阅读说明：本技术 一种锅炉受热面用层间冶金结合热喷涂涂层及制备方法 (Interlayer metallurgical bonding thermal spraying coating for boiler heating surface and preparation method ) 是由 李玉敏 刘立营 李太江 李巍 于 2019-10-09 设计创作，主要内容包括：一种锅炉受热面用层间冶金结合热喷涂涂层及制备方法,所述层间冶金结合热喷涂涂层的涂层材料为镍基自熔合金粉末,粉末粒径40-50微米；采用内送粉等离子喷涂方法,送粉位置距离喷枪出口15-25mm；通过控制送粉位置实现熔融液滴的过热,从而达到热喷涂涂层层间冶金结合；通过低熔点镍基自熔合金粉末的选择和控制粉末进入喷枪的位置,实现熔融液滴的过热的方式,获得了层间冶金结合、致密、基本无常规热喷涂涂层结构缺陷的热喷涂涂层。(a hot spraying coating for the interlayer metallurgical bonding of a boiler heating surface and a preparation method thereof are disclosed, wherein the coating material of the hot spraying coating for the interlayer metallurgical bonding is nickel-based self-fluxing alloy powder, and the particle size of the powder is 40-50 microns; adopting an internal powder feeding plasma spraying method, wherein the distance between the powder feeding position and the outlet of the spray gun is 15-25 mm; the overheating of the molten liquid drop is realized by controlling the powder feeding position, so that the interlayer metallurgical bonding of the thermal spraying coating is realized; the hot spraying coating which is interlaminar metallurgic bonded, compact and basically free of structural defects of the conventional hot spraying coating is obtained in a mode of overheating molten liquid drops by selecting low-melting-point nickel-based self-fluxing alloy powder and controlling the position of the powder entering a spray gun.)

1. The utility model provides a metallurgical bonding hot spraying coating between layer for boiler heating surface which characterized in that: the coating material of the interlayer metallurgical bonding thermal spraying coating is nickel-based self-fluxing alloy powder, and the particle size of the powder is 40-50 microns; the thickness of the interlayer metallurgical bonding thermal spraying coating reaches 1mm, and the interior of the coating is in metallurgical bonding.

2. the interlaminar metallurgical bonding thermal spray coating for the heating surface of the boiler as claimed in claim 1, characterized in that: the thermal spraying method of the interlayer metallurgical bonding thermal spraying coating is inner hole powder feeding atmospheric plasma spraying, wherein the plasma spray gun adopts an inner hole spray gun with an extended working section, the distance between the powder feeding position and the outlet of the spray gun is 15-25mm, and the overheating of molten liquid drops is realized by controlling the powder feeding position, so that the interlayer metallurgical bonding of the thermal spraying coating is realized, and a compact thermal spraying coating is formed.

3. The method for preparing the interlayer metallurgical bonding thermal spraying coating for the boiler heating surface, which is disclosed by claim 1 or 2, comprises the following steps of:

Step 1: drying the nickel-based self-fluxing alloy powder to be sprayed at a low temperature of not higher than 150 ℃;

step 2: spraying an anti-corrosion coating by using inner hole powder feeding atmospheric plasma spraying equipment, wherein a plasma spray gun of the inner hole powder feeding atmospheric plasma spraying equipment adopts an inner hole spray gun with an extended working section, and the distance between the powder feeding position and the spray gun outlet is 15-25 mm; the spraying process parameters are as follows: the current is 450-550A, the voltage is 65-75V, the Ar gas flow is 60-100 L.min < -1 >, the H2 gas flow is 7-15 L.min < -1 >, and the spraying distance is 120-130 mm; the spraying is carried out in multiple passes to the desired thickness.

Technical Field

The invention relates to a coating for improving interlayer metallurgical bonding of the coating and a preparation method thereof, in particular to an interlayer metallurgical bonding thermal spraying coating for a boiler heating surface and a preparation method thereof.

Background

The burst problem of four boiler tubes (water wall tubes, economizer tubes, superheater tubes and reheater tubes) is one of the main reasons influencing the safety and stable power generation of a power plant and causing huge economic loss. The reduction of the tube wall caused by the complicated corrosion atmosphere corrosion inside the hearth is the main reason for the four tubes of the boiler to burst. Particularly, along with the development of power station boilers to high parameters, large capacity and high environmental protection and the increasingly strict national requirement on ultralow emission of coal-fired units, low NOx burners and corresponding combustion technologies are increasingly used in power station boilers in China. The lack of oxygen in the primary combustion zone from low NOx combustion makes this type of corrosion increasingly more prevalent.

The thermal spraying technology is widely used for on-site corrosion protection of four pipes of a boiler due to the advantages of light equipment, flexible process, strong adaptability and the like. However, thermal spray coatings are not completely impervious to corrosive media (atmospheres, molten salts) due to their inherent coating microstructure, i.e., the presence of a large number of unbonded areas, cracks, pores, etc. in the coating. As the operating time progresses, the corrosive medium can directly pass through the alloy coating to reach the four tubes of the boiler along the microscopic defects (unbonded areas, cracks, pores, etc.) in the coating, and the corrosion propagates under the layer of the alloy coating, so that the alloy coating loses adhesion to fall off, and the protective effect is lost.

Therefore, with the use of low NOx burners and corresponding combustion technologies in power station boilers in China, the corrosion conditions of four tubes of the boiler are increasingly severe. A more compact protective layer with better corrosion resistance and a preparation method thereof are needed.

Disclosure of Invention

In view of the defects of the microstructure of the coating prepared by the existing thermal spraying technology, the invention aims to provide the interlaminar metallurgical bonding thermal spraying coating for the heating surface of the boiler and the preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

the interlayer metallurgical bonding thermal spraying coating for the heating surface of the boiler is prepared from nickel-based self-fluxing alloy powder, wherein the particle size of the powder is narrower than that of conventional plasma spraying powder, and is 40-50 microns; the thickness of the interlayer metallurgical bonding thermal spraying coating reaches 1mm, and the interior of the coating is in metallurgical bonding.

the thermal spraying method of the interlayer metallurgical bonding thermal spraying coating is inner hole powder feeding atmospheric plasma spraying, wherein the plasma spray gun is an improved inner hole spray gun, the working section of the spray gun is prolonged, the distance between the powder feeding position and the outlet of the spray gun is 15-25mm, and the overheating of molten liquid drops is realized by controlling the powder feeding position, so that interlayer metallurgical bonding of the thermal spraying coating is realized, and a compact thermal spraying coating is formed.

The preparation method of the interlayer metallurgical bonding thermal spraying coating for the heating surface of the boiler comprises the following steps:

step 1: drying the nickel-based self-fluxing alloy powder to be sprayed at a low temperature of not higher than 150 ℃;

Step 2: spraying an anti-corrosion coating by using inner hole powder feeding atmospheric plasma spraying equipment, wherein a plasma spray gun of the inner hole powder feeding atmospheric plasma spraying equipment adopts an inner hole spray gun with an extended working section, and the distance between the powder feeding position and the spray gun outlet is 15-25 mm; the spraying process parameters are as follows: the current is 450-550A, the voltage is 65-75V, the Ar gas flow is 60-100 L.min < -1 >, the H2 gas flow is 7-15 L.min < -1 >, and the spraying distance is 120-130 mm; the spraying is carried out in multiple passes to the desired thickness.

The layered structure (the interlayer is a combination area, cracks, pores and the like) is a typical microstructure of the thermal spraying coating, the typical microstructure (not compact) causes the coating to be limited in application, and particularly, the protective effect on corrosive media with penetrating characteristics such as atmosphere and molten salt is poor, and how to improve the compactness of the coating is a big difficulty.

Compared with pure nickel and the like, the nickel-based self-fluxing alloy has a lower melting point, and is more beneficial to heat absorption and melting of powder in a thermal spraying process to form liquid drops. The narrow powder particle size range is selected, the uniformity of the size of the liquid drops can be ensured, the overheating temperature of the liquid drops can be controlled more conveniently, and the heat transmission of the deposited and solidified liquid drops is ensured, so that the surface of the deposited and solidified liquid drops is secondarily melted, and the metallurgical bonding among the liquid drops is formed.

the adoption of the atmospheric plasma spraying process (the temperature of the center of the plasma is over ten thousand degrees) can ensure that the powder particles are fully melted. By adopting an internal powder feeding method, the residence time of the molten liquid drop in a high-temperature section can be prolonged by controlling the internal powder feeding position, for example, the working section of the spray gun is prolonged, and the distance between the powder feeding position and the outlet of the spray gun is 15-25mm, so that the molten liquid drop is overheated, the high overheating temperature can ensure that the overheated liquid drop secondarily melts the surface of the deposited solidified liquid drop to a certain depth, thereby forming metallurgical bonding between the liquid drop and the liquid drop, and finally forming the thermal spraying coating with internal metallurgical bonding along with the continuous accumulation of the liquid drop.

The invention achieves the metallurgical bonding between the liquid drop interlayers by selecting the low-melting-point nickel-based powder and controlling the melting overheating degree of the powder, thereby obtaining the compact thermal spraying coating which basically does not have the structural defects of the conventional thermal spraying coating. Compared with the nickel-based thermal spraying coating prepared by the conventional method, the nickel-based thermal spraying coating prepared by the invention with interlayer metallurgical bonding has the advantage that the high-temperature corrosion resistance is improved by more than 3 times.

The invention has the following advantages:

1) By adopting the preparation method of the thermal spraying coating with the interlayer metallurgical bonding, the thermal spraying coating which is compact and basically free of microstructure defects of the conventional thermal spraying coating is prepared, the service life of the thermal spraying coating in penetrating corrosive media such as atmosphere and molten salt is greatly prolonged, and the application range of the thermal spraying coating is expanded;

2) The invention adopts the atmospheric plasma spraying equipment, can realize the overheating of liquid drops only by reasonably controlling the inner powder feeding position, thereby achieving the aim of metallurgical bonding between coating layers, and has simple operation and no limitation of construction places, positions and the like.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments.