Pretreatment method for reducing defects of preset coating type laser cladding oxide ceramic coating and application

Abstract

The invention discloses a pretreatment method for reducing defects of a preset coating type laser cladding oxide ceramic coating, which aims at solving the problems of coating cracks, pores, insufficient bonding strength and the like caused by thermophysical property difference between oxide ceramic and a metal matrix, and comprises the following steps of: irradiating the surface of the matrix by laser to form an active layer; the preparation method comprises the following steps: preparing a preset coating by combining ultrasonic vibration assisted pressing, removing an adhesive by adopting a gradient degumming process, and finally carrying out laser cladding under the protection of argon to obtain the oxide ceramic coating which is free of cracks, low in porosity and good in interface bonding. The invention further provides a low-defect oxide ceramic coating, through laser surface activation, ultrasonic vibration auxiliary pressing and gradient degumming processes, the bonding strength of ceramic and a matrix is effectively improved, the defects of cracks and air holes are inhibited, the intrinsic structure of the ceramic is maintained, meanwhile, the coating is good in component and performance stability, and the service life of the coating is prolonged. The method is suitable for matrixes such as stainless steel, titanium alloy and aluminum alloy and various ceramic systems.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing technology, and specifically relates to a pretreatment method for reducing defects in pre-coated laser cladding oxide ceramic coatings, and also relates to a low-defect oxide ceramic coating based on the above pretreatment method. Background Art

[0002] Laser cladding is an advanced surface treatment process that can melt ceramic materials to overcome their difficult-to-process properties. This allows the production of ceramic coatings that form a metallurgical bond with the substrate and exhibit exceptional properties such as high hardness, wear resistance, and corrosion resistance. However, ceramic materials (such as Al2O3) differ significantly in melting point and thermal expansion coefficient from metal substrates (such as stainless steel). This difference in thermophysical properties can lead to intense thermal stress concentration at the ceramic-metal interface during the cladding process, which can cause defects such as cracks, delamination, or spalling of the coating. Furthermore, due to the high melting temperature and poor fluidity of ceramic powders, insufficient laser energy input can easily lead to the formation of unmelted particles or pores, resulting in a decrease in coating density. Rapid solidification, uneven melt pool convection, and uneven element diffusion can lead to element segregation within the coating, compromising its performance.

[0003] Currently, the main methods for preparing coatings by laser cladding are synchronous powder feeding and pre-coating. However, due to the limitations of the powder feeding mechanical structure, the existing synchronous device is difficult to meet the technical requirements when conveying ceramic powders with poor fluidity, and there are shortcomings such as serious powder waste during the cladding process. Therefore, the powder supply method used by most existing laser cladding ceramic coatings is the pre-coating method, such as patents CN101818343A, CN101705410A, CN1456707, etc. The method of mechanical pressing has also gradually matured, such as patent CN101158039A discloses a method for laser cladding to obtain a coating by pre-setting powder by tableting, and patent CN102618868A discloses a method for laser cladding to obtain a composite coating by pre-setting powder by extrusion. However, traditional mechanical pressing can easily cause uneven powder distribution, resulting in local energy absorption differences during cladding, further exacerbating the generation of pores and cracks.

[0004] In response to the above problems, the existing technology mainly alleviates them by optimizing the laser processing technology or designing a transition layer. For example, patent CN105506615A discloses a method for controlling the microstructure and thermal crack sensitivity of laser cladding coatings. However, this method is mainly applied to the powder feeding method, and its influence on the grain growth process may cause changes in coating performance. Patent publication number CN106048599A discloses a crack control method for laser cladding formed metal parts. This method improves the cladding forming structure by introducing vibration during the cladding process. However, its coating composition is an alloy and cannot solve some defects existing in the ceramic coating. Adding a transition layer increases process complexity and production costs.

[0005] Therefore, there is an urgent need to develop a method to reduce the defects of pre-coated laser cladding ceramic coatings to achieve efficient and stable preparation of low-defect ceramic coatings on metal substrates. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a method for reducing defects in pre-coated laser cladding ceramic coatings, thereby achieving efficient and stable preparation of low-defect oxide ceramic coatings on the surface of a metal substrate.

[0007] A second object of the present invention is to provide a low-defect oxide ceramic coating prepared on the surface of a metal substrate by a laser cladding process.

[0008] The technical solution adopted by the present invention to achieve one of the objectives is: a pre-treatment method for reducing defects in pre-coated laser cladding oxide ceramic coatings, comprising the following steps: S1. Grinding and laser irradiating the surface of a metal substrate to obtain a pre-treated substrate; S2. Mixing the oxide ceramic raw material powder with a binder to obtain a paste mixture; placing the paste mixture on the surface of the pretreated substrate and pressing it, while simultaneously using ultrasonic vibration as an auxiliary during the pressing process to obtain a pressed coating; S3. Performing a gradient temperature debonding treatment on the substrate with the pressed coating on the surface to obtain a substrate to be clad with a pre-coating.

[0009] The overall idea and inventive principle of the present invention are as follows: To address the problems of weak interface bonding, numerous pores, and cracks in oxide ceramic coatings prepared by laser cladding on metal substrates, the present invention optimizes the preparation method of oxide ceramic coatings by adding a pre-treatment operation before laser cladding. Innovatively, laser surface activation and ultrasonic vibration-assisted pressing technology are used to achieve the coordinated regulation of optimized bonding between the ceramic coating and the substrate and the uniformity of the pre-set coating structure. First, laser surface activation uses short-pulse laser to irradiate the substrate surface, removing the oxide layer on the surface of the metal substrate through different wavelengths and energy densities. The laser photothermal effect causes the substrate to heat up and induces surface micro-melting, forming an active layer with micron-level roughness, which greatly improves the mechanical anchoring ability between the powder to be clad and the substrate.

[0010] Secondly, ultrasonic vibration-assisted pressing introduces high-frequency vibration during the pre-coating pressing and molding stage, and uses the micro-jet impact generated by the ultrasonic cavitation effect to drive the powder particles to be evenly distributed and tightly packed, thereby reducing the local energy absorption difference during cladding caused by the uneven distribution of the pre-coating produced by mechanical pressing, and avoiding the generation of defects such as pores or cracks.

[0011] Finally, before laser cladding, the gradient debonding process is used to completely decompose and remove the binder, reducing the pores caused by binder volatilization during the laser cladding process and further reducing coating defects.

[0012] The present invention realizes the laser cladding preparation of low-defect oxide ceramic coating on the surface of metal substrate through the synergistic effect of the above three pre-treatment methods.

[0013] Furthermore, in step S1, the metal substrate includes one of Q235, 316L, 6061, Ti-6Al-4V, and Inconel718, and the surface of the metal substrate is pretreated by mechanical grinding.

[0014] Furthermore, in step S1, during the laser irradiation treatment, the laser power is 40-100W, the laser wavelength is 355nm-1064nm, the pulse frequency is 40-100kHz, and the single pulse energy density is 1.5J / cm 2 -8J / cm 2 , scanning speed is 200mm / s-1000mm / s.

[0015] In the present invention, the irradiation of the pulsed laser beam acts on the metal substrate. On the one hand, it can form a surface structure with micron-level roughness, thereby improving the mechanical anchoring ability of the powder to be clad and the metal substrate and reducing defects caused during the pressing process of the pre-coating. On the other hand, the laser action causes the surface of the substrate to be micro-melted to obtain an activation layer. The activation layer plays a transitional role between the pre-coating and the substrate, which is more conducive to the cladding processing of the oxide ceramic layer.

[0016] Furthermore, in step S2, the oxide ceramic raw material powder includes one or more of Fe2O3, CoO, Co3O4, NiO, CuO, ZnO, MnO2, Mn3O4, Cr2O3, Al2O3, ZrO2, CeO2, and Y2O3, and the particle size of the oxide ceramic raw material powder is 100-200 mesh. The pretreatment method of the present invention is also applicable to the pretreatment of the composite coating composed of the above-mentioned oxide ceramic powder and metal powder before laser cladding. However, relatively speaking, pure oxide ceramic coatings have relatively poor formability, are more prone to defects, and are more difficult to prepare on the surface of a metal substrate. Therefore, it is more suitable to use the pretreatment method provided by the present invention to reduce its defects.

[0017] Furthermore, in step S2, the binder is polyvinyl alcohol or polyethylene glycol; and in the paste mixture, the mass ratio of the oxide ceramic raw material powder to the binder is 85:15-95:5.

[0018] Furthermore, in step S2, during the pressing process, considering that the oxide ceramic powder has irregular particles and poor plasticity, the traditional pressing method easily leads to the problem of uneven local accumulation. The present invention controls the pressure of the pressing process and uses ultrasonic vibration to assist in the pressing process.

[0019] In the present invention, the vertical pressure of the pressing process is controlled to be 5-10MPa, the frequency of the ultrasonic vibration is 20-40kHz, and the holding time is 30-120s. Among them, the vertical pressure needs to be controlled at 5-10MPa. If the pressure during the pressing process is too high, it will lead to uneven distribution of powder in the pre-coated coating, causing local energy absorption differences during subsequent laser cladding, and producing defects such as pores or cracks; ultrasonic vibration assistance is introduced during the pressing process. In the presence of a binder, the continuation of the holding time allows the ultrasonic cavitation effect to exist in the paste mixture during the pressing process, and the internal distribution is homogenized under the impact of the generated micro-jet. Based on the above-mentioned pressing conditions, the pre-treatment method provided by the present invention can obtain a pre-coated structure with good density and uniformity under a relatively small pressing pressure, while also reducing the equipment requirements for pressing.

[0020] Furthermore, in the paste mixture configured by the present invention, the binder content is 5wt.%-15wt.%, which is slightly higher than the conventional process. Experimental studies have found that laser irradiation activation and ultrasonic assisted pressing cannot completely avoid the formation of defects such as pores and cracks in the coating. This is because the binder in the prefabricated coating will rapidly vaporize during laser cladding to produce pore defects, and at the same time cause violent fluctuations in the molten pool, resulting in poor coating density and increased element diffusion in the matrix, affecting the composition and performance of the coating. In addition, the presence of the binder may also produce residual carbides at high temperatures, resulting in a decrease in the toughness of the coating, and the formation of local conductive paths will cause defects such as a decrease in the corrosion resistance of the coating.

[0021] Therefore, the present invention incorporates a gradient temperature debonding process prior to laser cladding to completely decompose and remove the binder. Specifically, this gradient temperature debonding process is performed in two stages: the first stage is held at 160-220°C for 30-60 minutes; the second stage is held at 400-500°C for 10-20 minutes, with a heating rate of 4-6°C / min. The first stage corresponds to the binder's decomposition temperature, which is maintained for 30-60 minutes to completely decompose it. The second stage is held at a temperature above the binder's vaporization temperature to ensure its complete removal.

[0022] Furthermore, in step S3, the thickness of the pre-coating on the substrate to be clad is 0.5-2 mm.

[0023] The technical solution employed by the present invention to achieve the second objective is to provide a low-defect oxide ceramic coating, which is prepared on the surface of a metal substrate by laser cladding. Prior to laser cladding, the substrate to be clad is provided with a pre-coated substrate using the pretreatment method described in accordance with the first objective of the present invention.

[0024] The oxide ceramic coating provided by the present invention takes into account the significant differences in melting point and thermal expansion coefficient between the metal substrate and the oxide ceramic. Before laser cladding, the substrate is pre-treated by laser irradiation, the pre-coating is pressed with the assistance of ultrasonic vibration, and the residual binder is decomposed and removed using a gradient debonding process. This effectively prevents various defects of the oxide ceramic coating before laser cladding processing.

[0025] Furthermore, in the laser cladding, the laser power is 1000-1500W, the scanning speed is 4-8mm / s, the defocus amount is 12-15mm, the spot diameter is 3-4mm, the protective atmosphere is argon, and the flow rate is 8-15L / min.

[0026] In the present invention, based on a special pretreatment method, the surface of the metal substrate is activated, significantly reducing the energy required for cladding. This allows for high-quality bonding of the oxide ceramic coating to the metal substrate at relatively low power (e.g., 1000W), thereby achieving a low-defect coating while reducing thermal damage to the substrate. Furthermore, the scanning speed during laser cladding is set at 4-8 mm / s, which can adapt to the high density of the pre-deposited layer after gradient debonding, extend the molten pool residence time to ensure complete melting of the ceramic, and avoid residual unmelted ceramic particles. Based on preliminary experiments, the present invention optimizes and adjusts the argon flow rate to 8-15 L / min, ensuring molten pool stability while reducing airflow disturbances and further minimizing coating defects.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The pretreatment method for reducing defects in pre-coated laser cladding oxide ceramic coatings provided by the present invention effectively improves the bonding strength between the oxide ceramic coating and the metal substrate through laser surface activation, ultrasonic vibration-assisted pressing and gradient debonding process, thereby avoiding delamination defects; effectively reduces crack defects caused by uneven distribution of the pre-coating, and at the same time effectively avoids pore defects caused by volatilization of the binder in combination with the debonding process, effectively solving the defect problem of traditional laser cladding in preparing oxide ceramic coatings on the surface of the metal substrate.

[0028] (2) The pretreatment method provided by the present invention for reducing defects in pre-coated laser cladding oxide ceramic coatings optimizes and controls process parameters for metal substrates and ceramic materials, and is compatible with various metal substrates such as stainless steel, titanium alloy, aluminum alloy, and different oxide ceramic systems, and has a wide range of applications. The pretreatment method provided by the present invention ensures interface bonding strength while avoiding coating lattice distortion, maintains the intrinsic organizational structure of the ceramic, and ensures the purity of the coating composition and stable performance.

[0029] (3) The low-defect oxide ceramic coating provided by the present invention is first prepared by a special pretreatment method to obtain a substrate with a pre-coated substrate to be clad, and then the laser cladding operation is performed. The prepared oxide ceramic coating exhibits a good microstructure, fine and uniform grains, significantly reduced cracks and pore defects, and significantly improved coating density. It has a good inhibitory effect on pore defects in the laser-clad oxide ceramic coating, and the coating porosity is only 1.05%. It has broad application prospects in the fields of thermal barrier coatings and corrosion-resistant coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of a process for preparing an oxide ceramic coating on a metal substrate using a laser cladding process including a pre-treatment method provided in an embodiment of the present invention; Figure 2This is a surface SEM image of the pre-treated substrate obtained after laser irradiation in Example 1 of the present invention; Figure 3 1 is a cross-sectional comparison diagram of the ceramic coating prepared in Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0033] An embodiment of the present invention provides a method for preparing a low-defect oxide ceramic coating, which uses laser cladding to prepare the oxide ceramic coating on the surface of a metal substrate. The metal substrate comprises one of Q235, 316L, 6061 aluminum alloy, Ti-6Al-4V, and Inconel 718; the oxide ceramic raw material powder comprises one or more of Fe2O3, CoO, Co3O4, NiO, CuO, ZnO, MnO, MnO2, Mn3O4, Cr2O3, Al2O3, ZrO2, CeO2, and Y2O3, and the particle size of the oxide ceramic raw material powder is 100-200 mesh.

[0034] Before laser cladding, a pre-treatment method is first used to obtain a substrate to be clad with a pre-coating. The pre-treatment method includes the following steps: Step 1: Grind and laser irradiate the substrate surface to obtain a pre-treated substrate; wherein the grinding method is mechanical grinding to remove the oxide layer on the surface of the metal substrate; during the laser irradiation treatment, the laser power is 40-100W, the laser wavelength is 355nm-1064nm, the pulse frequency is 40-100kHz, and the single pulse energy density is 1.5J / cm 2 -8J / cm 2 , scanning speed is 200mm / s-1000mm / s.

[0035] Step 2: Mixing the oxide ceramic raw material powder and the binder in a mass ratio of 85:15-95:5 to obtain a paste mixture, wherein the binder is polyvinyl alcohol or polyethylene glycol; pre-placing the paste mixture on the surface of the pre-treated substrate and pressing, during the pressing process, controlling the vertical pressure to 5-10 MPa and simultaneously using ultrasonic vibration with a frequency of 20-40 kHz as an auxiliary, maintaining the pressure for 30-120 seconds to obtain a pressed coating; Step 3: The substrate with the pressed coating is subjected to a gradient temperature debonding process. This process is carried out in two stages: the first stage is at a temperature of 160-220°C for 30-60 minutes; the second stage is at a temperature of 400-500°C for 10-20 minutes, with a heating rate of 4-6°C / min. This results in a substrate to be clad with a pre-coated coating having a thickness of 0.5-2 mm.

[0036] Furthermore, in the laser cladding, the laser power is 1000-1500W, the scanning speed is 4-8mm / s, the defocus amount is 12-15mm, the spot diameter is 3-4mm, the protective atmosphere is argon, and the flow rate is 8-15L / min.

[0037] The present invention will be further described below with reference to specific examples, but they are not intended to limit the present invention.

[0038] Example 1 This embodiment provides a method for preparing a low-defect oxide ceramic coating. The method first uses a pretreatment method to obtain a substrate to be clad with a pre-coating, and then uses laser cladding to prepare the oxide ceramic coating on the surface of the metal substrate.

[0039] In this embodiment, the metal matrix is ​​Q235, and the oxide ceramic raw material powder is prepared by mixing Cr2O3, Mn3O4, Fe2O3, Co3O4, and NiO in equal molar ratios of the metal elements, with a particle size of 200 mesh. The preparation method includes the following steps: Step 1: The surface of the laser clad substrate is mechanically polished and placed under a laser power of 100W, a laser wavelength of 1064nm, a pulse frequency of 100kHz, and a single pulse energy density of 1.5J / cm 2 The substrate was irradiated with a laser at a scanning speed of 200 mm / s to obtain a pre-treated substrate. The surface of the pre-treated substrate after laser irradiation in this embodiment was observed using a scanning electron microscope (SEM), and a surface activation layer with a roughness of micrometer level was observed, such as Figure 2 shown.

[0040] Step 2: After the oxide ceramic raw material powder is placed in a vacuum and dried, polyvinyl alcohol is used as a binder at a mass ratio of raw material powder to binder of 95:5, and the mixture is evenly mixed into a paste to obtain a paste-like powder to be clad; the paste-like powder to be clad is pre-placed on the surface of the substrate for pressing. During the pressing process, ultrasonic vibration is used to assist the pressing, the vibration frequency is 20 kHz, a vertical pressure of 10 MPa is applied, and the pressure holding time is 120 s to obtain a pressed coating.

[0041] Step 3: Place the substrate with the pressed coating on the surface in a box furnace and heat it gradually at a heating rate of 5°C / min, keep it at 220°C for 30 minutes, and keep it at 500°C for 10 minutes to obtain a substrate to be clad with a pre-coating. The thickness of the pre-coating is 0.5 mm. Step 4: Place the substrate to be clad with a pre-coated coating in a laser processing equipment for cladding. The laser power is 1000W, the scanning speed is 4mm / s, the defocus is 15mm, the spot diameter is 3mm, the protective atmosphere is argon, and the flow rate is 8L / min. An oxide ceramic coating is prepared on the surface of the metal substrate.

[0042] Example 2 This embodiment provides a method for preparing a low-defect oxide ceramic coating. The method first uses a pretreatment method to obtain a substrate to be clad with a pre-coating, and then uses laser cladding to prepare the oxide ceramic coating on the surface of the metal substrate.

[0043] In this embodiment, the metal matrix is ​​316L, the oxide ceramic raw material powder is Al2O3, and the particle size is 100 mesh. The preparation method includes the following steps: Step 1: The surface of the laser clad substrate is mechanically polished and placed under a laser power of 40W, a laser wavelength of 355nm, a pulse frequency of 40kHz, and a single pulse energy density of 8J / cm 2 The substrate was irradiated with a laser at a scanning speed of 1000 mm / s to obtain a pre-treated substrate.

[0044] Step 2: After the oxide ceramic raw material powder is placed in a vacuum and dried, polyvinyl alcohol is used as a binder at a mass ratio of raw material powder to binder of 85:15, and the mixture is evenly mixed and blended into a paste to obtain a paste-like powder to be clad; the paste-like powder to be clad is pre-placed on the surface of the substrate for pressing. During the pressing process, ultrasonic vibration is used to assist the pressing, the vibration frequency is 40 kHz, a vertical pressure of 5 MPa is applied, and the pressure holding time is 30 seconds to obtain a pressed coating.

[0045] Step 3: Place the substrate with the pressed coating on the surface in a box furnace and heat it gradually at a heating rate of 5°C / min, keep it at 160°C for 60 minutes, and keep it at 400°C for 20 minutes to obtain a substrate to be clad with a pre-coating. The thickness of the pre-coating is 2 mm. Step 4: Place the substrate to be clad with a pre-coated coating in a laser processing equipment for cladding. The laser power is 1500W, the scanning speed is 8mm / s, the defocus is 12mm, the spot diameter is 4mm, the protective atmosphere is argon, and the flow rate is 15L / min. An oxide ceramic coating is prepared on the surface of the metal substrate.

[0046] Example 3 This embodiment provides a method for preparing a low-defect oxide ceramic coating. The method first uses a pretreatment method to obtain a substrate to be clad with a pre-coating, and then uses laser cladding to prepare the oxide ceramic coating on the surface of the metal substrate.

[0047] In this embodiment, the metal matrix is ​​6061 aluminum alloy, and the oxide ceramic raw material powder is a mixture of ZnO, CuO, and ZrO2 in a ratio of 50wt.%, 30wt.%, and 20wt.%, with a particle size of 200 mesh. The preparation method includes the following steps: Step 1: The surface of the laser clad substrate is mechanically polished and placed under a laser power of 60W, a laser wavelength of 532nm, a pulse frequency of 60kHz, and a single pulse energy density of 2J / cm 2 The substrate was irradiated with a laser at a scanning speed of 600 mm / s to obtain a pre-treated substrate.

[0048] Step 2: After the oxide ceramic raw material powder is placed in a vacuum and dried, polyvinyl alcohol is used as a binder at a mass ratio of raw material powder to binder of 90:10, and the mixture is evenly mixed and blended into a paste to obtain a paste-like powder to be clad; the paste-like powder to be clad is pre-placed on the surface of the substrate for pressing. During the pressing process, ultrasonic vibration is used to assist the pressing, the vibration frequency is 25 kHz, a vertical pressure of 5 MPa is applied, and the pressure holding time is 60 s to obtain a pressed coating.

[0049] Step 3: Place the substrate with the pressed coating on the surface in a box furnace and heat it gradually at a heating rate of 5°C / min, keep it at 180°C for 45 minutes, and keep it at 450°C for 15 minutes to obtain a substrate to be clad with a pre-coating. The thickness of the pre-coating is 1 mm. Step 4: Place the substrate to be clad with a pre-coated coating in a laser processing equipment for cladding. The laser power is 1200W, the scanning speed is 6mm / s, the defocus is 13mm, the spot diameter is 3mm, the protective atmosphere is argon, and the flow rate is 10L / min. An oxide ceramic coating is prepared on the surface of the metal substrate.

[0050] Example 4 This embodiment provides a method for preparing a low-defect oxide ceramic coating. The method first uses a pretreatment method to obtain a substrate to be clad with a pre-coating, and then uses laser cladding to prepare the oxide ceramic coating on the surface of the metal substrate.

[0051] In this embodiment, the metal matrix is ​​Ti-6Al-4V, and the oxide ceramic raw material powder is a mixture of Al2O3, Cr2O3, and Y2O3 in a ratio of 60wt.%, 25wt.%, and 15wt.%, with a particle size of 200 mesh. The preparation method includes the following steps: Step 1: The surface of the laser clad substrate is mechanically polished and placed under a laser power of 80W, a laser wavelength of 355nm, a pulse frequency of 80kHz, and a single pulse energy density of 4J / cm 2 The substrate was irradiated with a laser at a scanning speed of 800 mm / s to obtain a pre-treated substrate.

[0052] Step 2: Place the oxide ceramic raw material powder with a powder particle size of 200 mesh in a vacuum and dry it. Then use polyethylene glycol as a binder at a mass ratio of raw material powder to binder of 90:10, evenly mix and blend it into a paste to obtain a paste-like powder to be clad; pre-place the paste-like powder to be clad on the surface of the substrate for pressing. During the pressing process, ultrasonic vibration is used to assist the pressing with a vibration frequency of 30 kHz, a vertical pressure of 10 MPa, and a holding time of 90 seconds to obtain a pressed coating.

[0053] Step 3: Place the substrate with the pressed coating on the surface in a box furnace and heat it gradually at a heating rate of 5°C / min, keep it at 180°C for 45 minutes, and keep it at 450°C for 15 minutes to obtain a substrate to be clad with a pre-coating. The thickness of the pre-coating is 1 mm. Step 4: Place the substrate to be clad with a pre-coating in a laser processing equipment for cladding. The laser power is 1200W, the scanning speed is 6mm / s, the defocus is 14mm, the spot diameter is 3mm, the protective atmosphere is argon, and the flow rate is 10L / min. An oxide ceramic coating is prepared on the surface of the metal substrate.

[0054] Example 5 This embodiment provides a method for preparing a low-defect oxide ceramic coating. The method first uses a pretreatment method to obtain a substrate to be clad with a pre-coating, and then uses laser cladding to prepare the oxide ceramic coating on the surface of the metal substrate.

[0055] In this embodiment, the metal matrix is ​​Inconel 718, and the oxide ceramic raw material powder is a mixture of ZrO2, CeO2, and MnO2 in a ratio of 50wt.%, 30wt.%, and 20wt.%, with a particle size of 100 mesh. The preparation method includes the following steps: Step 1: The surface of the laser clad substrate is mechanically polished and placed under a laser power of 100W, a laser wavelength of 1064nm, a pulse frequency of 100kHz, and a single pulse energy density of 6J / cm 2 The substrate was irradiated with a laser at a scanning speed of 800 mm / s to obtain a pre-treated substrate.

[0056] Step 2: Place the oxide ceramic raw material powder with a powder particle size of 100 mesh in a vacuum and dry it. Then use polyethylene glycol as a binder at a mass ratio of raw material powder to binder of 85:15, evenly mix and blend it into a paste to obtain a paste-like powder to be clad. The paste-like powder to be clad is pre-placed on the surface of the substrate for pressing. During the pressing process, ultrasonic vibration is used to assist the pressing. The vibration frequency is 35 kHz, a vertical pressure of 10 MPa is applied, and the pressure holding time is 120 s to obtain a pressed coating.

[0057] Step 3: Place the substrate with the pressed coating on the surface in a box furnace and heat it gradually at a heating rate of 5°C / min, keep it at 180°C for 45 minutes, and keep it at 450°C for 15 minutes to obtain a substrate to be clad with a pre-coating. The thickness of the pre-coating is 1 mm. Step 4: Place the substrate to be clad with a pre-coating in a laser processing equipment for cladding. The laser power is 1500W, the scanning speed is 6mm / s, the defocus is 15mm, the spot diameter is 4mm, the protective atmosphere is argon, and the flow rate is 8L / min. An oxide ceramic coating is prepared on the surface of the metal substrate.

[0058] Comparative Example This comparative example provides a method for preparing an oxide ceramic coating, which includes first preparing a pre-coating on the surface of a metal substrate, and then preparing an oxide ceramic coating on the surface of the metal substrate by laser cladding.

[0059] The metal substrate and oxide ceramic raw material powder used in this comparative example were identical to those used in Example 1 (the metal substrate was Q235, and the oxide ceramic raw material powder consisted of a mixture of Cr2O3, Mn3O4, Fe2O3, Co3O4, and NiO in equal molar ratios of the metal elements, with a particle size of 200 mesh). The primary difference was that the comparative example employed only a conventional mechanical pressing process, applying a vertical pressure of 100 MPa and a holding time of 120 seconds to obtain the pre-coating. Subsequently, laser cladding was performed on the pre-coating using the same process parameters as in step 4 of Example 1 to obtain the oxide ceramic coating.

[0060] The oxide ceramic coatings obtained in Example 1 (using the pretreatment method provided by the present invention) and the comparative example (using the traditional mechanical pressing process) were observed using an optical microscope. Figure 3 As shown in the figure, the coating obtained by the traditional pressing process has coarse grains, obvious cracks and pores, loose coating structure and poor interface bonding. However, the coating of Example 1 exhibits a good microstructure, small and uniform grains, significantly reduced cracks and pores, and significantly improved coating density.

[0061] Image J software was used to quantitatively analyze the cross-sectional morphologies of the coatings of Example 1 and the comparative example. The porosity calculation results showed that the porosity of the coating of Example 1 was 1.05%, and that of the coating of the comparative example was 16.3%. That is, the porosity of the coating of Example 1 was approximately 93.6% lower than that of the comparative example, indicating that the pretreatment method provided by the present invention has a good inhibitory effect on the porosity defects of the laser cladding oxide ceramic coating.

[0062] Furthermore, after testing, the average hardness of the laser cladding coating of the comparative example was 210.8HV, and the average hardness of the pre-treated coating in Example 1 could reach 388.6HV, an increase of 84.35%. The wear resistance of the coating was tested using a ball-on-disc friction and wear tester. The results showed that the wear amount of the pre-treated coating was only 44.79% of that of the comparative example coating. The corrosion resistance of the coating in a NaCl solution with a mass concentration of 3.5% was tested using an electrochemical workstation. The results showed that the annual corrosion rate of the pre-treated coating provided in Example 1 was reduced by 36.74% compared to that of the comparative example coating. That is, the laser cladding coating prepared by the pre-treatment method of the present invention has been significantly improved in hardness, wear resistance and corrosion resistance.

[0063] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A pre-treatment method for reducing defects in pre-coated laser cladding oxide ceramic coatings, characterized in that: The following steps are involved: S1. Grinding and laser irradiating the surface of a metal substrate to obtain a pre-treated substrate; S2. Mixing the oxide ceramic raw material powder with a binder to obtain a paste mixture; placing the paste mixture on the surface of the pretreated substrate and pressing it, while simultaneously using ultrasonic vibration as an auxiliary during the pressing process to obtain a pressed coating; S3. Performing a gradient temperature debonding treatment on the substrate with the pressed coating on the surface to obtain a substrate to be clad with a pre-coating.

2. The pre-treatment method according to claim 1, wherein In step S1, the metal matrix includes one of Q235, 316L, 6061 aluminum alloy, Ti-6Al-4V, and Inconel 718.

3. The pre-treatment method according to claim 1, wherein In step S1, during the laser irradiation treatment, the laser power is 40-100W, the laser wavelength is 355nm-1064nm, the pulse frequency is 40-100kHz, and the single pulse energy density is 1.5-8J / cm 2 , scanning speed is 200-1000mm / s.

4. The pre-treatment method according to claim 1, characterized in that: In step S2, the oxide ceramic raw material powder includes one or more combinations of Fe2O3, CoO, Co3O4, NiO, CuO, ZnO, MnO, MnO2, Mn3O4, Cr2O3, Al2O3, ZrO2, CeO2, and Y2O3; the particle size of the oxide ceramic raw material powder is 100-200 mesh.

5. The pre-treatment method according to claim 1, characterized in that: In step S2, the binder is polyvinyl alcohol or polyethylene glycol; in the paste mixture, the mass ratio of the oxide ceramic raw material powder to the binder is 85:15-95:

5.

6. The pre-treatment method according to claim 1, characterized in that: In step S2, during the pressing process, the vertical pressure is 5-10 MPa, the frequency of the ultrasonic vibration is 20-40 kHz, and the holding time is 30-120 s.

7. The pre-treatment method according to claim 1, characterized in that: In step S3, the gradient temperature degumming treatment is carried out in two stages: the temperature of the first stage is 160-220°C, and the holding time is 30-60 minutes; the temperature of the second stage is 400-500°C, and the holding time is 10-20 minutes; the heating rate is 4-6°C / min.

8. The pre-treatment method according to claim 1, characterized in that: In step S3, the thickness of the pre-coating on the substrate to be clad is 0.5-2 mm.

9. A low-defect oxide ceramic coating prepared on the surface of a metal substrate by laser cladding, characterized in that: Before laser cladding, a pre-treatment method according to any one of claims 1 to 8 is used to obtain a substrate to be clad and provided with a pre-coating.

10. The low-defect oxide ceramic coating according to claim 9, characterized in that In the laser cladding, the laser power is 1000-1500W, the scanning speed is 4-8mm / s, the defocus amount is 12-15mm, the spot diameter is 3-4mm, the protective atmosphere is argon, and the flow rate is 8-15L / min.

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