A surface wear-resistant and corrosion-resistant coating for an electric power connection fitting and a preparation method thereof

Abstract

The application discloses a kind of electric power connection hardware surface wear-resistant corrosion-resistant coating and preparation method thereof.The preparation method of the application includes: alloy powder and ceramic powder dry pretreatment, alloy powder includes Fe, Ni, Cu three elements;Alloy powder is evenly laid on the substrate surface of electric power connection hardware using clamp, and ceramic powder is added into powder feeder;Substrate is placed into atmosphere protection box filled with argon, and protection gas is continuously passed in;Laser parameters and powder feeder parameters are set, powder feeder, laser switch are opened in turn, ceramic powder is synchronously injected into molten pool by powder feeder, laser alloying processing is carried out on the substrate surface, and wear-resistant corrosion-resistant coating is prepared.The wear-resistant corrosion-resistant coating structure of the application is dense, hardness is high, wear resistance, corrosion resistance is significantly improved, effectively solve the problem that connection hardware for electric power line is invalid in use process due to factors such as wear and corrosion, prolong the service life of hardware.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite coating and relates to a surface wear-resistant and corrosion-resistant coating of electric power connecting hardware and a laser alloying preparation method thereof. BACKGROUND

[0002] The connecting hardware is an important component of the power transmission line, and the normal operation of the circuit is ensured through cooperation with other devices. The failure of the connecting hardware can cause the entire power transmission line to malfunction, resulting in huge losses to the circuit system and economy. The working environment of the connecting hardware is 99% outdoors, and the harsh working environment created by various extreme weather conditions exacerbates the corrosion of the hardware, greatly shortening the service life of the hardware. The connecting hardware is affected by factors such as wind vibration, dancing, icing, sub-span vibration, and wire ice shedding jumping during operation, and is prone to wear and tear. The connecting hardware is usually made of low-carbon steel, which has low hardness and poor wear resistance, and is prone to failure due to wear and tear. During actual service, not only is it affected by one failure mode, but also multiple failure modes act together. Corrosive substances from the outside enter the wear and tear parts between the connecting hardware, accelerating the failure of the hardware.

[0003] In order to improve the wear resistance and corrosion resistance of the connecting hardware, some scholars at home and abroad carry out surface modification treatment on the surface of low carbon steel, such as surfacing, ion implantation, thermal spraying, laser surface alloying and the like. Among them, the spraying coating and the substrate are mechanically combined, and the bonding strength is low, which is easy to cause cracking and peeling in the actual use process; surfacing will cause great heat effect on the substrate, which is easy to cause deformation; the thickness of hot-dip galvanizing and electrodeposition coating is generally only dozens of microns, which is difficult to meet the demand of long-term service. The alloy coating obtained by laser surface alloying has high metallurgical bonding strength, dense structure, less defects, high degree of microcrystalline grain refinement, and can prepare a coating with high hardness, high wear resistance and corrosion resistance on the surface of the substrate with poor performance, which has attracted wide attention in the field of metal surface modification. Laser surface alloying is a surface technology that melts alloying elements and substrate surface together through the heat effect of laser and solid phase material, and then rapidly solidifies on the surface of the substrate to form an alloy coating. According to the different material supply modes, it is divided into pre-coating type and synchronous powder feeding type. The coating prepared by the pre-coating type has relatively poor uniformity, and the vaporization and decomposition of the binder can easily cause pollution and pores and other defects, which is not suitable for laser alloying preparation of various alloy / ceramic powder materials; compared with the pre-coating type, the synchronous powder feeding type is more stable, has better uniformity and higher efficiency. When two or more than two alloy / ceramic powders are laser alloyed by synchronous powder feeding, in order to avoid the problem of uneven powder feeding caused by the large difference in the density of the alloy / ceramic powders, the ball mill is usually used to mix the powders uniformly before adding them into the powder feeder. However, due to the hard and brittle characteristics of ceramic powders such as WC, they are easy to break during the ball milling process, which destroys their sphericity and accelerates their decomposition in the molten pool, resulting in a decrease in the content of ceramic reinforcing particles in the coating and a decrease in performance. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a laser alloying preparation method for a wear-resistant and corrosion-resistant coating on the surface of an electric power connecting hardware, which uses a combination of pre-alloyed powder and synchronous injection of ceramic powder to prepare a composite coating. Different elements or compounds react chemically in the molten pool to form one or more compound reinforcement phases. The dense metal or alloy matrix provides good corrosion resistance, and the ceramic second phase provides high hardness and high strength. The combination of the two forms a laser alloying layer with wear resistance and corrosion resistance.

[0005] The technical scheme of the present application is as follows: a preparation method for a wear-resistant and corrosion-resistant coating on the surface of an electric power connecting hardware, comprising:

[0006] Step 1: polishing the surface of the substrate of the electric power connecting hardware to remove the oxide scale and cleaning it thoroughly to isolate air for standby;

[0007] Step 2, dry pre-treatment of the alloy powder and the ceramic powder, the alloy powder comprising Fe, Ni and Cu;

[0008] Step 3, uniformly lay the alloy powder on the surface of the substrate by using a clamp, and add the ceramic powder into the powder feeder;

[0009] Step 4, place the substrate into an atmosphere protection box filled with argon, and continuously input the protection gas;

[0010] Step 5, set the parameters of the laser and the powder feeder, open the powder feeder and the laser switch in sequence, after laser irradiation of the molten pool, the alloy powder pre-placed on the surface of the substrate is completely melted to form a molten pool, the ceramic powder is synchronously injected into the molten pool through the powder feeder, laser alloying processing is carried out on the surface of the substrate, and a wear-resistant and corrosion-resistant coating is prepared.

[0011] The principle of the present application is as follows: after laser irradiation of the molten pool, the alloy powder pre-placed on the surface of the substrate is completely melted to form a molten pool, wherein Ni and Cu can form a face-centered cubic γ-(Ni, Cu) solid solution, and Fe also exists in the form of γ-Fe at high temperature, so in the molten pool, the three elements Fe, Ni and Cu all exhibit the same crystal structure. In addition, the atomic radii of the three elements are very close, so Fe will also be dissolved into the γ phase to finally form a face-centered cubic γ-(Fe, Ni, Cu) single-phase solid solution as the main component of the coating. The single-phase γ solid solution alloy organization formed by rapid solidification is uniform and dense, and often exhibits excellent corrosion resistance. Further adding ceramic powder particles as a reinforcing phase can effectively play the characteristics of high hardness and high wear resistance, can significantly improve the wear resistance on the basis of excellent corrosion resistance of the coating, and finally prepare a reinforced coating with wear resistance and corrosion resistance on the surface of the substrate.

[0012] The present application has obvious advantages in controlling the addition amount of ceramic powder and improving the uniformity of the coating organization, and the method can reduce the contact time of the ceramic powder and the high-temperature alloy melt, to a certain extent, inhibit the decomposition loss, and is beneficial to improve the wear resistance and corrosion resistance of the alloying layer.

[0013] Preferably, in step 2, the mass percentage of each element in the alloy powder is 25-60wt.% Ni, 0-10wt.% Al, 0-5wt.% Mn and 0.5-5wt.% Fe, and the balance is Cu, and the particle size of the alloy powder is 15-60μm; the ceramic powder is tungsten carbide ceramic powder, and the particle size is 30-100μm.

[0014] Although the tungsten carbide ceramic powder has a very high melting point and is difficult to melt, it can easily decarburize and dissolve in the high-temperature alloy to generate W xC and the like, thereby affecting the wear resistance performance, so the dissolution of the tungsten carbide ceramic powder should be reduced as much as possible during the coating preparation process. The melting point of the alloy powder is quite different from that of the tungsten carbide, and the alloy powder is completely melted to form a molten pool during the laser scanning process. If the tungsten carbide ceramic powder directly contacts the high-temperature alloy melt at this time, the tungsten carbide ceramic powder is extremely easy to dissolve. Therefore, the present application adopts the process mode of combining the pre-coating and the coaxial powder feeding (also called synchronous powder feeding), the low-melting-point alloy powder is laid on the surface of the substrate, and the tungsten carbide ceramic powder is synchronously injected into the molten pool through the powder feeder, so that the contact between the alloy melt and the tungsten carbide ceramic powder is reduced, the dissolution of the tungsten carbide ceramic powder is inhibited, and the wear resistance of the coating is improved.

[0015] Preferably, in step 2, the mass percentage of each element in the alloy powder is 50-60wt.% Ni, 3-5wt.% Al, 0.2-1wt.% Mn, 0.5-1wt.% Fe, and the balance is Cu, and the particle size of the alloy powder is 15-50μm.

[0016] Most preferably, in step 2, the mass percentage of each element in the alloy powder is 58.1wt.% Ni, 3.76wt.% Al, 0.52wt.% Mn, 0.65wt.% Fe, and the balance is Cu, and the particle size of the alloy powder is 15-30μm, and the prepared coating has the best wear resistance and corrosion resistance.

[0017] Preferably, in step 1, the substrate of the power connection fitting is low-carbon steel, alloy steel or aluminum alloy.

[0018] Preferably, in step 3, the powder laying thickness of the alloy powder is 0.5-1.0mm.

[0019] Preferably, in step 4, the protective gas is argon with a purity of more than 99.9%, and the protective gas flow rate is 4-15L / min.

[0020] Most preferably, the powder laying thickness is 0.8mm, and the protective gas flow rate is 10L / min, and the protective effect is the best.

[0021] Preferably, in step 5, the laser power is 800-2000W, the scanning speed is 4-12mm / s, the spot diameter is 2-6mm, the multi-pass coating overlap rate is 20%-50%, and the powder feeding amount of the ceramic powder is 5-15g / min.

[0022] More preferably, in step 5, the laser power is 1000-1800W, the scanning speed is 6-8mm / s, the spot diameter is 4-5mm, the multi-pass coating overlap rate is 30%-40%, and the powder feeding amount of the ceramic powder is 8-12g / min.

[0023] As the most preferred, in the step 5, the laser power is 1200W, the scanning speed is 6mm / s, the spot diameter is 4.2mm, the multi-pass coating lap rate is 30%, and the powder feeding amount of the ceramic powder is 10g / min, so that the prepared coating has the best wear resistance and corrosion resistance.

[0024] The application also provides a wear-resistant and corrosion-resistant coating prepared by the above method.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] (1) The application prepares a wear-resistant and corrosion-resistant coating on the surface of the electric power connection hardware by laser surface alloying, wherein the alloy powder containing Fe, Ni, Cu, Al and other elements is prepositioned on the surface of the base material, and the tungsten carbide ceramic powder is synchronously injected into the molten pool by a powder feeder. During the laser alloying process, the Fe, Ni, Cu and other elements form a γ-phase single-phase solid solution, which has excellent corrosion resistance. At the same time, the injected tungsten carbide ceramic powder has low dissolution degree, and most of it remains in the coating as a reinforcing phase to improve the hardness and wear resistance of the coating.

[0027] (2) The interface between the wear-resistant and corrosion-resistant coating prepared by the application and the base material is a metallurgical bond rather than a mechanical bond, and has high bonding strength. The coating formed by rapid solidification has uniform organization, high density and small grains. The thickness of the whole coating is controllable, the wear resistance and corrosion resistance are significantly improved, and the service life of the connection hardware in the power transmission line can be effectively prolonged. In addition, the laser alloying process has little thermal effect on the base material itself, and will not cause deformation of the base material.

[0028] (3) The application adopts the method of laser surface alloying, which is simple, controllable and efficient. The coating prepared by the method has high bonding strength with the base material, and the hardness, wear resistance and corrosion resistance of the coating are significantly improved. Compared with conventional surface technologies, the method is more green and environmentally friendly, and has a wide development prospect in the field of metal surface modification. BRIEF DESCRIPTION OF DRAWINGS

[0029] The drawings accompanying the specification of the application form a part of the application and serve to further understand the application. The schematic embodiments of the application and the description thereof are used to explain the application, and do not constitute an improper limitation on the application.

[0030] Figure 1 is the overall morphology diagram of the surface alloying layer of the sample of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1;

[0031] Figure 2 is the cross-sectional morphology diagram of the coating in Example 1 and Comparative Example 1;

[0032] Figure 3 is the cross-sectional morphology diagram of the coating in Comparative Example 2 and Comparative Example 3;

[0033] Figure 4 SEM morphology of coating cross-section for Example 1 and Comparative Example 1: (a) Comparative Example 1, (b) Example 1;

[0034] Figure 5 X-ray diffraction results of coating surface for Example 1 and Comparative Example 1;

[0035] Figure 6 SEM morphology of typical structure of upper, middle and bottom of coating for Comparative Example 1 and Example 1:

[0036] Figure 7 Dendritic structure and EDS scanning results of middle of coating for Comparative Example 1: (a) morphology, (b) line scanning results at grain, (c) composition of point A, (d) composition of point B, (e) composition of point C;

[0037] Figure 8 Micro-morphology of coating for Example 1 and corresponding composition analysis: (a) dendritic structure, (b) fishbone-like structure, (c) composition of point D, (d) composition of point E, (e) composition of point F;

[0038] Figure 9 Microhardness distribution curve and friction coefficient curve of cross-section of coating for Comparative Example 1 and Example 1: (a) microhardness curve, (b) friction curve;

[0039] Figure 10 Surface morphology of wear scar and corresponding cross-section profile after friction and wear test: (a) substrate, (b) Comparative Example 1, (c) Example 1;

[0040] Figure 11 Electrochemical polarization curve and impedance spectrum amplitude spectrum of substrate, coating of Comparative Example 1 and coating of Example 1: (a) polarization curve, (b) impedance spectrum amplitude spectrum;

[0041] Figure 12 Overall morphology of coating for Example 2;

[0042] Figure 13 Overall morphology of coating for Example 3;

[0043] Figure 14 Electrochemical test results of substrate, Comparative Example 2 and Example 2: (a) polarization curve, (b) impedance spectrum;

[0044] Figure 15 Flow chart of the preparation method of the wear-resistant and corrosion-resistant coating on the surface of the power connection fitting. DETAILED DESCRIPTION

[0045] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0046] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0047] The application will be further described with reference to the following specific examples, it should be noted that the specific examples are illustrative of the application and not limiting.

[0048] The application provides a preparation method of a wear-resistant and corrosion-resistant coating on the surface of an electric power connection fitting, as shown in Figure 15 The preparation method comprises the following steps:

[0049] Step 1, polishing the surface of the base material of the electric power connection fitting to remove the oxide scale and clean it, and isolating air for standby;

[0050] Step 2, drying and pretreating the alloy powder and the ceramic powder, wherein the alloy powder comprises five elements of Ni, Cu, Fe, Al and Mn;

[0051] Step 3, uniformly laying the alloy powder on the surface of the base material by using a clamp, and adding the ceramic powder into a powder feeder;

[0052] Step 4, placing the base material into an atmosphere protection box filled with argon, and continuously feeding the protection gas;

[0053] Step 5, setting the parameters of the laser and the powder feeder, sequentially opening the powder feeder and the laser switch, after laser irradiation of the molten pool, completely melting the alloy powder prepositioned on the surface of the base material to form a molten pool, synchronously injecting the ceramic powder into the molten pool through the powder feeder, and performing laser alloying processing on the surface of the base material to prepare the wear-resistant and corrosion-resistant coating.

[0054] Example 1

[0055] The Q235 steel is used as the base material in this embodiment, and the sample size is 100 mm x 70 mm x 10 mm. First, the surface (100 mm x 70 mm) of the sample is polished to remove the oxidation layer, rust, oil stains and other dirt, until the sample surface is smooth and bright. Then, the sample is cleaned with anhydrous ethanol and dried in a vacuum drying oven at 100°C for 4 h.

[0056] The alloy powder is evenly spread on the surface of the substrate by using a clamp and a coating tool, and the coating thickness is controlled at 0.8 mm. The tungsten carbide ceramic powder is added to the powder feeder. A YLS-2000 type semiconductor laser is used for laser alloying experiment. Before the experiment, the process parameters of the laser need to be optimized, so several groups of experiments as shown in Table 1 are designed. From the surface quality, a better cladding layer can be prepared when the power is 1200-1800 W and the scanning speed is 6-8 mm / s.

[0057] Table 1 Laser alloying process parameters and coating surface quality

[0058]

[0059] The laser process parameters used after optimization are as follows: laser power 1200 W, scanning speed 6 mm / s, spot size 4.2 mm, and multi-layer coating overlap rate 30%. The powder feeder switch and the laser switch are turned on, and the WC powder is directly injected into the molten pool under the above laser process parameters by using the synchronous powder feeding method while the laser beam scans the surface of the substrate. The powder feeding amount is set to 10 g / min, and the laser alloying layer is prepared. The whole experiment process is carried out in a high-purity argon atmosphere protection box, and the argon flow is continuously pumped in at a rate of 10 L / min.

[0060] Example 2

[0061] The coating material and the preparation method are the same as in Example 1, except that the composition of the alloy powder is different. In the alloy powder used in Example 3, the mass fraction of each element is 26.7wt.% Ni, 0.8wt.% Al, 0.20wt.% Fe, 1.0wt.% Mn, and the balance is Cu.

[0062] Example 3

[0063] The coating material and the preparation method are the same as in Example 1, except that the laser process parameters used are as follows: laser power 1400 W, and scanning speed 8 mm / s.

[0064] Comparative Example 1

[0065] The coating material and the preparation method are the same as those of Example 1, except that the powder feeding amount of the WC powder is 0 g / min, i.e. no WC ceramic powder is added to the molten pool.

[0066] Comparative Example 2

[0067] The coating material and the preparation method are the same as those of Example 1, except that the tungsten carbide ceramic powder is not added to the powder feeder, but is mixed uniformly with the alloy powder in a ball mill and then coated on the surface of the substrate with a thickness of 0.8 mm, wherein the mass fraction of the tungsten carbide ceramic powder is 35 wt.%.

[0068] Comparative Example 3

[0069] The coating material and the preparation method are the same as those of Example 1, except that the alloy powder is not coated on the surface of the substrate, but is added to the powder feeder together with the tungsten carbide ceramic powder, and the powder feeding amount is 10 g / min.

[0070] A metallographic sample perpendicular to the scanning direction is cut by a wire cutting machine, and the surface is smoothed and scratch-free through a standard grinding and polishing process, and chemical etching is performed using FeCl3 solution. The microstructure morphology of the coating cross-section is observed using a ZEISS EVO18 scanning electron microscope (SEM), and the composition is analyzed using a Nano Xflash Detector 5010 energy-dispersive spectrometer (EDS). The existing phases in the coating are identified using a D / max-Ultima IV X-ray diffractometer (XRD), wherein Cu-Ka rays are selected for scanning in the range of 20°-100°, the working voltage and current are 40 kV and 40 mA respectively, and the scanning speed is 10° / min.

[0071] The microhardness of the coating is tested using an HMV-2T Vickers microhardness tester, and the microhardness is measured from the surface layer to the substrate in the coating cross-section, and the average value is obtained by selecting three points at the same horizontal position, and the load is set to 200 g and the load time is 15 s. Before testing the wear resistance of the coating, the unmelted particles and oxides on the surface of the sample are removed using a metallographic sandpaper, and the sample is polished to be smooth and flat, and the test surface is kept with similar surface roughness. Then, a HT-1000 ball-on-disc friction and wear tester is used to perform dry friction and wear test at room temperature, and a Si3N4 steel ball with a diameter of 7 mm and a hardness of 2200 HV is used as the counter material. The load is set to 60 N, the rotation speed is 200 rpm, and the wear time is 60 min. The three-dimensional morphology of the wear track is observed and measured using a VK-X1000 laser confocal microscope.

[0072] Before corrosion resistance test, the electrochemical sample (size Φ14mmx6mm) was cut by wire cutting machine, and the coating surface was polished to smooth and then polished to no obvious scratch. CHI760E electrochemical workstation was used for test and data analysis, and three electrode system was used, in which saturated calomel electrode was used as reference electrode, platinum electrode was used as auxiliary electrode, and sample coating surface was used as working electrode. Before polarization curve test, the sample was placed in 3.5wt.% NaCl solution for OCP test for 30 min to stabilize the sample. The scan potential range e±0.5V was selected, and the scan speed was 0.001V / s. The potentiodynamic polarization curve test was carried out, and the Tafel curve fitting was carried out on the measured data by electrochemical software to obtain the corrosion potential (Ecorr) and the corrosion current (Icorr). When the alternating current impedance was tested, the alternating current amplitude was 10mV, and the frequency range was 0.01Hz-105Hz.

[0073] Figure 1 The overall morphology of the surface alloying layer of the sample of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 is shown in Figure 1. The surface of the coating of 1# sample obtained without adding WC ceramic powder in Comparative Example 1 is bright and smooth. The surface of the coating of 2# sample obtained by mixing alloy powder and WC ceramic powder and then powder laying and laser alloying in Comparative Example 2 is rough, with many pores and particle protrusions. The surface of the coating of 3# sample obtained by synchronously feeding alloy powder and WC ceramic powder and then laser alloying in Comparative Example 3 is poor in flatness, with many pores and cracking tendency. The surface of the coating of 4# sample obtained by powder laying of alloy powder and synchronously feeding WC ceramic powder and then laser alloying in Example 1 is relatively smooth, without obvious defects, and has the best surface quality.

[0074] Figure 2 The cross-sectional morphology of the coating in Example 1 and Comparative Example 1 under optical microscope is shown in Figure 2. It can be seen that under the process of Example 1, the coating has uniform structure without obvious defects, and the spherical WC particles are dispersedly distributed in the alloying layer, and the coating thickness is about 1.5mm. The coating in Comparative Example 1 also has very uniform structure, only with a small amount of small pores which are not timely escaped. Figure 3 The cross-sectional morphology of the coating in Comparative Example 2 and Comparative Example 3 is shown in Figure 3. Compared with Figure 2 Compared with the coating prepared by powder laying and synchronously feeding powder, the surface quality of the coating prepared by this process is obviously decreased, with small cracks and obvious cracking phenomenon through the coating. In addition, although the content of added WC ceramic powder is as high as 35wt.%, the coating does not retain a large number of spherical particles, indicating that most of the WC particles are dissolved in the molten pool under this process condition, and it is difficult to retain.

[0075] Figure 4The SEM morphology of the coating cross-section of Example 1 and Comparative Example 1 is uniform and dense, without obvious defects such as cracks and pores, and the interface between the coating and the substrate presents good metallurgical bonding. The coating of Example 1 has a large number of spherical particles and fine dendritic precipitated phases uniformly distributed in the interior, and the overall quality of the coating is good. The coating thickness of Comparative Example 1 is about 1.22 mm, and the coating thickness of Example 1 is about 1.56 mm, which is because the absorption rate of WC particles to the laser beam is high, and the substrate surface absorbs more energy when the laser is coaxially injected into the WC particles, so the melting depth increases and the coating thickness becomes larger.

[0076] Figure 5 The phase analysis results of the coating surface of Example 1 and Comparative Example 1 show that no diffraction peaks of the substrate are detected on the surface, indicating that the surface of the sample has been completely covered by the alloying layer. The surface of the coating of Comparative Example 1 is composed of a single-phase FCC γ-(Fe, Ni, Cu) solid solution, while the surface of the coating of Example 1 also detects the diffraction peaks of WC and W2C. The alloy powder used in the test is a typical nickel-copper alloy, in which Ni and Cu can form a γ-(Ni, Cu) solid solution, but due to the simultaneous melting of a thin layer of the substrate surface and the alloying material during the laser alloying process, the base element Fe enters the coating. The crystal structure and atomic radius of Fe, Ni and Cu are very close at high temperature, so Fe will also be dissolved into the γ phase, finally forming a FCC γ-(Fe, Ni, Cu) solid solution. Since the WC used in the test is a cast WC, it is mainly composed of WC and W2C two phases, so the peak of W2C in the coating is also high.

[0077] Figure 6 The SEM morphologies of the typical microstructure of the upper, middle and bottom of the coating in Comparative Example 1 and Example 1, respectively, can be observed that the coating of Comparative Example 1 is composed of a single-phase solid solution, and the microstructure from the bottom to the top is plane crystal, columnar crystal, dendritic crystal and equiaxed crystal. At the bottom of the molten pool, due to the quenching when the molten metal contacts the low-temperature substrate, according to the solidification theory, the large temperature gradient and small solidification rate at the interface between the coating and the substrate form plane crystal organization and epitaxial growth, and the existence of plane crystal indicates that good metallurgical bonding has been formed between the coating and the substrate. As the solid-liquid interface continues to advance, the grains grow along the direction of the maximum temperature gradient, gradually changing to columnar crystals. With the continuous advancement of the solid-liquid interface, the ratio of temperature gradient to solidification rate decreases, and the columnar crystals gradually change to dendritic crystals or equiaxed crystals. The upper and middle of the coating of Example 1 are similar, both composed of a γ phase substrate, spherical WC particles that are not completely dissolved, and fine dendritic or blocky structures distributed at the edge. A small amount of fishbone-like structure is also observed around some WC particles at the bottom of the coating. The substrate near the molten pool is the heat-affected zone, and due to the rapid cooling of laser alloying, the substrate organization at the interface is quenched to form typical lath-shaped martensite organization.

[0078] Figure 7 For the dendritic structure and EDS scanning results in the middle of the coating of Comparative Example 1, the coating is composed of a γ-(Fe, Ni, Cu) single-phase solid solution, EDS point scanning is performed on the inside of the grain (point A, point B) and the grain boundary (point C), and the results are as shown in Figure 7 c-e. The compositions at the inside of the grain and the grain boundary are mainly composed of Fe, Ni, and Cu, and also contain a small amount of Mn element, but the content of Fe and Ni is higher in the inside of the grain, and slightly decreases at the grain boundary, while Cu and Mn are enriched at the grain boundary. EDS line scanning (line scanning 1) is performed on grain I, grain II, and the grain boundary thereof in the figure, respectively, for analysis, Figure 7 The results in b more clearly reflect the changes in the distribution of main elements at the inside of the grain and the grain boundary, indicating that the single-phase solid solution has undergone a certain degree of segregation during the solidification process. This is because, in the non-equilibrium solidification process of the laser molten pool, due to the extremely fast solidification speed, the diffusion is insufficient, and the compositions of the liquid and solid phases at each temperature deviate from the equilibrium state composition, resulting in that the melt rich in Fe, Ni and other high-melting-point elements is solidified first to form a dendritic structure, and the melt rich in Cu, Mn and other low-melting-point elements is solidified later to form intergranular structure.

[0079] Figure 8 For the micro-morphology and corresponding composition analysis of the coating of Example 1, as shown in Figure 8 a and b, the WC particles in the coating inside are dissolved and decarburized from the edge and extend outward to form an interface with a width of about 1-2 μm. In this region, Fe, Ni, Cu in the alloy melt and W, C generated by the dissolution of WC, and other elements diffuse with each other to form different forms of carbides and are brought into other regions of the molten pool due to convection. The existence of the interface on the one hand ensures the formation of good metallurgical bonding between the WC particles and the γ-phase alloy substrate, and on the other hand also prevents the WC particles from further dissolving, so that they can remain in the coating as much as possible to play the role of a reinforcing phase. EDS analysis is performed on different forms of carbides, i.e. dendritic, blocky, and fishbone-like structures, and the results are as shown in Figure 8 c-e. The dendritic and blocky structures both contain a large amount of W and C elements, and the content of other metal elements is extremely low. According to the XRD results, it is speculated that they are WC or W2C formed by diffusion reaction in the molten pool after the decomposition or partial dissolution of WC; and in the fishbone-like structure, a large amount of Fe element is detected in addition to W and C elements, and according to related literature, it is speculated that it may be Fe3W3C carbide produced by dissolution reaction.

[0080] The absorption rate of WC particles to laser is much higher than that of common metal materials. When laser is injected into WC, the surface of WC is heated to a high temperature by laser beam, and then the particles are dissolved in the edge area after contacting with the alloy melt. A part of the WC particles with small size directly dissolves by collapsing and is broken into small particles of carbide which remains in the molten pool. Another part of the WC particles experiences dissolution and decarburization. At this time, the metal elements such as Ni, Cu and Fe diffuse into the WC particles, and the W and C atoms generated by the decomposition of WC diffuse outward to form a transition layer of several microns around the edge of the WC particles. When the conditions of certain concentration gradient and supercooling degree are met, new carbides will grow in the form of dendrites or fish bones around the original WC particles as the nucleation core. In addition, under the convection effect caused by the surface tension of the molten pool, a part of the newly precipitated carbide particles will be brought into the molten pool and exist independently or be dissolved and then re-solidified.

[0081] Figure 9 a is the microhardness distribution curve of the cross section of the coating of Comparative Example 1 and the coating of Example 1, and the average microhardness of the two is 244.73HV 0.2 and 355.27HV 0.2 , respectively, which is 1.4 times and 2.1 times the hardness of the substrate (172HV 0.2 ). It can be known from the microstructure analysis that the coating of Comparative Example 1 is a single-phase solid solution structure, and the hardness mainly depends on the solid solution strengthening, and the hardness is only slightly improved compared with the substrate. For the coating of Example 1, the high-hardness WC plays a role in bearing and transferring load in the coating, and the dendritic or fishbone-shaped WC, W2C, Fe3W3C and other carbides precipitated after the dissolution of WC particles are dispersedly distributed in the coating. The existence of these high-hardness second phases significantly improves the overall microhardness of the coating. Figure 9 b is the friction coefficient curve of the substrate and the coating. The friction curves of the substrate and the two coatings all experience a running-in stage and a stable wear stage: in the running-in stage, the friction contact surface is relatively smooth, at this time the contact mode between the coating and the friction pair is point contact, the contact stress is large, which leads to the rapid increase of the friction coefficient; then it gradually enters the stable wear stage, the contact mode between the grinding ball and the coating surface changes from point contact to surface contact, the contact area becomes larger, and the contact stress of the grinding ball decreases, thereby generating a stable friction coefficient. The friction coefficient of the coating of Comparative Example 1 is slightly lower than that of the substrate and has smaller fluctuations, and the friction coefficients of the two in the stable stage are 0.56 and 0.62, respectively. The friction coefficient of the coating of Example 1 is significantly reduced, which is only about 0.43. After adding WC, the remaining WC particles and the new phases of carbides precipitated after dissolution all play a significant dispersion strengthening effect, which hinders the indentation of the grinding ball and reduces the friction resistance, so the coating of Example 1 exhibits a lower friction coefficient.

[0082] Figure 10The wear volume of the substrate, the coating of Comparative Example 1 and the coating of Example 1 was 1.81 x 10 9 μm 3 , 1.06 x 10 9 μm 3 and 2.64 x 10 8 μm 3 , respectively, and the wear rate of the three materials was 99.88 μm 3 · N -1 · mm -1 , 58.45 μm 3 · N -1 · mm -1 and 14.59 μm 3 · N -1 · mm -1 , respectively. After laser alloying, the wear rate of the coating of Comparative Example 1 and the coating of Example 1 was reduced by 41.48% and 85.39% compared to the substrate, and the wear resistance was significantly improved, and the wear resistance of the coating of Example 1 was the best.

[0083] The electrochemical polarization curves of the substrate, the coating of Comparative Example 1 and the coating of Example 1 are shown in Figure 11 a. The self-corrosion potential of the coating of Comparative Example 1 and the coating of Example 1 was obviously shifted positively compared to the substrate, indicating that the corrosion resistance of the coating was better than that of the substrate. Although the self-corrosion potential of the coating was slightly reduced after adding WC particles, it was still significantly higher than that of the substrate. The electrochemical corrosion kinetic parameters of the coating and the substrate were calculated by Tafel extrapolation method and are shown in Table 2. Generally, the corrosion current density and the polarization resistance are used to evaluate the corrosion resistance. It can be seen that the corrosion current density of the coating of Comparative Example 1 and the coating of Example 1 was 5.19 x 10 -8 A / cm 2 and 6.00 x 10 -8 A / cm 2 , respectively, which was much smaller than the corrosion current density of the substrate 1.62 x 10 -5 A / cm 2 ; the polarization resistance of the coating of Comparative Example 1, the coating of Example 1 and the substrate was 851688.8 Ω, 761744.9 Ω and 2150 Ω, respectively. Therefore, the corrosion resistance of the coating of Comparative Example 1 was the best, and the addition of WC slightly reduced the corrosion resistance of the coating of Example 1, but it was still significantly better than that of the substrate.

[0084] The impedance spectrum amplitude spectrum of the substrate, the coating of Comparative Example 1 and the coating of Example 1 is shown in Figure 11 b. The impedance value of the coating of Comparative Example 1 in the low frequency region (0.01 Hz) was about 6.22 x 10 5 Ω·cm 2, the impedance value of the coating of Example 1 is about 4.68 x 10 5 Ω·cm 2 , and the impedance value of the substrate is about 900 Ω·cm 2 By comparison, it can be seen that the coating of Comparative Example 1 and the coating prepared by laser alloying in Example 1 have excellent corrosion resistance, which is consistent with the conclusion obtained from the electrochemical polarization curve.

[0085] From the above microstructure analysis, it can be seen that the coating of Comparative Example 1 is composed of a single-phase γ-(Fe, Ni, Cu) solid solution, and the microstructure is dense and the grain size is small. Compared with the carbon steel substrate, the Ni element and Cu element in the coating of Comparative Example 1 play an important role in corrosion resistance. In the initial stage of corrosion, the coating dissolves to form a passivation film, and the surface of the coating is covered with an oxide film composed of Ni(OH) 2 , Cu 2 O and the like. With the continuous progress of the corrosion process, oxides are continuously formed, and the oxide film becomes more continuous and dense, isolating the coating from the corrosive medium, reducing the corrosion channel, and better inhibiting the corrosion process. At the same time, insoluble corrosion products are deposited on the surface of the coating, weakening the micro-electrode corrosion effect and reducing the local difference in corrosion current. In this stage, more protective films are gradually formed, reducing the corrosion rate of the coating. After adding WC particles, the corrosion resistance of the coating decreases slightly, which may be due to the decrease in the content of the corrosion-resistant γ-(Fe, Ni, Cu) phase after adding WC particles, and the formation of a galvanic cell between the electrically conductive WC and the γ phase, increasing the micro-interface and the corrosion channel in the coating, resulting in a slight decrease in the overall corrosion resistance of the coating. However, overall, the corrosion resistance of the laser alloying coating is still much higher than that of the substrate.

[0086] Table 2 Corrosion parameters of Comparative Example 1, Example 1 and the substrate after electrochemical testing

[0087] Test sample Corrosion potential (V) Corrosion current density (A / cm 2 ) Polarization resistance (Ω) Comparative Example 1 0.524 5.19 x 10 -8 ]] 851688.8 Example 1 0.558 6.00 x 10 -8 ]] 761744.9 Substrate 0.924 1.62 x 10 -5 ]] 2150.0

[0088] Figure 12 、 Figure 13 The overall morphology of the coatings of Example 2 and Example 3, respectively, is shown in Figures 2 and 3. The interface between the coating and the substrate prepared under the alloying composition and laser process parameters also exhibits good metallurgical bonding characteristics, and the coating has a dense microstructure without cracks, pores and other defects. It can be seen that spherical WC particles are dispersed in the coating. The average microhardness of the coating of Example 2 is about 326.86 HV 0.2 , which is about 1.9 times higher than the hardness of the substrate, and the wear volume under the same conditions is 7.24 x 10 8 μm 3 , and the wear rate is 39.96 μm 3 ·N -1 ·mm -1The average microhardness of the coating of Example 3 is about 291.43 HV 0.2 , which is about 17 times higher than the hardness of the substrate, and the wear volume under the same conditions is 9.33 x 10 8 μm 3 , and the wear rate is 51.49 μm 3 ·N -1 ·mm -1 The wear resistance of the coatings of Example 2 and Example 3 is greatly improved. Figure 14 The electrochemical test results of the substrate, Comparative Example 2, and Example 2 show that the corrosion resistance of the coatings prepared by laser alloying in Example 2 and Example 3 is greatly improved compared with the substrate.

[0089] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the foregoing embodiments of the present application have been described in detail, those skilled in the art will still be able to modify the technical solutions described in the foregoing embodiments or make equivalent replacements of some parts without the need for creative labor. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. Although the specific embodiments of the present application have been described above, the description is not intended to limit the protection scope of the present application, and those skilled in the art should understand that various modifications or changes made to the technical solutions of the present application without the need for creative labor are still within the protection scope of the present application.

Claims

1. A method for preparing a wear-resistant and corrosion-resistant coating on the surface of electrical connection fittings, characterized in that, include: Step 1: Grind the base material surface of the power connection hardware to remove oxide scale and clean it thoroughly, then isolate it from air for later use. Step 2, drying pretreatment of alloy powder and ceramic powder, wherein the alloy powder contains three elements: Fe, Ni and Cu; Step 3: Use a clamp to evenly spread the alloy powder on the surface of the substrate, and add the ceramic powder into the powder feeder; Step 4: Place the substrate in a protective atmosphere chamber filled with argon gas and continuously circulate the protective gas. Step 5: Set the laser parameters and powder feeder parameters, turn on the powder feeder and laser switch in sequence. After the laser irradiates the molten pool, the alloy powder pre-placed on the substrate surface is completely melted to form a molten pool. Simultaneously inject ceramic powder into the molten pool through the powder feeder to perform laser alloying processing on the substrate surface and prepare a wear-resistant and corrosion-resistant coating. In step 1, the base material of the power connection fitting is low-carbon steel or alloy steel; In step 2, the alloy powder contains 25-60 wt.% Ni, 0-10 wt.% Al, 0-5 wt.% Mn, and 0.5-5 wt.% Fe, with the balance being Cu. The ceramic powder is tungsten carbide ceramic powder. In step 5, the laser power is 1200~1800W and the scanning speed is 6~8mm / s.

2. The preparation method according to claim 1, characterized in that, In step 2, the alloy powder has a particle size of 15-60 μm, and the ceramic powder has a particle size of 30-100 μm.

3. The preparation method according to claim 2, characterized in that, In step 2, the alloy powder contains the following elements in mass percentage: 50-60 wt.% Ni, 3-5 wt.% Al, 0.2-1 wt.% Mn, 0.5-1 wt.% Fe, with the balance being Cu. The particle size of the alloy powder is 15-50 μm.

4. The preparation method according to claim 1, characterized in that, In step 3, the thickness of the alloy powder is 0.5~1.0 mm.

5. The preparation method according to claim 1, characterized in that, In step 4, the protective gas is argon with a purity of 99.9% or higher, and the flow rate of the protective gas is 4~15L / min.

6. The preparation method according to claim 1, characterized in that, In step 3, the thickness of the alloy powder is 0.8 mm; in step 4, the flow rate of the protective gas is 10 L / min.

7. The preparation method according to claim 1, characterized in that, In step 5, the spot diameter is 2-6 mm, the overlap rate of the multi-coating layer is 20%-50%, and the powder feeding rate of ceramic powder is 5-15 g / min.

8. The preparation method according to claim 7, characterized in that, In step 5, the spot diameter is 4-5 mm, the overlap rate of the multi-coating layer is 30%-40%, and the powder feeding rate of ceramic powder is 8-12 g / min.

9. A wear-resistant and corrosion-resistant coating on the surface of electrical connection fittings, characterized in that, It is a wear-resistant and corrosion-resistant coating prepared by the method described in any one of claims 1-8.

Images