Preparation of modified white corundum powder and its application in ceramic shell surface material

Abstract

The present invention discloses a preparation method of modified white corundum powder and its application in ceramic shell surface materials, belonging to the technical field of precision casting auxiliary materials. The present invention first performs surface modification and structural modification on white corundum powder to obtain modified white corundum powder with low reactivity, and uses it as the main raw material for ceramic shell surface materials. By adding pre-sintered composite oxides and metal oxide powders containing trace elements in the alloy components to the modified white corundum powder, the wetting angle of the alloy on the shell surface is greatly improved, and the chemical reaction rate and ion migration probability between the alloy and the shell surface are reduced, thereby achieving the purpose of reducing sand adhesion on the surface of cast alloy blades. The raw material modification method disclosed in the present invention, as well as the multi-angle and all-round shell surface material formula, can effectively reduce the probability of chemical reactions on the blade surface, improve the qualified rate of blade casting, and provide a feasible solution to the problem of surface chemical sand adhesion during blade casting.

Description

Technical Field

[0001] The invention relates to the technical field of precision casting auxiliary materials, in particular to the preparation of modified white corundum powder and its application in ceramic shell surface layer materials. Background Art

[0002] Alumina is an important raw material for industrial production. Its basic properties, such as crystal structure, crystallinity, purity, particle size, and specific surface area, all have a significant impact on its industrial application performance. Currently, the production process for alumina primarily involves alkali roasting bauxite, followed by cleaning and acid leaching to remove impurities, to obtain high-purity alumina raw material. This is then followed by calcination and electric melting to produce a white corundum product with high crystallinity and a high α-alumina content. If the acid leaching and cleaning processes are not rigorously followed, a large amount of Na will remain in the product, resulting in a distinct β-alumina phase. If excessive impurity elements are not removed during production, the product will exhibit a distinct yellow-brown color, commonly known as brown corundum. Due to differences in purity and crystallinity, the two corundum products have significantly different application performance and fields.

[0003] An important application area for alumina powder is as an auxiliary material for the high-temperature casting of high-temperature alloy blades for aircraft engines and gas turbines, including mold shells, cores, and structural parts using alumina as the main raw material. Ceramic mold shells made from alumina have the characteristics of stable high-temperature performance, high strength, moderate porosity, and moderate stress yield. They are key products that provide the mold cavity for the casting of molten high-temperature alloys during precision casting and are typical high-temperature structural materials. The structure of the mold shell is divided into multiple layers. The material in direct contact with the alloy is called the surface layer material, and the layer that does not directly contact the alloy but provides key mechanical properties and dimensional stability is called the back layer. Both the surface layer and the back layer require alumina powder as the main raw material. Its surface reactivity, chemical stability, impurity type and content, crystal structure, and structural stability have a key impact on the yield of the cast product.

[0004] Research indicates that the white corundum raw material used in ceramic shell castings for engine blades requires the lowest possible impurity content and high-temperature reactivity, and the highest possible α-alumina content and crystal structure stability. However, current processes focus primarily on the purification of the alumina raw material, while few studies have examined key factors that influence ceramic shell performance, such as the alumina's crystal structure, particle size and gradation requirements, chemical composition control, and surface reactivity control.

[0005] From the perspective of precision casting blade technology, the formula design of the shell surface layer is the key to shell manufacturing, because this is the material that comes into direct contact with the high-temperature alloy liquid. In the existing shell manufacturing process, the surface layer material is mainly based on high-purity, high-stability white corundum powder as the base raw material, and single or multiple oxides or other additives are added as additives, gradually developing different formulas. Additives that have been disclosed in the prior art include: cobalt aluminate powder, graphite powder, acicular carbon, chopped carbon fiber, molybdenum oxide, tungsten oxide, hexagonal boron nitride, high-purity bauxite, calcium carbonate, etc.

[0006] From an application perspective, the complex shell surface products mentioned above are prone to surface chemical reactions and sand sticking during the alloy casting process due to defects in purity and crystallinity. Therefore, it is still necessary to control the purity, crystal phase, and reactivity of the corundum raw material through pretreatment, and to control the reaction between the shell surface and the alloy through the ingredients of the shell surface, so as to solve the surface sand sticking problem after blade casting. Summary of the Invention

[0007] The present invention aims to provide a method for preparing modified white corundum powder (subjecting surface modification and structural reshaping to the white corundum powder) and a ceramic shell surface layer material for precision casting based on the modified white corundum powder and supplemented by a pre-sintered composite oxide and metal oxide compound. The present invention first surface-modifies and structurally reshapes the white corundum powder to obtain the modified white corundum powder. Pre-sintered, low-activity composite oxides are then added to this modified white corundum powder / pre-sintered composite oxide composite powder. The metal oxide compound is then specifically added to the modified white corundum powder / pre-sintered composite oxide composite powder. The three powders are combined to address the problem of chemical sand adhesion on blade surfaces.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention: a method for preparing modified white corundum powder, comprising the following steps:

[0010] The modified white corundum powder is obtained by coating the surface of the white corundum powder with a surface modifier, drying, calcining and breaking up the powder; the surface modifier is one of aluminum sol, zirconium sol or aluminate solution or a mixture of two of the two in any proportion.

[0011] Furthermore, the purity of the white corundum powder is greater than 99%, and the (median) particle size is 20 to 50 μm.

[0012] Furthermore, the surface modifier is coated onto the surface of the white corundum powder by spraying.

[0013] Furthermore, the amount of the surface modifier is 1 to 6% of the weight of the white corundum powder.

[0014] Furthermore, the amount of the surface modifier is preferably 3% by weight of the white corundum powder.

[0015] Furthermore, the aluminate solution is obtained by diluting aluminate, and the dilution concentration is 2 to 50%.

[0016] Furthermore, the calcination temperature is 1000-1500° C., and the calcination time is 3-12 hours.

[0017] The purpose of the calcination process is to significantly reduce the chemical activity of the main mass powder (modified white corundum powder) in the surface layer, improve the crystallinity, significantly reduce the sharp edges and corners on the particle surface, reduce the concentration of surface defect sites, and inhibit the reaction rate between the alloy liquid and the surface layer material.

[0018] Furthermore, the calcination temperature is preferably 1300° C., and the calcination time is preferably 6 hours.

[0019] Furthermore, the breaking up is to break up the calcined product into powder with a median particle size of 30 to 50 μm.

[0020] Furthermore, the breaking up is performed by stirring.

[0021] Furthermore, before calcination, the method further comprises breaking up the dried product into powder with a median particle size of 30 to 50 μm.

[0022] The second technical solution of the present invention: a modified white corundum powder prepared according to the above preparation method.

[0023] The third technical solution of the present invention: an application of the above-mentioned modified white corundum powder in ceramic shell surface layer materials.

[0024] A fourth technical solution of the present invention is a ceramic shell surface layer material, comprising the modified white corundum powder, a pre-sintered composite oxide, and a metal oxide; the metal oxide containing one or more trace elements present in the casting alloy. Specifically, the metal oxide contains at least one trace element present in the master alloy used to cast the target blade.

[0025] The alloys used for casting high-temperature alloy blades of aircraft engines and gas turbines are generally high-temperature alloys based on Ni, including DZ417G, K417G, DZ4125, GH145, FGH98, GH1140, K409, etc., which contain trace elements such as Zr, Ce, Hf, Re, Fe, Co, Ti, V, Cr, Mo, Ru, Al, and Ta. These trace elements are also active metal components in casting alloys.

[0026] Furthermore, the pre-sintered composite oxide contains two or more low-activity metal ions. Pre-sintering can reduce the activity of the composite oxide.

[0027] Furthermore, the pre-sintered composite oxide includes one or more of pre-sintered zircon sand, pre-sintered mullite, pre-sintered kaolin, and pre-sintered halloysite; the pre-sintered zircon sand, pre-sintered mullite, pre-sintered kaolin, and pre-sintered halloysite are respectively pre-sintered by zircon sand, mullite, kaolin, and halloysite; the pre-sintering temperature is 1300-1600°C, and the time is 3-12h; the (median) particle size of the pre-sintered composite oxide is 10-50μm; the addition amount of the pre-sintered composite oxide is 10-90% of the total weight of the ceramic shell surface layer material.

[0028] Furthermore, the free SiO2 content of the zircon sand and mullite is not higher than 1wt%; and the zircon sand and mullite are high-purity powders.

[0029] Furthermore, the kaolin is purified kaolin in the form of rod-shaped or needle-shaped fibers; and the halloysite is purified halloysite in the form of tubular fibers.

[0030] Adding low-activity, metal-non-wetting composite oxides to the surface material can significantly reduce the wettability of the metal and the inner surface of the shell; adding fibrous raw materials to the surface material can increase the shell strength and further inhibit the chemical reaction rate between the alloy and the surface material.

[0031] Furthermore, the metal oxide includes one or more of ZrO2, CeO2, Cr2O3, Re2O7, Ta2O5, Co3O4, Mo2O3, Al2O3, and TiO2; the (median) particle size of the metal oxide is 0.2 to 10 μm; and the added amount of the metal oxide is 1 to 10% of the total weight of the ceramic shell surface layer material.

[0032] Furthermore, the ZrO2 is a fully stabilized ZrO2 formed by solid solution substitution of one of Y, Mg, and Al (i.e., Y2O3, MgO, or Al2O3 is introduced into the ZrO2 matrix). The production method is as follows: zirconium oxychloride and one of yttrium nitrate, magnesium chloride, or aluminum nitrate are used as raw materials, and the above raw materials are respectively proportioned according to the molar ratio of stabilizer ions in the ZrO2 matrix as yttrium oxide (4-8%), magnesium oxide (3-4%), and aluminum oxide (10-20%), and ammonia water is used as a coprecipitant to form a hydroxide precursor, which is then placed in an air atmosphere and heated to 1500-1650°C at a heating rate of 10°C / min and calcined for 6-10 hours. After cooling in the furnace, the precursor is broken up, ground, and graded to obtain products of different particle sizes (which can be prepared by oneself or directly purchased from the market). The purpose of stabilizing ZrO2 is to prevent further solid solution reaction between zirconium oxide and alloy components to form chemical sand sticking, and to prevent physical sand sticking caused by shell deformation due to phase transformation of unstabilized zirconium oxide during cooling.

[0033] These metal oxides are stable at high temperatures and readily form high-temperature compounds with the Al2O3 matrix, while not reacting chemically with the master alloy. They can be selectively added based on the master alloy's composition. The purpose of adding these metal oxides is to reduce the chemical gradient and element migration between the alloy surface and the surface material, thereby reducing the entropy transfer of trace elements from the alloy to the mold shell surface, thereby preventing chemical reactions and addressing chemical sand adhesion.

[0034] The present invention is based on solving the problem of serious surface sand adhesion during the casting process of alloy blades. First, a method for surface modification and structural modification of white corundum powder is invented to prepare modified white corundum powder to reduce the reaction activity of the white corundum powder, thereby fundamentally reducing the chemical reaction ability of the alloy liquid and the mold shell surface layer; in a further technology, in the process of preparing the mold shell surface layer slurry, the above-mentioned modified white corundum powder with reduced activity is used as a raw material, and then combined with a chemically inert composite oxide powder synthesized by pre-sintering to reduce the wettability of the alloy liquid and the mold shell surface layer, so as to further inhibit the chemical reaction rate between the two; in a further technology, a metal oxide powder containing trace elements in the alloy components is added to the above-mentioned low-activity modified white corundum powder / pre-sintered composite oxide powder slurry. From the perspective of chemical reaction kinetics, the chemical gradient between the mold shell surface layer and the faster-reacting metal in the alloy liquid is reduced, and the entropy increase migration of the alloy trace elements into the mold shell surface layer is reduced. Through the above three innovative technologies, the probability of chemical sand adhesion on the blade surface during the casting process can be fundamentally reduced, the qualified rate of blade casting can be effectively improved, and the casting level and production strength of high-temperature alloy blades can be enhanced.

[0035] The present invention discloses the following technical effects:

[0036] (1) The present invention first uses a surface modifier to modify the surface of white corundum powder, and then uses a calcination process to structurally modify the surface-modified white corundum powder. The combination of surface modification and structural modification significantly reduces the reactivity of the white corundum powder, and uses it as the main raw material for the ceramic shell surface layer material, fundamentally reducing the chemical reaction ability of the alloy liquid and the shell surface layer.

[0037] (2) The present invention uses white corundum powder that has undergone surface modification and structural modification as the main raw material, supplemented by chemically inert composite oxide powder synthesized in advance and metal oxide powder containing trace elements in the alloy components, to prepare the ceramic shell surface layer material. The above three powders work together to effectively reduce the chemical reaction ability between the shell surface layer and the alloy liquid, thereby solving the problem of chemical sand adhesion on the blade surface.

[0038] (3) The mold shell produced using the mold shell surface layer material of the present invention has the advantages of stable chemical properties and weak high-temperature reaction ability.

[0039] (4) The processing technology of the raw materials used for the shell surface layer material of the present invention is simple, and the purity requirement is high, but the cost is low, and there is no special rare metal in the raw materials, so the cost is low.

[0040] (5) The present invention suppresses the chemical reaction between the alloy and the shell surface layer from multiple angles and in all directions, effectively solving the problem of serious sand sticking to the blade surface during the casting process, greatly improving the yield rate of blade products, and solving the technical difficulties in the field of auxiliary materials for engine blade casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 The contact angle test diagrams of the ceramic shell and the alloy droplet in Examples 1-4 of the present invention, wherein (A) is Example 1; (B) is Example 2; (C) is Example 3; (D) is Example 4;

[0043] Figure 2 These are contact angle test diagrams of the ceramic shell and the alloy droplet in Comparative Examples 1-4 of the present invention, wherein (A) is Comparative Example 1; (B) is Comparative Example 2; (C) is Comparative Example 3; and (D) is Comparative Example 4. DETAILED DESCRIPTION

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0046] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0047] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] In the following examples and comparative examples, the contact angle between the high-temperature molten alloy and the simulated shell surface (surface layer) is used to characterize the wettability and reactivity of the two. The larger the wetting angle, the weaker the reaction between the two and the more difficult it is for the alloy to adhere to sand.

[0050] The purity of the white corundum powder used in the following examples and comparative examples is 99%.

[0051] The pre-sintered mullite powder used in the following examples and comparative examples was obtained by calcining high-purity mullite powder with a free SiO2 content of 1 wt% at a temperature of 1500°C for 6 hours.

[0052] The pre-sintered zircon sand used in the following examples and comparative examples was obtained by calcining high-purity zircon sand with a free SiO2 content of 1 wt% at a temperature of 1500°C for 6 hours.

[0053] The Y2O3-stabilized ZrO2 powder used in the following examples and comparative examples (i.e., Y2O3 is introduced into the ZrO2 matrix) has a molar content of Y2O3 of 8%, that is, the molar proportion of Y2O3 in the ZrO2 matrix is ​​8%, which is a common commercial product.

[0054] Example 1

[0055] (1) Preparation of modified white corundum powder (surface modification and structural modification of white corundum powder), the steps are as follows:

[0056] White corundum powder with a median particle size of 50 μm was selected, and the white corundum powder was blown up to a tumbling state using a suspended sand blowing machine. Aluminum sol containing 3% of the mass of the white corundum powder was gradually sprayed onto the surface of the suspended white corundum powder by a spray method. After all the spraying was completed, it was dried at 80°C, stirred and broken up to a median particle size of 50 μm, transferred to a box furnace at 1350°C and calcined for 6 hours, and stirred and broken up again to a median particle size of 50 μm to obtain modified white corundum powder.

[0057] (2) Preparation of ceramic shell surface material and integral shell for precision casting, the steps are as follows:

[0058] 1) Preparation of ceramic shell surface layer material: The modified white corundum powder prepared in step (1) is uniformly mixed with pre-sintered mullite powder with a median particle size of 50 μm in a mass ratio of 2:1 (the mass of the pre-sintered mullite powder accounts for 32.3% of the total weight of the mixed surface layer powder), and then TiO2 powder with a median diameter of 2 μm is added, the mass of which accounts for 3% of the total weight of the powder to obtain a mixed surface layer powder;

[0059] 2) Preparation of the integral shell: Take part of the above mixed surface layer powder and evenly disperse it in the silica sol (the mass ratio of the mixed surface layer powder to the silica sol is 1:3), and the rest is used to sprinkle sand binder. Glue, sand and dry the wax mold surface and repeat 3 times. When the surface layer thickness reaches 2mm, glue and sprinkle other back layer sand on the back of the wax mold. Repeat multiple times until the back layer thickness reaches 6mm. Subsequently, the shell is transferred to a 100℃ dewaxing furnace for dewaxing and calcined at a final firing temperature of 1300℃ for 8 hours to complete the sintering process to form a ceramic shell product; the ceramic shell product and DZ417G alloy are placed in a directional solidification furnace together (DZ417G alloy particles are placed in the cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550℃ at a rate of 5℃ / min and kept at this temperature for 30 minutes to simulate the casting process. After cooling, it is taken out. The average wetting angle between the DZ417G alloy and the ceramic shell surface (surface layer) is 111.5° (e.g. Figure 1 (As shown in A), and it was found that there was no obvious sand sticking point on the contact surface between the alloy and the shell.

[0060] Example 2

[0061] (1) Preparation of modified white corundum powder (surface modification and structural modification of white corundum powder), the steps are as follows:

[0062] White corundum powder with a median particle size of 50 μm was selected, and the white corundum powder was blown up to a tumbling state using a suspended sand blower. A 10% diluted aluminate solution with a mass percentage of 5% of the white corundum powder was gradually sprayed onto the surface of the suspended white corundum powder using a spray method. After all the spraying was completed, it was dried at 80°C, stirred and broken up to a median particle size of 50 μm, transferred to a 1350°C box furnace and calcined for 6 hours, and stirred and broken up again to a median particle size of 50 μm to obtain modified white corundum powder.

[0063] (2) Preparation of ceramic shell surface material and integral shell for precision casting, the steps are as follows:

[0064] 1) Preparation of ceramic shell surface layer material: The modified white corundum powder prepared in step (1) is uniformly mixed with pre-sintered zircon sand with a median particle size of 50 μm in a mass ratio of 1:1 (the mass of the pre-sintered zircon sand accounts for 47.5% of the total weight of the mixed surface layer powder), and then Cr2O3 powder with a median diameter of 2 μm is added, the mass of which accounts for 5% of the total weight of the powder to obtain a mixed surface layer powder;

[0065] 2) Preparation of the integral shell: Take part of the above mixed surface layer powder and evenly disperse it in the silica sol (the mass ratio of the mixed surface layer powder to the silica sol is 1:3), and the rest is used to sprinkle sand binder. Glue, sand and dry the wax mold surface and repeat 3 times. When the surface layer thickness reaches 2mm, glue and sprinkle other back layer sand on the back of the wax mold. Repeat multiple times until the back layer thickness reaches 6mm. Subsequently, the shell is transferred to a 100℃ dewaxing furnace for dewaxing and calcined at a final firing temperature of 1300℃ for 8 hours to complete the sintering process and form a ceramic shell product; the ceramic shell product and GH145 alloy are placed in a directional solidification furnace together (GH145 alloy particles are placed in the cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550℃ at a rate of 5℃ / min and kept warm for 30 minutes to simulate the casting process. It is then taken out after cooling. The average wetting angle between GH145 alloy and ceramic shell surface (surface layer) is 140.5° (as shown in Figure 2). Figure 1 (B)), and it was found that there was no obvious sand sticking point on the contact surface between the alloy and the shell.

[0066] Example 3

[0067] (1) Preparation of modified white corundum powder (surface modification and structural modification of white corundum powder), the steps are as follows:

[0068] White corundum powder with a median particle size of 50 μm was selected, and the white corundum powder was blown up to a tumbling state using a suspended sand blower. Zirconium sol with a mass percentage of 5% of the white corundum powder was gradually sprayed onto the surface of the suspended white corundum powder by a spray method. After all the spraying was completed, it was dried at 80°C, stirred and broken up to a median particle size of 50 μm, transferred to a box furnace at 1350°C and calcined for 6 hours, and stirred and broken up again to a median particle size of 50 μm to obtain modified white corundum powder.

[0069] (2) Preparation of ceramic shell surface material and integral shell for precision casting, the steps are as follows:

[0070] 1) Preparation of ceramic shell surface layer material: The modified white corundum powder prepared in step (1) is uniformly mixed with pre-sintered zircon sand with a median particle size of 50 μm in a mass ratio of 1:2 (the mass of the pre-sintered zircon sand accounts for 63.3% of the total weight of the mixed surface layer powder), and then Cr2O3 powder with a median diameter of 2 μm is added, the mass of which accounts for 5% of the total weight of the powder to obtain a mixed surface layer powder;

[0071] 2) Preparation of the integral shell: Take part of the above mixed surface layer powder and disperse it evenly in the silica sol (the mass ratio of the mixed surface layer powder to the silica sol is 1:3), and the rest is used to sprinkle sand binder, and perform gluing, sanding, and drying operations on the surface of the wax mold and repeat 3 times. When the surface layer thickness reaches 2mm, glue and sprinkle other back layer sand on the back of the wax mold, and repeat many times until the back layer thickness reaches 6mm. Subsequently, the entire shell is transferred to a 100℃ dewaxing furnace for dewaxing, and calcined at a final firing temperature of 1300℃ for 8 hours to complete the sintering process to form a ceramic shell product; the ceramic shell product and the GH145 alloy are placed in a directional solidification furnace together (GH145 alloy particles are placed in the cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550℃ at a rate of 5℃ / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the GH145 alloy and the ceramic shell surface (surface layer) is measured to be 133° (such as Figure 1 (C)), and it was observed that there were only a few sand sticking points on the contact surface between the alloy and the shell.

[0072] Example 4

[0073] (1) Preparation of modified white corundum powder (surface modification and structural modification of white corundum powder), the steps are as follows:

[0074] White corundum powder with a median particle size of 50 μm was selected, and the white corundum powder was blown up to a tumbling state using a suspended sand blowing machine. Aluminum sol containing 3% of the mass of the white corundum powder was gradually sprayed onto the surface of the suspended white corundum powder by a spray method. After all the spraying was completed, it was dried at 80°C, stirred and broken up to a median particle size of 50 μm, transferred to a box furnace at 1350°C and calcined for 6 hours, and stirred and broken up again to a median particle size of 50 μm to obtain modified white corundum powder.

[0075] (2) Preparation of ceramic shell surface material and integral shell for precision casting, the steps are as follows:

[0076] 1) Preparation of ceramic shell surface layer material: The modified white corundum powder prepared in step (1) is uniformly mixed with pre-sintered mullite powder with a median particle size of 50 μm in a mass ratio of 1:1 (the mass of the pre-sintered mullite powder accounts for 48.5% of the total weight of the mixed surface layer powder), and then Y2O3-stabilized ZrO2 powder with a median particle size of 2 μm is added, the mass of which accounts for 3% of the total weight of the powder to obtain a mixed surface layer powder;

[0077] 2) Preparation of the integral shell: Take part of the above mixed surface layer powder and evenly disperse it in the silica sol (the mass ratio of the mixed surface layer powder to the silica sol is 1:3), and the rest is used to sprinkle sand binder. Glue, sand and dry the wax mold surface and repeat 3 times. When the surface layer thickness reaches 2mm, glue and sprinkle other back layer sand on the back of the wax mold. Repeat multiple times until the back layer thickness reaches 6mm. Subsequently, the shell is transferred to a 100℃ dewaxing furnace for dewaxing and calcined at a final firing temperature of 1300℃ for 8 hours to complete the sintering process to form a ceramic shell product; the ceramic shell product and K417G alloy are placed in a directional solidification furnace together (K417G alloy particles are placed in the cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550℃ at a rate of 5℃ / min and kept at this temperature for 30 minutes to simulate the casting process. After cooling, it is taken out. The average wetting angle between K417G alloy and ceramic shell surface (surface layer) is 104.7° (as shown in Figure 2). Figure 1 (D)), and it was found that there was no obvious sand sticking point on the contact surface between the alloy and the shell.

[0078] Comparative Example 1

[0079] The same as Example 1, except that the surface modification and structural modification of the white corundum powder are not performed (i.e., step (1) is omitted), and pre-sintered composite oxides and metal oxide batching materials are not added. Only white corundum powder raw material with a median particle size of 50 μm is used as the surface layer powder to form the ceramic shell. After obtaining the ceramic shell product, the ceramic shell product and the DZ417G alloy are placed together in a directional solidification furnace (the DZ417G alloy particles are placed in the mold cavity of the ceramic shell product and are in direct contact with the surface layer), and the temperature is raised to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the DZ417G alloy and the ceramic shell surface (surface layer) is measured to be 89.5° (as shown in FIG. Figure 2 (As shown in A), and it was observed that obvious sand sticking points appeared on the contact surface between the alloy and the shell.

[0080] Comparative Example 2

[0081] The same as Example 2, except that, in the process of preparing the ceramic shell surface layer material and the integral shell for precision casting in step (2), no pre-sintered composite oxides and metal oxide compounding materials are added, and only the modified white corundum powder prepared in step (1) is used as the surface layer powder to form the ceramic shell. After obtaining the ceramic shell product, the ceramic shell product and the GH145 alloy are placed together in a directional solidification furnace (GH145 alloy particles are placed in the mold cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the GH145 alloy and the ceramic shell surface (surface layer) is measured to be 94.2° (as shown in FIG. Figure 2 (B)), and it was observed that obvious sand sticking points appeared on the contact surface between the alloy and the shell.

[0082] Comparative Example 3

[0083] The same as Example 3, except that, in the preparation process of the ceramic shell surface layer material and the integral shell for precision casting in step (2), no pre-sintered composite oxide is added, and only Cr2O3 powder with a median diameter of 2 μm is added to the modified white corundum powder, and the added mass accounts for 5% of the total weight of the powder to obtain a mixed surface layer powder. After obtaining the ceramic shell product, the ceramic shell product and the GH145 alloy are placed together in a directional solidification furnace (GH145 alloy particles are placed in the mold cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the GH145 alloy and the ceramic shell surface (surface layer) is measured to be 98° (such as Figure 2 (C)), and it was observed that obvious sand sticking points appeared on the contact surface between the alloy and the shell.

[0084] Comparative Example 4

[0085] The same as Example 1, except that, in the preparation process of the ceramic shell surface layer material and the integral shell for precision casting in step (2), no pre-sintered composite oxide is added, and the added metal oxide is Y2O3 stabilized ZrO2 powder with a median diameter of 2 μm, and the added mass accounts for 3% of the total weight of the powder to obtain a mixed surface layer powder. After obtaining the ceramic shell product, the ceramic shell product and the K417G alloy are placed together in a directional solidification furnace (the K417G alloy particles are placed in the cavity of the ceramic shell product and in direct contact with the surface layer), and the temperature is raised to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the K417G alloy and the ceramic shell surface (surface layer) is measured to be 100.3° (as shown in FIG. Figure 2 (D)), and it was observed that obvious sand sticking points appeared on the contact surface between the alloy and the shell.

[0086] Comparative Example 5

[0087] The same as Example 1, except that, in the preparation process of the modified white corundum powder in step (1), only the surface modification treatment of the white corundum powder raw material is performed, and no structural modification treatment is performed, that is, the calcination step is omitted. After obtaining the ceramic shell product, the ceramic shell product and the DZ417G alloy are placed together in a directional solidification furnace (the DZ417G alloy particles are placed in the mold cavity of the ceramic shell product and are in direct contact with the surface layer), and the temperature is raised to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the DZ417G alloy and the ceramic shell surface (surface layer) is measured to be 99.2°, and it is observed that obvious sand sticking points appear on the contact surface between the alloy and the shell.

[0088] Comparative Example 6

[0089] The same as Example 1, except that the surface modification and structural modification of the white corundum powder are not performed (i.e., step (1) is omitted), and the modified white corundum powder in step (2) is replaced by a white corundum powder raw material with a median particle size of 50 μm. After obtaining the ceramic shell product, the ceramic shell product and the DZ417G alloy are placed together in a directional solidification furnace (the DZ417G alloy particles are placed in the mold cavity of the ceramic shell product and are in direct contact with the surface layer), and the temperature is increased to 1550°C at a rate of 5°C / min, and kept warm for 30 minutes to simulate the casting process, and then taken out after cooling. The average wetting angle between the DZ417G alloy and the ceramic shell surface (surface layer) is measured to be 96°, and it is observed that obvious sand sticking points appear on the contact surface between the alloy and the shell.

[0090] Comparative Example 7

[0091] The same as Example 4, except that in step (2), an equal amount of unstabilized ordinary ZrO2 powder is used instead of the stabilized ZrO2 powder. After obtaining the ceramic shell product, the ceramic shell product and the K417G alloy are placed together in a directional solidification furnace (the K417G alloy particles are placed in the mold cavity of the ceramic shell product, in direct contact with the surface layer). The temperature is raised to 1550°C at a rate of 5°C / min and kept at this temperature for 30 minutes to simulate the casting process. The product is then taken out after cooling. The average wetting angle between the K417G alloy and the ceramic shell surface (surface layer) is measured to be 95.3°, and it is observed that obvious sand sticking points appear on the contact surface between the alloy and the shell.

[0092] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A ceramic shell surface material, characterized in that: The raw materials are: modified white corundum powder, pre-sintered composite oxide and metal oxide; the metal oxide contains one or more trace elements in the casting alloy component; The preparation steps of the modified white corundum powder include: coating the surface of the white corundum powder with a surface modifier, drying, calcining, and breaking up to obtain the modified white corundum powder; The surface modifier is one of aluminum sol, zirconium sol or aluminate solution or a mixture of the two in any proportion; The calcination temperature is 1000-1500°C and the time is 3-12 hours; The pre-sintered composite oxide includes one or more of pre-sintered zircon sand, pre-sintered mullite, pre-sintered kaolin, and pre-sintered halloysite; The metal oxide includes one or more of ZrO2, CeO2, Cr2O3, Re2O7, Ta2O5, Co3O4, Mo2O3, Al2O3, and TiO2; The ZrO2 is a fully stabilized ZrO2 formed by solid solution by atomic substitution of one of Y, Mg, and Al; The addition amount of the pre-sintered composite oxide is 10 to 63.3% of the total weight of the ceramic shell surface layer material; The added amount of the metal oxide is 1-10% of the total weight of the ceramic shell surface layer material.

2. The ceramic shell surface layer material according to claim 1, characterized in that: The purity of the white corundum powder is greater than 99%, and the particle size is 20 to 50 μm.

3. The ceramic shell surface layer material according to claim 1, characterized in that: The amount of the surface modifier used is 1-6% of the weight of the white corundum powder.

4. The ceramic shell surface layer material according to claim 1, characterized in that: The pre-sintered zircon sand, pre-sintered mullite, pre-sintered kaolin and pre-sintered halloysite are respectively formed by pre-sintering zircon sand, mullite, kaolin and halloysite; the pre-sintering temperature is 1300-1600°C and the time is 3-12 hours; the particle size of the pre-sintered composite oxide is 10-50 μm.

5. The ceramic shell surface layer material according to claim 4, characterized in that: The free SiO2 content of the zircon sand and mullite is not higher than 1wt%.

6. The ceramic shell surface layer material according to claim 1, characterized in that: The particle size of the metal oxide is 0.2 to 10 μm.

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