Method for improving thermal corrosion resistance of simple aluminide coating of inner cooling channel of blade

Abstract

The invention discloses a method for improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel through heat treatment, and belongs to the technical field of material surface treatment and modification. According to the treatment method, a simple aluminide coating is prepared on the surface of the nickel-based superalloy through a chemical vapor deposition technology, then a coating sample is heated to 1000 DEG C in an air environment in a muffle furnace through a heat treatment method, heat preservation is conducted for 20 h, a continuous and compact alpha-Al2O3 film with the thickness being about 2-3.5 microns is obtained, and the hot corrosion resistance of the film is improved. The process is simple, the cost is low, and the thermal corrosion resistance effect is remarkable. Compared with a coating sample which is not subjected to heat treatment, the corrosion weight increment of the sample subjected to heat treatment is obviously reduced, a corrosion film of the sample is more continuous and compact in the corrosion period compared with a corrosion film of the coating sample which is not subjected to heat treatment, and the thermal corrosion resistance is more excellent.

Description

Technical Field

[0001] The present invention belongs to the field of material surface treatment and modification, and relates to a method for improving the thermal corrosion resistance of simple aluminide coatings in the cold channel in the blade by using heat treatment. Background Art

[0002] Due to its advantages of high power, small size, fast start-up time and reliable operation, ship gas turbines have gradually replaced traditional steam turbines and diesel engines and have become the dominant power plant for large and medium-sized surface ships. Turbine blades are key components of gas turbines, and the requirements for their materials are getting higher and higher. Nickel-based high-temperature alloys have higher service temperatures than iron-based alloys and lower costs than cobalt-based alloys, so they have become the preferred material for gas turbine turbine blades.

[0003] In order to obtain a higher thrust-to-weight ratio, the turbine inlet temperature continues to increase, making the service conditions of turbine blades more demanding. They are in a high-temperature environment for a long time. The emergence and development of hollow blades (cooling channel size less than 0.5mm) have achieved air cooling to a certain extent and reduced the temperature of the blade body, but the temperature of the inner cooling channel can still be as high as 800℃ or above, and high-temperature oxidation will still occur. In addition, ships serve in the marine environment for a long time, and the sulfur in the fuel will react with the oxygen in the atmosphere at high temperature. 2+ , Cl - , Na + , K + In addition to the reaction, a salt film (mainly Na) was deposited on the surface of the internal cold channel. 2 SO 4 +NaCl), causing serious corrosion. The corrosion products will block the air film holes, which is an important reason for limiting the service life of the blade. Therefore, the protection of the inner cooling channel is very necessary. By applying a high-temperature protective coating on its surface, the service life of the blade can be significantly extended, which is also an effective way to solve the contradiction between the alloy's high-temperature corrosion resistance and mechanical properties.

[0004] Among high-temperature protective coatings, simple aluminide coatings with β-NiAl as the main component have attracted much attention due to their low density, high melting point, simple preparation and low cost. It will generate inert Al during corrosion 2 O 3 The film effectively blocks the direct contact between the corrosion salt and the substrate. However, the study found that the continuous dense Al is not fully formed 2 O 3 Before the film, the Al in the coating will also react with the corrosive salt (such as NaCl), resulting in volatile gaseous corrosion products (such as Cl). 2) will further damage the coating and the surface aluminum oxide film, thereby reducing the protective effect of the coating. For these reasons, simple aluminide coatings cannot protect alloys from corrosion for a long time in high-temperature corrosion environments, and some effective measures need to be taken to improve their corrosion resistance.

[0005] The corrosion resistance of simple aluminide coatings can be improved by adding alloying elements (such as Pt, Y, Si, etc.) and heat treatment. However, since the cost of adding alloying elements is high and the preparation process is complicated, the present invention aims to improve the corrosion resistance of simple aluminide coatings by heat treatment. Summary of the invention

[0006] The present invention is intended to provide a method for improving the thermal corrosion resistance of simple aluminide coatings in the inner cold channel. Before the corrosion test, a continuous dense α-Al was preformed on the coating surface by heat treatment before the corrosion test. 2 O 3 The film, barrier Al directly reacts with the deposited salt, thereby further improving the corrosion resistance of the coating.

[0007] The technical solution of the present invention is as follows:

[0008] A simple aluminide coating coated on the surface of a nickel-based high temperature alloy, the coating mainly consists of a β-NiAl phase, in which the atomic content of Al is 45%-65%.

[0009] The heat treatment process specifically comprises the following steps:

[0010] (1) Pretreat the surface of the coating sample to achieve surface cleaning.

[0011] (2) Heat treatment: In an air environment, the sample coated with aluminide coating is heated to 1000°C and kept in heat for 20 hours to obtain a continuous dense alumina film.

[0012] The coating sample described in step (1) above is obtained by penetrate Al on the nickel-based high temperature alloy by chemical vapor deposition (CVD) process.

[0013] The pretreatment in step (1) must ensure that the coating surface is free of oil and dust.

[0014] The mechanism of improving the thermal corrosion resistance of simple aluminide coatings by heat treatment is described in the present invention: Since Al in the coating easily reacts with corrosive salts, it forms a soluble salt (such as NaAlO) 2 ) and gaseous volatile products (such as Cl 2 ), quickly consume Al in the coating and destroy the density of the coating, so that the protective effect of the coating is reduced. The simple aluminide coating after heat treatment will form a continuous and dense α-Al on the surface 2 O 3The membrane, which is inert in the corrosion salt, does not directly react with the corrosion salt, can effectively hinder further corrosion of the coating sample. From the experimental results, it was found that the continuous α-Al obtained by the method of the present invention 2 O 3 The film has a thickness of about 2-3.5μm, which can effectively slow down the corrosion of corrosion salts on the coating.

[0015] During thermal corrosion, unheated coating samples, due to the continuous reaction of corrosive salts with coating elements, and generate volatile gaseous products, causing continuous Al 2 O 3 The formation of the film is hindered, the corrosion film of the coating is discontinuous and dense, and its cracks, holes and other defects can easily become fast channels for corrosive media, and the corrosion resistance of the coating is reduced. 2 O 3 The film is continuous and dense, not easy to fall off, and can inhibit corrosion of the coating for a long time, thereby improving the thermal corrosion resistance of the simple aluminum coating.

[0016] The present invention has the following beneficial technical effects:

[0017] (1) The invention has simple technology, low cost and obvious effect;

[0018] (2) α-Al obtained after heat treatment 2 O 3 The membrane is continuous and dense, without defects such as cracks and holes, which can effectively hinder the direct contact between the coating and the corrosive salt;

[0019] (3) The corrosion weight gain of the simple aluminide coating sample after heat treatment is significantly reduced, and the thermal corrosion resistance is significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cross-sectional photo of a simple aluminum-coated sample after heat treatment in Example 1.

[0021] Figure 2 Corrosion kinetic curve for heat-treated and unheated simple aluminide coating samples in Example 2 (corrosion salt 95 wt.%Na 2 SO 4 +5wt.%NaCl).

[0022] Figure 3 This is the cross-sectional morphology diagram of the simple aluminide coating sample after heat treatment in Example 2 after corrosion at 850°C for 50 hours.

[0023] Figure 4 This is the cross-sectional morphology diagram of the simple aluminide coating sample after corrosion at 850°C for 50 hours in Example 2. Specific implementation plan

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific examples, but the embodiments of the present invention are not limited thereto.

[0025] Example 1

[0026] A nickel-based high-temperature alloy was used as the substrate, and it was processed into a sheet sample with a size of 20mm×10mm×2mm by wire cutting, and a Φ1.5mm circular hole was drilled in the middle of the upper part of the sample to facilitate hanging during the test. After the metal substrate was treated with SiC sandpaper water grinding, ultrasonic cleaning and sandblasting, a simple aluminide coating was deposited on the substrate by chemical vapor deposition to complete the preparation of the coating sample.

[0027] The sample coated with simple aluminide coating was cleaned with deionized water and ethanol to remove surface oil stains, dried to room temperature, placed in a clean corundum crucible, and kept at 1000℃ in a muffle furnace for 20h. A continuous and dense α-Al 2 O 3 Film, thickness about 2-3.5μm.

[0028] Example 2

[0029] The heat-treated coating sample and the unheated coating sample were subjected to a thermal corrosion test of 850°C, with the corrosion salt of 95 wt.%Na 2 SO 4 +5wt.%NaCl. Its corrosion kinetics curve is as follows Figure 2 It can be seen that after 50 hours of corrosion at 850℃, the corrosion weight gain of the heat-treated coating sample is significantly lower than that of the unheat-treated coating sample, indicating that the thermal corrosion resistance of the heat-treated coating sample is significantly improved. Figure 3 and Figure 4 The cross-sectional morphology of a simple aluminide coating sample after corrosion at 850°C for 50 hours. It can be seen that the coating samples after heat treatment performed better, Al 2 O 3 The corrosion film is relatively continuous and dense, and no obvious cracks, holes and other defects are observed, which can still play an effective protective role. However, the corrosion of the coating sample without heat treatment is thicker, and obvious cracks and other defects are observed, which can easily become a fast channel for S, Cl and O to diffuse inward, and internal corrosion products are observed in the coating, and the corrosion resistance of the coating is reduced. Therefore, the thermal corrosion resistance of the coating sample after heat treatment has been significantly improved.

Claims

1. A method for improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment, characterized in that: First, a simple aluminide coating is prepared on the nickel-based high-temperature alloy using chemical vapor deposition technology, and then a heat treatment method is used to improve its thermal corrosion resistance, which mainly includes the following steps: (1) After the metal substrate is pretreated, a simple aluminide coating is deposited on the substrate using a chemical vapor deposition process to complete the preparation of the coating sample. (2) After pretreatment, the sample coated with a simple aluminide coating was kept at 1000°C in a muffle furnace for 20 h to obtain a continuous and dense oxide film with a thickness of about 2-3.5 μm.

2. According to claim 1, a method for improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment, characterized in that: The substrate pretreatment in step (1) includes using SiC sandpaper to smooth the substrate surface and remove pits, and using ethanol ultrasonic cleaning to ensure that the substrate surface is dust-free and oil-free.

3. The method of improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment according to claim 1, characterized in that: The coating sample pretreatment in step (2) includes cleaning with deionized water and ethanol to remove oil stains on the surface.

4. The method of improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment according to claim 1, characterized in that: The continuous and dense oxide film in step (2) is an α-Al2O3 film.

5. The method of improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment according to claim 2, characterized in that: The metal matrix is ​​a nickel-based high-temperature alloy.

6. The method of improving the thermal corrosion resistance of a simple aluminide coating of an inner cooling channel by heat treatment according to claim 4, characterized in that: The continuous and dense α-Al2O3 oxide film exhibits good corrosion resistance during hot corrosion.

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