CN101531519A - Composite high-temperature molybdenum disilicide-base material and preparation method thereof - Google Patents

Abstract

The invention relates to a composite high-temperature molybdenum disilicide-base material and a preparation method thereof. The method can prepare the composite high-temperature material under lower production cost, which has the highest room temperature toughness equivalent to that of high-temperature alloys, higher high temperature intensity, high temperature creep resistant performance and certain plastic processing performance; the substrate of the composite high-temperature material is a composite substrate composed of MoSi2 and Si3N4, wherein the average crystal grain size of the MoSi2 is smaller than 2 microns, and the average grain diameter of the Si3N4 particulates is smaller than 1 microns. The method adopts the following technical proposal: Mo2N powder or powder of Mo5Si3 or Mo3Si are used as initial powder to obtain composite powder Mo3Si-Mo5Si3-Si3N4 or Mo5Si3-MoSi2-Si3N4 after being processed by siliconization or nitridation-siliconization, the composite powder is further enhanced and mixed with materials such as Si powder, SiC powder and the like, and is pressing molded, and then a blank is sintered under the temperature of 1415 to 1550 DEG C, and finally the sintered blank is plastic deformed, thus obtaining a required dense article of the composite high-temperature material.

Description

Composite high-temperature molybdenum disilicide-base material and preparation method thereof

Technical field

The present invention relates to a kind of high-temperature structural material, particularly a kind of composite high-temperature molybdenum disilicide-base material and preparation method thereof.

Background technology

High-temperature structural material is the critical material in the equipment such as aircraft engine, thermal power generation unit, internal combustion turbine, oil engine, and its performance has determined the thermo-efficiency and the overall performance of this kind equipment to a great extent.Studies show that the hot strength and the high-temperature creep resistance of oxide ceramics are lower, non-oxide ceramics is as Si ₃N ₄, SiC etc., sintering character is poor, it is very complicated to cause must adding in a large number when sintering the sintering agent or its production technique that reduce the material at high temperature performances, and the room temperature toughness of intermetallic compound is low, hot strength and high-temperature creep resistance are lower.Existing ceramic base or intermetallic compound based composite material, owing to have many disadvantages at aspects such as material component, weave construction and preparation technologies, also can only improve its performance limitedly, have still that room temperature toughness is lower, a hot strength and high-temperature creep resistance is relatively poor or production cost shortcoming such as costliness too.

Existing MoSi ₂Polycrystalline material or with MoSi ₂In the matrix material for matrix, since aspects such as production technique, feed composition, MoSi ₂Crystal grain is comparatively thick, and average crystal grain diameter is generally 10～200 microns.

At present, preparation MoSi ₂One of method of base high temperature composite is directly with MoSi ₂Powder and Si ₃The mixing of strengthening phase such as N4, SiC, hot pressed sintering or HIP sintering become dense material.Because MoSi ₂Have between the Mo-Si atom in the crystal strong covalent linkage composition, atom in conjunction with closely, suppressed Mo, the migration at high temperature of Si atom, MoSi ₂～Si ₃N ₄, MoSi ₂～SiC or MoSi ₂～Si ₃N ₄～SiC base substrate must (just can sinter fine and close integral material at high temperature (1600～2000 ℃), high pressure under 20～80MPa) the acting in conjunction, production cost height but also remain with many defectives in the weave construction of material behind sintering not only, high sintering temperature can also cause Si in the base substrate ₃N ₄Phase decomposition or SiC phase mechanical property reduce, thereby have reduced the overall mechanical properties of high temperature composite.In addition, the composite granule of this mechanically mixing atom on crystal boundary behind the sintering does not have coherence, half coherence relation, Si usually ₃N ₄Refinement MoSi ₂The effect of aspects such as crystal grain, reinforcement crystal boundary is less.

Another kind method is to prepare MoSi by reaction sintering ₂Monophase materials or MoSi ₂Based composites.It equates an amount of Si, Mo powder and reinforcement other component uniform mixing and is pressed into base substrate, is heated to 1000～1400 ℃, and Si and Mo react and form MoSi ₂, reaction is carried out from spreading.Though reaction sintering method has advantage, as can using Mo, Si element powder cheaply, the Heating temperature of base substrate is lower etc. during sintering.But the shortcoming that many essence are also arranged is as MoSi ₂Become liquid phase to cause crystal grain comparatively thick in the transient melting that forms, can not inherit the form of Mo powder; MoSi in the sintering process ₂The temperature of phase sharply raises, melts, and causes that the gas of gasification of low volatilization point impurity and absorption breaks away from, at liquid MoSi ₂Cause the cavity mutually, subsequently MoSi ₂Solidify rapidly mutually a large amount of cavities and space are retained among the material; When strengthening phase content is higher in the base substrate, may induce reaction not exclusively; Also need behind the reaction sintering material is carried out processing such as hot pressing or hot isostatic pressing, increased the technology cost.

Summary of the invention

Problem to be solved by this invention is: a kind of composite high-temperature molybdenum disilicide-base material and preparation method thereof is provided, this method can prepare under the lower production cost can be under 900～1600 ℃ of atmospheric environments works better, the highest room temperature toughness can with superalloy quite, and have the high temperature composite of higher hot strength, high-temperature creep resistance and certain plastic deformation ability.

The basic ideas that address the above problem are: one, by silication Mo ₂N phase and nitrogenize Mo ₅Si ₃Phase, Mo ₃Si phase or MoSi ₂Obtain inner grain-size mutually and be refined to nanometer or other Mo of submicron order ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule after above-mentioned composite granule and Si complete reaction, becomes the MoSi of high temperature composite ₂-Si ₃N ₄Complex matrix.Two, have in the blank sintering process that liquid Si occurs mutually, concurrent intercrescence becomes reaction to form MoSi ₂Phase, these factors have promoted Mo, Si atomic diffusion, and blank can become integral material under normal pressure or less pressure, thereby has simplified the sintering process of high temperature composite; Three, press working sintering blank not only can change blank shapes, can also eliminate hole residual in the blank, improve Si in the complex matrix ₃N ₄The distribution of particulate, thereby the production cost of reduction hot parts, the performance of raising high temperature composite;

Composite high-temperature molybdenum disilicide-base material provided by the present invention is mainly by MoSi ₂, Si ₃N ₄And the material reinforcement phase composite, its special feature is: said MoSi ₂And Si ₃N ₄Constitute complex matrix, MoSi ₂Average grain size less than 2 microns, Si ₃N ₄The median size of particulate is less than 1 micron, Si ₃N ₄The volume ratio that accounts for complex matrix is greater than 5%, at MoSi ₂-Si ₃N ₄Part MoSi in the complex matrix ₂Crystal grain and part Si ₃N ₄Be coherence or semicoherent interface between the particulate, said material reinforcement is SiC, ZrC, HfC, Si mutually ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂, Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂In one or more, the volume ratio that material reinforcement accounts for high temperature composite mutually is 0～80%.

Si ₃N ₄Particulate can at high temperature keep stable, and difficult gathering is grown up.Work as Si ₃N ₄Particulate and tiny MoSi ₂Crystal grain constitutes the MoSi of high-temperature material jointly ₂～Si ₃N ₄During complex matrix, can strengthen crystal boundary effectively, suppress MoSi in the complex matrix ₂Grain growth, stabilized matrix microtexture improve MoSi ₂Crystal grain is 400～1000 ℃ middle temperature oxidation-resistance, adjust the thermal expansivity of complex matrix, thereby improve room temperature toughness, high-temp plastic, the middle temperature oxidation-resistance of complex matrix, improve the useful life longevity of complex matrix, and improve the heat cooperation between mutually of complex matrix and material reinforcement.

The adding material reinforcement can improve hot strength, high-temperature creep resistance and the room temperature toughness of high temperature composite mutually.When using under 1200～1600 ℃ of atmospheric environments, the preferable material strengthening phase is SiC.MoSi ₂, Si ₃N ₄, good consistency is arranged between the SiC, any chemical reaction does not at high temperature take place, weave construction is stable; MoSi ₂, Si ₃N ₄Can form fine and close SiO on the surface with SiC ₂Oxide film, the protection material inside is not continued oxidation; The SiC crystal can keep high intensity and high creep-resistant property in whole 1200～1600 ℃ of temperature ranges, be effective High-Temperature Strengthening phase; Multiple SiC particle, whisker, staple fibre and macrofiber commercially produced product have been arranged now, can be on top layers such as its surface-coated six side BN, graphite so that and form the weak interface structure between the complex matrix; So can improve hot strength, the high-temperature creep resistance of this patent high temperature composite mutually effectively 1200～1600 ℃ of temperature range SiC material reinforcement, improve room temperature toughness, and make this patent high temperature composite that good oxidation-resistance, good structure stability and stable mechanical performance be arranged.

It is as follows that the present invention prepares the method steps of above-mentioned composite high-temperature molybdenum disilicide-base material:

1) preparation Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule

1.1) selection Mo ₂The N powder is initial powder, perhaps selects Mo ₅Si ₃Or/and Mo ₃The Si powder is initial powder, and the median size of initial powder is 10 nanometers～100 micron;

1.2) above-mentioned initial powder is carried out following processing

With above-mentioned Mo ₂The initial powder of N carries out carrying out nitrogenize-siliconizing again after siliconizing or the siliconizing; Perhaps

With above-mentioned Mo ₅Si ₃Or/and Mo ₃The initial powder of Si carries out nitrogenize-siliconizing;

Said siliconizing is: make Mo ₂N and Si element complete reaction generate Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule

Said nitrogenize-siliconizing is: make Mo ₅Si ₃And Mo ₃Si or make Mo ₅Si ₃And MoSi ₂With nitrogen element complete reaction, generate Mo ₂N and Si ₃N ₄, and then carry out above-mentioned siliconizing, obtain Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule.

The total degree of nitrogenize-siliconizing is more than or equal to 1 time;

2) above-mentioned composite granule is mixed mutually with Si powder, material reinforcement, get compound, wherein material reinforcement is SiC, ZrC, HfC, Si mutually ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂, Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂In one or more, Si powder add-on under the situation of not considering the nitrogenize of Si element and loss in the sintering process by composite granule in Mo ₅Si ₃And/or Mo ₃Si and Si element complete reaction generate MoSi ₂Determine;

3) above-mentioned compound is pressed into blank;

4) sintering blank

4.1) pre-burning: blank is heated to 1200～1400 ℃, is incubated 1～60 minute, make the blank internal and external temperature even;

4.2) sintering: blank is heated to 1415～1550 ℃, is incubated 30～120 minutes, make Mo ₅Si ₃Phase, Mo ₃Si phase and Si element complete reaction all change MoSi into ₂Phase obtains the composite high-temperature molybdenum disilicide-base material blank;

5) eliminate the gap, obtain fine and close blank

Blank behind the sintering is heated to 1300～1650 ℃, to blank push, mold pressing, rolling or forging and pressing viscous deformation handle to obtain fine and close blank, total deformation is greater than 10%, perhaps

Directly obtain fine and close blank by hot pressing or HIP sintering, that is, sintering and viscous deformation are carried out simultaneously.

Because at Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Need in the preparation process of composite granule initial powder is carried out silication and/or nitrogenize and siliconizing repeatedly, until in powder, forming enough Si ₃N ₄Particulate.Initial powder diameter greatly then mean nitrogen, Siliciumatom diffuse to the required time of silt interior long, production efficiency is low; Then excessive Si when the powder diameter is too small ₃N ₄Particulate can form on the powder surface, influences the sintering character of composite granule.The optimized choice scope of initial powder median size is 40 nanometers to 4 micron.Can use multiple diverse ways to prepare initial powder, as MoO ₃Powder directly reduces and nitrogenize becomes Mo ₂The N powder, the metal molybdenum powder nitrogenize becomes Mo ₂The N powder, nitrogenize such as metal molybdenum filament, sheet become Mo ₂N mutually after again fragmentation become powder, arc melting prepares Mo ₅Si ₃Phase or Mo ₃Si mutually after again fragmentation become powder, reaction sintering prepares Mo ₅Si ₃Phase or Mo ₃Si mutually after again fragmentation become powder etc.Among these methods, use existing temperature programming method with MoO ₃Powder directly reduces and nitrogenize becomes Mo ₂The method of N powder has that technology is easy, production cost is low, Mo ₂Characteristics such as the N powder is tiny evenly, contaminating impurity is few are more suitable for preparing initial powder required for the present invention.

Nitrogenize and siliconizing can increase Si in the composite granule repeatedly ₃N ₄The volume content of particulate.Mo ₅Si ₃Powder or Mo ₃Si powder nitriding treatment, Mo ₂The Si that obtains after the N powder siliconizing ₃N ₄The volume of phase, the MoSi that obtains after fully reacting with above-mentioned powder and Si element ₂The ratio of the volume of phase is respectively 0.33,0.18 and 0.21.After repeatedly handling, after Mo2N powder silication-nitrogenize-silication-nitrogenize-silication, Si in the composite granule ₃N ₄The volume of phase is each Si that obtains that handles ₃N ₄The volume sum of phase.So, can adjust Si in the composite granule by molybdenum silicon compound composition, adjustment nitrogenize-methods such as siliconizing number of times in the control powder ₃N ₄The content of phase, thereby Si in the control high-temperature material complex matrix ₃N ₄The volume content of phase.When silication repeatedly, owing to MoSi occurs in the composite granule ₂Mutually, when subsequently nitrogenize and siliconizing, can form Si ₃N ₄The top layer hinders subsequently nitrogenize and siliconizing, so the last time before the siliconizing, preferably avoid occurring in the composite granule MoSi ₂Phase.But the add-on that can adjust element silicon the last time during siliconizing prepares Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule.

In the process of above-mentioned processing, by adjusting the temperature of nitrogenize and siliconizing, the Si that evenly separates out Nano grade or submicron rank size in silt interior ₃N ₄Particulate is simultaneously with Mo in the composite granule ₅Si ₃, Mo ₃Si or MoSi ₂Grain refining is to Nano grade or submicron rank size, thus can obtain behind sintering that crystal grain is tiny, microtexture evenly, part MoSi ₂Crystal grain and part Si ₃N ₄The MoSi that semicoherent interface is arranged between the particulate ₂～Si ₃N ₄Complex matrix.

The basic reaction of silication and nitrogenize is as follows:

$2\frac{1}{2}{\mathrm{Mo}}_{2}N+4\frac{7}{8}\mathrm{Si}={\mathrm{Mo}}_5{\mathrm{Si}}_3+\frac{5}{8}{\mathrm{Si}}_3{N}_4$

$1\frac{1}{2}{\mathrm{Mo}}_{2}N+2\frac{1}{8}\mathrm{Si}={\mathrm{Mo}}_3\mathrm{Si}+\frac{3}{8}{\mathrm{Si}}_3{N}_4$

$\frac{1}{2}{\mathrm{Mo}}_{2}N+2\frac{3}{8}\mathrm{Si}=\mathrm{Mo}{\mathrm{Si}}_2+\frac{1}{8}{\mathrm{Si}}_3{N}_4$

${\mathrm{Mo}}_5{\mathrm{Si}}_3+3\frac{1}{4}{N}_2=2\frac{1}{2}{\mathrm{Mo}}_{2}N+{\mathrm{Si}}_3{N}_4$

${\mathrm{Mo}}_3\mathrm{Si}+\frac{17}{12}{N}_2=1\frac{1}{2}{\mathrm{Mo}}_{2}N+\frac{1}{3}{\mathrm{Si}}_3{N}_4$

The add-on of Si can be estimated according to following formula in the compound in actual production:

Total add-on=building-up reactions amount+nitrogenizing reaction amount+steam raising amount+surplus

Here " building-up reactions amount " represents Mo ₅Si ₃Phase or Mo ₃Si mutually and Si element building-up reactions, all become MoSi ₂The Si amount that phase time consumed, " nitrogenizing reaction amount " are illustrated in above-mentioned building-up reactions and finish the direct mutually nitrogenize formation of Si Si in the preceding blank ₃N ₄The Si amount that is consumed, the Si amount that " steam raising amount " expression blank breaks away from by steam raising in each course of processing, extra Si number of elements of adding in " surplus " expression blank.The purpose that adds surplus is to reduce the possibility that occurs poor Si zone in blank, whole Mo in the blank behind the assurance sintering ₅Si ₃Phase or Mo ₃Si can become MoSi with the Si phase reaction mutually ₂Phase.Add loose surplus and help to loosen requirement, reduce production costs technological operations such as powder process, batch mixing, moulding, dewaxing, sintering.But unnecessary Si element need all be nitrided into Si after changing end ₃N ₄Phase is so should select suitable surplus according to design requirements.

Can use any existing process method to prepare compound, as refinements such as machine mixer or ball mill, the above-mentioned composite granule of mixing and silica flour, time is generally 0.25～8 hour, add material reinforcement phase particle, whisker, staple fibre and dispersion agent, softening agent, forming agent etc. then and continue to mix 0.25～8 hour acquisition compound, perhaps with behind the uniform mixing such as above-mentioned composite granule, silica flour and dispersion agent, softening agent, forming agent, with the material reinforcement compound compound that becomes of macrofiber mutually.Press the process requirements that viscous deformation behind sintering, the sintering etc. handles and the performance requirement of high temperature composite etc., whisker, staple fibre and macrofiber in the above-mentioned compound are arranged to processing such as, stack, combinations, make whisker in the compound, staple fibre and macrofiber that required distribution of orientations be arranged, after moulding, obtain the high-temperature material blank.

Following reaction appears in the blank sintering process of the present invention:

$\frac{7}{5}{\mathrm{Si}}_{\left(1\right)}+\frac{1}{5}{\mathrm{Mo}}_5{\mathrm{Si}}_{3\left(s\right)}={\mathrm{MoSi}}_{2\left(s\right)}$

$\frac{5}{3}{\mathrm{Si}}_{\left(1\right)}+\frac{1}{3}{\mathrm{Mo}}_3{\mathrm{Si}}_{\left(s\right)}={\mathrm{MoSi}}_{2\left(s\right)}$

Their reaction enthalpy is significantly less than the reaction enthalpy of Si element and Mo element.The Si element is molten into liquid phase after being heated to 1412 ℃, Si liquid and Mo ₅Si ₃React when contacting and form MoSi ₂Phase.Although instantaneous top temperature can reach on 2000 ℃, the new MoSi that forms ₂Remain solid mutually always, cover Mo ₅Si ₃On the particle, with Si liquid and solid-state Mo ₅Si ₃Be separated.Unreacted Si liquid is along Mo ₅Si ₃Particle surface launches, with Mo ₅Si ₃The MoSi of whole particle is surrounded in the formation that contacts and react ₂Thin layer, remaining Si liquid temporarily rests between the solid granulates.The Si atom must diffuse through solid-state MoSi later on ₂Ability and Mo behind the layer ₅Si ₃Continue reaction mutually and form new MoSi ₂Phase, speed of response are slow relatively, Si element and Mo in blank ₅Si ₃All completely dissolves mutually.Because speed of response is slow relatively, MoSi ₂The lasting temperature of layer is the medial temperature of a little higher than blank.And reaction enthalpy helps to improve the blank temperature inside, minimizing blank internal-external temperature difference.At 1412 ℃ of liquid Si phases and Mo ₃The Si phase reaction forms MoSi ₂Phase time, reaction enthalpy can be with the MoSi that newly forms ₂Heat phase is to partial melting, but can not be at liquid MoSi ₂The more Si element of fusing periphery forms more MoSi among entering reaction before solidifying mutually ₂Phase is carried out so instead would not spread certainly.But big Si liquid and the Mo that drips ₃Si directly contacts mutually then may form bigger MoSi ₂Molten drop becomes bigger MoSi after solidifying ₂Crystal grain.So.For Mo ₃Si phase volume content is far longer than Mo ₅Si ₃The Mo of phase volume content ₃Si-Mo ₅Si ₃-Si ₃N ₄Composite granule preferably carries out once gaseous state silication in short-term, the last time again at Mo after the siliconizing ₃The Si particle surface forms Mo ₅Si ₃The top layer.

In composite granule, increase Mo ₃Si phase or Mo ₅Si ₃The quantity of phase can increase the quantity of Si phase in the blank, thereby strengthens the sinterability of blank.But Mo ₃Si phase and Mo ₅Si ₃The existence of phase has reduced Si simultaneously ₃N ₄The stability of phase.After Heating temperature surpasses 1200 ℃, in vacuum environment, Si ₃N ₄Mutually can and Mo ₅Si ₃Phase or Mo ₃Si reacts mutually and forms MoSi ₂Phase and nitrogen.Because MoSi ₂Phase and Si ₃N ₄Mutually chemical reaction not taking place, increases MoSi in the composite granule ₂The quantity of phase has then increased Si ₃N ₄The stability of particulate.Use Mo ₅Si ₃Poor Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule although the coking property of blank is relatively poor relatively, after hot pressing or HIP sintering, can keep the submicron order crystalline structure preferably in complex matrix.Therefore, preferably add an amount of element silicon when the siliconizing, obtain required Mo according to the performance requirement of cost requirement and high-temperature material ₃Si-Mo ₅Si ₃-Si ₃N4 or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule.

On mechanism, sintering process of the present invention can be divided into three phases: pre-burning stage, liquid phase sintering stage and adjusting stage.Require to reduce the internal-external temperature difference of blank in the pre-burning stage, but require to stop Si in the composite granule simultaneously ₃N ₄Particulate breakup also prevents the excessive nitrogenize of Si particle, therefore will select suitable holding temperature and soaking time.Sintering stage blank becomes the integral material with certain density, homogeneous microstructure.Si particles fuse in this stage blank, Si liquid accumulates between the solid granulates, helps rotation, slip and the rearrangement of solid granulates, impels blank to shrink, and the Si atomic diffusion is passed through MoSi simultaneously ₂Top layer and inner Mo ₅Si ₃Phase or Mo ₃The Si phase reaction forms more MoSi ₂Phase.Along with the carrying out of sintering process, the MoSi of formation ₂Connect solid granulates mutually gradually.After forming extensively stable solid-state connection in the blank, position relative fixed between the solid granulates, obvious variation no longer takes place in blank shapes, liquid phase sintering stage this moment finishes, automatically enter the adjusting stage, so can only there be finite time in the liquid phase sintering stage of this patent blank, is generally 1～30 minute.Remaining Mo in the adjusting stage blank ₅Si ₃Phase, Mo ₃Si phase and Si phase reaction all change MoSi into ₂Phase, residue Si element all is nitrided into Si ₃N ₄Phase.

The density of blank reached maximum when the adjusting stage began, and this moment, the blank internal pore was called residual porosities.Can not free shrink at the adjusting stage blank, and reactant Mo ₅Si ₃Phase, Mo ₃Si mutually with Si volume sum mutually greater than reaction product MoSi ₂So the volume of phase is along with forming new MoSi ₂Phase forms between solid granulates widely, space that be evenly distributed, very tiny, is referred to as to react the space.Finishing back blank internal pore in whole sintering process is residual porosities and reaction space sum.Having of space helps Si element fast transferring and diffusion in blank, makes remaining Mo ₅Si ₃Or Mo ₃Si changes MoSi mutually fully into ₂Phase also helps nitride dielectric layers such as nitrogen or decomposition ammonia to be deep into blank inside simultaneously, forms Si on surface, space and Si element reaction ₃N ₄Particle is eliminated remaining Si element in the blank.

In sintering process, occur liquid phase in the blank, building-up reactions takes place, help the blank densification.Need not to add in addition sintering agent, under normal pressure or only apply less sintering pressure and have certain density to overcome the resistance that the relative blank of material reinforcement shrinks, blank can be sintered into, organize tiny and uniform integral material.No Si phase or Mo in sintering finishes the back blank ₅Si ₃Phase, Mo ₃Si is mutually residual, has guaranteed that high temperature composite has good high-temperature and normal temperature mechanical property and oxidation-resistance after eliminating the internal clearance.

The high temperature composite blank that obtains behind the above-mentioned sintering is carried out viscous deformation handle, can eliminate the blank internal clearance, improve material reinforcement and distribute mutually and heterogeneous microstructure, change the shape of blank.Need to prove that preparation method provided by the present invention makes the high temperature composite blank have certain high temperature viscous deformation performance.Another kind method is to apply big pressure when sintering, makes to set up blank constantly generation viscous deformation in sintering process that solid phase connects, and eliminates the internal clearance, directly obtains fine and close gapless high-temperature material blank after sintering finishes.

In order further to improve the performance of high temperature composite, in whole process of preparation, should completely cut off contacting of various raw materials, semifinished material or blank and Sauerstoffatom or oxonium ion as far as possible.For this reason, said initial powder, Si powder, non-oxidized substance material reinforcement phase SiC, ZrC, HfC, Si ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂In the oxygen element atom percentage content less than 1%, oxide material strengthening phase Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂The oxygen element atom percentage content of middle surface adsorption is less than 0.5%; Preparing, using protective medium to separate with extraneous oxygen element when preserving and use above-mentioned raw materials and composite granule, compound with blank, the atom percentage content of the oxygen molecule in the protective medium, Sauerstoffatom and oxonium ion is less than 0.5%; Blank when viscous deformation is handled behind sintering and sintering the using gas protective medium separate with extraneous oxygen element with extraneous oxygen element and separate, the atom percentage content of oxygen molecule and Sauerstoffatom is less than 0.1% in the gas shield medium; At mixed powder, the atom percentage content of Sauerstoffatom and oxonium ion is less than 0.5% in the subsidiary material such as the ball-milling additive that is added in the preforming, dispersion agent, softening agent, forming agent.

Studies show that: MoSi ₂, Si ₃N ₄After oxygen-containing mediums such as material such as SiC and atmosphere contacted, the Si atom on surface can react with Sauerstoffatom and form SiO ₂Phase or Sauerstoffatom be attracted to material surface, when sintering and the Si atomic reaction form SiO ₂Phase.These SiO behind the sintering ₂Still be retained in mutually intergranule, form the vitreous state SiO that thickness is 1 nanometer～1 micron ₂Film or coacervate.At existing MoSi ₂, Si ₃N ₄In the production process of the monophase materials of SiC etc. or matrix material, SiO ₂Normally kept wittingly or be incorporated among the blank, to improve the coking property of blank.But vitreous state SiO ₂Film or coacervate are at room temperature moulded, toughness is very low, are the area of origin and the extended channels of above-mentioned materials crackle when stressed, cause the room temperature toughness of material low.Vitreous state SiO after being heated to 1100～1200 ℃ ₂Begin mutually to soften, and along with the continuation of temperature raises, its softening rate is higher than MoSi far away ₂The softening rate of crystal grain, vitreous state SiO after temperature surpasses 1373～1473 ℃ ₂The creep strength of phase is reduced to and approaches zero, so distortion concentrates on vitreous state SiO when at high temperature material is stressed ₂In film or the coacervate, they still are the area of origin and the extended channel of crackle.SiO appears in high-temperature material ₂Reduce room temperature and high-temperature mechanical property when identical, therefore, should reduce SiO in the high temperature composite as far as possible ₂The content of phase or other oxide compound.Can the using gas protective medium in the production process, as argon gas, hydrogen etc.; When storage and use, except that the gas protective medium, can also use the liquid protective medium, as gasoline, kerosene, kerosene～paraffin mixed solution, kerosene and new LDPE (film grade) mixed solution etc.; Also can use the solid protective medium, as forming complete paraffin-protected film, new LDPE (film grade) protective membrane etc. on the powder surface.Isolation from oxygen atom, no Sauerstoffatom itself or the oxonium ion existence effectively of these protective mediums, do not influence later mixing, forming processes and when sintering, can eliminate fully.

Above-mentioned steps 1) the element silicon source is the gaseous state silicide in the siliconizing, and its dividing potential drop is 0.01～0.5MPa, and the siliconizing temperature is 450～1200 ℃, and the time is 0.5～12 hour; Nitrogen element source is a nitrogen in the nitriding treatment of step 1), ammonia or gaseous state nitride, and its dividing potential drop is 0.1～20MPa, and the nitriding treatment temperature is 450～1200 ℃, and the time is 0.5～12 hour.The silication medium can be SiCl ₄The mixed gas that mixes Deng gaseous state silicide and hydrogen, argon etc.; Nitride dielectric layer can be nitrogen, decomposition ammonia or nitrogen～hydrogen, nitrogen～argon-mixed.In siliconizing and nitriding treatment process, should fully stir powder, to reduce the treatment time.Between each the processing, also answer mechanical disintegration or ball milling powder with loose sintered compact of fragmentation and coacervate.

In order to simplify siliconizing technology, reduce production costs above-mentioned steps 1) in siliconizing preferably carry out like this: will contain Mo ₂The powder of N phase and Si powder uniform mixing feed hydrogen or argon gas earlier in reactor, more above-mentioned mixed powder is placed reactor, feed HCl gas or Cl gas then, closed reactor, the temperature of adjusting in the reactor is 450～1200 ℃, insulation, stirring powder make Mo ₂N and Si element reaction are transformed into Mo fully ₃Si-Mo ₅Si ₃-Si ₃N4 or Mo ₅Si ₃-MoSi ₂-Si ₃N.The purpose that feeds hydrogen or argon gas is to get rid of the atmosphere in the reactor and adjust the HCl gas that adds subsequently in the reactor or the concentration of Cl gas.The content that improves hydrogen can reduce the content that siliconizing finishes residual gaseous state silicon chlorides in the post-reactor.Silica flour and HCl or Cl reaction forms gaseous state silicon chlorides, gaseous state silicon chlorides and Mo in enclosed reaction vessel ₂The molybdenum atom on N powder surface reacts and forms MoSi ₂On molybdenum silicon compound top layer, Siliciumatom is to Mo ₂The N silt interior diffuses to form new Si ₃N ₄Particulate and more molybdenum silicon compound.After the Si powder is gasified totally in the reactor, Mo ₂Excessive and the macrobead silication deficiency of N small-particle silication.This post-reactor continues to keep sealing and heat-insulation pressure keeping.Along with the Siliciumatom diffusion, macrobead surface silicon content reduces, and changes Mo into ₅Si ₃Phase or Mo ₃The Si phase, and the small-particle top layer still is MoSi ₂Phase.So the small-particle surface silicon atoms reenters the silication medium, and in the large particle surface deposition, silicone content tends to balance in all powders.After 0.5～12 hour, silicone content back in a basic balance siliconizing finishes in all particles at the closed reactor heat-insulation pressure keeping.Owing to when carrying out above-mentioned siliconizing, can accurately control the add-on of element silicon, and the even content of element silicon in the powder of different shapes size, thereby guaranteed the quality of siliconizing.

Above-mentioned steps 1) in to Mo ₂N carries out preferably carrying out powder surface denitrogenation processing before the siliconizing mutually, that is, temperature by each powder surface, is used for reducing the nitrogen content on powder top layer, 5～60 minutes treatment times with flowing hydrogen less than 450 ℃; To Mo ₅Si ₃-Mo ₃Si carries out preferably carrying out the desiliconization processing of powder surface before the nitriding treatment mutually, that is, temperature by each powder surface, is used for reducing the silicone content on powder top layer, 5～60 minutes treatment times with flow HCl gas or Cl gas less than 450 ℃.When nitrogenize or siliconizing, at first form Si on the powder surface ₃N4 phase, and surperficial Si ₃N ₄The existence of phase has reduced Mo ₂N mutually or the contact area of molybdenum silicon compound and extraneous Siliciumatom or nitrogen-atoms and has reduced the coking property of composite granule.Therefore before silication or nitriding treatment, preferably Mo2N powder or molybdenum silicon compound powder are carried out surperficial denitrogenation or desiliconization processing, the content of nitrogen element or element silicon in the reduction powder top layer.

For Si ₃N ₄The composite granule that content is high, in order to improve its coking property, after siliconizing is finished the last time, be molybdenum element source and be that surface plating molybdenum and the processing of surface plating silicon are carried out to composite granule in the element silicon source with gaseous state molybdenum thing with the gaseous state silicide, treatment temp is less than 600 ℃, 5～60 minutes treatment times.MoCl can be selected in the molybdenum source ₅Deng, SiCl can be selected in the silicon source ₄Deng.

In above-mentioned steps 4 and the step 5); preferably feed the gas shield medium that contains nitrogen or decompose ammonia; promptly; feeding the protective medium that contains nitrogen or decompose ammonia behind pre-burning, sintering and the sintering viscous deformation treatment stage; wherein the dividing potential drop of nitrogen or decomposition ammonia is 0.01～5MPa, is used for reducing blank Si ₃N ₄Particulate decomposes, and makes when the sintering stage finishes that the complete nitrogenize of remaining Si element becomes Si in the blank ₃N ₄After Heating temperature surpasses 1200 ℃, in vacuum environment, Si ₃N ₄Mutually can and Mo ₅Si ₃Phase or Mo ₃Si reacts mutually and forms MoSi ₂Phase and nitrogen.Because this reaction has reduced Si in the complex matrix ₃N ₄The quantity of particulate has reduced the performance of high temperature composite.Feeding the protective medium that contains nitrogen or decompose ammonia behind pre-burning, sintering and the sintering viscous deformation treatment stage, can reduce Si in the blank ₃N ₄Particulate decomposes, and makes when the sintering stage finishes that the complete nitrogenize of remaining Si element becomes Si in the blank ₃N ₄Concrete protective medium can be selected nitrogen, decompose ammonia, nitrogen-argon-mixed, nitrogen-hydrogen gas mixture etc., and these gas shield media can stop Si in the blank ₃N ₄Particulate breakup, but can make simultaneously silicon grain or silicon liquid surfaces nitrided again, form thick relatively Si ₃N ₄Particle.

This patent composite powder and Si powder mix, and can be used for welding MoSi ₂Base high temperature composite part.The normal direction of face of weld should be consistent with the normal direction of face of weld place material reinforcement phase.The composition of scolder is mixed uniformly composite powder and silica flour, wherein can add the intensity that a small amount of SiC particle increases face of weld.Scolder is pressed into the uniform thin slice of thickness, inserts between face of weld, exert pressure, the method for whole heating of employing or resistive heating makes silicon grain fusing and composite granule reaction formation MoSi in the scolder ₂, simultaneously face of weld is connected into integral body.

Compared with prior art, advantage of the present invention is: matrix of the present invention is MoSi ₂And Si ₃N ₄The complex matrix of the grain refining that constitutes has improved the oxidation-resistance of matrix in mesophilic range, has adjusted the thermal expansivity of matrix; The present invention has in the blank sintering process that liquid Si occurs mutually, concurrent intercrescence becomes reaction to form MoSi ₂Phase, blank can be sintered into integral material under normal pressure or less pressure, thereby has simplified the sintering process of high temperature composite, has reduced production cost; Another advantage of the present invention is that the sintering blank has certain high temperature plasticity, can eliminate gap and the microtexture of improving material by plastic working.Thereby high temperature composite of the present invention has well behaved complex matrix, and complex matrix can reach best fit easily with strengthening phase, and not only production cost is lower, the hot strength of high temperature composite, high-temperature creep resistance and room temperature good toughness.

Embodiment

Embodiment 1

50 millimeters of preparation external diameters, 30 millimeters of internal diameters, the hollow disk of thick 6 millimeters high temperature composite.

In the kerosene medium be 1 micron Mo with mean particle size ₂N powder and Si powder uniform mixing, wherein Si grain weight amount is Mo ₂28% of N grain weight amount.Reactor is vacuumized, feed hydrogen then and make that the pressure of hydrogen is malleation (its main purpose is that the atmospheric medium in the reactor is got rid of) in the reactor, keep flow hydrogen gas, in reactor, add above-mentioned mixed powder, stir powder; By the speed reactor heating to 450 of 5 ℃/min ℃.Feeding HCl gas and making the concentration of HCl in the reactor is 50%, then closed reactor.Reactor heating to 1050 ℃ is incubated 5 hours, makes to adopt Mo ₂The silication of N powder becomes Mo ₅Si ₃-Si ₃N ₄Composite granule, wherein Si ₃N ₄Volume content be about 27%.

Composite granule and Si powder are added ball mill, and the weight of Si powder is 32% of composite granule weight.With kerosene is protective medium, and ball milling made each component refinement and uniform mixing in 6 hours, adds weight and is the polyethylene wax of composite granule weight 1% and continued ball milling 2 hours.Take out mixed powder, remove kerosene in nitrogen environment, the kerosene volume content in mixed powder is less than 5%.Selecting the SiC staple fibre is the material reinforcement phase, and its diameter and length are respectively 40～50 microns and 500～600 microns.With mixed powder, SiC staple fibre and polyethylene wax join in the stirrer, and wherein the weight of SiC staple fibre and polyethylene wax is respectively 38% and 12% of mixed powder weight.Be heated to 105 ℃, stir and take out after making each component uniform mixing in 2 hours, vacuum is got rid of gas wherein, adjusts temperature to 90 and ℃ obtains plastic mix.Obtain the plastic mix rod of 4 millimeters of diameters by tapered squeezing, wherein SiC staple fibre major axis is arranged in parallel, and is axially consistent with charge bar.Charge bar is spiraled into the annulus of 29 millimeters of internal diameters, 51.4 millimeters of external diameters, obtain 29 millimeters of internal diameters, 52 millimeters of external diameters, high 9.6 millimeters hollow disk blank through operations such as exhaust, extrusion molding, shapings.

Whole sintering process is carried out in nitrogen.Be heated to 800 ℃ of dewaxings, be heated to 15 minutes even blank temperature of 1300 ℃ of insulations, be heated to 1450 ℃ of insulations and carried out liquid phase sintering in 30 minutes, be heated to 1500 ℃ of insulations 60 minutes then, nitrogenize remains the Si phase, obtains the sintering blank of 29.8 millimeters of internal diameters, 50.2 millimeters of external diameters.

At 1500 ℃ of nitrogen environment counterdie pressed compact spare to thickness is 6.2 millimeters, eliminates internal void.The surface imperfection layer is removed in machining, obtains finished product.

Embodiment 2

The preparation length and width respectively are 80 millimeters, the high temperature composite sheet material that thickness is 1.2 millimeters.

Mean particle size is 0.5 micron Mo ₂The N powder is treated as Mo three times through silication, nitrogenize, silication ₅Si ₃～Si ₃N ₄Composite granule, wherein Si ₃N ₄Volume content be about 54%.Siliconizing technology is substantially the same manner as Example 1 for the first time, and difference is that the silication temperature is 950 ℃, and soaking time is 4 hours.After the siliconizing powder is directly put among the kerosene, do not contacted with air.The ball milling powder was eliminated caking in 4 hours.Reactor is vacuumized, feed nitrogen then and make that nitrogen gas pressure is a malleation in the reactor.Keep flow of nitrogen gas, in reactor, add above-mentioned powder, stir powder.By the reactor heating to 450 of 5 ℃/min ℃.Closed reactor and continue to feed nitrogen nitrogen pressure to the reactor be 1MPa.Reactor heating to 950 ℃ and to keep nitrogen pressure be 1MPa is incubated 8 hours, makes the powder nitrogenize.Nitrogenize finishes postcooling powder temperature to room temperature, directly puts among the kerosene then.Siliconizing technology is with for the first time identical for the second time.

Composite granule and Si powder are added ball mill, and the weight of Si powder is 23% of composite granule weight.With kerosene is protective medium, and ball milling made each component refinement and uniform mixing in 6 hours.Take out mixed powder, remove kerosene in nitrogen environment, the kerosene volume content in mixed powder joins mixed powder and polyethylene wax in the stirrer less than 5%, and the weight of polyethylene wax is 10% of mixed powder weight.Be heated to 105 ℃, stir and took out behind the uniform mixing in 1 hour, vacuum is got rid of gas wherein, adjusts temperature to 90 ℃ acquisition plastic mix.Selecting the SiC macrofiber is the material reinforcement phase, and its diameter is 110～120 microns.Plastic mix is pressed into the thin slice of 85 millimeters of the length of sides, 130 microns of thickness.With the macrofiber individual layer, single-orientated, evenly be closely packed on the thin slice, the orientation and the length of side direction consistent (or vertical) of thin slice are pressed into macrofiber among the thin slice then.With ten thin slice stacks, length of side alignment, the contiguous slices medium staple fibre is axially vertical.Vacuum exhaust, compacting obtains blank.

Whole sintering process is carried out in nitrogen.Be heated to 800 ℃ of dewaxings, be heated to 5 minutes even blank temperature of 1300 ℃ of insulations,, be heated to 1450 ℃ and be incubated 30 minutes and carry out hot pressed sintering, obtain blank behind the sintering blank pressurization 5MPa.

At 1500 ℃ of nitrogen environment counterdie pressed compact spare to thickness is 1.3 millimeters, eliminates internal void.The unnecessary limit of line cutting removal portion, the surface imperfection layer is removed in machining, obtains finished product.

Embodiment 3

20 millimeters of the preparation length of sides, thick 5 millimeters high temperature composite square.

The preparation method of composite granule and mixed powder is identical with embodiment 1.The adding median size is that 160 microns YSZ powder (yttria-stabilized zirconia powder) is a strengthening phase, and add-on is 20% of a mixed powder weight.Behind the uniform mixing compound is pressed into the blank of 8.5 millimeters of the length of side 26 mm thick

Sintering process is carried out in nitrogen.Be heated to 10 minutes even blank temperature of 1300 ℃ of insulations, be heated to 1450 ℃ of insulations and carried out liquid phase sintering in 30 minutes, be heated to 1500 ℃ of insulations 60 minutes then, nitrogenize residue Si phase.At 1500 ℃ of nitrogen environment counterdie pressed compact spare to thickness is 5.2 millimeters, eliminates internal void.The surface imperfection layer is removed in machining, obtains finished product.

Claims (8)

1, a kind of composite high-temperature molybdenum disilicide-base material is mainly by MoSi ₂, Si ₃N ₄And the material reinforcement phase composite, it is characterized in that said MoSi ₂And Si ₃N ₄Constitute complex matrix, MoSi ₂Average grain size less than 2 microns, Si ₃N ₄The median size of particulate is less than 1 micron, Si ₃N ₄The volume ratio that accounts for complex matrix is greater than 5%, at MoSi ₂-Si ₃N ₄Part MoSi in the complex matrix ₂Crystal grain and part Si ₃N ₄Be coherence or semicoherent interface between the particulate, said material reinforcement is SiC, ZrC, HfC, Si mutually ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂, Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂In one or more, the volume ratio that material reinforcement accounts for high temperature composite mutually is 0～80%.

2, the method for preparing the described composite high-temperature molybdenum disilicide-base material of claim 1, its step is as follows:

1) preparation Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule

1.1) selection Mo ₂The N powder is initial powder, perhaps selects Mo ₅Si ₃Or/and Mo ₃The Si powder is initial powder, and the median size of initial powder is 10 nanometers～100 micron;

1.2) above-mentioned initial powder is carried out following processing

With above-mentioned Mo ₂The initial powder of N carries out carrying out nitrogenize-siliconizing again after siliconizing or the siliconizing; Perhaps

With above-mentioned Mo ₅Si ₃Or/and Mo ₃The initial powder of Si carries out nitrogenize-siliconizing;

Said siliconizing is: make Mo ₂N and Si element complete reaction generate Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule;

Said nitrogenize-siliconizing is: make Mo ₅Si ₃And Mo ₃Si or make Mo ₅Si ₃And MoSi ₂With nitrogen element complete reaction, generate Mo ₂N and Si ₃N ₄, and then carry out above-mentioned siliconizing, obtain Mo ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N ₄Composite granule;

The total degree of nitrogenize-siliconizing is more than or equal to 1 time;

2) above-mentioned composite granule is mixed mutually with Si powder, material reinforcement, get compound, wherein material reinforcement is SiC, ZrC, HfC, Si mutually ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂, Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂In one or more, Si powder add-on under the situation of not considering the nitrogenize of Si element and loss in the sintering process by composite granule in Mo ₅Si ₃And/or Mo ₃Si and Si element complete reaction generate MoSi ₂Determine;

3) above-mentioned compound is pressed into blank;

4) sintering blank

4.1) pre-burning: blank is heated to 1200～1400 ℃, is incubated 1～60 minute, make the blank internal and external temperature even;

4.2) sintering: blank is heated to 1415～1550 ℃, is incubated 30～120 minutes, make Mo ₅Si ₃Phase, Mo ₃Si phase and Si element complete reaction all change MoSi into ₂Phase obtains the composite high-temperature molybdenum disilicide-base material blank;

5) eliminate the gap, obtain fine and close blank

Blank behind the sintering is heated to 1300～1650 ℃, to blank push, mold pressing, rolling or forging and pressing viscous deformation handle to obtain fine and close blank, total deformation is greater than 10%, perhaps

Directly obtain fine and close blank by hot pressing or HIP sintering, that is: sintering and viscous deformation are carried out simultaneously.

3, method according to claim 2 is characterized in that said initial powder, Si powder, non-oxidized substance material reinforcement phase SiC, ZrC, HfC, Si ₃N ₄, AlN, ZrN, ZrB, HfB ₂, ZrB ₂In the oxygen element atom percentage content less than 1%, oxide material strengthening phase Al ₂O ₃, Y ₂O ₃, HfO ₂, ZrO ₂The oxygen element atom percentage content of middle surface adsorption is less than 0.5%; Preparing, using protective medium to separate with extraneous oxygen element when preserving and use above-mentioned raw materials and composite granule, compound with blank, the atom percentage content of the oxygen molecule in the protective medium, Sauerstoffatom and oxonium ion is less than 0.5%; Blank when viscous deformation is handled behind sintering and sintering the using gas protective medium separate with extraneous oxygen element with extraneous oxygen element and separate, the atom percentage content of oxygen molecule and Sauerstoffatom is less than 0.1% in the gas shield medium; At mixed powder, the atom percentage content of Sauerstoffatom and oxonium ion is less than 0.5% in the subsidiary material such as the ball-milling additive that is added in the preforming, dispersion agent, softening agent, forming agent.

4, according to claim 2,3 described methods, it is characterized in that

The element silicon source is the gaseous state silicide in the siliconizing of step 1), and its dividing potential drop is 0.01～0.5MPa, and the siliconizing temperature is 450～1200 ℃, and the time is 0.5～12 hour;

Nitrogen element source is a nitrogen in the nitriding treatment of step 1), ammonia or gaseous state nitride, and its dividing potential drop is 0.1～20MPa, and the nitriding treatment temperature is 450～1200 ℃, and the time is 0.5～12 hour.

5, according to claim 2,3 described methods, it is characterized in that the siliconizing in the step 1) is: will contain Mo ₂The powder of N phase and Si powder uniform mixing feed hydrogen or argon gas earlier in reactor, more above-mentioned mixed powder is placed reactor, feed HCl gas or Cl gas then, closed reactor, the temperature of adjusting in the reactor is 450～1200 ℃, insulation, stirring powder make Mo ₂N and Si element reaction are transformed into Mo fully ₃Si-Mo ₅Si ₃-Si ₃N ₄Or Mo ₅Si ₃-MoSi ₂-Si ₃N.

6, according to claim 2,3 described methods, it is characterized in that

In step 1) to Mo ₂N carries out carrying out powder surface denitrogenation processing before the siliconizing mutually, that is, temperature by each powder surface, is used for reducing the nitrogen content on powder top layer, 5～60 minutes treatment times with flowing hydrogen less than 450 ℃;

To Mo ₅Si ₃-Mo ₃Si carries out carrying out the desiliconization processing of powder surface before the nitriding treatment mutually, that is, temperature by each powder surface, is used for reducing the silicone content on powder top layer, 5～60 minutes treatment times with flow HCl gas or Cl gas less than 450 ℃.

7, according to claim 2,3 described methods, it is characterized in that containing nitrogen or cracked ammonium gas shiled medium feeding viscous deformation the treatment stage behind pre-burning, sintering and the sintering, wherein the nitrogen or the dividing potential drop of decomposing ammonia are 0.01～5MPa, are used for reducing blank Si ₃N ₄Particulate decomposes, and makes when the sintering stage finishes that the complete nitrogenize of remaining Si element becomes Si in the blank ₃N ₄

8, method according to claim 5 is characterized in that containing nitrogen or cracked ammonium gas shiled medium feeding viscous deformation the treatment stage behind pre-burning, sintering and the sintering, and wherein the nitrogen or the dividing potential drop of decomposing ammonia are 0.01～5MPa, are used for reducing blank Si ₃N ₄Particulate decomposes, and makes when the sintering stage finishes that the complete nitrogenize of remaining Si element becomes Si in the blank ₃N ₄