High-entropy alloy coating, preparation method thereof and high-pressure plunger

Abstract

The invention discloses a high-entropy alloy coating, a preparation method thereof and a high-pressure plunger, and belongs to the technical field of coatings. The high-entropy alloy coating comprises the following raw materials in parts by mass: 2 to 2.3 parts of Co powder, 1.8 to 2.1 parts of Cr powder, 1.9 to 2.2 parts of Fe powder, 2 to 2.3 parts of Ni powder, 1 to 1.2 parts of Nb powder and 1 part of Al powder. The preparation method comprises the steps that after Co powder, Cr powder, Fe powder, Ni powder, Nb powder and Al powder are mixed according to the set mass ratio, a laser-ultrahigh frequency induction composite deposition forming method is adopted, the mixture is deposited on a base body in an inert atmosphere, and the high-entropy alloy coating is obtained. And excellent wear resistance and corrosion resistance are achieved. The high-entropy alloy coating is arranged on the contact surface of the high-pressure plunger and the inner wall of the pump body, and synergistic interaction of multiple properties such as wear resistance and corrosion resistance of the coating on the surface of equipment parts is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and particularly relates to a high-entropy alloy coating, a preparation method thereof, and a high-pressure plunger. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] A high-pressure plunger pump, also known as a positive displacement pump, is a hydraulic device that relies on the reciprocating motion of an internal high-pressure plunger in a cylinder block to change the volume of the cylinder block to achieve fluid suction and discharge. During the working process, the high-pressure plunger undergoes high-speed reciprocating friction with the inner surface of the pump body. Due to reasons such as eccentric wear and sealing form, it is extremely prone to wear. Coupled with the surface failure problem caused by the corrosion of the fluid medium, the operating efficiency and lifespan of the entire system are greatly reduced. At present, the performance of surface protection coatings with conventional alloy compositions is difficult to meet the service requirements of the surface of high-pressure plungers under complex working conditions.

[0004] Due to the "cocktail effect" generated by the combination of multiple elements, high-entropy alloys exhibit more excellent mechanical properties, corrosion resistance, and high-temperature oxidation resistance compared to conventional alloys. The reasonable combination of multiple elements can optimize the wear resistance and corrosion resistance of high-entropy alloy coatings. Among many high-entropy alloy systems, CoCrFeNi-based high-entropy alloys are prone to form a uniform single solid solution due to the similar atomic radii and electronegativities of their constituent elements, and have a greater regulation space in performance compared to conventional alloys. Summary of the Invention

[0005] Based on the current technical status, the purpose of the present invention is to provide a high-entropy alloy coating, a preparation method thereof, and a high-pressure plunger. The prepared high-entropy alloy coating has high hardness and high wear and corrosion resistance. When it is prepared on the surface of a high-pressure plunger, it can effectively improve the operating efficiency and lifespan of the system.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] In the first aspect, a high-entropy alloy coating includes the following raw materials in parts by weight: 2 - 2.3 parts of Co powder, 1.8 - 2.1 parts of Cr powder, 1.9 - 2.2 parts of Fe powder, 2 - 2.3 parts of Ni powder, 1 - 1.2 parts of Nb powder, and 1 part of Al powder.

[0008] In the second aspect, a preparation method of the above high-entropy alloy coating includes:

[0009] After mixing Co powder, Cr powder, Fe powder, Ni powder, Nb powder and Al powder in a set mass ratio, they are deposited on a substrate by a laser-ultra-high frequency induction composite deposition forming method under an inert atmosphere to obtain the high-entropy alloy coating.

[0010] In a third aspect, a high-pressure plunger has the above-mentioned high-entropy alloy coating provided on the contact surface with the inner wall of the pump body.

[0011] The beneficial effects of the present invention are as follows:

[0012] 1. Based on the CoCrFeNi-based high-entropy alloy, the present invention adds a set amount of Nb and Al elements to obtain a surface protection coating with excellent wear resistance and corrosion resistance. The solidification microstructure of the coating is mainly composed of columnar crystals and irregular equiaxed crystals. As the current density increases, due to the decrease in the temperature gradient during the cooling process of the molten pool, the irregular equiaxed crystals gradually become regular equiaxed crystals, and the area of the columnar dendrite region decreases, and the tissue distribution of the deposited coating is uniform and dense. The hardness of the coating is 300 - 750 HV, the friction coefficient is about 0.39, and the self-corrosion current density is at least 1.28×10 -4 A·cm -2 , which is greatly improved compared with the 45# steel substrate or other coatings.

[0013] 2. The present invention uses the laser-ultra-high frequency induction composite deposition technology to prepare the CoCrFeNiNb 0.3 Al high-entropy alloy coating. Due to the different melting points, densities, and diffusion rates of each element, it is easy to produce composition inhomogeneity or local segregation in the molten pool. However, the ultra-high frequency induction heat source can provide additional heat, extend the retention time of the molten pool, increase the element diffusion rate, and reduce the segregation phenomenon. By controlling the power of the ultra-high frequency induction heat source, the temperature of the molten pool is made more uniform, and the composition fluctuation is reduced. Therefore, by adjusting the current density of the ultra-high frequency induction heat source, the surface defects of the coating can be effectively suppressed, the generation of internal precipitates can be reduced, and further the coating density can be improved to obtain a coating material with ideal performance.

[0014] 3. The present invention prepares the CoCrFeNiNb 0.3 Al high-entropy alloy coating on the surface of a 45# steel substrate by the laser-ultra-high frequency induction composite deposition technology, which is of great significance for extending the service life of core friction pair components such as high-pressure plungers and ensuring the long-term safe operation of high-pressure plunger pumps. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0016] The distances or dimensions between parts in the figure are exaggerated for showing the positions of various parts, and the schematic diagram is only for illustration purposes.

[0017] Figure 1 They are scanning electron microscope pictures of the specimens prepared in each example and comparative example.

[0018] Figure 2 They are graphs of the microhardness measurement results of the specimens prepared in each example and comparative example.

[0019] Figure 3 They are graphs of the friction and wear test results of the specimens prepared in each example and comparative example.

[0020] Figure 4 They are potentiodynamic polarization curves of the specimens prepared in each example and comparative example.

[0021] Figure 5 It is a graph of the detection result of the internal cracking state of the specimen prepared in Example 5. Detailed Description of the Invention

[0022] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0023] It should be noted that the terms used herein are only for describing the specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] A high-entropy alloy coating, comprising the following raw materials in parts by weight: 2 - 2.3 parts of Co powder, 1.8 - 2.1 parts of Cr powder, 1.9 - 2.2 parts of Fe powder, 2 - 2.3 parts of Ni powder, 1 - 1.2 parts of Nb powder, and 1 part of Al powder.

[0025] Based on the CoCrFeNi-based high-entropy alloy for the coating composition, a set amount of Nb and Al elements are added. Among them, the solid solution strengthening of Nb and the precipitation strengthening of the Laves phase can ensure that the HEA exhibits better hardness and corrosion resistance. The role of the Al element is to promote the formation of a wear-resistant oxide glaze layer. The two work together to obtain a surface protective coating with excellent wear resistance and corrosion resistance.

[0026] Optionally, in the high-entropy alloy coating, the molar ratio of Co, Cr, Fe, Ni, Nb, and Al elements is 1:1:1:1:0.3:1, and the high-entropy alloy coating can be expressed as CoCrFeNiNb 0.3 Al coating. At this time, the high-entropy alloy coating has relatively high comprehensive performance.

[0027] Optionally, the particle sizes of the Co powder, Cr powder, Fe powder, Ni powder, Nb powder, and Al powder are 45-106 μm, which can be used in combination with the laser-ultra-high frequency induction composite deposition forming method to obtain a coating with a dense structure.

[0028] Optionally, the thickness of the high-entropy alloy coating is 0.4-4.0 mm.

[0029] In the second aspect, the preparation method of the above high-entropy alloy coating includes:

[0030] After mixing Co powder, Cr powder, Fe powder, Ni powder, Nb powder, and Al powder in a set mass ratio, use the laser-ultra-high frequency induction composite deposition forming method to deposit them on the substrate in an inert atmosphere to obtain the high-entropy alloy coating.

[0031] Since the laser-ultra-high frequency induction composite deposition forming method can combine a high-energy density laser beam with an induction heat source, reduce the temperature gradient, increase the effectiveness of the laser heat source, thereby improving the powder deposition rate and reducing problems such as cracking and porosity; the high-entropy alloy is composed of multiple main elements (usually ≥5 kinds), and the melting points, densities, and diffusion rates of each element are different, and it is easy to form a state of uneven composition or local segregation in the molten pool; however, the ultra-high frequency induction heat source can provide additional heat, extend the retention time of the molten pool, increase the element diffusion rate, and reduce the segregation phenomenon; and by controlling the power of the ultra-high frequency induction heat source, the temperature of the molten pool is made more uniform, reducing composition fluctuations, so as to obtain a coating with uniform composition and stable performance.

[0032] Optionally, in the laser-ultra-high frequency induction composite deposition forming method, the laser power is 1000-1400 W, the frequency of the ultra-high frequency induction heating current is 750-1150 kHz, and the current density of the ultra-high frequency induction heat source is 0.50-2.00×10 8 A / m 2 .

[0033] Optionally, after mixing the raw material powders, dry them at 110-120 °C for 2-3 h before deposition to reduce cracking and porosity.

[0034] Optionally, the inert atmosphere can be argon, helium, or an argon-helium mixed gas.

[0035] Optionally, the substrate is one or more of 45# steel, 316L stainless steel, or Inconel alloy.

[0036] Optionally, the moving speed of the substrate is 2 - 6 mm / s, the powder feeding rate is 10 - 13 g / min, and the thickness of the coating formed by one-time deposition is about 0.4 - 1.2 mm, so as to avoid quality problems caused by the temperature gradient between the inner and outer layers due to excessive thickness during one-time deposition.

[0037] Optionally, the number of deposition times is 1 - 5 times to obtain a coating with a set thickness.

[0038] Optionally, after deposition, it is air-cooled to room temperature.

[0039] In a third aspect, a high-pressure plunger has the above-mentioned high-entropy alloy coating provided on the contact surface with the inner wall of the pump body.

[0040] Optionally, the thickness of the high-entropy alloy coating is 0.4 - 4.0 mm, forming a structure with a hard outer layer and a tough inner layer with the high-pressure plunger substrate to reduce friction. The chemical properties of the coating and fewer surface defects can effectively inhibit the damage of corrosive media to the coating, so as to achieve the synergistic effect of multiple properties such as wear resistance and corrosion resistance on the surface coating of equipment parts.

[0041] Example 1

[0042] A CoCrFeNiNb 0.3 Al high-entropy alloy coating, the preparation raw materials include Co, Cr, Fe, Ni, Al and Nb powders. Each metal powder is a pure metal powder with a purity greater than 99.5 wt.%, and the shape is spherical powder with a particle size range of 45 - 106 μm.

[0043] In the preparation method of this example, the device provided by the Chinese patent "A Laser-Ultrahigh Frequency Induction Composite Deposition Forming Method and Device" with the application number 2022109038333 is used for laser-ultrahigh frequency induction composite deposition forming, including the following steps:

[0044] Select 45# steel as the substrate, polish the surface of the substrate with SiC sandpaper (#400), and clean it with anhydrous ethanol to remove oxides and other contaminants, and then install it on the moving platform.

[0045] Weigh the raw material powders in a molar ratio of 1:1:1:1:0.3:1, mix them evenly and dry them at 120 degrees Celsius, and then pour the dried raw material powders into the powder feeder.

[0046] Deposit under the protection of an inert gas (argon). During the deposition process, the laser power is 1200 W, the current frequency of the ultrahigh frequency induction heat source is 850 kHz, and the current density of the ultrahigh frequency induction heat source is 1.01×10 8 A / m 2, the moving speed of the metal substrate is 3 mm / s, and the powder feeding rate is 12 g / min. During the deposition process, the raw material powder is ejected from the laser deposition head and passes through the induction coil to reach the surface of the metal substrate. Synchronously, an alternating current is passed through the induction coil to heat the position of the deposition strengthening coating on the surface of the metal substrate and perform electromagnetic stirring on the liquid metal in the molten pool.

[0047] After one pass of cladding, it is air-cooled to room temperature to obtain a coating with a thickness of 1.2 mm, that is, a CoCrFeNiNb 0.3 Al high-entropy alloy coating, numbered U1, with a corresponding current density of 1.01×10 8 A / m 2 .

[0048] Example 2

[0049] A CoCrFeNiNb 0.3 Al high-entropy alloy coating, different from Example 1 in that the current density is increased to 1.14×10 8 A / m 2 , and the requirements for other raw materials and the process method are the same as those in Example 1, and the obtained coating is numbered U2.

[0050] Example 3

[0051] A CoCrFeNiNb 0.3 Al high-entropy alloy coating, different from Example 1 in that the current density is increased to 1.27×10 8 A / m 2 , and the requirements for other raw materials and the process method are the same as those in Example 1, and the obtained coating is numbered U3.

[0052] Comparative example

[0053] A CoCrFeNiNb 0.3 Al high-entropy alloy coating, different from Examples 1-3 in that: the current density is reduced to 0, that is, no ultra-high frequency induction heat source is applied, and only the laser cladding technology is used to prepare the coating. The requirements for other raw materials and the process method are the same as those in Example 1, and the sample number of the obtained coating is U0.

[0054] Performance detection

[0055] Samples of 15×10×10 mm are cut from the samples obtained in Example 1, Example 2, Example 3 and the comparative example by wire cutting. The cross-section of the coating is polished successively with 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1200-mesh, 1500-mesh and 2000-mesh sandpapers to remove the surface oil stain and oxide skin, and finally polished to a mirror surface with a metallographic polishing solution; the polished CoCrFeNiNb 0.3 Al high-entropy alloy coating is observed using a scanning electron microscope.

[0056] Observe the polished CoCrFeNiNb 0.3 Al high-entropy alloy coating by scanning electron microscope, take the Top position from the area near the surface of the coating, take the Bottom position from the area near the substrate of the coating, and take the Middle position from the area between the two, and further magnify to observe the microstructure. The results are as Figure 1 shown: Among them, (a1) is the Top position of the specimen U0 without coating in the comparative example, (a2) is the Middle position of the specimen U0 without coating in the comparative example, and (a1) is the Bottom position of the specimen U0 without coating in the comparative example; correspondingly, (b1), (b2) and (b3) are the microstructures at each position in the U1 coating of Example 1, (c1), (c2) and (c3) are the microstructures at each position in the U2 coating of Example 2, and (d1), (d2) and (d3) are the microstructures at each position in the U3 coating of Example 3.

[0057] It can be seen that: for the sample U0 prepared by laser cladding technology, the bottom region is mainly columnar crystals, with a small amount of irregular equiaxed crystals; the middle and top regions are mainly irregular equiaxed crystals, accompanied by a small amount of unbroken columnar crystals; as the current density increases, the irregular equiaxed crystals gradually become regular equiaxed crystals, the grain boundaries become narrower, the microstructure of the alloy changes, and the grain size shows a growing trend compared with U0, especially in the bottom region, where the grain growth is more obvious due to heat retention, showing an obvious columnar or coarsening trend.

[0058] Use a hardness tester to measure the cross-sectional hardness of the polished CoCrFeNiNb 0.3 Al high-entropy alloy coating. The test results are as Figure 2 shown. It can be seen that: the hardness of the prepared CoCrFeNiNb 0.3 Al high-entropy alloy coating is significantly higher than that of the 45# steel substrate (U0), and the highest hardness of the prepared high-entropy alloy coating can reach 750HV.

[0059] Conduct friction and wear tests on the prepared high-entropy alloy coating. The results are as Figure 3 shown. It can be seen that the friction coefficient of the prepared CoCrFeNiNb 0.3 Al high-entropy alloy coating is significantly reduced. Compared with the U0 specimen with a friction coefficient of 0.47, the friction coefficients of U1, U2 and U3 are relatively close, at 0.39.

[0060] Conduct electrochemical tests on the prepared high-entropy alloy coating. The potentiodynamic polarization curve is as Figure 4As shown, the polarization curves of the deposited coatings with different current intensities in 3.5 wt% NaCl solution at room temperature are presented. The corrosion potential of the deposited layer prepared without the assistance of ultra-high frequency induction heat source is -0.698 V. Compared with the three groups of deposited coatings prepared under the assistance of ultra-high frequency induction heat source, this corrosion potential is significantly higher than that of the coating prepared by pure laser cladding. At a current density of 1.14×10 8 A / m 2 , the corrosion current density is 1.28×10 -4 A·cm -2 , which is significantly lower than that of the U0 specimen (9.12×10 -4 A·cm -2 ). Meanwhile, at other current density parameters, the corrosion current density of the specimens is significantly lower than that of the U0 specimen. It can be observed from the polarization curves that there is a region with a small change in current density and a rapid increase in voltage for each coating, and this region is the passivation region of the polarization curve, indicating that a passivation film is formed on the material surface. The presence of the passivation film can effectively prevent the further erosion of the corrosion medium on the material. However, due to the small radius and strong penetration ability of Cl- ions, they are easily adsorbed on the material surface and react with the passivation film, resulting in the destruction of the local passivation film, thus inducing pitting corrosion. This process is manifested as a rapid increase in current density on the polarization curve, while the voltage changes little or even tends to be stable, and the potential at this time is the breakdown potential of the material. The higher the breakdown potential, the stronger the pitting corrosion resistance of the material, which also means better corrosion resistance. The breakdown potential of the pure laser cladding deposited coating is -0.109 V, while for the coatings prepared under the assistance of ultra-high frequency induction heat source, their breakdown potentials are all higher than that of the U0 specimen, indicating that the pitting corrosion resistance of these three groups of specimens is better than that of the U0 specimen. The electrochemical corrosion data are shown in Table 1, and it can be seen that: the self-corrosion current density of the CoCrFeNiNb 0.3 Al high-entropy alloy coating is slower than the corrosion rate of the U0 specimen. Especially for the U2 specimen, the self-corrosion current is 1.28×10 -4 A·cm -2 , and it has good corrosion resistance.

[0061] Table 1

[0062] specimen <![CDATA[Current density (A / m 2 )]]> <![CDATA[E corr (V)]]> <![CDATA[I corr (A·cm -2 )]]> <![CDATA[E b (V)]]> U0 Without UHF -0.698 <![CDATA[9.12×10 -4 > -0.109 U1 <![CDATA[1.01×10 8 > -0.379 <![CDATA[2.02×10 -4 > 0.167 U2 <![CDATA[1.14×10 8 > -0.369 <![CDATA[1.28×10 -4 > 0.215 U3 <![CDATA[1.27×10 8 > -0.409 <![CDATA[2.56×10 -4 > 0.226

[0063] Example 4

[0064] A high-pressure plunger, with 45# steel as the substrate, adopts the preparation method of Example 2 to prepare a coating on the contact surface with the inner wall of the pump body, so that the coating properties are the same as those of the U2 coating.

[0065] Example 5

[0066] A CoCrFeNiNb 0.3The Al high-entropy alloy coating, different from those in Examples 1, 2, 3 and the comparative examples, is air-cooled to room temperature after multi-pass and multi-layer cladding (4 passes and 3 layers). The other raw material requirements and process methods are the same as those in Example 1. From Figure 5 It can be seen that obvious cracks exist in the U0 specimen with pure laser cladding, while there are no obvious defects such as cracks and pores in the U1-U3 specimens obtained by composite deposition.

[0067] Compared with conventional alloys, when the laser-ultra-high frequency induction heat source composite deposition technology is applied to high-entropy alloy powders, it mainly faces challenges such as element segregation, high powder cost, crack / pore defects, and interface bonding problems in the early stage. In this application, the CoCrFeNiNb 0.3 Al alloy system can be adapted to the laser-ultra-high frequency induction heat source composite deposition technology. By reasonably optimizing process parameters and material design, the laser-ultra-high frequency induction heat source composite deposition technology can give full play to the advantages of high-entropy alloys, enabling them to be more widely used in fields such as high-temperature wear resistance and marine corrosion resistance.

[0068] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A high entropy alloy coating, characterized in that: The invention comprises the following raw materials in parts by weight: 2 to 2.3 parts of Co powder, 1.8 to 2.1 parts of Cr powder, 1.9 to 2.2 parts of Fe powder, 2 to 2.3 parts of Ni powder, 1 to 1.2 parts of Nb powder and 1 part of Al powder.

2. The high entropy alloy coating according to claim 1, characterized in that In the high entropy alloy coating, the molar ratio of Co, Cr, Fe, Ni, Nb and Al elements is 1:1:1:1:0.3:

1.

3. The high entropy alloy coating according to claim 1, characterized in that: The particle size of the Co powder, Cr powder, Fe powder, Ni powder, Nb powder and Al powder is 45-106 μm.

4. A method for preparing a high entropy alloy coating as claimed in any one of claims 1 to 3, characterized in that: After Co powder, Cr powder, Fe powder, Ni powder, Nb powder and Al powder with a set mass ratio are mixed, they are deposited on a substrate in an inert atmosphere using a laser-ultra-high frequency induction composite deposition forming method to obtain the high entropy alloy coating.

5. The method for preparing a high entropy alloy coating according to claim 4, characterized in that: In the laser-ultra-high frequency induction composite deposition forming method, the laser power is 1100-1300W, the ultra-high frequency induction heating current frequency is 750-1150kHz, and the ultra-high frequency induction heating power is 1.5-4.5kW.

6. The method for preparing a high entropy alloy coating according to claim 4, characterized in that: The raw material powders are mixed and dried at 110-120°C for 2-3 hours before deposition; Alternatively, the inert atmosphere may be argon, helium or an argon-helium mixed gas.

7. The method for preparing a high entropy alloy coating according to claim 4, characterized in that: The substrate moving speed is 1-5 mm / s, and the powder feeding rate is 10-13 g / min; Alternatively, the number of depositions is 1 to 5 times.

8. The method for preparing a high entropy alloy coating according to claim 4, characterized in that: After deposition, the solution was air-cooled to room temperature.

9. A high pressure plunger, characterized in that: The contact surface with the inner wall of the pump body is provided with a high entropy alloy coating as described in any one of claims 1-3.

10. The high pressure plunger according to claim 9, characterized in that: The thickness of the high entropy alloy coating is 0.8-1.2 mm.

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