CN106884136B - A kind of metal material surface nitriding deposition wear-resisting modified layer preparation method of duplex anti-friction - Google Patents

Abstract

The invention discloses a kind of preparation methods of metal material surface nitriding deposition wear-resisting modified layer of duplex anti-friction, belong to technical field of metal material surface treatment.After metal material workpiece surface is polished, is polished, is cleaned, it is placed on the anode potential platform in the nitriding furnace of hollow cathode discharge ion source, 10-15Pa is evacuated down in furnace, it is filled with ammonia and maintains operating air pressure 100-500Pa, 8h is nitrogenized in 440-520 DEG C of heat preservation, the nitriding deposition wear-resisting modified layer of duplex anti-friction is obtained after cooling.Sample is in anode potential, is not necessarily to ion bombardment, and nitrogen-atoms can also penetrate into austenitic matrix and form nitriding strengthening layer, effectively prevents edge effect problem, the hardness of whole surface is uniform；For metal works after anode nitriding, surface forms nitriding sedimentary, and properties of antifriction and wear resistance is obviously improved.

Description

A method for preparing a composite anti-friction and wear-resisting modified layer by nitriding deposition on the surface of a metal material

technical field

The invention belongs to the technical field of metal material surface treatment, and in particular relates to a preparation method of a metal material surface nitriding deposition compound anti-friction and wear-resisting modified layer.

Background technique

Due to the dense passivation film on the surface, austenitic stainless steel has excellent corrosion resistance in oxidizing media. However, due to its low surface hardness and poor wear resistance, it will fail due to severe wear in practical applications. Nitriding is widely used as an important engineering technology to improve the surface hardness and wear resistance of austenitic stainless steel. AISI 316 austenitic stainless steel is treated with low-temperature ion nitriding technology, the precipitation of nitrides is completely suppressed, and a single-phase nitrided layer is obtained. XRD shows that the diffraction peaks of the original austenite matrix shift to lower angles, forming new and wider diffraction peaks. This phase cannot be found in the ASTM card, so this new phase is called S phase. The discovery of S phase makes it possible to improve the hardness and wear resistance of stainless steel without reducing its original corrosion resistance.

In the conventional direct current ion nitriding (DCPN) process, ion bombardment can eliminate the surface passivation layer without depassivation treatment. However, due to the difference in electric field distribution due to the geometric shape of the workpiece, the degree of ion bombardment is different, which in turn causes the inhomogeneity of the surface temperature of the workpiece, and finally there is a difference in heat and mass transfer on the surface of the workpiece. AISI316L stainless steel has the problem of "edge effect" caused by the DCPN nitriding process. The hardness of the ring area is significantly higher than that of the center area, but the corrosion resistance is poor. The microstructure shows that the ring area is Cr2N phase, while the center area is S Mutually.

In order to overcome the shortcomings of DCPN technology, active screen ion nitriding technology (ASPN) was invented. In the nitriding process of ASPN, the workpiece is in a suspended state, and the ions no longer bombard the surface of the workpiece, so the problems of surface arcing and edge effects in DCPN are easily solved. ASPN technology has the advantages of simple equipment and convenient operation, and has become a hot spot in the field of ion nitriding research.

Contents of the invention

Aiming at the deficiencies of the conventional DC ion nitriding technology, the present invention provides a method for preparing a composite anti-friction and wear-resisting modified layer of nitriding deposition on the surface of metal materials, which is characterized in that it includes the following steps:

(1) Grinding and polishing the surface of the metal material workpiece, after cleaning with alcohol, place it on the anode potential platform in the hollow cathode discharge ion source nitriding furnace;

(2) Start the vacuum system to evacuate the nitriding furnace. When the vacuum in the furnace reaches 10-15Pa, fill the vacuum furnace with purified ammonia gas, so that the ammonia gas is evenly distributed in the entire nitriding furnace, and adjust The flow rate of ammonia gas keeps the pressure in the furnace at 100-500Pa;

(3) Turn on the power supply of the power supply system, and the ammonia gas in the furnace is ionized under the action of a high-voltage electric field to form NH _j ⁺ , N ⁺ and H ⁺ plasmas. After reaching the nitriding temperature, start to calculate the holding time;

(4) After the heat preservation is over, cut off the power supply and maintain the low pressure, let the workpiece cool with the furnace in an ammonia atmosphere, and leave the furnace when the temperature drops below 200°C to obtain a nitriding-deposited composite anti-friction and wear-resistant modified layer.

The metal material in step (1) is AISI304 austenitic stainless steel, which consists of: C 0.05wt%; Si0.80wt%; Mn 1.50wt%; Cr 17.5wt%; Ni 9.50wt%; i 0.011wt%; the balance is Fe.

In step (1), the hollow cathode discharge ion source nitriding furnace adopts a pulse power supply, the furnace wall is used as the anode, and the hollow stainless steel tube array is used as the discharge cathode, wherein the diameter of the hollow stainless steel tube is 8-10 mm.

The nitriding temperature in step (3) is 440-520° C., and the holding time is 8 hours.

The thickness of the nitriding-deposited composite friction-reducing and wear-resisting modified layer in step (4) is 6-16 μm.

During the nitriding process of the hollow cathode ion source, the reason for the formation of the nitriding layer on the metal surface is the sputtering of the reactive hollow cathode tube. In the reaction vacuum furnace, the dilute nitrogen-containing gas forms NH _j ⁺ , N ⁺ and H ⁺ plasma under the DC voltage between the hollow cathode tube and the anode, and these positive ions bombard the hollow under the acceleration of the voltage drop of the hollow cathode tube The surface of the cathode tube workpiece. The function of the energy generated by the bombardment is to heat the hollow cathode tube, promote the emission of secondary electrons on the surface of the workpiece, and generate the sputtering of the hollow cathode tube to eject carbon, nitrogen, oxygen, iron and other atoms from the surface of the workpiece. The sputtered Fe atoms can combine with the active N atoms near the workpiece surface (hollow cathode tube) to form FeN, and then deposit back to the surface of the hollow cathode tube under the action of backscattering. Under the action of ion bombardment and thermal activation, FeN will decompose as follows: FeN→Fe ₂ N→Fe ₃ N→Fe ₄ N, a large part of the decomposed N atoms will diffuse into the surface of the workpiece, and the other part of N atoms will be Return to the plasma region and continue to combine with the sputtered Fe atoms. The workpiece is placed on the anode potential stand, and the nitrided surface is composed of a large number of well-defined grains, the grain size of which is at the nanometer level, and these nitride grains originate from the sputtering of the hollow cathode tube.

The advantages of the present invention are: (1) the sample is at the anode potential, without ion bombardment, nitrogen atoms can also penetrate into the austenite matrix to form a nitrided strengthening layer, effectively avoiding the edge effect problem, and the hardness of the entire surface is uniform; ( 2) After austenitic stainless steel is anodized and nitrided, a nitriding deposit layer is formed on the surface, and the anti-friction and wear resistance properties are significantly improved, and the wear mechanism changes from a severe adhesion mechanism of the substrate to a slight oxidation and abrasive wear mechanism.

Description of drawings

Figure 1 SEM topography of the section of the nitrided layer at different temperatures;

Fig. 2 is the XRD patterns of AISI304 austenitic stainless steel matrix and the surface of nitriding samples at different temperatures;

Fig. 3 is the surface SEM image of the nitrided deposition composite anti-friction and wear-resisting modified layer;

Figure 4 is a comparison of microhardness between AISI304 austenitic stainless steel substrate and nitriding samples at different temperatures;

Fig. 5 is the friction coefficient-sliding time curve of AISI304 austenitic stainless steel substrate and samples with different nitriding temperatures;

Figure 6 is a three-dimensional morphology diagram of the wear marks of AISI304 austenitic stainless steel substrate and nitrided samples at different temperatures;

Figure 7 is the SEM morphology of the AISI304 austenitic stainless steel substrate and the wear marks of the nitriding samples at different temperatures.

Detailed ways

The present invention provides a method for preparing a composite friction-reducing and wear-resisting modified layer of nitriding deposition on the surface of a metal material. The present invention will be further described below in conjunction with the examples, but the present invention is not limited thereto.

Example 1

AISI304 austenitic stainless steel, its composition is (wt.%): 0.05C; 0.80Si; 1.50Mn; 17.5Cr; 9.50Ni; 0.013Mo; The surface of the sample was smoothed from coarse to fine with SiC sandpaper, and then polished. After cleaning with alcohol, place it on the anode potential platform in the nitriding furnace.

The furnace is evacuated to 15Pa, filled with ammonia gas and maintained at a working pressure of about 500Pa, the nitriding temperature is 440°C, the heat preservation nitriding treatment is carried out for 8 hours, and the furnace is cooled to below 200°C in an ammonia atmosphere to obtain a composite reduced nitriding deposition. The wear-resistant modified layer was observed by scanning electron microscope as shown in Figure 1(a). A nitrided layer with uniform thickness (about 6 μm) was prepared on the surface of AISI304 austenitic stainless steel, which has good corrosion resistance.

Example 2

AISI304 austenitic stainless steel, its composition is (wt.%): 0.05C; 0.80Si; 1.50Mn; 17.5Cr; 9.50Ni; 0.013Mo; The surface of the sample was smoothed from coarse to fine with SiC sandpaper, and then polished. After cleaning with alcohol, place it on the anode potential platform in the nitriding furnace.

The furnace is evacuated to 15Pa, filled with ammonia gas and maintained at a working pressure of about 500Pa, the nitriding temperature is 480°C, the heat preservation nitriding treatment is carried out for 8 hours, and the furnace is cooled to below 200°C in an ammonia atmosphere to obtain a composite reduced nitriding deposition. Wear-resistant modified layer, the cross-sectional morphology observed by scanning electron microscope is shown in Figure 1(b), the nitride layer on the surface of AISI304 austenitic stainless steel is thickened but accompanied by the precipitation of black phase.

Example 3

AISI304 austenitic stainless steel, its composition is (wt.%): 0.05C; 0.80Si; 1.50Mn; 17.5Cr; 9.50Ni; 0.013Mo; The surface of the sample was smoothed from coarse to fine with SiC sandpaper, and then polished. After cleaning with alcohol, place it on the anode potential platform in the nitriding furnace.

The furnace is evacuated to 15Pa, filled with ammonia gas and maintained at a working pressure of about 500Pa, the nitriding temperature is 520°C, the heat preservation nitriding treatment is carried out for 8 hours, and the furnace is cooled to below 200°C in an ammonia atmosphere to obtain the nitriding deposition composite reduction. The wear-resistant modified layer was observed by scanning electron microscope as shown in Figure 1(c). The thickness of the nitrided layer on the surface of AISI304 austenitic stainless steel reached 16 μm, and the proportion of black dot-like phase precipitation continued to expand.

Under dry friction conditions, UMT-3 friction and wear testing machine was used to investigate the friction and wear properties of the substrate and nitrided layer, and the friction pair was GCr15 ball (HRC 60) with Ф4mm. The friction and wear test conditions are: the normal load is 5N, the rotational speed is 300r/min, and the sliding time is 20min. The wear scar profile was measured by white light interferometer to evaluate the wear resistance of nitride layer.

Figure 2 is the XRD pattern of the AISI304 austenitic stainless steel substrate and the surface of the nitrided sample at different temperatures. The AISI304 austenitic stainless steel is mainly composed of austenite phases γ(111) and γ(200). For the sample treated with nitriding at 440°C, new broad diffraction peaks S(111) and S(200) appeared in the low-angle direction of the austenite γ(111) and γ(200) diffraction peaks, which Strength and displacement also change with nitriding temperature. The S phase is a supersaturated solid solution state of nitrogen atoms in austenite, while maintaining the original face-centered cubic structure of the expanded austenite, as the temperature rises to 480 ° C, the S(111) and S(200) phases The diffraction peaks are shifted to lower angles. After nitriding treatment at 520°C, the XRD pattern is mainly composed of S phase, CrN and martensite α phase, and a small amount of γ′-Fe ₄ N phase, and the metastable S phase changes at high temperature: S→CrN+α.

Hollow cathode ion source nitriding deposition composite anti-friction and wear-resisting modified layer has a uniform surface and bright silver color. This is because the surface of the sample treated with hollow cathode ion source permeation diffusion deposition does not undergo ion bombardment and sputtering, as shown in Figure 3 Example 3 The surface of the hollow cathode ion source was diffused and deposited to nitride the surface of the sample. It can be seen that there is an obvious deposition layer on the surface, which is composed of small particles with a diameter of 100 nanometers.

Figure 4 is a comparison chart of microhardness between AISI304 austenitic stainless steel substrate and nitriding samples at different temperatures. The austenitic stainless steel sample is at anodic potential and is no longer bombarded by nitrogen-containing positive ions, thus avoiding the edge effect problem, and the hardness of the entire surface is uniform. The hardness value of the sample in Example 1 is about 620HV _0.1 , nearly three times that of the untreated substrate (220HV _0.1 ). The surface hardness value of the sample in Example 2 increased to 940HV _0.1 , significantly higher than that of Example 1. This is because the nitrided layer obtained at low temperature (440°C) is thinner, and the measured hardness value is affected by the softer austenite matrix , failed to show the intrinsic hardness of the nitride layer. The hardness value of the sample in Example 3 reaches 1150HV _0.1 .

Fig. 5 is the friction coefficient-sliding time curve of AISI304 austenitic stainless steel substrate and samples with different nitriding temperatures. The friction coefficient of the original austenite matrix increases rapidly to 1.2 at the initial stage of sliding (the first 10s), and then rapidly decreases to 0.6. After 200s of sliding, the friction coefficient gradually increases, and stabilizes in the range of 0.8 to 1.0 in the later stage. In the first 200s, the friction coefficient of the low-temperature 440°C nitrided sample gradually increased, and then stabilized at around 0.75. However, the change of the friction coefficient of the 480°C and 520°C nitrided samples is similar to that of the original austenitic stainless steel, which first increases and then decreases and tends to be stable. The coefficient of friction is more severe. Overall, the coefficient of friction rate of the nitrided samples is slightly lower than that of the pristine austenitic stainless steels.

Figure 6 is a three-dimensional morphology characterization of AISI304 austenitic stainless steel substrate and nitrided sample wear marks using white light interferometer. It can be seen from Figure 6a that the wear scar on the surface of the substrate has a width of 800 μm and a depth of about 10 μm, showing obvious adhesion; the wear scar of the sample in Example 1 is narrowed to 450 μm (Figure 6b), and the depth is only 2 μm. The appearance is the same, showing adhesion; the wear scar of the sample in Example 2 becomes narrower and shallower, but there are small furrows (Figure 6c); the wear scar of the sample in Example 3 is relatively smooth, and the wear volume is much smaller than that of the untreated substrate ( Figure 6d), nitride deposition significantly improves the wear resistance of austenitic stainless steel.

Figure 7 is the SEM morphology of AISI304 austenitic stainless steel substrate and nitrided samples at different temperatures. The wear scars of the untreated austenitic matrix are wider, and there are a large number of uneven sheet-like deposits on the wear scars (Fig. 7a), indicating that severe adhesion has occurred; The adhesion phenomenon exists (Figure 7b), and the wear marks of the sample in Example 2 are slight, basically there is no adhesion phenomenon, but there are traces of abrasive grains (Figure 7c). The wear scar of the sample in Example 3 is relatively smooth (Fig. 7d), without sticking tendency, and the wear is the slightest. Compared with the substrate, the surface wear morphology of the nitrided sample changes greatly.

Nitriding deposition can prepare a high-hardness strengthening layer on the surface of AISI304 austenitic stainless steel to improve the wear resistance of the surface. The wear mechanism is mainly slightly abrasive and oxidative wear.

Claims (3)

1. A method for preparing a metal material surface nitriding deposition compound friction-reducing and wear-resisting modified layer, is characterized in that, comprises the following steps: (1) Grinding and polishing the surface of the metal material workpiece, after cleaning with alcohol, place it on the anode potential platform in the hollow cathode discharge ion source nitriding furnace; The metal material is AISI304 austenitic stainless steel, which is composed of: C 0.05wt%; Si 0.80wt%; Mn1.50wt%; Cr 17.5wt%; Ni 9.50wt%; Mo 0.013wt%; Ti0.011wt% ; The balance is Fe; The hollow cathode discharge ion source nitriding furnace adopts a pulse power supply, the furnace wall is used as an anode, and the hollow stainless steel tube array is used as a discharge cathode, wherein the diameter of the hollow stainless steel tube is 8 to 10 mm; (2) Start the vacuum system to evacuate the nitriding furnace. When the vacuum in the furnace reaches 10-15Pa, fill the vacuum furnace with purified ammonia gas, so that the ammonia gas is evenly distributed in the entire nitriding furnace, and adjust The flow rate of ammonia gas keeps the pressure in the furnace at 100-500Pa; (3) Turn on the power supply of the power supply system, and the ammonia gas in the furnace is ionized under the action of a high-voltage electric field to form NH _j ⁺ , N ⁺ and H ⁺ plasma, and after reaching the nitriding temperature, start to calculate the holding time; The nitriding temperature is 440-520°C, and the holding time is 8h; (4) After the heat preservation is over, cut off the power supply, maintain low pressure, and cool the workpiece with the furnace in an ammonia gas atmosphere. After the temperature drops below 200°C, it is released from the furnace to obtain a nitrided deposition composite anti-friction and wear-resistant modified layer; The thickness of the nitrided deposition composite anti-friction and wear-resisting modified layer is 6-16 μm; For the sample treated with nitriding at 440 °C, new and wider diffraction peaks S(111) and S(200) appeared in the low-angle direction of the austenite γ(111) and γ(200) diffraction peaks. As the temperature increased to 480°C, the diffraction peaks of S(111) and S(200) phases shifted to lower angles; after nitriding treatment at 520°C, the surface of the sample was mainly composed of S phase, CrN and The martensite α phase is the main one, and there is a small amount of γ′-Fe ₄ N phase. 2. A method for preparing a metal material surface nitriding deposition compound friction-reducing and wear-resisting modified layer, characterized in that, comprising the following steps: (1) Grinding and polishing the surface of the metal material workpiece, after cleaning with alcohol, place it on the anode potential platform in the hollow cathode discharge ion source nitriding furnace; The metal material is AISI304 austenitic stainless steel, which is composed of: C 0.05wt%; Si 0.80wt%; Mn1.50wt%; Cr 17.5wt%; Ni 9.50wt%; Mo 0.013wt%; Ti0.011wt% ; The balance is Fe; The hollow cathode discharge ion source nitriding furnace adopts a pulse power supply, the furnace wall is used as an anode, and the hollow stainless steel tube array is used as a discharge cathode, wherein the diameter of the hollow stainless steel tube is 8 to 10 mm; (2) Start the vacuum system to evacuate the nitriding furnace. When the vacuum in the furnace reaches 10-15Pa, fill the vacuum furnace with purified ammonia gas, so that the ammonia gas is evenly distributed in the entire nitriding furnace, and adjust The flow rate of ammonia gas keeps the pressure in the furnace at 100-500Pa; (3) Turn on the power supply of the power supply system, and the ammonia gas in the furnace is ionized under the action of a high-voltage electric field to form NH _j ⁺ , N ⁺ and H ⁺ plasmas. After reaching the nitriding temperature, start to calculate the holding time; The nitriding temperature is 520°C, and the holding time is 8h; (4) After the heat preservation is over, cut off the power supply, maintain low pressure, and cool the workpiece with the furnace in an ammonia gas atmosphere. After the temperature drops below 200°C, it is released from the furnace to obtain a nitrided deposition composite anti-friction and wear-resistant modified layer; The thickness of the nitrided deposition composite anti-friction and wear-resisting modified layer is 6-16 μm; After nitriding treatment at 520°C, the surface of the sample is mainly composed of S phase, CrN and martensite α phase, and a small amount of γ′-Fe ₄ N phase. 3. A method for preparing a composite anti-friction and wear-resisting modified layer of nitriding deposition on the surface of a metal material, characterized in that it comprises the following steps: (1) Use SiC sandpaper to grind the surface of the sample from coarse to fine, and then polish it; after cleaning with alcohol, place it on the anode potential platform in the hollow cathode discharge ion source nitriding furnace; The sample is AISI304 austenitic stainless steel, its composition is: 0.05wt.%C; 0.80wt.%Si; 1.50wt.%Mn; 17.5wt.%Cr; 9.50wt.%Ni; 0.013wt.%Mo ; 0.011wt.% Ti; Fe balance; Step (1) The hollow cathode discharge ion source nitriding furnace adopts a pulse power supply, the furnace wall is used as the anode, and the hollow stainless steel tube array is used as the discharge cathode, wherein the diameter of the hollow stainless steel tube is 8 to 10 mm; (2) Start the vacuum system to evacuate the nitriding furnace. When the vacuum in the furnace reaches 15Pa, fill the vacuum furnace with purified ammonia gas so that the ammonia gas is evenly distributed throughout the nitriding furnace and adjust the ammonia gas. The flow rate keeps the pressure in the furnace around 500Pa; (3) Turn on the power supply of the power supply system, and the ammonia gas in the furnace is ionized under the action of a high-voltage electric field to form NH _j ⁺ , N ⁺ and H ⁺ plasmas. After reaching the nitriding temperature, start to calculate the holding time; The nitriding temperature is 520°C, and the nitriding treatment is carried out for 8 hours; (4) After the heat preservation is over, cut off the power supply, maintain low pressure, and cool the workpiece with the furnace in an ammonia gas atmosphere. After the temperature drops below 200°C, it is released from the furnace to obtain a nitrided deposition composite anti-friction and wear-resistant modified layer; The nitriding deposition compound anti-friction and wear-resistant modified layer is mainly composed of S phase, CrN and martensite α phase, and a small amount of γ′-Fe ₄ N phase; The surface of the hollow cathode discharge ion source permeation and deposition nitriding sample has an obvious deposition layer, which is composed of small particles with a diameter of 100 nanometers.