Those in the aviation industry should be aware that the repair of hot-end components of aero-engines is extremely important. As for ceramic matrix composites, what are the technological characteristics of the repair of the hot end parts of the engine? Let's find out together!

As the heart of the aircraft, the function of the engine will directly affect the various policies of the aircraft function, and one of the parameters that can best reflect the function of the engine is the thrust-to-weight ratio. The goal of modern aero-engines is to continuously improve the thrust-to-weight ratio. The continuous increase of the thrust-to-weight ratio will inevitably lead to a further increase in the temperature before the turbine of the modern high-performance gas turbine engine. The turbine inlet temperature of the existing engine with a thrust-to-weight ratio of 10 grades has reached 1 800~2 000K, while the turbine inlet temperature of an engine with a thrust-to-weight ratio of 15~20 grades will reach 2 100~2 400K, which far exceeds the high temperature alloy materials in the engine. melting point temperature. At present, the materials of the engine hot-end parts with sophisticated technology can only meet the design requirements of the first-stage engine with a thrust-to-weight ratio of 10. To develop advanced aero-engines with higher thrust, it is necessary to conduct research on the design technology of new high-temperature resistant materials. At the same time, it is necessary to deal with a series of problems of light structure, strong durability and high reliability of aero-engines, which requires the use of new materials and process skills, especially on the hot-end components of aero-engines. Now, the technology of ceramic matrix composite materials with better high temperature resistance has become a developing trend in the manufacture of aero-engines. How to use ceramic matrix composites (CMC) to improve the structural performance of aero-engines and reduce costs is one of the primary technical problems faced by aero-engine manufacturing. The application of ceramic matrix composites in aero-engine hot-end components is more common in foreign reports. Some materials show that after the introduction of ceramic matrix composite materials in aero-engine hot-end components, the hot-end components can be operated in a high-temperature environment, and the flow rate of engine cooling gas can be reduced by 15% to 25%, which can effectively improve engine power. Although the research on ceramic matrix composites in China has achieved certain results, the research on the application of aero-engine hot-end components has just started and has not entered the engineering application stage.

1. Introduction to ceramic matrix composites

The ceramic matrix composite material is the introduction of the second phase material in the ceramic matrix to form a multi-phase composite material. Ceramics have the advantages of high temperature resistance, oxidation resistance, wear resistance, corrosion resistance, etc., but they have poor resistance and are difficult to process. Ceramic matrix composite material is an ultra-high temperature composite material, the operating temperature is as high as 1 650 ℃, under non-cooling conditions, it can work in an environment higher than 1 200 ℃ and has a high strength retention rate. Ceramic matrix composites have the characteristics of light weight, high modulus, high tensile strength, good vibration absorption, good temperature resistance, low cost and not easy to be damaged by fatigue. The density is only 1/4~1/3 of nickel-based alloys. And as the temperature increases, the strength does not decrease, even higher than at room temperature. Adding fibers to ceramics can greatly improve strength, improve brittleness, and increase application temperature. Continuous fiber toughened ceramic matrix composites have cracking behavior similar to metals, and are not sensitive to cracks, and overcome the fatal weaknesses of common ceramic materials such as brittleness and poor reliability. At present, the most widely used ceramic matrix composites are mainly carbon fiber toughened silicon carbide (Cf/SiC) and silicon carbide fiber toughened silicon carbide (SiCf/SiC). 2], SiCf/SiC is 1 450 ℃, these two materials have excellent functions such as high temperature strength, light weight, good corrosion resistance and wear resistance, and their high temperature ability will improve engine performance, thrust-to-weight ratio and fuel consumption rate. , which can be used in the production of long-life aero-engines. The structural design of the ceramic matrix composite reinforced turbine disk takes advantage of the low density of the ceramic matrix composite material, which can reduce the weight of the turbine disk. The density of SiC type is 2.0~2.5g/cm3, which is only 1/4~1/3 of superalloy and niobium alloy, and 1/10~1/9 of tungsten alloy. The key technologies for the use of ceramic matrix composites in engine hot-end components are: advanced silicon carbide fibers with high temperature stability, new fiber coatings, manufacturing processes to produce high-density composites, and environmental coatings that avoid functional degradation.

2. Process characteristics

Ceramic materials have excellent properties such as high hardness, high temperature resistance, and chemical corrosion resistance, but their brittleness and strong defect sensitivity limit their application in the field of thermal structural materials. Therefore, the focus of research on ceramic materials is how to overcome brittleness. There are many ways to improve the brittleness of ceramic materials, including continuous fiber toughening, phase transformation toughening, microcrack toughening, and whisker wafer toughening. Among them, the effect of continuous fiber toughening is remarkable, and it has been vigorously developed. Continuous fiber toughened silicon carbide matrix composites are the most studied ceramic matrix composites. The ceramic matrix composites used in aero-engine hot-end components are generally silicon carbide fiber-reinforced silicon carbide-based materials. Compared with conventional nickel-based alloys, its density is only 1/4~1/3 of the latter, and the acceptable temperature is 110~220℃ higher. The preparation process includes chemical vapor infiltration (CVI), precursor conversion (PIP), reactive melt sintering (RMI), reactive sintering (RB), and sol-gel (Sol-gel). The study showed that the final performance of the material depends largely on the level of preparation technology. In the long-term research and exploration process, it gradually tends to modern preparation methods represented by CVI and PIP processes.