MAX phase / alumina layered composite ceramic and in-situ synthesis preparation method thereof

Abstract

The invention provides an MAX phase / alumina layered composite ceramic and an in-situ synthesis preparation method thereof, and the method comprises the following steps: respectively preparing an alumina matrix layer and an MAX phase interface layer through a tape casting method, then alternately laminating the alumina matrix layer and the MAX phase interface layer, and finally carrying out hot pressed sintering to obtain a layered composite ceramic product. According to the invention, the layered composite ceramic which takes aluminum oxide as a matrix and MAX-phase ceramic as an interlayer is prepared through an in-situ synthesis technology, so that the effects of great toughening, strength increase without reduction and high damage tolerance are realized, and the fracture mode is converted from brittle fracture of aluminum oxide ceramic to safe stepped fracture. The strength and toughness of the aluminum oxide ceramic are successfully balanced and synergistically improved, and the industrial problem that strength and toughness cannot be both considered in a traditional aluminum oxide ceramic toughening technology is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ceramic materials, and relates to a layered composite ceramic and an in-situ synthesis preparation method thereof. BACKGROUND

[0002] Alumina ceramic is widely used in the fields of machinery, electronics, chemical industry and the like due to its low cost, high hardness, wear resistance, corrosion resistance and the like. However, the brittleness of the alumina ceramic hinders its application in many other fields. The brittleness of the alumina ceramic is difficult to change, but some measures can be taken to improve it. Common methods for toughening the alumina ceramic include: 1. particle toughening, such as adding metal Al, Cu and the like to toughen the material through particle pull-out and plastic deformation, but the toughening range is limited; 2. phase transformation toughening, such as introducing ZrO2 to improve the toughness of the material through crystal structure transformation, but the overall hardness of the material will decrease due to the low hardness of ZrO2 itself; 3. fiber / whisker toughening, but the production cost is high and the anisotropy is significant. Layered composite is an effective toughening technology currently widely used for alumina ceramic. However, traditional layered ceramic adopts a design of "strong matrix / weak interface", such as a weak interlayer design of graphite and porous ceramic, which improves the toughness while seriously sacrificing the strength and hardness of the material. SUMMARY

[0003] To solve the problem of the inability to balance the strength and toughness in the layered toughening technology of the alumina ceramic in the background art, the present application provides a MAX phase / alumina layered composite ceramic and an in-situ synthesis preparation method thereof. The MAX phase interlayer is generated in-situ to make a layered composite ceramic with alumina as the matrix and MAX phase ceramic as the interlayer, so as to realize the synergistic improvement of the strength and toughness of the material.

[0004] The present application provides an in-situ synthesis preparation method of a MAX phase / alumina layered composite ceramic, which comprises the following steps: Mixing alumina and an additive in a certain proportion to obtain alumina pre-prepared powder; Adding an organic solvent, a dispersant, a binder and a plasticizer to the alumina pre-prepared powder in a certain proportion, and ball-milling and uniformly mixing to obtain alumina matrix layer flow casting slurry; Flow casting the alumina matrix layer flow casting slurry to obtain an alumina matrix flow casting body; According to the stoichiometric ratio of the target MAX phase, weighing M source powder, A source powder and X source powder, ball-milling and uniformly mixing to obtain MAX phase pre-prepared powder; Adding an organic solvent, a dispersant, a binder and a plasticizer to the MAX phase pre-prepared powder in a certain proportion, and ball-milling and uniformly mixing to obtain MAX phase interface layer flow casting slurry; Flow casting the MAX phase interface layer flow casting slurry to obtain a MAX phase interface layer flow casting body; The laminated body is obtained by stacking the alumina matrix layer flow casting embryo and the MAX phase interface layer flow casting embryo according to the layered composite ceramic structure design, and the layered ceramic green body is obtained by hot pressing. After the layered ceramic green body is degreased, the MAX phase / alumina layered composite ceramic is obtained by hot pressing sintering.

[0005] Preferably, the alumina, sintering aid MgO and anhydrous ethanol are mixed into a mixture, which is uniformly mixed by ultrasonic dispersion and then put into a grinding machine to obtain a premixed slurry by ball milling; the slurry after ball milling is put into a rotary evaporator, dried and sieved to obtain an alumina pre-made powder; the mass ratio of the alumina to the sintering aid MgO is 99:1.

[0006] More preferably, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added to the alumina pre-made powder in proportion, which is uniformly milled by the alumina ball milling medium, and then vacuum degassing to obtain the alumina matrix layer flow casting slurry; the mass ratio of the alumina pre-made powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:5.

[0007] More preferably, the thickness of the matrix layer flow casting sheet layer of the alumina matrix layer flow casting embryo is 0.05-5mm.

[0008] Preferably, the stoichiometric ratio of the target MAX phase is (2-4):1:(1-3) in terms of the molar ratio of the M source powder, the A source powder and the X source powder; the M source powder comprises Ti powder, the A source powder comprises Al powder or Si powder, and the X source powder comprises C powder.

[0009] More preferably, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added to the MAX phase pre-made powder in proportion, which is uniformly milled by the alumina ball milling medium, and then vacuum degassing to obtain the MAX phase interface layer flow casting slurry; the mass ratio of the MAX phase pre-made powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:5.

[0010] More preferably, the thickness of the interface layer flow casting sheet layer of the MAX phase interface layer flow casting embryo is 0.05-2mm.

[0011] Preferably, the temperature of the hot pressing is 70℃, the pressure of the hot pressing is 10-100MPa; and the final thickness of the obtained layered ceramic green body is 1-100mm.

[0012] More preferably, the degreasing temperature of the layered ceramic green body is 500 DEG C, and the holding time is 1h; the layered ceramic green body after degreasing is loaded into a hot-pressing mold for hot-pressing sintering, the sintering temperature is 1400-2200 DEG C, the hot-pressing pressure is 2-50 Mpa, and the holding time is 2h.

[0013] Based on the above method, the application provides a MAX phase / alumina layered composite ceramic, which takes alumina as a matrix and MAX phase ceramic as a sandwich layer.

[0014] Compared with the prior art, the application has the following beneficial effects: (1) Synergistic optimization of strength and toughness: The application completely changes the traditional layered ceramic design idea of "exchanging strength for toughness", introduces MAX phase as a "strong sandwich layer", realizes toughening by using a layered structure, and avoids the problem of significant decrease in material strength and hardness caused by using graphite, porous ceramic and other "weak sandwich layers"; MAX phase ceramic itself has the toughness of metal and the strength and hardness of ceramic, and as a sandwich layer, it not only effectively toughens through crack deflection, bridging and other mechanisms, but also is a load-bearing unit, thereby realizing the synergistic improvement of material strength and toughness, and completely solving the performance core contradiction of traditional "weak interface" layered ceramics sacrificing strength for toughening; (2) High interfacial bonding strength of the material: Compared with the traditional method of physically mixing a second phase, the core advantage of the application lies in "in-situ synthesis"; the MAX phase generated by in-situ reaction and the alumina matrix form a "metallurgical bonding" interface through atomic diffusion; such interface is clean and free of impurities, and the interfacial bonding strength of the material is extremely high, which can maximize the load transmission and effectively avoid the problems of interface pollution, oxidation and weak bonding caused by physically introducing MAX phase powder, thereby providing a fundamental guarantee for the material to simultaneously obtain high strength and excellent toughening effect; (3) Multiple toughening and significantly improved damage tolerance: The layered structure design of the application, combined with the characteristics of MAX phase, realizes multiple toughening: first, the intrinsic toughening of MAX phase, the nano-layered structure of MAX phase can deform plastically through layer slip, pull-out and other ways under stress, and absorb a large amount of energy; second, crack propagation path regulation, when the crack encounters the tough MAX phase sandwich layer during propagation, it will deflect, branch and bridge, etc., greatly extending the crack propagation path and improving the fracture work; third, residual stress field toughening, due to the difference in thermal expansion coefficient between MAX phase and the alumina matrix, a beneficial residual stress will be formed in the interface area of the material after cooling, which can inhibit the initiation and propagation of cracks; through the synergistic effect of these multiple toughening mechanisms, the material changes from catastrophic brittle fracture of pure alumina to stable step-shaped fracture, significantly improving the reliability and damage tolerance of the material; (4) High degree of material densification, uniform and complete structure: through the organic combination of flow casting and hot-pressing sintering process, and combining with the design of reasonable sintering system, it is ensured that the process of reaction synthesis of MAX phase and the densification process of the aluminum oxide matrix can be coordinated with each other; the pressure provided by the hot-pressing process effectively promotes the densification, avoids the common interface pores and structural defects in the physical mixing method, so that the layered composite ceramic with nearly complete densification and uniform and complete structure can be obtained, which lays a structural foundation for realizing excellent mechanical properties; (5) High designability of material structure and performance: through adjusting the stoichiometric ratio of M source, A source and X source in the initial raw material of the MAX phase reaction layer, the thickness ratio of the substrate layer and the interlayer, the number of layers and the like, the present application can accurately control the type of the generated MAX phase such as Ti2AlC, Ti3SiC2, the content of the MAX phase, the thickness and distribution of the MAX phase interlayer, so as to realize the on-demand customization of the final mechanical properties of the composite material such as strength, toughness, hardness and even electrical properties, and broaden the application range.

[0015] In summary, through the "in-situ synthesis" technology, the layered composite ceramic with aluminum oxide as the matrix and MAX phase ceramic as the interlayer is successfully prepared, the toughness is greatly increased, the strength is not reduced but increased, the damage tolerance is high, and the fracture mode is changed from the brittle fracture of aluminum oxide ceramic to the safe step-shaped fracture. The present application successfully balances and synergistically improves the strength and toughness of aluminum oxide ceramic, and solves the industry problem that the strength and toughness cannot be considered in the traditional aluminum oxide ceramic toughening technology. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a schematic diagram of the layered structure of the present application.

[0017] Figure 2 It is a layer surface scanning electron microscope graph of Al2O3 / Ti2AlC layered ceramic material of Example 1, the dark gray layer is Al2O3 layer, the light gray layer is Ti2AlC layer, and the red dashed line is the bonding surface of adjacent layers. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear and explicit, the present application will be further described in detail in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0019] MAX phase ceramics (such as Ti3SiC2, Ti2AlC) are a kind of nanolaminated ceramics with excellent properties of both metals and ceramics, and have good strength and hardness; if the MAX phase is introduced into the alumina matrix as a "strong interlayer", it is expected to realize both reinforcement and toughening. Therefore, it has important practical significance to develop a MAX phase / alumina layered composite material with good interface bonding and controllable structure. The present application provides an in-situ synthesis preparation method of MAX phase / alumina layered composite ceramic, which is specifically as follows.

[0020] Firstly, an alumina matrix layer flow casting body is prepared, and the steps are as follows: The alumina is uniformly mixed with the additive in a certain proportion to obtain an alumina pre-prepared powder; specifically, 99 parts of alumina, 1 part of sintering aid MgO and anhydrous ethanol are mixed to form a mixture, which is uniformly mixed by ultrasonic dispersion and then put into a grinding machine, the ball-to-material ratio is 2:1, the ball milling time is 4h, and the pre-mixed slurry is obtained by ball milling; the slurry after ball milling is put into a rotary evaporator, dried and sieved, the drying temperature is 70 DEG C, and the dried product is sieved through a 100 mesh sieve, to obtain the alumina pre-prepared powder.

[0021] The organic solvent, dispersant, binder and plasticizer are added to the alumina pre-prepared powder in proportion, and the alumina matrix layer flow casting slurry is obtained by ball milling; specifically, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added to the alumina pre-prepared powder in proportion, and the alumina matrix layer flow casting slurry is obtained by ball milling with alumina ball milling medium and vacuum degassing. The mass ratio of the alumina pre-prepared powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:5; in actual operation, the weight of the alumina ball milling medium is 200 parts, and the ball milling time is 24h.

[0022] The alumina matrix layer flow casting slurry is made into an alumina matrix layer flow casting body by flow casting. Specifically, the thickness of the matrix layer flow casting sheet layer of the alumina matrix layer flow casting body is 0.05-5mm.

[0023] Then, the MAX phase interface layer flow casting body is prepared, and the steps are as follows: According to the stoichiometric ratio of the target MAX phase, the M source powder, the A source powder and the X source powder are weighed and ball milled to obtain the MAX phase pre-prepared powder; specifically, the molar ratio of the M source powder, the A source powder and the X source powder is (2-4):1:(1-3); the M source powder is Ti powder, the A source powder is Al powder or Si powder, and the X source powder is C powder.

[0024] The organic solvent, the dispersant, the binder and the plasticizer are added into the MAX phase pre-prepared powder in proportion, ball-milled uniformly to obtain the MAX phase interfacial layer flow slurry; specifically, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added into the MAX phase pre-prepared powder in proportion, ball-milled uniformly through the alumina ball milling medium, and then vacuum defoaming to obtain the MAX phase interfacial layer flow slurry. The mass ratio of the MAX phase pre-prepared powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:5; in actual operation, the weight part of the alumina ball milling medium is 200 parts, and the ball milling time is 24 h.

[0025] The MAX phase interfacial layer flow slurry is prepared into the MAX phase interfacial layer flow body through flow casting. Specifically, the thickness of the interface layer flow sheet of the MAX phase interfacial layer flow body is 0.05-2 mm.

[0026] Finally, the layered composite ceramic is prepared, and the steps are as follows: The alumina matrix layer flow body and the MAX phase interfacial layer flow body are stacked according to the structure design of the layered composite ceramic to obtain a stack, and hot-pressed to obtain a layered ceramic blank; specifically, the hot-pressing temperature is 70℃, and the hot-pressing pressure is 10-100 MPa; and the final thickness of the obtained layered ceramic blank is 1-100 mm. The layered structure diagram of the present application is shown in Figure 1 .

[0027] The layered ceramic blank is degreased and then hot-pressed and sintered to obtain the MAX phase / alumina layered composite ceramic. Specifically, the degreasing temperature of the layered ceramic blank is 500℃, and the holding time is 1 h; the degreased layered ceramic blank is loaded into a hot-pressing mold for hot-pressing and sintering, the sintering temperature is 1400-2200℃, the hot-pressing pressure is 2-50 MPa, and the holding time is 2 h.

[0028] The technical scheme and technical effect of the present application are further illustrated by the following examples and comparative examples.

[0029] Example 1 (1) Alumina pre-prepared powder is prepared: 99 parts of Al2O3 and 1 part of sintering aid MgO are added into an appropriate amount of anhydrous ethanol to prepare a mixed powder, which is ultrasonically dispersed for 30 min; then the mixed powder is put into a grinding machine with a ball-to-material ratio of 2:1, and ball-milled for 4 h to obtain a pre-mixed slurry; the pre-mixed slurry is put into a rotary evaporator and dried at 70℃; after the powder is dried, it is sieved through a 100-mesh sieve to obtain the alumina pre-prepared powder; (2) Preparation of MAX phase pre-powder: Ti, Al and C powders with a molar ratio of 3:1:2 were mixed uniformly, put into a ball mill for grinding for 2h, and then mixed uniformly. The MAX phase pre-powder was obtained by passing through a 100-mesh screen; (3) Preparation of alumina matrix layer tape casting slurry: 100 parts of alumina mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of glyceryl trioleate dispersant, and 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball mill barrel. At the same time, 200 parts of alumina ball milling medium was added and ball milled for 24h. Then, the ball milled slurry was vacuum degassed in a vacuum degassing machine for 30min to prepare the alumina matrix layer ceramic slurry; (4) Preparation of MAX phase interface layer tape casting slurry: 100 parts of MAX phase mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of glyceryl trioleate dispersant, and 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball mill barrel. At the same time, 200 parts of alumina ball milling medium was added and ball milled for 24h. Then, the ball milled slurry was vacuum degassed in a vacuum degassing machine for 30min to prepare the MAX phase interface layer ceramic slurry; (5) Casting: The slurries prepared in steps (3) and (4) were poured into the loading slot of the casting machine respectively; the alumina matrix layer ceramic slurry was cast into a matrix ceramic casting roll, and the thickness of the matrix layer casting sheet was 0.2mm; the MAX phase interface layer ceramic slurry was cast into an interface layer ceramic casting roll, and the thickness of the interface layer casting sheet was 0.05mm; (6) Layered warm pressing: The matrix ceramic casting roll and the interface layer ceramic casting roll prepared in step (5) were cut into pieces, and the layered body was obtained by stacking according to the design of the layered composite ceramic structure; the layered body was placed between two aluminum heating plates, the temperature was 70℃, the pressure was 20MPa, and the temperature and pressure were maintained for half an hour; a layered ceramic green body with a thickness of 20mm was obtained; (7) Glue removal and sintering: the layered ceramic green body obtained in step (6) was put into a high temperature furnace, the glue removal temperature was 500℃, and the temperature was maintained for 1h to remove the organic matter; then it was put into a hot pressing mold for hot pressing sintering, the sintering temperature was 1650℃, the temperature was maintained for 2h, the hot pressing pressure was 20MPa, and a layered composite ceramic product was obtained.

[0030] The fracture toughness test of the layered composite ceramic obtained in Example 1 did not suddenly decrease after the load reached the maximum value, the fracture mode was step-shaped fracture, and the fracture toughness was 7.6MPa·m 1 / 2 , and the bending strength was 580MPa.

[0031] Figure 2The layer scanning electron micrograph of the Al2O3 / Ti2AlC layered ceramic material of Example 1 shows that the layered ceramic material is obviously layered, the dark gray area in the figure corresponds to the Al2O3 matrix layer, the light gray area corresponds to the MAX phase interlayer of Ti2AlC, the red dashed line marks the interface of the adjacent layers, which embodies the design structure of "alumina matrix + MAX phase interlayer". The interface between the Al2O3 layer and the Ti2AlC layer is tightly combined, and there is no obvious pore or impurity, which is a "metallurgical bonding" interface brought by the "in-situ synthesis" process, which ensures the load transfer efficiency. Figure 2 The scale in the lower left corner shows "50 μm", combined with the parameters of Example 1: the thickness of the Al2O3 layer is 0.2mm, and the thickness of the Ti2AlC layer is 0.05mm, which can directly reflect the thickness ratio of the layered structure. Figure 2 The structure shown also corresponds to the core advantage of the application: Ti2AlC as a "strong interlayer" not only achieves toughening through a layered structure, but also maintains strength as a load-bearing unit, ultimately achieving a synergistic improvement in material strength and toughness.

[0032] Example 2 (1) Prepare alumina pre-mixed powder: mix 99 parts of Al2O3 and 1 part of sintering aid MgO with anhydrous ethanol to form a mixed powder, and ultrasonic dispersion for 30 min; put into a grinding machine, ball to material ratio is 2:1, ball milling time is 4h, get pre-mixed slurry; put the ball milled slurry into a rotary evaporator and dry at 70℃; after the powder is dried, sieve through a 100 mesh screen to obtain alumina pre-mixed powder; (2) Prepare MAX phase pre-mixed powder: mix Ti, Si and C powders in a molar ratio of 3:1:2, put into a ball mill and grind for 2h, then sieve through a 100 mesh screen to obtain MAX phase pre-mixed powder; (3) Prepare alumina matrix layer tape casting slurry: mix 100 parts of alumina mixed powder, 20 parts of polyvinyl alcohol, 20 parts of anhydrous ethanol, 0.5 parts of triolein dispersant, and 5 parts of dibutyl phthalate plasticizer, then add them into a ball milling barrel, and add 200 parts of alumina ball milling medium and mill for 24h, then vacuum degassing the ball milled slurry in a vacuum degassing machine for 30min to prepare an alumina matrix layer ceramic slurry; (4) Prepare MAX phase interface layer tape casting slurry: mix 100 parts of MAX phase mixed powder, 20 parts of polyvinyl alcohol, 20 parts of anhydrous ethanol, 0.5 parts of triolein dispersant, and 5 parts of dibutyl phthalate plasticizer, then add them into a ball milling barrel, and add 200 parts of alumina ball milling medium and mill for 24h, then vacuum degassing the ball milled slurry in a vacuum degassing machine for 30min to prepare a MAX phase interface layer ceramic slurry; (5) Casting: pour the slurry prepared in step (3) and step (4) into the loading tank of the casting machine, and cast the ceramic slurry of the aluminum oxide matrix layer to obtain a matrix ceramic casting roll, wherein the thickness of the matrix layer casting sheet is 0.2 mm; the ceramic slurry of the MAX phase interface layer is cast to obtain an interface layer ceramic casting roll, wherein the thickness of the interface layer casting sheet is 0.05 mm; (6) Laminated warm pressing: the casting green body prepared in step (5) is cut into pieces, and is laminated according to the design of the layered composite ceramic structure to obtain a laminated body; the laminated body is placed between two aluminum heating plates, the temperature is 70°C, the pressure is 20 MPa, and the temperature and pressure are maintained for half an hour; a layered ceramic green body with a thickness of 20 mm is obtained; (7) Degassing and sintering: the layered ceramic green body obtained in step (6) is placed in a high-temperature furnace, the degassing temperature is 500°C, and the temperature is maintained for 1 h to remove organic matter; then the degassed layered ceramic green body is loaded into a hot pressing mold for hot pressing and sintering, wherein the sintering temperature is 1650°C, the temperature is maintained for 2 h, and the hot pressing pressure is 20 MPa, to obtain a layered composite ceramic product.

[0033] The fracture toughness test of the layered composite ceramic obtained in Example 2 does not suddenly decrease after the load reaches the maximum value, the fracture mode is step-shaped fracture, and the fracture toughness is 7.9 MPa·m 1 / 2 , and the bending strength is 540 MPa.

[0034] Example 3 (1) Prepare the aluminum oxide pre-mixed powder: mix 99 parts of Al2O3, 1 part of sintering aid MgO, and anhydrous ethanol to prepare a mixed powder, and ultrasonic dispersion for 30 min; put it into a grinding machine, the ball-to-material ratio is 2:1, and the ball milling time is 4 h to obtain a pre-mixed slurry; the milled slurry is placed in a rotary evaporator and dried at 70°C; after drying, the powder is sieved through a 100 mesh sieve to obtain an aluminum oxide pre-mixed powder; (2) Prepare the MAX phase pre-mixed powder: mix Ti, Al and C powders with a molar ratio of 4:1:3 uniformly, put them into a ball mill and grind for 2 h, and then sieve through a 100 mesh sieve to obtain a MAX phase pre-mixed powder; (3) Prepare the aluminum oxide matrix layer casting slurry: mix 100 parts of aluminum oxide mixed powder, 20 parts of polyvinyl alcohol, 20 parts of anhydrous ethanol, 0.5 parts of triolein dispersant, and 5 parts of dibutyl phthalate plasticizer, then add them into a ball milling barrel, and add 200 parts of aluminum oxide ball medium for ball milling for 24 h, and then vacuum degassing the milled slurry in a vacuum degassing machine for 30 min to prepare an aluminum oxide matrix layer ceramic slurry; (4) Configuration of MAX phase interface layer flow slurry: 100 parts of MAX phase mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of triolein dispersant, 5 parts of dibutyl phthalate plasticizer are mixed and then added into the ball mill barrel, 200 parts of alumina ball milling medium is added at the same time, and then ball milling for 24h, then the slurry after ball milling is placed in a vacuum degassing machine for vacuum degassing for 30min to prepare MAX phase interface layer ceramic slurry; (5) Casting: the slurry prepared in steps (3) and (4) is poured into the loading tank of the casting machine, and the alumina matrix layer ceramic slurry is cast into a matrix ceramic casting roll, wherein the thickness of the matrix layer casting sheet is 0.2mm; the MAX phase interface layer ceramic slurry is cast into an interface layer ceramic casting roll, wherein the thickness of the interface layer casting sheet is 0.05mm; (6) Laminated warm pressing: the casting blank prepared in step (5) is cut into pieces, and a laminated body is obtained by laminating according to the design of layered composite ceramic structure; the laminated body is placed between two aluminum heating plates, the temperature is 70℃, the pressure is 20MPa, and the temperature and pressure are maintained for half an hour; a layered ceramic blank with a thickness of 20mm is obtained; (7) Glue removal and sintering: the layered ceramic blank obtained in step (6) is placed in a high temperature furnace, the glue removal temperature is 500℃, and the temperature is maintained for 1h to remove the organic matter; then the layered ceramic blank after glue removal is loaded into a hot pressing mold for hot pressing sintering, wherein the sintering temperature is 1650℃, the temperature is maintained for 2h, and the hot pressing pressure is 20MPa, to obtain a layered composite ceramic product.

[0035] The fracture toughness test of the layered composite ceramic obtained in Example 3 does not suddenly decrease after the load reaches the maximum value, the fracture mode is step-shaped fracture, and the fracture toughness is 6.8MPa·m 1 / 2 , and the bending strength is 500MPa.

[0036] Example 4 (1) Preparation of alumina pre-mixed powder: 99 parts of Al2O3 and 1 part of sintering aid MgO are added to absolute ethanol to prepare a mixed powder, which is ultrasonically dispersed for 30min; then it is put into a grinding machine with a ball-to-material ratio of 2:1, and ball milling for 4h to obtain a pre-mixed slurry; the slurry after ball milling is placed in a rotary evaporator and dried at 70℃; after drying, the powder is sieved through a 100 mesh sieve to obtain alumina pre-mixed powder; (2) Preparation of MAX phase pre-mixed powder: Ti, Al and C powders with a molar ratio of 2:1:1 are mixed uniformly and put into a ball mill for 2h to mix uniformly, and then sieved through a 100 mesh sieve to obtain MAX phase pre-mixed powder; (3) Preparation of tape casting slurry of aluminum oxide matrix layer: 100 parts of aluminum oxide mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of triolein dispersant, 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball milling barrel, 200 parts of aluminum oxide ball milling medium was added at the same time, and ball milling was carried out for 24 h, then the ball milled slurry was vacuum degassed in a vacuum degassing machine for 30 min to prepare the ceramic slurry of aluminum oxide matrix layer; (4) Preparation of tape casting slurry of MAX phase interface layer: 100 parts of MAX phase mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of triolein dispersant, 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball milling barrel, 200 parts of aluminum oxide ball milling medium was added at the same time, and ball milling was carried out for 24 h, then the ball milled slurry was vacuum degassed in a vacuum degassing machine for 30 min to prepare the ceramic slurry of MAX phase interface layer; (5) Tape casting: the slurries prepared in steps (3) and (4) were poured into the loading tank of the tape casting machine, the ceramic slurry of aluminum oxide matrix layer was tape cast to obtain a matrix ceramic tape casting roll, wherein the thickness of the matrix layer tape casting sheet was 0.2 mm; the ceramic slurry of MAX phase interface layer was tape cast to obtain an interface layer ceramic tape casting roll, wherein the thickness of the interface layer tape casting sheet was 0.05 mm; (6) Laminated warm pressing: the tape casting green body prepared in step (5) was cut into pieces, and was laminated according to the design of layered composite ceramic structure to obtain a laminated body; the laminated body was placed between two aluminum heating plates, the temperature was 70℃, the pressure was 20 MPa, and the temperature and pressure were maintained for half an hour; a layered ceramic green body with a thickness of 20 mm was obtained; (7) Glue removal and sintering: the layered ceramic green body obtained in step (6) was placed in a high temperature furnace, the glue removal temperature was 500℃, and the temperature was maintained for 1 h to remove the organic matter; then the layered ceramic green body after glue removal was loaded into a hot pressing mold for hot pressing sintering, the sintering temperature was 1650℃, the temperature was maintained for 2 h, and the hot pressing pressure was 20 MPa, to obtain a layered composite ceramic product.

[0037] The fracture toughness test of the layered composite ceramic obtained in Example 4 did not suddenly decrease after the load reached the maximum value, the fracture mode was step-shaped fracture, and the fracture toughness was 7.1 MPa·m 1 / 2 , and the bending strength was 510 MPa.

[0038] Comparative Example 1 (1) Preparation of aluminum oxide pre-mixed powder: 99 parts of Al2O3, 1 part of sintering aid MgO, and absolute ethanol were mixed to form a mixed powder, which was ultrasonically dispersed for 30 min; the mixed powder was placed in grinding balls, the ball-to-material ratio was 2:1, and the ball milling time was 4 h to obtain a pre-mixed slurry; the ball milled slurry was placed in a rotary evaporator and dried at 70℃; after the powder was dried, it was sieved through a 100 mesh sieve to obtain an aluminum oxide pre-mixed powder; (2) Preparation of alumina matrix layer tape casting slurry: 100 parts of alumina mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of triolein dispersant, 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball milling barrel, 200 parts of alumina ball milling medium was added at the same time, and ball milling was carried out for 24 h, then the slurry after ball milling was vacuum degassed in a vacuum degassing machine for 30 min to prepare an alumina matrix layer ceramic slurry; (3) Casting: pour the slurry into the loading tank of the casting machine, and the alumina matrix layer ceramic slurry is cast into a ceramic casting roll, wherein the thickness of the casting sheet layer is 0.2 mm; (4) Laminated warm pressing: the casting green body prepared in step (3) is cut into pieces and laminated; the laminated body is placed between two aluminum heating plates, the temperature is 70℃, the pressure is 20 MPa, and the temperature and pressure are maintained for half an hour; a ceramic green body is obtained; (5) Glue removal and sintering: the ceramic green body obtained in step (4) is placed in a high-temperature furnace, the glue removal temperature is 500℃, and the temperature is maintained for 1 h to remove the organic matter; then the layered ceramic green body after glue removal is loaded into a hot pressing mold for hot pressing sintering, wherein the sintering temperature is 1650℃, the temperature is maintained for 2 h, and the hot pressing pressure is 20 MPa, to obtain a layered ceramic product; The fracture toughness test of the alumina ceramic obtained in Comparative Example 1 suddenly decreases after the load reaches the maximum value, brittle fracture occurs, and the fracture toughness is 4.6 MPa·m 1 / 2 , indicating that the material has low toughness and poor impact resistance; the bending strength is 500 MPa.

[0039] Comparative Example 2 (1) Preparation of alumina pre-mixed powder: 99 parts of Al2O3 and 1 part of sintering aid MgO were added to absolute ethanol to prepare a mixed powder, which was ultrasonically dispersed for 30 min; put into grinding balls, the ball-to-material ratio was 2:1, and the ball milling time was 4 h to obtain a pre-mixed slurry; the slurry after ball milling was placed in a rotary evaporator and dried at 70℃; after the powder was dried, it was sieved through a 100 mesh sieve to obtain an alumina pre-mixed powder; (2) Preparation of MAX phase pre-mixed powder: commercially available Ti2AlC powder with a purity of >99.7% and a medium particle size of 1.13 pm was selected; (3) Preparation of alumina matrix layer tape casting slurry: 100 parts of alumina mixed powder, 20 parts of polyvinyl alcohol, 20 parts of absolute ethanol, 0.5 parts of triolein dispersant, 5 parts of dibutyl phthalate plasticizer were mixed and then added into a ball milling barrel, 200 parts of alumina ball milling medium was added at the same time, and ball milling was carried out for 24 h, then the slurry after ball milling was vacuum degassed in a vacuum degassing machine for 30 min to prepare an alumina matrix layer ceramic slurry; (4) The MAX phase interface layer slurry is prepared by: mixing 100 parts of Ti2AlC powder, 20 parts of polyvinyl alcohol, 20 parts of anhydrous ethanol, 0.5 parts of triolein dispersant, and 5 parts of dibutyl phthalate plasticizer, then adding them into a ball milling barrel, and adding 200 parts of alumina ball milling medium at the same time, and ball milling for 24 hours, and then vacuum degassing the slurry in a vacuum degassing machine for 30 minutes to prepare a MAX phase interface layer ceramic slurry; (5) Casting: the slurry prepared in steps (3) and (4) is poured into a loading tank of a casting machine, and the alumina matrix layer ceramic slurry is cast into a matrix ceramic casting roll, wherein the thickness of the matrix layer casting sheet is 0.2 mm; the MAX phase interface layer ceramic slurry is cast into an interface layer ceramic casting roll, wherein the thickness of the interface layer casting sheet is 0.05 mm; (6) Laminated warm pressing: the casting green body prepared in step (5) is cut into pieces, and is laminated according to the design of the layered composite ceramic structure to obtain a laminated body; the laminated body is placed between two aluminum heating plates, the temperature is 70℃, the pressure is 20 MPa, and the temperature and pressure are maintained for half an hour; a layered ceramic green body with a thickness of 20 mm is obtained; (7) Glue removal and sintering: the layered ceramic green body obtained in step (6) is placed in a high-temperature furnace, the glue removal temperature is 500℃, and the temperature is maintained for 1 hour to remove the organic matter; then the layered ceramic green body after glue removal is loaded into a hot pressing mold for hot pressing sintering, wherein the sintering temperature is 1650℃, the temperature is maintained for 2 hours, the hot pressing pressure is 20 MPa, and a layered composite ceramic product is obtained.

[0040] The fracture toughness test of the layered composite ceramic obtained in Comparative Example 2 does not suddenly decrease after the load reaches the maximum value, the fracture mode is step-shaped fracture, and the fracture toughness is 6.8 MPa·m 1 / 2 , indicating that the material has certain toughness and impact resistance, but the toughness and impact resistance are not as good as those of the present application; and the bending strength is 436 MPa.

[0041] From the above content, the present application has the following technical effects: I. Excellent toughening effect: Compared with pure alumina in Comparative Example 1, the toughness of the embodiments of the present application is improved by up to 72% (from 4.6 in Comparative Example 1 to 7.9 in Embodiment 2); even compared with the physically introduced MAX phase in Comparative Example 2, the embodiments 1, 2 and 4 of the present application also exhibit higher or comparable toughness, and the interface bonding is better; this is because the MAX phase (such as Ti3SiC2, Ti2AlC) itself is a tough ceramic with good plasticity and self-lubricating property; the MAX phase layer generated in situ in the present application does not match the thermal expansion coefficient of the alumina matrix, and forms beneficial residual stress in the material after cooling, which can effectively inhibit crack propagation; the characteristics of the MAX phase itself, the residual stress in the material and the crack deflection mechanism of the layered structure itself synergistically act to greatly improve the fracture toughness of the material; II. High overall strength of the material: While the toughness is greatly improved, the bending strength of the present application is not sacrificed, but rather improved by up to 16% in Embodiment 2; the physically introduced MAX phase in Comparative Example 2 has problems of contamination, oxidation and weak bonding at the interface, resulting in weak interface bonding and a significant decrease in strength (436 MPa); the present application generates a clean and strong metallurgical bonding interface between the MAX phase and the alumina matrix through atomic diffusion, and this strong interface can effectively transfer the load, so that the MAX phase sandwich truly plays a dual role of load bearing and toughening, thereby maintaining or even improving the overall strength of the material while toughening, and completely solving the performance core contradiction of sacrificing strength for toughening in traditional "weak interface" layered ceramics; III. Reliable damage tolerance: The fracture toughness test of the alumina ceramic obtained in Comparative Example 1 suddenly decreases after the load reaches the maximum value, and brittle fracture occurs; the fracture toughness test of the layered composite ceramic obtained in Embodiments 1-4 of the present application does not suddenly decrease after the load reaches the maximum value, and the fracture mode is stepwise fracture; this typical "stepwise fracture" of the present application indicates that the crack will be deflected, branched, bridged and other energy dissipation mechanisms when it encounters the MAX phase sandwich during the propagation process, avoiding catastrophic instantaneous fracture, and the material has higher reliability; IV. Strong designability of process and performance: By changing the stoichiometric ratio of the initial MAX phase powder (such as Ti:Al:C from 3:1:2 to 4:1:3 or 2:1:1), different types and proportions of MAX phases are synthesized, and different mechanical property combinations (toughness from 6.8 to 7.9, strength from 500 to 580) are finally obtained; this proves that by adjusting the process parameters, the performance of the final product can be "customized on demand"; V. High material density: By combining the flow casting and hot-pressing sintering process, and precisely controlling the sintering system (temperature, pressure, holding time), it is ensured that both the alumina matrix and the in-situ generated MAX phase layer can achieve a very high degree of densification, avoiding interface porosity, which is the basis for obtaining high strength.

[0042] In summary, the present application provides a clever material design and an optimized preparation process, which enables the prepared layered composite ceramic to achieve: a significant increase in toughness, with a maximum increase of 72% in fracture toughness; a non-decreasing but increasing strength, with a maximum bending strength of 580Mpa; high damage tolerance: the fracture mode of the alumina ceramic is changed from brittle fracture to safe stepwise fracture. The present application successfully balances and synergistically improves the strength and toughness of the alumina ceramic, opening up new possibilities for its application in harsh environments such as high-level armor, key structural parts, high-temperature resistant parts, etc.

[0043] The preferred embodiments of the present application are described in detail above in combination with the drawings and specific examples, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

Claims

1. A method for the in-situ synthesis of MAX phase / alumina layered composite ceramics, characterized in that, The application relates to a layered ceramic composite and a preparation method thereof. The alumina is mixed with additives in a certain proportion to obtain alumina pre-prepared powder; The organic solvent, the dispersant, the binder and the plasticizer are added into the alumina pre-prepared powder in a certain proportion, and the alumina pre-prepared powder is ball milled to obtain alumina matrix layer flow casting slurry; The alumina matrix layer flow casting slurry is prepared into an alumina matrix flow casting body through flow casting; The M source powder, the A source powder and the X source powder are weighed according to the stoichiometric ratio of the target MAX phase, and are ball milled to obtain MAX phase pre-prepared powder; The organic solvent, the dispersant, the binder and the plasticizer are added into the MAX phase pre-prepared powder in a certain proportion, and the MAX phase pre-prepared powder is ball milled to obtain MAX phase interface layer flow casting slurry; The MAX phase interface layer flow casting slurry is prepared into a MAX phase interface layer flow casting body through flow casting; The alumina matrix layer flow casting body and the MAX phase interface layer flow casting body are stacked according to the layered ceramic composite structure design to obtain a layered body, and the layered body is hot-pressed to obtain a layered ceramic blank; The layered ceramic blank is degreased and then hot-pressed and sintered to obtain the layered ceramic composite.

2. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 1, characterized in that: The alumina, the sintering aid MgO and anhydrous ethanol are mixed to obtain a mixed material, the mixed material is uniformly dispersed through ultrasonic dispersion, and then is placed into a grinding machine to obtain pre-mixed slurry through ball milling; the ball-milled slurry is placed into a rotary evaporator, dried and sieved to obtain alumina pre-prepared powder; the mass ratio of the alumina to the sintering aid MgO is 99:

1.

3. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 2, characterized in that: The organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added into the alumina pre-prepared powder in a certain proportion, and the alumina pre-prepared powder is ball milled through an alumina ball milling medium to obtain alumina matrix layer flow casting slurry; the mass ratio of the alumina pre-prepared powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:

5.

4. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 3, characterized in that: The matrix layer flow casting sheet layer of the alumina matrix layer flow casting body is 0.05-5mm thick.

5. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 1, characterized in that: The stoichiometric ratio of the target MAX phase is that the molar ratio of the M source powder, the A source powder and the X source powder is (2-4):1:(1-3); the M source powder comprises Ti powder, the A source powder comprises Al powder or Si powder, and the X source powder comprises C powder.

6. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 5, characterized in that: The organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate are added into the MAX phase pre-prepared powder in a certain proportion, and the MAX phase pre-prepared powder is ball milled through an alumina ball milling medium to obtain MAX phase interface layer flow casting slurry; the mass ratio of the MAX phase pre-prepared powder, the organic solvent anhydrous ethanol, the dispersant triolein, the binder polyvinyl alcohol and the plasticizer dibutyl phthalate is 100:20:20:0.5:

5.

7. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 6, characterized in that: The interface layer flow casting sheet layer of the MAX phase interface layer flow casting body is 0.05-2mm thick.

8. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 1, characterized in that: The temperature of the hot-pressing is 70 DEG C, and the pressure of the hot-pressing is 10-100MPa; and the final thickness of the obtained layered ceramic blank is 1-100mm.

9. The in-situ synthesis of MAX phase / alumina layered composite ceramic according to claim 8, characterized in that: The degassing temperature of the layered ceramic blank is 500 DEG C, and the holding time is 1 h; then the layered ceramic blank after degassing is loaded into a hot-pressing mold to perform hot-pressing sintering, the sintering temperature is 1400-2200 DEG C, the hot-pressing pressure is 2-50 MPa, and the holding time is 2 h.

10. A MAX phase / alumina layered composite ceramic prepared by the method of any one of claims 1-9, wherein: The layered composite ceramic takes alumina as a matrix and MAX phase ceramic as a sandwich layer.

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