Analysis of corrosion resistance and wear resistance of plasma sprayed nickel based abrasive seal coating

Product introduction

The rapid development of the modern aviation industry has a major impact on the performance of aircraft engines Increasingly stricter requirements are being set. High thrust, high efficiency and low fuel consumption have become the basic goals of engine design and manufacturing. To this end, the temperature of the engine inlet gas must be increased as much as possible and the gap between the rotor and stator components must be reduced. With abradable seal coating technology, a coating is applied to the inner surface of the compressor or casing by means of thermal spraying. When the blade rotates at a high speed of 3000-10000 rpm, the tip of the blade scrapes the sealing layer. Grooves are formed on the blade without damaging the blade tip, so that the ideal minimum airflow gap between the blade tip and the housing can be obtained, whichby greatly improving engine efficiency and reducing fuel consumption. The wear-resistant sealing coating has a simple production process, easy repair and performance adjustment, and good sealing effect. At the same time, it can protect the housing from heat insulation and reduce instability such as failures or surges caused by high temperature and high speed gas. Developed quickly.

Sandable sealant coatings are usually composite materials, usually composed of metal phase, non-metal phase and pores. Among them, the metal phase is the matrix phase, which has good strength, corrosion resistance and oxidation resistance. Commonly used metals are nickel, cobalt, copper, aluminum, etc. and their alloys. Non-metallic phases provide anti-friction and self-lubricating functions, such as graphite, hexagonal boron nitride, polyphenylene and diatomaceous earth, etc. Porosity can affect the hardness of the coatingReduce. The characteristics of this type of coating are that it must have good self-lubricating properties and wear resistance on the one hand, and it is required that the friction force of the tip of the sealing counterpart is small when scraping the coating, to ensure that the counterpart is not scratched ; on the other hand, it must be It has a certain hardness and good anti-erosion performance to resist the erosion and wear of high-speed airflow (the airflow is usually mixed with some solid particles) in the crevice flow channel. Therefore, the sandable performance and erosion resistance of the sandable seal coating are contradictory. Only by considering the coating\'s specific service environment and conducting extensive and systematic research and analysis in material structure design, preparation process optimization and performance evaluation, can we find the right point of alignment to ensure that thecoating is easy to sand. It also has sufficient anti-erosion performance and service life.

It is especially worth noting that the carrier-based aircraft that often serve under the harsh conditions of high humidity and high salt spray are prone to corrosion of engine parts, the corrosion failure is another major failure mode of the wear-resistant sealing coating. During this corrosion process, due to the pores in the Ni/graphite coating, the corrosive medium penetrates through the pore channels, gradually causing problems in the exchange of solutions inside and outside the coating, forming macroscopic corrosion cells on the surface and the inside of the coating, and accelerating the corrosion process of the coating. Corrosion of the internal metal phaseEclipse [5]. In addition, corrosive chloride ions in salt spray can also seriously damage the sealing layer. In additionn Structural defects, such as pores and cracks in the coating, provide rapid penetration channels for corrosive media, which cause crevice corrosion or pitting corrosion inside. to threaten.

While preparing sealing coating by traditional plasma spraying, due to the low flight speed of raw powder particles in the plasma jet, smoothing effect is relatively low weak, resulting in a loose coating structure, high porosity and low bond strength. Therefore, basic research should be conducted from the aspects of coating preparation process and structural design optimization to fundamentally improve the corrosion resistance of seal coatings. The Latest Domestic Development Of High Efficiency Supersonic Plasma Spraying (High Efficiency Supersonic Plasma Spraying)uses a jet acceleration scheme based primarily on mechanical compression and supplemented by pneumatic compression. A supersonic plasma jet that can reach twice the speed of sound and reach the flying speed of particles in the jet more than double that of traditional plasma spraying. Due to the increase in flight speed, the kinetic energy of the particles when they hit the substrate increases, the energy conversion efficiency is high, the droplet is completely dispersed, the content of defects such as pores in the coating is reduced, and the bonding strength is greatly improved. At the same time, the supersonic flight of the particles can shorten their residence time in the jet, effectively reducing the oxidation of the metal phase in the sealing coating and the combustion loss of the lubricating phase such as graphite. But until now, this type of spraying equipment has not been widely used in the preparation of wear resistantto sealing coatings.

Depending on the internal working conditions of the aircraft engine, medium and low temperature abrasive seal coating materials are mainly used in the engine fan and compressor parts and the materials used if metal components are used, mainly include aluminum-silicon alloys and nickel-based alloys. The nickel-based sealing coating can ensure the erosion resistance and strength of the coating in high-temperature environments, so that it is well applicable in high-temperature parts, such as high-pressure compressors. Therefore, in this study, domestic high-efficiency supersonic plasma spraying was used to deposit nickel-based (including nickel-graphite and nickel-chrome-aluminium-boron nitride) abrasive seal coatings, and the corrosion resistance and high-temperature friction and wear properties of the coatings weresystematically compared. To improve the comprehensive performance of the coating, it provides a reference for the preparation of high-quality sealing coating.

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