Nanocrystal-reinforced high-temperature-wear-resistant nitride coating and preparation method thereof

Abstract

The invention provides a nanocrystalline-reinforced high-temperature-wear-resistant nitride coating and a preparation method thereof. The coating is a single-layer coating and comprises three metal elements, the mass fraction of Ti ranges from 0.09% to 0.15%, the mass fraction of Nb ranges from 0.16% to 0.25%, the mass fraction of W ranges from 0.44% to 0.56%, and the balance is the element N. Cubic nanocrystalline particles with the side length being 15-35 nm are contained in the nitride coating, the peripheries of the nanocrystalline particles are wrapped by amorphous materials, and the mechanical property of the nitride coating can be remarkably improved through the structure. The overall thickness of the coating ranges from 1.5 micrometers to 3.0 micrometers, and the hardness of the coating can reach 13.4 GPa to 23.3 GPa. The coating and stainless steel have good film bonding strength, the coating shows excellent wear resistance in friction tests at 25 DEG C and 800 DEG C, and the bonding force of the coating and a stainless steel substrate is excellent. The coating is prepared on the surface of a sliding bearing part of a large water-turbine generator set, so that the high-temperature wear resistance of parts such as a bearing bush can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of surface engineering, and in particular relates to a nanocrystalline-reinforced high-temperature wear-resistant nitride coating and a preparation method thereof. Background Art

[0002] Bearings are key components of hydropower units. According to different load-bearing types, bearings of hydropower units can be divided into two categories: guide bearings and thrust bearings. Guide bearings are mainly used to bear the radial mechanical unbalance force of the rotating part of the unit, the electromagnetic unbalance force of the generator and the hydraulic unbalance force, to ensure that the swing of the unit axis is within the specified range and to prevent excessive radial vibration of the unit; thrust bearings are used to bear the weight of the rotating part of the entire hydro-generator unit and the axial water thrust of the turbine. The bearing surface inside the sliding bearing is in direct contact with the rotating parts of the unit, bearing a large positive pressure and a high relative motion speed. The bearing surface has been in service for a long time in a coupling environment of high load, strong abrasion, high stress, low-frequency vibration, and high temperature, and it is easy to have problems such as wear, scratches, and surface shedding. Preparing a high-temperature abrasion-resistant coating on the surface of the bearing and its friction pair can effectively protect the surface of the component and avoid severe wear, thereby extending the service life of the component.

[0003] Nitride coating is a ceramic coating with high hardness, high strength and film-base bonding, usually prepared using physical vapor deposition technology. Nitride coating has the advantages of simple preparation process, excellent performance and low cost. It can greatly improve the surface performance of the workpiece without changing the workpiece base material, making it wear-resistant, high-temperature resistant, oxidation-resistant and other properties. Therefore, it has been widely used in many fields such as aerospace, automotive industry, military equipment, etc. Summary of the invention

[0004] The present invention solves the problem of surface wear of sliding bearing components of large-scale hydro-turbine generator sets, solves the problem of low high-temperature tolerance of the surfaces of sliding bearing components of large-scale hydro-turbine generator sets, and solves the problem of easy oxidation and damage of the surfaces of sliding bearing components of large-scale hydro-turbine generator sets.

[0005] In order to solve the above problems, the present application is implemented through the following technical solutions: A method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating comprises the following steps: S1, cleaning the workpiece with a cleaning agent under ultrasonic conditions and drying with compressed air to obtain a workpiece to be coated; S2, installing the workpiece to be coated in step S1 on the substrate fixing table in the chamber, and setting the rotation speed of the substrate fixing table; S3, installing the target material on the target gun in the cavity, adjusting the distance between the substrate fixing platform and the target gun in step S2; heating to a certain temperature at a certain heating rate under the first vacuum degree, keeping the temperature for a certain time, and evacuating to the second vacuum degree; S4, at the second vacuum degree in step S3, setting the argon flow rate, nitrogen flow rate and flow rate of the gas outlet valve in the chamber to control the chamber to a third vacuum degree; S5. Under the third vacuum degree in step S4, a DC bias is applied to the substrate, a DC voltage is applied to the target gun of the alloy target, and the power density and magnetron sputtering deposition time are set to obtain a coated workpiece coated with a high temperature wear-resistant nitride coating.

[0006] The rotation speed in step S2 is 10-15 rpm.

[0007] In the step S3, the target material is a TiNbW alloy with an equal molar ratio, and the purity of the TiNbW alloy is above 99.5%.

[0008] In step S3, the distance between the substrate fixing platform and the target gun is 10-15 cm.

[0009] In step S3, the certain heating rate is 5°C / min to 15°C / min, and the certain temperature is 750°C to 1000°C.

[0010] In the step S4, the argon flow rate is 10-15 sccm; the nitrogen flow rate: argon flow rate = 1:5-1:4.

[0011] In step S5, the DC bias voltage is 85-120 V, the power of the DC voltage is 109-127 W, and the loading power density is 0.6-0.7 W / cm 2 .

[0012] Preferably, in step S1, the cleaning agent is acetone and alcohol, and the compressed gas is one of nitrogen and argon.

[0013] Preferably, the ultrasonic cleaning time in step S1 is 10 to 15 minutes.

[0014] Preferably, the first vacuum degree in step S3 is 0.5×10 -3 Torr~5 ×10 -3 Torr.

[0015] Preferably, the insulation time in step S3 is 1 to 3 h.

[0016] Preferably, the second vacuum degree in step S3 is 0.5×10 -6 Torr~ 5×10 -6 Torr.

[0017] Preferably, the third vacuum degree in step S4 is 0.5×10 -2 Torr~5×10 -2 Torr.

[0018] Preferably, the working magnetic field strength of the target surface of the magnetron sputtering target in step S5 is 0.02-0.07T.

[0019] Preferably, the deposition time of magnetron sputtering in step S5 is 120-300 min.

[0020] Most preferably, the mass fraction of the component in the high temperature wear resistant nitride coating in step S5 is Ti 0.14 Nb 0.23 W 0.56 N 0.07 .

[0021] The deposition rate of magnetron sputtering in step S5 is 5-25 nm / min.

[0022] The nanocrystalline-reinforced high-temperature wear-resistant nitride coating prepared by the method is characterized in that the coating is a single layer, the coating includes Ti, Nb, W, and N elements, and the coating contains FCC-type TiN structured cubic nanocrystalline particles.

[0023] The mass fraction of Ti in the high temperature wear resistant nitride coating is 0.09-0.15, the mass fraction of Nb is 0.16-0.25, the mass fraction of W is 0.44-0.56, and the rest is N element.

[0024] Preferably, the coating thickness is 1.5-3.0 μm.

[0025] Preferably, the side length of the FCC-type TiN structured cubic nanocrystalline particles in the coating is 15-65 nm.

[0026] The present invention provides a nanocrystalline reinforced high temperature wear resistant nitride coating and a preparation method thereof. The coating is a single-layer coating, which contains three metal elements, wherein the mass fraction of Ti is 0.09-0.14, the mass fraction of Nb is 0.16-0.25, the mass fraction of W is 0.44-0.56, and the rest is N element. The interior of the nitride coating contains cubic nanocrystalline particles with a side length of 15-35 nm, and the outer periphery of the nanocrystalline particles is wrapped by amorphous materials, and this structure can significantly improve its mechanical properties. The overall thickness of the coating is 1.5-3.0 μm, and the hardness can reach 13.4-23.3 GPa. The coating has a good film-base bonding strength with stainless steel, and the film-base bonding strength measured by a scratch tester is 13.5-24.2 N. The coating exhibits excellent wear resistance in friction tests at 25°C and 800°C, and its wear rate is 3.5-4.0×10 -6 mm 3 / m•N, and the wear rate is 1.2~3.8×10 -4 mm 3 / m•N.

[0027] The coating is prepared by reactive magnetron sputtering. A mixture of nitrogen and argon is introduced into the chamber. The magnetron sputtering coater used contains three anode target heads. A bias power supply can be used to assist in coating deposition. Each target head contains a DC power supply to load the metal target. The preparation process uses TiNbW alloy targets, and the molar composition of each alloy in the target is the same. The coating preparation includes the following steps: 1. Use acetone and alcohol to clean the surface of the workpiece to be coated, and then use compressed air to fully dry the surface of the component; 2. Install the workpiece to be coated on the substrate fixing table of the magnetron sputtering coating instrument. The substrate fixing table is rotatable and its rotation speed is controlled to 10~15 rpm; 3. Install TiNbW alloy target on the target gun of the equipment. The alloy purity of the target is 99.9%. Adjust the distance between the target gun and the substrate to 10~15 cm, close the chamber door, and use the combined vacuum pump to draw the vacuum degree in the chamber to 1*10 -3 Torr, raise the temperature of the substrate fixing table to 800 °C at a rate of 10 °C / min and keep it at that temperature for 1-3 h, then continue to vacuum to 2*10 -6 Torr; 4. Introduce argon into the chamber at a flow rate of 10-15 sccm. At the same time, introduce nitrogen so that the ratio of the flow rate of nitrogen to the flow rate of argon is between 1:5 and 1:4. By controlling the flow rate of the chamber outlet valve, the vacuum degree of the chamber is controlled to 1*10 -2 Torr; 5. Load a DC bias voltage of 85~120 V on the substrate, load a DC voltage on the target gun with the alloy target installed, and load a power density of 0.6~0.7 W / cm 2 , a coating is deposited on the surface of the workpiece, and the deposition time is controlled to be 180~320 min.

[0028] The crystal structure was tested by X-ray diffractometer (Bruker, D8 Advance Davinci); the morphology and composition were tested by scanning electron microscope (FEI, Quanta 250 FEG) equipped with energy dispersive spectrometer; the hardness of the coating was tested by nanoindenter (MTS, NANO G200); the morphology of the nanocrystals inside the coating was tested by transmission electron microscope (Talos F200); the adhesion test was conducted by coating adhesion automatic scratch tester (Zhongke Kaihua, WS-2005), specifically, scratching the coating surface until fine cracks appeared at the edge of the scratch and obvious acoustic emission signals were generated (refer to industry standard JB / T 8554-1997 "Scratch test method for adhesion of vapor deposited thin films to substrates"), the positive pressure is the adhesion between the coating and the film substrate; the high temperature wear resistance of the coating was tested by friction and wear tester (Anton Paar, THT), the test temperature was 800 ℃, the atmosphere was air, and 6 The stainless steel ball with a diameter of mm was used as the grinding pair, the positive pressure was set to 10N, the friction reciprocating length was 5 mm, the frequency was 2 Hz, and the test time was 60 min; Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a nanocrystalline reinforced high temperature wear resistant nitride coating and a preparation method thereof. The coating contains nanocrystalline particles with a size of tens of nanometers, which can significantly improve its mechanical properties. The coating exhibits excellent wear resistance in friction tests at 25°C and 800°C, and the coating has excellent bonding strength with the stainless steel substrate. The coating is prepared on the surface of the sliding bearing components of large hydro-turbine generator sets, which can greatly improve the high temperature wear resistance of components such as bearing bushes.

[0029] 2. The present invention provides a nanocrystalline reinforced high temperature wear resistant nitride coating and a preparation method thereof, which can be prepared on the surface of the sliding bearing component of a large hydro-turbine generator set to improve the high temperature wear resistance of the bearing component. The coating provided by the present invention comprises three metal elements, Ti, Nb and W, wherein the mass fraction of Ti is 0.09-0.15, the mass fraction of Nb is 0.16-0.25, the mass fraction of W is 0.44-0.56, and the rest is N element. The coating is a single layer with a total thickness of 1.5-3.0 μm. The coating is prepared using reactive magnetron sputtering technology, a mixed gas of nitrogen and argon is introduced into the cavity as a reaction gas, and a TiNbW alloy target is used for sputtering. The nitride coating provided by the present invention contains nanocrystalline particles with a size of tens of nanometers, which can significantly improve its mechanical properties. The coating exhibits excellent wear resistance in friction tests at 25°C and 800°C, and the coating has excellent bonding with the stainless steel substrate. The nitride coating of the present invention is prepared on the surface of the bearing bush of the turbine bearing, which can greatly improve the high temperature wear resistance of the bearing bush, thereby increasing the service life of the turbine bearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a cross-sectional morphology of a nanocrystalline-reinforced high-temperature wear-resistant nitride coating; Figure 2 This is a transmission electron microscope bright field image of a high temperature wear resistant nitride coating with fine nanocrystalline particles; Figure 3 It is the X-ray diffraction spectrum of nanocrystalline reinforced high temperature wear resistant nitride coating; Figure 4 This is a transmission electron microscope bright field image of a high temperature wear resistant nitride coating with relatively coarse nanocrystalline particles; Figure 5 It is the cross-sectional morphology of the nitride coating without nanocrystal reinforcement; Figure 6 This is a bright field transmission electron microscope image of a nitride coating without nanocrystal reinforcement. DETAILED DESCRIPTION

[0031] The following examples are only preferred embodiments of the present invention. Unless otherwise specified, the ultrasonic cleaning time is 10-15 minutes, and the compressed gas is one of nitrogen or argon. The working magnetic field strength of the target surface of the magnetron sputtering target is 0.02-0.07 T. The power of the DC voltage is 109-127 W.

[0032] Example 1 The present invention provides a nanocrystalline reinforced high temperature wear resistant nitride coating and a preparation method thereof, the specific preparation process is as follows: Use acetone and alcohol to ultrasonically clean the surface of the workpiece to be coated, and use compressed air to fully dry the surface of the component after cleaning; Then install the workpiece to be coated on the substrate fixing table of the magnetron sputtering coating instrument. The substrate fixing table is rotatable and its rotation speed is controlled to 10 rpm. Install a TiNbW alloy target on the target gun of the equipment. The alloy purity of the target is 99.9%. Adjust the distance between the target gun and the substrate to 10 cm. Close the chamber door and use a combined vacuum pump to pump the vacuum degree in the chamber to 1*10 -3 Torr, the temperature of the substrate fixing table was raised to 800 °C at a rate of 10 °C / min and kept at this temperature for 2 h, and then the vacuum was continued to be drawn to 2*10 - 6 Torr; Argon was introduced into the chamber at a flow rate of 12 sccm. Nitrogen was introduced at the same time so that the ratio of the flow rate of nitrogen to that of argon was 1:5. The vacuum degree of the chamber was controlled to 1*10 by controlling the flow rate of the chamber outlet valve. -2 Torr; A DC bias of 100 V was applied to the substrate, and a DC voltage was applied to the target gun with the alloy target installed. The loading power density was 0.663 W / cm 2 , the coating is deposited on the surface of the workpiece, and the deposition time is controlled to be 260 min.

[0033] The cross-sectional SEM morphology of the prepared coating is shown in Figure 1 The coating showed an obvious columnar crystal growth structure, the coating thickness was 2.7 μm, and the composition of the coating obtained by scanning with an energy spectrometer was Ti 0.14 Nb 0.23 W 0.56 N 0.07 (mass fraction); the transmission electron microscope bright field image of the prepared coating nanocrystals is as follows Figure 2 The coating contains a large number of uniformly distributed square nanocrystals between the two columnar crystals. The particle size of the nanocrystals is between 20 and 35 nm. Bright amorphous materials are distributed around the nanocrystals. Selected area electron diffraction analysis shows that the nanocrystals are FCC-like TiN structures. The X-ray diffraction pattern of the coating is as follows: Figure 3 As shown, the coating crystal structure is a TiN-type face-centered cubic structure (FCC).

[0034] Example 2 Use acetone and alcohol to ultrasonically clean the surface of the workpiece to be coated, and use compressed air to fully dry the surface of the component after cleaning; Then install the workpiece to be coated on the substrate fixing table of the magnetron sputtering coating instrument. The substrate fixing table is rotatable and its rotation speed is controlled to 13 rpm. Install a TiNbW alloy target on the target gun of the equipment. The alloy purity of the target is 99.6%. Adjust the distance between the target gun and the substrate to 10 cm. Close the chamber door and use a combined vacuum pump to pump the vacuum degree in the chamber to 2*10 -3 Torr, the temperature of the substrate fixing table was raised to 750 °C at a rate of 15 °C / min and kept at this temperature for 3 h, and then the vacuum was continued to be drawn to 2*10 - 6 Torr; Argon was introduced into the chamber at a flow rate of 10 sccm. Nitrogen was introduced at the same time so that the ratio of the flow rate of nitrogen to that of argon was 1:5. The vacuum degree of the chamber was controlled to 1.5*10 by controlling the flow rate of the chamber outlet valve. -2 Torr; A DC bias of 100 V was applied to the substrate, and a DC voltage was applied to the target gun with the alloy target installed. The loading power density was 0.663 W / cm 2 , the coating is deposited on the surface of the workpiece, and the deposition time is controlled to be 260 min.

[0035] The prepared coating composition is Ti 0.15 Nb 0.24 W 0.55 N 0.06 (mass fraction); the transmission electron microscope bright field image of the prepared coating nanocrystals is as follows Figure 4 A large number of nanocrystals also appeared between the two columnar crystals of the coating. The difference from Example 1 is that the particle size of the nanocrystals is between 20 and 65 nm, the distribution of the nanocrystals is uneven, and the surrounding amorphous areas are less obvious, but the nanocrystals are also FCC-like TiN structures.

[0036] Comparative Example 1 The difference between this embodiment and embodiment 1 is that the vacuum degree in the cavity is directly drawn to 2*10 -6 Torr, the operation of heating the substrate fixing table is cancelled to obtain the nitride coating.

[0037] The cross-sectional SEM morphology of the prepared coating is shown in Figure 5 The coating showed an obvious columnar crystal growth structure, the coating thickness was 2.5 μm, and the composition of the coating obtained by scanning with an energy spectrometer was Ti 0.09 Nb 0.16 W 0.44 N 0.10 (mass fraction); the transmission electron microscope bright field image of the prepared coating nanocrystals is as follows Figure 6 , no obvious nanocrystalline particles were found in the coating.

[0038] Comparative Example 2 The difference between this embodiment and embodiment 1 is that the TiNbW alloy target is changed to a TiNb alloy target, and the rest of the preparation process is the same as that of embodiment 1 to obtain a nitride coating.

[0039] Comparative Example 3 The difference between this embodiment and embodiment 1 is that the TiNbW alloy target is changed to a TiNb alloy target, and the vacuum degree in the cavity is directly drawn to 2*10 -6 Torr, the operation of heating the substrate fixing platform is cancelled, and the rest of the preparation process is the same as that in Example 1 to obtain a nitride coating.

[0040] The performance of the material prepared in the above embodiment was tested, and the comparison results with those in Example 1 are shown in Table 1.

[0041] Table 1

[0042] It can be seen from the above table that although the hardness and bonding force of the coating in some comparative examples are slightly better than those of the embodiment coating, the wear rate of the embodiment coating at 25 ℃ and 800 ℃ are always the best, among which the coating of embodiment 1 has better high temperature wear resistance, while the coating of embodiment 2 has better low temperature wear resistance. Therefore, it can be seen that adjusting the target material and the coating preparation temperature have a significant effect on the coating performance. On the one hand, the coating preparation temperature will affect the atomic escape efficiency and deposition rate in the target material, resulting in changes in the composition and thickness of the coating; on the other hand, the nanocrystals in the coating have specific composition conditions and generation temperature conditions. Therefore, nanocrystals can be generated inside the coating in the TiNbWN coating system and 750 ℃~1000 ℃, thereby obtaining the best coating performance. According to the results in the above table, the best technical effect can be obtained when the target material in the present invention is selected as TiNbW alloy and the coating temperature is selected as 800 ℃.

Claims

1. A method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating, characterized in that: The following steps are involved: S1, cleaning the workpiece with a cleaning agent under ultrasonic conditions and drying with compressed air to obtain a workpiece to be coated; S2, installing the workpiece to be coated in step S1 on the substrate fixing table in the chamber, and setting the rotation speed of the substrate fixing table; S3, installing the target material on the target gun in the cavity, adjusting the distance between the substrate fixing platform and the target gun in step S2; heating to a certain temperature at a certain heating rate under the first vacuum degree, keeping the temperature for a certain time, and evacuating to the second vacuum degree; S4, at the second vacuum degree in step S3, setting the argon flow rate, nitrogen flow rate and flow rate of the gas outlet valve in the chamber to control the chamber to a third vacuum degree; S5. Under the third vacuum degree in step S4, a DC bias is applied to the substrate, a DC voltage is applied to the target gun of the alloy target, and the power density and magnetron sputtering deposition time are set to obtain a coated workpiece coated with a high temperature wear-resistant nitride coating.

2. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: The rotation speed in step S2 is 10-15 rpm.

3. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: In the step S3, the target material is a TiNbW alloy with an equal molar ratio, and the purity of the TiNbW alloy is above 99.5%.

4. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: In step S3, the distance between the substrate fixing platform and the target gun is 10-15 cm.

5. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: In step S3, the certain heating rate is 5°C / min to 15°C / min, and the certain temperature is 750°C to 1000°C.

6. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: In the step S4, the argon flow rate is 10-15 sccm; the nitrogen flow rate: argon flow rate = 1:5-1:

4.

7. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: In step S5, the DC bias voltage is 85-120 V, the power of the DC voltage is 109-127 W, and the loading power density is 0.6-0.7 W / cm 2 .

8. The method for preparing a nanocrystalline reinforced high temperature wear resistant nitride coating according to claim 1, characterized in that: The deposition rate of magnetron sputtering in step S5 is 5-25 nm / min.

9. The nanocrystalline reinforced high temperature wear resistant nitride coating prepared by the method according to claims 1 to 8, characterized in that: The coating is a single layer, comprises Ti, Nb, W and N elements, and contains FCC-type TiN structured cubic nanocrystalline particles.

10. The high temperature wear resistant nitride coating according to claim 9, characterized in that: The mass fraction of Ti in the high temperature wear resistant nitride coating is 0.09-0.15, the mass fraction of Nb is 0.16-0.25, the mass fraction of W is 0.44-0.56, and the rest is N element.

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