A coating repair method for reuse of coated graphite crucible

Abstract

The present invention belongs to the technical field of composite coating preparation, and specifically relates to a coating repair method for reused coated graphite crucibles. This method laser remelts the plasma-sprayed lamellar structure to reduce the porosity of the coating surface. The laser-clad coating surface is then vacuum-hot-pressed, significantly reducing the porosity within the hot-pressed coating. Simultaneously, metallurgical bonds are formed between the coating and the substrate, and between the coatings themselves. Both laser cladding and vacuum hot-pressing densify the coating, significantly improving the performance of existing plasma-sprayed coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of composite coating preparation, and in particular relates to a coating repair method for reuse of a coated graphite crucible. Background Art

[0002] Graphite, resistant to high temperatures, easy to process, and with excellent thermal shock resistance, has become an important and widely used crucible and mold material for melting active metals. However, graphite is porous and absorbs a certain amount of gas and moisture at room temperature, some of which escapes when heated. Furthermore, graphite's high vapor pressure when heated causes it to form carbides directly or indirectly with many elements at high temperatures, affecting the purity of the metal. Therefore, plasma spraying is commonly used to apply a composite coating to the inner surface of graphite crucibles to prevent the introduction of carbon and other impurities. However, plasma sprayed coatings inevitably contain pores and cracks, which can cause the coating to fall off and become ineffective after melting, resulting in a single-use coated graphite crucible. This not only increases crucible manufacturing costs but also generates significant waste and increases post-processing costs.

[0003] In view of the shortcomings of the above-mentioned prior art, it is urgent to design a coating repair method for reuse of coated graphite crucibles. Summary of the Invention

[0004] The purpose of the present invention is to provide a coating repair method for reuse of coated graphite crucibles, which solves the problem of coating cracking and peeling caused by pores and microcracks in the coating after plasma spraying, repairs the pores and microcracks in the coating, improves the density, thermal shock resistance and oxidation resistance of the coating, and realizes multiple reuse of the coated graphite crucible.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A coating repair method for reuse of a coated graphite crucible, comprising the following steps:

[0007] (1) performing plasma spraying on the surface of a graphite crucible to prepare a composite coating, wherein the composite coating comprises one or more of Mo / Y2O3, Nb / ZrO2, and Nb / Y2O3;

[0008] (2) laser remelting the plasma sprayed lamellar structure, installing an anti-crack plate at the right-angle transition of the graphite crucible to reduce the porosity of the coating surface;

[0009] (3) Vacuum hot pressing the coating surface after laser cladding.

[0010] Furthermore, the plasma spraying process parameters in step (1) are: substrate preheating temperature 50-300°C, power 30kW, powder feed rate 1.35kg / h, spraying distance 10-20cm, and gun travel speed 6mm / s.

[0011] The laser cladding process parameters in step (2) are: laser power: 255 W; spot size: 1-2 mm; scanning speed: 46 mm / s; focal length: 330 mm; overlap rate: 50%.

[0012] The vacuum hot pressing process parameters in step (3) are: the vacuum degree of the vacuum sintering furnace is controlled at the Pa level, the pressure is set at 100kPa-6MPa, and the coating is vacuum hot pressed using oil pressure or air pressure.

[0013] In step (2), the graphite crucible is preheated to 50-60°C, and an external heater is used. An anti-crack plate is installed at the right-angle transition of the graphite crucible to prevent the coating from cracking due to slight deviations in mold processing and procedures during the cladding process, which may cause the laser to directly act on the right angle.

[0014] Set the laser power output and determine the mold motion program (rotation speed corresponds to laser scanning speed).

[0015] After the cladding is completed, the graphite crucible is removed and placed in a blast drying oven.

[0016] The graphite crucible after laser cladding is placed in a vacuum hot pressing furnace for hot pressing, and the appropriate pressure parameters are selected according to the type of coating and graphite model.

[0017] The repaired coated graphite crucible of the present invention can meet the requirement of multiple reuse of the crucible.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention proposes a coating repair method for reuse of coated graphite crucibles. The coating repaired by laser cladding and vacuum hot pressing technology can form a smooth, uniform, high-temperature resistant composite coating without pores or cracks. Under the combined action of laser cladding and vacuum hot pressing, the coating has excellent thermal shock resistance and can withstand 3-5 melting times in a high-temperature melt up to 1800K. It can provide a more favorable technical solution for improving the coating preparation process and enhancing the coating performance, and is of great significance for extending the service life of the coated graphite crucible, ensuring its service safety and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope photo of the plasma sprayed coating at 8000X;

[0021] Figure 2 This is a scanning electron microscope photo of the coating after laser cladding and vacuum hot pressing repair at 8000X. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to specific embodiments.

[0023] The method of the present invention works as follows: the plasma-sprayed lamellar structure is laser remelted to reduce the porosity of the coating surface; the laser-clad coating surface is then vacuum hot-pressed, which greatly reduces the porosity within the hot-pressed coating. At the same time, metallurgical bonds are formed between the coating and the substrate, and between the coatings. Both laser cladding and vacuum hot-pressing densify the coating, significantly improving the various properties of existing plasma-sprayed coatings.

[0024] Specifically, the present invention comprises the following steps:

[0025] (1) performing plasma spraying on the surface of a graphite crucible to prepare a composite coating, wherein the composite coating comprises one or more of Mo / Y2O3, Nb / ZrO2, and Nb / Y2O3;

[0026] (2) laser remelting the plasma sprayed lamellar structure, installing an anti-crack plate at the right-angle transition of the graphite crucible to reduce the porosity of the coating surface;

[0027] (3) Vacuum hot pressing is performed on the coating surface after laser cladding.

[0028] Furthermore, the plasma spraying process parameters in step (1) are: substrate preheating temperature 50-300°C, power 30kW, powder feed rate 1.35kg / h, spraying distance 10-20cm, and gun travel speed 6mm / s.

[0029] The laser cladding process parameters in step (2) are: laser power: 255 W; spot size: 1-2 mm; scanning speed: 46 mm / s; focal length: 330 mm; overlap rate: 50%.

[0030] The vacuum hot pressing process parameters in step (3) are: the vacuum degree of the vacuum sintering furnace is controlled at the Pa level, the pressure is set at 100kPa-6MPa, and the coating is vacuum hot pressed using oil pressure or air pressure.

[0031] In step (2), the graphite crucible is preheated to 50-60°C, and an external heater is used. An anti-crack plate is installed at the right-angle transition of the graphite crucible to prevent the coating from cracking due to slight deviations in mold processing and procedures during the cladding process, which may cause the laser to directly act on the right angle.

[0032] Set the laser power output and determine the mold motion program (rotation speed corresponds to laser scanning speed).

[0033] After the cladding is completed, the graphite crucible is removed and placed in a blast drying oven.

[0034] The graphite crucible after laser cladding is placed in a vacuum hot pressing furnace for hot pressing, and the appropriate pressure parameters are selected according to the type of coating and graphite model.

[0035] Example 1

[0036] The main process of laser cladding treatment in this embodiment is as follows:

[0037] (1): The preheating temperature of the graphite crucible is 50-60℃, and the process is equipped with an external heater.

[0038] (2): Clean the clamping mold and install the crucible and anti-crack plate:

[0039] The anti-crack plate is installed at the right-angle transition of the graphite crucible to prevent the coating from cracking due to the direct action of the laser on the right angle due to slight deviations in mold processing and procedures during the cladding process.

[0040] (3): Preheat the bottom plate of the graphite crucible to 50-60℃.

[0041] (4): Turn on the laser cooling water and the argon gas device.

[0042] (5): Set the laser power output and determine the mold movement program (rotation speed corresponds to laser scanning speed).

[0043] The laser cladding process parameters are: laser power: 255W; spot size: 1-2mm; scanning speed: 46mm / s; focal length: 330mm; overlap rate: 50%.

[0044] (6): Turn on the laser and crucible motion program for laser cladding.

[0045] (7): After the cladding is completed, remove the graphite crucible and place it in a blast drying oven.

[0046] The vacuum hot pressing process in this embodiment is as follows:

[0047] (8): The graphite crucible after laser cladding in (7) is placed in a vacuum hot pressing furnace for hot pressing; the vacuum hot pressing process parameters are: the vacuum degree of the vacuum sintering furnace is controlled at the Pa level, and the pressure is set at 100kPa-6MPa; the appropriate pressure parameters are selected according to the type of coating and the graphite model.

[0048] (9): The repaired coated graphite crucible can meet the requirements of multiple reuse of the crucible.

[0049] like Figure 1 As shown in the scanning electron microscope photo of the plasma sprayed coating at 8000X, there are pores and cracks running through the entire coating, including transverse cracks and vertical cracks, a clear lamellar structure, an extremely uneven surface, and poor bonding performance.

[0050] like Figure 2As shown in the scanning electron microscope photo of the coating under 8000X after laser cladding and vacuum hot pressing repair, it can be seen that the pores of the coating are filled, the surface is flat and uniform, the mechanically bonded lamellar structure is transformed into a metallurgical bond, and the bonding strength is greatly improved.

[0051] Testing of the coating's bonding strength revealed that after laser cladding and vacuum hot pressing, the coating's bond to the graphite substrate was stronger than the bond between the Y2O3 coating and the substrate itself. The bond strength after laser treatment ranged from 5 to 11 MPa, while the untreated bond strength was approximately 0.5 to 3 MPa, demonstrating that laser cladding and vacuum hot pressing significantly improve the coating's bonding strength.

[0052] The beneficial effects of the present invention are as follows:

[0053] The present invention proposes a coating repair method for reuse of coated graphite crucibles. The coating repaired by laser cladding and vacuum hot pressing technology can form a smooth, uniform, high-temperature resistant composite coating without pores or cracks. Under the combined action of laser cladding and vacuum hot pressing, the coating has excellent thermal shock resistance and can withstand 3-5 melting times in a high-temperature melt up to 1800K. It can provide a more favorable technical solution for improving the coating preparation process and enhancing the coating performance, and is of great significance for extending the service life of the coated graphite crucible, ensuring its service safety and reducing costs.

Claims

1. A coating repair method for reuse of coated graphite crucible, characterized in that: The following steps are involved: (1) Plasma spraying is performed on the surface of a graphite crucible to prepare a composite coating, wherein the composite coating includes one or more of Mo / Y2O3, Nb / ZrO2, and Nb / Y2O3, with a substrate preheating temperature of 50-300°C, a power of 30kW, a powder feeding rate of 1.35kg / h, a spraying distance of 10-20cm, and a gun travel speed of 6mm / s; (2) The plasma sprayed layer structure was laser remelted, and a crack prevention plate was installed at the right-angle transition of the graphite crucible to reduce the porosity of the coating surface. The laser cladding process parameters were: laser power: 255W; spot size: 1-2mm; scanning speed: 46mm / s; focal length: 330mm; overlap rate: 50%; (3) The coating after laser cladding is vacuum hot pressed; the vacuum hot pressing process parameters are: the vacuum degree of the vacuum sintering furnace is controlled at the Pa level, and the pressure is set at 100kPa-6MPa.

2. The coating repair method for reuse of coated graphite crucible according to claim 1, characterized in that: In the step (3), the coating is vacuum hot-pressed using oil pressure or air pressure.

3. The coating repair method for reuse of coated graphite crucible according to claim 2, characterized in that: In step (2), the graphite crucible is preheated to a temperature of 50-60° C., and an external heater is used in the process.

4. The coating repair method for reuse of coated graphite crucible according to claim 3, characterized in that: The coating repaired in step (3) can withstand 3-5 melting times in a high temperature melt up to 1800K.

5. The coating repair method for reuse of coated graphite crucible according to claim 4, characterized in that: After step (3) laser cladding, the bonding strength between the coating and the graphite substrate is higher than the bonding strength between the coatings.

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