Method for solving expansion cracking of ceramic and refractory metal composite core

Abstract

The invention belongs to the field of mold cores for aerospace, electronic information, precision investment casting and the like, and particularly relates to a method for solving expansion cracking of a ceramic and refractory metal composite mold core. The method comprises the following steps: (1) calculating according to thermal expansion coefficients of selected refractory metal and a ceramic core ceramic material, and reducing the size of a refractory metal core in equal proportion; (2) the outer surface of the refractory metal mold core is evenly coated with a solid higher alkane substance to prepare a buffer layer, and coating is conducted 1-3 times; (3) the refractory metal mold core is placed at the connecting part of the blade ceramic mold core or the part where the special-shaped hole needs to be reserved; and in the subsequent heating process, the buffer layer is heated, melted and decomposed, and a volume expansion space is provided for the refractory metal mold core. According to the invention, the problem of expansion cracking of the ceramic and refractory metal composite core caused by the expansion coefficient difference between the refractory metal core and the ceramic core is solved, the yield is improved, and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of cores used in aerospace, electronic information, and precision investment casting, and specifically provides a method for solving the expansion cracking of composite cores made of ceramics and refractory metals. Background Technology

[0002] With the development of the aviation industry, the requirements for engine turbine blades are becoming increasingly stringent. Generally, alumina-fired ceramic rods are used as connecting or pre-drilled parts at the ceramic core connection points or where pre-drilled holes are required. In the later stages of the process, the ceramic rods need to be removed. However, due to the high-temperature processing involved in the process, some ceramic rods adhere to the substrate. When removing the ceramic rods, they may break and become impossible to remove, resulting in the scrapping of the workpiece.

[0003] Refractory metal cores are made by preparing a complete protective coating on the surface of the refractory metal to resist ablation and melting during the casting process. In subsequent processes, the integrity of the coating is destroyed by chemical methods. During the heat treatment stage, without the protection of the coating, the refractory metal (taking molybdenum as an example) is heated in air. When the temperature rises to 520°C, the molybdenum begins to be slowly oxidized to form Mo2O3. When the temperature rises above 600°C, the molybdenum is rapidly oxidized to MoO3. MoO3 has a melting point of 795°C, but it will undergo significant sublimation below the melting point. Therefore, the refractory metal molybdenum core can be completely removed through the above series of reactions.

[0004] However, due to the different coefficients of thermal expansion between metal and ceramic materials, the ceramic core may crack during the core heat treatment process due to the volume expansion of the refractory metal core, resulting in core scrap. Therefore, a method is needed to solve the problem of expansion cracking of ceramic-refractory metal composite cores caused by the volume expansion of the refractory metal core, in order to improve the yield of ceramic-refractory metal composite cores. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for solving the expansion cracking of ceramic and refractory metal composite cores, thereby solving the problem of cracking of ceramic and refractory metal composite cores caused by the difference in expansion coefficients between refractory metal cores and ceramic cores, and improving the yield of ceramic and refractory metal composite cores.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for solving the expansion cracking of ceramic-refractory metal composite cores includes the following steps:

[0008] (1) Based on the thermal expansion coefficients of the selected refractory metal and ceramic core materials, the size of the refractory metal core is reduced proportionally.

[0009] (2) On the outer surface of the refractory metal core, evenly coat a solid high-level alkane material to prepare a buffer layer, and coat 1-3 times;

[0010] (3) Place the refractory metal core at the connecting part of the blade ceramic core or the part where a special-shaped hole needs to be reserved; in the subsequent heating process, the buffer layer is heated, melted and decomposed to provide a volume expansion space for the refractory metal core.

[0011] In the method for solving the expansion cracking of the ceramic and refractory metal composite core, in step (2), the refractory metal core is placed in a container containing ethanol and ultrasonically cleaned for 20-30 seconds; after draining the ethanol, the refractory metal core is dried with a hair dryer for use.

[0012] In the method for solving the expansion cracking of the ceramic and refractory metal composite core, in step (2), the material of the buffer layer is paraffin or rosin.

[0013] In the method for solving the expansion cracking of the ceramic and refractory metal composite core, in step (2), the buffer layer material is placed in a metal container and heated to melting in an oven to form a buffer solution; the refractory metal core is immersed in the molten buffer solution for 1-5 seconds and taken out to wait for cooling and setting to form a buffer layer.

[0014] In the method for solving the expansion cracking of the ceramic and refractory metal composite core, in step (2), the thickness of the buffer layer is 0.01mm-1mm.

[0015] The design idea of the present application is to use a solid high-level alkane material as a buffer layer, and use the characteristics of the solid high-level alkane material that melts and decomposes under heat to provide a buffer space between different thermal expansion coefficient material combinations; and solve the damage of the volume expansion of the material with a large thermal expansion coefficient to the material with a small thermal expansion coefficient under high temperature.

[0016] Compared with the prior art, the method for solving the expansion cracking of the ceramic and refractory metal composite core has the following advantages and beneficial effects:

[0017] The present application uses a solid high-level alkane material such as paraffin to prepare a buffer layer, and the buffer layer is decomposed under heat in the subsequent core heat treatment process to provide a volume expansion space for the refractory metal core, solving the problem of ceramic core cracking caused by the volume expansion of the refractory metal core. The process and method provided by the present application are simple and easy to implement, and can also be popularized to the production of other types of products, with a broad prospect. DETAILED DESCRIPTION

[0018] In the implementation process, the application provides a method for solving the expansion cracking of a ceramic and refractory metal composite core, which comprises the following steps in sequence: firstly, proportionally reducing the size of the refractory metal core; then uniformly coating a paraffin or rosin or other solid high-level alkane material on the outer surface of the refractory metal core to prepare a buffer layer; then placing the refractory metal core at the connecting part of the blade ceramic core or the part where a special-shaped hole needs to be reserved; in the subsequent heating process, the paraffin layer or the rosin layer is melted and decomposed by heat, thereby providing a space for the volume expansion of the refractory metal core.

[0019] The application will be further described below in combination with the following examples.

[0020] Example 1

[0021] In this example, a method for solving the expansion cracking of a ceramic and refractory metal composite core comprises the following steps:

[0022] (1) cleaning the refractory metal core: 50 refractory metal molybdenum cores with an aluminum oxide coating, a diameter of 1 mm and a length of 15 mm are placed in a container containing ethanol for ultrasonic cleaning for 15 seconds; after draining the ethanol, the refractory metal molybdenum cores are dried with a hair dryer for standby use.

[0023] (2) placing the paraffin in a metal container and placing it in an oven at 60℃ to melt.

[0024] (3) coating the paraffin buffer layer:

[0025] Firstly, the cleaned refractory metal molybdenum cores are loaded into a special tool; then the refractory metal molybdenum cores are immersed in the molten paraffin liquid for 1 time, the time is 3 seconds, and the refractory metal molybdenum cores are taken out to wait for cooling and setting, the thickness of the paraffin layer is 0.1 mm; finally, the refractory metal cores are placed at the connecting part of the blade ceramic core and the part where a special-shaped hole needs to be reserved, and the ceramic and refractory metal composite core is prepared, and finally 50 pieces of ceramic and refractory metal composite cores are prepared;

[0026] (4) appearance inspection of the ceramic core: 50 pieces of ceramic and refractory metal composite cores are inspected, and no cracking phenomenon occurs in the final inspection.

[0027] Example 2

[0028] In this example, a method for solving the expansion cracking of a ceramic and refractory metal composite core comprises the following steps:

[0029] (1) cleaning the refractory metal core: 50 refractory metal molybdenum cores with an aluminum oxide coating, a diameter of 1 mm and a length of 15 mm are placed in a container containing ethanol for ultrasonic cleaning for 15 seconds; after draining the ethanol, the refractory metal molybdenum cores are dried with a hair dryer for standby use.

[0030] (2) Put the rosin into a metal container, and put into an oven at 120℃ to heat to melt.

[0031] (3) Coating rosin buffer layer:

[0032] First, the cleaned refractory metal molybdenum core is loaded into a special tool; then the refractory metal molybdenum core is immersed in the molten rosin liquid for 2 times, each time for 3 seconds, and taken out to wait for cooling and setting, the thickness of the rosin layer is 0.1mm; finally, the refractory metal core is placed at the connecting part of the blade ceramic core and the part where the special-shaped hole needs to be reserved, and the ceramic and refractory metal composite core is prepared, and finally 50 pieces of ceramic and metal composite cores are prepared;

[0033] (4) Appearance inspection of ceramic core: 50 pieces of ceramic and metal composite cores are inspected, and no cracking phenomenon appears in the final inspection.

[0034] The implementation results show that the application solves the problem of expansion cracking of the ceramic and refractory metal composite core caused by the difference in expansion coefficient between the refractory metal core and the ceramic core, improves the yield, and reduces the production cost.

[0035] The above examples are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and essence of the application shall be covered within the protection scope of the application.

Claims

1. A method of solving the expansion cracking of a ceramic and refractory metal composite core, characterized by, The method comprises the following steps: (1) according to the thermal expansion coefficient of the selected refractory metal and ceramic core ceramic material, the size of the refractory metal core is proportionally reduced; (2) a buffer layer is coated on the outer surface of the refractory metal core by uniformly coating solid high-level alkane material, and the coating is performed 1-3 times; (3) the refractory metal core is placed at the connecting part of the blade ceramic core or the part where a special-shaped hole needs to be reserved; in the subsequent heating process, the buffer layer is melted and decomposed by heat, thereby providing a space for the volume expansion of the refractory metal core.

2. The method of solving the expansion cracking of the ceramic and refractory metal composite core according to claim 1, characterized in that, In step (2), the refractory metal core is cleaned, and the refractory metal core is placed in a container containing ethanol and ultrasonically cleaned for 20-30 seconds; after the ethanol is drained, the refractory metal core is dried with a hair dryer for standby.

3. The method of claim 2, wherein the ceramic and refractory metal composite core is formed by, In step (2), the material of the buffer layer is paraffin or rosin.

4. The method of claim 3, wherein the ceramic and refractory metal composite core is formed by, In step (2), the buffer layer material is placed in a metal container and heated to melting in an oven to form a buffer solution; the refractory metal core is immersed in the molten buffer solution for 1-5 seconds, and then taken out to wait for cooling and setting to form a buffer layer.

5. The method for solving the expansion cracking of the ceramic and refractory metal composite core according to claim 1 or 4, characterized in that, In step (2), the thickness of the buffer layer is 0.01mm-1mm.