Alumina-based gradient ceramic as well as preparation method and application thereof

Abstract

The invention provides alumina-based gradient ceramic as well as a preparation method and application thereof, and belongs to the technical field of ceramic materials. A gradient structure design is adopted, based on a non-linear component distribution mode, the ratio of aluminum oxide to zirconium oxide is optimized, a sintering aid is added, aluminum oxide-based composite powder is synthesized through high-energy ball milling, a mold is filled with the aluminum oxide-based composite powder in a layered mode according to the gradient design after the aluminum oxide-based composite powder is dried, and the compact aluminum oxide-based gradient ceramic is obtained through a hot pressing sintering process. The alumina-based gradient ceramic prepared by the invention has high Vickers hardness (greater than or equal to 21 GPa), high strength (greater than 850 MPa) and high fracture toughness (greater than 7 MPa.m < 1 / 2 >), and has excellent mechanical properties, and the fracture toughness and the strength are greatly improved on the premise of ensuring that the Vickers hardness is not reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and particularly to an alumina-based gradient ceramic and its preparation method and application. Background Art

[0002] Due to its excellent properties such as high Vickers hardness, wear resistance, corrosion resistance, and high temperature resistance, alumina ceramics are widely used in the fields of machinery, electronics, chemical engineering, biomedicine, etc. However, its inherent low strength and low fracture toughness severely limit its application in more demanding environments. The strength and fracture toughness of alumina ceramics are mainly affected by factors such as its crystal structure, grain size, and porosity. Its crystal structure is of the corundum type, with coexistence of covalent bonds and ionic bonds and high bond energy, resulting in its high brittleness and poor impact resistance. In addition, alumina ceramics are prone to abnormal grain growth and pores during the sintering process, which further reduces their mechanical properties. In order to improve the strength and fracture toughness of alumina ceramics, traditional methods mainly use doping modification techniques, by introducing second-phase particles, whiskers, fibers and other reinforcing phases, or through mechanisms such as solid solution strengthening and fine grain strengthening to improve their mechanical properties. However, these methods often have the following limitations: Doping modification often comes at the expense of other properties of alumina ceramics. For example, introducing second-phase particles may reduce its high-temperature properties, corrosion resistance, etc. Moreover, although doping modification can improve the strength and toughness of alumina ceramics to a certain extent, the improvement amplitude is limited and it is difficult to meet the growing application requirements. Summary of the Invention

[0003] The purpose of the present invention is to provide an alumina-based gradient ceramic and its preparation method and application, to solve the problems of low strength and fracture toughness of alumina ceramics. The alumina-based gradient ceramic prepared by the present invention has greatly improved fracture toughness and strength on the premise of ensuring that its Vickers hardness does not decrease.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of an alumina-based gradient ceramic, comprising the following steps:

[0006] According to the non-linear component distribution mode, mix the required proportions of oxides with sintering aids and grinding solvents, and perform high-energy ball milling treatment to obtain mixed slurries with different gradient components; the oxides are alumina and zirconia;

[0007] After drying the mixed slurries, obtain alumina-based composite powders with different gradient components;

[0008] Set different gradient layers according to the non-linear component distribution method, lay the alumina-based composite powder with different gradient components into the mold in sequence according to the thickness requirements of each gradient layer, and perform hot pressing sintering to obtain an alumina-based gradient ceramic;

[0009] The non-linear component distribution method is calculated by Formula 1;

[0010] Based on the total volume fraction of 100% of Al2O3 and ZrO2, the different gradient components are formed by the change of the volume fraction of Al2O3 and ZrO2. The composition of each gradient changes linearly in one dimension along x. Formula 1 is used to calculate the composition distribution of each gradient layer:

[0011]

[0012] In Formula 1, f1(x) is the volume fraction of Al2O3 in any single-layer gradient layer, vol%; d is the total number of gradient layers, x is the gradient layer number corresponding to each gradient, x = 1 to d and x is an integer; p is the gradient component distribution index, p > 0 and p ≠ 1.

[0013] Preferably, d = 4 to 6, p = 0.1 to 0.6.

[0014] Preferably, the sintering aids include magnesium oxide and lanthanum oxide; the mass ratio of the magnesium oxide to the lanthanum oxide is (1 to 2):(2 to 4).

[0015] Preferably, the mass ratio of the oxide to the sintering aid is (0.5 to 1.5):100.

[0016] Preferably, the rotation speed of the high-energy ball milling treatment is 2300 to 2700 r / min, the treatment time is 4 to 8 h, and the grinding medium is zirconia balls with a diameter of 0.1 to 0.5 mm.

[0017] Preferably, the total thickness of the gradient layer is 3 to 4 mm, and the thickness of each gradient layer is the same; the mold is a graphite mold, and the diameter of the graphite mold is 30 to 50 mm.

[0018] Preferably, the conditions of the hot pressing sintering include: the sintering pressure is 40 to 100 MPa, the sintering temperature is 1400 to 1600 °C, and the heat preservation time is 1.5 to 3 h.

[0019] Preferably, the heating rate for heating to the temperature of the hot pressing sintering is 5 to 10 °C / min.

[0020] The present invention provides an alumina-based gradient ceramic prepared by the preparation method described in the above technical solution, with a Vickers hardness ≥ 21 GPa, a strength ≥ 850 MPa, and a fracture toughness ≥ 7 MPa·m 1 / 2 .

[0021] The present invention provides the application of the alumina-based gradient ceramic described in the above technical solution in the fields of aerospace or bulletproof composite armor.

[0022] The present invention provides a preparation method of an alumina-based gradient ceramic. By adopting a gradient structure design, based on different non-linear component distribution modes, through optimizing the ratio of alumina to zirconia and adding a sintering aid, an alumina-based composite powder is synthesized by high-energy ball milling. After drying, it is filled into a mold layer by layer according to the gradient design, and a dense alumina-based gradient ceramic is obtained by a hot pressing sintering process. Compared with the traditional linear distribution mode, the non-linear distribution mode adopted in the present invention has very small interfacial stress, so the mechanical properties are greatly improved. For the traditional linear distribution mode, the distribution mode and its mechanical properties are not coordinated. The main reason is that when the gradient layer transitions, there is a large tensile stress at the interface, which causes many microcracks inside the ceramic and reduces its mechanical properties.

[0023] The alumina-based gradient ceramic prepared by the present invention has both high Vickers hardness (≥21 GPa), high strength (>850 MPa) and high fracture toughness (>7 MPa·m1 / 2), and has excellent mechanical properties. On the premise of ensuring that the Vickers hardness of the alumina-based gradient ceramic prepared by the present invention does not decrease, the fracture toughness and strength are greatly improved. Its high-performance advantage stems from the synergistic strengthening effect of the gradient structure design and the nano-powder. Based on the zirconia toughening alumina mechanism, through the synergistic effect of combining the traditional nano-powder strengthening mechanism with the gradient structure, through multiple mechanisms such as grain refinement strengthening, gradient stress design, crack propagation control and multi-scale interface optimization, the synergistic improvement of "high strength - high toughness" can be realized, providing a general idea for the mechanical property optimization of gradient ceramic matrix composites.

[0024] The synergistic mechanism between the nano-particulate and gradient structure in the present invention is as follows: The zirconia-alumina nano-powders have extremely high specific surface area and surface energy, and the diffusion rate during sintering is accelerated, which can form a matrix with a higher degree of densification, reduce defects such as pores, and thus improve the overall strength. In the gradient structure, the composition or grain size continuously changes from the surface layer to the interior. Due to the differences in thermal expansion coefficient or elastic modulus, compressive residual stress will be formed at the interface. This stress field can offset the tensile stress generated by the external load and inhibit the initiation and propagation of cracks. The non-uniformity (such as the elastic modulus gradient) at the gradient interface will force the crack propagation path to deflect or branch. The crack propagation requires more energy consumption, thereby improving the fracture toughness. The synergistic effect between the two lies in that in the gradient structure, after sintering of the nano-powders, a part of nano-crystalline regions (high strength and low toughness) and micro-crystalline regions (low strength and high toughness) will be generated, and the two are alternately distributed. Under the action of external forces, the nano-crystalline regions bear the main load, while the micro-crystalline regions absorb energy through plastic deformation (such as grain boundary slip), realizing the synergistic improvement of strength and toughness. The gradient structure formed by sintering of the nano-powders has a more continuous interface transition, which can reduce the stress concentration at the transition surface in traditional laminated composites.

[0025] In the present invention, magnesium oxide and lanthanum oxide are added as sintering aids to promote sintering, accelerate the densification of ceramics, and improve their toughness and strength.

[0026] The method of the present invention has controllable process and is applicable to the large-scale preparation of high-performance ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Field emission scanning electron microscope image of the alumina-based composite powder prepared in Example 1;

[0028] Figure 2 Surface microtopography of the Al2O3 / ZrO2 gradient ceramic prepared in Example 2;

[0029] Figure 3 Cross-sectional view of the gradient ceramic prepared in Example 3 taken by a super-depth-of-field 3D microscope;

[0030] Figure 4 Cross-sectional view of the gradient ceramic prepared in Example 5 taken by a super-depth-of-field 3D microscope;

[0031] Figure 5 Crack propagation mode of the gradient ceramic prepared in Example 3 taken by a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0032] In the present invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well-known to those skilled in the art.

[0033] The present invention provides a method for preparing an alumina-based gradient ceramic, comprising the following steps:

[0034] According to the non-linear component distribution mode, oxides in required proportions are mixed with sintering aids and grinding solvents, and high-energy ball milling treatment is carried out to obtain mixed slurries with different gradient components; the oxides are alumina and zirconia;

[0035] After drying the mixed slurries, alumina-based composite powders with different gradient components are obtained;

[0036] According to the non-linear component distribution mode, different gradient layers are set, and the alumina-based composite powders with different gradient components are sequentially laid into a mold according to the thickness requirements of each gradient layer, and hot pressing sintering is carried out to obtain an alumina-based gradient ceramic;

[0037] The non-linear component distribution mode is calculated by formula 1;

[0038] Based on the total volume fraction of 100% of Al2O3 and ZrO2, the different gradient components are formed by the change of the volume fractions of Al2O3 and ZrO2. The components of each gradient change linearly and continuously along the x-axis in one dimension. The component distribution of each gradient layer is calculated by using formula 1:

[0039]

[0040] In formula 1, f1(x) is the volume fraction of Al2O3 in any single-layer gradient layer, vol%; d is the total number of gradient layers, x is the gradient layer number corresponding to each gradient, x = 1 to d and x is an integer; p is the gradient component distribution index, p > 0 and p ≠ 1.

[0041] In the present invention, the gradient component change of each gradient layer is formed by the change of the volume fractions of alumina and zirconia in the oxides, and the sintering aids in each gradient layer have nothing to do with the formation of the gradient layer.

[0042] As a preferred embodiment of the present invention, d = 4 - 6, p = 0.1 - 0.6.

[0043] In formula 1 of the present invention, d represents the total number of gradient layers, and x represents from the first layer to the dth layer. When d = 6, x is respectively 1, 2, 3, 4, 5, 6. According to formula 1, f1(x) of each gradient layer is obtained, that is, the volume fraction of Al2O3 in each gradient layer.

[0044] In the present invention, the sintering aids preferably include magnesium oxide and lanthanum oxide; the mass ratio of magnesium oxide to lanthanum oxide is preferably (1 - 2):(2 - 4), and more preferably 1.4 - 2:3.2 - 3.5.

[0045] In the present invention, the mass ratio of the oxide to the sintering aid is preferably (0.5 - 1.5):100, more preferably 0.8 - 1.3:100, and further preferably 1 - 1.11:100.

[0046] In the present invention, the grinding solvent is preferably anhydrous ethanol; the mass ratio of the total mass of the oxide and the sintering aid to the mass of the grinding solvent is preferably (1 - 1.5):(1.8 - 2.5), more preferably 1:1.8.

[0047] The present invention preferably mixes the oxide, the sintering aid, and the grinding solvent in a high-energy ball mill for high-energy ball milling treatment to obtain a mixed slurry.

[0048] In the present invention, the rotation speed of the high-energy ball milling treatment is preferably 2300 - 2700 r / min, more preferably 2400 - 2600 r / min, the treatment time is preferably 4 - 8 h, more preferably 4.8 - 5 h, and the grinding medium is preferably zirconia balls with a diameter of 0.1 - 0.5 mm.

[0049] After completing the high-energy ball milling treatment, the present invention preferably dries the obtained slurry by a rotary evaporator to remove anhydrous ethanol, then dries it in a vacuum drying oven for 24 h, and then grinds it with an agate mortar and passes through a 200-mesh sieve to obtain an alumina-based composite powder with a diameter < 100 nm.

[0050] In the present invention, the drying method of the mixed slurry is preferably rotary evaporation and drying in an electric heating oven in sequence.

[0051] The present invention preferably places the alumina-based composite powder into a graphite mold, determines the thickness of each gradient layer according to requirements, evenly spreads each gradient layer of powder in the graphite mold until all the powder is spread, places the graphite pressing head on the mixed powder, and after laying, puts the graphite mold into a hot pressing furnace for hot pressing sintering to obtain an alumina-based gradient ceramic.

[0052] In the present invention, the total thickness of the gradient layer is independently preferably 3 - 4 mm, more preferably 3.5 - 3.8 mm, and further preferably 3.6 - 3.75 mm, and the thickness of each gradient layer is the same; the mold is a graphite mold, and the diameter of the graphite mold is preferably 30 - 50 mm.

[0053] In the present invention, the conditions of the hot pressing sintering preferably include: the sintering pressure is 40 - 100 MPa, more preferably 75 - 90 MPa, and further preferably 80 - 85 MPa, the sintering temperature is 1400 - 1600 °C, more preferably 1450 - 1500 °C, and the holding time is 1.5 - 3 h, more preferably 2 - 2.5 h.

[0054] In the present invention, the heating rate for heating to the temperature of the hot press sintering is preferably 5 to 10 °C / min, more preferably 7 to 8 °C / min.

[0055] The present invention provides an alumina-based gradient ceramic prepared by the preparation method described in the above technical solution, with a Vickers hardness ≥ 21 GPa, a strength ≥ 850 MPa, and a fracture toughness ≥ 7 MPa·m 1 / 2 。

[0056] The present invention provides the application of the alumina-based gradient ceramic described in the above technical solution in the fields of aerospace or bulletproof composite armor. The present invention has no special limitation on the method of the application, and the application methods well-known in the art can be used.

[0057] The following describes the specific embodiments of the present invention in detail, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0058] The following experimental methods and detection methods are all conventional methods unless otherwise specified; the following reagents and raw materials are all commercially available unless otherwise specified.

[0059] Example 1

[0060] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution mode as an example, the total number of gradient layers d is set to 6 layers, the gradient composition distribution mode is set to p = 0.1, the total thickness of the gradient layer is 4 mm, and the single-layer thickness is 0.67 mm. x takes values of 1, 2, 3, 4, 5, and 6 respectively. The volume fraction of Al2O3 in each gradient layer is calculated according to Formula 1, and at the same time, the volume fraction is converted into a mass fraction to obtain the ratio of each gradient layer in Table 1. Six kinds of Al2O3 / ZrO2 composite ceramic powders are prepared according to the ratio.

[0061] Table 1 Raw material ratios of each gradient layer in Example 1

[0062]

[0063]

[0064] First, heat all the raw material powders at 850 °C for 3 h to remove adsorbed water. Weigh accurately the amounts of each oxide, and uniformly mix Al2O3 and ZrO2 according to the ratios shown in Table 1. At the same time, add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 1:100, and the mass ratio of magnesium oxide to lanthanum oxide is 1:2, to obtain mixed powders with different gradient compositions;

[0065] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball-milling tank with ZrO2 (diameter 0.1 - 0.5 mm) as the ball-milling medium according to the mass ratio of 1:1.8, and ball-mill for 5 h at a rotation speed of 2400 r / min. After ball-milling, dry the mixed slurry by a rotary evaporator to remove absolute ethanol. After drying, put the mixed powder into a vacuum drying oven and dry for 24 h. Grind the dried mixed powder with an agate mortar, and then pass through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm;

[0066] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method in Table 1. Control the total thickness of the gradient layer at 4 mm, and evenly spread the composite powder of each layer in the graphite mold until all six layers of powder are spread. Place the graphite press head on the mixed powder; put the graphite mold filled with the composite powder into a hot press furnace for sintering, with a sintering pressure of 40 MPa, a sintering temperature of 1400 °C, a heating rate of 10 °C / min, and hold for 1.5 h to obtain Al2O3 / ZrO2 gradient ceramics.

[0067] Example 2

[0068] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution method as an example, the total number of layers d of the gradient layer is set to 5 layers, the gradient composition distribution method is set to p = 0.2, the total thickness of the gradient layer is 3.5 mm, and the single-layer thickness is 0.7 mm. x takes values of 1, 2, 3, 4, and 5 respectively. Calculate the volume fraction of Al2O3 in each gradient layer according to formula 1, and at the same time convert the volume fraction into a mass fraction to obtain the ratios of each gradient layer in Table 2. Prepare 5 kinds of Al2O3 / ZrO2 composite ceramic powders according to the ratios.

[0069] Table 2 Raw material ratios of each gradient layer in Example 2

[0070]

[0071]

[0072] First, heat all the raw material powders at 850 °C for 3 h to remove the adsorbed water. Weigh accurately the amounts of each oxide, and uniformly mix Al2O3 and ZrO2 according to the ratios shown in Table 2. Meanwhile, add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 0.8:100. The mass ratio of magnesium oxide to lanthanum oxide is 2:3.5 to obtain mixed powders with different gradient compositions.

[0073] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball-milling jar with ZrO2 (diameter 0.1 - 0.5 mm) as the ball-milling medium according to the mass ratio of 1:1.8, and ball-mill for 5 h at a rotation speed of 2450 r / min. After ball-milling, the mixed slurry is dried by a rotary evaporator to remove absolute ethanol. After drying, put the mixed powder into a vacuum drying oven and dry for 24 h. The dried mixed powder is ground by an agate mortar and then sieved through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm.

[0074] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method in Table 2. Control the total thickness of the gradient layer at 3.5 mm, and evenly spread the composite powder of each layer in the graphite mold until all five layers of powder are spread. Place the graphite pressure head on the mixed powder; put the graphite mold filled with the composite powder into a hot-pressing furnace for sintering. The sintering pressure is 80 MPa, the sintering temperature is 1450 °C, the heating rate is 5 °C / min, and keep the temperature for 2 h to obtain Al2O3 / ZrO2 gradient ceramics.

[0075] Example 3

[0076] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution method as an example, the total number of layers d of the gradient layer is set to 6 layers, the gradient composition distribution method is set to p = 0.3, the total thickness of the gradient layer is 3 mm, then the single-layer thickness is 0.5 mm. x takes values of 1, 2, 3, 4, 5, and 6 respectively. Calculate the volume fraction of Al2O3 in each gradient layer according to Formula 1, and at the same time convert the volume fraction into a mass fraction to obtain the ratio of each gradient layer in Table 3. Prepare 6 kinds of Al2O3 / ZrO2 composite ceramic powders according to the ratio requirements.

[0077] Table 3 Raw material ratios of each gradient layer in Example 3

[0078]

[0079]

[0080] First, heat all the raw material powders at 850 °C for 3 h to remove the adsorbed water. Weigh accurately the amounts of each oxide, and uniformly mix Al2O3 and ZrO2 according to the ratios shown in Table 3. At the same time, add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 0.6:100, and the mass ratio of magnesium oxide to lanthanum oxide is 1.8:3.8 to obtain mixed powders with different gradient compositions;

[0081] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball milling tank with ZrO2 (diameter 0.1 - 0.5 mm) as the ball milling medium according to the mass ratio of 1:1.8, and ball mill for 5 h at a rotation speed of 2600 r / min. After ball milling, the mixed slurry is dried by a rotary evaporator to remove absolute ethanol. After drying, put the mixed powder into a vacuum drying oven and dry for 24 h. The dried mixed powder is ground by an agate mortar and then passed through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm;

[0082] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method shown in Table 3. Control the total thickness of the gradient layer at 3 mm, and evenly spread the composite powder of each layer in the graphite mold until all six layers of powder are spread. Place the graphite pressing head on the mixed powder; put the graphite mold filled with the composite powder into a hot press furnace for sintering. The sintering pressure is 100 MPa, the sintering temperature is 1500 °C, the heating rate is 8 °C / min, and keep the temperature for 1.5 h to obtain a dense Al2O3 / ZrO2 gradient ceramic.

[0083] Example 4

[0084] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution method as an example, the total number of layers d of the gradient layer is set to 4 layers, the gradient composition distribution method is set to p = 0.4, the total thickness of the gradient layer is 3.6 mm, and the single-layer thickness is 0.9 mm. x takes values of 1, 2, 3, and 4 respectively. Calculate the volume fraction of Al2O3 in each gradient layer according to Formula 1, and at the same time convert the volume fraction into a mass fraction to obtain the ratios of each gradient layer in Table 4. Prepare 4 kinds of Al2O3 / ZrO2 composite ceramic powders according to the ratios.

[0085] Table 4 Raw material ratios of each gradient layer in Example 4

[0086]

[0087]

[0088] First, heat all the raw material powders at 850 °C for 3 h to remove the adsorbed water. Weigh accurately the amounts of each oxide, and uniformly mix Al2O3 and ZrO2 according to the ratios shown in Table 4. At the same time, add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 0.8:100. The mass ratio of magnesium oxide to lanthanum oxide is 1.7:3.5 to obtain mixed powders with different gradient compositions;

[0089] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball-milling tank with ZrO2 (diameter 0.1 - 0.5 mm) as the ball-milling medium according to the mass ratio of 1:1.8, and ball-mill for 4.8 h at a rotation speed of 2560 r / min. After ball-milling, the mixed slurry is dried by a rotary evaporator to remove absolute ethanol. After drying, put the mixed powder into a vacuum drying oven and dry for 24 h. The dried mixed powder is ground by an agate mortar and then passed through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm;

[0090] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method in Table 4. Control the total thickness of the gradient layer at 3.6 mm. Uniformly spread the composite powder of each layer in the graphite mold until all four layers of powder are spread. Place the graphite pressure head on the mixed powder; put the graphite mold filled with the composite powder into a hot-pressing furnace for sintering. The sintering pressure is 85 MPa, the sintering temperature is 1500 °C, the heating rate is 7 °C / min, and keep the temperature for 2.5 h to obtain Al2O3 / ZrO2 gradient ceramics.

[0091] Example 5

[0092] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution method as an example, the total number of layers d of the gradient layer is set to 6 layers, the gradient composition distribution method is set to p = 0.5, the total thickness of the gradient layer is 3.8 mm, then the single-layer thickness is 0.63 mm. x takes values of 1, 2, 3, 4, 5, and 6 respectively. Calculate the volume fraction of Al2O3 in each gradient layer according to Formula 1, and at the same time convert the volume fraction into a mass fraction to obtain the ratio of each gradient layer in Table 5. Prepare 6 kinds of Al2O3 / ZrO2 multiphase ceramic powders according to the ratio requirements.

[0093] Table 5 Raw material ratios of each gradient layer in Example 5

[0094]

[0095]

[0096] First, heat all the raw material powders at 850 °C for 3 h to remove the adsorbed water. Weigh accurately the amounts of each oxide. Mix Al2O3 and ZrO2 uniformly according to the ratios shown in Table 5 respectively. At the same time, add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 1.11:100. The mass ratio of magnesium oxide to lanthanum oxide is 1.4:3.2 to obtain mixed powders with different gradient compositions;

[0097] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball-milling tank with ZrO2 (diameter 0.1 - 0.5 mm) as the ball-milling medium according to the mass ratio of 1:1.8 and ball-mill for 5 h at a rotation speed of 2580 r / min. After ball-milling, the mixed slurry is dried by a rotary evaporator to remove the absolute ethanol. After drying, put the mixed powder into a vacuum drying oven and dry for 24 h. The dried mixed powder is ground by an agate mortar and then passed through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm;

[0098] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method in Table 5. Control the total thickness of the gradient layer at 3.8 mm. The composite powder of each layer is evenly paved in the graphite mold until all six layers of powders are paved. Place the graphite pressing head on the mixed powder. Put the graphite mold filled with the composite powder into a hot-pressing furnace for sintering. The sintering pressure is 90 MPa, the sintering temperature is 1450 °C, the heating rate is 7 °C / min, and keep the temperature for 1.8 h to obtain a dense Al2O3 / ZrO2 gradient ceramic.

[0099] Example 6

[0100] Taking an Al2O3 / ZrO2 gradient ceramic with a non-linear composition distribution method as an example, the total number of layers d of the gradient layer is set to 6 layers, the gradient composition distribution method is set to p = 0.6, the total thickness of the gradient layer is 3.75 mm, then the single-layer thickness is 0.625 mm. x takes values of 1, 2, 3, 4, 5, and 6 respectively. Calculate the volume fraction of Al2O3 in each gradient layer according to Formula 1. At the same time, convert the volume fraction into a mass fraction to obtain the ratio of each gradient layer in Table 6. Prepare 6 kinds of Al2O3 / ZrO2 multiphase ceramic powders according to the ratio requirements.

[0101] Table 6 Raw material ratios of each gradient layer in Example 6

[0102]

[0103]

[0104] First, heat all the raw material powders at 850 °C for 3 h to remove adsorbed water. Accurately weigh the amounts of each oxide, uniformly mix Al2O3 and ZrO2 according to the ratios shown in Table 6 respectively, and simultaneously add sintering aids magnesium oxide and lanthanum oxide according to the mass ratio of the total mass of Al2O3 and ZrO2 to the sintering aid of 1.3:100. The mass ratio of magnesium oxide to lanthanum oxide is 1.4:3.5 to obtain mixed powders with different gradient compositions;

[0105] Pour the mixed powders with different gradient compositions and absolute ethanol into a polytetrafluoroethylene ball-milling jar with ZrO2 (diameter 0.1 - 0.5 mm) as the ball-milling medium according to the mass ratio of 1:1.8, and ball-mill for 5.5 h at a rotational speed of 2500 r / min. After ball-milling, the mixed slurry is dried to remove absolute ethanol by a rotary evaporator. After drying, the mixed powder is placed in a vacuum drying oven and dried for 24 h. The dried mixed powder is ground by an agate mortar and then passed through a 200-mesh sieve to obtain alumina-based composite powders with different gradient compositions and a diameter < 100 nm;

[0106] Place the obtained alumina-based composite powders with different gradient compositions into a graphite mold with a diameter of 50 mm according to the distribution method shown in Table 6. Control the total thickness of the gradient layer at 3.75 mm. The composite powder of each layer is evenly paved in the graphite mold until all six layers of powder are paved. Place the graphite pressing head on the mixed powder. Put the graphite mold filled with the composite powder into a hot-pressing furnace for sintering. The sintering pressure is 75 MPa, the sintering temperature is 1500 °C, the heating rate is 7.5 °C / min, and keep the temperature for 1.5 h to obtain a dense Al2O3 / ZrO2 gradient ceramic.

[0107] Characterization and performance testing

[0108] 1) Perform field emission scanning electron microscope testing on the composite powder prepared in Example 1. The test results are as Figure 1 shown. It can be seen from Figure 1 that the particle size of the composite powder prepared in Example 1 is uniform and less than 100 nm.

[0109] 2) Figure 2 is the surface microtopography diagram of the Al2O3 / ZrO2 gradient ceramic prepared in Example 2. It can be found that the Al2O3 / ZrO2 gradient ceramic has a dense microstructure and no pores are found on the surface. Therefore, this process can obtain a dense gradient ceramic.

[0110] 3) Take pictures of the Al2O3 / ZrO2 gradient ceramics prepared in Example 3 and Example 5 by a super-depth-of-field 3D microscope. The cross-sectional views of the obtained gradient ceramics are as Figure 3 and Figure 4 shown. The various gradient surfaces of the gradient ceramic can be clearly observed.

[0111] 4)Figure 5 It is the crack propagation mode of the P = 0.3 gradient ceramic prepared in Example 3 photographed by a scanning electron microscope. It can be found that the gradient ceramic is a mixed fracture mode of transgranular and intergranular fractures, and crack deflection is found at some grains.

[0112] 5) Detect the mechanical properties of the alumina-based gradient ceramics prepared in Examples 1 to 6. Cut the sintered samples by a diamond wire saw. The cutting dimensions required by the national standard GB / T6569-2006 are length (40 mm) × width (4 mm) × height (3 mm), and then carry out grinding, machining and polishing annealing treatments. The mechanical property results are shown in Table 7:

[0113] Table 7 Mechanical properties of the alumina-based gradient ceramics in Examples 1 to 6

[0114]

[0115] According to Table 7, the Vickers hardness of the alumina-based gradient ceramic prepared by the present invention is ≥21 GPa, the strength is >850 MPa, and the fracture toughness is >7 MPa·m 1 / 2 , therefore, the mechanical properties of the alumina-based gradient ceramic prepared by the technical solution of the present invention are excellent.

[0116] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing an alumina-based gradient ceramic, characterized in that, It includes the following steps: According to the non-linear component distribution method, oxides in required proportions are mixed with sintering aids and grinding solvents, and high-energy ball milling treatment is carried out to obtain mixed slurries with different gradient components; the oxides are alumina and zirconia; After drying the mixed slurries, alumina-based composite powders with different gradient components are obtained; According to the non-linear component distribution method, different gradient layers are set, and the alumina-based composite powders with different gradient components are sequentially laid into a mold according to the thickness requirements of each gradient layer, and hot pressing sintering is carried out to obtain alumina-based gradient ceramics; The non-linear component distribution method is calculated by Formula 1; Based on the total volume fraction of 100% of Al2O3 and ZrO2, the different gradient components are formed by the change of the volume fractions of Al2O3 and ZrO2. The components of each gradient change linearly continuously along x in one dimension, and Formula 1 is used to calculate the component distribution of each gradient layer: In Formula 1, f1(x) is the volume fraction of Al2O3 in any single-layer gradient layer, vol%; d is the total number of gradient layers, x is the gradient layer number corresponding to each gradient, x = 1 to d and x is an integer; p is the gradient component distribution index, p > 0 and p ≠ 1.

2. The preparation method according to claim 1, wherein d = 4 to 6, p = 0.1 to 0.

6.

3. The preparation method according to claim 1, wherein The sintering aids include magnesium oxide and lanthanum oxide; the mass ratio of magnesium oxide to lanthanum oxide is (1 to 2):(2 to 4).

4. The preparation method according to claim 1 or 3, characterized in that, The mass ratio of the oxides to the sintering aids is (0.5 to 1.5):

100.

5. The preparation method according to claim 1, characterized in that, The rotation speed of the high-energy ball milling treatment is 2300 to 2700 r / min, the treatment time is 4 to 8 h, and the grinding medium is zirconia balls with a diameter of 0.1 to 0.5 mm.

6. The preparation method according to claim 1, wherein The total thickness of the gradient layer is 3 to 4 mm, and the thickness of each gradient layer is the same; the mold is a graphite mold, and the diameter of the graphite mold is 30 to 50 mm.

7. The preparation method according to claim 1 or 6, characterized in that, The conditions of the hot pressing sintering include: the sintering pressure is 40 to 100 MPa, the sintering temperature is 1400 to 1600 °C, and the heat preservation time is 1.5 to 3 h.

8. The preparation method according to claim 7, characterized in that, The heating rate for heating to the temperature of the hot pressing sintering is 5 to 10 °C / min.

9. The alumina-based gradient ceramic prepared by the preparation method according to any one of claims 1 to 8, characterized in that, Vickers hardness ≥ 21 GPa, strength ≥ 850 MPa, fracture toughness ≥ 7 MPa·m 1 / 2 .

10. Application of the alumina-based gradient ceramic according to claim 9 in the fields of aerospace or bulletproof composite armor.

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