A high-porosity and high-strength silicon-based ceramic, its preparation method and application, and a method for removing ceramic cores for titanium alloy casting

Abstract

The present invention provides a high-porosity and high-strength silicon-based ceramic, a preparation method and application thereof, and a method for removing a ceramic core for titanium alloy castings. The raw materials of the silicon-based ceramic include solid powder and a binder. The solid powder includes 60-100wt% silicon dioxide, 0-20wt% kaolin, and 0-20wt% calcium hydroxide; wherein the kaolin content is greater than 0, and the calcium hydroxide content is greater than 0; and the mass ratio of the solid powder to the binder is 1:0.01-0.05. The present invention uses silicon dioxide as the raw material and kaolin and calcium hydroxide powders as mineralizers, which can effectively promote the sintering of the material and the formation of cristobalite, increase the open porosity of the silicon-based ceramic, improve the collapsibility, and simultaneously form new phases that combine with each other to form a skeleton to enhance the mechanical properties of the silicon-based ceramic.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic cores for titanium alloy castings, and more specifically to a high-porosity and high-strength silicon-based ceramic, a preparation method and application thereof, and a method for removing ceramic cores for titanium alloy castings. Background Art

[0002] The hollow blades of aircraft engines and gas turbines are precision parts that are subjected to high temperature and high pressure conditions on the turbine rotor at the rear end of the calcination chamber. They are usually manufactured using an alloy melt casting process. The template material for the hollow part of the hollow blade is called a ceramic core. It is a prefabricated part that needs to be formed and sintered before casting. It needs to be pre-filled into the ceramic shell to provide shape stability and high-temperature mechanical properties during casting. After casting is completed, the ceramic core is chemically removed to form the hollow blade. The dimensional stability and mechanical properties of the ceramic core are key auxiliary materials that determine whether the hollow cavity of the blade can be successfully generated and provide a continuous airflow channel. It is one of the high-end and key ceramic products used in precision casting.

[0003] At present, the ceramic cores used at home and abroad mainly include aluminum-based ceramic cores and silicon-based ceramic cores. Aluminum-based ceramic cores have better thermal strength and thermal stability, and are structurally stable during sintering and use, without high- and low-temperature crystal transformations, and have good high-temperature resistance. However, aluminum-based ceramic cores are difficult to de-core, which inhibits their widespread practical application and development. Compared with aluminum-based ceramic cores, silicon-based ceramic cores have the advantages of low sintering temperature, better controllability of cristobalite conversion rate, small thermal expansion coefficient, and good de-coring performance. However, silicon oxide-based cores also generally have problems such as low high-temperature strength, large deformation, and reaction with titanium alloys, which affect the production qualification rate and cost of alloy blades. Summary of the Invention

[0004] Based on the above technical problems existing in the prior art, the present invention provides a high-porosity and high-strength silicon-based ceramic. The raw materials of the silicon-based ceramic include solid powder and a binder. The silicon-based ceramic uses silicon dioxide as a raw material and kaolin and calcium hydroxide as mineralizers, and has the characteristics of high porosity and high strength.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A high-porosity and high-strength silicon-based ceramic, wherein the raw materials of the silicon-based ceramic include solid powder and a binder, and the solid powder is composed of the following components:

[0007] Silicon dioxide 60-100 wt%

[0008] Kaolin 0-20wt%

[0009] Calcium hydroxide 0-20wt%;

[0010] Among them, the content of kaolin is greater than 0, and the content of calcium hydroxide is greater than 0;

[0011] The mass ratio of the solid powder to the binder is 1:0.01-0.05.

[0012] In some embodiments, the average particle size of the silicon dioxide is 25-40 μm; the average particle size of the kaolin is 0.5-5 μm; and the average particle size of the calcium hydroxide is 0.5-2 μm.

[0013] The present invention also provides a method for preparing the silicon-based ceramic according to any of the above embodiments, the method comprising the following steps:

[0014] Silicon dioxide, kaolin and calcium hydroxide powders are mixed evenly to obtain a mixed powder; a binder aqueous solution is then added and mixed evenly; the mixture is then placed in a mold and pressed to obtain a green body; the green body is dried and then sintered to obtain a silicon-based ceramic.

[0015] In some embodiments, the sintering temperature is 1250-1450°C.

[0016] In some embodiments, the sintering time is 3-6 hours.

[0017] In some embodiments, the binder is polyvinyl alcohol; and the concentration of the binder aqueous solution is 3-10 wt %.

[0018] In some embodiments, the solid-to-liquid ratio of the mixed powder to the binder aqueous solution is 15-20 g:1-3 mL.

[0019] In some embodiments, the preparation method comprises the following steps:

[0020] S1. Mix silicon dioxide powder, kaolin powder and calcium hydroxide powder evenly and dry them at a temperature of 100-120°C;

[0021] S2. ball milling the dried powder to obtain a mixed powder; wherein the ball-to-material ratio is 2:1;

[0022] S3, adding the binder solution to the mixed powder, mixing evenly and then passing through a 100 mesh sieve; wherein the solid-liquid ratio is 15-20g:1-3mL;

[0023] S4, taking the powder under the sieve and placing it in a mold for pressing at a pressure of 3-10 MPa and a holding time of 30-60 s to obtain a green body;

[0024] S5, fully drying the green body at a temperature of 100-120° C.;

[0025] S6. Place the dried green body in a muffle furnace and sinter it at a temperature of 1250-1450° C. to obtain silicon-based ceramics.

[0026] The present invention also provides a ceramic core for titanium alloy casting, wherein the ceramic core comprises a silicon-based ceramic and a coating on the silicon-based ceramic, wherein the silicon-based ceramic is any one of the silicon-based ceramics described above or a silicon-based ceramic obtained by the preparation method of any one of the silicon-based ceramics described above; and the coating comprises yttrium oxide.

[0027] In some embodiments, the thickness of the coating is greater than 100 nm; preferably, 150-300 μm; more preferably, 150-250 μm.

[0028] The present invention also provides a method for preparing a ceramic core for titanium alloy casting, the method comprising the following steps:

[0029] The silicon-based ceramic is prepared according to any of the above preparation methods, and then an yttrium oxide coating is sprayed on the surface of the silicon-based ceramic to obtain the ceramic core.

[0030] In some embodiments, a yttrium oxide coating is sprayed on the surface of the silicon-based ceramic by a plasma spraying method to obtain the ceramic core.

[0031] The present invention also provides a method for removing the ceramic core for titanium alloy casting, which comprises the following steps:

[0032] (1) using the ceramic core for titanium alloy casting or the ceramic core obtained by the above-mentioned method for preparing the ceramic core for titanium alloy casting as a template to cast a titanium alloy to obtain a casting;

[0033] (2) placing the casting with the ceramic core in a mixed alkali solution and boiling it while ultrasonically treating the casting;

[0034] (3) After cooling, take out the casting and soak it in water to remove the residual alkali solution;

[0035] (4) immersing the casting treated in step (3) in a hydrochloric acid solution containing a corrosion inhibitor, reacting at a temperature of 80-100° C., and simultaneously performing ultrasonic treatment;

[0036] (5) Repeat steps (2) to (4) until the ceramic core is completely removed.

[0037] In some embodiments, the mixed alkali solution includes 30-60 wt % potassium hydroxide and 5-15 wt % sodium carbonate.

[0038] In some embodiments, the corrosion inhibitor is at least two of copper salts, molybdates, tungstates, zinc salts, potassium iodate, tropaeolum orange, quaternary ammonium salts, Mannich base, hexadecyltrimethylammonium bromide, sodium lauroylamino acid, and sodium lauryl sulfate.

[0039] In some embodiments, in step (2), the casting with the silicon-based ceramic core is boiled in the mixed alkali solution for 12-36 hours at a pressure of natural atmospheric pressure.

[0040] In some embodiments, in step (4), the concentration of the hydrochloric acid solution is ≤6 mol / L; preferably, 4-6 mol / L.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The silicon-based ceramic of the present invention uses silicon dioxide as a raw material and kaolin and calcium hydroxide powder as mineralizers, which can effectively promote the sintering of the material and the formation of cristobalite, increase the open porosity of the silicon-based ceramic core, improve the collapsibility, and simultaneously form new phases that combine with each other to form a skeleton to enhance the mechanical properties of the ceramic core. The silicon-based ceramic is used as a ceramic core for titanium alloy casting, and yttrium oxide is used as a coating on its surface, which can effectively improve the chemical reaction inertness between the ceramic core and the titanium alloy.

[0043] The preparation method of the silicon-based ceramic provided by the present invention enables the obtained silicon-based ceramic to have excellent room-temperature high-temperature bending strength, high porosity and good dissolution performance.

[0044] The ceramic core removal method provided by the present invention inhibits the reaction between hydrochloric acid and titanium alloy under high temperature and high concentration hydrochloric acid solution conditions, can effectively remove the ceramic core while avoiding damage to the titanium alloy during the core removal process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is the XRD pattern of the silicon-based ceramic core for titanium alloy casting prepared in Example 1 of the present invention;

[0046] Figure 2 This is an SEM image of the fracture of the silicon-based ceramic core prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0049] Example 1

[0050] The preparation of silicon-based ceramics includes the following steps:

[0051] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 17:1:2. Mix and dry thoroughly in an oven at 120°C.

[0052] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0053] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0054] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for a holding time of 30-60 s to obtain a green compact;

[0055] S5. The green body is transferred to an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered to silicon-based ceramic at 1300° C.

[0056] The XRD analysis patterns and SEM images of the silicon-based ceramics prepared in this embodiment are shown in FIG. Figure 1 and Figure 2 shown.

[0057] Comparative Example 1

[0058] The preparation of silicon-based ceramics includes the following steps:

[0059] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 19.5:0.5:0, mix, and dry thoroughly in an oven at 120°C.

[0060] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0061] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0062] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 6-12 MPa for a holding time of 30-60 s to obtain a green compact;

[0063] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0064] Comparative Example 2

[0065] The preparation of silicon-based ceramics includes the following steps:

[0066] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 19:1:0, mix them, and dry them in an oven at 120°C.

[0067] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0068] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0069] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for 30-60 seconds to obtain a green compact;

[0070] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0071] Comparative Example 3

[0072] The preparation of silicon-based ceramics includes the following steps:

[0073] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 18:2:0, mix them, and dry them in an oven at 120°C.

[0074] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0075] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0076] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for 30-60 seconds to obtain a green compact;

[0077] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0078] Comparative Example 4

[0079] The preparation of silicon-based ceramics includes the following steps:

[0080] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 18:1:1, mix them, and dry them thoroughly in an oven at 120°C.

[0081] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0082] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0083] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for 30-60 seconds to obtain a green compact;

[0084] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0085] Comparative Example 5

[0086] The preparation of silicon-based ceramics includes the following steps:

[0087] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 16:1:3. Mix and dry thoroughly in an oven at 120°C.

[0088] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain ceramic core powder, with a ball-to-material ratio of 2:1;

[0089] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0090] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for 30-60 seconds to obtain a green compact;

[0091] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0092] Comparative Example 6

[0093] The preparation of silicon-based ceramics includes the following steps:

[0094] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 15:1:4. Mix and dry thoroughly in an oven at 120°C.

[0095] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0096] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0097] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for a holding time of 30-60 s to obtain a green compact;

[0098] S5. The green body is transferred into an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered at 1300° C. to obtain silicon-based ceramics.

[0099] Example 2

[0100] The preparation of a silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0101] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 17:1:2. Mix and dry thoroughly in an oven at 120°C.

[0102] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0103] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0104] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for a holding time of 30-60 s to obtain a green compact;

[0105] S5, transferring the green body into an oven at 100°C for drying; placing the dried green body in a muffle furnace and sintering it into silicon-based ceramic at 1300°C;

[0106] S6. A 200 μm yttrium oxide coating is sprayed on the surface of the silicon-based ceramic by a plasma spraying method to obtain a silicon-based ceramic core for titanium alloy casting.

[0107] Comparative Example 7

[0108] The preparation of a silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0109] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 17:1:2. Mix and dry thoroughly in an oven at 120°C.

[0110] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0111] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0112] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for a holding time of 30-60 s to obtain a green compact;

[0113] S5, transferring the green body into an oven at 100°C for drying; placing the dried green body in a muffle furnace and sintering it into silicon-based ceramic at 1300°C;

[0114] S6. A 100 μm yttrium oxide coating is sprayed on the surface of the silicon-based ceramic by a plasma spraying method to obtain a silicon-based ceramic core for titanium alloy casting.

[0115] Comparative Example 8

[0116] The preparation of a silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0117] S1. Weigh 20 g of silicon dioxide, kaolin, and calcium hydroxide powder in order to ensure a mass ratio of 17:1:2. Mix and dry thoroughly in an oven at 120°C.

[0118] S2. The dried powder is transferred into a ball mill and ball milled for 10-16 hours to obtain a ceramic core mixed powder with a ball-to-material ratio of 2:1;

[0119] S3. Add 1-3 mL of 3-10 wt% polyvinyl alcohol aqueous solution to the mixed powder, mix well, and pass through a 100 mesh sieve;

[0120] S4. Weigh a certain mass of the undersize powder and place it in a mold for pressing at a pressure of 3-10 MPa for a holding time of 30-60 s to obtain a green compact;

[0121] S5. The green body is transferred to an oven at 100° C. for drying; the dried green body is placed in a muffle furnace and sintered to silicon-based ceramic at 1300° C.

[0122] S6. A 300 μm yttrium oxide coating is sprayed on the surface of the silicon-based ceramic by a plasma spraying method to obtain a silicon-based ceramic core for titanium alloy casting.

[0123] Example 3

[0124] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0125] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation casting was performed to obtain a casting;

[0126] (2) immersing the casting in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiling for 8 h at a natural atmospheric pressure while ultrasonically treating the casting;

[0127] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0128] (4) Immersing the castings soaked in deionized water in a hydrochloric acid solution containing copper chloride and nasturtium orange, keeping the temperature at 90°C for 4 hours, and simultaneously subjecting the castings to ultrasonic treatment; wherein the concentrations of copper chloride, nasturtium orange, and hydrochloric acid are 10 g / L, 1 mmol / L, and 6 mol / L, respectively;

[0129] (5) The casting is removed and repeatedly soaked in deionized water, and then placed in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiled for 8 h. The casting is alternately treated with alkaline and acid solutions until the core is completely removed.

[0130] Comparative Example 9

[0131] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0132] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation casting was performed to obtain a casting;

[0133] (2) immersing the casting in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiling for 8 h at a natural atmospheric pressure while ultrasonically treating the casting;

[0134] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0135] (4) immersing the casting treated in step (3) in a hydrochloric acid solution containing copper chloride and nasturtium orange, keeping the temperature at 90° C. for 4 hours, and simultaneously performing ultrasonic treatment on the casting; wherein the concentrations of copper chloride, nasturtium orange, and hydrochloric acid are 10 g / L, 1 mmol / L, and 3 mol / L, respectively;

[0136] (5) The casting is removed and repeatedly soaked in deionized water, and then placed in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiled for 8 h. The casting is alternately treated with alkaline and acid solutions until the core is completely removed.

[0137] Comparative Example 10

[0138] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0139] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation casting was performed to obtain a casting;

[0140] (2) immersing the casting in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiling for 8 hours at a natural atmospheric pressure while ultrasonically treating the casting;

[0141] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0142] (4) immersing the casting treated in step (3) in a 6 mol / L hydrochloric acid solution and keeping it at 90° C. for 4 hours while ultrasonically treating the casting;

[0143] (5) The casting is removed and repeatedly soaked in deionized water, and then placed in a mixed solution containing 50 wt% potassium hydroxide and 10 wt% sodium carbonate and boiled for 8 h. The casting is alternately treated with alkaline and acid solutions until the core is completely removed.

[0144] Comparative Example 11

[0145] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0146] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation pouring was performed to obtain a casting;

[0147] (2) immersing the casting in a mixed solution containing 30 wt% potassium hydroxide and 10 wt% sodium carbonate and boiling for 8 hours at a natural atmospheric pressure while ultrasonically treating the casting;

[0148] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0149] (4) Immerse the casting treated in step (3) in a hydrochloric acid solution containing copper chloride and nasturtium orange, keep the temperature at 90°C for 4 hours, and simultaneously perform ultrasonic treatment on the casting. The concentrations of copper chloride, nasturtium orange, and hydrochloric acid are 10 g / L, 1 mmol / L, and 6 mol / L, respectively;

[0150] (5) Take out the casting and soak it repeatedly in deionized water, then immerse it in a mixed solution of 30wt% potassium hydroxide and 10wt% sodium carbonate and boil it for 8 hours. The casting is treated alternately with alkaline and acid solutions until the core is completely removed.

[0151] Comparative Example 12

[0152] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0153] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation casting was performed to obtain a casting;

[0154] (2) immersing the casting in a mixed solution containing 50 wt% potassium hydroxide and 5 wt% sodium carbonate and boiling for 8 h at a natural atmospheric pressure while ultrasonically treating the casting;

[0155] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0156] (4) immersing the casting treated in step (3) in a hydrochloric acid solution containing copper chloride and nasturtium orange, keeping the temperature at 90° C. for 4 hours, and simultaneously performing ultrasonic treatment on the casting; wherein the concentrations of copper chloride, nasturtium orange, and hydrochloric acid are 10 g / L, 1 mmol / L, and 6 mol / L, respectively;

[0157] (5) The casting is taken out and repeatedly soaked in deionized water, and then placed in a mixed solution containing 50wt% potassium hydroxide and 5wt% sodium carbonate and boiled for 8 hours. The casting is alternately treated with alkaline and acid solutions until the core is completely removed.

[0158] Comparative Example 13

[0159] The removal of silicon-based ceramic core for titanium alloy casting comprises the following steps:

[0160] (1) Using the silicon-based ceramic core prepared in Example 2 as a template, titanium alloy simulation casting was performed to obtain a casting;

[0161] (2) immersing the casting in a 50 wt% potassium hydroxide solution and boiling it for 8 h at atmospheric pressure while ultrasonically treating the casting;

[0162] (3) Take out the casting and soak it repeatedly in deionized water to remove the residual alkali solution;

[0163] (4) Immerse the casting in a hydrochloric acid solution containing copper chloride and nasturtium orange, keep it at 90°C for 4 hours, and simultaneously perform ultrasonic treatment on the casting; wherein the concentrations of copper chloride, nasturtium orange, and hydrochloric acid are 10 g / L, 1 mmol / L, and 6 mol / L, respectively.

[0164] (5) The casting is taken out and repeatedly soaked in deionized water, and then placed in a 50wt% potassium hydroxide solution and boiled for 8 hours. The casting is alternately treated with alkaline and acid solutions until the core is completely removed.

[0165] The silicon-based ceramics and titanium alloy casting silicon-based ceramic cores prepared in Examples 1-2 and Comparative Examples 1-8 were tested for their product expansion rate, open porosity, room temperature strength, high temperature strength, and inertness to reaction with titanium alloy. The results are shown in Table 1:

[0166] Table 1

[0167]

[0168]

[0169] As can be seen from Table 1, the simultaneous addition of two mineralizers can significantly improve the room temperature strength, high temperature strength and open porosity of the ceramic core; and when the thickness of the yttrium oxide coating is greater than 100 μm, it can play a good isolation role and prevent the reaction between the silicon-based ceramic core and the titanium alloy.

[0170] The silicon-based ceramic core for titanium alloy casting prepared in Example 2 was removed using the removal methods of Example 3 and Comparative Examples 9-13. The complete removal time of each group was recorded. The results are shown in Table 2:

[0171] Table 2

[0172] Complete core removal time (h) Changes in lye Acid changes Example 3 36 White turbidity Brown turbid solution Comparative Example 9 48 White turbidity Brown turbid solution Comparative Example 10 36 White turbidity Black turbid solution Comparative Example 11 48 White turbidity Brown turbid solution Comparative Example 12 48 White turbidity Brown turbid solution Comparative Example 13 60 White turbidity Brown turbid solution

[0173] As can be seen from Table 2, the ceramic core can be effectively removed by combining alternating high-temperature immersion in alkali and acid solutions with ultrasonic dispersion. Increasing the concentration of potassium hydroxide and adding sodium carbonate can effectively shorten the core removal time. The use of a composite corrosion inhibitor can effectively inhibit the corrosion of titanium alloy by high-concentration hydrochloric acid.

[0174] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0175] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a ceramic core for titanium alloy casting, characterized in that: The following steps are involved: The silicon dioxide, kaolin and calcium hydroxide powders are mixed uniformly to obtain a mixed powder; a binder aqueous solution is then added and mixed uniformly; the green body is pressed and formed to obtain a green body; the green body is dried and sintered to obtain a silicon-based ceramic; and an yttrium oxide coating is sprayed on the surface of the silicon-based ceramic to obtain the ceramic core; The mixed powder is composed of the following components by weight: Silicon dioxide 75-85wt% Kaolin 5-20wt% Calcium hydroxide 5-20wt%; The mass ratio of the mixed powder to the binder is 1:0.01-0.05; Mass ratio of silicon dioxide, kaolin and calcium hydroxide: 17:1:2; The binder is polyvinyl alcohol; The average particle size of the silicon dioxide is 25-40 μm; the average particle size of the kaolin is 0.5-5 μm; the average particle size of the calcium hydroxide is 0.5-2 μm; The sintering temperature is 1250-1450° C.; and the thickness of the coating is greater than 100 μm.

2. The method for preparing a ceramic core for titanium alloy casting according to claim 1, wherein: The heat preservation sintering time is 3-6h.

3. The method for preparing a ceramic core for titanium alloy casting according to claim 1, wherein: The concentration of the binder aqueous solution is 3-10 wt %.

4. The method for preparing a ceramic core for titanium alloy casting according to claim 1, wherein: The solid-to-liquid ratio of the mixed powder to the binder aqueous solution is 15-20 g:1-3 mL.

5. The method for preparing a ceramic core for titanium alloy casting according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Mix silicon dioxide powder, kaolin powder and calcium hydroxide powder evenly and dry them at a temperature of 100-120°C; S2. ball milling the dried powder to obtain a mixed powder; wherein the ball-to-material ratio is 2:1; S3, adding a binder aqueous solution to the mixed powder, mixing evenly and then passing through a 100-mesh sieve; wherein the solid-liquid ratio of the mixed powder to the binder aqueous solution is 15-20 g:1-3 mL; S4, taking the powder under the sieve and placing it in a mold for pressing at a pressure of 3-10 MPa and a holding time of 30-60 s to obtain a green body; S5, fully drying the green body at a temperature of 100-120° C.; S6, placing the dried green body in a muffle furnace and sintering it at a temperature of 1250-1450° C. to obtain the silicon-based ceramic; S7. Spraying an yttrium oxide coating on the surface of the silicon-based ceramic to obtain the ceramic core.

6. A ceramic core obtained by the preparation method according to any one of claims 1 to 5.

7. A method for removing a ceramic core for titanium alloy casting, characterized in that: The following steps are involved: (1) Using the ceramic core as a template to cast titanium alloy to obtain a casting; (2) The casting with the silicon-based ceramic core is placed in a mixed alkali solution and boiled while ultrasonically treating the casting; (3) After cooling, take out the casting and soak it in water to remove the residual alkali solution; (4) immersing the casting treated in step (3) in a hydrochloric acid solution containing a corrosion inhibitor, reacting at a temperature of 80-100° C. while performing ultrasonic treatment; (5) Repeat steps (2) to (4) until the ceramic core is completely removed; Wherein, the mixed alkali solution comprises 30-60wt% potassium hydroxide and 5-15wt% sodium carbonate; The corrosion inhibitor is a mixture of copper salt and tropaeolum; the concentration of the hydrochloric acid solution is ≤6 mol / L.

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