A method for preparing a columnar crystal yttria / magnesia composite ceramic powder

Abstract

The application relates to a preparation method of a columnar crystal yttrium oxide / magnesium oxide composite ceramic powder, relates to the field of composite ceramic materials, and aims to solve the problems that the existing Y2O3-MgO ceramic is difficult to form columnar crystals and has poor mechanical properties. The method comprises the following steps: step one: drying magnesium powder and a diluent; step two: uniformly mixing the dried magnesium powder and the diluent to obtain a mixture; and step three: loading the mixture into a high-pressure reactor, igniting the mixture, carrying out a high-temperature combustion synthesis reaction, keeping warm after the reaction, opening the nozzle, spraying the high-temperature melt, and obtaining the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder after liquid-phase cooling of the high-temperature melt. The method can achieve the effects of columnar crystal strengthening and fine-grain strengthening. Due to the high content of columnar crystals and the small grain size, the strength and toughness of the ceramic are obviously increased. The application is used for preparing the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite ceramic materials, in particular to a preparation method of columnar crystal yttrium oxide / magnesium oxide composite ceramic powder. BACKGROUND

[0002] Y2O3-MgO nano-composite material is widely studied as a representative infrared transparent ceramic due to its excellent thermal and optical properties, and has wide application prospects in the fields of infrared window, solid-state laser and transparent armor. However, the mechanical properties of Y2O3-MgO nano-composite ceramic are poor, which seriously hinders its application, and therefore there is an urgent need to develop a new type of transparent ceramic material with high strength and wide-band high-transparency.

[0003] At present, the preparation methods of Y2O3-MgO composite ceramic powder mainly include sol-gel method, glycine-nitrate method, flame spray pyrolysis method and solid phase ball milling method, etc. The Y2O3-MgO composite ceramic powder prepared by these methods has equiaxed grains in the composite ceramic after sintering, and the mechanical properties of the composite ceramic are poor, which limits the application of Y2O3-MgO composite ceramic.

[0004] For most ceramics, introducing columnar crystals into the ceramic can greatly improve the fracture toughness and strength. There are mainly two methods for introducing columnar crystals into the ceramic, the first method is to add a small amount of columnar crystal / whisker micron powder or nano powder to the ceramic matrix to prepare a columnar crystal-containing ceramic. When the amount of columnar crystal / whisker is small, it is easy to be unevenly distributed, resulting in large performance difference. When the amount is large, the nano powder not only has the problems of easy agglomeration and grain growth, but also with the increase of the amount, the columnar crystal / whisker plays a role as a skeleton, which is difficult to sinter and dense, thereby greatly reducing the strengthening and toughening effect. The second method is to add an inducer to the ceramic powder, and columnar crystal ceramic can be prepared in situ during the sintering process. The inducer of this method is rare earth oxide. This in-situ method improves the content of columnar crystal, thereby improving the performance of the ceramic. At present, there are literatures reported on the columnar crystal strengthening and toughening of Al2O3-ZrO2 and SiN3 ceramics, but there is no report on columnar crystal in Y2O3-MgO ceramic. SUMMARY

[0005] The present application is to solve the problem that the existing Y2O3-MgO ceramic is difficult to form columnar crystal and has poor mechanical properties, and provides a preparation method of columnar crystal yttrium oxide / magnesium oxide composite ceramic powder.

[0006] The preparation method of columnar crystal yttrium oxide / magnesium oxide composite ceramic powder of the present application comprises the following steps:

[0007] Step one: dry the magnesium powder and diluent; the diluent is a mixture of magnesium oxide and yttrium oxide, wherein the mass fraction of magnesium oxide in the total mass of the diluent is 0-28.19%;

[0008] Step two: mix the dry magnesium powder and diluent uniformly to obtain a mixture; wherein the mass fraction of the magnesium powder in the mixture is 13.45%-24.2%, and the mass fraction of the diluent is 75.8-86.55%;

[0009] Step three: load the mixture into a high-pressure reactor, fill O2 or O2 mixed gas into the high-pressure reactor, the lower end of the reactor has a nozzle with a nozzle diameter of 1-5 mm, ignite the mixture, and perform high-temperature combustion synthesis reaction, the reaction temperature is 3300-4500 K, after the reaction, a high-temperature melt is formed, and the high-temperature melt is sprayed out after the nozzle is opened, and the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder is obtained after the high-temperature melt is cooled in liquid phase; wherein the high-temperature melt spray pressure is set to 10-40 MPa.

[0010] Further, the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder obtained in step three is sintered to obtain submicron columnar crystal yttrium oxide / magnesium oxide composite ceramic.

[0011] Further, the sintering process is pressureless sintering, hot-pressing sintering, spark plasma sintering or flash sintering.

[0012] Preferably, the sintering process conditions are: heating rate 5-100 ℃ / min, sintering temperature 1100-1500 ℃, and holding time 5 min-3 h.

[0013] Further, the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder obtained in step three is first high-energy ball milled to 100-500 nm, and then sintered. The high-energy ball milling speed is 1000-2000 r / min, and the ball milling time is 6-12 h.

[0014] Further, the columnar crystal yttrium oxide / magnesium oxide composite ceramic powder obtained in step three is first sand milled to 50-500 nm, and then sintered. The sand mill motor speed is 1500-2030 r / min, and the sand milling time is 4-10 h.

[0015] Principle of the application:

[0016] The present application obtains high-temperature ceramic melt by super-high temperature combustion synthesis between magnesium powder and oxygen, the chemical reaction is shown as formula (1), the high-temperature melt is rapidly cooled in liquid phase, and micron-sized metastable supersaturated solid solution and amorphous mixture ceramic powder are obtained. In the combustion synthesis process, different reaction systems have different process characteristics, and a large number of experiments and theoretical work are needed to realize, optimize and stabilize the process. For Y2O3-MgO system, the melting point of the oxide is high, and a very high temperature is needed to completely melt the oxide. In addition, the particle size of the magnesium powder raw material is large (about 44 μm), the uniformity of the high-temperature melt after reaction needs to be verified, and because the activity of magnesium powder is high and it is easy to volatilize, the safety problem needs to be solved in the high-temperature and high-pressure reaction process, a large number of experimental exploration and theoretical analysis are needed to ensure the safety and reliability of the process. After the preliminary process research, the uniform mixing of the high-temperature melt can be realized, and the safety of the method is ensured.

[0017]

[0018] Whether the metastable supersaturated solid solution and amorphous mixture obtained by rapid cooling of the high-temperature melt can induce columnar crystals is closely related to the material system and process parameters, and it is still difficult to reasonably predict by theory at present, and needs to be verified by experiment. After process optimization, the micron-sized metastable Y2O3-MgO supersaturated solid solution and amorphous mixture ceramic powder prepared by the present application can induce high-density columnar crystals in situ in the ceramic during subsequent high-temperature sintering. The formation of columnar crystals is through the method of high-temperature melt combined with liquid rapid cooling to obtain the high-temperature stable phase m-Y2O3 of Y2O3, and in the sintering process, m-Y2O3 transforms into the low-temperature stable phase c-Y2O3 and grows along the preferred orientation direction, forming high-density columnar crystals, thereby improving the strength and toughness of Y2O3-MgO composite ceramic. In addition, according to the Y2O3-MgO phase diagram, the solid solubility of the two phases is extremely low, but in the high-temperature melt state, they can realize mutual solubility, and this solid solution state can be preserved by rapid cooling. In the sintering process, the supersaturated solid solution precipitates and forms nanoscale or submicron-sized small particles in the grain interior, the existence of such small particles will hinder the migration of grain boundaries during grain growth, thereby realizing the control of the grain size of Y2O3-MgO ceramic, achieving the effect of columnar crystal strengthening and fine-grain strengthening, and further improving the strength of the composite ceramic.

[0019] The obtained micron-sized metastable Y2O3-MgO supersaturated solid solution and amorphous mixture ceramic powder is sintered, columnar crystals are in-situ induced in the process of m-Y2O3 transforming into c-Y2O3, the Y2O3-MgO supersaturated solid solution can be desolvated and precipitated to form nano-enhanced phase during sintering, high-density and uniformly-distributed columnar crystal intracrystalline / intercrystalline composite nanostructure is formed, and thus high-strength and high-toughness columnar crystal yttrium oxide / magnesium oxide composite ceramic is obtained.

[0020] The beneficial effects of the present application are as follows:

[0021] 1. The present application obtains micron-sized metastable Y2O3-MgO supersaturated solid solution and amorphous mixture ceramic powder for the first time, and the components in the powder are uniformly distributed.

[0022] 2. In the sintering densification process of the metastable Y2O3-MgO supersaturated solid solution and amorphous mixture ceramic powder prepared by the present application, m-Y2O3 transforms into low-temperature stable phase c-Y2O3 and grows along the preferred orientation direction, forming high-density columnar crystals with submicron size, and the length of the columnar crystals can be controlled by adjusting the sintering process parameters. Such structure has not been reported in the prior Y2O3-MgO composite ceramic.

[0023] 3. In the sintering densification process of the metastable Y2O3-MgO supersaturated solid solution and amorphous mixture ceramic powder prepared by the present application, the Y2O3-MgO supersaturated solid solution formed by mutual solubility at high temperature desolvates and precipitates, and nano-enhanced phase small particles are in-situ generated inside, the existence of the small particles hinders the migration of grain boundaries in the process of grain growth, thereby controlling the grain size of the Y2O3-MgO ceramic and achieving the effect of fine-grain strengthening, and further improving the strength of the composite ceramic.

[0024] 4. The ceramic powder prepared by the present application can obtain columnar crystal yttrium oxide / magnesium oxide composite ceramic in the densification process, and due to the high content of columnar crystals and small grain size, the strength and toughness of the ceramic are significantly increased. When the sintering temperature is 1000-1500℃, the hardness of the yttrium oxide / magnesium oxide composite ceramic is 10-15GPa, and the fracture toughness is 3-5MPa·m 1 / 2 Compared with the prior art, the fracture toughness is increased by about 50%.

[0025] 5. The present application can prepare a large amount of supersaturated solid solution columnar crystal powder, and the preparation cost of the powder is low, the benefit is high, and the present application has high industrial production prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 XRD patterns of the columnar crystal yttria / magnesia composite ceramic powder prepared in Example 1 after heat treatment at different temperatures;

[0027] Figure 2 Cross-section and element distribution of the columnar crystal yttria / magnesia composite ceramic powder prepared in Example 1;

[0028] Figure 3 Micro-morphology of the yttria / magnesia composite ceramic powder prepared in Example 1 after heat treatment;

[0029] Figure 4 Micro-morphology of the columnar crystal yttria / magnesia ceramic fracture surface prepared in Example 1;

[0030] Figure 5 Micro-morphology of the columnar crystal yttria / magnesia ceramic fracture surface after thermal etching prepared in Example 1. DETAILED DESCRIPTION

[0031] The technical solution of the present application is not limited to the following specific embodiments, and also includes any combination of the specific embodiments.

[0032] Specific embodiment one: the preparation method of the columnar crystal yttria / magnesia composite ceramic powder in the embodiment, comprising the following steps:

[0033] Step one: dry the magnesium powder and the diluent; the diluent is a mixture of magnesia and yttria, wherein the magnesia accounts for 0-28.19% of the total mass of the diluent;

[0034] Step two: mix the dried magnesium powder and the diluent uniformly to obtain a mixture; wherein the mass fraction of the magnesium powder in the mixture is 13.45%-24.2%, and the mass fraction of the diluent is 75.8-86.55%;

[0035] Step three: load the mixture into a high-pressure reactor, fill O2 or O2 mixed gas into the high-pressure reactor, and the reactor has a nozzle at the lower end, the nozzle has a nozzle diameter of 1-5 mm, ignite the mixture, and perform high-temperature combustion synthesis reaction, the reaction temperature is 3300-4500 K, after the reaction, a high-temperature melt is formed, and the high-temperature melt is cooled by liquid phase cooling to obtain the columnar crystal yttria / magnesia composite ceramic powder; wherein the high-temperature melt is sprayed at a pressure of 10-40 MPa.

[0036] When the magnesium powder and diluent are mixed uniformly, various mixing methods such as ball-milling mixing and stirring mixing can be used, but since the magnesium powder is very active, the friction and collision of the milling balls or stirring rods can generate heat, causing danger, so the mixing time and temperature need to be controlled during mixing. Therefore, the resonance mixing method is preferably used in the present application. Resonance mixing is a paddle-free mixing technology that uses vibration transmission energy to realize the mixing of materials, which can avoid the physical damage or dangerous accidents caused by the friction and collision of the milling balls or the shearing of the paddles during the ball-milling mixing or paddle mixing process.

[0037] Specific embodiment two: In the step one of the present embodiment, the magnesium powder is dried in a vacuum, inert gas or reducing gas. The other steps and parameters are the same as those in specific embodiment one.

[0038] Specific embodiment three: In the step one of the present embodiment, the drying temperature is 50-100℃, and the drying time is 12-24h. The other steps and parameters are the same as those in specific embodiment one or two.

[0039] Specific embodiment four: In the step one of the present embodiment, the magnesium oxide accounts for 13.16%-22.18% of the total mass of the diluent; in the step two, the mass fraction of the magnesium powder in the mixed material is 16.77%-22.77%, and the mass fraction of the diluent is 77.23%-83.23%. The other steps and parameters are the same as those in one of specific embodiments one to three.

[0040] The selection of the raw material range in the present embodiment can make the volume ratio of Y2O3 and MgO in the obtained yttria / magnesia composite ceramic powder be 50:50. When the volume ratio of Y2O3 and MgO is 50:50, they are second phases to each other, at this time, the pinning effect is the strongest, making the grain size of the Y2O3-MgO composite ceramic the smallest and the light transmission performance the best.

[0041] Specific embodiment five: In the step three of the present embodiment, the O2 mixed gas is a mixture of oxygen and inert gas. The other steps and parameters are the same as those in one of specific embodiments one to four.

[0042] The inert gas in the present embodiment is argon (Ar), which has the lowest cost.

[0043] Specific embodiment six: In the step three of the present embodiment, the liquid phase is water or a salt solution. The other steps and parameters are the same as those in one of specific embodiments one to five.

[0044] The salt solution in the present embodiment is a sodium chloride solution, which has the lowest cost.

[0045] Embodiment seven: the columnar crystal yttria / magnesia composite ceramic powder obtained in step three is sintered to obtain submicron columnar crystal yttria / magnesia composite ceramic. The other steps and parameters are the same as one of embodiments one to six.

[0046] Embodiment eight: the sintering process is pressureless sintering, hot-press sintering, spark plasma sintering or flash sintering. The other steps and parameters are the same as embodiment seven.

[0047] Embodiment nine: the sintering process is under the conditions of heating rate 5-100℃ / min, sintering temperature 1100-1500℃, and holding time 5min-3h. The other steps and parameters are the same as embodiment seven or eight.

[0048] Embodiment ten: the columnar crystal yttria / magnesia composite ceramic powder obtained in step three is high-energy ball milled to 100-500nm before sintering. The high-energy ball milling speed is 1000-2000r / min, and the ball milling time is 6-12h. The other steps and parameters are the same as embodiment seven.

[0049] The ball milling before sintering can reduce the size of the powder, improve the sintering activity of the powder, reduce the sintering temperature, and reduce the grain size of the sintered ceramic.

[0050] Embodiment eleven: the columnar crystal yttria / magnesia composite ceramic powder obtained in step three is sand milled to 50-500nm before sintering. The sand mill motor speed is 1500-2030r / min, and the sand milling time is 4-10h. The other steps and parameters are the same as embodiment seven.

[0051] The sand milling mainly reduces the size of the powder, improves the sintering activity, reduces the sintering temperature, and reduces the grain size of the sintered ceramic. The difference between sand milling and ball milling is that sand milling can mill the powder to a smaller size.

[0052] The following embodiments of the present application are described in detail. The following embodiments are implemented on the basis of the technical scheme of the present application, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present application is not limited to the following embodiments.

[0053] Embodiment 1:

[0054] The preparation method of the columnar crystal Y2O3 / 50vol% MgO composite ceramic powder in this embodiment is specifically completed according to the following steps:

[0055] I. Dry the magnesium powder, yttria powder and magnesia powder, vacuum dry the magnesium powder at a vacuum degree of 0.06 MPa, the drying temperature is 80℃, and the drying time is 12 h; directly dry the yttria powder and magnesia powder, the drying temperature is 80℃, and the drying time is 12 h;

[0056] II. Mix the dried 30.5 g of magnesium powder, 27.5 g of magnesia powder and 109.4 g of yttria powder uniformly by resonance mixing method, and then pass through a 60 mesh sieve to obtain a mixture;

[0057] III. Put the mixture into a high-pressure reactor, fill O2, set the oxygen pressure to 19.1 MPa, provide a nozzle at the lower end of the high-pressure reactor, the nozzle has a size of Φ2 mm, place the high-pressure reactor above a water cooling device, ignite the mixture by an electric resistance wire, perform high-temperature combustion synthesis reaction, form a high-temperature melt after the reaction, keep warm for 7 s, then open the nozzle, and spray the high-temperature melt out of the nozzle under high temperature and high pressure into the water cooling device to perform liquid phase cooling, thereby obtaining yttria / magnesia composite ceramic powder; the water cooling device is an atomizing tower containing a cooling liquid phase, and the cooling liquid phase is water;

[0058] IV. Obtain columnar yttria / magnesia composite ceramic by spark plasma sintering of the powder obtained in step III, and the spark plasma sintering conditions are as follows: sintering temperature 1200℃, sintering pressure 50 MPa, heating rate 100℃ / min, and keeping warm for 10 min;

[0059] V. Anneal the yttria / magnesia composite ceramic obtained in step IV in air, and the annealing conditions are as follows: annealing temperature 1000℃, and annealing time 10 h.

[0060] The fracture toughness of the ceramic prepared in this embodiment is tested by indentation method, and the performance before annealing is as follows: fracture toughness 2.6 MPa·m 1 / 2 , and hardness 12.9 GPa; and the performance after annealing is as follows: fracture toughness 3.4 MPa·m 1 / 2 , and hardness 11.0 GPa.

[0061] The phase composition and microstructure of the yttria / magnesia composite ceramic powder obtained in Example 1 are analyzed. Figure 1 is the XRD pattern of the columnar yttria / magnesia composite ceramic powder prepared in Example 1 after heat treatment at different temperatures, ■ represents m-Y2O3, ● represents c-Y2O3, and ♦ represents MgO. Before heat treatment, the phase composition of the powder is m-Y2O3, cubic MgO and a small amount of c-Y2O3. After heat treatment, m-Y2O3 in the powder gradually converts to c-Y2O3, and at 1000℃, the powder is completely converted to c-Y2O3, and the final phase composition of the powder is c-Y2O3 and cubic MgO. Figure 2is the cross-section and EDS analysis of the composite ceramic powder obtained in step three of Example 1, Figure 2 The atomic percentage of the three elements O, Mg and Y in different positions in the middle of the table 1, Point 1 and Point 2 correspond to Figure 2 In the left side of the figure in the middle of the table 1, Point 1 and Point 2, Plane Scan is the atomic percentage of the three elements O, Mg and Y in the entire cross-section. When the volume ratio of Y2O3 and MgO is 50:50, the atomic ratio of Y and Mg is 1:2, and the result of Plane Scan is that the atomic ratio of Y and Mg is close to 1:2, indicating that the volume ratio of Y2O3 and MgO in the synthesized powder is 50:50. Point 1, that is, the atomic ratio of Y and Mg in the light color phase is greater than 1:2, while Point 2, that is, the atomic ratio of Y and Mg in the dark color phase is less than 1:2. This result indicates that Y2O3 and MgO realize mutual solubility at high temperature, and this solid solution state is preserved in the powder obtained by rapid cooling. At the same time, the atomic percentage of O in the light color phase is less than that in the dark color phase, indicating that the atomic percentage of O in the light color phase is less than that in the dark color phase. Figure 2 In the middle of the table 1, it can be seen that there are dendrites in the composite ceramic powder, and the dendrites are solid solutions of yttria and magnesia.

[0062] Figure 3 is the surface microstructure of the yttria / magnesia composite ceramic powder after heat treatment, from Figure 3 As can be seen from the middle of the table 1, there are high-density columnar crystals on the surface of the composite ceramic, and the radial size of the columnar crystals is about 30-100 nm. Figure 4 is the fracture morphology of the yttria / magnesia composite ceramic before and after annealing by spark plasma sintering, the left figure is before annealing, and the right figure is after annealing. Both before and after annealing, the pulled-out columnar crystals (yellow arrows) and the holes after pulling out (green arrows) can be observed on the fracture surface. During sintering, the supersaturated solid solution in metastable state decomposes and precipitates to form a small amount of columnar crystals. The higher heating and cooling rate and the shorter holding time make the microstructure of the sintered ceramic not reach a complete steady state, and there is still a high solid solubility. During the annealing process, the columnar crystals further precipitate and grow, so that more columnar crystal structures that play a toughening role during fracture can be observed on the fracture surface of the annealed ceramic.

[0063] In order to more clearly observe the microstructure inside the prepared yttria / magnesia composite ceramic, the sample was heat etched at 1000°C for 2h, and the microstructure of the fracture surface after heat etching is shown in Figure 5 , wherein the right figure is an enlarged view of the red box in the left figure. As can be seen from the middle of the table 1, Figure 5 It can be seen from the middle of the table 1 that the inside of the ceramic is composed of submicron Y2O3 and MgO, and the grain size is between 500-800 nm, and a high density of columnar crystals is observed in the intergranular and intragranular.

[0064] Table 1

[0065] Position O / at% Mg / at% Y / at% Point 1 61.93 23.91 14.16 Point2 52.26 33.75 13.99 Plane Scan 53.98 29.74 16.28

[0066] Example 2

[0067] The preparation method of the columnar crystal Y2O3 / 50vol%MgO composite ceramic powder in this embodiment is specifically completed by the following steps:

[0068] I. Dry the magnesium powder, yttrium oxide powder and magnesium oxide powder, vacuum dry the magnesium powder at a vacuum degree of 0.06 MPa, the drying temperature is 80℃, and the drying time is 12h; directly dry the yttrium oxide powder and the magnesium oxide powder, the drying temperature is 80℃, and the drying time is 12h;

[0069] II. After the dried 32.6g of magnesium powder, 23.8g of magnesium oxide powder and 108.8g of yttrium oxide powder are uniformly mixed by resonance mixing method, pass through a 60 mesh sieve to obtain a mixture;

[0070] III. Put the mixed material into a high-pressure reactor, fill O2, set the oxygen pressure to 20.34 MPa, the lower end of the high-pressure reactor is provided with a nozzle, the nozzle size is Φ2mm, place the high-pressure reactor above the water cooling device, ignite the mixed material by the resistance wire, and carry out high-temperature combustion synthesis reaction, after the reaction, form a high-temperature melt, keep warm for 10s, then open the nozzle, the high-temperature melt is sprayed out through the nozzle under high temperature and high pressure, and sprayed into the water cooling device for liquid phase cooling, and the yttrium oxide / magnesium oxide composite ceramic powder is obtained; the water cooling device is an atomizing tower containing a cooling liquid phase, and the cooling liquid phase is water.

[0071] IV. The powder obtained in step III is subjected to hot-pressing sintering to obtain columnar crystal yttrium oxide / magnesium oxide composite ceramic, and the hot-pressing sintering conditions are as follows: sintering temperature 1300℃, sintering pressure 40 MPa, heating rate 20℃ / min, and holding time 1h;

[0072] V. Anneal the yttrium oxide / magnesium oxide composite ceramic obtained in step IV in air, and the annealing conditions are as follows: annealing temperature 1000℃, and annealing time 10h.

[0073] The fracture toughness of the ceramic prepared in this embodiment is tested by indentation method, and the performance before annealing is as follows: fracture toughness 3.2MPa·m 1 / 2 , hardness 12.5GPa; and the performance after annealing is as follows: fracture toughness 3.7MPa·m 1 / 2 , hardness 11.2GPa.

[0074] Example 3

[0075] The preparation method of the columnar crystal Y2O3 / 40vol%MgO composite ceramic powder in this embodiment is specifically completed by the following steps:

[0076] I. Dry the magnesium powder, yttria powder and magnesia powder, vacuum dry the magnesium powder at a vacuum degree of 0.06 MPa, the drying temperature is 80℃, and the drying time is 12h; directly dry the yttria powder and magnesia powder, the drying temperature is 80℃, and the drying time is 12h;

[0077] II. Mix the dried 30.7g magnesium powder, 11.7g magnesia powder and 131.3g yttria powder uniformly by resonance mixing method and pass through a 60 mesh sieve to obtain a mixture;

[0078] III. Put the mixture into a high-pressure reactor, fill O2, set the oxygen pressure to 19.15 MPa, provide a nozzle at the lower end of the high-pressure reactor, the nozzle size is Φ2mm, place the high-pressure reactor above a water cooling device, ignite the mixture by an electric resistance wire, perform high-temperature combustion synthesis reaction, form a high-temperature melt after the reaction, keep warm for 7s, then open the nozzle, the high-temperature melt is sprayed out through the nozzle under high temperature and high pressure, and sprayed into the water cooling device to perform liquid phase cooling, thereby obtaining yttria / magnesia composite ceramic powder; the water cooling device is an atomizing tower containing a cooling liquid phase, and the cooling liquid phase is water.

[0079] IV. Obtain columnar crystal yttria / magnesia composite ceramic by discharging plasma sintering of the powder obtained in step III, the discharge plasma sintering conditions are: sintering temperature 1100℃, sintering pressure 50 MPa, heating rate 100℃ / min, and keeping warm for 5min;

[0080] V. Anneal the yttria / magnesia composite ceramic obtained in step IV in air, the annealing conditions are: annealing temperature 1000℃, and annealing time 24h.

[0081] The fracture toughness of the ceramic prepared in this embodiment is tested by indentation method, the performance before annealing is: fracture toughness 2.9MPa·m 1 / 2 , hardness 13.0GPa; the performance after annealing is: fracture toughness 3.3MPa·m 1 / 2 , hardness 12.1GPa.

[0082] Example 4:

[0083] The preparation method of the columnar crystal Y2O3 / 30vol%MgO composite ceramic powder in this embodiment is completed according to the following steps:

[0084] I. Dry the magnesium powder and yttria powder, vacuum dry the magnesium powder at a vacuum degree of 0.06 MPa, the drying temperature is 80℃, and the drying time is 12h; directly dry the yttria powder and magnesia powder, the drying temperature is 80℃, and the drying time is 12h;

[0085] II. 28.4 g of dried magnesium powder and 154.2 g of yttria powder are mixed uniformly by resonance mixing method and then passed through a 60-mesh sieve to obtain a mixture;

[0086] III. The mixture is loaded into a high-pressure reactor, O2 is filled, the oxygen pressure is set to 17.8 MPa, a nozzle is arranged at the lower end of the high-pressure reactor, the size of the nozzle is Φ2 mm, the high-pressure reactor is placed above a water cooling device, the resistance wire is ignited to perform high-temperature combustion synthesis reaction of the mixture, a high-temperature melt is formed after the reaction, and the temperature is kept for 7 s, then the nozzle is opened, the high-temperature melt is sprayed out through the nozzle under high temperature and high pressure, and is sprayed into the water cooling device to perform liquid phase cooling, thereby obtaining yttria / magnesia composite ceramic powder; the water cooling device is an atomization tower containing a cooling liquid phase, and the cooling liquid phase is water.

[0087] IV. The powder obtained in step III is subjected to hot-pressing sintering to obtain columnar yttria / magnesia composite ceramic, and the hot-pressing sintering conditions are as follows: sintering temperature 1200℃, sintering pressure 30 MPa, heating rate 20℃ / min, and holding time 1 h;

[0088] V. The yttria / magnesia composite ceramic obtained in step IV is annealed in air, and the annealing conditions are as follows: annealing temperature 1000℃, and annealing time 10 h.

[0089] The fracture toughness of the ceramic prepared in this embodiment is tested by indentation method, and the performance before annealing is as follows: fracture toughness 3.0 MPa·m 1 / 2 , and hardness 11.8 GPa; and the performance after annealing is as follows: fracture toughness 3.5 MPa·m 1 / 2 , and hardness 11.2 GPa.

Claims

1. A method for preparing columnar yttrium oxide / magnesium oxide composite ceramics, characterized in that, The method comprises the following steps: Step one: dry the magnesium powder and diluent; the diluent is a mixture of magnesium oxide and yttrium oxide, wherein the mass fraction of magnesium oxide in the total mass of the diluent is 0-28.19%; Step two: mix the dried magnesium powder and diluent uniformly to obtain a mixture; wherein the mass fraction of magnesium powder in the mixture is 13.45%-24.2%, and the mass fraction of the diluent is 75.8-86.55%; Step three: load the mixture into a high-pressure reactor, fill O2 or O2 mixed gas into the high-pressure reactor, the reactor has a nozzle at the lower end, the nozzle has a nozzle diameter of 1-5 mm, ignite the mixture, and perform high-temperature combustion synthesis reaction, the reaction temperature is 3300-4500K, after the reaction, a high-temperature melt is formed, and the high-temperature melt is sprayed out after the nozzle is opened, and the columnar crystal yttria / magnesia composite ceramic powder is obtained after the high-temperature melt is cooled in liquid phase; wherein the high-temperature melt spraying pressure is set to 10-40MPa; Sinter the columnar crystal yttria / magnesia composite ceramic powder obtained in step three to obtain submicron columnar crystal yttria / magnesia composite ceramic.

2. The method of claim 1, wherein the columnar crystal yttria / magnesia composite ceramic is prepared by the steps of: preparing a slurry of a mixture of a magnesium compound and a yttrium compound; and sintering the slurry to form the columnar crystal yttria / magnesia composite ceramic. The magnesium powder in step one is dried in vacuum, inert or reducing gas.

3. The method for preparing columnar yttrium oxide / magnesium oxide composite ceramic according to claim 1 or 2, characterized in that, The drying temperature in step one is 50-100℃, and the drying time is 12-24h.

4. The method of claim 1, wherein the columnar crystal yttria / magnesia composite ceramic is prepared by the steps of: preparing a slurry of a mixture of a magnesium compound and a yttrium compound; and sintering the slurry to form the columnar crystal yttria / magnesia composite ceramic. In step one, the mass fraction of magnesium oxide in the total mass of the diluent is 13.16%-22.18%; in step two, the mass fraction of magnesium powder in the mixture is 16.77%-22.77%, and the mass fraction of the diluent is 77.23%-83.23%.

5. The method for preparing columnar yttrium oxide / magnesium oxide composite ceramics according to claim 1, characterized in that, The O2 mixed gas in step three is a mixture of oxygen and inert gas.

6. The method for preparing columnar yttrium oxide / magnesium oxide composite ceramic according to claim 1, characterized in that, The sintering process is pressureless sintering, hot-pressing sintering, spark plasma sintering or flash sintering.

7. The method of claim 1 or 6, wherein the columnar crystal yttria / magnesia composite ceramic is prepared by the steps of: preparing a slurry of a mixture of a magnesium compound and a yttrium compound; and sintering the slurry. The sintering process conditions are: heating rate 5-100℃ / min, sintering temperature 1100-1500℃, and holding time 5min-3h.

8. The method of claim 1, wherein the columnar yttria / magnesia composite ceramic is prepared by the steps of: preparing a slurry of a mixture of a magnesium compound and a yttrium compound; and sintering the slurry to form the columnar yttria / magnesia composite ceramic. First, the columnar crystal yttria / magnesia composite ceramic powder obtained in step three is high-energy ball milled to 100-500nm, and then sintered; the high-energy ball milling speed is 1000-2000r / min, and the ball milling time is 6-12h.

9. The method of claim 1, wherein the columnar yttria / magnesia composite ceramic is prepared by the steps of: preparing a slurry of a mixture of a magnesium compound and a yttrium compound; and sintering the slurry to form the columnar yttria / magnesia composite ceramic. First, the columnar crystal yttria / magnesia composite ceramic powder obtained in step three is sand milled to 50-500nm, and then sintered; the sand mill motor speed is 1500-2030r / min, and the sand milling time is 4-10h.

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