A method for preparing a ceramic matrix composite coating by using a high-speed laser cladding process

Abstract

The present invention provides a method for preparing a ceramic matrix composite coating by using a high-speed laser cladding process, which comprises the following steps: performing rust removal and degreasing pretreatment on a substrate; drying a ZrB₂-SiC composite ceramic powder at 50-70 °C; loading the ZrB₂-SiC composite ceramic powder into a powder feeder of a high-speed laser cladding device, feeding it into the high-speed laser cladding device equipped with a synchronous powder feeding head, making the laser focus formed by the emission of a high-speed cladding laser head coincide with the powder spot focus formed by the powder feeding of the synchronous powder feeding head, then adjusting the coincidence position of the two foci to be at a distance of 1-1.5 mm above the surface of the substrate, and performing high-speed laser cladding on the substrate under a local inert gas protection atmosphere. The present invention uses high-speed laser cladding to clad pure ceramic powder on the surface of a common iron-based alloy, and by optimizing process parameters, controls the dilution effect in the high-speed laser cladding process to form a continuous gradient ceramic matrix composite coating.

Description

Technical Field

[0001] The present invention belongs to the field of composite coatings, and relates to a method for preparing a ceramic-based composite coating, specifically to a method for preparing a ceramic-based composite coating by using a high-speed laser cladding process. Background Art

[0002] The metal-ceramic composite coating combines the good toughness of metal materials and the high strength of ceramic materials. Preparing a layer of metal-ceramic composite coating on the surface of parts can play a good protective role, especially in high-temperature environments, the metal-ceramic composite coating has high performance that traditional pure metal coatings do not possess. Laser cladding technology is one of the main technologies for preparing metal-ceramic composite coatings.

[0003] Laser cladding technology is to simultaneously melt powders and the substrate by a high-energy laser beam to form a dense coating with metallurgical bonding on the substrate surface. Research shows that the ceramic phase-reinforced metal matrix composite coating prepared by this technology can significantly improve the mechanical properties of the coating. For example, Guo et al. prepared a NiCoCrAlY-35wt% ZrB2 metal-ceramic composite coating on the surface of pure Ti by laser cladding technology. The hardness of the coating increased by nearly 5 times compared with the substrate, reaching 9000 MPa (Rare Metal Materials and Engineering, 2013, 42(8): 1547-1551.).

[0004] High-speed laser cladding is a new surface modification technology developed from traditional laser cladding. It not only inherits the advantages of traditional laser cladding (wide range of processable materials, high coating bonding strength, high coating density), but also can redistribute the laser energy by adjusting the distance between the laser focus and the powder spot relative to the substrate. During the high-speed laser cladding process, about 90% of the laser energy is used for melting the powder, and the remaining energy acts on melting the substrate. The redistributed laser energy is more suitable for heating high-melting-point powders. On the one hand, more laser energy acts on the powder to make it melt more fully, and on the other hand, less laser energy acts on the substrate to relieve the excessive dilution of the substrate.

[0005] However, there are still the following problems in the current research on the preparation of metal-ceramic composite coatings by high-speed laser cladding technology. (1) The powders used for laser cladding are all obtained by mechanically mixing metal powders and ceramic powders. This makes it difficult to ensure that the high-melting-point ceramic particles in the mixed powders are fully melted and the low- and medium-melting-point metal powders are not over-ablated under a constant laser power. (2) The metal phase still accounts for a relatively large content in the prepared metal-ceramic composite coatings, which limits the mechanical properties of the coatings at higher temperatures. Therefore, under the constraints of the above two problems, if the content of ceramic particles in the mixed powders is increased to increase the ceramic phase content of the coatings, it will make the melting of ceramic powders more insufficient and the metal powders over-ablated, resulting in the problem of poor coating quality. Summary of the Invention

[0006] To solve the above problems, the object of the present invention is to provide a method for preparing a ceramic matrix composite coating by high-speed laser cladding technology. This method directly uses pure ceramic powders as the cladding material, controls the dilution degree of the metal matrix to the coating by adjusting the process parameters of high-speed laser cladding, and controls the reverse dilution and diffusion degree of the matrix elements acting as the metal components of the coating in the molten pool, thereby preparing a brand-new continuous gradient structure ceramic matrix composite coating on the surface of the iron-based alloy at one time.

[0007] To achieve the above object, the present invention provides a method for preparing a ceramic matrix composite coating by high-speed laser cladding technology, including the following steps:

[0008] 1) Perform rust removal and degreasing pretreatment on the substrate;

[0009] 2) Dry the ZrB2-SiC composite ceramic powder at 50-70 °C for 20-40 minutes; this step is used to ensure the fluidity and continuity of the ZrB2-SiC composite ceramic powder.

[0010] 3) Load the ZrB2-SiC composite ceramic powder into a powder feeder, feed it into a high-speed laser cladding device equipped with a synchronous powder feeding head, coincide the laser focus formed by the high-speed cladding laser head with the powder spot focus formed by the synchronous powder feeding head, then adjust the coincidence position of the two foci to be 1-1.5 mm above the surface of the substrate, and perform high-speed laser cladding on the substrate under a local inert gas protection atmosphere.

[0011] Among them, the process parameters of high-speed laser cladding are: laser power 2-3 kW, scanning speed 80-150 mm / s, powder feeding rate 3.7-4.1 g / min, overlapping rate 70%-90%, and spot diameter 2-3 mm.

[0012] As described above, the substrate is an iron-based alloy.

[0013] Preferably, the iron-based alloy is carbon steel, alloy steel or cast iron.

[0014] As described above, the rust removal and degreasing treatment process in step 1) is as follows: polish the substrate with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then ultrasonically clean with acetone or absolute ethanol to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic cleaning time is 5 minutes.

[0015] As described above, the preparation method of the ZrB2-SiC composite ceramic powder in step 2) is as follows:

[0016] a. Mix ZrB2 ultrafine powder and SiC ultrafine powder according to the proportion that ZrB2 ultrafine powder accounts for 70 wt% and SiC ultrafine powder accounts for 30 wt% to prepare a mixture.

[0017] b. Add the mixture to distilled water according to the solid content of 25 - 40 wt%, then add 2 - 5 wt% of binder, and make a slurry under the condition of high-speed magnetic stirring, where the stirring speed is 1000 - 1500 revolutions per minute and the stirring time is 40 - 60 minutes.

[0018] c. Use spray granulation equipment to prepare spherical ZrB2-SiC composite ceramic powder, with the inlet air temperature of 170 - 190 °C, the outlet temperature of 120 - 140 °C, the fan frequency of 20 - 25 Hz, and the feeding speed of 35 - 45 revolutions per minute.

[0019] d. Sieving the powder: Pass the powder through a 400-mesh sieve to obtain ZrB2-SiC composite ceramic powder with a particle size less than or equal to 38 μm.

[0020] As described above, the particle size of the ZrB2 ultrafine powder in step a is 0.5 - 1.0 μm, and the purity is 99.5%; the particle size of the SiC ultrafine powder is 0.8 - 2.0 μm, and the purity is 99.5%.

[0021] As described above, the binder in step b is PVA.

[0022] As described above, the inert atmosphere in step 3) is an argon atmosphere.

[0023] The present invention provides a method for preparing a ceramic matrix composite coating by a high-speed laser cladding process. This method prepares a brand-new continuous gradient structure metal-ceramic matrix composite coating on the surface of an iron-based alloy.

[0024] In the process of preparing the metal-ceramic composite coating in the present invention, pure ceramic powder is used as the cladding material, and the iron-based alloy is used as the substrate. The metal in the substrate diffuses into the coating and mixes with the melted ceramic powder, and a metal-ceramic composite coating is formed after solidification.

[0025] By controlling the diffusion and mass transfer effect of the substrate, the present invention enables incomplete diffusion to occur in the coating, ultimately forming a coating with a continuous gradient structure. The method adopted in the present invention does not require multi-layer cladding and can form the required coating in one step, simplifying the process compared with the prior art.

[0026] The continuous gradient coating structure prepared by the present invention solves the problem of incompatibility between metal and ceramic materials. The matrix elements gradually increase from the top to the bottom of the coating, achieving continuous matching of the phase composition and thermal properties between the coating and the substrate, and improving the bonding strength and cohesive strength between the coating and the substrate.

[0027] The continuous gradient coating structure prepared by the present invention ensures that a very high content of ceramic phase accumulates at the top of the coating. Within a range of about 140 μm from the coating surface in the depth direction, the volume content of the ceramic phase at the top of the coating is as high as 73%, enabling the coating to exhibit excellent mechanical properties at both room temperature and high temperature. Compared with the prior art, the preparation of a high-content ceramic matrix composite coating is achieved. The surface hardness of the coating is as high as 1700 HV 0.5 or more at room temperature; in a high-temperature environment of 80〇 °C, the surface hardness of the coating still remains above 1000 HV5. From the bottom to the top of the coating, the matrix phase elements gradually decrease, and the ceramic phase elements gradually increase, achieving a continuous gradient distribution of the coating structure and properties.

[0028] The method adopted in the present invention can be used to enhance the surface hardness and wear resistance of other metal components, especially the surface mechanical properties under high-temperature service conditions, and to improve the comprehensive service performance of moving components of heavy-duty equipment in extremely harsh environments. It can replace traditional metal matrix composite coating materials with a relatively low content of ceramic particles.

[0029] [[ID=1■4]]The beneficial effects of the present invention are as follows:

[0030] The present invention provides a method for preparing a ceramic matrix composite coating using a high-speed laser cladding process. This method abandons the traditional method of mixing metal and ceramic powders and directly uses pure ceramic powders. The substrate diffused into the coating acts as the metal phase and completes the mixing by itself under the action of the melt pool convection. By adjusting the process parameters, the reverse dilution and diffusion degree of the substrate elements in the melt pool are controlled, and finally a coating structure with a continuous gradient is formed in one step. The formed coating-substrate bonding interface presents a perfect metallurgical bond, and the top of the coating exhibits excellent mechanical properties at both room temperature and high temperature, with a gradient effect of being hard on the outside and tough on the inside. This method has a simple process, simple materials, and is easy to implement. Description of the Drawings

[0031] Figure 1 It is a typical morphology of the ZrB2-SiC composite ceramic powder used in the present invention.

[0032] Figure 2Macrograph of sample 1 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel prepared by the method provided by the present invention. Among them, Figure 2 (a) is the cross-sectional optical microscope morphology, Figure 2 (b) is the surface morphology.

[0033] Figure 3 is Figure 2 Secondary electron microscopic morphology of the coating cross-section of sample 1 in Figure 3 (a) is the secondary electron microscopic morphology of the coating cross-section; Figure 3 (b) is the variation diagram of the contents of Fe, Cr, Zr, and Si elements from the top to the bottom of the coating.

[0034] Figure 4 is Figure 2 Hardness test results of sample 1 in Figure 4 (a) is the hardness distribution from the top to the bottom of the coating at room temperature; Figure 4 (b) is the hardness change of the coating surface at different temperatures.

[0035] Figure 5 Macrograph of sample 2 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention. Among them, Figure 5 (a) is the cross-sectional optical microscope morphology, Figure 5 (b) is the surface morphology.

[0036] Figure 6 Macrograph of sample 3 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention. Among them, Figure 6 (a) is the cross-sectional optical microscope morphology, Figure 6 (b) is the surface morphology.

[0037] Figure 7 Macrograph of sample 4 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention.

[0038] Figure 8 Macrograph of sample 5 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention.

[0039] Figure 9 Macrograph of sample 6 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention.

[0040] Figure 10Macromorphology of the specimen 7 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention in Example 8.

[0041] Figure 11 Macromorphology of the specimen 8 of the ZrB2-SiC composite ceramic coating on the surface of 304 stainless steel obtained by the method provided by the present invention in Example 9. Specific embodiments

[0042] The embodiments of the present invention will be described in detail and comprehensively below, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0043] Materials:

[0044] 1. The ZrB2 ultrafine powder was purchased from Hunan Huawei Jingcheng Material Technology Co., Ltd., with a particle size of 0.5 - 1.0 μm and a purity of 99.5%.

[0045] 2. The SiC ultrafine powder was purchased from Hunan Huawei Jingcheng Material Technology Co., Ltd., with a particle size of 0.8 - 2.0 μm and a purity of 99.5%.

[0046] 3. The high-speed laser cladding equipment (equipped with a synchronous powder feeder) and the powder feeder were purchased from Nanjing Zhongke Yuchen Laser Technology Co., Ltd. The equipment model of the high-speed laser cladding equipment is: RC-LCD-4000-IPG type.

[0047] Example 1 Preparation of ZrB2-SiC composite ceramic powder

[0048] 1. Mix the ZrB2 ultrafine powder and the SiC ultrafine powder according to the proportion that the ZrB2 ultrafine powder accounts for 70 wt% and the SiC ultrafine powder accounts for 30 wt% to prepare a mixture;

[0049] 2. Add the mixture to distilled water according to the proportion of a solid content of 38 wt%, then add 4 wt% of the binder, and make a slurry under the condition of high-speed magnetic stirring, where the stirring speed is 1400 revolutions per minute and the stirring time is 50 min;

[0050] 3. Use a spray granulation equipment to prepare spherical ZrB2-SiC composite ceramic powder, with an inlet air temperature of 180 °C, an outlet temperature of 130 °C, a fan frequency of 23 Hz, and a feeding speed of 40 revolutions per minute;

[0051] 4. Powder sieving: Sieve the powder through a 400-mesh sieve to obtain ZrB2-SiC composite ceramic powder with a particle size less than or equal to 38 μm. The typical morphology of the powder is as Figure 1 shown.

[0052] After sieving, ZrB2-SiC composite ceramic powder with a particle size above 38 μm was also obtained. Additionally, the powder was sieved through a 220-mesh sieve to obtain ZrB2-SiC composite ceramic powder with a particle size in the range of 38 - 65 μm, in order to detect the effect of preparing a coating from ZrB2-SiC composite ceramic powder with a particle size above 38 μm.

[0053] It should be noted that under the process parameters of this embodiment, the ZrB2-SiC composite ceramic powder with a particle size less than or equal to 38 μm obtained by sieving through a 400-mesh sieve was further sieved (800-mesh), and it was found that its minimum particle size was still ≥15 μm, meeting the requirements for the fluidity of the powder for laser cladding.

[0054] Example 2 Preparation of a ZrB2-SiC ceramic matrix composite coating on the surface of 304 stainless steel by high-speed laser cladding

[0055] 1. Sand the surface of the 304 stainless steel to be clad with sandpaper, and then perform rust removal and degreasing pretreatment: Specifically, sand the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then ultrasonically clean the surface with acetone or absolute ethanol to remove the oil stains and impurities. The ultrasonic power is 150 W, and the total ultrasonic cleaning time is 5 minutes.

[0056] 2. Dry the ZrB2-SiC composite ceramic powder with a particle size of 15 - 38 μm prepared in Example 1 at 60 °C for 30 minutes to improve the fluidity of the powder.

[0057] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of a high-speed laser cladding device, send it into the high-speed laser cladding device equipped with a synchronous powder feeding head, and perform high-speed laser cladding under a local argon protection atmosphere; specimen 1 was made.

[0058] The above-mentioned local inert gas (argon) protection atmosphere refers to an inert gas protection atmosphere formed locally with the matrix molten pool (the matrix melting range) as the center by the powder feeding protection gas feeding device and the laser head protection gas feeding device equipped in the high-speed laser cladding device during the laser cladding process. Since high-speed laser cladding requires low oxygen / oxygen-free conditions to avoid material oxidation, a low oxygen / oxygen-free inert gas atmosphere is formed around the reaction. Adopting a local protection atmosphere can avoid waste caused by large-scale introduction of inert gas and reduce the usage cost of the inert gas (argon in this embodiment).

[0059] The specific process parameters are: laser power: 2.5 kW; scanning speed: 120 mm / s; the distance of the overlapping point above the matrix is 1 mm; overlapping rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0060] The position where the laser focus coincides with the powder spot focus is defined as the coincidence point. In this embodiment, the position adjustment of the substrate in the high-speed laser cladding equipment is carried out by combining the existing reciprocating platform and robotic arm, so that it reaches the specified relative position with the high-speed cladding laser head in the high-speed laser cladding equipment. To ensure the consistency of experimental conditions, the subsequent embodiments are also adjusted in the same way. Of course, other existing technologies or equipment can also be used to adjust the position of the substrate.

[0061] Detect the effect of sample 1 with a ZrB2-SiC ceramic matrix composite coating cladded on the surface of 304 stainless steel:

[0062] Use electrical discharge machining to prepare samples and observe the coating morphology with an optical microscope, as Figure 2 shown; among them, Figure 2 (a) is the cross-sectional morphology, Figure 2 (b) is the surface morphology. It can be seen from Figure 2 (a) that there are only a small number of irregular pores in the coating, and a perfect metallurgical bond is formed between the coating and the 304 stainless steel substrate; it can be seen from Figure 2 (b) that there are no obvious cracks on the surface of the coating.

[0063] Further use an electron microscope and an energy spectrum analyzer to observe the microscopic morphology and element distribution of the coating to determine whether the coating conforms to the continuous gradient distribution. The results are as Figure 3 shown. It can be seen from Figure 3 (a) that the coating and the substrate form a metallurgical bond, and due to the buoyancy effect of SiC during the cladding process, an aggregation layer is formed at the top of the coating. It can be clearly found from the test of the element content from the top to the bottom of the coating in Figure 3 (b) that the matrix phase elements Fe and Cr increase in gradient from the top to the bottom of the coating; the ceramic phase elements Zr and Si decrease in gradient from the top to the bottom of the coating, conforming to the distribution characteristics of a continuous gradient. This continuous gradient structure makes the thermal properties between the coating and the 304 stainless steel substrate gradually approach from the top to the bottom of the coating, thereby improving the bonding strength and cohesive strength of the coating.

[0064] Use a Vickers hardness tester and, in accordance with the national standard "GB 7997-1987 Test Method for Vickers Hardness of Cemented Carbides", conduct room temperature hardness tests and high temperature hardness tests to explore the hardness distribution of the coating cross-section at room temperature and the hardness change at different temperatures. The results are as Figure 4 shown. Among them, it can be seen from Figure 4 (a) that the surface hardness of the coating of sample 1 is as high as 1700HV 0.5 or more at room temperature, and shows a trend of gradually decreasing from the coating surface to the substrate. It can be seen from Figure 4(b) It can be seen that the surface hardness of the coating shows a slow and gradual downward trend with the increase of temperature. Even in an environment of 800 °C, the surface hardness of the coating still remains above 1000 HV5.

[0065] Therefore, in a room-temperature environment, the hardness change from the top to the bottom of the coating is positively correlated with the ceramic-phase elements and negatively correlated with the metal-phase elements. The surface of the coating shows extremely high hardness both at room temperature and high temperature. This is mainly attributed to the continuous gradient distribution of the coating, resulting in a higher ceramic-phase content at the top of the coating, thereby increasing the surface hardness of the coating, meeting the requirements of engineering practical applications.

[0066] Example 3 High-speed laser cladding of ZrB2-SiC ceramic matrix composite coating on the surface of 304 stainless steel

[0067] 1. Sand the surface of the 304 stainless steel to be clad with sandpaper, and then carry out pre-treatment for rust removal and degreasing: specifically, sand the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then ultrasonically clean the surface oil and impurities with acetone or absolute ethanol. The ultrasonic power is 150 W, and the total ultrasonic time is 5 minutes.

[0068] 2. Dry the ZrB2-SiC composite ceramic powder with a particle size of 38 - 65 μm prepared in Example 1 at 70 °C for 40 minutes to improve the fluidity of the powder.

[0069] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, send it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; prepare Specimen 2. The specific process parameters are: laser power: 2.5 kW; scanning speed: 120 mm / s; the distance of the overlap point above the substrate is 1 mm; overlap rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0070] Detect the effect of Specimen 2 of the ZrB2-SiC ceramic matrix composite coating clad on the surface of 304 stainless steel:

[0071] Cut the sample by electric spark machining, and observe the coating morphology with an optical microscope, as Figure 5 shown; among them, Figure 5 (a) is the cross-sectional morphology, Figure 5 (b) is the surface morphology. From Figure 5 (a), it can be seen that when the particle size of the powder is relatively large, a large number of pores appear in the coating; from Figure 5 (b), it can be seen that there are a large number of pores and cracks visible to the naked eye on the surface of the coating. Thus, it can be known that this is mainly caused by the insufficient melting of the large-particle ceramic powder.

[0072] Using a Vickers hardness tester, according to the national standard "GB 7997-1987 Test Method for Vickers Hardness of Cemented Carbides", room temperature hardness testing was carried out. The highest hardness of the coating was only 1200 HV 0.5 This is mainly because there are many unmelted powders, pores and cracks in the coating. Due to the poor coating quality and low room temperature hardness, it can no longer meet the practical engineering needs, so high temperature hardness testing was no longer carried out.

[0073] ZrB2-SiC composite ceramic powders larger than 65 μm are more difficult to melt, so cladding testing was no longer carried out.

[0074] Example 4 High-speed Laser Cladding of ZrB2-SiC Ceramic Matrix Composite Coating on the Surface of 304 Stainless Steel

[0075] 1. Sand the surface of the 304 stainless steel to be clad with sandpaper, and then carry out rust removal and degreasing pretreatment: specifically, sand the surface of the 304 stainless steel to be clad with #200, #400 and #800 sandpapers for 3 minutes each in turn, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic time is 5 minutes.

[0076] 2. Dry the ZrB2-SiC powder with a particle size of 15-38 μm prepared in Example 1 at 50 °C for 40 minutes to improve the fluidity of the powder.

[0077] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, send it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; make Specimen 3. The specific process parameters are: laser power: 2.5 kW; scanning speed: 200 mm / s; the distance of the overlap point above the substrate is 1.5 mm; overlap rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0078] Detect the effect of Specimen 3 of the ZrB2-SiC ceramic matrix composite coating clad on the surface of 304 stainless steel:

[0079] Use electrical discharge machining to prepare samples, and observe the coating morphology with an optical microscope, as Figure 6 shown; among them, Figure 6 (a) is the cross-sectional morphology, Figure 6 (b) is the surface morphology. It can be seen from Figure 6 (a) that when the scanning speed is too fast, due to the reduction of the heat input on the substrate surface, a large number of defects are generated at the coating-substrate bonding interface; it can be seen from Figure 6 (b) that due to more defects at the coating-substrate bonding surface, a small part of the coating has peeled off under the action of internal stress.

[0080] Due to the poor interface quality of the coating and the existence of internal cracks, it can no longer meet the practical engineering requirements, so the room temperature and high temperature hardness tests are no longer carried out.

[0081] Example 5 High-Speed Laser Cladding of ZrB2-SiC Ceramic Matrix Composite Coating on the Surface of 304 Stainless Steel

[0082] 1. Polish the surface of the 304 stainless steel to be clad with sandpaper, and then carry out rust removal and degreasing pretreatment: specifically, polish the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in turn, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150W, and the total ultrasonic time is 5 minutes.

[0083] 2. Dry the ZrB2-SiC powder with a particle size of 15 - 38μm prepared in Example 1 at 60°C for 30 minutes to improve the fluidity of the powder.

[0084] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, send it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; make specimen 4.

[0085] The specific process parameters are: laser power: 2.5kW; scanning speed: 60mm / s; the distance of the overlapping point above the substrate is 1.5mm; overlapping rate: 85%; spot diameter: 2mm; powder feeding rate: 3.9g / min; the protective gas is argon.

[0086] Use electrical discharge machining to prepare samples, and observe the cross-sectional morphology of the coating with an optical microscope. As Figure 7 shown in the cross-sectional optical microscope morphology. It can be seen that when the scanning speed is too slow, due to the increase in the heat input on the substrate surface, the coating and the substrate are fully convected during the cladding process, so that more metal phases in the substrate diffuse into the coating, and the continuous gradient degree of the coating weakens.

[0087] Use a Vickers hardness tester to carry out room temperature hardness tests according to the national standard "GB 7997-1987 Test Method for Vickers Hardness of Cemented Carbides". The highest hardness of the coating is only 870HV 0.5 . This is mainly because the metal phases from the substrate in the coating have occupied the main phase. Due to the low room temperature hardness, it can no longer meet the practical engineering requirements, so the high temperature hardness test is no longer carried out.

[0088] Example 6 High-Speed Laser Cladding of ZrB2-SiC Ceramic Matrix Composite Coating on the Surface of 304 Stainless Steel

[0089] 1. Polish the surface of the 304 stainless steel to be clad with sandpaper, and then carry out rust removal and degreasing pretreatment: specifically, polish the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic cleaning time is 5 minutes.

[0090] 2. Dry the ZrB2 - SiC powder with a particle size of 15 - 38 μm prepared in Example 1 at 50 °C for 20 minutes to improve the fluidity of the powder.

[0091] 3. Load the ZrB2 - SiC composite ceramic powder into the powder feeder of a high - speed laser cladding equipment, feed it into the high - speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high - speed laser cladding under a local argon - protection atmosphere; make Specimen 5.

[0092] The specific process parameters are: laser power: 2 kW; scanning speed: 150 mm / s; the distance of the overlap point above the substrate is 1.3 mm; overlap rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0093] Cut the sample by electric spark machining, and observe the cross - sectional morphology of the coating with an optical microscope, as Figure 8 shown. It can be seen that under these process parameters, only a small amount of irregular pores exist in the coating, a perfect metallurgical bond is formed between the coating and the 304 stainless steel substrate, and no cracks are found in the coating.

[0094] Use a Vickers hardness tester to conduct room - temperature hardness testing according to the national standard "GB 7997 - 1987 Test Method for Vickers Hardness of Cemented Carbides". The highest hardness of the coating reaches 1670 HV 0.5 . It meets the requirements of engineering applications.

[0095] Example 7 High - speed Laser Cladding of ZrB2 - SiC Ceramic - based Composite Coating on the Surface of 304 Stainless Steel

[0096] 1. Polish the surface of the 304 stainless steel to be clad with sandpaper, and then carry out rust removal and degreasing pretreatment: specifically, polish the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic cleaning time is 5 minutes.

[0097] 2. Dry the ZrB2 - SiC composite ceramic powder with a particle size of 15 - 38 μm prepared in Example 1 at 50 °C for 30 minutes to improve the fluidity of the powder.

[0098] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; make sample 6. The specific process parameters are: laser power: 3 kW; scanning speed: 80 mm / s; the distance of the overlapping point above the substrate is 1.5 mm; overlapping rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0099] Use electrical discharge machining to prepare samples, and observe the cross-sectional morphology of the coating with an optical microscope, as Figure 9 shown. It can be seen that only a small amount of irregular pores exist in the coating under these process parameters, a perfect metallurgical bond is formed between the coating and the 304 stainless steel substrate, and no cracks are found in the coating.

[0100] Use a Vickers hardness tester, and conduct room temperature hardness testing according to the national standard "GB 7997-1987 Test Method for Vickers Hardness of Cemented Carbides". The highest hardness of the coating reaches 1620 HV 0.5 , meeting the requirements of engineering applications.

[0101] Example 8 High-Speed Laser Cladding of ZrB2-SiC Ceramic Matrix Composite Coating on the Surface of 304 Stainless Steel

[0102] 1. Polish the surface of the 304 stainless steel to be clad with sandpaper, and then carry out rust removal and degreasing pretreatment: specifically, polish the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic time is 5 minutes.

[0103] 2. Dry the ZrB2-SiC powder with a particle size of 15-38 μm prepared in Example 1 at 60 °C for 30 minutes to improve the fluidity of the powder.

[0104] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; make sample 7. The specific process parameters are: laser power: 3.5 kW; scanning speed: 120 mm / s; the distance of the overlapping point above the substrate is 0.5 mm; overlapping rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0105] Use electrical discharge machining to prepare samples, and observe the cross-sectional morphology of the coating with an optical microscope, as Figure 10As shown in the figure. It can be seen that when the laser power is too high and the distance between the coincidence point of the laser focus and the powder spot focus and the substrate surface is too close, more energy generated during the cladding process will be distributed to the substrate. This method approaches the energy distribution method of traditional laser cladding. Therefore, during this process, the coating and the substrate are fully convective, causing more metal phases in the substrate to diffuse into the coating, and the continuous gradient degree of the coating weakens.

[0106] Using a Vickers hardness tester, according to the national standard "GB 7997-1987 Test Method for Vickers Hardness of Cemented Carbides", the hardness test at room temperature was carried out. The highest hardness of the coating was only 840 HV0.5. This is mainly because the metal phase from the substrate in the coating has occupied the main phase. Due to the low hardness at room temperature, the coating can no longer meet the practical engineering needs, so the high-temperature hardness test was no longer carried out.

[0107] Example 9 High-Speed Laser Cladding of ZrB2-SiC Ceramic Matrix Composite Coating on the Surface of 304 Stainless Steel

[0108] 1. Sand the surface of the 304 stainless steel to be clad with sandpaper, and then perform pre-treatment for rust removal and degreasing: Specifically, sand the surface of the 304 stainless steel to be clad with #200, #400, and #800 sandpapers for 3 minutes each in sequence, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the oil stains and impurities on the surface. The ultrasonic power is 150 W, and the total ultrasonic time is 5 minutes.

[0109] 2. Dry the ZrB2-SiC powder with a particle size of 15 - 38 μm prepared in Example 1 at 70 °C for 20 minutes to improve the fluidity of the powder.

[0110] 3. Load the ZrB2-SiC composite ceramic powder into the powder feeder of the high-speed laser cladding equipment, send it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, and carry out high-speed laser cladding under a local argon protection atmosphere; make specimen 8. The specific process parameters are: laser power: 1.7 kW; scanning speed: 120 mm / s; the distance of the coincidence point above the substrate is 2.0 mm; overlap rate: 85%; spot diameter: 2 mm; powder feeding rate: 3.9 g / min.

[0111] Use electrical discharge machining to prepare samples, and observe the cross-sectional morphology of the coating with an optical microscope, as Figure 11 shown. It can be seen that when the laser power is too low and the distance between the coincidence point of the laser focus and the powder spot focus and the substrate surface is too far, less of the limited laser energy generated during the cladding process is distributed to the substrate, resulting in a shallower melting pool area of the substrate, limited interdiffusion between the substrate metal and the coating, and insufficient melting of the ceramic powder at this energy. Therefore, the interface between the coating and the substrate has poor bonding, and there are many large defects in the coating. The coating quality under this parameter is poor and can no longer meet the practical engineering needs.

[0112] As can be seen from the above embodiments, the present invention provides a method for preparing a continuous gradient ceramic-based coating on the surface of an iron-based alloy. A coating with excellent room-temperature and high-temperature properties can be obtained within the process parameter range defined by this method. When the particle size of the ZrB2-SiC composite ceramic powder used exceeds the defined range, incomplete melting of the ceramic powder will occur, affecting the coating quality. When the laser power exceeds the range used in the present invention, being too high will cause a weakened continuous gradient degree of the coating, and being too low will result in incomplete melting of the ceramic powder. When the scanning speed exceeds the range used in the present invention, being too fast will generate a large number of defects at the coating-substrate bonding interface, and being too slow will cause a weakened continuous gradient degree of the coating. When the overlapping point exceeds the range used in the present invention, being too far will result in poor bonding at the coating and substrate interface and more large defects in the coating, and being too close will cause a weakened continuous gradient degree of the coating. All of these will not meet the requirements of engineering applications. However, the coating prepared within the range used in the present invention can meet the requirements of engineering applications.

[0113] In summary, the method for preparing a ceramic-based composite coating by high-speed laser cladding provided by the present invention aims at the problem of poor compatibility between ceramic and metal materials, designs and prepares a continuous gradient coating structure, and realizes the perfect combination of the two materials. This continuous gradient coating structure is specifically manifested as follows: (1) the metal phase elements gradually decrease from the bottom to the top of the coating; (2) the ceramic phase elements gradually increase from the bottom to the top of the coating. Finally, the high content of metal phase elements at the bottom of the coating ensures reliable metallurgical bonding between the coating and the substrate; the high content of ceramic phase elements at the top of the coating ensures excellent properties of the coating at high temperatures. Through hardness experiments at room temperature and high temperatures, it is confirmed that the coating described in the present invention has more excellent comprehensive properties.

[0114] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a ceramic matrix composite coating by using a high-speed laser cladding process, characterized in that, It includes the following steps: 1) Conduct rust removal and degreasing pretreatment on the substrate; 2) Dry the ZrB2-SiC composite ceramic powder at 50 - 70 °C for 20 - 40 minutes; 3) Load the ZrB2-SiC composite ceramic powder into the powder feeder of a high-speed laser cladding equipment, feed it into the high-speed laser cladding equipment equipped with a synchronous powder feeding head, make the laser focus formed by the high-speed cladding laser head coincide with the powder spot focus formed by the synchronous powder feeding head, then adjust the coincidence position of the two foci to be 1 - 1.5 mm above the substrate surface, and conduct high-speed laser cladding on the substrate under a local inert gas protection atmosphere; Among them, the process parameters of high-speed laser cladding are: laser power 2 - 3 kW, scanning speed 80 - 150 mm / s, powder feeding rate 3.7 - 4.1 g / min, overlapping rate 70% - 90%, spot diameter 2 - 3 mm; The substrate is a ferrous alloy; The preparation method of the ZrB2-SiC composite ceramic powder in step 2) is: a. Mix ZrB2 ultrafine powder and SiC ultrafine powder according to the proportion that ZrB2 ultrafine powder accounts for 70 wt% and SiC ultrafine powder accounts for 30 wt% to prepare a mixture; b. Add the mixture to distilled water according to the proportion of solid content of 25 - 40 wt%, then add 2 - 5 wt% of binder, and make a slurry under the condition of high-speed magnetic stirring, where the stirring speed is 1000 - 1500 revolutions per minute and the stirring time is 40 - 60 min; c. Use a spray granulation equipment to prepare spherical ZrB2-SiC composite ceramic powder, with the inlet air temperature of 170 - 190 °C, the outlet temperature of 120 - 140 °C, the fan frequency of 20 - 25 Hz, and the feeding speed of 35 - 45 revolutions per minute; d. Powder sieving: Sieve the powder through a 400-mesh sieve to obtain ZrB2-SiC composite ceramic powder with a particle size less than or equal to 38 μm.

2. The method according to claim 1, characterized in that, The ferrous alloy is carbon steel, alloy steel or cast iron.

3. The method according to claim 1, characterized in that The rust removal and degreasing treatment process in step 1) is: Polish the substrate with #200, #400 and #800 sandpapers for 3 minutes each in turn, and then use acetone or absolute ethanol for ultrasonic cleaning to remove the surface oil stains and impurities, with an ultrasonic power of 150 W and a total ultrasonic time of 5 minutes.

4. The method according to claim 1, wherein The particle size of the ZrB2 ultrafine powder in step a is 0.5 - 1.0 μm and the purity is 99.5%; the particle size of the SiC ultrafine powder is 0.8 - 2.0 μm and the purity is 99.5%.

5. The method according to claim 1, characterized in that, The binder in step b is PVA.

6. The method according to claim 1, wherein The inert atmosphere in step 3) is an argon atmosphere.

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