Gradient coating preparation method combined with gas phase aluminizing process

Abstract

The invention discloses a gradient coating preparation method combined with a gas phase aluminizing process, and relates to the technical field of thermal spraying, and the gradient coating preparation method comprises the following technological processes: S1, carrying out sand blasting treatment on a common gas turbine hot part material GH3536, and then carrying out transferred arc activation treatment on the sand-blasted surface by using vacuum plasma equipment; s2, Ni < 23 > Co < 20 > Cr < 12 > Al < 4 > Ta < 0.6 > Y powder is sprayed; s3, spraying of Ni < 23 > Co < 20 > Cr < 10 > Al < 0.6 > Y powder is conducted; s4, spraying of Ni20Cr10Al powder is carried out; s5, Ni5Al powder is sprayed; s6, a beta-NiAl layer containing an Al2O3 protective film is prepared on the surface of the coating and the surface of the part through the gas phase aluminizing technology; gradient coatings with different components are prepared through atmospheric plasma spraying, and finally a beta-NiAl layer containing an Al2O3 protective film is formed on the surfaces of the gradient coatings through gas phase aluminizing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal spraying, in particular to a gradient coating preparation method combined with a gas phase aluminizing process. BACKGROUND

[0002] Thermal spraying technology has a very wide application in the field of gas turbines, mainly including thermal barrier coatings applied to turbine blades, gas phase aluminizing coatings, thermal barrier coatings of combustion chambers, and seal coating of casings. However, except for the seal coating, the remaining pure metal coatings and ceramic coatings are difficult to prepare a thick coating of more than 1mm, but the seal coating is difficult to resist the high-temperature molten salt corrosion environment of the gas turbine due to its own structural characteristics, and the technical threshold of this type of coating is high. Therefore, the present application aims to make a gradient coating with high temperature resistance, corrosion resistance and sealing function by combining thermal spraying process with gas phase aluminizing. SUMMARY

[0003] The present application aims to provide a gradient coating preparation method combined with a gas phase aluminizing process to solve the problems raised in the background art.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solution: a gradient coating preparation method combined with a gas phase aluminizing process, comprising the following process flow:

[0005] S1: After sandblasting the common gas turbine hot part material GH3536, the surface after sandblasting is activated by transfer arc using a vacuum plasma device;

[0006] S2: Spray Ni23Co20Cr12Al4Ta0.6Y powder as the bottom bonding layer, the spraying thickness is 0.2-0.3mm;

[0007] S3: Spray Ni23Co20Cr10Al0.6Y powder, the spraying thickness is 0.3-0.4mm;

[0008] S4: Spray Ni20Cr10Al powder, the thickness is 0.3-0.4mm;

[0009] S5: Spray Ni5Al powder, the coating thickness is 0.3-0.4mm;

[0010] S6: Use the gas phase aluminizing process to prepare a layer of β-NiAl containing Al2O3 protective film on the coating and the surface of the part.

[0011] 3、Preferably, the process flow of the gas phase aluminizing process in step S6 is:

[0012] A1, sandblasting to remove rust and oil stains on the surface of the workpiece, 120 mesh alumina sand, pressure 0.3MPa;

[0013] A2. Preparation of aluminizing agent: Mix 50% Al powder, 40% alumina powder, and 10% AlCl3 according to the mass fraction, with a particle size of 100-200 mesh, and stir evenly.

[0014] A3. Packing the workpiece into the furnace: Spread the prepared powder evenly on the bottom of the crucible to a thickness of 30mm.

[0015] Place the workpiece in, and finally completely cover the workpiece and test piece with powder;

[0016] A4. Sealing: Cover the box and seal the gaps with refractory putty.

[0017] A5. Aluminizing treatment: Place the crucible containing the parts and test pieces into a muffle furnace and heat to 1080℃.

[0018] Keep warm for 5 hours, then cool in the furnace to below 100°C before being removed from the furnace.

[0019] Preferably, in steps S2, S3, S4, and S5, different processes are used to prepare gradient coatings, and the coefficient of thermal expansion of the coating gradually decreases in each step, gradually reducing the difference between the coefficient of thermal expansion and that of the substrate.

[0020] Preferably, the specific reaction principle in step S6 is as follows:

[0021] AlCl3 + Al → 3AlCl2

[0022] 3AlCl2→[Al]+2AlCl3

[0023] [Al] represents active aluminum atoms.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention is a gradient coating preparation method combined with vapor phase aluminizing process. By preparing gradient coatings of different compositions using atmospheric plasma spraying, vapor phase aluminizing is finally used to form a β-NiAl layer containing an Al2O3 protective film on the surface of the gradient coating. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example:

[0028] A method for preparing gradient coatings using a vapor-phase aluminizing process includes the following process flow:

[0029] S1: After sandblasting the common gas turbine hot component material GH3536, a transfer arc activation treatment is performed on the sandblasted surface using a vacuum plasma equipment; before spraying, a vacuum plasma spraying equipment is used to switch the positive and negative electrodes of the surface to be sprayed and the spray gun, so that the part to be sprayed is connected to the negative electrode, and impurities, oxide film and other substances on the surface to be sprayed are peeled off, the sprayed surface is activated, the bonding strength between the coating and the substrate is improved, and support is provided for the subsequent thick metal gradient coating;

[0030] S2: Spray Ni23Co20Cr12Al4Ta0.6Y powder as the bottom adhesive layer, with a spray thickness of 0.2-0.3mm;

[0031] S3: Spray Ni23Co20Cr10Al0.6Y powder, with a coating thickness of 0.3-0.4mm;

[0032] S4: Spray Ni20Cr10Al powder, thickness 0.3-0.4mm;

[0033] S5: Spray Ni5Al powder, coating thickness 0.3-0.4mm;

[0034] S6: Using a vapor phase aluminizing process, a β-NiAl layer containing an Al2O3 protective film is prepared on the surface of the coating and parts.

[0035] The flow of the vapor phase aluminizing process in step S6 is as follows:

[0036] A1. Sandblasting removes rust and oil stains from the workpiece surface using 120-mesh alumina sand at a pressure of 0.3 MPa.

[0037] A2. Preparation of aluminizing agent: Mix 50% Al powder, 40% alumina powder, and 10% AlCl3 according to the mass fraction, with a particle size of 100-200 mesh, and stir evenly.

[0038] A3. Packing the workpiece into the furnace: Spread the prepared powder evenly on the bottom of the crucible to a thickness of 30mm.

[0039] Place the workpiece in, and finally completely cover the workpiece and test piece with powder;

[0040] A4. Sealing: Cover the box and seal the gaps with refractory putty.

[0041] A5. Aluminizing treatment: Place the crucible containing the parts and test pieces into a muffle furnace, heat it to 1080℃, hold it at that temperature for 5 hours, and then cool it down to below 100℃ with the furnace before removing it from the furnace.

[0042] In steps S2, S3, S4, and S5, different processes are used to prepare gradient coatings. The coefficient of thermal expansion of the coating gradually decreases in each step, gradually reducing the difference between the coefficient of thermal expansion and the substrate, achieving better thermal matching, and preventing the coating from peeling off from the substrate due to thermal expansion mismatch during high-temperature operation.

[0043] The specific reaction principle in step S6 is as follows:

[0044] AlCl3 + Al → 3AlCl2

[0045] 3AlCl2→[Al]+2AlCl3

[0046] [Al] represents active aluminum atoms; to improve the low Al content in Ni5Al coatings, which makes it difficult to form an effective alumina protective film, a β-NiAl layer containing an Al2O3 protective film is formed on the surface of Ni5Al thermal spray coating using a vapor phase aluminizing process.

[0047] Case 1:

[0048] S1, the part is sandblasted, and then the part is placed in a vacuum plasma equipment. The surface to be sprayed is cleaned and activated using a transfer arc, and a reverse current of 20A is applied.

[0049] S2, using supersonic flame spraying to coat Ni23Co20Cr12Al4Ta0.6Y powder as the base adhesive layer, with a coating thickness of 0.2-0.3mm;

[0050] S3, Ni23Co20Cr10Al0.6Y powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0051] S4, Ni20Cr10Al powder is sprayed using an atmospheric plasma spraying device to a thickness of 0.3-0.4mm;

[0052] S5, Ni5Al powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0053] S6 uses a vapor phase aluminizing process. Specifically, the part is placed in an alumina crucible, and aluminum powder, alumina powder, and aluminum chloride powder are added as aluminizing agents. The crucible is sealed with refractory mud, and the part is heated to 1080℃ and held for 4 hours to prepare a β-NiAl layer containing an Al2O3 protective film on the surface of the Ni5Al coating. The coating thickness is about 50μm.

[0054] Case 2:

[0055] S1, the part is sandblasted, and then the part is placed in a vacuum plasma equipment. The surface to be sprayed is cleaned and activated using a transfer arc, and a reverse current of 20A is applied.

[0056] S2, using atmospheric plasma spraying of Ni23Co20Cr12Al4Ta0.6Y powder as the bottom bonding layer, with a spraying thickness of 0.2-0.3mm;

[0057] S3, Ni23Co20Cr10Al0.6Y powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0058] S4, Ni20Cr10Al powder is sprayed using an atmospheric plasma spraying device to a thickness of 0.3-0.4mm;

[0059] S5, Ni5Al powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0060] S6 uses a vapor phase aluminizing process. Specifically, the part is placed in an alumina crucible, and aluminum powder, alumina powder, and aluminum chloride powder are added as aluminizing agents. The crucible is sealed with refractory mud, and the part is heated to 1080℃ and held for 5 hours to prepare a β-NiAl layer containing an Al2O3 protective film on the surface of the Ni5Al coating. The coating thickness is about 60μm.

[0061] Case 3:

[0062] S1, the part is sandblasted, and then the part is placed in a vacuum plasma equipment. The surface to be sprayed is cleaned and activated using a transfer arc, and a reverse current of 20A is applied.

[0063] S2, using vacuum plasma spraying of Ni23Co20Cr12Al4Ta0.6Y powder as the bottom bonding layer, with a spraying thickness of 0.2-0.3mm;

[0064] S3, Ni23Co20Cr10Al0.6Y powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0065] S4, Ni20Cr10Al powder is sprayed using an atmospheric plasma spraying device to a thickness of 0.3-0.4mm;

[0066] S5, Ni5Al powder is sprayed using an atmospheric plasma device, with a coating thickness of 0.3-0.4mm;

[0067] S6 uses a vapor phase aluminizing process. Specifically, the part is placed in an alumina crucible, and aluminum powder, alumina powder, and aluminum chloride powder are added as aluminizing agents. The crucible is sealed with refractory mud, and the part is heated to 1080℃ and held for 6 hours to prepare a β-NiAl layer containing an Al2O3 protective film on the surface of the Ni5Al coating. The coating thickness is about 70μm.

[0068] By taking advantage of the gradually decreasing thermal expansion coefficient of gradient coatings, the span between the thermal expansion coefficients of the substrate and the coating can be gradually reduced, so that pure metal coatings with a thickness of more than 1 mm can be made to prevent failure. Combined with the vapor phase aluminizing process, the thermal protection of the coating can be achieved by utilizing the anti-oxidation protection function of the surface Al2O3.

[0069] In Case 1, the underlying adhesive layer, after being activated by a transfer arc, exhibited high bonding strength with the substrate, exceeding 75 MPa, thanks to the supersonic flame spraying process. The Al2O3 protective layer on the surface of the coating in Case 1 enhanced its oxidation resistance; after oxidation at 850℃ for 100 hours, Case 1 showed a weight gain of only 11.9 mg / cm³. 2 The presence of surface alumina effectively prevents the oxidation of elements such as Ni, Co, and Cr in the coating, and no oxide layer was observed in the substrate, providing effective protection.

[0070] In Case 2, the bottom adhesive layer was applied using an atmospheric plasma process. The bonding strength of the bottom coating in Case 2 was 42 MPa. After oxidation at 850℃ for 100 hours, Case 2 showed a weight gain of 15.2 mg / cm³. 2 The matrix did not undergo oxidation.

[0071] In Case 3, the bottom adhesive layer was applied using a vacuum plasma process, directly after step S1, which further reduced the oxygen content of the bottom layer. The bonding strength of the bottom coating in Case 3 was 58 MPa, and after oxidation at 850℃ for 100 hours, the weight gain in Case 3 was 12.7 mg / cm³. 2 The matrix did not undergo oxidation.

[0072] Each of the above innovations enhances the coating's bonding strength and high-temperature resistance. By changing the material and gradually reducing the range of the coating's thermal expansion coefficient, pure metal coatings of 1 mm or more can be prepared. Through three case studies, it can be found that cleaning the substrate with a transfer arc can significantly improve the coating's bonding strength. In addition, the β-NiAl layer containing an Al2O3 protective film prepared by the vapor phase aluminizing process provides thermal protection for both the coating and the substrate in high-temperature oxidation experiments, preventing the oxidation of the materials and fully demonstrating the effectiveness of this invention.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a gradient coating using a vapor-phase aluminizing process, characterized in that: The process includes the following steps: S1: After sandblasting the common gas turbine hot component material GH3536, the surface after sandblasting is activated by transfer arc using vacuum plasma equipment. S2: Spray Ni23Co20Cr12Al4Ta0.6Y powder as the bottom adhesive layer, with a spray thickness of 0.2-0.3mm; S3: Spray Ni23Co20Cr10Al0.6Y powder, with a coating thickness of 0.3-0.4mm; S4: Spray Ni20Cr10Al powder, thickness 0.3-0.4mm; S5: Spray Ni5Al powder, coating thickness 0.3-0.4mm; S6: Using a vapor phase aluminizing process, a β-NiAl layer containing an Al2O3 protective film is prepared on the surface of the coating and parts.

2. The method for preparing a gradient coating combined with a vapor-phase aluminizing process according to claim 1, characterized in that: The flow of the vapor phase aluminizing process in step S6 is as follows: A1. Sandblasting removes rust and oil stains from the workpiece surface using 120-mesh alumina sand at a pressure of 0.3 MPa. A2. Preparation of aluminizing agent: Mix 50% Al powder, 40% alumina powder, and 10% AlCl3 according to the mass fraction, with a particle size of 100-200 mesh, and stir evenly. A3. Packing the workpiece into the furnace: Spread the prepared powder evenly on the bottom of the crucible to a thickness of 30mm, put the workpiece in, and finally completely cover the workpiece and test piece with powder. A4. Sealing: Cover the box and seal the gaps with refractory putty. A5. Aluminizing treatment: Place the crucible containing the parts and test pieces into a muffle furnace, heat it to 1080℃, hold it at that temperature for 5 hours, and then cool it down to below 100℃ with the furnace before removing it from the furnace.

3. The method for preparing a gradient coating combined with a vapor-phase aluminizing process according to claim 1, characterized in that: In steps S2, S3, S4, and S5, different processes are used to prepare gradient coatings. In each step, the coefficient of thermal expansion of the coating gradually decreases, thus gradually reducing the difference between the coefficient of thermal expansion and that of the substrate.

4. The method for preparing a gradient coating combined with a vapor-phase aluminizing process according to claim 1, characterized in that: The specific reaction principle in step S6 is as follows: AlCl3 + Al → 3AlCl2 3AlCl2→[Al]+2AlCl3 [Al] represents active aluminum atoms.