A method for preparing a thermal barrier coating of nickel-based superalloy K435

Abstract

The application discloses a preparation method of a nickel-based high-temperature alloy K435 thermal barrier coating and belongs to the technical field of high-temperature protective coating. The application aims at solving the problems of insufficient bonding strength and poor oxidation resistance of the bonding layer between the existing thermal barrier coating and the base alloy. The method comprises the following steps: 1, preparing a NiCoCrAlYMn alloy powder; 2, plasma spraying; and 3, spraying a ceramic top layer material. The application is used for the preparation of the nickel-based high-temperature alloy K435 thermal barrier coating.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high-temperature protective coating. BACKGROUND

[0002] K435 is a nickel-based precipitation-hardened equiaxed crystal cast high-temperature alloy, which can be used at temperatures up to 900℃, has high high-temperature strength and good heat corrosion resistance, and is widely used in the manufacture of high-temperature components such as guide vanes of gas turbines. This alloy can maintain the stability and durability of the structure in extreme high-temperature environments, thereby ensuring the efficient and reliable operation of the gas turbine. However, as the thrust and thrust-to-weight ratio of the gas turbine increase, the turbine inlet temperature continues to rise, and higher requirements are placed on the mechanical properties of the high-temperature alloy used for the corresponding parts. At the same time, in the harsh environment of high temperature and corrosive medium, the surface of K435 alloy is still inevitably subjected to the dual attack of oxidation and hot corrosion. Over time, these erosion effects gradually accumulate, leading to a significant decline in the surface properties of the alloy, which in turn affects the working efficiency and safety of the entire gas turbine. Therefore, it is necessary to develop and improve the surface coating technology of high-temperature alloys to improve their temperature resistance and oxidation resistance.

[0003] In view of this challenge, it is particularly important to develop a thermal barrier coating that can significantly improve the high-temperature oxidation resistance and thermal stability of K435 alloy. Such a coating acts like a protective armor for the alloy, effectively isolating it from the high-temperature corrosive environment and prolonging its service life.

[0004] Thermal barrier coating (TBC) is a widely used coating technology in high-temperature environments. By preparing a ceramic coating with low thermal conductivity and high thermal shock resistance on the surface of a high-temperature alloy, the temperature of the substrate alloy can be effectively reduced, and the service life of the blade parts can be extended. The thermal barrier coating currently used in practical applications between high-temperature gas and turbine blades provides a heat shield and protection performance, and is of a double-layer structure: the surface layer is a ceramic layer, and the inner layer is a metal bonding layer. In the composition of the thermal barrier coating, the bonding layer plays a crucial role. Its performance is directly related to the durability and reliability of the entire coating system, and determines whether the coating can remain stable at high temperatures for a long time to provide effective protection for the substrate alloy. The bonding layer not only has good oxidation resistance, but also has good adhesion, which can reduce the mismatch of the thermal expansion coefficient between the ceramic face layer and the high-temperature alloy substrate. Although the traditional NiCoCrAlY bonding layer already has certain oxidation resistance, when faced with more severe high-temperature service conditions, the bonding layer between the traditional thermal barrier coating and the substrate alloy often has problems such as insufficient bonding strength and poor oxidation resistance, which limits its application effect and performance, and cannot meet the long-term use requirements.

[0005] Therefore, modifying the NiCoCrAlY bonding layer to further enhance its oxidation resistance and thermal stability has become an important direction of current research. SUMMARY

[0006] The present application aims to solve the problems of insufficient bonding strength and poor oxidation resistance between the existing thermal barrier coating and the substrate alloy, and further provides a preparation method of a nickel-based superalloy K435 thermal barrier coating.

[0007] A preparation method of a nickel-based superalloy K435 thermal barrier coating, which is carried out according to the following steps:

[0008] I. Preparation of NiCoCrAlYMn alloy powder:

[0009] According to the mass percentage of 20%-26% of Co, 18%-22% of Cr, 8%-12% of Al, 0.3%-1% of Y, 0.5%-1% of Mn and the balance of Ni, the raw materials are weighed, then the weighed raw materials are subjected to mechanical alloying treatment, and finally dried to obtain the NiCoCrAlYMn alloy powder;

[0010] II. Plasma spraying:

[0011] The NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate by using the plasma spraying technology to obtain the NiCoCrAlYMn bonding layer;

[0012] III. Spraying of ceramic top layer material:

[0013] The ceramic top layer material is sprayed on the NiCoCrAlYMn bonding layer by using the plasma spraying technology to obtain the nickel-based superalloy K435 thermal barrier coating.

[0014] The beneficial effects of the present application are:

[0015] The present application significantly improves the oxidation resistance and thermal stability of the coating by adding Mn element in the NiCoCrAlY bonding layer, prolonging the service life of the nickel-based superalloy K435;

[0016] The addition of Mn element in the present application also improves the microstructure and element distribution of the coating, enhances the interfacial bonding force between the bonding layer and the substrate and the ceramic layer, and improves the bonding strength of the coating; Mn element can reduce the thermal conductivity of the bonding layer, which helps to reduce the temperature gradient of the whole coating and improve the thermal shock resistance of the coating. The preparation method of the present application is simple and easy to operate, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1The schematic diagram and scanning coating cross-section of the thermal barrier coated nickel-based superalloy K435 prepared in Example 1, 1 is K435 substrate, 2 is NiCoCrAlYMn bond coat, 3 is ceramic top coat;

[0018] Figure 2 The oxidation weight gain curve of the thermal barrier coated nickel-based superalloy K435 prepared in Example 1 and Comparative Experiment 1 under high temperature oxidation at 900℃;

[0019] Figure 3 The cross-section and element mapping of the thermal barrier coated nickel-based superalloy K435 prepared in Example 1 after high temperature oxidation at 900℃ for 20h. DETAILED DESCRIPTION

[0020] Detailed implementation one: a method for preparing a thermal barrier coating of nickel-based superalloy K435, which is carried out according to the following steps:

[0021] I. Preparation of NiCoCrAlYMn alloy powder:

[0022] According to the mass percentage of 20% to 26% of Co, 18% to 22% of Cr, 8% to 12% of Al, 0.3% to 1% of Y, 0.5% to 1% of Mn and the balance of Ni, the raw materials are weighed, then the weighed raw materials are subjected to mechanical alloying treatment, and finally dried to obtain the NiCoCrAlYMn alloy powder;

[0023] II. Plasma spraying:

[0024] The NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate by plasma spraying technology to obtain the NiCoCrAlYMn bond coat.

[0025] III. Spraying of ceramic top coat material:

[0026] The ceramic top coat material is sprayed on the NiCoCrAlYMn bond coat by plasma spraying technology to obtain the thermal barrier coating of nickel-based superalloy K435.

[0027] The Mn element in the embodiment can cause the refinement of the grains in the base material and increase the number of grain boundaries. The increase of the grain boundaries provides more channels for heat transfer, thereby improving the thermal conductivity of the material. At the same time, the doping element can also increase the energy of the grain boundaries, so that the hot electrons are more likely to cross the grain boundaries. The increase of such energy helps to accelerate the process of heat transfer inside the material, thereby improving the thermal conductivity. Therefore, the embodiment can significantly improve the high-temperature performance of the NiCoCrAlY bonding layer by adjusting the alloy composition, optimizing the microstructure and introducing a new strengthening mechanism, so that it can better adapt to the complex and changeable high-temperature corrosion environment, and provide more comprehensive and lasting protection for the K435 nickel-based cast high-temperature alloy.

[0028] The beneficial effects of the embodiment are:

[0029] The embodiment significantly improves the oxidation resistance and thermal stability of the coating by adding the Mn element in the NiCoCrAlY bonding layer, prolongs the service life of the nickel-based high-temperature alloy K435;

[0030] The addition of the Mn element in the embodiment also improves the microstructure and element distribution of the coating, enhances the interfacial bonding force between the bonding layer and the substrate and the ceramic layer, and improves the bonding strength of the coating; the Mn element can reduce the thermal conductivity of the bonding layer, which helps to reduce the temperature gradient of the whole coating and improve the thermal shock resistance of the coating. The preparation method of the present application is simple and easy to operate, and is suitable for industrial production.

[0031] Specific embodiment two: the difference between the embodiment and the specific embodiment one is that the raw materials in step one are Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder; the particle size of the raw materials in step one is 30-50 μm. The others are the same as those in the specific embodiment one.

[0032] Specific embodiment three: the difference between the embodiment and the specific embodiment one or two is that the mechanical alloying treatment in step one is specifically performed as follows: using grinding balls with a diameter of 8-10 mm, under the conditions of a ball-to-material mass ratio of (10-20): 1 and a ball milling speed of 300-400 r / min, the mechanical alloying treatment is performed for 2-20 h. The others are the same as those in the specific embodiment one or two.

[0033] Specific embodiment four: the difference between the embodiment and the specific embodiment one to three is that the drying in step one is specifically performed under the condition of a temperature of 100-200℃ for 5-10 h. The others are the same as those in the specific embodiment three.

[0034] Embodiment five: the difference between this embodiment and one of the embodiments one to four is that the pretreated K435 substrate in step two is specifically obtained by sequentially performing oil removal, sand blasting, cleaning and preheating treatment on the nickel-based superalloy K435. The others are the same as the embodiments one to four.

[0035] In this embodiment, all the substrate surfaces are pre-sandblasted to roughen the sample surface to meet the requirements of the spraying roughness. The sandblasting angle cannot be perpendicular to the workpiece surface to avoid embedding the sand particles directly into the workpiece surface. The sample surface after sandblasting treatment can be cleaned with acetone to remove oil. The substrate after sandblasting treatment is preferably sprayed within 2-3 hours, otherwise if the substrate surface is contaminated (usually oxidized and rusted), it cannot be used normally and needs to be sandblasted again.

[0036] Meanwhile, the substrate surface needs to be preheated. A plasma torch is used for preheating, and the powder feeder matched with the torch needs to be closed during operation. The moving speed of the torch needs to be uniform to prevent the substrate from oxidizing during preheating due to temperature rise, thereby affecting the bonding strength of the plasma sprayed coating and the substrate.

[0037] Embodiment six: the difference between this embodiment and one of the embodiments one to five is that the sandblasting treatment is specifically performed by using white corundum sand with a particle size of 10-30 mesh under the conditions of a sandblasting air pressure of 0.4-0.6 MPa, a sandblasting angle of 70-80° and a sandblasting distance of 100-200 mm; the preheating is specifically performed by using a plasma torch under the condition of a temperature of 300-400°C. The others are the same as the embodiments one to five.

[0038] Embodiment seven: the difference between this embodiment and one of the embodiments one to six is that the plasma spraying technology in step two is specifically performed under the conditions of an arc current of 400-600 A, a spraying distance of 100-300 mm, a powder feeding amount of 15-50 g / min, a torch moving speed of 100-300 mm / s, an oxygen flow rate of 40-70 L / min, a propane flow rate of 40-60 L / min and an air flow rate of 50-500 L / min. The others are the same as the embodiments one to six.

[0039] Embodiment eight: the difference between this embodiment and one of the embodiments one to seven is that the ceramic top layer material in step three is alumina ceramic or yttria-stabilized zirconia ceramic. The others are the same as the embodiments one to seven.

[0040] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the yttria-stabilized zirconia ceramic is a mixture of Y2O3 and ZrO2; the mass percentage of Y2O3 in the yttria-stabilized zirconia ceramic is 8%, and the rest is ZrO2; the particle size of the yttria-stabilized zirconia ceramic is 45 μm to 90 μm. The others are the same as specific embodiments one to eight.

[0041] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the plasma spraying technology in step three is specifically carried out under the conditions of an arc current of 400 A to 600 A, a spraying distance of 50 mm to 110 mm, a powder feeding amount of 20 g / min to 50 g / min, a spraying gun moving speed of 30 mm / s to 100 mm / s, a nitrogen gas flow of 300 L / min to 2000 L / min, and a hydrogen gas flow of 5 L / min to 50 L / min. The others are the same as specific embodiments one to nine.

[0042] The beneficial effects of the present application are verified by the following examples:

[0043] Example one:

[0044] A preparation method of a nickel-based high-temperature alloy K435 thermal barrier coating, which is carried out according to the following steps:

[0045] I. Preparation of NiCoCrAlYMn alloy powder:

[0046] Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder are weighed according to the mass percentages of 23.9% of Co, 19.9% of Cr, 11.9% of Al, 1.0% of Y, 0.6% of Mn and the balance of Ni as raw materials, then the raw materials are mechanically alloyed under the conditions of a ball-to-charge mass ratio of 10:1 and a ball milling speed of 400 r / min for 10 h, and finally dried at a temperature of 150 ℃ for 8 h to obtain the NiCoCrAlYMn alloy powder;

[0047] The average particle size of the raw materials is 45 μm;

[0048] II. Plasma spraying:

[0049] The NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate by plasma spraying technology under the conditions of an arc current of 600 A, a spraying distance of 250 mm, a powder feeding amount of 50 g / min, a spraying gun moving speed of 100 mm / s, an oxygen flow of 70 L / min, a propane flow of 55 L / min and an air flow of 100 L / min to obtain a NiCoCrAlYMn bonding layer;

[0050] III. Spraying ceramic top layer material:

[0051] The ceramic top layer material is sprayed on the NiCoCrAlYMn bonding layer under the conditions of a current of 500 A, a spraying distance of 100 mm, a powder feeding amount of 50 g / min, a spraying gun moving speed of 100 mm / s, a nitrogen flow of 2000 L / min and a hydrogen flow of 11 L / min by using the plasma spraying technology to obtain the nickel-based superalloy K435 covered with the thermal barrier coating.

[0052] The pretreated K435 substrate in step two is specifically obtained by sequentially performing oil removal, sand blasting, cleaning and preheating treatment on the nickel-based superalloy K435;

[0053] The oil removal is specifically performed by using alcohol and acetone to ultrasonically clean oil stains for 10 min under the condition of a power of 300 W;

[0054] The sand blasting treatment is specifically performed by using white corundum sand with a sand particle size of 16 mesh under the conditions of a sand blasting air pressure of 0.6 MPa, a sand blasting angle of 70° and a sand blasting distance of 150 mm by using compressed air;

[0055] The cleaning is specifically performed by using acetone to clean the oil removal;

[0056] The preheating is specifically performed by using a plasma spraying gun under the condition of a temperature of 300℃.

[0057] The ceramic top layer material in step three is yttria-stabilized zirconia ceramic; the yttria-stabilized zirconia ceramic is a mixture of Y2O3 and ZrO2; the mass percentage of Y2O3 in the yttria-stabilized zirconia ceramic is 8%, and the balance is ZrO2; the average particle size of the yttria-stabilized zirconia ceramic is 45 μm.

[0058] Comparative Experiment One: The difference between the present comparative experiment and Example One is that the addition of Mn is omitted in step one, and Co powder, Cr powder, Al powder, Y powder and Ni are weighed as raw materials according to the mass percentages of 24% of Co, 20% of Cr, 12% of Al, 1% of Y and the balance of Ni. The others are the same as in Example One.

[0059] Figure 1 The schematic diagram and the scanning coating cross-sectional diagram of the nickel-based superalloy K435 covered with the thermal barrier coating prepared in Example One, 1 is the K435 substrate, 2 is the NiCoCrAlYMn bonding layer, and 3 is the ceramic top layer. As can be seen from the diagram, it is a typical double-layer thermal barrier coating structure, including a nickel-based superalloy substrate, an 8YSZ ceramic surface layer and a secondary surface layer of the NiCoCrAlYMn bonding layer.

[0060] Figure 2The weight gain curve of K435 substrate, the thermal barrier coating prepared by example one and the thermal barrier coating prepared by comparative experiment one under 900℃ high temperature oxidation. From the figure, the weight gain of K435 alloy without adhesive layer and ceramic top layer is 4.98mg / cm 2 The weight gain of the thermal barrier coating prepared by comparative experiment one is 3.26mg / cm 2 The weight gain of the thermal barrier coating prepared by example one is 2.5mg / cm 2 Therefore, the oxidation corrosion resistance of K435 alloy with coating is obviously higher than that without coating, and the coating with Mn is better than the traditional NiCoCrAlY adhesive layer.

[0061] Figure 3 The cross-section and element surface scan of the thermal barrier coating prepared by example one after 900℃ high temperature oxidation for 20h. From the figure, the adhesive strength and oxidation resistance of the coating are good after 20h oxidation, and there is no coating peeling.

Claims

1. A method of producing a thermal barrier coating of nickel-based superalloy K435, characterized in that It is carried out according to the following steps: I. Preparation of NiCoCrAlYMn alloy powder: According to the mass percentage of 20%-26% of Co, 18%-22% of Cr, 8%-12% of Al, 0.3%-1% of Y, 0.5%-1% of Mn and the balance of Ni, the raw materials are weighed, then the weighed raw materials are subjected to mechanical alloying treatment, and finally dried to obtain NiCoCrAlYMn alloy powder; The raw materials are Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder; the particle size of the raw materials is 30-50 μm; II. Plasma spraying: Using plasma spraying technology, the NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate to obtain a NiCoCrAlYMn bonding layer; The plasma spraying technology is specifically carried out under the conditions of an arc current of 400-600 A, a spraying distance of 100-300 mm, a powder feeding amount of 15-50 g / min, a spraying gun moving speed of 100-300 mm / s, an oxygen flow rate of 40-70 L / min, a propane flow rate of 40-60 L / min and an air flow rate of 50-500 L / min; III. Spraying of ceramic top layer material: Using plasma spraying technology, ceramic top layer material is sprayed on the NiCoCrAlYMn bonding layer to obtain a nickel-based high-temperature alloy K435 thermal barrier coating; The ceramic top layer material is alumina ceramic or yttria-stabilized zirconia ceramic.

2. The method of claim 1, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: The mechanical alloying treatment in step I is specifically carried out according to the following steps: using grinding balls with a diameter of 8-10 mm, under the conditions of a ball-to-material mass ratio of (10-20):1 and a ball milling speed of 300-400 r / min, the mechanical alloying treatment is carried out for 2-20 h. ​ 3. The method of claim 1, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: (a) depositing a bond coat on a substrate; (b) depositing a thermal barrier coating on the bond coat; and (c) depositing a top coat on the thermal barrier coating. The drying in step I is specifically carried out at a temperature of 100-200°C for 5-10 h.

4. The method of claim 1, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: The pretreated K435 substrate in step II is specifically obtained by sequentially performing oil removal, sandblasting, cleaning and preheating treatment on the nickel-based high-temperature alloy K435. ​ 5. The method of claim 4, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: depositing a bond coat on a substrate; depositing a thermal barrier coating on the bond coat; and depositing a top coat on the thermal barrier coating. The sandblasting treatment is specifically carried out using white corundum sand with a particle size of 10-30 mesh, under the conditions of a sandblasting air pressure of 0.4-0.6 MPa, a sandblasting angle of 70-80° and a sandblasting distance of 100-200 mm; the preheating is specifically carried out using a plasma torch at a temperature of 300-400°C.

6. The method of claim 1, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: The yttria-stabilized zirconia ceramic is a mixture of Y2O3 and ZrO2; the mass percentage of Y2O3 in the yttria-stabilized zirconia ceramic is 8%, and the balance is ZrO2; the particle size of the yttria-stabilized zirconia ceramic is 45-90 μm. ​ 7. The method of claim 1, wherein the nickel-based superalloy K435 thermal barrier coating is prepared by the steps of: The plasma spraying technique described in Step three is specifically performed under the conditions of an arc current of 400 A to 600 A, a spraying distance of 50 mm to 110 mm, a powder feeding amount of 20 g / min to 50 g / min, a spraying gun moving speed of 30 mm / s to 100 mm / s, a nitrogen gas flow of 300 L / min to 2000 L / min, and a hydrogen gas flow of 5 L / min to 50 L / min. ​

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