Method for realizing low-temperature nitriding strengthening of metal surface by utilizing plasma catalysis

Abstract

The invention discloses a method for realizing low-temperature nitriding strengthening of a metal surface by utilizing plasma catalysis, and belongs to the field of chemical surface treatment of metal. The method comprises the following steps that firstly, a metal workpiece is placed in a plasma reaction furnace, the gas ratio of nitrogen to hydrogen is adjusted to be 3: 1, and catalyst particles are introduced; a high-frequency plasma generator is started, plasma is applied at the temperature of 300 DEG C or below for a catalytic reaction, the reaction time is 2-4 hours, and the air pressure is maintained to be 100-200 Pa; adsorption and diffusion of nitrogen atoms are accelerated through the catalyst, and low-temperature nitriding strengthening of the surface of the workpiece is achieved. Results show that compared with a traditional process, the method has the advantages that the temperature is obviously reduced, the surface hardness is improved to 1100-1300 HV, the thickness of an infiltrated layer reaches 40-60 microns, and meanwhile, the energy consumption is reduced by 30-40%. According to the method, through a plasma catalysis mechanism, the defects of traditional high-temperature nitriding, such as grain coarsening and residual stress concentration, are avoided, and a reliable way is provided for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical surface treatment of metals, and particularly relates to a method for low-temperature nitriding of metal surfaces by plasma catalysis. BACKGROUND

[0002] Metal surface nitriding is a key technology for improving the hardness, wear resistance and fatigue resistance of workpieces, and is widely used in the fields of automobiles, aerospace and mechanical manufacturing. Traditional nitriding methods, such as gas nitriding and ion nitriding, are usually carried out at high temperatures above 500°C, using the diffusion of nitrogen atoms on the metal surface to form a nitride layer. High-temperature operation can ensure sufficient penetration of nitrogen atoms, but brings significant energy consumption and thermal deformation problems of workpieces, especially for precision parts. For example, the deformation rate of tool steel can reach 5-8% when nitriding at 500°C, and the processing time is long (4-8 hours), resulting in low efficiency and high cost. With the increasing demand for green manufacturing in industry, the environmental defects of high-temperature processes are further magnified, and improvement solutions are urgently needed.

[0003] Existing technologies attempt to reduce the nitriding temperature to alleviate the problem, such as using low-temperature plasma-assisted nitriding. The plasma environment can activate gas molecules, promoting the dissociation and adsorption of nitrogen atoms, but traditional methods do not introduce high-efficiency catalysts, resulting in slow diffusion rate of nitrogen atoms at low temperature (nitriding layer thickness of only 20-30 μm), and limited hardness improvement. In some studies, catalysts such as rare earth elements are added, but due to uneven dispersion of the catalyst and poor plasma matching, the process stability is poor, and discontinuous layers or loose structures are easily produced on the surface below 300°C, limiting its industrial application. In addition, existing low-temperature processes have problems of catalyst residue and surface cleanliness, affecting the service life of workpieces.

[0004] The present application addresses the above deficiencies by proposing a method for low-temperature nitriding of metal surfaces by plasma catalysis, the core innovation of which lies in the synergistic effect of specific catalysts and plasma parameters. By high-efficiency catalysis of catalysts (such as iron or nickel nanoparticles) in the plasma field, the activity and diffusion rate of nitrogen atoms are enhanced, and the gas ratio and gas pressure are regulated to form a dense nitriding layer below 300°C, solving the problems of deformation, energy consumption and efficiency. This method not only significantly reduces the operating temperature, but also improves the quality and universality of nitriding, filling the gaps in existing technologies and providing a reliable solution for metal strengthening. SUMMARY

[0005] To solve the problem of high temperature and poor quality of traditional nitriding.

[0006] To solve the above problems, the present application provides the following technical solutions: A method for low-temperature nitriding of metal surfaces by plasma catalysis, characterized in that it comprises the following steps: S1: providing a metal workpiece, and pre-treating the surface of the workpiece; S2: placing the workpiece in a plasma reaction furnace; S3: introducing a mixed gas of nitrogen and hydrogen, the volume ratio of nitrogen to hydrogen being 3:1; S4: introducing a catalyst into the reaction environment, the catalyst being nano-sized metal particles; S5: starting a high-frequency plasma generator, the frequency being set to 13.56±0.5 MHz; S6: adjusting the temperature of the reaction furnace to 280-320°C, and the gas pressure to 100-200 Pa; S7: maintaining the nitriding treatment time for 2-4 hours; S8: after the treatment is completed, turning off the plasma, cooling to room temperature, and taking out the workpiece.

[0007] Preferably, the metal workpiece in S1 is a stainless steel, tool steel or aluminum alloy substrate.

[0008] Preferably, the pre-treatment of the workpiece in S1 includes ultrasonic cleaning to remove oil stains, and then ion sputtering to clean the surface, the sputtering time being 10-20 minutes.

[0009] Preferably, the gas flow rate of the mixed gas in S3 is 200-300 sccm (standard cubic centimeter per minute).

[0010] Preferably, the catalyst in S4 is selected from nano-sized particles of iron, nickel, cobalt or their alloys, the particle size being 20-50 nm.

[0011] Preferably, the catalyst is sprayed in the form of a suspension onto the surface of the workpiece, the spraying thickness being 5-10 μm, and the sprayed workpiece is dried.

[0012] Preferably, the power density of the high-frequency plasma generator in S5 is 0.5-1.0 W / cm 2 .

[0013] Preferably, a DC pulse bias is applied during the nitriding treatment in S7, the bias value being -100 to -300 V.

[0014] Preferably, the cooling process in S8 adopts a gradient cooling method, and the cooling rate is 5°C / min.

[0015] Preferably, the method further includes surface detection of the workpiece after the treatment, and XRD or a hardness tester is used to analyze the nitriding layer.

[0016] The method for realizing low-temperature nitriding strengthening of a metal surface by using plasma catalysis has the following effects and advantages: 1、This patent, the processing temperature is greatly reduced, and effective nitriding is realized at a low temperature of 280-320°C through plasma catalysis, the temperature is reduced by nearly 200°C, and energy consumption of a heat source is reduced by 30-40%.

[0017] 2、This patent, the nitriding efficiency is significantly improved, the treatment time is shortened to 2-3 hours through catalysis, the time is shortened by 40-50%, and the patent is suitable for mass production.

[0018] 3、This patent, the surface hardness and wear resistance are enhanced, the workpiece surface hardness reaches 1300 HV, and the penetration layer thickness is 40-60 μm.

[0019] 4、This patent, the deformation risk is extremely small, the workpiece deformation rate is low under low-temperature operation, and the size precision is maintained. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a flow chart of a method for realizing low-temperature nitriding strengthening of a metal surface through plasma catalysis in the application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application, It should be noted that, in this document, relationship terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations, and the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such a process, method, article or device. Without more limitations, the elements defined by the statement "comprising" do not exclude the presence of additional identical elements in the process, method, article or device including the elements.

[0022] Embodiment 1 Reference Figure 1 This embodiment provides a method for realizing low-temperature nitriding strengthening of a metal surface through plasma catalysis, which is suitable for the field of chemical surface treatment of metals and includes the following implementation contents. Experimental purpose: A method for low-temperature nitriding of metal surface by plasma catalysis, the method is tested for nitriding effect on stainless steel at low temperature (300°C), and the temperature is compared with traditional difference.

[0023] Experimental materials: 304 stainless steel sheet (50x50x5 mm, surface Ra≤0.8 μm); catalyst: iron nanoparticles (purity 99.9%, particle size 30 nm, 0.5 g); gas: nitrogen (purity 99.999%) and hydrogen (purity 99.999%) with volume ratio 3:1.

[0024] Experimental equipment: PE-2000 plasma furnace, high-frequency generator, temperature sensor, vacuum pump.

[0025] Experimental steps: S1: workpiece pretreatment, ultrasonic cleaning (ethanol for 10 minutes) → ion sputtering cleaning (Ar atmosphere, 20 minutes, to remove oxides); S2: catalyst coating, suspend iron nanoparticles in ethanol, spray onto the surface of the workpiece (thickness 10 μm), dry at 80°C for 10 minutes; S3: load the reaction furnace: load the workpiece into the furnace cavity, vacuum to <10 -3 Pa; S4: gas inlet: adjust the gas mixture ratio (nitrogen:hydrogen=3:1), gas flow rate 250 sccm; S5: start plasma: set high-frequency frequency 13.56 MHz, power density 0.8 W / cm 2 ; S6: control conditions, heat to 300°C (heating rate 10°C / min), maintain temperature ±2°C, pressure 150 Pa, treatment time 3 hours; S7: gradient cooling (5°C / min), take out at room temperature; S8: post-treatment, measure hardness and penetration layer thickness.

[0026] Experimental results: details are shown in Table 1.

[0027] Table 1: test results of Example 1

[0028] Example 1: a method for low-temperature nitriding of metal surface by plasma catalysis, the significant improvement of hardness is attributed to the "plasma-catalysis synergistic effect" of iron nano-catalyst: high-frequency plasma dissociates nitrogen into high-activity nitrogen ions (N +), while nano-iron catalyst promotes the penetration of nitrogen atoms into the γ-Fe lattice by reducing the activation energy of the reaction, forming a dense nitride layer, and its fine-grain strengthening effect directly enhances the hardness. The thickness of the case layer reaches 48 μm, which is due to the optimization of low-temperature diffusion kinetics: the kinetic energy of nitrogen ions increases due to the plasma electric field, which breaks through the low-temperature diffusion barrier; at the same time, the "nitrogen atom overflow effect" is formed on the surface of the catalyst, the diffusion coefficient is improved, and low-temperature rapid diffusion is achieved. Energy consumption is reduced to 52 MJ / m 2 Thanks to the triple energy-saving mechanism: the ionization efficiency of high-frequency plasma is improved at low pressure; the catalyst reduces the hydrogen dissociation side reaction; low-temperature operation reduces heat radiation loss by 50%. The deformation rate of only 0.8% is jointly affected by "low-temperature stress inhibition" and "gradient cooling": the thermal stress caused by the difference in thermal expansion coefficient at 300°C is reduced, and the gradient cooling avoids the stress of martensitic phase transformation, resulting in low residual stress.

[0029] Example 2 This example provides a method for low-temperature nitriding and strengthening of metal surfaces using plasma catalysis, which investigates the influence of catalyst type, including the following implementation content: Experimental purposes: A method for low-temperature nitriding and strengthening of metal surfaces using plasma catalysis, which compares the differences in nitriding performance of iron and nickel catalysts, and optimizes the selection.

[0030] Experimental materials: 304 stainless steel sheet (50x50x5 mm, surface Ra≤0.8 μm); catalyst: nickel nanoparticles (20 nm), each 0.5 g; gas: nitrogen (purity 99.999%) and hydrogen (purity 99.999%) with a volume ratio of 3:1.

[0031] Experimental steps: S1: Workpiece pretreatment, ultrasonic cleaning (ethanol for 10 minutes) → ion sputtering cleaning (Ar atmosphere, 20 minutes, to remove oxides); S2: Catalyst coating, suspend nickel nanoparticles in ethanol, spray onto the workpiece surface (thickness 10 μm), dry at 80°C for 10 minutes; S3: Load the reaction furnace: load the workpiece into the furnace cavity, vacuum to <10 -3 Pa; S4: Gas inlet: adjust the gas mixture ratio (nitrogen: hydrogen = 3:1), gas flow rate 250 sccm; S5: Start the plasma: set the high-frequency frequency to 13.56 MHz, power density 0.8 W / cm 2 ; S6: Control conditions, heat to 300°C (heating rate 10°C / min), maintain temperature ±2°C, pressure 150 Pa, treatment time 3 hours; S7: Gradient cooling (5 °C / min), room temperature extraction; S8: Post-treatment, measure hardness and case depth.

[0032] Experimental results: see Table 2 for details.

[0033] Table 2: Example 2 test results

[0034] Example 2 A method for low-temperature nitriding and strengthening of metal surfaces using plasma catalysis, under the same process parameters (300 °C, 150 Pa, 3 hours), the nickel catalyst group obtained higher hardness (1300 HV) and case depth (52 μm). The key to the hardness jump of the nickel catalyst group to 1300 HV is the nanocomposite strengthening induced by nickel catalysis, and the high-density CrN nanocrystals and γ'-Fe4N phases are generated in the surface layer of the nickel group, and the strengthening effect makes the hardness increase. Nickel nanoparticles (20 nm) form a stronger local electric field distortion in the plasma field due to higher d-band electron density, which improves the efficiency of nitrogen ions (N + ) dissociation into atomic nitrogen; at the same time, the lattice constant of nickel (0.352 nm) is more suitable for γ-Fe (0.364 nm), which reduces the nitrogen atom diffusion interface energy barrier and accelerates the grain boundary penetration, thus generating a thicker nitrogen-rich layer. Energy consumption is maintained at 52 MJ / m 2 is due to the deliberate control of process parameters (temperature, time, power) to be completely consistent, and the energy saving effect is achieved by system optimization, and the catalyst replacement does not consume additional energy. The deformation rate of 0.9% is achieved by precise control of residual stress, and although the nickel group has a slight Kirkendall vacancy, low-temperature (300 °C) operation inhibits the accumulation of thermal stress, and gradient cooling stabilizes the residual stress at -200 MPa, which is lower than that of the iron group (-150 MPa) but still within the material elastic limit, avoiding the expansion of microcracks.

[0035] Example 3 This example provides a method for low-temperature nitriding and strengthening of metal surfaces using plasma catalysis, which optimizes the treatment time, including the following implementation: Experimental purpose: A method for low-temperature nitriding and strengthening of metal surfaces using plasma catalysis, to study the nitriding effect under different treatment times (2-4 hours) to determine the optimal time.

[0036] Experimental raw materials: 304 stainless steel sheet (50x50x5 mm, surface Ra≤0.8 μm); catalyst: iron nanoparticles (purity 99.9%, particle size 30 nm, 0.5 g); gas: nitrogen (purity 99.999%) and hydrogen (purity 99.999%) at a volume ratio of 3:1.

[0037] Experimental procedure: S1: pretreatment, workpiece ultrasonic cleaning (ethanol, 10 min) → ion sputtering (Ar gas, 20 min, 5x10 -2 Pa) → spraying iron catalyst suspension (ethanol solvent, thickness 10 μm) → 80°C drying for 10 min; S2: vacuum pumping to 5x10 -3 Pa → mixed gas inlet (flow rate 250 sccm) → start plasma (power density 0.8 W / cm 2 ) → heating to 300±2°C (rate 10°C / min) → constant pressure 150 Pa; S3: group processing, group A: processing time 2 hours → gradient cooling (5°C / min); group B: processing time 4 hours → same cooling; S4: post-processing, measure hardness and case depth.

[0038] Experimental results: details are shown in Table 3.

[0039] Table 3: test results of Example 3

[0040] Example 3: a method for low-temperature nitriding and strengthening of metal surface by plasma catalysis. With the extension of processing time, the hardness increases in steps (1150→1280 HV). In short-time processing (2 hours), although the plasma catalysis quickly generates surface nitride, the nitrogen atoms are not fully diffused to the grain boundaries, resulting in low hardness (1150 HV). When the processing time is extended to 3 hours (Example 1), the iron catalyst continuously provides a diffusion channel, the nitrogen concentration gradient is optimized, and a continuous hardened layer is formed, with the hardness jumping to 1250 HV. When the processing time is 4 hours, the deep diffusion is saturated (thickness 55 μm), but the Hall-Petch strengthening effect is weakened due to excessive grain growth and nitride coarsening, and the hardness increment is narrowed. The case depth increases (35→55 μm), and the actual thickness ratio of 2→4 hours is 35:55≈1.57 times, which is slightly higher than the theoretical value, due to the catalyst reducing the activation energy. The key inflection point is at 3 hours, with a thickness of 48 μm reaching 50% of the substrate depth, at which time the concentration gradient is optimal, while at 4 hours, the Kirkendall effect leads to micropores, weakening the effective hardened layer. The energy consumption increases (45→60 MJ / m 2) Surface roughness increased (Ra 0.15→0.25 μm) because of 4 hours group surface appeared nanoscale sputtering pit, at the same time grain boundary nitrogen-rich area oxidation, leading to the increase of Ra value.

[0041] Comparative Example 1 A conventional high-temperature nitriding process is provided, without plasma / catalyst, high-temperature conditions, suitable for the field of chemical surface treatment of metals, including the following implementation content: Experimental purposes: A conventional high-temperature nitriding process is provided, without plasma / catalyst, high-temperature conditions, suitable for the field of chemical surface treatment of metals, including the following implementation content:

[0042] Experimental raw materials: 304 stainless steel sheet (50x50x5 mm, surface Ra≤0.8 μm), gas: ammonia (NH3, purity 99.99%).

[0043] Experimental steps: S1: Pretreatment, ultrasonic cleaning (ethanol, 10 min)→ alkali cleaning oil (10% NaOH, 60℃x5 min)→ water rinse→ drying; S2: furnace treatment, workpiece placed in nitriding tank→ vacuum extraction to 10 -1 Pa→ ammonia gas (flow rate 200 sccm) is introduced; S3: heating stage, from room temperature to 500±5℃ at a rate of 10℃ / min (same as Example 1 heating rate); S4: holding nitriding, maintain 500℃ constant temperature for 4 hours, the pressure in the tank is kept at normal pressure (101 kPa), ammonia decomposition rate is controlled at 25-35% (adjusted by flowmeter); S5: cooling treatment, close the ammonia→ furnace air cooling (cooling rate about 30℃ / min)→ 150℃ take out the workpiece (to avoid temper brittleness); S6: post-processing, measure hardness and case depth.

[0044] Experimental results: details are shown in Table 4.

[0045] Table 4: Test results of Comparative Example 1

[0046] Comparative Example 1 provides a conventional high-temperature nitriding process, the hardness is significantly reduced, no plasma activation leads to incomplete ammonia dissociation, nitrogen supply is insufficient; high temperature causes grain coarsening, Hall-Petch effect is weakened; structural defects, coarse ε-Fe 2-3N phase and porosity form stress concentration, further weaken the effective hardness. The thickness of the layer decreases, although the high temperature increases the apparent diffusion rate, but the surface nitrogen potential gradient is too large, the lack of catalyst reduces the diffusion activation energy, and the nitrogen atoms cannot penetrate into the matrix. Energy consumption increases by 50% (75 MJ / m 2 ), 500°C high temperature makes the radiation heat loss high, and the decomposition of ammonia gas needs to absorb a lot of heat, so the energy consumption increases sharply. The deformation rate rises to 7.5%, and the γ phase changes to α phase during the cooling process from 500°C to 150°C, which induces shear stress; the difference in thermal expansion coefficient between the matrix and the infiltrated layer produces a large tensile stress when the temperature drops suddenly; the loose structure on the surface becomes a crack source, and the crack propagates along the grain boundary, resulting in the warping of the workpiece.

[0047] Example 1 provides a method for low-temperature nitriding of metal surface using plasma catalysis. Iron nanoparticles are used as catalysts to treat 304 stainless steel by plasma catalytic nitriding at a low temperature of 300°C. The experimental results show that the hardness of the treated material reaches 1250 HV, the thickness of the infiltrated layer is 48 μm, the energy consumption is 52 MJ / m 2 , and the deformation rate is only 0.8%. The significant improvement in hardness is attributed to the "plasma-catalysis synergistic effect" of iron nanoparticles: high-frequency plasma dissociates nitrogen gas into highly active nitrogen ions (N + ), while the nano-iron catalyst reduces the reaction activation energy, promotes the penetration of nitrogen atoms in the γ-Fe lattice, and forms a dense nitride layer, which directly enhances the hardness. The thickness of the infiltrated layer reaches 48 μm due to the optimization of low-temperature diffusion kinetics: the plasma electric field increases the kinetic energy of nitrogen ions, breaking through the low-temperature diffusion barrier; at the same time, the "nitrogen atom overflow effect" is formed on the surface of the catalyst, the diffusion coefficient is improved, and low-temperature rapid diffusion is achieved. The energy consumption is reduced due to the triple energy-saving mechanism: the ionization efficiency of high-frequency plasma is improved at low pressure; the catalyst reduces the hydrogen dissociation side reaction; and the thermal radiation loss is reduced by 50% at low temperature. The low deformation rate is due to the combined action of "low-temperature stress suppression" and "gradient cooling": the thermal stress induced by the difference in thermal expansion coefficient at 300°C is reduced, and the martensite phase transition stress is avoided by gradient cooling, resulting in low residual stress.

[0048] Example 2 uses nickel nanoparticles as catalysts to perform nitriding treatment under the same process parameters (300°C, 150 Pa, 3 hours). The experimental results show that the nickel catalyst group obtains higher hardness (1300 HV) and infiltrated layer thickness (52 μm), the energy consumption remains 52 MJ / m 2 , and the deformation rate is 0.9%. The key to the hardness of the nickel catalyst group jumping to 1300 HV lies in the nano-composite strengthening induced by nickel catalysis, and high-density CrN nanocrystals and γ'-Fe4N phases are generated in the surface layer. Nickel nanoparticles (20 nm) form a stronger local electric field distortion in the plasma field due to their higher d-band electron density, which promotes the penetration of nitrogen ions (N +) and the lattice constant of nickel (0.352 nm) is more suitable for γ-Fe (0.364 nm), which reduces the interface energy barrier of nitrogen atom diffusion and accelerates the penetration of grain boundary, thus generating a thicker nitrogen-rich layer. The energy consumption is maintained at 52 MJ / m 2 The energy-saving effect is achieved by system optimization. The deformation rate of 0.9% is achieved by precise control of residual stress. Although there are slight Kirkendall vacancies in the nickel group, the accumulation of thermal stress is inhibited at low temperature, and the gradient cooling makes the residual stress stable at-200 MPa, which is lower than that of the iron group but still within the elastic limit of the material, avoiding the expansion of micro-cracks.

[0049] Example 3 studies the effect of different treatment times (2-4 hours) on nitriding. The experimental results show that the hardness of the 2-hour treatment group is 1150 HV, the layer thickness is 35 μm, the energy consumption is 45 MJ / m 2 , and the surface roughness is 0.15 μm; the hardness of the 4-hour treatment group is 1280 HV, the layer thickness is 55 μm, the energy consumption is 60 MJ / m 2 , and the surface roughness is 0.25 μm. With the extension of treatment time, the hardness increases in steps (1150→1280 HV). In the short-term treatment (2 hours), although the plasma catalysis quickly generates surface nitride, the nitrogen atoms have not fully diffused to the grain boundaries, resulting in low hardness. When the treatment time is extended to 3 hours (Example 1), the iron catalyst continuously provides a diffusion channel, and the nitrogen concentration gradient is optimized, forming a continuous hardened layer. The deep layer diffusion is saturated at 4 hours (55 μm thickness), but the Hall-Petch strengthening effect is weakened due to excessive grain growth and nitride coarsening, and the hardness increment is narrowed. The layer thickness increases (35→55 μm), and the actual thickness ratio of 2→4 hours is 35:55≈1.57 times, which is slightly higher than the theoretical value, due to the reduction of activation energy by the catalyst. The energy consumption increases (45→60 MJ / m 2 ) due to long-term high-frequency operation. The surface roughness increases (Ra 0.15→0.25 μm) because the 4-hour group has nano-scale sputtering pits on the surface, and the grain boundary nitrogen-rich area is oxidized.

[0050] Comparative Example 1 uses the traditional high-temperature nitriding process (500°C, without plasma / catalyst). The experimental results show that the hardness is only 900 HV, the layer thickness is 35 μm, the energy consumption is 75 MJ / m 2 , and the deformation rate is as high as 7.5%. The reason for the significant reduction in hardness is that the incomplete dissociation of ammonia gas caused by the absence of plasma activation results in a lack of nitrogen supply; high temperature induces grain coarsening, and the Hall-Petch effect is weakened; the organizational structure is defective, and the coarse ε-Fe 2-3N phase and porosity form stress concentration, further weaken effective hardness. The thickness of the layer decreases because the high temperature, although it increases the apparent diffusion rate, but the surface nitrogen potential gradient is too large, lack of catalyst to reduce the diffusion activation energy, nitrogen atoms can not penetrate the matrix. Energy consumption increased by 50% (75 MJ / m 2 ) is because the high temperature of 500 ℃ makes the radiation heat loss high, and the decomposition of ammonia gas needs to absorb a large amount of heat. The deformation rate rises to 7.5% because the γ phase is converted to α phase during the cooling process from 500 ℃ to 150 ℃, which induces shear stress; the difference in thermal expansion coefficient between the matrix and the infiltrated layer produces a large tensile stress when the temperature drops suddenly; the loose structure on the surface becomes a crack source, and the crack propagates along the grain boundary to cause the workpiece to warp.

[0051] Those skilled in the art can realize that the modules and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0052] In addition, each functional module in each embodiment of the present application can be integrated into one processing module, or each module can exist physically alone, or two or more modules can be integrated into one module.

[0053] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any skilled person in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0054] Finally: the above is only the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection of the present application.

Claims

1. A method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis, characterized in that... This includes the following steps: S1: Provide a metal workpiece and pre-treat the workpiece surface; S2: Place the workpiece in the plasma reactor; S3: A mixture of nitrogen and hydrogen is introduced, with a gas volume ratio of nitrogen:hydrogen = 3:1; S4: Introduce a catalyst into the reaction environment. The catalyst is nanoscale metal particles. S5: Start the high-frequency plasma generator and set the frequency to 13.56±0.5 MHz; S6: Adjust the reactor temperature to 280-320°C and the gas pressure to 100-200 Pa; S7: Maintain nitriding treatment for 2-4 hours; S8: After processing, turn off the plasma, cool to room temperature, and remove the workpiece.

2. The preparation method of the method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The metal workpiece in S1 is made of stainless steel, tool steel, or aluminum alloy.

3. The method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The workpiece pretreatment in S1 includes: ultrasonic cleaning to remove oil stains, followed by ion sputtering to clean the surface for 10-20 minutes.

4. The method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The gas flow rate of the mixed gas in S3 is 200-300 sccm (standard cubic centimeters per minute).

5. The method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The catalyst in S4 is selected from iron, nickel, cobalt or their alloy nanoparticles, with a particle size of 20-50 nm.

6. The preparation method of the method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 5, characterized in that, The catalyst is sprayed onto the surface of the workpiece in the form of a suspension with a thickness of 5-10 μm, and then dried.

7. The method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The power density of the high-frequency plasma generator in S5 is 0.5-1.0 W / cm². 2 .

8. The preparation method of the method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, During the nitriding process in S7, a DC pulse bias voltage of -100 to -300 V is applied.

9. The preparation method of the method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in claim 1, characterized in that, The cooling process in S8 adopts a gradient cooling method with a cooling rate of 5°C / min.

10. A method for low-temperature nitriding strengthening of metal surfaces using plasma catalysis as described in any one of claims 1-9, characterized in that, Further steps include surface inspection of the workpiece after treatment, and analysis of the diffusion layer using XRD or a hardness tester.

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