed repeatedly, and harsh environment for use requires material to have excellent heat shock resistance and thermal fatigue property.Traditional pottery, the direct conjugant of metal may be peeled off because of the interface thermal stress and lose efficacy, and forming thermal stress mitigation type Functionally Graded Materials is that head it off has been opened up approach.Functionally Graded Materials is the ideal material at some high temperature difference positions such as engine inlet of airborne vehicle, space shuttle, and its principal character is that component structure and physical parameter change continuously.
The Functionally Graded Materials main preparation methods has that powder compacting, physical vaporous deposition PVD, chemical vapour deposition technique CVD, self-propagating reaction are synthetic, plasma spraying, laser sintered and centrifugal casting etc.Powder metallurgic method is with composition gradient lamination structures such as feed particulate material such as metal, pottery and whiskers, through compacting, sintering and make Functionally Graded Materials.Heat-stable ceramic is used for temperature end, and metal material or plastics are used for low-temperature end.Form mutually or raising ceramic phase toughness for reinforced metal, can mix whisker.The PVD method is to make the metal deposition of heating evaporation carry out the method for coating on substrate, in metal, semimetal, send into reacting gass such as oxygen, nitrogen and hydrocarbon after, potteries such as synthesis oxide, chloride and carbide, and being deposited on the substrate.Physical vaporous deposition has vacuum coating, sputter and ion plating etc.Vacuum coating is that merely heating of metal makes its hydatogenesis; Sputtering method is to hit by electronics or ion, makes the metal deposition that sputters out on substrate; Ion plating is by the metal vapors ionization, obtains the good and fine and close deposit of caking property.Chemical vapour deposition technique is that halide gas is carried out heating and decomposition, and metal or semimetal are deposited on the substrate surface, perhaps mists such as the carbide that generates, chloride is sent into reaction tube, and the compound that heating is generated is deposited on the substrate.From to spread the thermal response method be the element powders that will constitute compound with metal dust by the gradient composition filling, with cold isostatic compaction, put into reaction vessel, at one end light a fire.Because volume changes during reaction, so reaction vessel (hydrostatic pressing or air pressure) pressurization in a certain way, to guarantee the finished product densification.Plasma spraying method with plasma spraying machine blow out have metal, the pottery mixed-powder and plasma jet the test with basis material on.
Above-mentioned preparation method or complicated technology or the equipment of requirement, or need in preparation process, change material composition or technological parameter constantly.Lacking simple and convenient preparation method, is the major reason that the limitation function functionally gradient material (FGM) further develops.Therefore, if the metal or the ceramic forming material means of maturation can be used for preparing Functionally Graded Materials, have great importance undoubtedly.And because traditional production technique such as metal castings, forming process of ceramics, preparation all be the basic product uniformly of microstructure and property, the hardening constituent in the composite material also is equally distributed usually.Therefore, these are tradition and ripe production technology, can not directly be used for preparing component structure and physical parameter continually varying Functionally Graded Materials.
Transition metal such as Fe, Ni, Co belong to ferromagnetic substance, have ferromagnetism below Curie temperature.Most potteries all are weak magnetic substances, and magnetic field is not had sensitiveness basically.Utilize the difference of magnetic property between metal and the ceramic constituent element, our group adopted the pressure filtration molding method successfully to prepare functionally gradient material (FGM) in magnetostatic field in 2003.This technology has been authorized patent of invention.
In the past few years, our group updates on original experiment basis, and makes a breakthrough.At present, we have successfully adopted the pressure filtration molding method to prepare functionally gradient material (FGM) in pulsed magnetic field.The present invention is with the pottery (Al of ferromagnetic metal (transition metal such as Fe, Ni, Co) with weak magnetic
2O
3, ZrO
2, SiC, AlN, Si
3N
4) slurry formed, in pulsed magnetic field, adopting the fixed shaping of pressure filtration molding method, sintering prepares strong magnetic-weak magnetic gradient material then.Compare with preparation functionally gradient material (FGM) under the magnetostatic field, utilize the easier realization of pulsed magnetic field big magnetic field intensity and magnetic field gradient, and particle is subjected to the reinforcement and lax effect repeatedly, easier strong magnetic-weak magnetic gradient material of preparing various gradients of magnetic force under pulsed magnetic field.
Outstanding advantage of the present invention utilizes ceramic pressure filtration molding method to produce strong magnetic-weak magnetic gradient material exactly, by adjusting magnetic field intensity, magnetic field gradient, slurry composition, viscosity and other preparation technology parameter, can in very big thickness range, prepare composition easily and change continuously and controlled functionally gradient material (FGM).
Summary of the invention
The purpose of this invention is to provide strong magnetic-weak magnetic gradient material pressure filtration molding preparation method in a kind of pulsed magnetic field.
Its step is:
1) mould is prepared
α-gypsum and β-gypsum mixed type land plaster are mixed with water, and adding organic additive, its content is 5～25% of gypsum quality, stir cast after 3～8 minutes, solidify, harden the gypsum mold that makes after drying by calcium plaster, in the environment of 25～38 ℃ of temperature, relative humidity 20～30%, preserve;
2) pulp preparation
With particle size is the stainless iron powder of ferromagnetism, nickel powder or the cobalt powder of 0.1～100 μ m, with particle size be the ZrO of 0.1～100 μ m
2, SiC, AlN, Si
3N
4, B
4C, SiO
2, TiC, Y
2O
3, Al
2O
3In one or more by 0.1～10: 1 mixed, add deionized water, reach 30～55vol% to solid concentration, and regulate pH value to 3～10, ball milling 1～10h in ball mill, ultrasonic dispersion processing 1～15min with hydrochloric acid or ammoniacal liquor, make the disperse slurry, the humidity of slurry is 20%～50%, and temperature is 30～60 ℃, and viscosity is 1～100mPas;
3) pressure filtration molding in the pulsed magnetic field
The disperse slurry is injected plaster mold, and mould applies pulsed magnetic field outward, and magnetic field intensity is 0.1～5.0T, and magnetic field gradient is 0.1～50T/m, and magnetizing time is 1～30min, subsequently slurry is exerted pressure, and carries out pressurize and handle;
4) sintering
Solidify, go mould and slowly oven dry under 35～60 ℃; the green compact that obtain are sinter molding in graphite or protection of nitrogen gas environment; be warming up to 500～1200 ℃; heating rate is 100～400 ℃/h; insulation 1～3h; be heated to 1000～1600 ℃ again, insulation 1～3h cools to 100～400 ℃ of taking-ups at last with the furnace.
Described pulsed magnetic field is the magnetic field that the pulse current that utilizes capacitor to spark to produce produces by coil.The organic additive that adds is polyethylene glycol oxide, melmac or phenolic resins.Applied pressure is 0.1～10Mpa, and the dwell time is 10～100min.
Advantage of the present invention is:
1) by changing magnetic field intensity and magnetic field gradient, can prepare the functionally gradient material (FGM) of all thickness in very big composition range, composition changes continuously and is controlled;
2) prepare Functionally Graded Materials down with magnetostatic field and compare, particle is subjected to the reinforcement and lax effect repeatedly, easier strong magnetic-weak magnetic gradient material of preparing various gradients of power under the pulsed magnetic field;
3) utilize ripe ceramic pressure filtration molding method that the work simplification of production strong magnetic-weak magnetic gradient material, cost are reduced.
Embodiment
Strong magnetic of the present invention-weak magnetic gradient material preparation method is with ferromagnetic metal (in stainless iron, nickel powder, the cobalt powder a kind of) and pottery (ZrO
2, SiC, AlN, Si
3N
4, B
4C, SiO
2, TiC, Al
2O
3In one or more) mixed-powder and deionized water form slurry, pours into dies cavity and be shaped in magnetic field, pressure filtration molding is carried out in pressurization subsequently.Slurry is subjected to the effect of magnetic force, builds up to two ends in mould respectively, forms component gradient.The blank that obtains is made strong magnetic-weak magnetic gradient material behind curing, sintering.
Concrete steps of the present invention are as follows:
1) porous mold is prepared
Press filtration is owing to being by porous mold the operative liquid medium to be leached and moulding, so porous mold is very important.The press filtration mould should satisfy the requirement of filter-pressing process to porous filter material, satisfies the requirement to mould structure again.Press filtration will have desirable strainability on the one hand with porous material, promptly have enough little pore, narrow air vent aperture distribution, the porosity and the transmission coefficient of appropriateness, on the other hand, for guaranteeing the size and dimension of formed body, these porous materials must have enough rigidity and intensity, easily controlling dimension and shape.In addition, porous material should have enough durabilitys or can carry out model modification neatly.These materials comprise that gypsum is material modified, porous metals, porous organic material and composite porous.This law adopts gypsum material modified, adds the later materials of organic additive modification such as polyethylene glycol oxide, melmac, phenolic resins exactly in gypsum, and mechanical strength and durability are higher.Can adjust the porosity and water filtering performance by the ratio that changes organic additive and gypsum.
The temperature of institute's water can influence the setting time of calcium plaster in the mould manufacturing, can influence the expansion of calcium plaster again.Along with the rising of water temperature, will accelerate the setting time of calcium plaster, expand then to reduce.Mineral matter in the water also can be deposited in the mould, influences the performance of mould.Therefore, should adopt pure running water in the production, water temperature is 15～25 ℃.The porosity, intensity and the structure of mould in the scale effect of gypsum and water.Along with the raising of plaster-water ratio, the intensity and the density of mould all increase, and water absorption rate then reduces, and the control plaster-water ratio is 1.3～1.5.Add polyethylene glycol oxide, its content is 5～25% of gypsum quality.The mixing time of control gypsum 3～8 minutes.The back gypsum mold need drying of being solidified, being hardened and make by calcium plaster of cast is discharged the surplus water that has neither part nor lot in hydration reaction.The gypsum mold that is used for slip casting should be fully dry, but can not drying undue (humidity 3～20%).The baking temperature of mould is at 50～70 ℃.When the temperature in the drier still more than 38 ℃ the time, should not take out mould, otherwise easy to crack.Gypsum mold is deposited in the plane of dustless no dirt, 25～38 ℃ of temperature, relative humidity 20～30%.
2) pulp preparation
Adopt strong magnetic metal powder (in stainless iron, nickel powder, the cobalt powder a kind of, particle size is at 0.1～100 μ m) and ceramic powders (ZrO
2, SiC, AlN, Si
3N
4, B
4C, SiO
2, TiC, Y
2O
3, Al
2O
3In one or more, particle size is at 0.1～100 μ m) in 0.1～10: 1 ratio is formed mixed-powder, mixed-powder is constantly added in the deionization aqueous solvent, and constantly add hydrochloric acid or ammoniacal liquor to regulate the pH value, make it to remain 3～10, reach 30～55vol% to solid concentration, in ball mill, stir 1～10h, make the slurries of even dispersion.Because fine particle is easy to reunite, and is the slurry of nanometer and sub-micron for granularity, adopt ultrasonic wave to carry out the disperse processing.
The humidity of slurry cast is 20～50%, and temperature is 30～60 ℃.Ensureing under the good flow implementations, should reduce the humidity of slurry as far as possible.The humidity of slurry is more little, and it is fast more to eat slurry speed, and the air shrinkage of annotating part is low more, and the useful life of mould is long more.
3) pressure filtration molding in the pulsed magnetic field
The cast extrusion forming is the critical process that pressure filtration molding prepares strong magnetic-weak magnetic gradient material in the employing pulsed magnetic field in the pulsed magnetic field.Gypsum mold is on every side that temperature is under 25～28 ℃ of conditions during cast, is to eliminate attachment and differentiation die-face, uses soda solution wiping mould.Be uniformly dispersed, stable mud injects pressure filtration molding with mould, mould applies pulsed magnetic field outward, pulsed magnetic field is produced by solenoid coil by pulse current.
Be subjected to the effect of magnetic force, the metal constituent element is poly-partially to specific direction, forms component gradient.In pulsed magnetic field, the ferromagnetic metal particle is magnetized and Xiang Yiduan attracts, and weak magnetic ceramics particle is then driven to the other end under the barometric gradient effect.Weaken pulsed magnetic field intensity and magnetic field gradient, component gradient reduces.Improve pulsed magnetic field intensity and magnetic field gradient, component gradient then increases.Adjusting magnetic field intensity is 0.1～5.0, and magnetic field gradient is 0.1～50T/m, and control magnetizing time 1～30min obtains required component gradient, subsequently pressurization.0.1～10Mpa and pressurize 10～100min exert pressure.Bigger pressure helps improving micro-uniformity and whole uniformity, but residual stress is big in the molding blank, may cause in the demoulding and the dry run and ftracture.
4) sintering
Base substrate after the curing goes slowly to dry down at 35～60 ℃ behind the mould.This moment, base substrate plasticity was lower, and the outer surface of complicated base substrate is different with inner rate of drying, can produce very high shrinkage stress and ftractureed.In this case, must be held in the high humility of the dry environment of parison soma, with the evaporation rate of control billet surface layer moisture.Perhaps adopt microwave action, to the whole heating of base substrate, quickening the base substrate internal moisture spreads to the outside, the inside and outside temperature of base substrate is reached unanimity, cooperate again with the high water vapor pressure of external environment condition, then the moisture of base substrate can slowly be got rid of equably, and base substrate shrinks consistent, thereby eliminates or the minimizing drying stress.According to the difference of particulate component, green compact can be in the ordinary sinter stove sintering, perhaps be anti-oxidation sintering in the environment of protection.Heating rate is 100～400 ℃/h to 500～1200 ℃, and insulation 1～3h is incubated 1～3h after being heated to 1000～1600 ℃, cools to 100～400 ℃ of taking-ups at last with the furnace.
The functionally gradient material (FGM) of all thickness that can prepared composition in very large range changes by the present invention, and composition changes continuously, and the finished product internal flaw is few, and structure is tight.
Embodiment 1:
1) mix with pure running water with α-gypsum and β-gypsum, and add polyethylene glycol oxide, its content is 10% of gypsum quality, stirs cast after 4 minutes.Calcium plaster solidifies, harden the gypsum mold that makes after drying, and the mould inside die cavity is to be the disk of 50mm for 30mm, diameter highly.
2) average particle size particle size is that nickel by powder and the average particle size particle size of 3 μ m are the Al of 0.9 μ m
2O
3Powder is formed mixed-powder in proportion at 1: 1, mixed-powder is constantly joined in the deionization aqueous solvent, and constantly to add hydrochloric acid is 3 to regulate the pH value, reaches 40vol% to solid concentration.Stir 4h in ball mill, adopt ultrasonic wave to carry out the disperse processing and make slurry, the humidity of slurry is 30%, and temperature is 35 ℃, and viscosity is 20mPas.
3) the mould temperature is 25 ℃ during slip casting, and slurry is charged in the plaster mold.Mould applies pulsed magnetic field outward, and pulsed magnetic field is produced by solenoid coil by pulse current, and magnetic field intensity is 0.4T, and magnetic field gradient is 3T/m, and magnetizing time is 5min, the 0.2Mpa that exerts pressure subsequently, and pressurize 80min.
4) base substrate after the curing is at 40 ℃ of slowly oven dry down, sintering green compact under the powdered graphite protection.Heating rate with 300 ℃/h is heated to 800 ℃ of insulation 2h, is heated to 1400 ℃ with 200 ℃/h then, insulation 1h.Cool to 200 ℃ of taking-ups with the furnace.
Example 1 prepared sample is carried out the electron microprobe line analysis, find that its composition changes continuously, Ni reduces to 0% of opposite side by 92% of a side.Sample interior does not have macroscopic interface and exists, and does not have pore substantially.To the sample thermal shock test that circulates, the thermal shock cracking does not take place under 800 ℃ of temperature difference, chilling condition.Under 600 ℃ of temperature difference, slow cooling condition through 800 circulations crackle does not appear.
Embodiment 2:
1) mixes with α-gypsum and β-gypsum pure running water with 20 ℃, and adding phenolic resins, its content is 10% of gypsum quality, stir cast after 4 minutes, calcium plaster is solidified, hardens the gypsum mold that makes after drying, and the mould inside die cavity is to be the disk of 50mm for 30mm, diameter highly.
2) choosing average particle size particle size is that having of 4 μ m more ferromagnetic drillings end and average particle size particle size are the ZrO of 2.2 μ m
2Powder is formed mixed-powder in proportion at 1: 2, mixed-powder is constantly joined in the deionization aqueous solvent, and constantly to add hydrochloric acid is 4.2 to regulate pH value, reaches 45vol% to solid concentration, stir 4h in ball mill, and the employing ultrasonic wave carries out the disperse processing.The humidity that obtains pouring into a mould slurry is 35%, and temperature is 40 ℃, and viscosity is 35mPas.
3) the mould temperature is 27 ℃ during slip casting, and slurry is charged in the plaster mold, and mould applies pulsed magnetic field outward, pulsed magnetic field is produced by solenoid coil by pulse current, and magnetic field intensity is 0.4T, and magnetic field gradient is 3T/m, magnetizing time is 8min, the 0.3Mpa that exerts pressure subsequently, and pressurize 60min.
4) base substrate after the curing is at 40 ℃ of slowly oven dry down, sintering green compact under the powdered graphite protection.Heating rate with 300 ℃/h is heated to 800 ℃ of insulation 2h, is heated to 1500 ℃ with 200 ℃/h then, insulation 2h.Cool to 300 ℃ of taking-ups with the furnace.
Example 2 prepared samples are carried out the electron microprobe line analysis, find that its composition changes continuously, drillings is 0% by 94% of a side to opposite side, and no macroscopic interface exists, and there is a small amount of little pore inside.To the thermal shock test that circulates of the sample of gained, the thermal shock cracking does not take place under 800 ℃ of temperature difference, chilling condition, under 600 ℃ of temperature difference, slow cooling condition through 100 circulations crackle does not appear.
Embodiment 3:
1) mixes with α-gypsum and β-gypsum pure running water with 20 ℃, and adding melmac, its content is 10% of gypsum quality, stir cast after 4 minutes, calcium plaster is solidified, hardens the gypsum mold that makes after drying, and the mould inside die cavity is to be the disk of 50mm for 30mm, diameter highly.
2) choosing average particle size particle size is that more ferromagnetic stainless iron powder of having of 10 μ m and average particle size particle size are that the SiC powder of 5.2 μ m is formed mixed-powder in proportion at 1: 4, mixed-powder is constantly joined in the deionization aqueous solvent, and constantly to add hydrochloric acid be 4.5 to regulate the pH value, reach 40vol% to solid concentration, in ball mill, stir 5h, and adopt ultrasonic wave to carry out the disperse processing.The humidity that obtains pouring into a mould slurry is 30%, and temperature is 35 ℃, and viscosity is 60mPas.
3) the mould temperature is 27 ℃ during slip casting, and slurry is charged in the plaster mold, and mould applies pulsed magnetic field outward, pulsed magnetic field is produced by solenoid coil by pulse current, and magnetic field intensity is 0.6T, and magnetic field gradient is 5T/m, magnetizing time is 5min, the 0.3Mpa that exerts pressure subsequently, and pressurize 60min.
4) base substrate after the curing is at 40 ℃ of slowly oven dry down, sintering green compact under nitrogen protection.Heating rate with 200 ℃/h is heated to 700 ℃ of insulation 2h, is heated to 1250 ℃ with 200 ℃/h then, insulation 2h.Cool to 300 ℃ of taking-ups with the furnace.
Example 3 prepared samples are carried out the electron microprobe line analysis, find that its composition changes continuously, stainless iron powder is 0% by 96% of a side to opposite side, and no macroscopic interface exists, and there is a small amount of little pore inside.To the thermal shock test that circulates of the sample of gained, the thermal shock cracking does not take place under 800 ℃ of temperature difference, chilling condition, under 600 ℃ of temperature difference, slow cooling condition through 100 circulations crackle does not appear.
Embodiment 4:
1) mix with pure running water with α-gypsum and β-gypsum, and add polyethylene glycol oxide, its content is 10% of gypsum quality, stirs cast after 4 minutes.Calcium plaster solidifies, harden the gypsum mold that makes after drying, and the mould inside die cavity is to be the disk of 50mm for 30mm, diameter highly.
2) choosing average particle size particle size is that more ferromagnetic nickel powder of having of 5.2 μ m and average particle size particle size are the Al of 2.0 μ m
2O
3Powder contains 5% Y
2O
3Form mixed-powder in proportion at 1: 3, mixed-powder is constantly joined in the deionization aqueous solvent, and constantly with salt acid for adjusting pH value to 3.8, reach 45vol% to solid concentration, in ball mill, stir 6h, and adopt ultrasonic wave to carry out the disperse processing.The humidity that obtains pouring into a mould slurry is 40%, and temperature is 35 ℃, and viscosity is 30mPas.
3) the mould temperature is 27 ℃ during slip casting, and slurry is charged in the gypsum mold, and mould applies pulsed magnetic field outward, pulsed magnetic field is produced by solenoid coil by pulse current, and magnetic field intensity is 0.1T, and magnetic field gradient is 1T/m, magnetizing time is 15min, the 1.5Mpa that exerts pressure subsequently, and pressurize 50min.
4) base substrate after the curing is at 40 ℃ of slowly oven dry down, sintering green compact under nitrogen protection.Heating rate with 300 ℃/h is heated to 800 ℃ of insulation 2h, is heated to 1400 ℃ with 200 ℃/h then, insulation 2h.Cool to 200 ℃ of taking-ups with the furnace.
Example 4 prepared samples are carried out the electron microprobe line analysis, find that it is 0% by 92% of a side to opposite side that its composition changes nickel powder continuously, no macroscopic interface exists, and inside does not have pore.To the thermal shock test that circulates of the sample of gained, the thermal shock cracking does not take place under 800 ℃ of temperature difference, chilling condition, under 600 ℃ of temperature difference, slow cooling condition through 150 circulations crackle does not appear.
Embodiment 5:
1) mix with pure running water with α-gypsum and β-gypsum, and add melmac, its content is 10% of gypsum quality, stirs cast after 4 minutes.Calcium plaster solidifies, harden the gypsum mold that makes after drying, and the mould inside die cavity is to be the disk of 50mm for 30mm, diameter highly.
2) choosing average particle size particle size is that the equal particle size of the more ferromagnetic stainless iron powder peace of having of 3 μ m is the Si of 0.9 μ m
3N
4Powder is formed mixed-powder in proportion at 1: 1, mixed-powder is constantly joined in the deionization aqueous solvent, and constantly ammonification water is regulated pH value to 9.5, reaches 40vol% to solid concentration, stir 3h in ball mill, and the employing ultrasonic wave carries out the disperse processing.The humidity that obtains pouring into a mould slurry is 40%, and temperature is 35 ℃, and viscosity is 55mPas.
3) the mould temperature is 27 ℃ during slip casting, and slurry is charged in the gypsum mold, and mould applies pulsed magnetic field outward, pulsed magnetic field is produced by solenoid coil by pulse current, and magnetic field intensity is 0.3T, and magnetic field gradient is 2T/m, magnetizing time is 5min, the 1.5Mpa that exerts pressure subsequently, and pressurize 80min.
4) base substrate after the curing is at 40 ℃ of slowly oven dry down, sintering green compact under the powdered graphite protection.Heating rate with 200 ℃/h is heated to 800 ℃ of insulation 2h, is heated to 1250 ℃ with 200 ℃/h then, insulation 2h.Cool to 200 ℃ of taking-ups with the furnace.
Example 5 prepared samples are carried out the electron microprobe line analysis, find that it is 0% by 90% of a side to opposite side that its composition changes continuously stainless iron powder, no macroscopic interface existence, inside does not have pore.To the thermal shock test that circulates of the sample of gained, the thermal shock cracking does not take place under 800 ℃ of temperature difference, chilling condition, under 600 ℃ of temperature difference, slow cooling condition through 150 circulations crackle does not appear.
Claims (4)
1. strong magnetic-weak magnetic gradient material pressure filtration molding preparation method in the pulsed magnetic field is characterized in that its step is:
1) mould is prepared
α-gypsum and β-gypsum mixed type land plaster are mixed with water, and adding organic additive, its content is 5～25% of gypsum quality, stir cast after 3～8 minutes, solidify, harden the gypsum mold that makes after drying by calcium plaster, in the environment of 25～38 ℃ of temperature, relative humidity 20～30%, preserve;
2) pulp preparation
With particle size is the stainless iron powder of ferromagnetism, nickel powder or the cobalt powder of 0.1～100 μ m, with particle size be the ZrO of 0.1～100 μ m
2, SiC, AlN, Si
3N
4, B
4C, SiO
2, TiC, Y
2O
3, Al
2O
3In one or more by 0.1～10: 1 mixed, add deionized water, reach 30～55vol% to solid concentration, and regulate pH value to 3～10, ball milling 1～10h in ball mill, ultrasonic dispersion processing 1～15min with hydrochloric acid or ammoniacal liquor, make the disperse slurry, the humidity of slurry is 20%～50%, and temperature is 30～60 ℃, and viscosity is 1～100mPas;
3) pressure filtration molding in the pulsed magnetic field
The disperse slurry is injected plaster mold, and mould applies pulsed magnetic field outward, and magnetic field intensity is 0.1～5.0T, and magnetic field gradient is 0.1～50T/m, and magnetizing time is 1～30min, subsequently slurry is exerted pressure, and carries out pressurize and handle;
4) sintering
Solidify, go mould and slowly oven dry under 35～60 ℃; the green compact that obtain are sinter molding in graphite or protection of nitrogen gas environment; be warming up to 500～1200 ℃; heating rate is 100～400 ℃/h; insulation 1～3h; be heated to 1000～1600 ℃ again, insulation 1～3h cools to 100～400 ℃ of taking-ups at last with the furnace.
2. strong magnetic-weak magnetic gradient material pressure filtration molding preparation method in a kind of pulsed magnetic field according to claim 1 is characterized in that described pulsed magnetic field is the magnetic field that the pulse current that utilizes capacitor to spark to produce produces by coil.
3. strong magnetic-weak magnetic gradient material pressure filtration molding preparation method in a kind of pulsed magnetic field according to claim 1, the organic additive that it is characterized in that described adding is polyethylene glycol oxide, melmac or phenolic resins.
4. strong magnetic-weak magnetic gradient material pressure filtration molding preparation method is characterized in that described applied pressure is 0.1～10Mpa in a kind of pulsed magnetic field according to claim 1, and the dwell time is 10～100min.
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| CN102211346B (en) * | 2011-06-08 | 2012-09-19 | 浙江大学 | Method for preparing functionally graded material through pressure filtration forming in motional magnetic field |
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