A kind of AlN-B4C based metal ceramic and its preparation method and application

Abstract

The present invention discloses an AlN-B4C-based cermet, its preparation method and application, and belongs to the technical field of composite materials. The material uses AlN and B4C as ceramic phases, and uses TiCoMoNb alloy as the active bonding phase according to the thermodynamic design of the phase diagram. Through long-term ball milling, deep activation and uniform dispersion of the powder are achieved. Combined with the hot pressing sintering process, B4C is prompted to react in situ with the bonding phase to generate high-hardness borides such as NbTiB2 and TiMoB4, and Nb2C carbides, thereby constructing a "chemically inert interface + physical barrier" dual protection system. The prepared cermet has high density, high toughness and excellent resistance to molten aluminum corrosion, and has significant application value in the field of manufacturing key components of high-temperature aluminum melting equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and in particular relates to an AlN-B4C based cermet and a preparation method and application thereof. Background Art

[0002] During high-temperature molten aluminum processing, such as aluminum smelting, die-casting, and hot-dip coating, liquid aluminum exhibits strong chemical corrosion properties, resulting in a high failure rate for components in direct contact with the liquid aluminum. This significantly restricts production efficiency and product quality assurance. Therefore, the development of materials with excellent resistance to molten aluminum corrosion has become the core of technological breakthroughs in this field.

[0003] Aluminum nitride (AlN) ceramics are considered a promising material for resistant to molten aluminum corrosion due to their excellent thermodynamic stability. However, as a typical covalently bonded compound, AlN suffers from inherent brittleness and low sintering activity. In the absence of sintering aids, AlN is difficult to form a dense microstructure through conventional sintering processes. This material property limits its direct engineering application in high-temperature molten aluminum environments.

[0004] AlN-based cermets offer an effective technical solution to these problems. Research has shown that by introducing metals such as Ti, Mo, Co, and Nb into the AlN matrix as a binder phase, the plastic deformation capability of the metal phase can be exploited to improve the toughness of the material, and material densification can be achieved with the aid of efficient sintering techniques such as spark plasma sintering (SPS). The corrosion resistance of such materials against molten aluminum is primarily due to the chemical stability of the AlN matrix and the low solubility of metal binder phases such as Mo and Nb in molten aluminum. However, existing research indicates that under extreme service conditions, liquid aluminum can still penetrate and corrode along the metal-ceramic interface, reflecting the limitations of its protective mechanism.

[0005] Boron carbide (B4C), with its ultra-high hardness and excellent chemical inertness, offers new possibilities for further improving material properties. However, simply combining B4C with AlN makes sintering and densification of the material more difficult. Experimental data shows that in the absence of a metallic binder phase, the relative density of pure AlN-B4C ceramics prepared by hot pressing only reaches 84.6%.

[0006] In summary, innovative technical solutions are urgently needed to achieve the synergistic integration of the excellent chemical stability of B4C and the performance advantages of AlN ceramics, while overcoming the sintering barriers caused by the introduction of B4C, thereby systematically improving the density, toughness and molten aluminum corrosion resistance of AlN-based ceramic materials. Summary of the Invention

[0007] In response to the above-mentioned prior art, the present invention provides an AlN-B4C-based cermet and its preparation method and application, which solve the problems of insufficient toughness and sintering of ceramic materials in the prior art.

[0008] The AlN-B4C-based cermet of the present invention introduces a TiCoMoNb alloy binder phase and forms a low-melting-point liquid phase during the sintering process to fill the pores between the ceramic particles, resulting in a density much higher than that of pure AlN-B4C ceramics. The plastic deformation ability of the metal binder phase effectively absorbs and dissipates crack propagation energy. At the same time, the fine dispersed new phase generated in situ may also improve the toughness of the AlN-B4C-based cermet through mechanisms such as crack deflection and bridging. Moreover, boron carbide (B4C) exhibits unique active reaction characteristics during the hot pressing sintering process, undergoing an in-situ chemical reaction with the TiCoMoNb metal binder phase to generate a series of complex borides (such as NbTiB4 and TiMoB4) and carbides (such as Nb2C) with high hardness.

[0009] To address the inherent brittleness of ceramic materials, the present invention consumes B4C through an in-situ reaction, allowing the system to accommodate a higher proportion of plastic TiCoMoNb metal binder phase. Under the action of external load, the metal phase effectively absorbs and dissipates crack tip energy through plastic deformation; at the same time, the in-situ generated hard particles further inhibit crack propagation through mechanisms such as crack deflection and bridging. The synergistic effect of these multiple toughening mechanisms significantly improves the toughness of the AlN-B4C ceramic matrix. In addition, the introduction of cobalt (Co) in the binder phase gives the material excellent resistance to thermal mechanical fatigue. Under conditions of repeated thermal cycling such as casting and hot-dip plating, it can effectively inhibit fatigue crack initiation and propagation, thereby improving the long-term service reliability of the material.

[0010] The present invention also adopts a long-term step-by-step mechanical alloying and activation process. The first step is long-term ball milling (50-60 hours) to mechanically alloy the TiCoMoNb bonding phase, and the second step is long-term ball milling (45 hours) to achieve microscopic uniform compounding of AlN, B4C and the activated bonding phase and further surface activation; the finally prepared AlN-B4C-based cermet forms a stable AlN layer at the interface between AlN and aluminum liquid in the aluminum liquid. B4C has strong chemical inertness and can form a complex boride phase with the bonding phase, together constructing a dense "chemically inert interface + physical barrier" dual protection system between the ceramic matrix and the molten aluminum.

[0011] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: to provide an AlN-B4C-based cermet, with AlN-B4C as a hard phase and a TiCoMoNb alloy as a binder phase, the mass fraction of the hard phase in the cermet is 85-90%, and the mass fraction of the binder phase in the cermet is 10-15%.

[0012] On the basis of the above technical solution, the present invention can also be improved as follows.

[0013] Furthermore, the mass ratio of AlN and B4C in the hard phase is 1:1.

[0014] Furthermore, the mass ratio of Ti:Co:Mo:Nb in the binder phase is 1.62~2.435:2.00~3.00:3.25~4.88:3.15~4.725.

[0015] The present invention also provides a method for preparing an AlN-B4C-based cermet, comprising the following steps:

[0016] S1: Ti powder, Co powder, Mo powder and Nb powder are mixed and ball-milled and then dried to obtain TiCoMoNb alloy powder;

[0017] S2: TiCoMoNb alloy powder, AlN powder and B4C powder are mixed and ball-milled and then dried to obtain composite powder;

[0018] S3: hot pressing and sintering the composite powder in a vacuum or inert atmosphere, and obtaining AlN-B4C based cermet after cooling.

[0019] Furthermore, the ball milling in S1 is wet ball milling carried out in anhydrous ethanol, with a ball-to-material ratio of 10:1, a rotation speed of 250-300 r / min, and a time of 50-60 h.

[0020] Furthermore, the ball milling in S2 is wet ball milling carried out in anhydrous ethanol, with a ball-to-material ratio of 10:1, a rotation speed of 200-300 r / min, and a time of 45 h.

[0021] Furthermore, the drying in S1 and S2 is performed at 90-100° C. and vacuum drying for 20 h.

[0022] Furthermore, the hot pressing sintering is performed by heating the temperature to 1650-1750°C at a rate of 100°C / min and then keeping the temperature at 45-55 MPa for 10 min.

[0023] The present invention also provides the application of AlN-B4C based cermet in the preparation of molten aluminum corrosion resistant material.

[0024] The beneficial effects of the present invention are: 1. The fracture toughness of the AlN-B4C-based cermet of the present invention reaches 5.46 MPa·m 1 / 2 , purer AlN-B4C ceramics (4.18MPa·m 1 / 2 ) increased by approximately 30.6%;

[0025] 2. The AlN-B4C-based cermet of the present invention has a high density of up to 90.1%, which is beneficial for improving corrosion resistance;

[0026] 3. The corrosion rate of the AlN-B4C-based cermet in 700°C molten aluminum is as low as 1.13×10 -4 mm / h, compared with AlN-B4C ceramics without binder phase (corrosion rate 2.71×10 -4 mm / h) decreased by about 58.3%;

[0027] 4. The long-term step-by-step mechanical alloying and activation process (more than 90 hours of ball milling) adopted in the preparation method of the present invention achieves microscopic uniform compounding of AlN, B4C and the activated binder phase and further surface activation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the relationship between the density / compactness of ceramic materials and the binder phase content;

[0029] Figure 2 This is the SEM image of AlN-B4C-15;

[0030] Figure 3 XRD patterns of the AlN-B4C-based cermets prepared in Examples 1 and 2 and the AlN-B4C-based ceramics prepared in the comparative example;

[0031] Figure 4 Graph showing the relationship between corrosion depth and corrosion time for the AlN-B4C-based cermets prepared in Examples 1 and 2 and the AlN-B4C-based ceramics prepared in the comparative example;

[0032] Figure 5 The figure is a relationship curve of the average corrosion rates of the AlN-B4C based cermets prepared in Examples 1 and 2 and the AlN-B4C based ceramics prepared in the comparative example. DETAILED DESCRIPTION

[0033] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

[0034] Example 1

[0035] An AlN-B4C-based cermet, wherein the mass fraction of a hard phase is 85% (the mass ratio of AlN to B4C is 1:1) and the mass fraction of a binder phase is 15% (the mass ratio of Ti:Co:Mo:Nb is 2.435:3.00:4.88:4.725).

[0036] The AlN-B4C-based cermet of this embodiment is prepared by the following steps:

[0037] S1: Ti powder, Co powder, Mo powder and Nb powder were mixed in proportion, and ball milled in a planetary ball mill at a ball-to-material ratio of 10:1, a rotation speed of 300 r / min, and anhydrous ethanol as a medium for 60 h. After ball milling, the mixture was vacuum dried at 100°C for 20 h to obtain TiCoMoNb alloy powder;

[0038] S2: TiCoMoNb alloy powder, AlN powder and B4C powder were mixed in proportion and ball-milled in a planetary ball mill at a ball-to-material ratio of 10:1, a rotation speed of 300 r / min and anhydrous ethanol as a medium for 45 h. After ball milling, the mixture was vacuum-dried at 100°C for 20 h to obtain a composite powder.

[0039] S3: The composite powder is loaded into a graphite mold, and the temperature is raised to 1700°C at 100°C / min in a vacuum environment. Then, a pressure of 50 MPa is applied, and the temperature is kept at this temperature for 10 minutes. After cooling, the AlN-B4C-based cermet AlN-B4C-15 is obtained.

[0040] Example 2

[0041] An AlN-B4C-based cermet, wherein the mass fraction of a hard phase is 90% (the mass ratio of AlN to B4C is 1:1) and the mass fraction of a binder phase is 10% (the mass ratio of Ti:Co:Mo:Nb is 1.62:2.00:3.25:3.15).

[0042] The AlN-B4C-based cermet of this embodiment is prepared by the following steps:

[0043] S1: Ti powder, Co powder, Mo powder and Nb powder were mixed in proportion, and ball milled in a planetary ball mill at a ball-to-material ratio of 10:1, a rotation speed of 250 r / min, and anhydrous ethanol as a medium for 50 h. After ball milling, the mixture was vacuum dried at 90°C for 20 h to obtain TiCoMoNb alloy powder;

[0044] S2: TiCoMoNb alloy powder, AlN powder and B4C powder were mixed in proportion and ball-milled in a planetary ball mill at a ball-to-material ratio of 10:1, a rotation speed of 200 r / min, and anhydrous ethanol as a medium for 45 h. After ball milling, the mixture was vacuum-dried at 100°C for 20 h to obtain a composite powder.

[0045] S3: The composite powder was loaded into a graphite mold, and the temperature was raised to 1700°C at 100°C / min in a nitrogen environment. Then, a pressure of 50 MPa was applied and the temperature was kept at this temperature for 10 minutes. After cooling, the AlN-B4C-based cermet AlN-B4C-10 was obtained.

[0046] Comparative Example

[0047] An AlN-B4C based ceramic, wherein the mass ratio of AlN to B4C is 1:1.

[0048] The AlN-B4C-based ceramic of this comparative example was prepared by the following steps:

[0049] S1: AlN powder and BC powder were mixed in a certain proportion, and ball milled in a planetary ball mill at a ball-to-powder ratio of 10:1, a rotation speed of 200 r / min, and anhydrous ethanol as a medium for 45 h. After ball milling, the mixture was vacuum dried at 100°C for 20 h to obtain a composite powder;

[0050] S2: The composite powder is loaded into a graphite mold, and the temperature is raised to 1700°C at 100°C / min in a vacuum environment. Then, a pressure of 50 MPa is applied, and the temperature is kept at this temperature for 10 minutes. After cooling, the AlN-B4C-based ceramic AlN-B4C-0 is obtained.

[0051] Experimental Example 1

[0052] Density / compactness measurement: The density / compactness measurement was performed on the AlN-B4C based cermets prepared in Examples 1 and 2 and the AlN-B4C based ceramics prepared in the comparative example. The results are shown in FIG. Figure 1 As shown in the figure, the density / compactness of the comparative AlN-B4C-based ceramics are lower than those of the AlN-B4C-based metal ceramics of Examples 1 and 2, while the density / compactness of the AlN-B4C-based metal ceramics of Examples 1 and 2 are not much different, indicating that the introduction of the TiCoMoNb alloy binding phase and the formation of a low-melting-point liquid phase during the sintering process fill the pores between the ceramic particles. At the same time, the long-term mechanical activation treatment improves the sintering activity of the powder, so that the density of the composite material is significantly improved.

[0053] Experimental Example 2

[0054] Microscopic analysis: The AlN-B4C based cermet obtained in Example 1 was analyzed using a scanning electron microscope. Figure 2 As shown in FIG5 , the TiCoMoNb alloy binder phase is evenly distributed among the ceramic particles, indicating that the long-term mechanical activation treatment of the TiCoMoNb alloy binder phase makes it highly evenly distributed during the sintering process, forming a dense composite structure.

[0055] Experimental Example 3

[0056] XRD analysis: X-ray diffraction analysis was performed on the AlN-B4C based cermets prepared in Examples 1 and 2 and the AlN-B4C based ceramics prepared in the comparative example. The results are shown in FIG. Figure 3 In addition to the main crystalline phases of AlN and B4C, the AlN-B4C based cermets prepared in Examples 1 and 2 also produced NbTiB2, Nb2C, TiMoB 44 , MoB2, confirming the in-situ reaction of B4C and binder phase elements during the sintering process.

[0057] Experimental Example 4

[0058] Molten aluminum corrosion test: The AlN-B4C-based cermets prepared in Examples 1 and 2 and the AlN-B4C-based ceramics prepared in the comparative example were processed by wire electrospark cutting into 6×6×8 mm cuboids. Five samples were cut from each of them. The surfaces were successively ground and polished to a mirror finish with 40180 sandpaper. The thickness of the samples before corrosion was measured using a micrometer. The samples were then placed in a graphite crucible filled with 700°C molten aluminum for corrosion experiments. The samples were heated and kept warm in a pit-type resistance furnace. The samples were taken out after corrosion for 2 days, 4 days, 6 days, 8 days, and 10 days, respectively. The test results are shown in the figure below. Figures 4 and 5 As shown in the figure, AlN-B4C-15 has the best resistance to molten aluminum corrosion, followed by AlN-B4C-10, and AlN-B4C-0 is the weakest, indicating that B4C reacts in situ with elements such as Ti, Mo, and Nb in the binder phase to generate specific, diffusely distributed complex boride phases such as NbTiB2 and TiMoB4. These in situ generated refractory, high hardness, and chemically stable complex boride phases, combined with the TiN interface layer generated by the reaction of Ti and AlN, and the extremely low solubility of Mo and Nb elements themselves in molten aluminum (<0.01at.%), jointly construct a dense "chemically inert interface + physical barrier" dual protection system between the ceramic matrix and molten aluminum, greatly improving the corrosion resistance of AlN-B4C-based cermets.

[0059] Experimental Example 5

[0060] Performance test: Vickers hardness and fracture toughness tests were performed on the AlN-B4C-based cermets prepared in Examples 1 and 2 and the AlN-B4C-based ceramics prepared in the comparative example. The performance parameters are shown in Table 1 based on the results of the above experimental examples.

[0061] Table 1 Performance parameters

[0062]

[0063] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. An AlN-B4C-based cermet, characterized by: The AlN-B4C-based cermet has AlN-B4C as a hard phase and a TiCoMoNb alloy as a binder phase. The mass fraction of the hard phase in the cermet is 85-90%, and the mass fraction of the binder phase in the cermet is 10-15%. The mass ratio of AlN and B4C in the hard phase is 1:

1. The mass ratio of Ti:Co:Mo:Nb in the binder phase is 1.62-2.435:2.00-3.00:3.25-4.88:3.15-4.

725.

2. The method for preparing the AlN-B4C based cermet according to claim 1, characterized in that: The following steps are involved: S1: Ti powder, Co powder, Mo powder and Nb powder are mixed and ball-milled and then dried to obtain TiCoMoNb alloy powder; S2: TiCoMoNb alloy powder, AlN powder and B4C powder are mixed and ball-milled and then dried to obtain composite powder; S3: hot pressing and sintering the composite powder in a vacuum or inert atmosphere, and obtaining AlN-B4C based cermet after cooling.

3. The method for preparing the AlN-B4C-based cermet according to claim 2, wherein: The ball milling in S1 is a wet ball milling carried out in anhydrous ethanol, with a ball-to-material ratio of 10:1, a rotation speed of 250-300 r / min, and a time of 50-60 h.

4. The method for preparing the AlN-B4C-based cermet according to claim 2, wherein: The ball milling in S2 was wet ball milling carried out in anhydrous ethanol, with a ball-to-material ratio of 10:1, a rotation speed of 200-300 r / min, and a time of 45 h.

5. The method for preparing the AlN-B4C based cermet according to claim 2, wherein: The drying in S1 and S2 was carried out at 90-100°C and vacuum drying for 20 h.

6. The method for preparing the AlN-B4C based cermet according to claim 2, wherein: The hot pressing sintering is to raise the temperature to 1650-1750° C. at a rate of 100° C. / min, and then keep the temperature at 45-55 MPa for 10 minutes.

7. Use of the AlN-B4C based cermet according to claim 1 in the preparation of molten aluminum corrosion resistant materials.

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