CN101386546B - Self-reacting alumina-base composite ceramic mold core for fine casting and preparation method thereof - Google Patents

Abstract

The invention provides a self-reactive alumina-based composite ceramic core for precision casting and a preparation method thereof. The composite ceramic core is composed of corundum powder and in-situ synthesized aluminum titanate, magnesium dititanate and mullite. The composite ceramic core is made of the following raw materials in weight ratio: 70-85% of corundum powder of different particle sizes, 0-2% of magnesium oxide powder, 8-20% of titanium dioxide powder, 6-10% of kyanite powder, and adding Carbon powder accounting for 1-3% of the total mass of the four raw materials is used as a collapsible agent. The method is prepared by mixing the above-mentioned raw materials, forming them by dry pressing, and firing them at high temperature. Adding other raw materials to the alumina matrix of the present invention, the prepared ceramic core has good high temperature chemical stability and thermal stability; the thermal expansion coefficient is low; the shrinkage rate after sintering is small, and the room temperature and high temperature strength all meet the requirements of the precision casting ceramic core. Require.

Description

Self-reactive alumina-based composite ceramic core for precision casting and preparation method thereof

technical field

The invention relates to the field of refractory ceramic materials, in particular to a ceramic core for precision casting, which is mainly used to form a hollow inner cavity for efficiently cooling hollow blades of a new generation of gas turbines.

Background technique

Modern aero-engines urgently need to improve the working performance of gas turbine engines. The first is to increase the gas temperature of the turbine, which determines the actual increase of the effective power of the power plant. For example, if the gas temperature is increased from 1200°C to 1350°C, the fuel consumption rate can be reduced by 8%. . The new generation of high-efficiency gas turbines has continuously developed hollow blades for high-efficiency cooling. The cooling structure of the blades has evolved from traditional convection, backflow, impingement holes, and film cooling to the current high-efficiency divergent air cooling method. At present, the temperature before the turbine of advanced engines requires It reaches 1757°C.

In addition to being surrounded by molten metal and under harsh working conditions like conventional casting, cores for investment casting also need to withstand the effects of dewaxing and roasting. Therefore, the core should meet the following requirements: high refractoriness, low thermal expansion rate, stable size, sufficient strength, good chemical stability, and easy removal.

Silica-based ceramic cores are mainly used for casting columnar crystal blades with lower pouring temperatures. When the operating temperature is higher than 1550°C (such as single crystal casting), the high-temperature stability of silicon-based ceramic cores decreases, and they are prone to creep deformation, and The active elements (Al, Hf, C) in the alloy are strongly adsorbed on its surface, which limits its application. Alumina (corundum) is an excellent high-temperature solid material with a melting point as high as 2054°C, high strength and good chemical stability. It is a promising ceramic core matrix material. For alumina-based cores, due to the high refractoriness, high chemical stability, and thermal stability of alumina itself, it provides a performance guarantee as a core.

So far, foreign alumina-based ceramic cores have met the conditions of single crystal and eutectic casting. The former Soviet Union has applied alumina ceramic cores to the production of single crystal hollow blades since the 1970s. It is at the forefront of the world in terms of research and application. Although silicon-based ceramic cores are mostly used in the production of directional and single crystal blades in Britain, the United States and other countries, alumina ceramic cores have also been used in complex thin-walled single crystal blades and eutectic blades.

Now there are already some foreign companies specializing in the production of ceramic cores, which can be used for the production of military and civilian products. After decades of development, their core products have formed a professional and large-scale operation. Some related raw and auxiliary materials, equipment and other varieties Complete, high quality and stable performance provide excellent external conditions for the development of ceramic cores. It has a complete set of implementation standards in terms of raw material control, preparation process, testing methods and performance testing. Due to the extensive involvement of computers, the complexity, precision and smoothness of ceramic cores have been greatly improved, and the control of various parameters in the production process is more precise, ensuring high-level commercial production of ceramic cores. At the same time, the application of various auxiliary equipment such as laser core repairing machine has greatly improved the production efficiency and core qualification rate. In my country, the research and development of alumina ceramic cores has just started in recent years. Except for a few aviation factories, most of the precision casting factories are still unable to produce precision castings with complex inner cavities. At the same time, there is no commercialized ceramic core supplier, the production equipment is relatively simple, and the process parameters cannot be accurately controlled. Compared with foreign countries, the gap is obvious.

The emergence of high-efficiency air-cooled blades will make the manufacture of cores a key technology. Compared with traditional blades, high-efficiency air-cooled blades have a more complex cooling structure and thinner blade walls. This will make the manufacturing process of the core more complex, smaller in size and higher in performance requirements. In order to adapt to this change, it is imperative to study composite ceramic cores that can be used in harsher environments. Compared with single-component ceramics, composite ceramics can improve fracture strength, fracture toughness and high temperature resistance, and can reduce sintering temperature and high temperature deflection. The improvement of these properties is very beneficial to ceramic cores with complex and fine structures.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and to provide a self-reactive alumina-based composite ceramic core for precision casting. It has the advantages of high temperature resistance, high temperature chemical stability and phase stability, high dimensional stability, impact resistance and easy removal.

The self-reactive alumina-based composite ceramic core for precision casting of the present invention is composed of corundum powder and in-situ synthesized aluminum titanate, magnesium dititanate and mullite, and the composite ceramic core is composed of the following weight distribution: Raw material ratio: 70-85% corundum powder of different particle sizes, 0-2% magnesium oxide powder, 8-20% titanium dioxide powder, 6-10% kyanite powder, and add 1% of the total mass of the four raw materials ~3% carbon powder as friable agent.

In the above-mentioned self-reactive alumina-based composite ceramic core for precision casting, the weight ratio of coarse grain, medium grain and fine grain in the corundum powder of different particle sizes is: coarse grain: medium grain: fine grain=1:2:1 , the coarse particle size is 200-800 μm, the medium particle size is 7-25 μm, the fine particle size is 0.5-6 μm, and there is corundum micropowder accounting for at least 1wt% of the total corundum powder, and the average particle size is 0.75-3 μm.

The content of alumina in the kyanite powder is greater than 60wt%, the content of _Fe2O3 is less than 1.5wt%, and the content of _{TiO2 is} less than 2wt%, and the refractoriness of the kyanite powder is higher than 1825°C. The raw material requirements of the magnesium oxide powder are as follows: the content of magnesium oxide is greater than 98wt%, the content of alkaline impurities is less than 0.2wt%, and the particle size of the magnesium oxide powder is less than 0.08mm. The raw material requirements of the titanium dioxide powder are as follows: the content of titanium dioxide is greater than 99wt%, the content of alkaline impurities is less than 0.2wt%, and the particle size of the titanium dioxide powder is less than 0.05mm.

The present invention also provides a method for preparing the self-reactive alumina-based composite ceramic core for precision casting, the steps of which are as follows:

(1) The alumina substrates of different particle sizes, i.e. corundum powder, are first mixed evenly, and then mixed with the magnesium oxide powder, kyanite powder, titanium dioxide powder and carbon powder in a mixing machine, and the mixed material is dried press forming;

(2) Place the above-mentioned formed billet in a high-temperature sintering furnace for sintering. The process of heating and heating during sintering is a continuous heating process. Keep warm for 5-10 hours under the range, and then cool with the furnace.

In the above method, in the sintering process of step (2), kyanite powder decomposes to generate mullite and silicon dioxide, and silicon dioxide and corundum micropowder generate mullite by in-situ reaction in the core sintering process; core sintering At this time, the corundum micropowder and titanium dioxide powder and magnesium oxide powder were used to synthesize the second phase of aluminum titanate and magnesium dititanate in situ respectively.

Compared with the prior art, the present invention has the following advantages and effects: the proposed alumina-based composite ceramic core utilizes the high melting point of aluminum titanate, is close to zero expansion coefficient, has low thermal conductivity, and has good thermal shock resistance, etc. The characteristics of the advantages, using the in-situ synthesis process in the core sintering process to synthesize magnesium dititanate with the same crystal form as aluminum titanate, and mullite with excellent high-temperature performance, the two form a solid solution with aluminum titanate to Inhibit the decomposition of aluminum titanate in the temperature domain, and meet the mechanical properties of the composite ceramic core. In the present invention, certain additives are added to the alumina matrix, which can be sintered at a relatively low temperature and obtain a certain strength, and the aluminum titanate and mullite generated by the in-situ reaction can be used to increase the high temperature of the alumina-based composite ceramic core. Thermal shock and high temperature creep properties. The additives added to the alumina matrix in the present invention can reduce the sintering temperature of the ceramic core, and these second phases synthesized in situ during the sintering process can improve the thermal shock resistance and high temperature creep performance of the alumina matrix composite ceramic core wait. The shrinkage rate of the prepared ceramic core is small, and the room temperature and high temperature strength all meet the requirements of the ceramic core for precision casting; the high temperature chemical stability and thermal stability are good; and the thermal expansion coefficient is low. The raw materials in the ratio of raw materials provided by the invention have almost no high-temperature creep after being sintered by a suitable sintering system.

Detailed ways

Below in conjunction with example the present invention will be further described.

Example 1

The in-situ synthetic alumina-based composite ceramic core for precision casting of the present invention is composed of raw material ingredients in weight percent:

85% of corundum powder, 6% of kyanite powder, 1% of magnesium oxide powder, 8% of titanium dioxide powder, plus 2% carbon powder by the mass of the aforementioned raw materials as a collapsible agent.

Among them, the corundum powder is composed of powders with different particle size ratios: coarse grain: medium grain: fine grain = 1:2:1.

Mix corundum powder with different particle size ratios evenly, and then mix them evenly with magnesium oxide powder, titanium dioxide powder, kyanite powder and carbon powder. After pressing and forming, keep it at a temperature of 1350-1550°C for 5-10 hours, and get this product after cooling in the furnace. Invented ceramic core blanks.

Boil the saturated NaOH solution, put the ceramic core in it and cook for 1 to 3 hours, supplemented by high-pressure water flushing, the core collapses.

Example 2

The in-situ synthetic alumina-based composite ceramic core for precision casting of the present invention is composed of raw material ingredients in weight percent:

70% of corundum powder, 10% of kyanite powder, 0% of magnesium oxide powder, 20% of titanium dioxide powder, plus 2% carbon powder by the mass of the aforementioned raw materials as a collapsible agent.

Among them, the corundum powder is composed of powders with different particle size ratios: coarse grain: medium grain: fine grain = 1:2:1.

Mix corundum powder with different particle size ratios evenly, and then mix them evenly with magnesium oxide powder, titanium dioxide powder, kyanite powder and carbon powder. After pressing and forming, keep it at a temperature of 1350-1550°C for 5-10 hours, and get this product after cooling in the furnace. Invented ceramic core blanks.

Boil the saturated NaOH solution, put the ceramic core in it and cook for 1 to 3 hours, supplemented by high-pressure water flushing, the core collapses.

Example 3

The in-situ synthetic alumina-based composite ceramic core for precision casting of the present invention is composed of raw material ingredients in weight percent:

75% of corundum powder, 8% of kyanite powder, 2% of magnesium oxide powder, 15% of titanium dioxide powder, and 2% of the mass of the aforementioned raw materials plus carbon powder as a collapsible agent.

Among them, the corundum powder is composed of powders with different particle size ratios: coarse grain: medium grain: fine grain = 1:2:1.

Mix corundum powder with different particle size ratios evenly, and then mix them evenly with magnesium oxide powder, titanium dioxide powder, kyanite powder and carbon powder. After pressing and forming, keep it at a temperature of 1350-1550°C for 5-10 hours, and get this product after cooling in the furnace. Invented ceramic core blanks.

Boil the saturated NaOH solution, put the ceramic core in it and cook for 1 to 3 hours, supplemented by high-pressure water flushing, the core collapses.

Example 4

The in-situ synthetic alumina-based composite ceramic core for precision casting of the present invention is composed of raw material ingredients in weight percent:

83.6% of corundum powder, 7.6% of kyanite powder, 0% of magnesium oxide powder, 8.8% of titanium dioxide powder, plus 2% carbon powder by mass of the aforementioned raw materials as a collapsible agent.

Among them, the corundum powder is composed of powders with different particle size ratios: coarse grain: medium grain: fine grain = 1:2:1.

Mix corundum powder with different particle size ratios evenly, and then mix them evenly with magnesium oxide powder, titanium dioxide powder, kyanite powder and carbon powder. After pressing and forming, keep it at a temperature of 1350-1550°C for 5-10 hours, and get this product after cooling in the furnace. Invented ceramic core blanks.

Boil the saturated NaOH solution, put the ceramic core in it and cook for 1 to 3 hours, supplemented by high-pressure water flushing, the core collapses.

Example 5

The in-situ synthetic alumina-based composite ceramic core for precision casting of the present invention is composed of raw material ingredients in weight percent:

73.6% of corundum powder, 7.6% of kyanite powder, 2% of magnesium oxide powder, 16.8% of titanium dioxide powder, plus 2% carbon powder of the aforementioned raw material mass as a collapsible agent.

Among them, the corundum powder is composed of powders with different particle size ratios: coarse grain: medium grain: fine grain = 1:2:1.

Mix corundum powder with different particle size ratios evenly, and then mix them evenly with magnesium oxide powder, titanium dioxide powder, kyanite powder and carbon powder. After pressing and forming, keep it at a temperature of 1350-1550°C for 5-10 hours, and get this product after cooling in the furnace. Invented ceramic core blanks.

Boil the saturated NaOH solution, put the ceramic core in it and cook for 1 to 3 hours, supplemented by high-pressure water flushing, the core collapses.

Claims (2)

1. Self-reactive alumina-based composite ceramic core for precision casting, characterized in that: the composite ceramic core is composed of corundum powder and in-situ synthesized aluminum titanate, magnesium dititanate and mullite, the composite The ceramic core is made of the following raw materials in the weight ratio: 70-85% of corundum powder of different particle sizes, 0-2% of magnesium oxide powder, 8-20% of titanium dioxide powder, 6-10% of kyanite powder, and adding 1-3% carbon powder of the total mass of the four raw materials is used as a collapsible agent, the weight ratio of the magnesium oxide powder is not 0; the weight ratio of coarse, medium and fine particles in the corundum powder of different particle sizes It is: coarse grain: medium grain: fine grain = 1:2:1, the grain size of the coarse grain is 200-800 μm, the grain size of the medium grain is 7-25 μm, and the grain size of the fine grain is 0.5-6 μm, and at least there are 1wt% corundum powder, the average particle size is 0.75-3μm; the alumina content in the kyanite powder is greater than 60wt%, the _Fe2O3 content is less than 1.5wt% _, and the _TiO2 content is less than 2wt%. The refractoriness is higher than 1825°C; the raw material requirements of the magnesium oxide powder are: the magnesium oxide content is greater than 98wt%, the alkali impurity content is less than 0.2wt%, and the particle size of the magnesium oxide powder is less than 0.08mm; the raw material requirements of the titanium dioxide powder It is: the content of titanium dioxide is greater than 99wt%, the content of alkaline impurities is less than 0.2wt%, and the particle size of titanium dioxide powder is less than 0.05mm; the composite ceramic core is made by the following steps: (1) First mix the corundum powders with different particle sizes evenly, then add them together with the magnesium oxide powder, kyanite powder, titanium dioxide powder and carbon powder to mix in the mixing machine, and the mixed material is formed by dry pressing; (2) Place the above-mentioned formed billet in a high-temperature sintering furnace for sintering. The process of heating and heating during sintering is a continuous heating process. Keep warm for 5-10 hours under the range, and then cool with the furnace. 2. the preparation method of self-reactive alumina-based composite ceramic core for precision casting as claimed in claim 1, is characterized in that comprising the steps: (1) First mix the corundum powders with different particle sizes evenly, then add them together with the magnesium oxide powder, kyanite powder, titanium dioxide powder and carbon powder to mix in the mixing machine, and the mixed material is formed by dry pressing; (2) Place the above-mentioned formed billet in a high-temperature sintering furnace for sintering. The process of heating and heating during sintering is a continuous heating process. Keep warm for 5-10 hours under the range, and then cool with the furnace.