Preparation method of aluminum nitride ceramic toughened by aluminum nitride whiskers, dispersed zirconium nitride and enhanced in particle size grading

Abstract

The invention discloses a preparation method of aluminum nitride ceramic toughened by aluminum nitride whiskers, dispersed zirconium nitride and enhanced in particle size grading, and relates to the technical field of aluminum nitride ceramic materials. Submicron fine powder and micron large-particle aluminum nitride powder are graded to enhance the heat conductivity, and the large-particle aluminum nitride powder and crystal whiskers are subjected to surface modification to solve the sintering activity problem; aluminum nitride whiskers are added to enhance the heat conductivity and the fracture toughness; and a zirconium oxide reaction precursor is added, so that in-situ reaction is performed in the sintering process to generate dispersed zirconium nitride particles to strengthen the bending strength. The method has the advantages that a plurality of strengthening means have a synergistic effect, the strengthening defects are mutually compensated, the strengthening effects are mutually promoted, and the obtained aluminum nitride ceramic substrate has high comprehensive performance and has high commercial value and practical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum nitride ceramic materials, and particularly relates to a preparation method of aluminum nitride ceramics with toughening by aluminum nitride whiskers, dispersion of zirconium nitride, and particle size grading enhancement. Background Art

[0002] With the continuous progress of integrated circuit chip technology, while the chip performance is improved, its power and heat generation are also significantly increased. The chip size and packaging volume are developing towards miniaturization, posing new challenges to packaging technology, packaging materials, and the heat dissipation performance of the system.

[0003] As an emerging packaging system material, ceramic substrates generally have excellent insulation performance, high thermal conductivity, high chemical stability, and high strength, and are more suitable for the packaging of power electronic products. Currently, the commonly used ceramic substrate materials mainly include: alumina, zirconia toughened alumina, beryllium oxide, aluminum nitride, silicon nitride, etc.

[0004] Aluminum nitride has a relatively high thermal conductivity base, generally reaching 170 - 220 W / m·K, is non-toxic and environmentally friendly, has a high breakdown voltage, low dielectric constant and dielectric loss. However, its toughness is poor, the flexural strength generally reaches 300 - 400 MPa, and the fracture toughness generally reaches 2 - 4 MPa·m 1 / 2 , in the actual application of aluminum nitride ceramic substrates, they may need to withstand impacts, vibrations, high temperature difference thermal cycles, etc. It is necessary to strengthen the aluminum nitride ceramic materials, explore new strengthening means and optimize the preparation process to meet their actual use requirements.

[0005] CN108863393 discloses a preparation method of high-strength and high-thermal-conductivity aluminum nitride ceramic materials. Using 200nm ultrafine aluminum nitride powder as the basis, adding composite additives, pre-sintering at 1300°C - 1500°C for 1 - 5 hours in an atmospheric-pressure nitrogen-containing reducing atmosphere, and then sintering at 1500°C - 1800°C for 3 - 10 hours in a nitrogen atmosphere to prepare fine-grained ceramics with a thermal conductivity of 180 W / m·k and a flexural strength of 550 MPa.

[0006] CN105777169 discloses an aluminum nitride whisker-reinforced aluminum nitride ceramic material for electronic parts. Adding 5 - 32 wt% of aluminum nitride whiskers to the aluminum nitride ceramic, and using the characteristics of high fracture strength and large elastic modulus of ceramic whiskers to improve the mechanical properties of the aluminum nitride ceramic material, making it have higher reliability when used as an electronic packaging substrate, and the manufacturing method is simple and easy to realize industrial production.

[0007] CN103553691 discloses a method for preparing a particle-dispersed toughened aluminum nitride ceramic substrate for high-power LED lighting packaging, wherein 3-12wt% of a toughening phase is added, and the toughening phase is one or a composite of any of molybdenum, tungsten, niobium, molybdenum carbide, tungsten carbide, and niobium carbide. The fracture toughness of the AlN substrate is effectively improved through the toughening mechanisms of crack deflection bending, crack bridging, and residual stress.

[0008] The above methods have their own advantages, but there are also some problems, such as the need for waterproofing of nano-scale ultrafine aluminum nitride powder, the use of highly dangerous gas sources such as hydrogen cyanide, the shortening of the aspect ratio of the whiskers after long-term ball milling, the loss of their whisker structural characteristics and strengthening capabilities, and the toughening effect of the toughening phase is not obvious enough. Summary of the invention

[0009] In view of the problems existing in the above-mentioned background technology, the present invention aims to provide a method for preparing aluminum nitride ceramics with aluminum nitride whisker toughening, dispersed zirconium nitride and enhanced particle size grading.

[0010] The key technical principle of the present invention is:

[0011] Introducing aluminum nitride whiskers into aluminum nitride ceramics, the structural characteristics of the whiskers make them a heat conduction path in aluminum nitride ceramics, which can improve the intrinsic thermal conductivity of the ceramics, and greatly enhance the fracture toughness of the ceramics through crack deflection effect, whisker debonding effect, whisker pull-out effect, and whisker bridging effect. However, due to the bridging effect of whiskers in the ceramic body structure, the liquid phase of the sintering aid cannot diffuse, migrate, and coat well during the sintering process, resulting in a decrease in the sintering activity of the ceramics. After sintering, there are some non-densified areas and sintering defects in the ceramics, which reduce the density and bending strength and need to be reinforced.

[0012] A certain amount of sintering aid phase is coated on the surface of the whisker, the corresponding nitrate of the selected auxiliary phase component is dissolved in ethanol, and then precipitated and coated on the surface of the whisker, and nitrogen is passed through at the decomposition temperature corresponding to the nitrate to keep it warm, so as to obtain a loose, highly active and uniform auxiliary phase coating.

[0013] Introducing dispersed zirconium nitride particles into aluminum nitride ceramics can strengthen the grain boundaries of aluminum nitride ceramics, change the crack propagation path, induce more transgranular fractures, and improve the strength and fracture toughness of the ceramics. However, the intrinsic thermal conductivity of zirconium nitride is very low, about 20W / m·K, and it enters aluminum nitride ceramics as a composite phase, so its morphology, existence position and total amount of addition need to be controlled.

[0014] The amount of zirconium nitride added should not be too high to reduce its adverse effect on the thermal conductivity of aluminum nitride ceramics. After a trace amount is added, the dispersion of zirconium nitride will increase, making it less likely to self-agglomerate. It should also be controlled to exist only at the aluminum nitride grain boundary and not grow into the interior of the aluminum nitride grains.

[0015] The introduction of zirconium nitride is carried out by a method of in-situ reaction of zirconia to generate dispersed zirconium nitride particles. The reaction precursor can be selected from one or several of zirconia, 3mol% yttria-stabilized zirconia, zirconium carbonate, and zirconium nitrate, and is prepared by the sol-gel method or directly used as nano-powder, D 50 <300nm.

[0016] The introduced precursor will decompose into zirconia at high temperature. Zirconia has good chemical stability and will not diffuse into the aluminum nitride lattice. Zirconia will react in-situ with aluminum nitride at about 1500-1700 °C to generate nano-zirconium nitride microspheres, which are dispersed between aluminum nitride particles, pinning and strengthening the aluminum nitride grain boundaries, and can have a significant strengthening effect on the ceramic, but a small amount of alumina will be generated simultaneously, increasing the oxygen content of the additive phase, from Y 4 Al 2 O 9 (YAM) to Y 3 Al 5 O 12 (YAG) transformation, which can improve the sintering activity, but will also reduce the thermal conductivity of the ceramic to a certain extent.

[0017] 8AlN + 6ZrO 2 → 6ZrN + 4Al 2 O 3 + N 2

[0018] 2Y 2 O 3 + Al 2 O 3 → Y 4 Al 2 O 9 (YAM)

[0019] 3Y 2 O 3 + 5Al 2 O 3 → 2Y 3 Al 5 O 12 (YAG)

[0020] Using aluminum nitride ceramic powder with particle size grading can improve the density of the ceramic green body, introduce large particle high thermal conductivity grains, and improve the thermal conductivity of the ceramic. However, the sintering activity of large particle aluminum nitride ceramic powder is low, and the increase in the average grain size after sintering will reduce the flexural strength of the ceramic.

[0021] To solve the problem of poor sintering activity of large - particle aluminum nitride powder, it is pre - oxidized and then coated with a certain amount of sintering aid phase: dissolve the corresponding nitrates of the sintering aid phase components in ethanol, and then precipitate and coat them on the surface of large - particle aluminum nitride. Keep it warm with nitrogen passing through at the decomposition temperature corresponding to the nitrates to obtain a loose, highly active and uniform coating of the sintering aid phase.

[0022] The large - particle aluminum nitride powder is first pre - oxidized to form a nano - scale oxide film on the surface. The composition of the oxide film is a non - stoichiometric compound of aluminum and oxygen, AlO x (x < 1.5). After the nitrates of the sintering aid phase are coated and calcined at high temperature, they decompose into the oxides of the sintering aid phase, which can combine well with the oxide film on the surface of the aluminum nitride particles, improving the sintering activity of the large - particle aluminum nitride powder during the sintering process.

[0023] 2AlN + xO 2 →2AlO x +N 2

[0024] 2Y(NO 3 ) 3 →Y 2 O 3 +3N 2 O 5

[0025] mY 2 O 3 +nAlO x →Y 4 Al 2 O 9 (YAM) / YAlO 3 (YAP) / Y 3 Al 5 O 12 (YAG)

[0026] Use the surface - modified large - particle aluminum nitride powder and sub - micron - sized aluminum nitride fine powder for secondary or tertiary grading. The sub - micron - sized aluminum nitride fine powder is only dispersion - modified to avoid its difficulty in dispersing in the solvent at the initial stage of preparing the ball - milled slurry, and there is no need to add an excessive amount of solvent for the dispersion of the aluminum nitride fine powder to avoid difficulties in adjusting the slurry viscosity.

[0027] Aluminum nitride whiskers and graded large-particle aluminum nitride powders can improve the thermal conductivity and toughness of ceramics, but will reduce the strength and sintering activity; dispersed zirconium nitride particles can improve the strength and toughness of ceramics, improve the sintering aid activity of the additive phase, but will reduce the thermal conductivity of ceramics. Each single strengthening method has its own advantages and disadvantages, and has different degrees of improvement or reduction in different performance directions of ceramics. Combining them can make up for each other's shortcomings in strengthening and promote each other's strengthening effects. And aiming at different application targets and directions, through the control of the ceramic preparation process, the synergistic effect of strengthening, toughening and high thermal conductivity can be achieved.

[0028] To achieve the above object, the present invention also optimizes some key technical processes, and the specific technical solutions are as follows:

[0029] S1 Dispersion modification of aluminum nitride fine powder: Put 100 parts of aluminum nitride fine powder, 60-70 parts of absolute ethanol, 0.2-1 part of dispersion modifier, and 500 parts of zirconia grinding balls into a ball mill tank, and ball mill eight times, with each time being thirty minutes and the intermittent time being ten minutes, and the ball mill speed being 200-400 r / min. After ball milling, place the slurry in a vacuum oven at 45°C for drying, and after drying, pass through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby;

[0030] Preferably, the oxygen content of the aluminum nitride fine powder in step S1 is less than 1 wt%, the particle size distribution is narrow, and 0.5 μm ≤ D 50 ≤ 5 μm.

[0031] Preferably, the dispersion modifier in step S1 is one or more of castor oil, fish oil, polyethylene glycol 2000, oleic acid, paraffin wax, and titanate coupling agent.

[0032] Preferably, the material of the ball mill tank in step S1 is organic materials such as nylon and polytetrafluoroethylene, and stainless steel, agate and other materials are not used.

[0033] S2 Surface modification of large-particle aluminum nitride powder: First, perform high-temperature calcination on the large-particle aluminum nitride powder under an air atmosphere condition, then dissolve 0.5-3 parts of the composite sintering aid nitrate in 20-35 parts of ethanol, add 100 parts of the calcined large-particle aluminum nitride powder, stir ultrasonically and heat at 60°C to evaporate the ethanol, heat to 900-1000°C at 2.5°C / min under a nitrogen atmosphere for one hour, and set insulation at the decomposition temperature point of the corresponding nitrate to obtain modified large-particle aluminum nitride powder for standby;

[0034] Preferably, the oxygen content of the large-particle aluminum nitride powder in step S2 is less than 1 wt%, the particle size distribution is narrow, and 5 μm ≤ D 50 ≤ 100 μm.

[0035] Preferably, the maximum heat preservation temperature range of the calcination in step S2 is between 500 and 750 °C, and the heat preservation time is between 20 and 60 minutes.

[0036] Preferably, the composite sintering aid nitrate in step S2 is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

[0037] In step S3, surface modification of aluminum nitride whiskers: 0.5 - 3 parts of the composite sintering aid nitrate is dissolved in 30 parts of ethanol, 100 parts of aluminum nitride whiskers are added, ultrasonically stirred and heated at 60 °C to evaporate the ethanol, heated to 900 - 1000 °C at 2.5 °C / minute under a nitrogen atmosphere and calcined for one hour, and heat preservation is set at the decomposition temperature point of the corresponding nitrate to obtain modified aluminum nitride whisker powder for standby.

[0038] Preferably, the oxygen content of the aluminum nitride whiskers in step S3 is less than 1 wt%, the length is between 5 and 250 μm, and the aspect ratio is between 10 and 50. Figure 1 。

[0039] Preferably, the composite sintering aid nitrate in step S3 is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

[0040] In step S4, ball milling and mixing: 85 - 97 parts of graded aluminum nitride powder, 15 - 25 parts of ethanol, 0.2 - 1 part of dispersant dissolved in advance, 0.5 - 3 parts of composite sintering aid, 0.5 - 2 parts of zirconia reaction precursor, and 500 parts of zirconia grinding balls are put into the ball milling tank. Each ball milling time is 30 minutes, the intermittent time is 10 minutes, the ball milling speed is 200 - 400 r / minute, ball milling is carried out four times, 0.2 - 2 parts of binder is added, and the binder needs to be dissolved in 2 - 20 parts of ethanol in advance to form a sol, then ball milling is carried out four times, 3 - 15 parts of modified aluminum nitride whisker powder is added, and finally ball milling is carried out for 15 minutes. The grinding balls are filtered out, the mixed slurry is dried and sieved through a 60 - mesh sieve to obtain mixed ceramic powder;

[0041] Preferably, in the graded aluminum nitride powder in step S4, the modified aluminum nitride fine powder accounts for 10 - 90 wt%, and the modified large - particle aluminum nitride powder accounts for 10 - 90 wt%.

[0042] Preferably, the dispersant in step S4 is selected from one of castor oil and fish oil.

[0043] Preferably, the composite sintering aid in step S4 is selected from two or more of yttrium oxide, calcium carbonate, lanthanum oxide, lithium carbonate, and magnesium oxide, and nano - powder is used, D 50 <300 nm.

[0044] Preferably, the zirconia reaction precursor in step S4 can be selected from one or more of zirconia, 3mol% yttria-stabilized zirconia, zirconium carbonate, and zirconium nitrate, prepared by the sol-gel method, or directly used as nanopowder, D 50 < 300 nm.

[0045] Preferably, the binder described in step S4 can be polyvinyl butyral.

[0046] S5 Compression molding, select a two-way compression molding die for the desired target ceramic shape, uniformly load the mixed ceramic powder, raise the pressure to 50 - 80 MPa at a pressure increase rate of 100 MPa / minute, hold the pressure for 1 - 3 minutes, and demold to obtain a compression-molded blank;

[0047] S6 Cold isostatic pressing, after soft-sealing the compression-molded blank, perform cold isostatic pressing treatment, with both the pressure increase and decrease rates being 100 MPa / minute, and hold the pressure at 200 MPa for a maximum of five minutes;

[0048] S7 Debinding, press a boron nitride ceramic plate on the compression-molded blank, perform debinding in a flowing air atmosphere, with a heating rate of 1 °C / minute, a maximum holding temperature of 600 °C, a holding time of 2 - 5 hours, and set the holding temperature according to the selected organic components at their volatilization temperature points. The process temperature curve is shown in Figure 2 ;

[0049] S8 Ceramic sintering, press a boron nitride ceramic plate on the compression-molded blank, perform staged sintering in a nitrogen atmosphere. When a non-oxide form is selected in the sintering aid, set the holding temperature at its corresponding decomposition temperature point. The process temperature curve is shown in Figure 3 ;

[0050] Preferably, the sintering holding temperature in step S8 can be selected from 1650 °C to 1850 °C, and the holding time can be selected from 2 - 4 hours.

[0051] S9 Post-treatment and performance testing, polish the sintered ceramic substrate, cut it into the required size, and perform tests on thermal conductivity, flexural strength, fracture toughness, hardness, etc.

[0052] Preferably, the thermal conductivity of the obtained aluminum nitride ceramic product > 150 W / m·K, the flexural strength > 450 MPa, and the fracture toughness > 9 MPa·m 1 / 2 , and for different application targets and directions, individual performance indicators can be higher.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] By synergistically using various performance enhancement methods such as strengthening heat conduction with graded large - particle aluminum nitride powder, toughening with aluminum nitride whiskers, and dispersion strengthening with second - phase particles, the disadvantages of the enhancements are mutually compensated, and the enhancement effects promote each other. Some detailed processes in the ceramic preparation process are optimized, making the entire ceramic preparation process more stable and further improving the comprehensive performance of the aluminum nitride ceramic substrate. Description of the Drawings

[0055] Figure 1 It is a SEM photograph of aluminum nitride whiskers.

[0056] Figure 2 It is a temperature curve graph of the general debinding and degassing process.

[0057] Figure 3 It is a temperature curve graph of the sintering process (Example 2).

[0058] Figure 4 It shows the situation of zirconium nitride microspheres inside the ceramic after sintering.

[0059] Figure 5 It is a SEM photograph of the fracture surface of the ceramic after sintering. Detailed Embodiments

[0060] The present invention will be further described below in conjunction with the embodiments and the drawings, but it should not be construed as a limitation to the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0061] Example 1

[0062] Put 100 parts of D 50 0.9 - μm aluminum nitride fine powder, 60 parts of absolute ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls into a ball - milling tank, ball - mill for four hours, dry and then pass through a 60 - mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0063] Put D 50 5 - μm large - particle aluminum nitride powder is calcined in an air atmosphere, with a heating rate of 10 °C / minute, a maximum holding temperature of 700 °C, and a holding time of 30 minutes.

[0064] Dissolve 0.2 part of yttrium nitrate, 0.2 part of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol, add 100 parts of the calcined large - particle aluminum nitride powder, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, with a heating rate of 2.5 °C / minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, and the maximum calcination temperature is 1000 °C, hold for one hour to obtain modified large - particle aluminum nitride powder for standby.

[0065] Dissolve 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 parts of calcium nitrate in 25 parts of ethanol. Add 100 parts of aluminum nitride whiskers, stir ultrasonically and heat at 60 °C to evaporate the ethanol. Under a nitrogen atmosphere, with a heating rate of 2.5 °C / minute, hold at 130 °C, 500 °C, 550 °C, and 800 °C for one hour respectively, with a maximum calcination temperature of 1000 °C and hold for one hour to obtain modified aluminum nitride whisker powder for standby.

[0066] Put 95 parts of graded aluminum nitride powder, among which 90 wt% is modified fine aluminum nitride powder, 10 wt% is modified large particle aluminum nitride powder, 25 parts of ethanol, 0.5 parts of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 parts of calcium carbonate, 1.5 parts of 3 mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls into a ball mill tank. The ball milling speed is 200 r / minute, ball mill for two hours, add 1 part of polyvinyl butyral, and polyvinyl butyral needs to be dissolved in 8 parts of ethanol in advance to form a sol. Ball mill for two hours, add 5 parts of modified aluminum nitride whisker powder, ball mill for fifteen minutes, filter out the grinding balls, dry the mixed slurry and pass through a 60-mesh sieve to obtain mixed ceramic powder.

[0067] Uniformly load 8 g of mixed ceramic powder into a 40×24 mm rectangular mold, raise the pressure to 60 MPa at a rate of 100 MPa / minute, hold the pressure for 1 minute, and demold to obtain a molded blank.

[0068] Soft-seal the molded blank and perform cold isostatic pressing at 200 MPa for five minutes.

[0069] Press a boron nitride ceramic plate on the molded blank, and perform degreasing and debinding in a flowing air atmosphere. The heating rate is 1 °C / minute, hold at 200 °C and 350 °C for one hour respectively, hold at 600 °C for two hours, and then cool with the furnace.

[0070] Press a boron nitride ceramic plate on the molded blank, and perform sintering in a nitrogen atmosphere. Adopt a segmented heating method, raise the temperature to 850 °C at 5 °C / minute, hold for one hour, raise the temperature to 1500 °C at 5 °C / minute, hold for one hour, raise the temperature to 1650 °C at 2.5 °C per minute, hold for four hours, lower the temperature to 1200 °C at 5 °C / minute, and lower the temperature to room temperature at 10 °C / minute to complete sintering, and then polish.

[0071] Example 2

[0072] Put D 50 Put 100 parts of 0.9 μm aluminum nitride fine powder, 60 parts of absolute ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls into a ball mill tank, ball mill for four hours, dry and pass through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0073] Put D 50The 5-μm large-particle aluminum nitride powder is calcined in an air atmosphere at a heating rate of 10 °C / minute, with a maximum holding temperature of 700 °C and a holding time of 30 minutes.

[0074] Dissolve 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol. Add 100 parts of the calcined large-particle aluminum nitride powder, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, heat at a rate of 2.5 °C / minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, with a maximum calcination temperature of 1000 °C and hold for one hour to obtain the modified large-particle aluminum nitride powder for standby.

[0075] Dissolve 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol. Add 100 parts of aluminum nitride whiskers, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, heat at a rate of 2.5 °C / minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, with a maximum calcination temperature of 1000 °C and hold for one hour to obtain the modified aluminum nitride whisker powder for standby.

[0076] Put 90 parts of graded aluminum nitride powder, including 70 wt% of modified fine aluminum nitride powder and 30 wt% of modified large-particle aluminum nitride powder, 25 parts of ethanol, 0.5 part of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 part of calcium carbonate, 1.5 parts of 3 mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls into a ball mill can. The ball mill rotates at 200 r / minute for two hours. Add 1 part of polyvinyl butyral, which needs to be dissolved in 8 parts of ethanol in advance to form a sol, ball mill for two hours, add 5 parts of modified aluminum nitride whisker powder, ball mill for 15 minutes, filter out the grinding balls, dry the mixed slurry and pass through a 60-mesh sieve to obtain the mixed ceramic powder.

[0077] Uniformly load 8 g of the mixed ceramic powder into a 40×24 mm rectangular mold, raise the pressure to 60 MPa at a rate of 100 MPa / minute, hold the pressure for 1 minute, and demold to obtain a molded blank.

[0078] After the molded blank is softly sealed, it is subjected to cold isostatic pressing at 200 MPa for five minutes.

[0079] Press a boron nitride ceramic plate on the molded blank and perform debinding and degumming in a flowing air atmosphere at a heating rate of 1 °C / minute, hold for one hour at 200 °C and 350 °C respectively, hold for two hours at 600 °C, and then cool with the furnace.

[0080] Press a boron nitride ceramic plate on the molded green compact, sinter in a nitrogen atmosphere, adopt a segmented heating method, heat up to 850 °C at 5 °C per minute, hold for one hour, heat up to 1500 °C at 5 °C per minute, hold for one hour, heat up to 1700 °C at 2.5 °C per minute, hold for four hours, cool down to 1200 °C at 5 °C per minute, and cool down to room temperature at 10 °C per minute to complete sintering, then grind and polish.

[0081] Example 3

[0082] Put 100 parts of D 50 0.9 μm aluminum nitride fine powder, 60 parts of absolute ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls into a ball mill tank, ball mill for four hours, dry and pass through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0083] Put 100 parts of D 50 Calcine 10 μm large particle aluminum nitride powder in an air atmosphere, with a heating rate of 10 °C per minute, a maximum holding temperature of 700 °C, and a holding time of 30 minutes.

[0084] Dissolve 0.2 part of yttrium nitrate, 0.2 part of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol, add 100 parts of the calcined large particle aluminum nitride powder, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, with a heating rate of 2.5 °C per minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, and the maximum calcination temperature is 1000 °C, hold for one hour to obtain modified large particle aluminum nitride powder for standby.

[0085] Dissolve 0.2 part of yttrium nitrate, 0.2 part of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol, add 100 parts of aluminum nitride whiskers, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, with a heating rate of 2.5 °C per minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, and the maximum calcination temperature is 1000 °C, hold for one hour to obtain modified aluminum nitride whisker powder for standby.

[0086] Put 95 parts of graded aluminum nitride powder, including 60 wt% of modified aluminum nitride fine powder, 40 wt% of modified large particle aluminum nitride powder, 25 parts of ethanol, 0.5 part of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 part of calcium carbonate, 0.5 part of 3 mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls into a ball mill tank, with a ball mill rotation speed of 200 r / min, ball mill for two hours, add 1 part of polyvinyl butyral, which needs to be dissolved in 8 parts of ethanol in advance to form a sol, ball mill for two hours, add 5 parts of modified aluminum nitride whisker powder, ball mill for 15 minutes, filter out the grinding balls, dry the mixed slurry and pass through a 60-mesh sieve to obtain the mixed ceramic powder.

[0087] 0.8 g of mixed ceramic powder was evenly loaded into a φ12.7 mm cylindrical mold, and the pressure was increased to 60 MPa at a rate of 100 MPa per minute, held for 1 minute, and then demolded to obtain a molded green body.

[0088] The molded green body was cold isostatically pressed after soft sealing, and held at 200 MPa for five minutes.

[0089] A boron nitride ceramic plate was pressed on the molded green body, and debinding was carried out in a flowing air atmosphere. The heating rate was 1 °C per minute, held at 200 °C and 350 °C for one hour respectively, held at 600 °C for two hours, and then cooled with the furnace.

[0090] A boron nitride ceramic plate was pressed on the molded green body, and sintering was carried out in a nitrogen atmosphere. A segmented heating method was adopted, heated to 850 °C at 5 °C per minute, held for one hour, heated to 1500 °C at 5 °C per minute, held for one hour, heated to 1850 °C at 2.5 °C per minute, held for four hours, cooled to 1200 °C at 5 °C per minute, and cooled to room temperature at 10 °C per minute to complete sintering, and then polished.

[0091] The properties of the aluminum nitride ceramic substrates prepared in the above three examples were tested, and the results are shown in the following table. The thermal conductivity was tested by the thin film radial method, the flexural strength was tested by the three-point bending method, and the fracture toughness was tested by the single-edge V-notch beam method.

[0092] Thermal conductivity W / m·k Flexural strength MPa <![CDATA[Fracture toughness MPa·m 1 / 2 > Example 1 149 474 9.55 Example 2 158 463 10.32 Example 3 192 430 8.68

Claims

1. A method for preparing aluminum nitride ceramics having aluminum nitride whisker toughening, dispersed zirconium nitride and enhanced particle size distribution, characterized in that: The specific strengthening methods include the following: The parts in the following text all represent parts by mass; S1 aluminum nitride powder modification and grading, large-particle aluminum nitride powder is surface modified, aluminum nitride fine powder is dispersed and modified, and secondary / tertiary particle grading is performed; S2 is strengthened by adding modified aluminum nitride whiskers with a pre-coated composite sintering aid on the surface; S3 adds nano-scale zirconium oxide reaction precursor, and during the sintering process, zirconium dioxide reacts in situ to generate dispersed zirconium nitride particles, strengthening the grain boundary structure of aluminum nitride ceramics.

2. The preparation method according to claim 1, characterized in that: S1 medium and large particle size distribution of aluminum nitride powder is narrow and 5μm≤D 50 ≤100μm, D 50 is the volume median diameter of the particle size; the surface modification treatment is carried out in two steps, first oxidation calcination, and then coating with a composite sintering aid; 2.1 Oxidation calcination: high temperature calcination is carried out under air atmosphere conditions, the maximum holding temperature range of calcination is between 500 and 750°C, and the holding time is between 20 and 60 minutes; 2.2 Coating the composite sintering aid, fully dissolve 0.5-3 parts of the composite sintering aid nitrate in 20-35 parts of ethanol, add 100 parts of calcined large-particle aluminum nitride powder, ultrasonically stir and heat to volatilize the ethanol, heat to 900-1000°C at 2.5°C / min in a nitrogen atmosphere and calcine for one hour, and set insulation at the decomposition temperature point corresponding to the nitrate; the sintering aid nitrate is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

3. The preparation method according to claim 1, characterized in that: The particle size distribution of aluminum nitride fine powder in S1 is narrow and 0.5μm≤D 50 ≤5μm;D 50 The volume median diameter of the particle size is as follows: 100 parts of aluminum nitride fine powder, 0.2-2 parts of a dispersing modifier, and 60-70 parts of an ethanol solvent are mixed and ball-milled for a total of four hours, and the mixture is dried and passed through a 60-mesh sieve; the dispersing modifier is one or more of castor oil, fish oil, polyethylene glycol 2000, oleic acid, paraffin, and a titanate coupling agent.

4. The preparation method according to claim 1, characterized in that: In the graded aluminum nitride powder in S1, the modified aluminum nitride fine powder accounts for 10-90wt%, and the modified large-particle aluminum nitride powder accounts for 10-90wt%. In the three-level gradation, the modified large-particle aluminum nitride powder can be selected from two particle sizes.

5. The preparation method according to claim 1, characterized in that: The length of the aluminum nitride whiskers in S2 is between 5 and 250 μm, and the aspect ratio is between 10 and 50; 0.5 to 3 parts of the composite sintering aid nitrate are fully dissolved in 20 to 35 parts of ethanol, 100 parts of aluminum nitride whiskers are added, ultrasonic stirring and heating are performed to volatilize the ethanol, and the mixture is heated to 900 to 1000° C. at 2.5° C. / min in a nitrogen atmosphere and calcined for one hour, and insulation is set at the decomposition temperature point corresponding to the nitrate; the sintering aid nitrate is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

6. The preparation method according to claim 1, characterized in that: The zirconium oxide reaction precursor in S3 is selected from one or more of zirconium dioxide, 3 mol% yttrium-stabilized zirconium oxide, zirconium carbonate, and zirconium nitrate, and is prepared by a sol-gel method, or directly using nanopowder. 50 <300nm,D 50 is the volume median diameter of the particle size.

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