Preparation method of high-hardness high-temperature steam oxidation-resistant composite structure coating

Abstract

The application relates to a preparation method of a high-hardness high-temperature steam oxidation-resistant composite structure coating, which comprises the following steps: S1, pretreating the surface of a workpiece needing to prepare a coating; S2, preparing an aluminum-containing nickel-based or aluminum-containing cobalt-based metal primer layer with a thickness of 80-150 microns on the surface of the workpiece; and S3, selecting a suspension liquid with a certain proportion and content of yttrium silicate, alumina micropowder and an organic solvent as raw materials, and preparing a ceramic top layer with a thickness of 100-350 microns on the surface of the primer layer by adopting an atmospheric plasma spraying technology in an external powder feeding mode. The preparation method can regulate the wear resistance of the coating, meanwhile, the cracking and peeling phenomena caused by thermal stress during the heating and cooling processes of the coating can be avoided, and the long-acting high-temperature steam corrosion resistance of the coating can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material engineering, and particularly relates to a preparation method of a high-hardness high-temperature steam oxidation-resistant composite structure coating. BACKGROUND

[0002] Increasing the steam temperature or steam pressure can effectively improve the power generation efficiency of a steam turbine unit. Compared with subcritical and supercritical power generation technologies, the ultra-supercritical power generation technology is an advanced and efficient power generation technology, and the steam temperature is as high as 600 DEG C or higher, which is about 4% higher than the thermal efficiency of a supercritical unit, and the advantages are more obvious. The significant increase in steam temperature not only can improve the economic value, but also can reduce the coal consumption and reduce the carbon dioxide emission, which has important ecological and social effects.

[0003] The increase of steam temperature brings the increase of power generation efficiency, but also brings great challenges to the used materials. Compared with subcritical and supercritical steam turbine units, the corrosion rate of metal components in the ultra-supercritical unit in the high-temperature steam environment is significantly increased, which can cause the decrease of heat exchange efficiency of the heat exchange pipe, the acceleration of the pipe wall thickness thinning rate, and the impact of the pipe inner oxide skin on the blade surface to cause the blade damage. For the key moving pair components such as high main valve, high regulating valve, medium-pressure main steam valve and medium-pressure regulating valve, the rapid high-temperature steam oxidation can form an oxide skin on the sealing surface of the valve shell and the valve core, which can cause the gap to be small, and the valve jam phenomenon occurs in the operation. The falling of the oxide skin can also aggravate the severity of the jam and further cause the wear of the fitting surface. The jam of the inlet valve can cause the sudden fluctuation of the unit load, affect the normal load regulation and load carrying capacity of the unit, and exist the risk of causing the unit overspeed in the emergency shutdown, which brings great safety risk to the unit operation. In addition, the valve jam usually needs to be disassembled and processed, and the valve disassembly and repair needs to consume nearly a month of repair processing time, which causes great economic loss to the power plant and affects the normal operation of the power plant. Therefore, the treatment of the inlet valve jam is imminent.

[0004] Since oxidation only occurs on the surface of the material, modifying the oxidized surface by coating technology is a cost-effective solution to improve the service life of metal components. Yttrium silicate ceramics have been proven to have excellent high-temperature steam and water oxidation resistance. Due to the potential application on the surface of SiCf-SiC composite material blades in the new generation of aircraft engines, yttrium silicate has been widely studied. However, in addition to high-temperature steam corrosion, wear caused by valve opening and closing also exists in valve pairs. Therefore, yttrium silicate needs to be further modified to improve its hardness and wear resistance. The commonly used coating processes include slurry brushing-sintering, electrophoretic deposition, and atmospheric plasma spraying. The sintering temperature of the former two methods is usually higher than 1400℃, so they are not suitable for metal substrates. Atmospheric plasma spraying has the characteristics of small thermal effect on the substrate and simple operation, but conventional atmospheric plasma spraying uses powder with a diameter of tens of microns as raw material. The powder is melted inside the plasma flame, flattened and solidified after impacting the substrate, and a large number of lamellar structures are formed inside the coating. Limited interlamination bonding allows high-temperature steam to reach the substrate along the unbound lamellar interface, so the as-sprayed coating does not have high-temperature steam corrosion protection. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a preparation method of a high-hardness high-temperature steam oxidation-resistant composite structure coating, which can regulate the wear resistance of the coating and avoid cracking and peeling caused by thermal stress during the heating and cooling process of the coating, thereby realizing the long-term high-temperature steam corrosion resistance of the coating.

[0006] The technical scheme adopted by the present application is as follows: a preparation method of a high-hardness high-temperature steam oxidation-resistant composite structure coating, comprising the following steps:

[0007] S1: pretreating the surface of a workpiece in need of coating preparation;

[0008] S2: preparing an aluminum-containing nickel-based or aluminum-containing cobalt-based metal primer layer with a thickness of 80-150μm on the surface of the workpiece;

[0009] S3: selecting a suspension liquid containing yttrium silicate and aluminum oxide micropowder and an organic solvent in a certain proportion as raw material, and preparing a ceramic top layer with a thickness of 100-350μm on the surface of the primer layer by atmospheric plasma spraying technology through the external powder feeding mode.

[0010] Specifically, the pretreatment of the surface of the workpiece in need of coating preparation specifically includes oil removal, sandblasting and rust removal, and surface roughening.

[0011] Specifically, the preparation process of the primer layer adopts one of plasma spraying, supersonic flame spraying and cold spraying; when plasma spraying is adopted, the particle size of the spraying powder is between 35-65 μm, and when cold spraying or supersonic flame spraying is adopted, the particle size of the spraying powder is between 10-45 μm.

[0012] Specifically, the powder material of the primer layer adopts one of nickel-based, cobalt-based, nickel-chromium-based or cobalt-chromium-based material, wherein the aluminum content is higher than 6wt%.

[0013] Specifically, the particle size of the yttrium silicate and alumina micropowder is between 50-300 nm, and the organic solvent is a combustible organic liquid.

[0014] Specifically, the mass ratio of the yttrium silicate and alumina micropowder is between 10:0 and 6:4.

[0015] Specifically, in the step S3, the temperature of the molten droplet formed after the melting of the microparticle in the process of the atmospheric plasma spraying of the suspension liquid is not lower than 2800℃, and the porosity of the ceramic top layer is not higher than 1.5%.

[0016] Specifically, the surface temperature of the substrate in the process of the atmospheric plasma spraying for preparing the ceramic top layer is not higher than 150℃.

[0017] The present application has the following beneficial effects: the present application realizes the high-temperature steam corrosion protection of the surface of the heat-resistant steel by combining the excellent high-temperature steam corrosion resistance of the yttrium silicate material and the high-density coating structure obtained by the submicron and nanometer scale suspension liquid raw material, further regulates the wear resistance of the coating by the controllable addition of the high-hardness alumina in the yttrium silicate material; on the other hand, the high-aluminum-content primer layer is used to enhance the bonding strength between the composite ceramic top layer and the substrate, to relieve the difference in the thermal expansion coefficient between the two, to avoid the cracking and peeling of the coating caused by the thermal stress during the heating and cooling process, so that the long-term high-temperature steam corrosion resistance of the coating can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The step flow chart of the preparation method of the present application is shown in the figure;

[0019] Figure 2 The cross-sectional structure diagram of the NiAl / Y2SiO5-Al2O3 composite coating prepared by the supersonic flame spraying and the plasma spraying in Example 1 is shown in the figure;

[0020] Figure 3 The structure diagram of the oxidation corrosion of the P91 heat-resistant steel after the high-temperature steam corrosion at 650℃ / 500 h is shown in the figure;

[0021] Figure 4The structural schematic diagram of the oxidation corrosion of the NiAl / Y2SiO5-Al2O3 composite coating in Example 1 after high-temperature steam corrosion at 650 DEG C for 500 h is shown. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application.

[0023] As shown in Figure 1 The present application provides a preparation method of a high-hardness high-temperature steam oxidation-resistant composite structure coating, comprising the following steps:

[0024] S1: pretreating the surface of a workpiece in need of preparing a coating;

[0025] S2: preparing an aluminum-containing nickel-based or aluminum-containing cobalt-based metal primer layer with a thickness of 80-150 μm on the surface of the workpiece;

[0026] S3: selecting a suspension liquid with a certain proportion of yttrium silicate and aluminum oxide micropowder and an organic solvent as raw materials, and preparing a ceramic top layer with a thickness of 100-350 μm on the surface of the primer layer by using an atmospheric plasma spraying technology in an external powder feeding mode.

[0027] For better effect, the pretreatment of the surface of the workpiece in need of preparing a coating specifically comprises oil removal, sand blasting and rust removal, and surface roughening, so as to improve the surface quality of the workpiece and further improve the coating effect.

[0028] For better effect, the preparation process of the primer layer adopts one of plasma spraying, high-velocity oxygen fuel spraying, and cold spraying; when plasma spraying is adopted, the particle size of the spraying powder is 35-65 μm, and when cold spraying or high-velocity oxygen fuel spraying is adopted, the particle size of the spraying powder is 10-45 μm.

[0029] For better effect, the powder material of the primer layer adopts one of nickel-based, cobalt-based, nickel-chromium-based, or cobalt-chromium-based material, wherein the aluminum content is higher than 6wt%.

[0030] For better effect, the particle size of yttrium silicate and alumina micropowder is between 50-300 nm to ensure the uniformity of the micropowder in the suspension, and the organic solvent is a combustible organic liquid such as ethanol and acetone, which can further increase the temperature of the powder particles in the plasma flame. Since the ceramic particles in the suspension are as small as sub-micron, complete melting can occur at a lower plasma power, so a smaller inner wall plasma spraying equipment is used to obtain a high-density coating, which is also suitable for the inner wall coating preparation of tubular parts with a diameter of not less than 80 mm.

[0031] For better effect, the mass ratio of yttrium silicate and alumina micropowder is between 10:0 and 6:4; in specific use, the workpiece surface coating material used in the environment where wear and high-temperature steam corrosion coexist can increase the proportion of high-hardness alumina micropowder, and the workpiece surface coating material mainly used in high-temperature steam corrosion can reduce the proportion of alumina micropowder, and the ceramic top layer is mainly composed of yttrium silicate resistant to high-temperature steam corrosion.

[0032] For better effect, the temperature of the molten droplets formed after the melting of the particles in the process of spraying the suspension by atmospheric plasma is not less than 2800℃, so that the porosity of the ceramic top layer is not higher than 1.5%, thereby ensuring excellent steam insulation effect. Since the nano and sub-micron yttrium silicate and alumina powder particles are small in size, the molten droplets in the plasma spraying flame are very small, and the surface roughness of the coating after completion can be as low as Ra 1.5 μm, and the coating can avoid the adhesion of foreign matters caused by high surface roughness during use.

[0033] For better effect, the surface temperature of the substrate during the preparation of the ceramic top layer by atmospheric plasma spraying is not higher than 150℃, which prevents the formation of longitudinal cracks in the ceramic layer during deposition. After spraying is completed, the cooling speed can be reduced by cladding to prevent longitudinal cracks in the ceramic layer due to rapid cooling.

[0034] In addition, parts such as valve spools and valve stems that need to be assembled with other parts after the preparation of the composite structure ceramic coating need to be surface processed by grinding to make the surface roughness reach Ra 0.4 μm or below to meet the sealing and assembly requirements. The thickness of the ceramic coating is 100-250 μm thicker than the conventional one.

[0035] The following will be specifically described in conjunction with the embodiments:

[0036] Example 1

[0037] The P91 heat-resistant stainless steel plate is used as the base material. First, the surface of the base material is cleaned and roughened by sand blasting process, and the surface roughness after treatment is Ra 4.5-8.5 μm. Second, the NiAl intermetallic compound is used as the primer layer material, the alloyed spherical NiAl intermetallic compound powder with a particle size of 10-45 μm prepared by gas atomization method is used as the raw material, and the primer layer is prepared by kerosene fuel supersonic flame spraying, with nitrogen as the powder feeding gas, the kerosene flow rate is 22.4 l / h, the oxygen flow rate is 943 SLPM, the spraying distance is 380 mm, the powder feeding rate is 75 g / min, the spraying gun moving speed is 1000 mm / s, and the coating thickness is 0.12 mm. Finally, the single yttrium silicate powder with a particle size of 50-200 nm and the alumina powder are used as the raw materials, the weight ratio of the two is 9:1, the analytical pure ethanol is used as the solvent, the suspension is prepared by ultrasonic and mechanical stirring, the proportion of the ceramic powder in the suspension is 2 / 10, the atmospheric plasma spraying is used to prepare the surface composite ceramic layer, before spraying, the surface is heated by plasma flame flow to remove the water and organic matter adsorbed on the surface of the intermetallic compound, the plasma arc power is set to 42 kW, the argon flow rate is 50 l / min, the hydrogen flow rate is 8 l / min, the peristaltic pump is used for external feeding of the suspension, the feeding rate is 80 ml / min, the spraying distance is 95 mm, and the spraying gun scanning speed is 500 mm / s. The final composite ceramic coating thickness is 250 μm. The cross-sectional structure of the coating is shown in Figure 2 The lower layer is the NiAl primer layer, the coating porosity is only 0.6%, the upper layer is the yttrium silicate / alumina composite coating, the coating porosity is 0.73%, and no obvious porosity and crack defects are found at the interface between the coating and the base material and between the two layers. The P91 heat-resistant alloy steel and the sample after coating preparation are subjected to 500 h high-temperature steam corrosion test under the condition of 650 ℃ and 25 MPa high-temperature steam corrosion, and the test results are shown in Figure 3 and Figure 4 The coating is prepared on all surfaces of the sample. The cross section of the sample after test is shown in Figure 2 The oxide layer thickness on the surface of the P91 heat-resistant stainless steel without coating is as high as 65 μm or more, while no reaction layer appears on the surface of the sample with the protective layer, and no corrosion product is formed at the interface between the P91 and the coating. The coating has excellent high-temperature water vapor corrosion resistance.

[0038] Example 2

[0039] A P92 heat-resistant stainless steel pipe with a diameter of 130 mm and a length of 100 mm was used as a base material. First, the surface of the base material was cleaned and roughened by sandblasting, and the surface roughness after treatment was Ra 4.5-8.5 μm. Second, a CoNiCrAlY antioxidant alloy was used as a primer layer material, and an alloyed spherical powder with a particle size of 10-35 μm prepared by gas atomization was used as a raw material. The primer layer was prepared by internal hole atmospheric plasma spraying, with nitrogen as the powder feeding gas, a plasma arc power of 18 kW, an argon flow rate of 30 l / min, a hydrogen flow rate of 2 l / min, a powder feeding rate of 20 g / min, a spraying distance of 30 mm, a circular tube rotating speed of 300 rpm, and a plasma torch moving speed of 50 mm / s. The thickness of the coating was 0.10 mm. Finally, a suspension was prepared by combining ultrasonic and mechanical stirring, with a particle size of 50-200 nm and a single yttrium silicate powder and an alumina powder as raw materials, a weight ratio of 8:1, and analytical pure acetone as a solvent. The proportion of ceramic powder in the suspension was 1.5 / 10. The surface layer composite ceramic layer was prepared by using an internal diameter plasma spraying device. Before spraying, the surface was heated by plasma flame scanning to remove moisture and organic matter adsorbed on the surface of the intermetallic compound layer. The plasma arc power was selected as 21 kW, the argon flow rate was 35 l / min, the hydrogen flow rate was 3 l / min, the suspension was fed by using a pneumatic pump, the feeding rate was 40 ml / min, the spraying distance was 30 mm, the circular tube rotating speed was 300 rpm, the torch moving speed was 50 mm / s, compressed air was used to cool the outer wall of the circular tube, and an infrared thermometer was used to measure the temperature of the outer wall of the circular tube. The cooling gas flow rate was adjusted to ensure that the outer wall temperature was not higher than 120℃, and the final ceramic layer thickness was 180 μm. After the coating was prepared, the workpiece was wrapped with heat preservation cotton and slowly cooled. Metallographic observation results showed that the porosity of the CoNiCrAlY primer layer was 1.5%, the porosity of the yttrium silicate / alumina composite coating was 0.97%, and no obvious porosity and crack defects were found at the interface between the coating and the base material and between the two layers. A 500 h high-temperature steam corrosion test was conducted on P92 heat-resistant alloy steel and the sample with a prepared coating under high-temperature steam corrosion conditions of 650℃ and 15 MPa. The coating was prepared on all surfaces. The oxidation layer thickness on the surface of the P92 heat-resistant stainless steel without a coating was more than 47 μm, while no reaction layer appeared on the surface of the sample with a protective layer, and no corrosion products were formed at the interface between P92 and the coating. The coating has excellent high-temperature water vapor corrosion resistance.

[0040] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. The embodiments should therefore be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. No reference signs in the claims should be considered as limiting the scope of the claims with respect to the figures of the patent document.

Claims

1. A method for producing a high-hardness, high-temperature-steam-oxidation-resistant composite structure coating, characterized by, The method comprises the following steps: S1: pretreating the surface of a workpiece in need of a coating; S2: preparing an aluminum-containing nickel-based or aluminum-containing cobalt-based primer layer with a thickness of 80-150 μm on the surface of the workpiece; S3: selecting a suspension liquid of yttrium silicate and alumina micropowder with an organic solvent as raw materials, and preparing a ceramic top layer with a thickness of 100-350 μm on the surface of the primer layer by means of atmospheric plasma spraying technology through an external powder feeding mode, wherein the ceramic top layer is mainly composed of yttrium silicate; The powder material of the primer layer is one of nickel-based, cobalt-based, nickel-chromium-based or cobalt-chromium-based materials, wherein the aluminum content is higher than 6wt%; The particle size of the yttrium silicate and alumina micropowder is 50-300 nm, and the organic solvent is a combustible organic liquid.

2. The method for preparing a high-hardness, high-temperature steam oxidation-resistant composite coating according to claim 1, characterized in that: The pretreatment of the surface of the workpiece in need of a coating specifically comprises oil removal, sand blasting and rust removal, and surface roughening.

3. The method for preparing a high-hardness, high-temperature steam oxidation-resistant composite coating according to claim 1, characterized in that: The preparation process of the primer layer adopts one of plasma spraying, high-velocity oxy-fuel spraying and cold spraying; when plasma spraying is adopted, the particle size of the sprayed powder is 35-65 μm, and when cold spraying or high-velocity oxy-fuel spraying is adopted, the particle size of the sprayed powder is 10-45 μm.

4. The method for preparing a high-hardness, high-temperature steam oxidation-resistant composite coating according to claim 1, characterized in that: In step S3, the temperature of the molten droplets formed after the melting of the microparticles in the process of atmospheric plasma spraying of the suspension liquid is not lower than 2800℃, and the porosity of the ceramic top layer is not higher than 1.5%.

5. The method for preparing a high-hardness, high-temperature steam oxidation-resistant composite coating according to claim 1, characterized in that: The surface temperature of the substrate in the process of atmospheric plasma spraying for preparing the ceramic top layer is not higher than 150℃.

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