Plasma electrolytic nitriding method for laser cladding of high-entropy alloy layer

Abstract

The invention belongs to the technical field of material surface modification, and discloses a plasma electrolytic nitriding method for a laser cladding high-entropy alloy layer, which comprises the following steps: S1, providing an electrolyte for plasma electrolytic nitriding; s2, the pretreated workpiece serves as an anode, graphite serves as a cathode, a power source is switched on, and the anode and the cathode are immersed in the electrolyte in the high-voltage environment with the voltage being 270-350 V; s3, after the voltage is slowly reduced to 140 V to 260 V, liquid-phase plasma electrolytic nitriding treatment is conducted for 5 min to 25 min; wherein a FeCoCrNi high-entropy alloy layer is formed on the workpiece through laser cladding treatment in a cladding manner. The plasma electrolysis nitriding technology is used for nitriding the high-entropy alloy cladding coating subjected to laser cladding, a high-quality nitriding layer with higher surface hardness, higher wear resistance and corrosion resistance and a compact and controllable structure can be obtained, the method is more environmentally friendly and energy-saving, the effect on stainless steel and other materials difficult to treat is remarkable, and thermal deformation of a workpiece can be greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface modification, and in particular relates to a plasma electrolytic nitriding method for a laser cladding high entropy alloy layer. Background Art

[0002] Alloy steels have excellent hot workability and hardenability, which contribute to their commendable overall mechanical properties, making them widely used in precision components for the aerospace, aviation, and defense industries. However, their low surface hardness and poor tribological properties hinder their application.

[0003] Nitriding, a common surface modification technology, is a cost-effective way to improve the hardness and wear resistance of alloy steels. However, conventional nitriding technology can only produce single-phase iron nitride on alloy steels with relatively low hardness. This limitation can affect the service life and safety of alloy steels when used under extreme wear conditions.

[0004] High entropy alloys (HEAs) are composed of five or more elements with atomic fractions ranging from 5% to 35%, and have attracted great attention. HEAs exhibit unique characteristics such as slug-like diffusion kinetics, lattice distortion effects, cocktail effects of properties, and high entropy effects, which make their structure stable, with good ductility and corrosion resistance. For elements containing a large amount of strong nitrides (e.g., Al, Cr, Fe), the nitriding process is conducive to the formation of hard nitrides such as AlN, CrN, and Fe4N. Plasma electrolytic diffusion technology is a new type of thermochemical heat treatment technology, including plasma electrolytic nitriding (PEN), plasma electrolytic carburizing (PEC), plasma electrolytic nitrocarburizing / carbonitriding (PENC / PECN), and plasma electrolytic boronizing (PEB), which belongs to the category of high-speed diffusion treatment. In particular, in the PECN process, due to the simultaneous diffusion of C and N, the diffusion coefficients of C and N increase, which is conducive to the formation of interstitial solid solution. Its advantages include but are not limited to: (1) It can accelerate the diffusion of interstitial elements and achieve rapid hardening within a few minutes. (2) The treated samples can be quickly cooled in the same solution without additional treatment. (3) The equipment is simple and inexpensive, can be operated at room temperature and atmospheric pressure, and is environmentally friendly. As an emerging material system, high entropy alloys have a relatively flexible elemental composition and can contain a variety of nitride-forming elements. Nitriding high entropy alloys is expected to produce a nitrided layer containing a variety of nitrides on the surface of the material. At present, research on ion nitriding of HEA coatings mainly focuses on the use of gas ion nitriding, and there is little research on the nitriding of HEA coatings by plasma electrolytic nitriding. This study aims to fill the gap in this field. Summary of the Invention

[0005] In view of this, and to address the problems raised in the above background technology, the present invention aims to provide a plasma electrolytic nitriding method for laser-clad high-entropy alloy layers. Specifically, the plasma electrolytic nitriding technology is used to nitride the clad FeCoCrNi layer of the material, thereby significantly improving the hardness, wear resistance, and corrosion resistance of the laser-clad FeCoCrNi high-entropy alloy layer.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A plasma electrolytic nitriding method for laser cladding high entropy alloy layer comprises the following steps:

[0008] S1 provides an electrolyte for plasma electrolytic nitriding;

[0009] S2. The pretreated workpiece is used as an anode and graphite as a cathode. The power is turned on and the anode and cathode are immersed in an electrolyte under a high voltage environment of 270 to 350 V.

[0010] S3. After the voltage is slowly reduced to 140-260 V, liquid plasma electrolytic nitriding treatment is performed for 5-25 min;

[0011] S4. Turn off the power and remove the workpiece after nitriding treatment for cleaning and drying;

[0012] Wherein, a high entropy alloy layer is formed on the workpiece by laser cladding treatment, and the composition of the high entropy alloy layer is FeCoCrNi.

[0013] Preferably, in step S1, each 1L of the electrolyte includes:

[0014] Ammonium chloride, 50-200g;

[0015] Ammonia water, 50-300 mL;

[0016] Potassium chloride, 1-10g;

[0017] Deionized water, balance.

[0018] Preferably, in step S2, the pretreatment includes: soaking the workpiece in a degreasing solution for 5 to 10 minutes and then rinsing with deionized water; then polishing the surface of the workpiece; ultrasonically cleaning the polished workpiece in acetone for 3 to 10 minutes and then rinsing with ultrapure water, and drying with cold air.

[0019] Preferably, the degreasing liquid comprises 60-80 g of sodium hydroxide, 20-60 g of sodium carbonate, 15-30 g of trisodium phosphate dodecahydrate and 5-10 g of sodium silicate added to every 1 L of water.

[0020] Preferably, the polishing includes polishing the workpiece surface using 320#, 600#, 1000# and 2000# sandpaper in sequence.

[0021] Preferably, in step S2, before immersing the anode and cathode in the electrolyte, the method further includes: controlling the temperature of the electrolyte to 20-25°C.

[0022] Preferably, in step S2, the anode and cathode are immersed in the electrolyte at a speed of 0.5 mm / s under the high-pressure environment, and the immersion depth of the anode is ensured to be the same as the height of the workpiece.

[0023] Preferably, in step S3, the electrolyte is stirred by a stirring device while the liquid phase plasma electrolytic nitriding treatment is being performed.

[0024] Preferably, in step S3, the electrolyte is cooled by a cooling device while the liquid phase plasma electrolytic nitriding treatment is being performed, so as to control the electrolyte temperature to be 20-25°C.

[0025] Preferably, in step S4, the cleaning and drying of the workpiece includes: placing the workpiece in acetone for ultrasonic cleaning for 8 to 10 minutes, then rinsing with ultrapure water, and drying with cold air.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention utilizes plasma electrolytic nitriding technology to perform nitriding treatment on the laser-clad high-entropy alloy cladding coating. Compared with traditional gas or salt bath nitriding, the core advantages of plasma electrolytic nitriding (PEN) technology are its high efficiency and fast speed (nitriding temperature is reduced by 100-200°C, and time is shortened by more than 50%). It can obtain a high-quality nitrided layer with higher surface hardness, stronger wear and corrosion resistance, and a dense and controllable structure. At the same time, it is more environmentally friendly and energy-saving (no toxic media are required), has significant effects on difficult-to-treat materials such as stainless steel (cathode sputtering removes the passivation film), and can significantly reduce thermal deformation of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 2 are cross-sectional scans of the workpieces after nitriding treatment in the embodiments of the present invention and the comparative examples; the thickness of the nitriding layer in Example 1 is 52.8 μm, the thickness of the nitriding layer in Example 2 is 53.7 μm, the thickness of the nitriding layer in Example 3 is 50.7 μm, the thickness of the nitriding layer in Comparative Example 1 is 32.5 μm, and the thickness of the nitriding layer in Comparative Example 2 is 28.2 μm.

[0029] Figure 2 3 is a comparison chart of the surface hardness of the high entropy alloy layer of the workpiece after nitriding treatment in the embodiment of the present invention and the comparative example; the surface hardness of the high entropy alloy layer of the workpiece in Example 2 reaches a maximum of 1297 HV.

[0030] Figure 3 The figure shows the comparison of the surface friction and wear of the high entropy alloy layer of the workpiece after nitriding treatment in the embodiment of the present invention and the comparative example. The surface friction and wear performance of the high entropy alloy layer of the workpiece in the second embodiment is the best, and the wear rate is the lowest, reaching 1.1194*10 -6 g·N -1 ·m -1 . DETAILED DESCRIPTION

[0031] To further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments. The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the content disclosed in the specification, so that people familiar with the technology can understand and read them. They are not used to limit the limitations of the implementation of the present invention and therefore have no technical significance. Any structural modifications, changes in proportional relationships, or adjustments in size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and objectives that can be achieved by the present invention. At the same time, terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for ease of description and are not used to limit the scope of implementation. Changes or adjustments in their relative relationships should also be considered as the scope of implementation of the present invention without substantially changing the technical content. It should be noted that the terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way are interchangeable where appropriate for the embodiments of the present application described herein.

[0032] In the present invention, HT250 gray cast iron is used as a workpiece (substrate), and a high entropy alloy layer is formed on the surface of the workpiece (substrate) by laser cladding treatment, and the composition of the high entropy alloy layer is FeCoCrNi.

[0033] Example 1

[0034] S1 provides an electrolyte for plasma electrolytic nitriding;

[0035] Dissolve 50-200g of ammonium chloride, 50-300ml of aqueous ammonia, and 1-10g of potassium chloride in deionized water to prepare 1L of electrolyte. Ammonium chloride and aqueous ammonia are used as a combined nitrogen source to avoid the drawback of aqueous ammonia being easily evaporated at high temperatures when used as the sole nitrogen source.

[0036] S2. Using the pretreated workpiece as the anode and graphite as the cathode, connect the power supply, control the electrolyte temperature to 20-25°C, and immerse the anode and cathode into the electrolyte at a high voltage of 270-350V at a speed of 0.5mm / s, ensuring that the anode is immersed to the same depth as the workpiece. Maintain this voltage (270-350V) for a period of time to ensure stable discharge.

[0037] The pretreatment includes:

[0038] First, the workpiece is immersed in a degreasing solution for 5 to 10 minutes and then rinsed with deionized water; the degreasing solution comprises 60 to 80 g of sodium hydroxide, 20 to 60 g of sodium carbonate, 15 to 30 g of trisodium phosphate dodecahydrate, and 5 to 10 g of sodium silicate added per 1 L of water;

[0039] Then, use 320#, 600#, 1000#, and 2000# sandpaper to polish the surface of the workpiece in sequence;

[0040] Finally, the polished workpiece was ultrasonically cleaned in acetone for 3 to 10 minutes, then rinsed with ultrapure water and dried with cold air.

[0041] S3. After slowly reducing the voltage to 140-160 V, perform liquid-phase plasma electrolytic nitriding treatment for 5-25 minutes, and cool the electrolyte (control the electrolyte temperature at 20-25° C.) and stir during the treatment.

[0042] S4. Turn off the power, take out the workpiece after nitriding treatment, and put the workpiece into acetone for ultrasonic cleaning for 8 to 10 minutes, then rinse with ultrapure water and dry with cold air.

[0043] Example 2

[0044] S1 provides an electrolyte for plasma electrolytic nitriding;

[0045] Dissolve 50-200 g of ammonium chloride, 50-300 ml of ammonia water, and 1-10 g of potassium chloride in deionized water to prepare 1 L of electrolyte.

[0046] S2. Using the pretreated workpiece as the anode and graphite as the cathode, connect the power supply, control the electrolyte temperature to 20-25°C, and immerse the anode and cathode into the electrolyte at a high voltage of 270-350V at a speed of 0.5mm / s, ensuring that the anode is immersed to the same depth as the workpiece. Maintain this voltage (270-350V) for a period of time to ensure stable discharge.

[0047] The pretreatment includes:

[0048] First, the workpiece is immersed in a degreasing solution for 5 to 10 minutes and then rinsed with deionized water; the degreasing solution comprises 60 to 80 g of sodium hydroxide, 20 to 60 g of sodium carbonate, 15 to 30 g of trisodium phosphate dodecahydrate, and 5 to 10 g of sodium silicate added per 1 L of water;

[0049] Then, use 320#, 600#, 1000#, and 2000# sandpaper to polish the surface of the workpiece in sequence;

[0050] Finally, the polished workpiece was ultrasonically cleaned in acetone for 3 to 10 minutes, then rinsed with ultrapure water and dried with cold air.

[0051] S3. After slowly reducing the voltage to 170-190 V, perform liquid-phase plasma electrolytic nitriding treatment for 5-25 minutes, and cool the electrolyte (control the electrolyte temperature at 20-25° C.) and stir during the treatment.

[0052] S4. Turn off the power, take out the workpiece after nitriding treatment, and put the workpiece into acetone for ultrasonic cleaning for 8 to 10 minutes, then rinse with ultrapure water and dry with cold air.

[0053] Example 3

[0054] S1 provides an electrolyte for plasma electrolytic nitriding;

[0055] Dissolve 50-200 g of ammonium chloride, 50-300 ml of ammonia water, and 1-10 g of potassium chloride in deionized water to prepare 1 L of electrolyte.

[0056] S2. Using the pretreated workpiece as the anode and graphite as the cathode, connect the power supply, control the electrolyte temperature to 20-25°C, and immerse the anode and cathode into the electrolyte at a high voltage of 270-350V at a speed of 0.5mm / s, ensuring that the anode is immersed to the same depth as the workpiece. Maintain this voltage (270-350V) for a period of time to ensure stable discharge.

[0057] The pretreatment includes:

[0058] First, the workpiece is immersed in a degreasing solution for 5 to 10 minutes and then rinsed with deionized water; the degreasing solution comprises 60 to 80 g of sodium hydroxide, 20 to 60 g of sodium carbonate, 15 to 30 g of trisodium phosphate dodecahydrate, and 5 to 10 g of sodium silicate added per 1 L of water;

[0059] Then, use 320#, 600#, 1000#, and 2000# sandpaper to polish the surface of the workpiece in sequence;

[0060] Finally, the polished workpiece was ultrasonically cleaned in acetone for 3 to 10 minutes, then rinsed with ultrapure water and dried with cold air.

[0061] S3. After slowly reducing the voltage to 200-220 V, perform liquid-phase plasma electrolytic nitriding treatment for 5-25 minutes, and cool the electrolyte (control the electrolyte temperature at 20-25° C.) and stir during the treatment.

[0062] S4. Turn off the power, take out the workpiece after nitriding treatment, and put the workpiece into acetone for ultrasonic cleaning for 8 to 10 minutes, then rinse with ultrapure water and dry with cold air.

[0063] Comparative Example 1

[0064] S1 provides an electrolyte for plasma electrolytic nitriding;

[0065] Dissolve 50-200 g of ammonium chloride, 50-300 ml of ammonia water, and 1-10 g of potassium chloride in deionized water to prepare 1 L of electrolyte.

[0066] S2. Use the pretreated workpiece as the anode and graphite as the cathode, turn on the power, control the electrolyte temperature to 20-25°C, and adjust the voltage to 170-190V, immerse the anode and cathode into the electrolyte at a speed of 0.5mm / s, and ensure that the immersion depth of the anode is the same as the height of the workpiece.

[0067] The pretreatment includes:

[0068] First, the workpiece is immersed in a degreasing solution for 5 to 10 minutes and then rinsed with deionized water; the degreasing solution comprises 60 to 80 g of sodium hydroxide, 20 to 60 g of sodium carbonate, 15 to 30 g of trisodium phosphate dodecahydrate, and 5 to 10 g of sodium silicate added per 1 L of water;

[0069] Then, use 320#, 600#, 1000#, and 2000# sandpaper to polish the surface of the workpiece in sequence;

[0070] Finally, the polished workpiece was ultrasonically cleaned in acetone for 3 to 10 minutes, then rinsed with ultrapure water and dried with cold air.

[0071] S3. Perform liquid phase plasma electrolytic nitriding treatment at a voltage of 170 to 190 V for 5 to 25 minutes.

[0072] S4. Turn off the power, take out the workpiece after nitriding treatment, and put the workpiece into acetone for ultrasonic cleaning for 8 to 10 minutes, then rinse with ultrapure water and dry with cold air.

[0073] Comparative Example 2

[0074] S1 provides an electrolyte for plasma electrolytic nitriding;

[0075] Dissolve 50-200 g of ammonium chloride, 50-300 ml of ammonia water, and 1-10 g of potassium chloride in deionized water to prepare 1 L of electrolyte.

[0076] S2. Using the pretreated workpiece as the anode and graphite as the cathode, connect the power supply, control the electrolyte temperature to 20-25°C, and immerse the anode and cathode into the electrolyte at a high voltage of 270-350V at a speed of 0.5mm / s, ensuring that the anode is immersed to the same depth as the workpiece. Maintain this voltage (270-350V) for a period of time to ensure stable discharge.

[0077] The pretreatment comprises: polishing the surface of the workpiece with 320#, 600#, 1000# and 2000# sandpaper in sequence; ultrasonically cleaning the polished workpiece in acetone for 3 to 10 minutes, then rinsing with ultrapure water, and drying with cold air.

[0078] S3. After adjusting the voltage to 170-190 V, perform liquid-phase plasma electrolytic nitriding treatment for 5-25 minutes, and cool the electrolyte (control the electrolyte temperature at 20-25° C.) and stir during the treatment.

[0079] S4. Turn off the power, take out the workpiece after nitriding treatment, and put the workpiece into acetone for ultrasonic cleaning for 8 to 10 minutes, then rinse with ultrapure water and dry with cold air.

[0080] In summary, the workpieces obtained after processing in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were tested and compared, and the following results were obtained: Figures 1 to 3 The test comparison results shown in the figure show that, based on these comparison results, it can be seen that Comparative Examples 1 and 2 are experiments based on Example 2. Through the microhardness and friction and wear performance of the comparative examples, it is concluded that degreasing pretreatment and placing the workpiece under high pressure have better nitriding effects. Among them, the nitriding layer thickness in Example 2 reaches the thickest 53.7μm, the surface hardness of the workpiece high entropy alloy layer reaches the highest 1297HV, the friction and wear performance is the best, and the wear rate is the lowest, reaching 1.1194*10 -6 g·N -1 ·m -1 .

[0081] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A plasma electrolytic nitriding method for laser cladding high entropy alloy layer, characterized in that: The steps include: S1 provides an electrolyte for plasma electrolytic nitriding; S2. The pretreated workpiece is used as an anode and graphite as a cathode. The power is turned on and the anode and cathode are immersed in an electrolyte under a high voltage environment of 270 to 350 V. S3. After the voltage is slowly reduced to 140-260 V, liquid plasma electrolytic nitriding treatment is performed for 5-25 min; S4. Turn off the power and remove the workpiece after nitriding treatment for cleaning and drying; Wherein, a high entropy alloy layer is formed on the workpiece by laser cladding treatment, and the composition of the high entropy alloy layer is FeCoCrNi.

2. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S1, each 1L of the electrolyte includes: Ammonium chloride, 50-200g; Ammonia water, 50-300 mL; Potassium chloride, 1-10g; Deionized water, balance.

3. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S2, the pretreatment includes: soaking the workpiece in degreasing liquid for 5 to 10 minutes and then rinsing with deionized water; then polishing the surface of the workpiece; ultrasonically cleaning the polished workpiece in acetone for 3 to 10 minutes and then rinsing with ultrapure water, and drying with cold air.

4. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 3, characterized in that: The degreasing liquid comprises 60-80 g of sodium hydroxide, 20-60 g of sodium carbonate, 15-30 g of trisodium phosphate dodecahydrate and 5-10 g of sodium silicate added to every 1 L of water.

5. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 3, characterized in that: The polishing includes sequentially using 320#, 600#, 1000# and 2000# sandpaper to polish the surface of the workpiece.

6. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S2, before immersing the anode and cathode in the electrolyte, the method further includes: controlling the temperature of the electrolyte to be 20-25°C.

7. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S2, the anode and cathode are immersed in the electrolyte at a speed of 0.5 mm / s under the high-pressure environment, and the immersion depth of the anode is ensured to be the same as the height of the workpiece.

8. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S3, the electrolyte is stirred by a stirring device while the liquid phase plasma electrolytic nitriding treatment is being performed.

9. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S3, the electrolyte is cooled by a cooling device while the liquid phase plasma electrolytic nitriding treatment is being performed, so as to control the electrolyte temperature to be 20-25°C.

10. The plasma electrolytic nitriding method for laser cladding high entropy alloy layer according to claim 1, characterized in that: In step S4, the cleaning and drying of the workpiece includes: placing the workpiece in acetone for ultrasonic cleaning for 8 to 10 minutes, then rinsing with ultrapure water, and drying with cold air.

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