Preparation method of nickel-based superalloy K435 thermal barrier coating

Abstract

The invention 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 coatings. The invention aims to solve the problems of insufficient bonding strength and poor oxidation resistance of a bonding layer between an existing thermal barrier coating and a matrix alloy. The method comprises the following steps: 1, preparing NiCoCrAlYMn alloy powder; 2, plasma spraying; and 3, spraying a ceramic top layer material. The method is used for preparing the nickel-based high-temperature alloy K435 thermal barrier coating.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature protective coatings. Background Art

[0002] K435 is a nickel-based precipitation-hardened equiaxed crystal casting high-temperature alloy with an operating temperature of up to 900°C. It has high high-temperature strength and good heat-corrosion resistance and is widely used in the manufacture of high-temperature components such as guide blades of gas turbines. This alloy can maintain structural stability and durability in extreme high-temperature environments, thereby ensuring efficient and reliable operation of gas turbines. However, with the increase in gas turbine thrust and thrust-to-weight ratio, the turbine inlet temperature continues to increase, which puts higher requirements on the mechanical properties of the high-temperature alloys used in the corresponding parts. At the same time, in the harsh environment of high temperature and corrosive media, the surface of the K435 alloy is still inevitably attacked by oxidation and thermal corrosion. Over time, these erosions will gradually accumulate, resulting in a significant decrease 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 bearing capacity 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 is like a layer of protective armor for the alloy, which can effectively isolate the high-temperature corrosion environment and extend the service life of the alloy.

[0004] Thermal barrier coating (TBC) is a coating technology widely used in high-temperature environments. By preparing a ceramic coating with low thermal conductivity and high thermal shock resistance on the surface of high-temperature alloys, the temperature of the base alloy can be effectively reduced and the service life of blade parts can be extended. At present, the thermal barrier coatings that provide thermal insulation and protection between high-temperature gas and turbine blades in actual application are all double-layer structures: the surface layer is a ceramic layer and the inner layer is a metal bonding layer. In the composition of thermal barrier coatings, the bonding layer plays a vital role. Its performance is not only directly related to the durability and reliability of the entire coating system, but also determines whether the coating can remain stable for a long time at high temperatures and provide effective protection for the base alloy. The bonding layer must not only have good oxidation resistance, but also have good adhesion, which can reduce the mismatch of thermal expansion coefficients between the ceramic surface layer and the high-temperature alloy substrate. Although the traditional NiCoCrAlY bonding layer has a certain antioxidant ability, when facing more severe high-temperature service conditions, the bonding layer between the traditional thermal barrier coating and the base alloy often has problems such as insufficient bonding strength and poor oxidation resistance, which limits its application effect and performance and cannot meet the needs of long-term use.

[0005] Therefore, modifying the NiCoCrAlY bonding layer to further enhance its antioxidant properties and thermal stability has become an important direction of current research. Summary of the invention

[0006] The present invention aims to solve the problems of insufficient bonding strength and poor oxidation resistance of the bonding layer between the existing thermal barrier coating and the base alloy, and further provides a method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating.

[0007] A method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating is carried out according to the following steps:

[0008] 1. Preparation of NiCoCrAlYMn alloy powder:

[0009] Weighing raw materials according to mass percentages of 20% to 26% Co, 18% to 22% Cr, 8% to 12% Al, 0.3% to 1% Y, 0.5% to 1% Mn and the balance Ni, then subjecting the weighed raw materials to mechanical alloying treatment, and finally drying to obtain NiCoCrAlYMn alloy powder;

[0010] 2. Plasma spraying:

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

[0012] 3. Spraying ceramic top layer material:

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

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

[0015] The present invention significantly improves the oxidation resistance and thermal stability of the coating by adding Mn element to the NiCoCrAlY bonding layer, thereby extending the service life of the nickel-based high-temperature alloy K435.

[0016] The addition of Mn element in the present invention also improves the microstructure and element distribution of the coating, strengthens the interface 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, help reduce the overall temperature gradient of the coating, and improve the thermal shock resistance of the coating. The preparation method of the present invention is simple and easy to implement, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1Schematic diagram and scanning coating cross-sectional diagram of a nickel-based high-temperature alloy K435 covered with a thermal barrier coating prepared in Example 1, 1 is a K435 substrate, 2 is a NiCoCrAlYMn bonding layer, and 3 is a ceramic top layer;

[0018] Figure 2 The oxidation weight gain curves of the K435 substrate, the nickel-based high-temperature alloy K435 covered with a thermal barrier coating prepared in Example 1 and the comparative experiment 1 under high-temperature oxidation at 900°C;

[0019] Figure 3 The cross-sectional view and element scan of the nickel-based high-temperature alloy K435 covered with a thermal barrier coating prepared in Example 1 after high-temperature oxidation at 900°C for 20 hours. DETAILED DESCRIPTION

[0020] Specific implementation method 1: This implementation method is a method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating, which is carried out according to the following steps:

[0021] 1. Preparation of NiCoCrAlYMn alloy powder:

[0022] Weighing raw materials according to mass percentages of 20% to 26% Co, 18% to 22% Cr, 8% to 12% Al, 0.3% to 1% Y, 0.5% to 1% Mn and the balance Ni, then subjecting the weighed raw materials to mechanical alloying treatment, and finally drying to obtain NiCoCrAlYMn alloy powder;

[0023] 2. Plasma spraying:

[0024] The NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate by plasma spraying technology to obtain a NiCoCrAlYMn bonding layer;

[0025] 3. Spraying ceramic top layer material:

[0026] The ceramic top layer material is sprayed on the NiCoCrAlYMn bonding layer by plasma spraying technology to obtain the nickel-based high-temperature alloy K435 thermal barrier coating.

[0027] In this embodiment, the Mn element can cause the refinement of the grains in the matrix material and increase the number of grain boundaries. The increase in grain boundaries provides more channels for the transfer of heat, thereby improving the thermal conductivity of the material. At the same time, the doping elements can also increase the energy of the grain boundaries, making it easier for thermal electrons to cross the grain boundaries. This increase in energy helps to accelerate the heat transfer process inside the material, thereby improving thermal conductivity. Therefore, this 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 this embodiment are:

[0029] In this embodiment, by adding Mn element to the NiCoCrAlY bonding layer, the oxidation resistance and thermal stability of the coating are significantly improved, and the service life of the nickel-based high-temperature alloy K435 is extended;

[0030] The addition of Mn element in this embodiment also improves the microstructure and element distribution of the coating, strengthens the interface 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, help reduce the overall temperature gradient of the coating, and improve the thermal shock resistance of the coating. The preparation method of the present invention is simple and easy to implement, and is suitable for industrial production.

[0031] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the raw materials in step 1 are Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder; the particle size of the raw materials in step 1 is 30 μm to 50 μm. The rest is the same as specific implementation method 1.

[0032] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the mechanical alloying treatment described in step 1 is specifically carried out according to the following steps: using grinding balls with a diameter of 8 mm to 10 mm, with a ball-to-material mass ratio of (10 to 20):1 and a ball milling speed of 300 r / min to 400 r / min, the mechanical alloying treatment is carried out for 2 h to 20 h. Other steps are the same as those of specific implementation method 1 or 2.

[0033] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the drying in step 1 is carried out at a temperature of 100° C. to 200° C. for 5 to 10 hours. The rest is the same as specific embodiment 3.

[0034] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the pretreated K435 substrate described in step 2 is obtained by sequentially degreasing, sandblasting, cleaning and preheating the nickel-based high-temperature alloy K435. The rest is the same as specific embodiments 1 to 4.

[0035] In order to roughen the sample surface to meet the spraying roughness requirements, all substrate surfaces in the test are sandblasted in advance. The sandblasting angle cannot be perpendicular to the workpiece surface to prevent sand particles from being directly embedded in the workpiece surface. The sample surface after sandblasting can be cleaned and degreased with acetone. The substrate after sandblasting is preferably sprayed within 2h to 3h, otherwise if the substrate surface is contaminated (usually oxidized and rusted), it cannot be used normally and needs to be sandblasted again.

[0036] At the same time, the substrate surface needs to be preheated. Use a plasma spray gun for preheating. During the operation, the powder feeder that matches the spray gun should be turned off, and the spray gun should move at a uniform speed to prevent the substrate from oxidizing due to the increase in temperature during the preheating process, thereby affecting the bonding strength between the plasma spray coating and the substrate.

[0037] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that: the sand blasting is performed using white corundum sand with a sand particle size of 10-30 mesh, under the conditions of a sand blasting pressure of 0.4MPa-0.6MPa, a sand blasting angle of 70°-80°, and a sand blasting distance of 100mm-200mm; the preheating is performed using a plasma spray gun at a temperature of 300°C-400°C. The rest is the same as specific embodiments 1 to 5.

[0038] Specific embodiment 7: This embodiment is different from specific embodiments 1 to 6 in that the plasma spraying technology described in step 2 is specifically carried out under the conditions of arc current of 400A to 600A, spraying distance of 100mm to 300mm, powder feeding amount of 15g / min to 50g / min, spray gun moving speed of 100mm / s to 300mm / s, oxygen flow rate of 40L / min to 70L / min, propane flow rate of 40L / min to 60L / min and air flow rate of 50L / min to 500L / min. Others are the same as specific embodiments 1 to 6.

[0039] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the ceramic top layer material in step 3 is alumina ceramic or yttria-stabilized zirconia ceramic. The rest is the same as specific embodiments 1 to 7.

[0040] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in 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 balance is ZrO2; the particle size of the yttria-stabilized zirconia ceramic is 45μm to 90μm. Other features are the same as specific embodiments 1 to 8.

[0041] Specific embodiment 10: This embodiment is different from specific embodiments 1 to 9 in that the plasma spraying technology described in step 3 is specifically carried out under the conditions of arc current of 400A to 600A, spraying distance of 50mm to 110mm, powder feeding amount of 20g / min to 50g / min, spray gun moving speed of 30mm / s to 100mm / s, nitrogen flow rate of 300L / min to 2000L / min and hydrogen flow rate of 5L / min to 50L / min. Others are the same as specific embodiments 1 to 9.

[0042] The following examples are used to verify the beneficial effects of the present invention:

[0043] Embodiment 1:

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

[0045] 1. Preparation of NiCoCrAlYMn alloy powder:

[0046] Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder are weighed as raw materials according to the mass percentage of 23.9% Co, 19.9% ​​Cr, 11.9% Al, 1.0% Y, 0.6% Mn and the balance Ni, and then the weighed raw materials are mechanically alloyed for 10 hours using a grinding ball with a diameter of 8 mm, at a ball-to-material mass ratio of 10:1 and a ball mill speed of 400 r / min, and finally dried at a temperature of 150° C. for 8 hours to obtain NiCoCrAlYMn alloy powder;

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

[0048] 2. Plasma spraying:

[0049] Plasma spraying technology was used to spray NiCoCrAlYMn alloy powder onto the surface of the pretreated K435 substrate under the conditions of arc current of 600A, spraying distance of 250mm, powder feeding amount of 50g / min, spray gun moving speed of 100mm / s, oxygen flow rate of 70L / min, propane flow rate of 55L / min and air flow rate of 100L / min to obtain a NiCoCrAlYMn bonding layer;

[0050] 3. Spraying ceramic top layer material:

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

[0052] The pretreated K435 substrate described in step 2 is specifically obtained by sequentially performing degreasing, sandblasting, cleaning and preheating treatments on the nickel-based high-temperature alloy K435;

[0053] The oil removal is specifically to use alcohol and acetone to ultrasonically clean the oil stains for 10 minutes at a power of 300W;

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

[0055] The cleaning specifically involves cleaning and degreasing with acetone;

[0056] The preheating is performed by using a plasma spray gun at a temperature of 300°C.

[0057] The ceramic top layer material described 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 remainder is ZrO2; the average particle size of the yttria-stabilized zirconia ceramic is 45μm.

[0058] Comparative Experiment 1: This comparative experiment is different from Example 1 in that the addition of Mn is omitted in step 1, and Co powder, Cr powder, Al powder, Y powder and Ni are weighed as raw materials according to the mass percentage of 24% Co, 20% Cr, 12% Al, 1% Y and the balance Ni. The rest is the same as Example 1.

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

[0060] Figure 2The following are the oxidation weight gain curves of the K435 substrate, the nickel-based high-temperature alloy K435 coated with a thermal barrier coating prepared in Example 1 and the comparative experiment 1 under high-temperature oxidation at 900°C. As can be seen from the figure, after 20 hours of high-temperature oxidation at 900°C, the K435 alloy without a bonding layer and a ceramic top layer increases by 4.98 mg / cm 2 The thermal barrier coating of NiCoCrAlY bonding layer prepared in experiment 1 increased by 3.26 mg / cm 2 The thermal barrier coating of NiCoCrAlYMn bonding layer prepared in Example 1 gained 2.5 mg / cm 2 It can be seen that the oxidation corrosion resistance of the coated K435 alloy is significantly higher than that of the uncoated material, and the coating with Mn is better than the traditional NiCoCrAlY bonding layer.

[0061] Figure 3 The cross-sectional view and elemental scans of the nickel-based high-temperature alloy K435 coated with a thermal barrier coating prepared in Example 1 after high-temperature oxidation at 900°C for 20 hours. As can be seen from the figure, after 20 hours of oxidation, the bonding strength and anti-oxidation effect of the coating are good, and there is no coating peeling.

Claims

1. A method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating, characterized in that It is carried out in the following steps:

1. Preparation of NiCoCrAlYMn alloy powder: Weighing raw materials according to mass percentages of 20% to 26% Co, 18% to 22% Cr, 8% to 12% Al, 0.3% to 1% Y, 0.5% to 1% Mn and the balance Ni, then subjecting the weighed raw materials to mechanical alloying treatment, and finally drying to obtain NiCoCrAlYMn alloy powder; 2. Plasma spraying: The NiCoCrAlYMn alloy powder is sprayed on the surface of the pretreated K435 substrate by plasma spraying technology to obtain a NiCoCrAlYMn bonding layer; 3. Spraying ceramic top layer material: The ceramic top layer material is sprayed on the NiCoCrAlYMn bonding layer by plasma spraying technology to obtain the nickel-based high-temperature alloy K435 thermal barrier coating.

2. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 1, characterized in that The raw materials described in step one are Co powder, Cr powder, Al powder, Y powder, Mn powder and Ni powder; the particle size of the raw materials described in step one is 30μm to 50μm.

3. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 1, characterized in that The mechanical alloying treatment described in step 1 is specifically carried out according to the following steps: using grinding balls with a diameter of 8mm to 10mm, at a ball-to-material mass ratio of (10 to 20):1 and a ball mill speed of 300r / min to 400r / min, mechanical alloying treatment is carried out for 2h to 20h.

4. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 1, characterized in that The drying described in step 1 is specifically carried out at a temperature of 100° C. to 200° C. for 5 h to 10 h.

5. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 1, characterized in that The pretreated K435 substrate described in step 2 is specifically obtained by sequentially performing degreasing, sandblasting, cleaning and preheating treatments on the nickel-based high-temperature alloy K435.

6. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 5, characterized in that The sandblasting treatment is specifically carried out using white corundum sand with a sand particle size of 10 mesh to 30 mesh, under the conditions of a sandblasting pressure of 0.4 MPa to 0.6 MPa, a sandblasting angle of 70° to 80° and a sandblasting distance of 100 mm to 200 mm; the preheating is specifically carried out using a plasma spray gun at a temperature of 300° to 400°C.

7. The method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating according to claim 1, characterized in that The plasma spraying technology described in step 2 is specifically carried out under the conditions of arc current of 400A to 600A, spraying distance of 100mm to 300mm, powder feeding amount of 15g / min to 50g / min, spray gun moving speed of 100mm / s to 300mm / s, oxygen flow rate of 40L / min to 70L / min, propane flow rate of 40L / min to 60L / min and air flow rate of 50L / min to 500L / min.

8. The method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating according to claim 1, characterized in that The ceramic top layer material described in step 3 is alumina ceramic or yttria-stabilized zirconia ceramic.

9. The method for preparing a nickel-based high-temperature alloy K435 thermal barrier coating according to claim 8, characterized in 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 balance is ZrO2; the particle size of the yttria-stabilized zirconia ceramic is 45 μm to 90 μm.

10. The method for preparing a thermal barrier coating of a nickel-based high-temperature alloy K435 according to claim 1, characterized in that The plasma spraying technology described in step three is specifically carried out under the conditions of arc current of 400A to 600A, spraying distance of 50mm to 110mm, powder feeding amount of 20g / min to 50g / min, spray gun moving speed of 30mm / s to 100mm / s, nitrogen flow rate of 300L / min to 2000L / min and hydrogen flow rate of 5L / min to 50L / min.

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