A confined enhanced plasma nitriding method and apparatus

Abstract

The application provides a confined enhanced plasma nitriding method and device, and relates to the technical field of metal material surface treatment. The nitriding method comprises the steps of pretreatment, etching, nitriding and cooling. The device comprises a chamber, an arc source unit, an auxiliary anode unit, a sample loading unit, a confined enhancement unit, a gas supply unit and a vacuum pumping unit. The confined shielding cover surrounds the arc source, the auxiliary anode and the sample holder to form a closed confined shielding space, and a negative bias voltage can be applied through an external power supply. The application constrains the diffusion volume of the plasma through the confined enhancement technology, greatly improves the concentration of the local plasma and active nitrogen particles, cooperates with the arc auxiliary discharge and the sample negative bias regulation, significantly accelerates the nitriding rate, effectively increases the nitriding layer depth and surface hardness, and the obtained nitriding layer is dense, uniform and firmly combined with the substrate. The application is suitable for efficient surface strengthening treatment of various metal materials such as stainless steel, and has outstanding technical advantages and industrial application value.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for metallic materials, and specifically to a confined enhanced plasma nitriding method and equipment. Background Technology

[0002] Nitriding is one of the key methods to improve the surface properties of metal components. It can significantly improve the surface hardness, wear resistance and corrosion resistance of materials, thereby extending the service life of parts and enhancing the reliability and operating efficiency of equipment. It has wide applications in industries such as machinery manufacturing, automobiles, aerospace, and mold making.

[0003] While traditional nitriding technology can achieve the aforementioned surface strengthening effects, it suffers from an extremely low nitriding rate, typically only 0.8-1.5 μm / h. This results in long processing cycles and high production costs, severely limiting its application in large-scale industrial production. To improve nitriding efficiency, plasma nitriding technology has been gradually developed and applied. Its comprehensive advantages, including high efficiency, energy saving, environmental friendliness, and low deformation, have made it an important process for surface strengthening of high-end components. Among these, arc-assisted plasma nitriding technology, by introducing arc discharge, can increase the nitriding rate to 4-5 μm / h, significantly shortening processing time, reducing production costs, and demonstrating promising prospects for industrial application.

[0004] However, existing arc-assisted plasma nitriding technology still has significant shortcomings: the depth of the nitrided layer on the surface of metal materials is limited, making it difficult to meet the needs of deep strengthening; at the same time, the surface hardness of the treated metal materials still fails to reach higher performance standards, making it unsuitable for applications with stringent surface performance requirements. These defects limit the further promotion and application of arc-enhanced plasma nitriding technology, becoming a key technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a confined enhanced arc-assisted plasma nitriding method and apparatus. The confined enhanced plasma nitriding method can not only significantly improve the depth and surface hardness of the nitrided layer on the surface of metal materials, but also has a high nitriding rate.

[0006] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a confined enhanced plasma nitriding method, comprising the following steps: S1. Pretreatment: After cleaning and drying, the metal sample is placed in the chamber of the confined enhanced plasma nitriding equipment and inside the confined shielding space formed by the confined shielding cover. The chamber is then evacuated. S2. Etching: After the vacuuming in step S1 is completed, inert gas is introduced into the chamber, and the arc source and auxiliary anode located in the confined shield are activated. At the same time, a negative bias voltage is applied to the metal sample, and a glow discharge is generated using arc-assisted glow discharge technology to perform plasma etching on the metal sample in step S1. S3, Nitriding: After the plasma etching in step S2 is completed, the inert gas is stopped, nitrogen-containing gas is introduced into the chamber, and the arc source and the auxiliary anode located in the confined shield are started. At the same time, pulsed negative bias voltages are applied to the metal sample and the confined shield respectively to perform confined enhanced arc assisted plasma nitriding treatment on the metal sample. S4. Cooling: After the confined enhanced arc assisted plasma nitriding treatment described in step S3 is completed, the chamber is cooled so that the metal sample is cooled to room temperature along with the chamber, thus obtaining a metal sample with a nitrided layer.

[0007] In one possible implementation, the vacuum level of the chamber after evacuation in step S1 is ≤2.0×10⁻⁶. 2 Pa.

[0008] In one possible implementation, the inert gas in step S2 is argon gas with a pressure of 0.3~0.4 Pa.

[0009] In one possible implementation, the etching time in step S2 is 10 to 120 minutes.

[0010] In one possible implementation, the current of the arc source in steps S2 and S3 is 70-150 A, and the current of the auxiliary anode is 30-70 A.

[0011] In one possible implementation, a chromium target, a titanium target, or a titanium-aluminum target is used as the arc source in steps S2 and S3.

[0012] In one possible implementation, the pulsed negative bias voltage in steps S2 and S3 is -20 V to -200 V.

[0013] In one possible implementation, the nitrogen-containing gas in step S3 is N2 or a mixture of N2 and H2, with a pressure of 1-1.5 Pa, the purity of the N2 being ≥99.99%, and the purity of the N2 and H2 mixture being ≥99.99%.

[0014] In one possible implementation, the temperature of the confined arc-assisted plasma nitriding treatment in step S3 is 300~500 °C.

[0015] In one possible implementation, the time for the confined enhanced arc-assisted plasma nitriding treatment in step S3 is 1 to 4 hours.

[0016] In one possible implementation, the nitriding layer in step S4 has a thickness of 7.3~31 μm and a hardness of 320~550 HV0.2.

[0017] In a second aspect, the present invention provides a confined enhanced plasma nitriding apparatus, comprising: A chamber is used to provide a closed reaction space; An arc source unit includes a protective arc source and an arc source DC power supply; the arc source is installed on the side wall of the chamber and is used to emit electrons, which collide with the working gas and ionize under the action of an electric field to generate arc plasma; the arc source DC power supply is located outside the chamber and is electrically connected to the arc source to supply power to the arc source. An auxiliary anode unit includes an auxiliary anode and an auxiliary anode DC power supply; the auxiliary anode is disposed opposite to the arc source and is mounted on the side wall of the chamber by a bracket for stabilizing and guiding arc discharge; the auxiliary anode DC power supply is disposed outside the chamber and electrically connected to the auxiliary anode to supply power to the auxiliary anode; The sample loading unit includes a sample holder and a pulsed DC power supply. The sample holder is disposed in the central region inside the chamber, and the pulsed DC power supply is disposed outside the chamber and electrically connected to the sample holder. It is used to apply a negative bias voltage to the sample to attract positive ions to bombard the sample surface. The confinement enhancement unit includes a confinement shield and a shield DC power supply; the confinement shield is disposed inside the chamber and surrounds the arc source, the auxiliary anode, and the sample holder to form a confinement shield space, which is used to limit the diffusion volume of the plasma and form a local discharge space; the shield DC power supply is disposed outside the chamber and is electrically connected to the confinement shield, which is used to apply a negative bias voltage to the confinement shield. A gas supply unit includes an air inlet pipe and a gas supply device; one end of the air inlet pipe penetrates the side wall of the chamber and enters its interior, and the other end of the air inlet pipe is connected to the gas supply device for supplying gas into the chamber. The vacuum pump unit includes an outlet and a vacuum pump. The outlet is located on the side wall of the chamber away from the inlet pipe. The vacuum pump is located outside the chamber and connected to the outlet, and is used to remove the gas inside the chamber.

[0018] In one possible implementation, the confined shield is spherical, cylindrical, or square, and the average distance between the inner wall of the confined shield and the sample surface is ≤15 cm.

[0019] In one possible implementation, the distance between the arc source and the auxiliary anode is 10-30 cm.

[0020] In one possible implementation, the arc source unit further includes a baffle that is movably disposed in front of the arc source for shielding the target surface of the arc source when it is not in operation or when isolation is required.

[0021] The positive and progressive effects of this invention are as follows: This invention provides a confined enhanced plasma nitriding method and equipment, which addresses the technical pain points of existing plasma nitriding processes, such as slow nitriding rate, insufficient nitrided layer depth, low surface hardness, uneven plasma distribution, and poor process stability. Through structural innovation and process co-design, it achieves substantial progress in plasma nitriding technology. Its positive effects are mainly reflected in the following aspects: (1) The invention effectively confines the plasma through a confinement enhancement mechanism, significantly increasing the concentration of local plasma and active nitrogen particles. This breaks through the bottleneck of slow plasma nitriding rate in traditional plasma, significantly improving the efficiency of nitriding treatment on the surface of metal materials and achieving highly efficient surface strengthening.

[0022] (2) This invention effectively optimizes the microstructure of the nitrided layer by coordinating and controlling the entire process of pretreatment, etching, nitriding and cooling, so that the thickness of the nitrided layer and the surface hardness are increased simultaneously. The nitrided layer is dense and uniform, and is firmly bonded to the substrate, taking into account both high hardness and good toughness, thus solving the problem of poor performance of traditional nitriding.

[0023] (3) This invention effectively optimizes the microstructure of the nitrided layer by coordinating and controlling the entire process of pretreatment, etching, nitriding and cooling, so that the thickness of the nitrided layer and the surface hardness are increased simultaneously. The nitrided layer is dense and uniform, and is firmly bonded to the substrate, taking into account both high hardness and good toughness, thus solving the problem of poor performance of traditional nitriding. Attached Figure Description

[0024] Figure 1 The image shows the GD-OES nitriding depth data of the nitrided stainless steels prepared in Examples 1-3 and Comparative Examples 1-2.

[0025] Figure 2 The image shows the indentation morphology of the nitrided stainless steel prepared in Example 1 after Vickers hardness testing.

[0026] Figure 3 The image shows the indentation morphology of the nitrided stainless steel prepared in Example 2 after Vickers hardness testing.

[0027] Figure 4 The image shows the indentation morphology of the nitrided stainless steel prepared in Comparative Example 1 after Vickers hardness testing.

[0028] Figure 5 The image shows the indentation morphology of the nitrided stainless steel prepared in Example 3 after Vickers hardness testing.

[0029] Figure 6 The image shows the indentation morphology of the nitrided stainless steel prepared in Comparative Example 2 after Vickers hardness testing.

[0030] Figure 7 This is a schematic diagram of a confined enhanced plasma nitriding device provided in Example 4.

[0031] Figure Labels 1-Cavity, 2-Arc source, 3-Arc source DC power supply, 4-Baffle, 5-Auxiliary anode, 6-Auxiliary anode DC power supply, 7-Sample rack, 8-Pulse DC power supply, 9-Confinement shield, 10-Shield DC power supply, 11-Inlet pipe, 12-Gas supply device, 13-Outlet, 14-Vacuum pump. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the present invention.

[0033] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0035] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a confined enhanced plasma nitriding method, comprising the following steps: S1. Pretreatment: After cleaning and drying, the metal sample is placed in the chamber of the confined enhanced plasma nitriding equipment and inside the confined shielding space formed by the confined shielding cover. The chamber is then evacuated. In step S1, the oil, oxide layer, dust, and adsorbed impurities on the surface of the metal sample are first removed by cleaning and drying to prevent impurities from hindering the adsorption and diffusion of nitrogen atoms. At the same time, residual moisture is removed to prevent byproducts from being generated during the plasma reaction and contaminating the nitriding layer, thus ensuring the bonding force and purity of the nitriding layer with the substrate. Then, the chamber is evacuated to remove air (especially oxygen) from the chamber, preventing secondary oxidation of the metal sample surface at high temperatures. This also provides a clean and low-pressure reaction environment for plasma discharge, ensuring the efficiency of subsequent gas ionization and plasma stability.

[0036] S2. Etching: After the vacuuming in step S1 is completed, inert gas is introduced into the chamber, and the arc source and auxiliary anode located in the confined shield are activated. At the same time, a negative bias voltage is applied to the metal sample, and a glow discharge is generated using arc-assisted glow discharge technology to perform plasma etching on the metal sample in step S1. In step S2, high-energy inert gas plasma is generated by arc-assisted glow discharge to bombard the surface of the metal sample, further removing the residual oxide layer and impurities on its surface. At the same time, the surface is micro-roughened to increase its specific surface area, form more active sites, and significantly improve the adsorption efficiency of nitrogen atoms on its surface. A negative bias voltage is applied to the metal sample to attract positive plasma ions to accelerate the bombardment of the surface, enhance the etching depth and uniformity, and put the surface of the metal sample in a highly active state, creating favorable conditions for the rapid penetration of nitrogen atoms.

[0037] S3, Nitriding: After the plasma etching in step S2 is completed, the inert gas is stopped, nitrogen-containing gas is introduced into the chamber, and the arc source and the auxiliary anode located in the confined shield are started. At the same time, pulsed negative bias voltages are applied to the metal sample and the confined shield respectively to perform confined enhanced arc assisted plasma nitriding treatment on the metal sample. In step S3, the synergistic effect of "confined shield + double negative bias + arc-enhanced discharge" overcomes the shortcomings of traditional nitriding from three aspects: plasma density, active nitrogen concentration, and nitrogen atom diffusion. After applying a negative bias to the confined shield, a local strong electric field is constructed, confining the plasma within the shielded space and significantly compressing the plasma diffusion volume. This increases the plasma density within the confined space several times, resulting in a higher concentration of active nitrogen particles (N...). +The concentration of nitrogen (N atoms) is significantly increased. High-concentration active nitrogen particles are rapidly adsorbed on the sample surface, forming a high-nitrogen surface layer. This provides an extremely high concentration gradient for nitrogen atoms to diffuse into the matrix, directly accelerating the diffusion rate of nitrogen atoms and providing a sufficient nitrogen source for the large-scale generation of high-hardness nitrides. The arc source and auxiliary anode discharge in synergy, generating high-energy electrons that efficiently ionize nitrogen-containing gas, significantly improving the generation efficiency of active nitrogen particles and providing a continuous and strong driving force for the nitriding reaction. At the same time, the auxiliary anode guides the arc discharge, optimizing the spatial distribution of plasma, allowing nitrogen atoms to uniformly penetrate into the sample surface, ensuring the uniformity of the nitrided layer thickness and hardness. The negative bias voltage of the sample attracts high-energy nitrogen ions to accelerate and bombard the surface, directly injecting nitrogen atoms into the sample surface layer. At the same time, a large number of crystal defects are generated. These defects act as "fast channels" for nitrogen atom diffusion, further increasing the diffusion rate of nitrogen atoms and deepening the nitrided layer. The defect network generated by ion bombardment reduces the diffusion activation energy of nitrogen atoms in the matrix, enabling nitrogen atoms to penetrate into the interior more quickly and form a thicker nitrided layer in the same time. At the same time, it promotes the uniform precipitation of high-hardness nitrides within the nitrided layer.

[0038] S4. Cooling: After the confined enhanced arc assisted plasma nitriding treatment described in step S3 is completed, the chamber is cooled so that the metal sample is cooled to room temperature along with the chamber, thus obtaining a metal sample with a nitrided layer.

[0039] In step S4, the sample is cooled to room temperature in a vacuum state to prevent the high-temperature sample from contacting the air and causing oxidation of the nitrided layer, thus maintaining the fine and uniform distribution of the nitride phase and ensuring high hardness and good toughness.

[0040] In summary, the confined enhanced plasma nitriding method provided by this invention, through the synergy of pretreatment, etching, confined nitriding and cooling, especially the use of confined shielding and double negative bias technology during the nitriding process, achieves significant improvements in nitriding layer depth, surface hardness and nitriding rate from multiple dimensions such as surface cleanliness, plasma density, active nitrogen concentration and nitrogen atom diffusion driving force.

[0041] In one possible implementation, the vacuum level of the chamber after evacuation in step S1 is ≤2.0×10⁻⁶. 2 Pa. Vacuum degree ≤ 2.0 × 10⁻⁶ 2 Pa can effectively prevent secondary oxidation of metal samples in a high-temperature plasma environment, ensuring the purity of the nitriding layer and its adhesion to the substrate; at the same time, it provides ideal conditions for subsequent stable and efficient arc discharge and plasma generation, preventing impurity gases from interfering with the ionization process.

[0042] In one possible implementation, the inert gas in step S2 is argon, with a pressure of 0.3~0.4 Pa. Argon is chemically stable, does not react with the sample or chamber, and is an ideal plasma carrier; moreover, it readily ionizes to form high-energy Ar. + Ions can effectively bombard the sample surface; a pressure range of 0.3~0.4 Pa can effectively maintain a stable glow discharge and ensure plasma density.

[0043] In one possible implementation, the etching time in step S2 is 10-120 min. An etching time of 10-120 min ensures that surface contaminants and oxide layers are removed, achieving sufficient activation, while avoiding unnecessary material loss and time waste caused by over-etching, thus achieving a better balance between cleaning effect and process efficiency.

[0044] In one possible implementation, the current of the arc source in steps S2 and S3 is 70-150 A, and the current of the auxiliary anode is 30-70 A. The 70-150 A current of the arc source and the 30-70 A current of the auxiliary anode provide stable and sufficient energy to the arc source and auxiliary anode, ensuring the generation of high-density, high-energy arc plasma, efficiently ionizing the working gas, and providing a strong driving force for etching and nitriding.

[0045] In one possible implementation, a chromium target, titanium target, or titanium-aluminum target is used as the arc source in steps S2 and S3. Chromium, titanium, and titanium-aluminum metal targets can generate metal ions during the discharge process, exhibiting high sputtering yield and good conductivity, and can produce stable, high-density argon plasma. These ions can combine with nitrogen atoms to form extremely hard metal nitrides (such as CrN and TiN) on the sample surface, which is beneficial for further improving the performance of the nitriding layer.

[0046] In one possible implementation, the pulsed negative bias voltage in steps S2 and S3 is -20 V to -200 V. This pulsed negative bias voltage range of -20 V to -200 V provides a controllable driving force for ion bombardment, effectively attracting ions to activate the surface and promoting diffusion.

[0047] In one possible implementation, the nitrogen-containing gas in step S3 is N2 or an N2 / H2 mixture, with a pressure of 1-1.5 Pa. The purity of the N2 is ≥99.99%, and the purity of the N2 / H2 mixture is ≥99.99%. Using high-purity (≥99.99%) N2 or N2 / H2 mixture ensures the purity of the nitrogen source and prevents impurities from being incorporated into the nitriding layer and affecting its performance. In the N2 / H2 mixture, N2 is the main nitrogen source, and H2, as a reducing gas, can effectively remove the oxide layer on the sample surface while inhibiting the formation of brittle phases in the nitriding layer and improving its toughness. The pressure range of 1-1.5 Pa ensures that the nitrogen-containing gas is fully ionized to form a high concentration of active nitrogen particles, while maintaining a stable discharge state, ensuring that the nitriding reaction proceeds efficiently and uniformly.

[0048] In one possible implementation, the temperature of the confined arc-assisted plasma nitriding treatment in step S3 is 300~500 ℃. The temperature range of 300~500 ℃ is highly compatible with the confined arc-assisted plasma nitriding process of the present invention, which can achieve a balance between high hardness and good toughness while ensuring the density, uniformity and bonding strength with the substrate of the nitrided layer.

[0049] In one possible implementation, the confined arc-assisted plasma nitriding treatment in step S3 takes 1 to 4 hours. The nitriding time of 1 to 4 hours can be adjusted according to the target nitrided layer thickness and performance requirements, ensuring both nitriding depth and hardness while also considering production efficiency.

[0050] In one possible implementation, the nitrided layer in step S4 has a thickness of 7.3~31 μm and a hardness of 320~550 HV0.2. The thicker nitrided layer of 7.3~31 μm can significantly extend the wear resistance and corrosion resistance life of the metal parts; the higher surface hardness of 320~550 HV0.2 can effectively improve the wear resistance and fatigue resistance of the material, enabling the treated metal parts to meet more stringent working conditions.

[0051] In a second aspect, the present invention provides a confined enhanced plasma nitriding apparatus, comprising: A chamber is used to provide a closed reaction space; An arc source unit includes a protective arc source and an arc source DC power supply; the arc source is installed on the side wall of the chamber and is used to emit electrons, which collide with the working gas and ionize under the action of an electric field to generate arc plasma; the arc source DC power supply is located outside the chamber and is electrically connected to the arc source to supply power to the arc source. An auxiliary anode unit includes an auxiliary anode and an auxiliary anode DC power supply; the auxiliary anode is disposed opposite to the arc source and is mounted on the side wall of the chamber by a bracket for stabilizing and guiding arc discharge; the auxiliary anode DC power supply is disposed outside the chamber and electrically connected to the auxiliary anode to supply power to the auxiliary anode; The sample loading unit includes a sample holder and a pulsed DC power supply. The sample holder is disposed in the central region inside the chamber, and the pulsed DC power supply is disposed outside the chamber and electrically connected to the sample holder. It is used to apply a negative bias voltage to the sample to attract positive ions to bombard the sample surface. The confinement enhancement unit includes a confinement shield and a shield DC power supply; the confinement shield is disposed inside the chamber and surrounds the arc source, the auxiliary anode, and the sample holder to form a confinement shield space, which is used to limit the diffusion volume of the plasma and form a local discharge space; the shield DC power supply is disposed outside the chamber and is electrically connected to the confinement shield, which is used to apply a negative bias voltage to the confinement shield. A gas supply unit includes an air inlet pipe and a gas supply device; one end of the air inlet pipe penetrates the side wall of the chamber and enters its interior, and the other end of the air inlet pipe is connected to the gas supply device for supplying gas into the chamber. The vacuum pump unit includes an outlet and a vacuum pump. The outlet is located on the side wall of the chamber away from the inlet pipe. The vacuum pump is located outside the chamber and connected to the outlet, and is used to remove the gas inside the chamber.

[0052] This invention provides a confined enhanced plasma nitriding device that, through the physical constraint of a confined shield and the electrostatic constraint of electrons by the applied negative bias voltage, concentrates highly active plasma generated by arc discharge around a metal sample at a high density. This significantly increases the flux of active nitrogen particles bombarding the metal sample surface, resulting in a surge in the number of nitrogen atoms penetrating the metal sample per unit time, thereby increasing the average nitriding rate to several times that of conventional techniques. Under the continuous, powerful bombardment and diffusion drive of high-density plasma, nitrogen atoms can diffuse into the metal matrix more rapidly and deeply. This device can easily prepare a thicker, more effective nitrided layer, solving the problems of shallow nitriding layers and insufficient hardening depth in conventional techniques. Due to the higher concentration of nitrogen solid solution and a denser strengthening phase obtained on the surface, the surface hardness of the workpiece treated by this device is significantly improved. At the same time, the high-density and uniform plasma environment is conducive to the formation of a uniformly structured, gently gradient nitrided layer, and also helps to simultaneously improve the wear resistance, corrosion resistance, and fatigue strength of the nitrided layer. Furthermore, the confined enhancement unit structure of the equipment is relatively independent, allowing for easy integration into existing arc-enhanced or conventional plasma nitriding equipment without major modifications to the main unit. This enables existing production lines to undergo technological upgrades at a lower cost. The significant increase in nitriding rate directly shortens the process cycle and reduces energy consumption and labor time per unit. Simultaneously, higher nitriding efficiency means that more workpieces can be processed or better performance can be achieved in the same amount of time, which is beneficial for improving production efficiency and capacity.

[0053] In one possible implementation, the confined shield is spherical, cylindrical, or square, and the average distance between the inner wall of the confined shield and the sample surface is ≤15 cm. The spherical, cylindrical, or square confined shield can flexibly adapt to the chamber structure and the installation of internal components; the average distance between the inner wall and the sample surface is ≤15 cm, ensuring that the plasma is effectively confined within the confined space, preventing diffusion, significantly increasing the plasma density around the sample, and ensuring uniform plasma distribution for consistent nitriding effects.

[0054] In one possible implementation, the distance between the arc source and the auxiliary anode is 10-30 cm. This distance range of 10-30 cm allows the arc source and auxiliary anode to work together efficiently, stably guiding the arc discharge and ensuring the generation of uniform, high-density arc plasma, providing stable energy support for subsequent etching and nitriding.

[0055] In one possible implementation, the arc source unit further includes a baffle movably disposed in front of the arc source to shield the target surface of the arc source when it is not in operation or when isolation is required. The movable baffle shielding the arc source target surface when not in operation or during isolation effectively prevents impurity deposition and sputtering damage to the target surface, protects the arc source's performance stability, and extends its service life.

[0056] The above-described embodiments can be combined in any way to obtain the embodiments of this application.

[0057] The technical solution of the present invention will be further described below with reference to specific embodiments and comparative examples. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0058] Example 1 This embodiment provides a confined enhanced plasma nitriding method, including the following steps: S1. Pretreatment: Place the 304 stainless steel disc in a beaker containing cleaning solution and put it into an ultrasonic cleaner. First, ultrasonically clean it in acetone for 15 minutes to remove oil and organic contaminants; then transfer it to anhydrous ethanol for 10 minutes to replace residual acetone and further clean it. Immediately after cleaning, dry the surface of the 304 stainless steel disc with high-purity nitrogen. Then, place the 304 stainless steel disc in an 80 ℃ oven for 5 minutes to ensure thorough removal of adsorbed moisture and residual solvent. Using clean tweezers, place the dried 304 stainless steel disc horizontally on the sample holder in the chamber. Ensure good contact between the 304 stainless steel disc and the sample holder to guarantee the effectiveness of subsequent bias application. Close and lock the chamber door to ensure its airtightness. Turn on the mechanical pump to perform a rough evacuation of the chamber. When the chamber pressure drops to about 5 Pa, turn on the molecular pump and continue evacuating until the chamber pressure is below 2.0 × 10⁻⁶ Pa. -2 Pa.

[0059] S2, Etching: Maintaining a base vacuum of <2.0×10⁻⁶ -2Under the condition of Pa, high-purity argon gas (Ar, purity ≥99.999%) is introduced into the chamber through a mass flow controller. By adjusting the inlet and outlet valves, the working pressure in the chamber is dynamically balanced and stabilized at 0.3 Pa. A chromium (Cr) target is selected as the cathode for the arc source. First, the pulsed DC power supply is turned on to apply an initial -400 V DC pulse base negative bias voltage to the 304 stainless steel disc, which is used to strongly attract argon ions to accelerate and bombard the sample surface. Subsequently, the auxiliary anode DC power supply and the arc source DC power supply are turned on sequentially or simultaneously. The output current of the arc source DC power supply is set to 150 A, and the current of the auxiliary anode DC power supply is set to 70 A. Under the above parameters, the high-density argon plasma generated by the arc discharge is excited in the chamber. Due to the application of a high base negative bias voltage, a strong sheath electric field is formed on the surface of the 304 stainless steel disc. Argon ions gain high kinetic energy in the sheath electric field and bombard the sample surface perpendicularly. Through momentum transfer, the argon ions sputter contaminant atoms and some matrix atoms from the 304 stainless steel disc, which are then removed by the vacuum system. The 304 stainless steel disc was subjected to plasma etching cleaning for 120 minutes using the above parameters to remove surface contaminants and activate the disc.

[0060] S3. Nitriding: After etching in step S2, the argon gas path is shut off, and a high-purity nitrogen-hydrogen mixture is introduced into the chamber through a mass flow controller. The N2 purity is ≥99.999%, the H2 purity is ≥99.999%, and the mixing ratio is N2:H2=3:1. The hydrogen in the mixture reduces any trace oxides that may be generated and promotes nitrogen activity. The inlet and outlet valves are adjusted to precisely stabilize the working pressure in the chamber at 1 Pa. The DC power supply for the arc source (150 A) and the DC power supply for the auxiliary anode (70 A) are kept on to maintain a stable arc discharge between the cathode (Cr target) and the auxiliary anode. The bias voltage of the pulsed DC power supply applied to the sample holder is adjusted to -100 V, and the nitriding temperature is set to 500 °C. Under the combined action of the arc discharge and the negative bias voltage of the substrate, N2 and H2 gases are largely ionized and dissociated, forming a nitrogen-rich mixture in the chamber. + N 2+ H +Highly reactive plasma containing active nitrogen atoms was used. The arc source, auxiliary anode, and sample holder were all located within a confined shield. The DC power supply to the shield was activated, applying a -50 V DC negative voltage to the confined shield. The physical enclosure of the confined shield primarily confined the plasma within a limited space around the 304 stainless steel disc, reducing the radial loss of active particles. The negative voltage on the shield created an electrostatic barrier that repelled electrons, confining more high-energy electrons to the vicinity of the 304 stainless steel disc, significantly increasing the probability of collisional ionization between electrons and neutral nitrogen molecules in this region. The synergistic effect of these two effects significantly improved the plasma density, nitrogen active particle flux, and ion bombardment flux on the surface of the 304 stainless steel disc, and also greatly increased the nitriding rate and nitrided layer thickness. Under these parameters, confined enhanced arc-assisted plasma nitriding treatment was performed for 3 hours.

[0061] S4. Cooling: After nitriding in step S3, turn off the DC power supply to the shield, pulse DC power supply, auxiliary anode DC power supply, and arc source DC power supply, and shut off the gas path of the nitrogen-hydrogen mixture. Start the furnace cooling water circulation system integrated into the vacuum chamber wall. Cooling water flows through the chamber jacket to cool the high-temperature chamber wall and internal space. Throughout the cooling process, the vacuum pumping system continues to operate to maintain a high vacuum state within the chamber, preventing the high-temperature 304 stainless steel discs from contacting air and undergoing surface oxidation, which would damage the newly formed nitrided layer. The temperature inside the chamber is monitored in real time using thermocouples installed within the chamber. Continuous cooling water circulation continues until the monitored temperature drops to 50°C, allowing the 304 stainless steel discs to cool naturally to near room temperature in a vacuum environment. The 304 stainless steel discs are then removed, completing the confined enhanced arc-assisted plasma nitriding treatment of the 304 stainless steel discs, resulting in nitrided stainless steel.

[0062] Example 2 This embodiment provides a confined enhanced plasma nitriding method, including the following steps: S1. Pretreatment: Same as in Example 1.

[0063] S2, Etching: Maintaining a base vacuum of <2.0×10⁻⁶ -2Under the condition of Pa, high-purity argon gas (Ar, purity ≥99.999%) is introduced into the chamber through a mass flow controller. By adjusting the inlet and outlet valves, the working pressure in the chamber is dynamically balanced and stabilized at 0.4 Pa. A titanium target is selected as the cathode for the arc source. First, the pulsed DC power supply is turned on to apply an initial -100 V DC pulse base negative bias voltage to the 304 stainless steel disc, which is used to strongly attract argon ions to accelerate and bombard the sample surface. Subsequently, the auxiliary anode DC power supply and the arc source DC power supply are turned on sequentially or simultaneously. The output current of the arc source DC power supply is set to 70 A, and the current of the auxiliary anode DC power supply is set to 30 A. Under the above parameters, the high-density argon plasma generated by the arc discharge is excited in the chamber. Due to the application of a high base negative bias voltage, a strong sheath electric field is formed on the surface of the 304 stainless steel disc. Argon ions gain high kinetic energy in the sheath electric field and bombard the sample surface perpendicularly. Through momentum transfer, the argon ions sputter contaminant atoms and some matrix atoms from the 304 stainless steel disc, which are then removed by the vacuum system. The 304 stainless steel disc was subjected to plasma etching cleaning for 10 minutes using the above parameters to remove surface contaminants and activate the disc.

[0064] S3, Nitriding: After etching in step S2, the argon gas path is shut off, and high-purity nitrogen gas (N2 purity ≥ 99.999%) is introduced into the chamber through a mass flow controller. The inlet and outlet valves are adjusted to precisely stabilize the working pressure in the chamber at 1.2 Pa. The DC power supply for the arc source (70 A) and the DC power supply for the auxiliary anode (30 A) are kept on to maintain a stable arc discharge between the cathode (Cr target) and the auxiliary anode. The pulsed DC power supply applied to the sample holder is maintained at -100 V, and the nitriding temperature is set to 300 °C. The arc source, auxiliary anode, and sample holder are all located within a confined shield. The DC power supply for the shield is activated, applying a -100 V negative DC voltage to the confined shield. Under these parameters, confined enhanced arc-assisted plasma nitriding treatment is performed for 2 hours. S4. Cooling: Same as in Example 1.

[0065] Example 3 This embodiment provides a confined enhanced plasma nitriding method, including the following steps: S1. Pretreatment: Same as in Example 1.

[0066] S2, Etching: Maintaining a base vacuum of <2.0×10⁻⁶ -2Under the condition of Pa, high-purity argon gas (Ar, purity ≥99.999%) is introduced into the chamber through a mass flow controller. By adjusting the inlet and outlet valves, the working pressure in the chamber is dynamically balanced and stabilized at 0.4 Pa. A titanium-aluminum target is selected as the cathode of the arc source. First, the pulsed DC power supply is turned on to apply an initial -100 V DC pulse base negative bias voltage to the 304 stainless steel disc, which is used to strongly attract argon ions to accelerate and bombard the sample surface. Subsequently, the auxiliary anode DC power supply and the arc source DC power supply are turned on sequentially or simultaneously. The output current of the arc source DC power supply is set to 100 A, and the current of the auxiliary anode DC power supply is set to 50 A. Under the above parameters, the high-density argon plasma generated by the arc discharge is excited in the chamber. Due to the application of a high base negative bias voltage, a strong sheath electric field is formed on the surface of the 304 stainless steel disc. Argon ions gain high kinetic energy in the sheath electric field and bombard the sample surface perpendicularly. Through momentum transfer, the argon ions sputter contaminant atoms and some matrix atoms from the 304 stainless steel disc, which are then removed by the vacuum system. The 304 stainless steel discs were subjected to plasma etching cleaning for 60 minutes using the above parameters to remove surface contaminants and achieve activation.

[0067] S3. Nitriding: After etching in step S2, shut off the argon gas path and introduce a high-purity nitrogen-hydrogen mixture into the chamber via a mass flow controller. The N2 purity is ≥99.999%, the H2 purity is ≥99.999%, and the mixing ratio is N2:H2=4:1. The hydrogen in the mixture reduces any trace oxides that may be generated and promotes nitrogen activity. Adjust the inlet and outlet valves to precisely stabilize the working pressure in the chamber at 1.2 Pa. Keep the arc source DC power supply (100 A) and the auxiliary anode DC power supply (50 A) on to maintain a stable arc discharge between the cathode (Cr target) and the auxiliary anode. Maintain the pulsed DC power supply applied to the sample holder at -100 V and set the nitriding temperature to 400 ℃. The arc source, auxiliary anode, and sample holder are all located within a confined shield. Activate the shield's DC power supply to apply a -200 V negative DC voltage to the confined shield. Under the above parameters, confined enhanced arc-assisted plasma nitriding treatment was performed for 2 hours.

[0068] S4. Cooling: Same as in Example 1.

[0069] Comparative Example 1 This comparative example provides a confined enhanced plasma nitriding method without external applied voltage, comprising the following steps: S1. Pretreatment: Same as in Example 1.

[0070] S2, Etching: Same as in Example 1.

[0071] S3, Nitriding: After etching in step S2, the argon gas path is shut off, and a high-purity nitrogen-hydrogen mixture is introduced into the chamber through a mass flow controller. The N2 purity is ≥99.999%, the H2 purity is ≥99.999%, and the mixing ratio is N2:H2=3:1. The hydrogen in the mixture reduces any trace oxides that may be generated and promotes the activity of nitrogen. The inlet and outlet valves are adjusted to precisely stabilize the working pressure in the chamber at 1 Pa. The DC power supply for the arc source (150 A) and the DC power supply for the auxiliary anode (70 A) are kept on to maintain a stable arc discharge between the cathode (Cr target) and the auxiliary anode. The pulsed DC power supply applied to the sample holder is maintained at -400 V, and the nitriding temperature is set to 500 °C. The arc source, auxiliary anode, and sample holder are all located within a confined shield, but a negative voltage of -0 V is applied to the confined shield, i.e., no external voltage is applied. Under the above parameters, arc-assisted plasma nitriding is performed for 2 hours.

[0072] S4. Cooling: Same as in Example 1.

[0073] Comparative Example 2 This comparative example provides a plasma nitriding method for an infinite-domain shield, comprising the following steps: S1. Pretreatment: Same as in Example 1.

[0074] S2, Etching: Same as in Example 1.

[0075] S3. Nitriding: After etching in step S2, the argon gas path is shut off, and a high-purity nitrogen-hydrogen mixture is introduced into the chamber through a mass flow controller. The N2 purity is ≥99.999%, the H2 purity is ≥99.999%, and the mixing ratio is N2:H2=3:1. The hydrogen in the mixture reduces any trace oxides that may be generated and promotes the activity of nitrogen. The inlet and outlet valves are adjusted to precisely stabilize the working pressure in the chamber at 1 Pa. The DC power supply for the arc source (150 A) and the DC power supply for the auxiliary anode (70 A) are kept on to maintain a stable arc discharge between the cathode (Cr target) and the auxiliary anode. The pulsed DC power supply applied to the sample holder is maintained at -400 V, the nitriding temperature is set to 500 °C, and an infinity shield is installed inside the chamber. Under these parameters, arc-assisted plasma nitriding is performed for 2 hours.

[0076] S4. Cooling: Same as in Example 1.

[0077] Example 4 This embodiment provides a confined enhanced plasma nitriding device, the structure of which is as follows: Figure 7 As shown, it includes chamber 1, arc source unit, auxiliary anode unit, sample loading unit, confinement enhancement unit, gas supply unit and vacuum unit.

[0078] Chamber 1 is a sealed stainless steel cavity with an inner wall treated to prevent splashing and resist corrosion, providing a clean and sealed reaction space. Multiple sealing interfaces are pre-installed on the side walls of Chamber 1 for installing wires and pipes for various functional components, ensuring vacuum sealing and electrical insulation. Thermocouples are also installed on the inner wall of Chamber 1 to monitor the temperature inside.

[0079] The arc source unit includes an arc source 2, an arc source DC power supply 3, and a baffle 4. The arc source 2 is a hot cathode arc source, installed on the side wall of the chamber 1, with the target surface of the arc source 2 facing the inside of the chamber 1. It is used to emit electrons, which collide and ionize with the working gas (high-purity Ar, nitrogen-containing gas) under the action of an electric field to generate arc plasma. The arc source DC power supply 3 is located outside the chamber 1 and is electrically connected to the arc source 2 through a high-voltage resistant wire, providing adjustable DC power supply to regulate the arc discharge intensity. The baffle 4 is made of high-temperature resistant metal and is movably installed in front of the arc source 2. It is opened and closed by a motor drive. In the non-working state or when isolation is required, it shields the target surface of the arc source 2 to prevent impurity deposition or damage from misoperation.

[0080] The auxiliary anode unit includes an auxiliary anode 5 and an auxiliary anode DC power supply 6. The auxiliary anode 5 is made of copper alloy and is fixed to the side wall of the chamber 1 opposite to the arc source 2 by an insulating bracket, maintaining a distance of 18 cm from the arc source 2. It is used to stabilize and guide the arc discharge and optimize the plasma spatial distribution. The auxiliary anode DC power supply 6 is located outside the chamber 1 and is electrically connected to the auxiliary anode 5 through a high-voltage resistant wire. It provides an adjustable DC positive bias voltage and works in conjunction with the arc source DC power supply 3 to form a stable discharge electric field.

[0081] The sample loading unit includes a sample holder 7 and a pulsed DC power supply 8. The sample holder 7 is a rigid stainless steel support, located in the central area inside the chamber 1, for loading stainless steel samples; the pulsed DC power supply 8 is located outside the chamber 1 and is electrically connected to the sample holder 7, applying an adjustable negative bias voltage to attract positive plasma ions to bombard the sample surface.

[0082] The confinement enhancement unit includes a confinement shield 9 and a shield DC power supply 10. The confinement shield 9 is a cylindrical structure located inside the chamber 1, with an average distance of 10 cm between its inner wall and the sample surface. It completely surrounds the arc source 2, auxiliary anode 5, and sample holder 7, forming a confinement shielding space that restricts plasma diffusion volume and increases plasma density around the sample. The shield DC power supply 10 is located outside the chamber 1 and is electrically connected to the confinement shield 9 via a high-voltage resistant wire. It applies an adjustable DC negative bias voltage to construct a confinement electric field and constrain plasma distribution.

[0083] The gas supply unit includes an inlet pipe 11 and a gas supply device 12. The inlet pipe 11 is made of stainless steel, with one end penetrating through the side wall of the chamber 1 and entering its interior, and the other end connected to the gas supply device 12 outside the chamber 1. The gas supply device 12 includes a high-purity argon cylinder, a high-purity nitrogen cylinder, a high-purity hydrogen cylinder, and corresponding flow control valves for accurately delivering the working gas.

[0084] The vacuum pumping unit includes an outlet 13 and a vacuum pump 14. The outlet is located on the side wall of chamber 1 away from the inlet pipe 11. The vacuum pump 14, consisting of a mechanical pump and a molecular pump, is connected to the outlet 13 and can pump the vacuum level of chamber 1 to 2.0 × 10⁻⁶. -2 Below Pa, a clean vacuum environment is provided for plasma discharge.

[0085] Performance Testing and Result Analysis The performance of the 304 stainless steel discs obtained by plasma nitriding treatment in Examples 1-3 and Comparative Examples 1-2 was tested using the following methods: Glow discharge emission spectroscopy (GD-OES) test: A glow discharge emission spectrometer (GDA 750HP) equipped with a depth profile mode was used. The discharge gas was high-purity argon (purity ≥99.999%); the discharge voltage was 600-800 V; and the discharge current was 20-40 mA.

[0086] Surface hardness test: Vickers hardness tester was used to measure the hardness of a 304 stainless steel disc.

[0087] Figure 1The graphs show GD-OES nitriding depth data for the nitrided stainless steels prepared in Examples 1-3 and Comparative Examples 1-2. The horizontal axis represents the distance extending from the surface of the nitrided stainless steel into the substrate, in micrometers (μm); the vertical axis represents the relative signal intensity of nitrogen (typically wt.%) measured by GD-OES at each corresponding depth. Higher values ​​indicate higher nitrogen content at that depth. Each curve in the graph shows the depth distribution of nitrogen concentration from the surface to the interior of the nitrided stainless steel. The curves generally show a decreasing trend, gradually decreasing from the highest value at the surface to the background level of the substrate. The depth at which the nitrogen concentration drops to near the substrate level is typically defined as the nitriding layer thickness. As shown in the curves in the figure, the nitriding time of the nitrided stainless steel in Example 1 was 2 hours, the nitrided layer thickness was 31 μm, and the nitriding rate was 15.5 μm / h; the nitriding time of the nitrided stainless steel in Example 2 was 2 hours, the nitrided layer thickness was 15.6 μm, and the nitriding rate was 7.8 μm / h; the nitriding time of the nitrided stainless steel in Example 3 was 2 hours, the nitrided layer thickness was 10.2 μm, and the nitriding rate was 5.1 μm / h; the nitriding time of the nitrided stainless steel in Comparative Example 1 was 2 hours, the nitrided layer thickness was 12.3 μm, and the nitriding rate was 6.15 μm / h; and the nitrided stainless steel in Comparative Example 2 was 2 hours, the nitrided layer thickness was 7.3 μm, and the nitriding rate was 3.65 μm / h.

[0088] The curve for Example 1 shows the highest value and the gentlest decay across the entire depth range. This indicates that the nitrided stainless steel in Example 1 not only has a high surface nitrogen concentration but also exhibits the strongest ability for nitrogen atoms to diffuse inward, resulting in the highest nitriding efficiency. The nitriding rates of Examples 1 and 2 are significantly higher than those of Comparative Examples 1 and 2, fully demonstrating the efficiency advantages of the present invention.

[0089] The difference in nitriding rates between Example 1 and Comparative Examples 1 and 2 directly reflects the fundamental differences in plasma density and nitrogen atom supply capacity between different technical solutions. Example 1 employed a "confined shield + applied -50 V negative voltage" solution. The shield physically confines the plasma, reducing the loss of active particles; the negative voltage on the shield repels electrons, confining them near the 304 stainless steel disc, significantly increasing local plasma density and ionization rate. The 304 stainless steel disc surface obtained the highest flux of highly active nitrogen particles, resulting in the strongest bombardment and penetration dynamics, thus achieving the highest surface concentration, deepest penetration, and highest efficiency. Comparative Example 1 used only a confined shield without applying voltage, exhibiting only a physical confinement effect and lacking the potential regulation to constrain electrons. The increase in plasma density was limited, therefore the nitriding effect was better than the unshielded Comparative Example 2, but far inferior to Example 1. Comparative Example 2 only used traditional arc-enhanced nitriding without a shield, resulting in free plasma diffusion, the lowest density, and the greatest loss of active nitrogen particles. Therefore, the nitrogen supply and penetration capacity were the weakest, the layer thickness was the shallowest, and the surface concentration was the lowest.

[0090] Figure 2 The image shows the indentation morphology of the nitrided stainless steel prepared in Example 1 after Vickers hardness testing. The clearly defined black rhomboid area in the image is a typical indentation formed by the diamond pyramid indenter pressing into the material surface under the test force during the Vickers hardness test. The uniformity and lack of skewness of the indentation indicate that the thickness and hardness distribution of the nitrided layer are uniform, and the process stability is good. The absence of cracks or peeling indicates that the nitrided layer is firmly bonded to the substrate, and no excessive internal stress was introduced during the nitriding process. The surface hardness of the nitrided stainless steel prepared in Example 1 was measured to be 550 HV0.2.

[0091] Figure 3 The image shows the indentation morphology of the nitrided stainless steel prepared in Example 2 after Vickers hardness testing. The image still shows a typical rhomboid indentation from Vickers hardness testing, but the diagonal length of the indentation is significantly greater than that of Example 1. The sharpness of the indentation edge is slightly inferior to that of Example 1, and slight "indentation edge blurring" is visible in some areas, reflecting that the density and uniformity of the nitrided layer in Example 2 are not as good as those in Example 1. This is directly related to insufficient plasma density and low nitrogen atom penetration efficiency. The surface hardness of the nitrided stainless steel prepared in Example 2 was measured to be 430 HV0.2.

[0092] Figure 4 The image shows the indentation morphology of the nitrided stainless steel prepared in Comparative Example 1 after Vickers hardness testing. The image shows a typical rhomboid indentation from the Vickers hardness test, but the diagonal length of the indentation is significantly longer than that of Example 1 and Example 2. The longer the diagonal of the indentation, the lower the hardness value. This indicates that the hardness of the nitrided layer in Comparative Example 1 is significantly lower than that of Example 1 and Example 2; the sharpness of the indentation edge is significantly inferior to that of Examples 1 and 2, with some areas showing "blurred indentation edges" or even slight edge chipping. This reflects that the density, uniformity, and adhesion to the substrate of the nitrided layer in Comparative Example 1 are inferior to the former two, which is directly related to insufficient plasma density, low nitrogen atom penetration efficiency, and insufficient nitride formation. The surface hardness of the nitrided stainless steel prepared in Comparative Example 1 was measured to be 400 HV0.2.

[0093] Figure 5The image shows the indentation morphology of the nitrided stainless steel prepared in Example 3 after Vickers hardness testing. The diagonal length of the indentation in Example 3 is significantly greater than that in Example 1, indicating that the hardness of the nitrided layer in Example 3 is lower than that in Example 1. The surface hardness of the nitrided stainless steel prepared in Example 3 was measured to be 320 HV0.2. On the one hand, the current of the arc DC power supply auxiliary anode DC power supply in Example 3 is lower than that in Example 1, resulting in low plasma generation efficiency, insufficient generation of active nitrogen particles, weak driving force for the nitriding reaction, and difficulty for nitrogen atoms to fully penetrate and form a high-hardness phase. On the other hand, since the voltage of the external shield in Example 3 is -200V, it forms a significant competition with the substrate bias voltage, resulting in insufficient diffusion depth of nitrogen atoms into the substrate, thinner nitrided layer, lower proportion of effective strengthening layer, and limited overall hardness performance.

[0094] Figure 6 The image shows the indentation morphology of the nitrided stainless steel prepared in Comparative Example 2 after Vickers hardness testing. The diagonal length of the indentation in Comparative Example 2 is significantly greater than that in Example 1, indicating that the hardness of the nitrided layer in Comparative Example 2 is lower than that in Example 1. The surface hardness of the nitrided stainless steel prepared in Comparative Example 2 was measured to be 350 HV0.2. This is directly related to insufficient plasma density, low nitrogen atom penetration efficiency, and incomplete nitride formation.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A confined-area enhanced plasma nitriding method, characterized in that, Includes the following steps: S1. Pretreatment: After cleaning and drying, the metal sample is placed in the chamber of the confined enhanced plasma nitriding equipment and inside the confined shielding space formed by the confined shielding cover. The chamber is then evacuated. S2. Etching: After the vacuuming in step S1 is completed, inert gas is introduced into the chamber, and the arc source and auxiliary anode located in the confined shield are activated. At the same time, a negative bias voltage is applied to the metal sample, and a glow discharge is generated using arc-assisted glow discharge technology to perform plasma etching on the metal sample in step S1. S3, Nitriding: After the plasma etching in step S2 is completed, the inert gas is stopped, nitrogen-containing gas is introduced into the chamber, and the arc source and the auxiliary anode located in the confined shield are started. At the same time, pulsed negative bias voltages are applied to the metal sample and the confined shield respectively to perform confined enhanced arc assisted plasma nitriding treatment on the metal sample. S4. Cooling: After the confined enhanced arc assisted plasma nitriding treatment described in step S3 is completed, the chamber is cooled so that the metal sample is cooled to room temperature along with the chamber, thus obtaining a metal sample with a nitrided layer.

2. The confined-area enhanced plasma nitriding method according to claim 1, characterized in that, The vacuum level of the chamber after evacuation in step S1 is ≤2.0×10⁻⁶. 2 Pa.

3. The confined-area enhanced plasma nitriding method according to claim 1, characterized in that, The inert gas mentioned in step S2 is argon, with a pressure of 0.3~0.4 Pa; And / or, the etching time in step S2 is 10~120 min.

4. The confined-area enhanced plasma nitriding method according to claim 1, characterized in that, In steps S2 and S3, the current of the arc source is 70-150 A, and the current of the auxiliary anode is 30-70 A. And / or, in steps S2 and S3, a chromium target, a titanium target, or a titanium-aluminum target is used as the arc source; And / or, the pulse negative bias voltage described in steps S2 and S3 is -20 V to -200 V.

5. The confined-area enhanced plasma nitriding method according to claim 1, characterized in that, The nitrogen-containing gas mentioned in step S3 is N2 or a mixture of N2 and H2, with a pressure of 1-1.5 Pa. The purity of the N2 is ≥99.99%, and the purity of the N2 and H2 mixture is ≥99.99%. And / or, the temperature of the confined enhanced arc assisted plasma nitriding treatment in step S3 is 300~500 ℃; And / or, the time for the confined enhanced arc-assisted plasma nitriding treatment in step S3 is 1~4 h.

6. The confined-area enhanced plasma nitriding method according to claim 1, characterized in that, The thickness of the nitrided layer in step S4 is 7.3~31 μm and the hardness is 320~550 HV0.

2.

7. A confined-area enhanced plasma nitriding device, characterized in that, include: Chamber (1) is used to provide a closed reaction space; The arc source unit includes a protective arc source (2) and an arc source DC power supply (3); the arc source (2) is installed on the side wall of the chamber (1) and is used to emit electrons, which collide with the working gas under the action of an electric field and ionize to generate arc plasma; the arc source DC power supply (3) is located outside the chamber (1) and is electrically connected to the arc source (2) to supply power to the arc source (2); An auxiliary anode unit includes an auxiliary anode (5) and an auxiliary anode DC power supply (6); the auxiliary anode (5) is disposed opposite to the arc source (2) and is mounted on the side wall of the chamber (1) by a bracket for stabilizing and guiding arc discharge; the auxiliary anode DC power supply (6) is disposed outside the chamber (1) and is electrically connected to the auxiliary anode (5) to supply power to the auxiliary anode (5); The sample loading unit includes a sample holder (7) and a pulsed DC power supply (8). The sample holder (7) is located in the central region inside the chamber (1). The pulsed DC power supply (8) is located outside the chamber (1) and is electrically connected to the sample holder (7). It is used to apply a negative bias voltage to the sample to attract positive ions to bombard the sample surface. The confinement enhancement unit includes a confinement shield (9) and a shield DC power supply (10); the confinement shield (9) is disposed inside the chamber (1) and surrounds the arc source (2), the auxiliary anode (5) and the sample holder (7) to form a confinement shield space, which is used to limit the diffusion volume of the plasma and form a local discharge space; the shield DC power supply (10) is disposed outside the chamber (1) and electrically connected to the confinement shield (9), which is used to apply a negative bias voltage to the confinement shield (9); The gas supply unit includes an air inlet pipe (11) and a gas supply device (12); one end of the air inlet pipe (11) penetrates the side wall of the chamber (1) and enters its interior, and the other end of the air inlet pipe (11) is connected to the gas supply device (12) for supplying gas into the chamber (1); The vacuum pump unit includes an outlet (13) and a vacuum pump (14). The outlet (13) is located on the side wall of the chamber (1) away from the inlet pipe (11). The vacuum pump (14) is located outside the chamber (1) and connected to the outlet (13) to remove gas from the chamber (1).

8. The confined enhanced plasma nitriding apparatus according to claim 7, characterized in that, The confinement shield (9) is spherical, cylindrical or square, and the average distance between the inner wall of the confinement shield (9) and the sample surface is ≤15 cm.

9. The confined enhanced plasma nitriding apparatus according to claim 7, characterized in that, The distance between the arc source (2) and the auxiliary anode (5) is 10~30 cm.

10. The confined enhanced plasma nitriding apparatus according to claim 7, characterized in that, The arc source (2) unit also includes a baffle (4), which is movably disposed in front of the arc source (2) to shield the target surface of the arc source (2) when it is not in operation or when isolation is required.

Images