Amorphous nitride coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of surface engineering, and particularly discloses an amorphous nitride coating which comprises nitrogen and metal elements, and the metal elements comprise Al, Cr, Fe, Ni and Co. The molar ratio of the nitrogen content to the total content of the metal elements is (0.7-1.05): 1; the thickness of the coating is 3.5-7 [mu] m, the hardness can reach 7.8-14.5 Gpa, the coating has good film-substrate bonding strength with stainless steel, and the film-substrate bonding strength of the coating is 15.3-30.6 N measured by a scratch tester; the composite material has good oxidation resistance and can be used for oxidation resistance of key parts of a water-turbine generator set.

Description

Technical Field

[0001] The invention belongs to the technical field of surface engineering and relates to an amorphous nitride coating and a preparation method and application thereof. Background Art

[0002] Surface oxidation of key components of hydro-turbine generator sets is one of the important reasons for their failure. Surface oxidation will reduce the structural strength and load-bearing capacity of components, thereby increasing the risk of component failure; after the surface oxidation of parts such as the stator winding of the generator, a layer of oxide will be formed, which will affect the physical properties of the metal such as electrical conductivity and thermal conductivity; if the oxide on the metal surface is incomplete or loose and porous, the oxidation process of the metal will be accelerated, forming a vicious cycle and causing component failure. Preparing an anti-oxidation coating on the surface of key components of a hydro-turbine generator set is one of the important technologies to avoid severe oxidation and extend its service life. The coating has high preparation efficiency, excellent performance and low cost, and can play an important role in the field of surface anti-oxidation of hydro-turbine generator sets. Physical vapor deposition coating is a commonly used surface coating. Its preparation is a process of converting the target material from a solid state to a gaseous state and then depositing it on the surface of the substrate to form a film. Physical vapor deposition coating has excellent adhesion, density and uniformity.

[0003] In the selection of coating materials, high-entropy materials with multiple principal elements have attracted extensive attention due to their excellent comprehensive mechanical, anti-oxidation and corrosion resistance properties. Amorphous materials have disordered atomic arrangement and no grain boundaries, which reduces defects at the grain boundaries, thereby reducing the nucleation points during the oxidation process and improving the anti-oxidation performance; on the other hand, amorphous materials can form a uniform oxide layer, reducing the risk of local oxidation.

[0004] At present, amorphous coatings are mainly prepared using technologies such as thermal spraying and physical vapor deposition. Amorphous coatings prepared using thermal spraying technology have encountered some difficulties in the field of anti-oxidation applications. This is because, on the one hand, a large number of grain boundaries will be generated during the preparation process, resulting in insufficient anti-oxidation performance of the coating; on the other hand, most of the coatings prepared by spraying technology are amorphous alloy coatings, and alloys are very easy to react with oxygen molecules in a high-temperature oxygen environment and become ineffective. Physical vapor deposition amorphous nitride coatings are a good solution. Physical vapor deposition coatings have fewer grain boundaries and dense coatings, and nitride ceramic coatings usually have better anti-oxidation performance than alloys. The difficulty of physical vapor deposition amorphous nitride coatings is that the addition of nitrogen can easily cause the coating to lose its original amorphous structure and form a nitride phase, thereby affecting the performance of the coating. Summary of the invention

[0005] The invention provides a high entropy nitride amorphous coating containing multiple principal elements, which is used for the anti-oxidation of key parts of a hydro-generator set.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solution: an amorphous nitride coating, the coating comprising nitrogen and metal elements, the metal elements comprising Al, Cr, Fe, Ni and Co; and the molar ratio of nitrogen content to the total content of metal elements is 0.7 to 1.05:1.

[0007] Furthermore, the coating thickness is 3.5-7 μm.

[0008] Furthermore, the molar ratio of Al, Cr, Fe, Co and Ni in the metal elements is 3.5-5: 10.2-12.5: 8.7-9.5: 12.8-14.5: 15.8-18.2.

[0009] The present invention also relates to a method for preparing the coating, which is deposited on a substrate by magnetron sputtering, and specifically comprises the following steps:

[0010] S1. Clean and dry the substrate, and install it on the substrate fixing table of the magnetron sputtering coating device, with the surface on which the coating needs to be deposited exposed on the side facing the target;

[0011] S2. Three target materials, Al, NiFe and CrCo, are installed on the target gun of the magnetron sputtering coating device, and the device is evacuated;

[0012] S3. Argon and nitrogen are introduced into the equipment, the substrate fixing table rotates and is loaded with a DC bias, and a DC voltage is loaded on the target guns installed with Al, NiFe and CrCo targets respectively, and the coating is deposited on the substrate until the required thickness is reached.

[0013] Furthermore, the substrate is made of stainless steel, and before the sputtering coating, the surface is cleaned with water, ethanol and ultrasonic treatment, and then blown dry with dry compressed air.

[0014] Furthermore, the vacuum degree in S2 is evacuated to 5*10 -5 Pa.

[0015] Furthermore, the argon flow rate in S3 is between 35 and 55 sccm, and the nitrogen flow rate is 25 sccm; the vacuum degree is controlled to be 0.8 to 1.2 Pa.

[0016] Furthermore, in S3, the substrate fixing table has a rotation speed of 20 rpm and a DC bias voltage of 85-115V.

[0017] Furthermore, the DC voltage power density on the NiFe and CrCo target guns is between 0.76 and 0.82 W / cm 2 ; The DC voltage loading power density of the target gun installed with Al is 0.63~0.71W / cm 2 ; The deposition time is controlled to be 60 to 300 minutes.

[0018] The invention also relates to the application of the coating in the anti-oxidation of a hydro-generator set.

[0019] The present invention has the following beneficial effects:

[0020] The amorphous nitride coating provided by the present invention has a hardness of 7.8 to 14.5 Gpa, and has a good film-base bonding strength with stainless steel. The film-base bonding strength measured by a scratch tester is 15.3 to 30.6 N. It has good anti-oxidation performance and can serve for a long time on the surface of key parts of a hydro-generator set.

[0021] The coating preparation method provided by the present invention performs film coating by magnetron sputtering technology, introduces argon and nitrogen into the cavity as reaction gases, uses two alloy target materials and one pure metal target material for co-sputtering, has a simple process, and the obtained coating has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is the cross-sectional morphology and coating thickness of the coating in Example 1.

[0023] Figure 2 It is the XRD diffraction pattern of the coating in Example 1.

[0024] Figure 3 This is the surface morphology of Example 1 after oxidation.

[0025] Figure 4 It is the cross-sectional morphology and coating thickness of the coating in Example 2.

[0026] Figure 5 It is the XRD diffraction pattern of the coating in Example 2.

[0027] Figure 6 This is the surface morphology of Example 2 after oxidation. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] The present invention has calculated the coating element system and selected the AlCrFeCoNiN system, which has a strong amorphous forming ability and can obtain an amorphous nitride coating in a physical vapor deposition method. The element screening of the present invention follows the optimal selection strategy for amorphous forming ability. By summarizing the existing research work, the present invention uses three parameters, "mixing entropy ΔS", "mixing enthalpy ΔH" and "atomic volume mismatch δ", to calculate the amorphous forming ability of the multi-component nitride system. Among them, the atomic volume mismatch ci and r i is the atomic fraction and atomic radius of the ith element, is the average atomic radius; enthalpy of mixing Ω ij is the enthalpy of mixing for a binary system; entropy of mixing R is the gas constant R = 8.31446261815324 J·K -1 ·mol -1 The study found that when the above three parameters of the multi-component system meet the conditions of δ ≥ 9, -57 ≤ ΔH ≤ -5.5 kJ / mol, and 7 ≤ ΔS ≤ 15 J / (K·mol), the system has a strong amorphous forming ability. This work calculated the δ, ΔH and ΔS of common nitride systems, as shown in Table 1.

[0030] Table 1

[0031] Multicomponent nitride system Atomic volume mismatch δ Mixing enthalpy ΔH Mixing entropy ΔS AlCrFeCoNiN 17.6053 -56.5589 14.90984 AlCrSiTiZrN 21.70306 -104.863 14.90984 AlCrNiSiTiN 19.32441 -82.5514 14.90984 AlCoCrCuFeNiN 16.58639 -45.5626 16.18616 AlCrMoTaTiZrN 27.22707 -79.5089 16.18616 AlCrTiZrNbN 20.86085 -93.1493 14.90984 CoCrFeNiN 17.3199 -56.48 13.38087 FeCoNiCrCuAlMoN 18.75565 -41.941 17.28848 FeCoNiCrCuAlN 23.764 -45.5626 16.18616 AlCrTaTiZrN 18.61886 -93.3724 14.90984 TiVCrAlZrN 21.85473 -97.2768 14.90984 VxDJ 22.47995 -93.8186 14.90984 AlCrSiTiBN 24.09879 -71.8421 13.38087 AlTiNbSiN 21.8286 -104.32 13.38087 AlCrMnMoNiZrN 29.86162 -76.2364 16.18616 AlCrNbSiTiVN 18.93207 -87.52 16.18616

[0032] When the system contains Fe element but does not contain Cu element, the mixing entropy ΔS, mixing enthalpy ΔH and atomic volume mismatch δ that meet the above requirements can be obtained. Since the Al element has many advantages in anti-oxidation, the present invention designs a multi-component nitride system of AlCrFeCoNiN.

[0033] Example 1

[0034] The present invention provides an oxidation-resistant high-entropy amorphous nitride coating and a preparation method thereof, and the specific preparation process is as follows:

[0035] Soak the stainless steel substrate to be coated in an alcohol beaker, then place the beaker in an ultrasonic cleaning machine, and use water-insulated ultrasound to clean the surface of the stainless steel substrate; use dry compressed air to fully dry the surface of the stainless steel substrate to be coated; install the stainless steel substrate into the cavity of the coating instrument and fix it on a rotatable substrate fixing table, exposing the surface to be coated on the side facing the target;

[0036] Install three kinds of targets, Al, NiFe and CrCo, on the target gun of the equipment, and make sure that the NiFe target is installed on the strong magnetic target gun. Close the cavity door, and use a mechanical pump combined with a molecular pump to pump the vacuum degree in the cavity to 5*10 -5 Pa;

[0037] Argon gas was introduced into the chamber with a flow rate of 50 sccm, and nitrogen gas was introduced at a flow rate of 25 sccm. The vacuum degree of the chamber was controlled to be 1.0 Pa by controlling the closing degree of the outflow valve of the gas in the chamber;

[0038] The rotation speed of the substrate holding table was set to 20 rpm, and a DC bias of 100 V was applied to the substrate.

[0039] A DC voltage is applied to the target gun with NiFe and CrCo installed, and the loading power density is 0.76W / cm 2 , a DC voltage is applied to the target gun mounted with Al, and the loading power density is 0.63W / cm 2 , the deposition time is controlled to be 300min.

[0040] The obtained coating was tested for crystal structure using an X-ray diffractometer (Bruker, D8 Advance Davinci); the morphology and composition were tested using a scanning electron microscope (FEI, Quanta 250FEG) equipped with an energy dispersive spectrometer; the hardness of the coating was tested using a nanoindenter (MTS, NANO G200); the morphology of the interior of the coating was tested using a transmission electron microscope (Talos F200); the adhesion was tested using an automatic scratch tester for coating adhesion (Zhongke Kaihua, WS-2005), specifically, scratching the surface of the coating until a small crack appears at the edge of the scratch. The positive pressure of the scratch is the bonding strength between the coating and the membrane substrate; a high-temperature tube furnace was used to conduct a high-temperature oxidation test on the coating, the test temperature was 500°C, the atmosphere was air, and the test time was 5h.

[0041] The cross-sectional SEM morphology of the coating prepared in Example 1 is as follows: Figure 1 The coating showed an obvious columnar crystal growth structure, the coating thickness was 6.8 μm, and the composition of the coating obtained by scanning with an energy spectrometer was Al 0.044 Cr 0.12 Fe 0.086 Co 0.13 Ni 0.18 N 0.44 ; The X-ray diffraction pattern of the coating is as follows Figure 2 As shown in the figure, there is no obvious peak in the X-ray diffraction curve, and the surface coating is an amorphous structure. The surface SEM morphology of the coating after oxidation at 500℃ is shown in the figure. Figure 3 As shown, the coating surface is dense and has no cracks.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that the flow rate of the introduced nitrogen is 0, and the high entropy alloy coating is obtained.

[0044] The cross-sectional SEM morphology of the prepared coating is shown in Figure 4 The coating showed an obvious columnar crystal growth structure, and the columnar crystals were coarser. The coating density was not as dense as that of the coating in Example 1. The coating thickness was 4.7 μm. The composition of the coating obtained by scanning with an energy spectrometer was Al 0.25 Cr 0.24 Fe 0.15 Co0.16 Ni 0.20 (mole fraction); the X-ray diffraction pattern of the coating is as follows Figure 5 As shown in the figure, the X-ray diffraction curve shows a peak representing the Bcc phase, indicating that the coating of Example 2 is a Bcc single-phase coating. The surface SEM morphology of the coating after oxidation at 500°C is shown in the figure. Figure 6 As shown in the figure, after oxidation, the coating was subjected to surface stress and other effects, resulting in a large number of small cracks, indicating that the coating has poor antioxidant properties.

[0045] Example 3

[0046] The difference between this embodiment and embodiment 1 is that the flow rate of the introduced nitrogen is 50, and the rest of the preparation process is the same as that of embodiment 1 to obtain a nitride coating.

[0047] Example 4

[0048] The difference from Example 1 is that the CrCo alloy target is changed to a Cr target, and the rest of the preparation process is the same as that of Example 1 to obtain a nitride coating.

[0049] Example 5

[0050] The difference from Example 1 is that before the gas is introduced into the cavity, the temperature of the substrate fixing table is first increased to 500° C. at a rate of 10° C. / min. The rest of the preparation process is the same as that of Example 1 to obtain a nitride coating.

[0051] Example 6

[0052] The difference from Example 1 is that the FeNi alloy target is adjusted to a pure Ni target, and the rest of the preparation process is the same as that of Example 1 to obtain a nitride coating.

[0053] The above embodiments and the prepared materials were subjected to performance tests, and the specific results are shown in Table 2.

[0054] Table 2

[0055] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Crystal structure Amorphous Bcc phase Nitride phase Amorphous Bcc phase Nitride phase Thickness(μm) 6.8 4.7 4.5 3.8 18.2 5.9 Hardness(GPa) 8.9 5.6 11.5 12.3 4.5 9.4 Binding force (N) 18.2 11.9 15.8 21.4 10.1 17.9 Structure after oxidation at 500℃ Amorphous Oxide Nitride + Oxide Amorphous Oxide Nitride + Oxide 500℃ coating surface No cracks Small cracks Lots of cracks Small cracks Lots of cracks Lots of cracks

[0056] As can be seen from Table 1 above, Examples 1 and 4 can obtain amorphous nitride coatings, and after oxidation at 500°C, the structure does not change and no cracks are generated on the surface, showing the best antioxidant performance. Whether surface cracks are generated has a significant effect on the antioxidant properties of the coating. Once obvious cracks are formed on the surface of the coating during the oxidation process, it indicates that oxygen molecules can quickly pass through the coating protection through the cracks, thereby causing the coating protection to fail. The hardness and bonding strength of the coatings in Examples 3 and 6 are slightly better than those in Example 1, but they both form oxide phases after oxidation and a large number of cracks appear on the surface, indicating that their antioxidant properties are poor. Both Examples 2 and 5 failed to form an amorphous structure, so the hardness and bonding strength are lower than those in Example 1. According to the results in the above table, the target materials in the present invention are selected as NiFe, CrCo and Al, and the AlCrFeCoNiN coating system is prepared. The coating temperature is selected as room temperature, and the nitrogen flow rate is selected as 25sccm to obtain the best coating performance.

[0057] The above embodiments describe the preferred implementation of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An amorphous nitride coating, characterized in that: The coating is an amorphous nitride coating, which comprises nitrogen and metal elements, wherein the metal elements comprise Al, Cr, Fe, Ni and Co; and the molar ratio of the nitrogen content to the total content of the metal elements is 0.7-1.05:

1.

2. The coating according to claim 1, characterized in that: The coating thickness is 3.5 to 7 μm.

3. The coating according to claim 1 or 2, characterized in that: The molar ratio of Al, Cr, Fe, Co and Ni in the metal elements is 3.5-5: 10.2-12.5: 8.7-9.5: 12.8-14.5: 15.8-18.

2.

4. The method for preparing the coating according to any one of claims 1 to 3, characterized in that: The coating is deposited onto the substrate by magnetron sputtering, which specifically includes the following steps: S1. Clean and dry the substrate, and install it on the substrate fixing table of the magnetron sputtering coating device; S2. Three target materials, Al, NiFe and CrCo, are installed on the target gun of the magnetron sputtering coating device, and the device is evacuated; S3. Argon and nitrogen are introduced into the equipment, the substrate fixing table rotates and is loaded with a DC bias, and a DC voltage is loaded on the target guns installed with Al, NiFe and CrCo targets respectively, and the coating is deposited on the substrate until the required thickness is reached.

5. The preparation method according to claim 4, characterized in that: The substrate is made of stainless steel. Before sputtering coating, the surface is cleaned with water, ethanol and ultrasonic treatment, and then blown dry with dry compressed air.

6. The preparation method according to claim 4, characterized in that: S2 vacuum degree is drawn to 5*10 -5 Pa.

7. The preparation method according to claim 4, characterized in that: In S3, the argon flow rate is between 35 and 55 sccm, and the nitrogen flow rate is 25 sccm; the vacuum degree is controlled to be 0.8 to 1.2 Pa.

8. The preparation method according to claim 4, characterized in that: In S3, the substrate fixing table rotation speed is 20rpm, and the DC bias voltage is 85-115V.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The DC voltage power density on the NiFe and CrCo target guns is between 0.76 and 0.82 W / cm 2 ; The DC voltage loading power density of the target gun installed with Al is 0.63~0.71W / cm 2 ; The deposition time is controlled to be 60 to 300 minutes.

10. Use of the coating according to any one of claims 1 to 3 or the coating prepared by the method according to any one of claims 4 to 9 in the anti-oxidation of a hydro-turbine generator set.

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