Alumina-based ceramic shell face layer slurry added with nano metal organic framework and preparation method thereof

Abstract

The application relates to the field of nickel-based single crystal superalloy blade investment casting, in particular to an alumina-based ceramic shell surface layer slurry added with a nano metal organic framework and a preparation method thereof. The slurry comprises: 75-82 wt% of white corundum powder, 18-25 wt% of silica sol binder; in the silica sol binder, 0-0.3 wt% of a defoaming agent, 0-0.3 wt% of a wetting agent, 0.05-0.2 wt% of a nano metal organic framework, and the rest is silica sol. The silica sol binder is added into a batching bucket, white corundum powder is added and continuously stirred until uniform, and deionized water is continuously added to adjust the viscosity, so as to form the alumina-based ceramic shell surface layer slurry. The application can enhance the air permeability of the ceramic shell, improve the smoothness of the ceramic shell surface layer and the strength of the ceramic shell, and has the characteristics of simple operation, strong adjustability and stable slurry.

Description

TECHNICAL FIELD

[0001] The application relates to the field of nickel-based single crystal superalloy blade investment casting, in particular to an alumina-based ceramic shell surface layer slurry added with a nano metal organic framework and a preparation method thereof. BACKGROUND

[0002] Advanced development of the aircraft engine industry puts strict requirements on the surface quality of cast products. The air permeability, surface smoothness and bending strength of the ceramic shell in the investment casting process are key factors directly determining the qualification rate of cast products. In terms of the surface quality of the castings, the shell usually needs good air permeability, which is beneficial to the escape of gas during the casting process; good surface smoothness, which avoids defects such as gas holes and sand sticking on the alloy surface during the casting process; sufficient wet strength, which avoids cracking during preparation, transportation and use; and sufficient high-temperature strength, which can withstand the thermal stress generated during the solidification of the metal liquid during the casting process, so as to prevent the shell from deforming, cracking and leaking.

[0003] At present, advanced ceramic enterprises generally use reinforcing agents to improve the shell quality and increase the yield. The reinforcing agent is mainly added in two ways, namely, directly dispersed in the slurry and dispersed in the binder and then mixed with the slurry. Generally, the reinforcing agent directly dispersed in the slurry is easy to agglomerate or float, and the slurry is relatively turbid, and the dispersion form of the reinforcing agent in the slurry is not easy to observe; the reinforcing agent added to the binder avoids direct entanglement and clumping with the slurry, and the dispersion effect can be observed directly and timely measures can be taken to improve the dispersion effect.

[0004] In order to improve the air permeability of the shell, the common improvement method of the reinforcing agent in the industry is that the reinforcing agent is decomposed into gas after high-temperature calcination, leaving pores. Common such reinforcing agents are usually organic high-molecular composite and carbon fiber which are not resistant to high temperature and easy to decompose. In order to improve the surface smoothness of the shell, the common improvement method of the reinforcing agent in the industry is mainly to promote grain refinement, improve structural uniformity and reduce defect size. Common such reinforcing agents are mainly nano carbon. In order to improve the bending strength of the shell, the common improvement method of the reinforcing agent in the industry is mainly high-molecular polymer long molecular chain network wrapping particles, hydrogen bond formation between particles and high-molecular polymer adhesion. Common such reinforcing agents are usually organic high-molecular polymers. However, the organic high-molecular polymers and carbon fiber still need to be improved in terms of hydrophilicity, dispersibility and environmental protection. The accumulation of nano carbon at the ceramic grain boundary may promote the interface reaction between the ceramic and the alloy during the shell casting process, thereby increasing defects. Therefore, it is of great significance to find a reinforcing agent which has excellent hydrophilicity, good dispersibility, green environmental protection and excellent performance effect of reinforcing the shell, for improving the surface quality of the investment casting ceramic shell. SUMMARY

[0005] In view of the above problems, the present application aims to provide an alumina-based ceramic shell surface layer slurry added with a nano metal organic framework and a preparation method thereof, so as to improve the air permeability, surface finish and bending strength of the current ceramic shell and improve the stability of the ceramic shell for investment casting.

[0006] The present application is realized by the following technical solutions:

[0007] An alumina-based ceramic shell surface layer slurry added with a nano metal organic framework, according to mass percentage, the slurry comprises: 75-82wt% of 320-mesh white corundum powder, 18-25wt% of silica sol binder; the composition and content of the silica sol binder are as follows: 0-0.3wt% of defoaming agent, 0-0.3wt% of wetting agent, 0.05-0.2wt% of nano metal organic framework, and the rest is silica sol.

[0008] The alumina-based ceramic shell surface layer slurry added with a nano metal organic framework, the white corundum powder is used as the refractory material of the ceramic shell surface layer, and the fused corundum powder is used, and the content of alpha-alumina in the fused corundum powder is above 95.0wt%.

[0009] The alumina-based ceramic shell surface layer slurry added with a nano metal organic framework, the silica sol is a water-based silica sol, and the parameters are as follows: the content of silicon oxide is 29-32wt%, the content of sodium oxide is not more than 0.5wt%, the density is 1.15-1.21g / cm 3 , the room temperature viscosity is not higher than 8Pa·s, the pH is 9.5-10.5, and the particle size of the silica sol is 8-15nm.

[0010] The alumina-based ceramic shell surface layer slurry added with a nano metal organic framework, the type of the nano metal organic framework is an aluminum-based nano metal organic framework Al-Fum, and the morphology is a two-dimensional irregular sheet layer, and the parameters are as follows: the ligand is fumaric acid, the specific surface area is 750-1100m 2 / g, the vertical pore is 0.51*0.54-0.74*0.78nm 2 , and the pore volume is 0.58-0.85cm 3 / g.

[0011] The preparation method of the alumina-based ceramic shell surface layer slurry added with a nano metal organic framework comprises the following steps:

[0012] (1) taking the nano metal organic framework as a shell reinforcing phase, mixing, stirring and ultrasonic dispersing the nano metal organic framework and the silica sol to form a transparent solution;

[0013] (2) adding defoaming agent and wetting agent into the transparent solution, uniformly stirring according to the rotation speed of 280-320rpm to obtain a silica sol binder;

[0014] (3) Add the silica sol binder into the batching barrel, add white corundum powder, and continue stirring at a rotation speed of 180-220 rpm for 48 h to uniformly disperse the white corundum powder in the silica sol binder;

[0015] (4) Add deionized water to adjust the viscosity of the slurry to 28-35 Pa·s to form an alumina-based ceramic shell surface layer slurry for shell coating of the shell surface layer.

[0016] The design idea of the present application is:

[0017] From the practical aspects of simple operation, convenient storage and transportation, green environmental protection, and for the purpose of improving the permeability of the shell, improving the surface finish of the shell, and improving the strength of the shell, a suitable reinforcing agent is sought. The organic polymer fiber in the traditional industry is slightly weak in hydrophilicity, dispersibility and environmental protection, and the nano carbon can easily intensify the interface reaction between the alloy and the ceramic, thereby causing casting defects and sand sticking. The present application uses the method of adding nano metal organic framework (MOF for short) to prepare a ceramic shell surface layer slurry. The ligand fumaric acid in the aluminum-based nano metal organic framework Al-Fum (also known as MIL-53(Al)-FA) contains a hydrophilic carboxyl group, which ensures that Al-Fum is completely dissolved and dispersed in the silica sol binder, thereby avoiding the agglomeration of the shell slurry. The simple molecular structure of fumaric acid ensures the complete removal of the reinforcing agent during the sintering process of the shell, so as to prepare a ceramic shell with good permeability, excellent surface finish and high strength.

[0018] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0019] 1) The aluminum-based nano metal organic framework Al-Fum can be stably dispersed in the silica sol. The ligand of the aluminum-based nano metal organic framework Al-Fum is fumaric acid (with two carboxyl groups), and the carboxyl group ensures its hydrophilicity and uniform dispersibility in the water-based silica sol. Al-Fum is very stable in air and aqueous solution and only slowly decomposes in strong alkaline conditions. Therefore, by adding Al-Fum to the silica sol with water as the solvent, stable dispersion of Al-Fum can be achieved.

[0020] 2) Enhance the permeability of the ceramic shell. During the sintering process of the shell, Al-Fum decomposes at the thermal decomposition temperature, and the main generated substances are CO2, H2O and Al2O3. The carbon dioxide and water vapor will escape, and the alumina will remain inside the ceramic. The escaped gas will leave fine pores inside the ceramic, which will be connected to form a permeable channel, thereby enhancing the permeability of the ceramic shell.

[0021] 3) Improve the surface smoothness of the ceramic shell. On the one hand, Al-Fum itself can be used as a conversion precursor of nano-carbon, which can derive part of the nano-carbon during the sintering process of the shell, and accumulate on the edge of the ceramic particles inside the shell to achieve the purpose of grain refinement, making the shell surface layer dense and smooth; with further temperature rise, Al-Fum is completely oxidized in air to form carbon dioxide and water vapor, which escapes from the ceramic interior and forms pores. Due to the expansion of the wax pattern during temperature rise, stress is generated on the surface of the shell, which tends to produce cracks. However, when the growth direction of the pores and cracks of the ceramic is not parallel, the growth of the cracks can be inhibited.

[0022] 4) Improve the bending strength of the ceramic shell. On the one hand, the fumaric acid ligand of Al-Fum has the ability to provide two hydrogen bonds, which can cause hydrogen bond reactions between the particles of the shell powder and generate hydrogen bond forces, thereby improving the strength of the ceramic green body and the finished product; on the other hand, the inhibition of crack growth by Al-Fum is conducive to further improving the bending strength. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figures 1-5 The macroscopic morphology of the ceramic shell with different contents of aluminum-based nano-metal organic framework reinforcing phase. Among them, Figure 1 is an alumina ceramic shell without adding aluminum-based nano-metal organic framework in the silica sol binder, Figure 2 is an alumina ceramic shell with 0.05wt% aluminum-based nano-metal organic framework added in the silica sol binder, Figure 3 is an alumina ceramic shell with 0.1wt% aluminum-based nano-metal organic framework added in the silica sol binder, Figure 4 is an alumina ceramic shell with 0.15wt% aluminum-based nano-metal organic framework added in the silica sol binder, Figure 5 is an alumina ceramic shell with 0.2wt% aluminum-based nano-metal organic framework added in the silica sol binder.

[0024] Figure 6 The test results of the wet green body bending strength at room temperature and the sintered product high temperature bending strength of the ceramic shell with different contents of aluminum-based nano-metal organic framework reinforcing phase. DETAILED DESCRIPTION

[0025] In the specific implementation process, the application provides an alumina-based ceramic shell surface layer slurry added with a nano metal organic framework and a preparation method thereof. The slurry comprises: 75-82 wt% of 320-mesh white corundum powder, and 18-25 wt% of a silica sol binder. The composition and content of the silica sol binder are as follows: 0-0.3 wt% of a defoaming agent, 0-0.3 wt% of a wetting agent, 0.05-0.2 wt% of a nano metal organic framework, and the rest is silica sol. Preferably, the composition and content of the silica sol binder are as follows: 0.1-0.3 wt% of a defoaming agent, 0.1-0.3 wt% of a wetting agent, 0.05-0.15 wt% of a nano metal organic framework, and the rest is silica sol. The method comprises the following steps: adding the silica sol binder into a batching bucket, then adding the white corundum powder into the silica sol binder, continuously stirring until uniform, continuously adding a proper amount of deionized water to adjust the viscosity to 28-35 Pa·s, and forming the alumina-based ceramic shell surface layer slurry for shell coating of a shell surface.

[0026] The application will be further described in detail below in combination with the drawings and specific examples.

[0027] Example 1

[0028] In this embodiment, a preparation method of a ceramic shell surface layer slurry added with a nano metal organic framework comprises the following steps:

[0029] (1) An aluminum-based nano metal organic framework (Al-Fum) powder is used as a shell reinforcing phase, mixed with a silica sol at a certain mass ratio, stirred, and ultrasonically dispersed to form a transparent solution.

[0030] The silica sol is an aqueous silica sol, and the parameters are as follows: a silicon oxide content of 30-32 wt%, a sodium oxide content of not more than 0.5 wt%, a density of 1.18-1.20 g / cm 3 , a room temperature viscosity of not higher than 8 Pa·s, and a silica sol particle size of 8-15 nm.

[0031] (2) A defoaming agent (such as YQ-C01 or FA900 defoaming agent) and a wetting agent (such as WET-10s or YQ-D01 wetting agent) are added to the transparent solution, and stirring is performed at a rotation speed of 300 rpm to obtain a silica sol binder.

[0032] In this embodiment, the composition and content of the silica sol binder are as follows: 0.3 wt% of a defoaming agent, 0.3 wt% of a wetting agent, 0.05 wt%, 0.1 wt%, 0.15 wt%, or 0.2 wt% of an aluminum-based nano metal organic framework (Al-Fum), and the rest is silica sol.

[0033] (3) Add the silica sol binder into the batching barrel, slowly add the 320 mesh white corundum powder according to the mass ratio of 1:3.8 between the silica sol binder and the white corundum, continue to stir for 48 h at the speed of 200 rpm, so that the white corundum powder is uniformly dispersed in the silica sol binder. Add deionized water to the uniformly stirred slurry to adjust the viscosity of the slurry to 28-35 Pa·s, and form an alumina-based ceramic shell surface layer slurry for shell coating of the shell surface layer.

[0034] Example 2

[0035] An alumina-based ceramic shell surface layer slurry added with an aluminum-based nanometal organic framework was prepared according to the preparation method of Example 1, and a ceramic shell was prepared using the slurry; at the same time, an alumina-based ceramic shell without adding an aluminum-based nanometal organic framework was prepared as a control sample, and the other conditions of the surface layer slurry were the same as those of Example 1.

[0036] In this example, the preparation process of the ceramic shell is as follows:

[0037] Step 1, respectively prepare the surface layer slurry, the transition layer slurry, and the back layer slurry;

[0038] Step 2, immerse the combined wax mold module into the surface layer slurry, uniformly coat the slurry on the surface of the wax mold, then perform sanding and drying treatment on the wax mold, and then perform coating, sanding, and drying treatment on the transition layer and the back layer slurry, and repeat the coating, sanding, and drying treatment on the back layer slurry several times before sealing the slurry;

[0039] Step 3, perform steam dewaxing on the shell module prepared in Step 2 to obtain a shell wet blank;

[0040] Step 4, perform baking on the shell wet blank after the dewaxing treatment in Step 3 to obtain a shell.

[0041] As shown in Figures 1-5 , the ceramic shells were prepared using the above two slurries. When the aluminum-based nanometal organic framework was not added, cracks were easily generated on the surface of the ceramic shell, while the ceramic shell added with 0.05wt%-0.2wt% aluminum-based nanometal organic framework had a smooth surface without cracks.

[0042] As shown in Figure 6 , the ceramic shell samples prepared using the above two slurries were used for the bending strength test, and the test results showed that when the aluminum-based nanometal organic framework was not added, the wet blank strength and the sintered shell strength of the ceramic shell were 6.287 MPa and 10.125 MPa, respectively, while the wet blank strength and the sintered strength of the ceramic shell added with 0.1wt% aluminum-based nanometal organic framework were increased to 11.921 MPa and 18.931 MPa, respectively.

[0043] The embodiment results show that the present application can improve the permeability of the ceramic shell, improve the surface smoothness of the ceramic shell, and improve the strength of the ceramic shell by adding the aluminum-based nano metal organic framework as a reinforcing phase in the ceramic shell surface layer slurry. In particular, the ceramic shell with 0.05wt%-0.2wt% aluminum-based nano metal organic framework added in the silica sol binder has a wet strength of 6.44MPa-11.921MPa, a sintering strength of 13.921MPa-18.931MPa, and a more significant improvement in sintering strength, thereby improving the yield of the investment casting. At the same time, the present application meets the requirements of simple operation, convenient storage and transportation, and green environmental protection, and has the characteristics of stable slurry, simple operation, and strong applicability.

[0044] Those skilled in the art will readily understand that the above description is only an embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An alumina-based ceramic shell facecoat slurry with added nanometal organic framework, characterized in that, The slurry comprises, by mass percentage: 75~82 wt% of 320 mesh white corundum powder, 18~25 wt% of silica sol binder; the composition and content of the silica sol binder are as follows: 0~0.3 wt% of defoaming agent, 0~0.3 wt% of wetting agent, 0.05~0.2 wt% of nano metal organic framework, and the rest is silica sol; The nano metal organic framework species is aluminum-based nano metal organic framework Al-Fum, and the morphology is two-dimensional irregular sheet layer, and the parameters are as follows: the ligand is fumaric acid, the specific surface area is 750-1100 m 2 / g, the vertical pore is 0.51*0.54-0.74*0.78 nm 2 , and the pore volume is 0.58-0.85 cm 3 / g.

2. The nanometal-organic framework added alumina-based ceramic facecoat slip slurry of claim 1, wherein, The white corundum powder is used as the ceramic shell surface layer refractory material, and the fused corundum powder is used, and the content of alpha-alumina in the fused corundum powder is above 95.0 wt%.

3. The nanometal-organic framework added alumina-based ceramic facecoat slip of claim 1, wherein, The silica sol is an aqueous silica sol with the following parameters: silica oxide content of 29-32 wt%, sodium oxide content of not more than 0.5 wt%, density of 1.15-1.21 g / cm 3 , room temperature viscosity of not higher than 8 Pa-s, pH of 9.5-10.5, and silica sol particle size of 8-15 nm.

4. A method of preparing a nano metal organic framework added alumina based ceramic facecoat slurry as claimed in any one of claims 1 to 3, characterized by, The method comprises the following steps: (1) taking the nano metal organic framework as the shell reinforcing phase, mixing, stirring and ultrasonic dispersing the nano metal organic framework and the silica sol to form a transparent solution; (2) adding the defoaming agent and the wetting agent into the transparent solution, uniformly stirring at a rotating speed of 280~320 rpm to obtain the silica sol binder; (3) adding the silica sol binder into a batching barrel, adding the white corundum powder, and continuously stirring at a rotating speed of 180~220 rpm for 48 h to uniformly disperse the white corundum powder in the silica sol binder; (4) adding deionized water to adjust the viscosity of the slurry to 28~35 Pa·s, forming an alumina-based ceramic shell surface layer slurry, and the slurry is used for coating the shell of the shell surface layer.

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