High-binding-force nickel-based wear-resistant coating with gradient structure and preparation method thereof

Abstract

The invention belongs to the technical field of functional coatings, and particularly relates to a high-binding-force nickel-based wear-resistant coating with a gradient structure and a preparation method of the high-binding-force nickel-based wear-resistant coating. The coating is of a gradient structure and is composed of a middle layer and a surface layer, and the middle layer is prepared from, by mass, 2%-5% of Fe, 1%-3% of B, 2%-5% of Si, 5%-20% of Cr, less than 0.05% of C and the balance Ni; and the component of the surface layer is Ni60 / 35WC or Ni45 / 35WC. According to the coating, by adding the middle layer and combining subsonic flame spraying with the laser remelting process, element diffusion between the base body and the middle layer and element diffusion between the middle layer and the surface layer are achieved through laser remelting by means of the low-melting-point characteristic of the middle layer, metallurgical bonding is achieved, and therefore the high bonding strength is obtained; and the problems of large expansion coefficient difference between the coating and the matrix, easy cracking and the like are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of functional coatings, and in particular relates to a high-bonding nickel-based wear-resistant coating with a gradient structure and a preparation method thereof. Background Art

[0002] Thermal sprayed metal / ceramic composite coatings have high hardness, good wear resistance and corrosion resistance, and flexible spraying positions, and have broad application prospects in the fields of hot molds, rolling mills, etc. However, the thermal spray coating and the substrate are often mainly mechanically bonded, and the bonding strength is relatively low. Among them, the subsonic spray bonding strength is about 30MPa, and the supersonic spray bonding strength is about 70MPa. In addition, although adding a certain proportion of ceramic particles to the metal powder can improve the hardness and wear resistance of the thermal spray coating, the expansion coefficient of the metal / ceramic composite coating is quite different from that of the metal substrate. During the heating and cooling process, cracks are easily formed due to the large difference in expansion coefficients. Therefore, coating cracking and peeling are the main causes of thermal spray coating failure.

[0003] In order to improve the bonding strength of the spray coating, the composite preparation technology of remelting the spray coating through heat sources such as flame / electromagnetic induction / laser has been widely studied. Among them, laser remelting has the characteristics of high energy density and small heat-affected zone. It can melt the interface between the coating and the substrate through instantaneous high temperature to form a metallurgical bond, while minimizing the impact on the substrate.

[0004] The invention patent with publication number CN 110699626A discloses a laser remelting method for thermal sprayed metal / ceramic coatings for cavitation resistance. The preparation method is to prepare a metal / ceramic composite coating on a substrate by thermal spraying, and then perform laser remelting on the metal / ceramic composite coating. Under the high-density energy of the laser, the surface of the metal / ceramic composite coating is remelted to form a new structure, and the coating structure performance is enhanced after cooling. Although this method can improve the bonding strength between the metal / ceramic coating and the substrate, there is still a problem of too large a difference in expansion coefficient between the metal / ceramic coating and the metal substrate.

[0005] The invention patent with publication number CN 106367707 B discloses a laser remelting method for supersonic sprayed WC-12Co coating, which is used to strengthen the supersonic sprayed WC-12Co coating on the surface of H13 hot working die steel. This technology uses supersonic spraying to spray a layer of WC-12Co coating on the surface of H13 hot working die steel after sandblasting. After heat preservation and cooling to room temperature, the WC-12Co coating is re-melted with the surface of H13 hot working die steel by laser remelting to form a metallurgical bond. After cooling, the coating structure performance is enhanced and the coating wear resistance is improved. The coating needs to be kept at 850℃ for 2 hours after spraying before laser remelting, which has high time and energy costs, and heat preservation at high temperature will greatly change the performance of the substrate.

[0006] The invention patent with publication number CN 101112701 A discloses a thermal spray gradient coating processing method based on multiple laser remelting. The main innovation of this method is to use multiple laser remelting methods to perform composite processing on the thermal spray gradient coating, which overcomes the shortcomings that the various sub-coatings of the gradient coating cannot all achieve metallurgical bonding without laser remelting or one laser remelting, the gradient structure in the coating will be destroyed, and the thermal spray lamellar structure in the gradient coating cannot be eliminated. In the embodiment of the patent, five laser remeltings are used to prepare a 100μm coating each time, and the preparation process is complicated and the efficiency is low. Summary of the invention

[0007] In view of the problems of poor bonding strength between existing metal / ceramic coatings and substrates, large difference in expansion coefficients, easy cracking, complex preparation process, and great impact on the substrate, the present invention provides a high-bonding nickel-based wear-resistant coating with a gradient structure and a preparation method thereof.

[0008] In order to achieve the above objectives, the specific technical solutions are as follows:

[0009] The invention provides a high-bonding nickel-based wear-resistant coating with a gradient structure. The coating has a gradient structure and consists of an intermediate layer and a surface layer. The intermediate layer has the following components: by mass percentage, Fe=2%-5%, B=1-3%, Si=2-5%, Cr=5%-20%, C content is less than 0.05%, and the balance is Ni; the surface layer is composed of Ni60 / 35WC or Ni45 / 35WC powder.

[0010] The high-bonding nickel-based wear-resistant coating of the present invention adopts a gradient structure design, and realizes an orderly transition from the surface metal / ceramic coating with high hardness and high expansion coefficient to the metal substrate through targeted intermediate layer component design. The intermediate layer relieves stress and reduces the cracking tendency. At the same time, it is completely melted during the laser remelting process to play a bonding role, thereby achieving the purpose of improving the bonding strength.

[0011] Among them, the melting point of Ni is 1453℃, which is lower than that of common pure metals, which is conducive to full melting during laser remelting to form a eutectic pool; at the same time, Ni has good wettability, and the selection of Ni-based intermediate layer can be better combined with the surface Ni-based tungsten carbide coating during the remelting process. B, as a commonly used element in self-fluxing alloy powder, can significantly reduce the melting point of alloy powder, which is conducive to full melting of the sprayed layer during laser remelting. Taking into account the content of B, it can be controlled at 1% to 3%, such as 1%, 1.5%, 2%, 2.5%, and 3%. The addition of Fe element can improve the diffusion effect of the intermediate layer and the Fe-based matrix during laser remelting and strengthen the combination of the matrix and the intermediate layer, but the content of Fe element should not be too high. Taking into account the content of Fe element, it can be controlled at 2% to 5%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. Cr element is an important element of the intermediate layer of the present invention. Cr can form carbides or borides to improve the hardness of the coating. At the same time, Cr is a key element to improve the corrosion resistance of the coating. In order to ensure the overall gradient effect of the coating, the hardness of the middle layer should not be too high. Considering the addition of Cr, the amount is controlled to be 5%-20%, such as 5%, 7%, 9%, 11%, 13%, 15%, etc. C exists as an impurity in the middle layer. Too high carbon content will form carbides, resulting in too high hardness and affecting the corrosion resistance of Cr. It will also increase the carbon equivalent and increase the cracking tendency. Therefore, the C content in the middle layer should be strictly controlled below 0.05%. The Si element can reduce the surface tension of the melt, enhance fluidity, make the eutectic pool spread more evenly, and reduce defects such as pores and unfused. At the same time, Si combines with other elements (such as Cr and Mo) to form hard phases (such as silicides), which improves the hardness, wear resistance and high temperature strength of the material. However, excessive silicon may lead to an increase in brittle phases (such as coarse silicides) and damage toughness. Therefore, it is necessary to balance strength and plasticity. Considering the addition of Si, the amount is controlled to be 2%-5%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0012] The present invention also provides a method for preparing a high-bonding nickel-based wear-resistant coating with a gradient structure, comprising the following steps:

[0013] (1) Intermediate layer subsonic flame spraying;

[0014] (2) Laser remelting of the intermediate layer;

[0015] (3) Surface subsonic flame spraying;

[0016] (4) Surface laser remelting.

[0017] In the above step (1), the intermediate layer is prepared by selecting chromium powder, iron powder, silicon powder, boron powder, carbon powder and nickel powder according to mass percentage to obtain a composite powder; in the step (1), the intermediate layer composite powder is sprayed on the surface of the substrate (such as H13 hot working die steel) by subsonic flame spraying technology to form an intermediate layer coating, and the spraying conditions include: oxygen pressure of 0.5-0.7MPa, acetylene pressure of 0.12-0.15MPa, compressed air pressure of 0.6-0.8MPa, powder feeding rate of 330-420g / min, substrate preheating temperature of 70-120°C, spraying distance of 250-300mm, and average movement speed of the spray gun of 200-250mm / s.

[0018] In the above step (2), the intermediate layer is laser remelted to form a transition layer; during the laser remelting process, the laser power is 2000-4500W, the scanning speed is 5-20mm / s, and the rectangular spot size is (25×3)-(22×2.5)mm 2 , the substrate preheating temperature is 20 ~ 200 ℃.

[0019] In the above step (3), a surface powder is sprayed on the intermediate layer by subsonic flame spraying technology to form a surface coating, and the spraying conditions include: oxygen pressure of 0.5-0.7MPa, acetylene pressure of 0.12-0.15MPa, compressed air pressure of 0.6-0.8MPa, powder feeding rate of 330-420g / min, substrate preheating temperature of 70-120°C, spraying distance of 250-300mm, and average movement speed of the spray gun of 200-250mm / s.

[0020] In the above step (4), the surface coating is laser remelted to form a wear-resistant coating; during the laser remelting process, the laser power is 2000-3000W, the scanning speed is 5-20mm / s, and the rectangular spot size is (25×3)-(22×2.5)mm 2 , the substrate preheating temperature is 20 ~ 200 ℃.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The coating of the present invention combines the addition of an intermediate layer, subsonic flame spraying and laser remelting processes, and utilizes the low melting point characteristics of the intermediate layer. Through laser remelting, the element diffusion between the substrate and the intermediate layer, and between the intermediate layer and the surface layer is achieved, and metallurgical bonding is achieved, thereby obtaining high bonding strength. It can be used for key structures such as rollers and bearings that require high bonding strength and can withstand impact loads and alternating hot and cold environments. Compared with other laser remelting processes, the present invention obtains a gradient transition layer under specific spraying conditions, so that laser remelting can be completed without high-temperature preheating. The wear-resistant coating of the present invention can form a strong metallurgical bond between the layers, and the bonding strength is high; and the coating of the present invention only requires two laser remeltings to prepare a 0.2-1.2 mm thick composite coating, which is highly efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the metallographic structure diagram of the wear-resistant coating of Example 1;

[0024] Figure 2 This is a tensile bonding strength curve of the wear-resistant coating of Example 1;

[0025] Figure 3 is a hardness curve diagram of the wear-resistant coating of Example 1;

[0026] Figure 4 This is a SEM image of the interface between the middle layer of the wear-resistant coating and the substrate in Example 2;

[0027] Figure 5 This is the element distribution diagram at the interface between the middle layer of the wear-resistant coating and the substrate in Example 2. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0029] Example 1

[0030] A method for preparing a high-bonding nickel-based wear-resistant coating with a gradient structure comprises the following steps:

[0031] (1) Preparation of composite powder: According to the mass percentage of each component element: Fe = 3%, B = 2%, Si = 2%, Cr = 9%, C = 0.02%, and the balance is Ni, chromium powder, iron powder, silicon powder, boron powder, carbon powder, and nickel powder are selected and mixed evenly by mechanical mixing, and then the mixed powder is dried in an electric heating blast drying oven to obtain a composite powder;

[0032] (2) Surface pretreatment of H13 hot working die steel: Before spraying, the die steel is first degreased with a degreaser, and then the surface is cleaned again with dry sandblasting;

[0033] (3) Subsonic flame spraying of the intermediate layer: The composite powder is added to the subsonic thermal spraying equipment, and the subsonic thermal spraying technology is used to spray the surface of the H13 hot working die steel, and finally a nickel-based intermediate layer is prepared on its surface; the specific spraying process parameters are: the H13 hot working die steel substrate is preheated before spraying and the preheating temperature is 90°C, the oxygen pressure is 0.5MPa, the acetylene pressure is 0.12MPa, the compressed air pressure is 0.7MPa, the spraying distance is 250mm, the powder feeding rate is 420g / min, and the average speed of the spray gun is 200mm / s.

[0034] (4) Laser remelting of the intermediate layer: After spraying, the intermediate layer coating is laser remelted (argon is the protective gas during the laser remelting process) to form a eutectic pool to achieve metallurgical bonding between the intermediate layer and the substrate; the laser remelting process parameters are: before remelting, the substrate is preheated with oxygen flame at a preheating temperature of 200°C, the laser power is 2000W, the laser wavelength is 400nm, and the rectangular spot size is 25×3mm 2 , scanning speed 5mm / s.

[0035] (5) Subsonic flame spraying of the surface layer: repeat step 3, except that the powder used for the surface layer is commercial Ni60 / 35WC powder;

[0036] (6) Surface laser remelting: Repeat step 4, except that the laser remelting power is 2500W.

[0037] The interface between the wear-resistant coating and the substrate in Example 1 was observed under an optical microscope to obtain the metallographic structure of the coating. Figure 1 ,Depend on Figure 1 It can be seen that a uniform coating with a total thickness of about 850 μm is formed on the substrate surface, and the interface between the coating and the substrate material is well bonded.

[0038] The tensile bonding strength test method is to open a hole in the center of the sample so that the piston fits the center hole. The sample and the piston are in the same plane and then sprayed and remelted. Then the coating is pulled apart using a tensile testing machine. Repeat three times and record them as #1, #2, and #3. Figure 2 This is a tensile bonding strength curve of the wear-resistant coating of Example 1. It can be seen that the average bonding strength of the coating of this example is above 150 MPa.

[0039] The hardness test was carried out using a hardness tester and a metallographic specimen, with a load of 0.2 kg. The hardness curve of the wear-resistant coating of Example 1 is shown in FIG. Figure 3 As shown, the surface hardness is about 700HV0.2 , the hardness of the middle layer is about 400HV 0.2 , 45# steel base hardness is about 300HV 0.2 .

[0040] Example 2

[0041] The preparation method is similar to that of Example 1, except that the laser remelting power in step (4) is 3000 W.

[0042] Figure 4 , Figure 5 They are respectively the SEM image and element distribution diagram of the interface between the middle layer of the wear-resistant coating and the substrate of Example 2. Figure 4 , Figure 5 It can be seen that an element diffusion layer of about 10 μm is formed between the intermediate layer and the substrate, and the Fe and Ni elements diffuse significantly. It can be determined that a metallurgical bond is formed between the intermediate layer and the substrate in this embodiment, and therefore has a higher bonding strength.

[0043] It can be seen from the above embodiments that the present invention adopts a gradient structure design and a targeted intermediate layer component design, combined with subsonic flame spraying and laser remelting technology, to achieve metallurgical bonding between the coating and the substrate; the gradient wear-resistant coating prepared by the process method of the present invention has the characteristics of high bonding strength, small difference in expansion coefficient between the coating and the substrate, and not easy to crack.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-bonding nickel-based wear-resistant coating with a gradient structure, characterized in that: The coating has a gradient structure and consists of an intermediate layer and a surface layer. The intermediate layer has the following composition: by mass percentage, Fe=2%-5%, B=1-3%, Si=2-5%, Cr=5%-20%, C content is less than 0.05%, and the balance is Ni; the surface layer is composed of Ni60 / 35WC or Ni45 / 35WC powder.

2. The method for preparing a high-bonding nickel-based wear-resistant coating with a gradient structure according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Intermediate layer subsonic flame spraying; (2) Laser remelting of the intermediate layer; (3) Surface subsonic flame spraying; (4) Surface laser remelting.

3. The preparation method according to claim 2, characterized in that: In the step (1), chromium powder, iron powder, silicon powder, boron powder, carbon powder and nickel powder are selected according to mass percentage to prepare the intermediate layer composite powder.

4. The preparation method according to claim 3, characterized in that: In the step (1), a subsonic flame spraying technique is used to spray the intermediate layer composite powder on the surface of the substrate, and the spraying conditions include: an oxygen pressure of 0.5-0.7 MPa, an acetylene pressure of 0.12-0.15 MPa, a compressed air pressure of 0.6-0.8 MPa, a powder feeding rate of 330-420 g / min, a substrate preheating temperature of 70-120° C., a spraying distance of 250-300 mm, and an average movement speed of the spray gun of 200-250 mm / s.

5. The preparation method according to claim 2, characterized in that: The laser remelting conditions in step (2) include: the laser power is 2000-4500W, the scanning speed is 5-20mm / s, and the rectangular spot size is (25×3)-(22×2.5)mm 2 , the substrate preheating temperature is 20 ~ 200 ℃.

6. The preparation method according to claim 2, characterized in that: In the step (3), subsonic flame spraying technology is used to spray the surface powder, and the spraying conditions include: oxygen pressure of 0.5-0.7MPa, acetylene pressure of 0.12-0.15MPa, compressed air pressure of 0.6-0.8MPa, powder feeding rate of 330-420g / min, substrate preheating temperature of 70-120°C, spraying distance of 250-300mm, and average movement speed of the spray gun of 200-250mm / s.

7. The preparation method according to claim 2, characterized in that: The laser remelting conditions in step (4) include: the laser power is 2000-3000W, the scanning speed is 5-20mm / s, and the rectangular spot size is (25×3)-(22×2.5)mm 2 , the substrate preheating temperature is 20 ~ 200 ℃.

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