Rare earth doped high-entropy alloy resistant to chloride ion corrosion and preparation method of rare earth doped high-entropy alloy

Abstract

The invention provides a chloride ion corrosion resistant rare earth doped high-entropy alloy coating and a preparation method thereof, the chemical formula of a rare earth high-entropy alloy is CoCrFeNiMoSi-xLa2O3, and X is more than or equal to 0.1% and less than or equal to 3%. The invention aims to solve the problem that the existing high-entropy alloy is poor in forming and has more pores and impurities, so that the corrosion resistance of the alloy is restricted. By doping the rare earth oxide, the grain boundary can be purified, and the alloy structure can be improved. The preparation method comprises the steps that alloy powder is prepared through vacuum gas atomization, then the alloy powder is mixed through a planetary ball mill, the composite coating is prepared through laser cladding, and the rare earth high-entropy alloy is obtained. The experimental process is easy to operate, large-scale production can be achieved, and by means of combined treatment of the laser cladding technology and the rare earth doped high-entropy alloy, the alloy structure can be effectively improved, the passivation effect can be remarkably improved, the self-corrosion potential can be improved, the self-corrosion current density can be reduced, the corrosion resistance of the surface of the high-entropy alloy can be enhanced, and the service life of the alloy material can be prolonged.

Description

Technical Field

[0001] The present invention relates to the field of high entropy alloys, and in particular to a rare earth doped high entropy alloy resistant to chloride ion corrosion and a preparation method thereof. Background Art

[0002] Since high entropy alloys were first proposed by Taiwan scholar Ye Junwei in 2004, they have attracted widespread attention from scholars due to their high entropy effect in thermodynamics, lattice distortion effect in structure, hysteresis diffusion effect in dynamics, and cocktail effect in performance. Due to the existence of these "four major effects", they often have excellent mechanical properties, high hardness, good thermal stability and corrosion resistance. Adding corrosion-resistant elements (Co, Mo, Ni) to high entropy alloys can form a dense passivation film on the alloy surface, which can significantly improve the corrosion resistance of the coating. High entropy alloys with BCC+FCC dual-phase structure have good mechanical properties, but there are obvious phase potential differences between different phase structures, resulting in chemical corrosion. Rare earth oxides are dispersed at grain boundaries and in grains, which can refine grains, improve uniform distribution of elements, purify alloy coatings, reduce the generation of cracks or pores, and thus improve the corrosion resistance of materials. Therefore, high entropy alloy coatings doped with rare earths have broad application prospects.

[0003] At present, the preparation of high entropy alloy coatings is mainly based on laser cladding, mechanical alloying, 3D printing, vapor deposition, thermal spraying, and electrochemical deposition. In general, the process is cumbersome and complicated, the cost is high, and the coating forming efficiency is low. Therefore, exploring a simpler, faster, and high-performance coating preparation method has become a very urgent engineering problem. Laser cladding is a new surface modification technology. It forms a metallurgically bonded additive cladding layer on the surface of the base by adding cladding materials to the surface of the substrate and using a high-energy-density laser beam to melt it together with a thin layer on the surface of the substrate. It can significantly improve the wear resistance, corrosion resistance, or high-temperature oxidation resistance of the alloy material surface, thereby achieving the purpose of surface modification or repair, meeting the special working conditions of the material surface while saving a lot of economic costs. At the same time, laser cladding technology has the characteristics of low dilution rate and good metallurgical bonding, so the application prospects of laser cladding technology are very broad. Summary of the invention

[0004] The purpose of the present invention is to provide a rare earth doped high entropy alloy resistant to chloride ion corrosion and a preparation method thereof, which solves the problem that the alloy coating is prone to pitting corrosion and improves the corrosion resistance of the high entropy alloy in chloride ion solution.

[0005] The present invention discloses a rare earth doped high entropy alloy resistant to chloride ion corrosion. The rare earth high entropy alloy is expressed as CoCrFeNiMoSi-xLa2O3, wherein 0.1%≤X≤3%, for example, 0.02, 0.05, 0.08, 0.12, 0.15, but not limited to the listed values, and is composed of the following element components according to atomic percentage: Co is 15% to 25%, Cr is 15% to 25%, Fe is 15% to 25%, Ni is 15% to 25%, Mo is 15% to 25%, Si is 15% to 25%, and the sum of the above components is 100%.

[0006] Among the above materials, the purity of each element in the selected raw materials is not less than 99.95%.

[0007] 0007. In the present invention, by doping rare earth oxides, the grains can be refined, the uniform distribution of elements can be improved, the alloy coating can be purified, and the generation of cracks or pores can be reduced, thereby improving the corrosion resistance of the material, making it easier to form a dense passivation film, and preventing chloride ions from further corroding the alloy coating.

[0008] The method for preparing the above-mentioned rare earth-doped high-entropy alloy coating resistant to chloride ion corrosion comprises the following steps.

[0009] S1. Preparation of high entropy alloy powder.

[0010] The hexavalent high entropy alloy powder is prepared by vacuum gas atomization technology, screened according to the particle size requirements, dried to remove moisture, and vacuum packaged for later use.

[0011] S2. Composite powder mixing and substrate pretreatment.

[0012] S2-1. Add nano-sized rare earth oxide particles to the high entropy alloy element powder with equal atomic ratio prepared in step S1, and then mix the powders in a ball mill.

[0013] S2-2. Grind the surface of the 45# substrate to make it smooth, remove the oil stains on the surface of the substrate, clean it with an ultrasonic cleaner, and then clean it with anhydrous ethanol. Dry it and set it aside.

[0014] S3. Preparation of composite coating.

[0015] Before laser cladding, the substrate sheet should be preheated at a temperature of 150-400°C for 0.5-4 hours.

[0016] Turn on argon protection, clean the powder delivery pipeline, add the prepared composite powder, place the preheated substrate, start the laser water cooling box, set the laser cladding parameters, and then carry out laser cladding experiments to prepare rare earth doped high entropy alloy composite coatings.

[0017] S4. Coating surface treatment.

[0018] After the laser cladding is completed, the sample is taken out and cooled to room temperature in the air, the unmelted particles and powder on the coating surface are cleaned, and the sample is cut into a size suitable for testing by wire cutting for later use.

[0019] During the laser cladding process, protective gas is used, preferably argon gas, to prevent other impurities from entering the coating.

[0020] In the present invention, in the above step S3, the laser power is 900-1400 W, the powder feeding speed is 16-20 r / min, the scanning speed is 6-9 mm / s, the spot diameter is 1.5-2.5 mm, and the overlap rate is 30-50%.

[0021] In the present invention, the thickness of the prepared rare earth doped high entropy alloy coating is 1mm-3mm.

[0022] In the present invention, the sample except for the coating surface to be tested is encapsulated with insulating materials to form a working electrode, and then an electrochemical test is carried out in a three-electrode system.

[0023] In the present invention, only the surface of the coating to be tested is exposed on the sample to be tested, and the other surfaces of the substrate are quickly solidified and encapsulated with insulating material epoxy resin AB glue.

[0024] In the present invention, the insulating material is epoxy resin AB glue, but is not limited to epoxy resin, and insulating tape can also be used.

[0025] In the present invention, the electrolyte of the three-electrode system is 3.5% NaCl.

[0026] The present invention has the following beneficial effects.

[0027] (1) The chloride ion corrosion-resistant CoCrFeNiMoSi-xLa2O3 high entropy alloy provided by the present invention has a higher corrosion potential and a lower corrosion current density in a chloride ion solution by doping with rare earth oxides.

[0028] (2) The rare earth oxide-modified high entropy alloy coating prepared by laser cladding in the present invention has good metallurgical bonding with the substrate, can effectively improve the alloy structure, and has no cracks or bubbles in the coating.

[0029] (3) The preparation method provided by the present invention is simple to operate and has high molding efficiency. It can meet the special working conditions of the material surface while saving a lot of economic costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 XRD patterns of the high entropy alloys prepared in Examples 1, 2, 3 and 4.

[0031] Figure 2This is a SEM image of the high entropy alloy prepared in Example 1 of the present invention.

[0032] Figure 3 The polarization curves of the high entropy alloys prepared in Examples 1, 2, 3 and 4 of the present invention in 3.5% NaCl are shown. Implementation

[0033] The present invention will be further described in detail below in conjunction with the embodiments, but is not limited to the following embodiments.

[0034] Specific embodiment 1.

[0035] This embodiment provides a rare earth-doped high entropy alloy resistant to chloride ion corrosion, and the expression of the rare earth high entropy alloy is CoCrFeNiMoSi.

[0036] The specific implementation plan for preparing the rare earth-doped high entropy alloy coating resistant to chloride ion corrosion in this embodiment includes the following steps.

[0037] S1. Preparation of high entropy alloy powder.

[0038] The hexavalent high entropy alloy powder is prepared by vacuum gas atomization technology, and then the alloy powder with a particle size range of 45-300 μm is screened according to the particle size requirements, and the powder is dried to remove moisture and vacuum packaged for standby use.

[0039] S2. Composite powder preparation and matrix pretreatment.

[0040] S2-1. Add nano-sized rare earth oxide particles to the high entropy alloy element powder with equal atomic ratio obtained in step S1, and then perform ball milling in a ball mill. The ball milling time is not less than 3 hours, and the ball milling direction is changed every 10 minutes. After each ball milling for 1 hour, cool for 10 minutes.

[0041] S2-2. Use 45# steel plate as the substrate, polish the surface of the substrate with 300-2000 mesh sandpaper to remove oil stains on the surface of the substrate, clean it with an ultrasonic cleaner, and then clean it with anhydrous ethanol, dry it and set it aside.

[0042] S3. Preparation of composite coating.

[0043] Before laser cladding, the substrate sheet was preheated at 200 °C for 2 h.

[0044] Turn on argon protection, clean the powder feeding pipeline, add the prepared composite powder, place the preheated substrate, start the laser water cooling box, and set the laser cladding parameters: laser power is 1000W, powder feeding speed is 18r / min, scanning speed is 6mm / s, spot diameter is 2mm, and overlap rate is 33%.

[0045] S4. Coating surface treatment.

[0046] After the laser cladding is completed, the sample is taken out and cooled to room temperature in the air, the unmelted particles and powder on the coating surface are cleaned, and the sample is cut into a suitable size for testing by wire cutting for subsequent testing.

[0047] The surface of the test sample was polished with 300-2000 mesh metallographic sandpaper. The sample was rotated 90° before each sandpaper change to ensure that the scratches from the last polishing were removed. Then, a diamond agent with a particle size of 1 μm was used to polish the sample in a polishing machine until it showed a mirror effect. After that, the sample was made into an electrode with epoxy resin, exposing only the surface of the coating to be tested. The electrochemical test was carried out in a classic three-electrode system. The test environment was 3.5% NaCl solution, the Pt sheet was the counter electrode, the high entropy alloy sample was the working electrode, and the saturated calomel electrode was the reference electrode.

[0048] Specific embodiment 2.

[0049] This embodiment is basically the same as Embodiment 1, except that:

[0050] The expression of the rare earth high entropy alloy is CoCrFeNiMoSi-1%La2O3.

[0051] Specific embodiment 3.

[0052] This embodiment is basically the same as Embodiment 2, except that:

[0053] The expression of the rare earth high entropy alloy is CoCrFeNiMoSi-2%La2O3.

[0054] Specific embodiment 4.

[0055] This embodiment is basically the same as Embodiment 3, except that:

[0056] The expression of the rare earth high entropy alloy is CoCrFeNiMoSi-3%La2O3.

[0057] The high entropy alloy coatings prepared in Examples 1-4 were subjected to X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests, and the results were as follows: Figure 1 and Figure 2 shown.

[0058] XRD test: the scanning angle 2θ range is 20-100°, and the scanning speed is 1° / min.

[0059] SEM test: The electrochemically corroded samples were observed using a Zeiss Supra55 VP scanning electron microscope. Alloy corrosion occurred preferentially at the grain boundaries.

[0060] The high entropy alloy prepared in the above embodiment was subjected to polarization curve test in 3.5% NaCl solution, and the test range was -1.1 to 1.0 V. The test results are as follows: Figure 3 shown.

[0061] The rare earth oxide doped high entropy alloy obtained by this experimental method has a clear passivation range, a lower corrosion current density and a higher corrosion potential, and has excellent corrosion resistance in chloride ion solution.

[0062] The rare earth oxide doped high entropy alloy CoCrFeNiMoSi-1%La2O3 obtained in this experimental method has excellent corrosion resistance. The corrosion potential in 3.5%NaCl solution is -0.61V and the corrosion current density is 1.02×10-5A / cm².

[0063] Combined with the analysis of Example 4, it can be seen that when rare earth oxides are added excessively, too many impurities cannot be removed in time, resulting in reduced corrosion resistance of the alloy.

Claims

1. A rare earth doped high entropy alloy resistant to chloride ion corrosion, characterized in that: The rare earth high entropy alloy is expressed as CoCrFeNiMoSi-xLa2O3, wherein 0.1%≤X≤3%, and is composed of the following element components in atomic percentage: Co is 15%-25%, Cr is 15%-25%, Fe is 15%-25%, Ni is 15%-25%, Mo is 15%-25%, Si is 15%-25%, and the sum of the above components is 100%.

2. The rare earth doped high entropy alloy according to claim 1, characterized in that: The microstructure of the rare earth doped high entropy alloy is a face-centered cubic structure, a body-centered cubic structure and a Si-rich intermetallic compound.

3. A rare earth doped high entropy alloy coating according to claims 1-2, characterized in that: The preparation method of the rare earth doped high entropy alloy coating is at least one of laser cladding, mechanical alloying, 3D printing, vapor deposition, thermal spraying, or electrochemical deposition, preferably laser cladding, more specifically, conventional laser cladding is preferred.

4. The method for preparing a rare earth doped high entropy alloy according to claims 1 to 3, characterized in that: The preparation method comprises: preparing alloy powder by vacuum gas atomization, mixing the alloy powder in a ball mill, and preparing a composite coating by laser cladding to obtain a rare earth high entropy alloy.

5. A rare earth doped high entropy alloy coating resistant to chloride ion corrosion according to claims 1 to 4, characterized in that: The following steps are involved: S1. Preparation of high entropy alloy powder The high entropy alloy powder with equal atomic ratio is prepared by vacuum gas atomization technology and dried in a drying oven; S2. Composite powder preparation and matrix pretreatment S2-1, adding nano-sized rare earth oxide particles to the high entropy alloy element powder with equal atomic ratio prepared in step S1, and then mixing the powders in a ball mill; S2-2, polish the surface of the 45# substrate to make it smooth, remove the oil stains on the surface of the substrate, clean it with an ultrasonic cleaner, and then clean it with anhydrous ethanol, dry it and set it aside; S3. Composite coating preparation Before laser cladding, the substrate sheet is preheated at a temperature of 150-400°C for 0.5-4 hours, and then laser cladding is performed to prepare the coating.

6. The method for preparing a rare earth doped high entropy alloy resistant to chloride ion corrosion according to claim 5, characterized in that: Argon gas protection is used during the laser cladding process to prevent other impurities from entering the coating. The laser power is 900-1400W, the powder feeding speed is 16-20r / min, the scanning speed is 6-9mm / s, the spot diameter is 1.5-2.5mm, and the overlap rate is 30-50%.

7. The rare earth doped high entropy alloy coating resistant to chloride ion corrosion according to claim 6, characterized in that: The thickness of the rare earth doped high entropy alloy coating is 1 mm to 3 mm.

8. The method for preparing a chloride ion corrosion resistant rare earth doped high entropy alloy coating according to claim 5, characterized in that: In step S1, the particle size range of the high entropy alloy powder is 45-300 μm, and the particle size range of the rare earth oxide in step S2-1 is 50-450 nm.

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