Metal piece and coating method

Abstract

The invention discloses a metal piece and a coating method, the metal piece comprises a metal base material, a binding layer, a gradient layer and an outer layer, the binding layer covers the surface of the metal base material, the gradient layer comprises a first functional layer, a second functional layer and a third functional layer which are stacked in sequence, and the outer layer covers the surface of the metal base material. The first functional layer covers the surface, deviating from the metal base material, of the bonding layer, the second functional layer covers the surface, deviating from the bonding layer, of the first functional layer, and the third functional layer covers the surface, deviating from the first functional layer, of the second functional layer; and the outer layer covers the surface, deviating from the second functional layer, of the third functional layer. The metal part provided by the invention has good high-temperature stability, can effectively prolong the service life of a mold in a high-temperature environment when being applied to the mold, and can be applied to PVD surface coating protection of a glass forming mold.

Description

Technical Field

[0001] This application relates to the field of glass optical component manufacturing technology, and in particular to a metal part and a coating method. Background Technology

[0002] Currently, to achieve low-cost, high-precision mass production of aspherical optical components, the industry's molding technologies can be mainly categorized into four types: plastic injection molding, high-temperature glass molding, precision grinding (direct processing of glass blanks using ultra-precision machine tools), and composite processing (combining grinding and polishing processes). Among these, high-temperature glass molding technology offers advantages such as high resolution, excellent stability, and low cost. However, the most critical issue in high-temperature glass molding technology lies in extending the mold's lifespan under prolonged high-temperature (650℃) conditions. Summary of the Invention

[0003] In view of this, this application provides a metal part and a coating method that can solve the above-mentioned technical problems, and the metal part has good high-temperature stability.

[0004] The first aspect of this application provides a metal part, the metal part comprising a metal substrate, a bonding layer, a gradient layer and an outer layer, the bonding layer covering the surface of the metal substrate, the gradient layer comprising a first functional layer, a second functional layer and a third functional layer stacked sequentially, the first functional layer covering the surface of the bonding layer opposite to the metal substrate, the second functional layer covering the surface of the first functional layer opposite to the bonding layer, the third functional layer covering the surface of the second functional layer opposite to the first functional layer, and the outer layer covering the surface of the third functional layer opposite to the second functional layer.

[0005] In some embodiments, the bonding layer includes chromium nitride, the first functional layer includes chromium nitride and aluminum chromium nitride, the second functional layer includes aluminum chromium nitride, the third functional layer includes aluminum chromium nitride and chromium nitride, and the outer layer includes aluminum chromium nitride.

[0006] In some embodiments, in the first functional layer, the atomic content of chromium is N1, the sum of the atomic contents of chromium and aluminum is M1, and N1 / M1 is 0.70~0.85; in the second functional layer, the atomic content of chromium is N2, the sum of the atomic contents of chromium and aluminum is M2, and N2 / M2 is 0.40~0.45; in the third functional layer, the atomic content of chromium is N3, the sum of the atomic contents of chromium and aluminum is M3, and N3 / M3 is 0.35~0.40.

[0007] In some embodiments, the atomic content of chromium in the outer layer is N4, the sum of the atomic contents of chromium and aluminum is M4, and the N4 / M4 ratio is 0.30~0.35.

[0008] In some embodiments, the thickness of the bonding layer is 50 nm to 100 nm, and the thickness of the outer layer is 400 nm to 500 nm.

[0009] In some embodiments, the thickness of the first functional layer is 300 nm to 500 nm, the thickness of the second functional layer is 300 nm to 500 nm, and the thickness of the third functional layer is 300 nm to 400 nm.

[0010] A second aspect of this application provides a method for coating a metal part, comprising the following steps: Provide metal substrates; A bonding layer is formed on the surface of the metal substrate; A gradient layer is formed on the surface of the bonding layer opposite to the metal substrate; An outer layer is formed on the surface of the gradient layer that is opposite to the bonding layer; The gradient layer comprises a first functional layer, a second functional layer, and a third functional layer stacked sequentially. The first functional layer covers the surface of the bonding layer opposite to the metal substrate, the second functional layer covers the surface of the first functional layer opposite to the bonding layer, and the third functional layer covers the surface of the second functional layer opposite to the first functional layer.

[0011] In some embodiments, the step of “forming a bonding layer on the surface of the metal substrate” includes: in a coating apparatus, starting a chromium target with a power of 790 kW to 810 kW, and simultaneously introducing nitrogen and an inert gas, wherein the flow rate of the inert gas is 0.47 to 0.49 of the total gas flow rate.

[0012] In some embodiments, the step of “forming an outer layer on the surface of the gradient layer away from the bonding layer” includes: in the coating equipment, starting an aluminum-chromium alloy target with a power of 800kW to 900kW, and simultaneously introducing nitrogen and an inert gas, wherein the flow rate of the inert gas is 0.60 to 0.70 of the total gas flow rate.

[0013] In some embodiments, the step of "forming a gradient layer on the surface of the bonding layer away from the metal substrate" includes a first stage, a second stage, and a third stage in sequence. The first stage includes: simultaneously starting a chromium target and an aluminum-chromium alloy target in the coating equipment, adjusting the power of the chromium target to 650 kW to 800 kW, adjusting the power of the aluminum-chromium alloy target to 50 kW to 100 kW, and simultaneously introducing nitrogen and an inert gas, with the inert gas flow rate being 0.48 to 0.56% of the total gas flow rate; the second stage includes: adjusting the power of the chromium target to 400 kW to 650 kW, adjusting the power of the aluminum-chromium alloy target to 100 kW to 400 kW, and adjusting the inert gas flow rate to 0.55 to 0.65% of the total gas flow rate; the third stage includes: adjusting the power of the chromium target to 100 kW to 400 kW, and adjusting the power of the aluminum-chromium alloy target to 400 kW to 800 kW. kW, and adjust the flow rate of the inert gas to 0.60~0.70 of the total gas flow rate.

[0014] The metal component provided in this application has a bonding layer, a gradient layer, and an outer layer sequentially formed on the surface of a metal substrate. The bonding layer covers the surface of the metal substrate. The gradient layer includes a first functional layer, a second functional layer, and a third functional layer stacked sequentially. The first functional layer covers the surface of the bonding layer opposite to the metal substrate, the second functional layer covers the surface of the first functional layer opposite to the bonding layer, the third functional layer covers the surface of the second functional layer opposite to the first functional layer, and the outer layer covers the surface of the third functional layer opposite to the second functional layer. The bonding layer provides stable substrate support and improves the adhesion between the gradient layer and the metal substrate. The gradient layer comprises three functional layers, which work together to improve wear resistance and enhance the toughness of the gradient layer at high temperatures. The outer layer forms a thermal barrier layer to further improve the coating's high-temperature oxidation resistance and high-temperature stability. This application achieves excellent high-temperature stability in the metal parts by layering different coatings. When these metal parts are used as mold materials in high-temperature glass molding technology, they can effectively extend the service life of the molds in high-temperature environments. They can be applied to PVD surface coating protection for glass forming molds. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a metal part provided in one embodiment of this application.

[0016] Figure 2 This is a schematic flowchart of a metal coating method provided in one embodiment of this application.

[0017] Explanation of main component symbols: metal part 100, metal substrate 10, bonding layer 20, gradient layer 30, first functional layer 31, second functional layer 32, third functional layer 33, outer layer 40.

[0018] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0019] To better understand the above-mentioned objectives, features, and advantages of the embodiments of this application, the application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the features in the embodiments of this application can be combined with each other.

[0020] The following description sets forth numerous specific details to provide a thorough understanding of the embodiments of this application. The described implementations are only a portion, not all, of the embodiments described herein. All other implementations obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of the embodiments of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of this application belong. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application.

[0022] Please see Figure 1This application provides a metal part 100, which includes a metal substrate 10, a bonding layer 20, a gradient layer 30, and an outer layer 40. The bonding layer 20 covers the surface of the metal substrate 10. The gradient layer 30 includes a first functional layer 31, a second functional layer 32, and a third functional layer 33 stacked sequentially. The first functional layer 31 covers the surface of the bonding layer 20 facing away from the metal substrate 10, the second functional layer 32 covers the surface of the first functional layer 31 facing away from the bonding layer 20, and the third functional layer 33 covers the surface of the second functional layer 32 facing away from the first functional layer 31. The outer layer 40 covers the surface of the third functional layer 33 facing away from the second functional layer 32. In this application, the bonding layer 20 provides stable substrate support and improves the adhesion between the gradient layer 30 and the metal substrate 10. The gradient layer 30 includes three functional layers, which work together to improve the wear resistance and toughness of the gradient layer 30 at high temperatures. The outer layer 40 is used to form a thermal barrier layer to further improve the coating's resistance to high-temperature oxidation and high-temperature stability. By combining the bonding layer 20, the gradient layer 30, and the outer layer 40, the metal part 100 has good high-temperature stability and mechanical properties. When the metal part 100 is used to make molds and applied in the glass production process, it can improve the impact resistance and high-temperature oxidation resistance of the mold surface, and improve problems such as pitting and adhesion after the mold has been subjected to high temperatures.

[0023] In some embodiments, the bonding layer 20 includes chromium nitride, the first functional layer 31 includes chromium nitride and aluminum chromium nitride, the second functional layer 32 includes aluminum chromium nitride, the third functional layer 33 includes aluminum chromium nitride and chromium nitride, and the outer layer 40 includes aluminum chromium nitride. The use of chromium nitride in the bonding layer 20 and the partial inclusion of chromium nitride in the first functional layer 31 helps the bonding layer 20 provide stable substrate support and improves the adhesion between the gradient layer 30 and the metal substrate 10. In high-temperature glass molding technology, the mold surface is prone to pitting due to the high-temperature environment (650°C) and continuous stamping, which in turn makes the surface of the finished glass product prone to defects. Therefore, the mold needs frequent rework and polishing, reducing the mold's efficiency. Furthermore, oxides on the mold surface easily react with the glass under high-temperature conditions and adhere to the mold surface, causing difficulties in demolding the mold and glass over long periods of processing. The first functional layer 31, the second functional layer 32, and the third functional layer 33 all contain chromium aluminum nitride. Since aluminum atoms are larger than chromium atoms, the chromium aluminum nitride forms a fine-grained composite structure with chromium nitride, which improves the coating's fracture toughness and enhances its wear resistance, thereby improving the mold's impact resistance. The outer layer 40 contains chromium aluminum nitride, and a (CrAl)₂O₃ protective layer can be formed on its surface, preventing adhesion to glass and improving the mold's efficiency in high-temperature environments.

[0024] In some embodiments, in the first functional layer 31, the atomic content of chromium is N1, the sum of the atomic contents of chromium and aluminum is M1, and N1 / M1 is 0.70~0.85; in the second functional layer 32, the atomic content of chromium is N2, the sum of the atomic contents of chromium and aluminum is M2, and N2 / M2 is 0.40~0.45; in the third functional layer 33, the atomic content of chromium is N3, the sum of the atomic contents of chromium and aluminum is M3, and N3 / M3 is 0.35~0.40. For example, the value of N1 / M1 can be 0.70, 0.73, 0.75, 0.78, 0.8, 0.83, 0.84, 0.85, or any value within the range of any two of the above values. The N2 / M2 value can be 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, or any value within the range of any two of the above values. The N3 / M3 value can be 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, or any value within the range of any two of the above values. By controlling the atomic ratio of chromium and aluminum in each functional layer within the above range, exhibiting a gradual trend, the ratio of Al, Cr, and N in each functional layer can be adjusted. This allows the atoms of different elements to interact and stack during the deposition process, which can improve the microstructure within the coating, enhance the coating's density, and contribute to improving the coating's toughness and high-temperature stability.

[0025] In some embodiments, in the outer layer 40, the atomic content of chromium is N4, and the sum of the atomic contents of chromium and aluminum is M4, with an N4 / M4 ratio of 0.30 to 0.35. For example, the value of N4 / M4 can be 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, or any value within the range of any two of the above values. Controlling the atomic ratio of chromium and aluminum in the outer layer 40 within the above range helps the outer layer 40 to form a thermal barrier layer, improving the high-temperature oxidation resistance and high-temperature stability of the metal part 100.

[0026] In some embodiments, the thickness of the bonding layer 20 is 50 nm to 100 nm, and the thickness of the outer layer 40 is 400 nm to 500 nm. For example, the thickness of the bonding layer 20 can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any value within the range of any two of the above values; the thickness of the outer layer 40 can be 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, 460 nm, 470 nm, 480 nm, 490 nm, 500 nm, or any value within the range of any two of the above values. Controlling the thickness of the bonding layer 20 and the outer layer 40 within the above ranges helps to improve the mechanical properties of the metal part 100 and extend its high-temperature service life.

[0027] In some embodiments, the thickness of the first functional layer 31 is 300 nm to 500 nm, the thickness of the second functional layer 32 is 300 nm to 500 nm, and the thickness of the third functional layer 33 is 300 nm to 400 nm. For example, the thickness of the first functional layer 31 can be 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm, or any value within the range of any two of the above values. The thickness of the second functional layer 32 can be 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm, or any value within the range of any two of the above values. The thickness of the third functional layer 33 can be 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, or any value within the range of any two of the above values. Controlling the thickness of the first functional layer 31, the second functional layer 32, and the third functional layer 33 within the above range helps to improve the wear resistance and high-temperature toughness of the coating and extend the high-temperature service life of the metal part 100.

[0028] Please see Figure 2 This application also provides a coating method for a metal part 100, comprising the following steps: S1. Provide a metal substrate 10; S2. A bonding layer 20 is formed on the surface of the metal substrate 10; S3. A gradient layer 30 is formed on the surface of the bonding layer 20 that is away from the metal substrate 10; S4. An outer layer 40 is formed on the surface of the gradient layer 30 that is opposite to the bonding layer 20; The gradient layer 30 includes a first functional layer 31, a second functional layer 32 and a third functional layer 33 stacked in sequence. The first functional layer 31 covers the surface of the bonding layer 20 away from the metal substrate 10, the second functional layer 32 covers the surface of the first functional layer 31 away from the bonding layer 20, and the third functional layer 33 covers the surface of the second functional layer 32 away from the first functional layer 31.

[0029] In some embodiments, the step of "forming a bonding layer 20 on the surface of the metal substrate 10" includes: in a coating apparatus, starting a chromium target with a power of 790 kW to 810 kW, and simultaneously introducing nitrogen and an inert gas, with the inert gas flow rate being 0.47 to 0.49 of the total gas flow rate. For example, the power of the chromium target can be 790 kW, 795 kW, 800 kW, 805 kW, 810 kW, or any value within the range of any two of the above values, and the inert gas flow rate can be 0.47, 0.48, 0.49 of the total gas flow rate, or any value within the range of any two of the above values. By controlling the ratio of the chromium target power and the gas flow rate within the above range, a bonding layer 20 containing chromium nitride can be formed.

[0030] In this application, once the power of the target material, the gas flow rate, and the thickness of the coating are determined, the time required to form a coating of that thickness can be determined.

[0031] In some embodiments, the step of "forming an outer layer 40 on the surface of the gradient layer 30 away from the bonding layer 20" includes: in a coating apparatus, starting an aluminum-chromium alloy target with a power of 800kW to 900kW, and simultaneously introducing nitrogen and an inert gas, with the inert gas flow rate being 0.60 to 0.70% of the total gas flow rate. For example, the power of the aluminum-chromium alloy target can be 800kW, 820kW, 840kW, 860kW, 880kW, 900kW, or any value within the range of any two of the above values; the inert gas flow rate can be 0.60, 0.62, 0.64, 0.66, 0.68, 0.70% of the total gas flow rate, or any value within the range of any two of the above values. By controlling the power and gas flow rate ratio of the aluminum-chromium alloy target within the above range, an outer layer 40 containing aluminum chromium nitride can be formed.

[0032] In some embodiments, the step of "forming a gradient layer 30 on the surface of the bonding layer 20 facing away from the metal substrate 10" includes a first stage, a second stage, and a third stage in sequence. The first stage includes: simultaneously starting a chromium target and an aluminum-chromium alloy target in a coating apparatus, adjusting the power of the chromium target from 790kW~810kW to 650kW~800kW, and adjusting the power of the aluminum-chromium alloy target from 0kW to 50kW~100kW, while simultaneously introducing nitrogen and an inert gas, with the inert gas flow rate being 0.48~0.56% of the total gas flow rate. The second stage includes: adjusting the power of the chromium target from 650kW~800kW to 400kW~650kW, and adjusting the power of the aluminum-chromium alloy target from 50kW~100kW to 100kW~400kW. The first stage involves adjusting the power of the chromium target from 400kW to 650kW to 100kW to 400kW, and adjusting the power of the aluminum-chromium alloy target from 100kW to 400kW to 400kW to 800kW, while adjusting the inert gas flow rate to 0.60% to 0.70% of the total gas flow rate. By controlling the target power and gas flow rate ratios within the above ranges for each stage, the chromium and aluminum composition ratio of each functional layer can be adjusted to form a gradient layer 30 with a specific chromium to aluminum ratio, which helps to improve the wear resistance and high-temperature resistance of the gradient layer 30.

[0033] For example, in the first stage, the power of the chromium target can be gradually adjusted to 650kW, 700kW, 750kW, 800kW or any value within the range of any two of the above values; the power of the aluminum-chromium alloy target can be gradually adjusted to 50kW, 60kW, 70kW, 80kW, 90kW, 100kW or any value within the range of any two of the above values; and the flow rate of the inert gas can be 0.48, 0.50, 0.52, 0.54, 0.56 of the total gas flow rate or any value within the range of any two of the above values. In the second stage, the power of the chromium target can be gradually adjusted to 400kW, 450kW, 500kW, 550kW, 600kW, 650kW, or any value within the range of any two of the above values. The power of the aluminum-chromium alloy target can be gradually adjusted to 100kW, 150kW, 200kW, 250kW, 300kW, 350kW, 400kW, or any value within the range of any two of the above values. The flow rate of the inert gas can be 0.55, 0.58, 0.60, 0.63, 0.65 of the total gas flow rate, or any value within the range of any two of the above values. In the third stage, the power of the chromium target can be gradually adjusted to 100kW, 200kW, 300kW, 400kW, or any value within the range of any two of the above values. The power of the aluminum-chromium alloy target can be gradually adjusted to 400kW, 500kW, 600kW, 700kW, 800kW, or any value within the range of any two of the above values. The flow rate of the inert gas can be 0.60, 0.62, 0.64, 0.66, 0.68, 0.70 of the total gas flow rate, or any value within the range of any two of the above values.

[0034] Example 1 A high-power pulsed magnetron sputtering (HiPIMS) coating system was used, equipped with a Cr target and an AlCr alloy target. The Cr target contained 99.9% Cr, and the AlCr alloy target contained 60% Al, resulting in an Al and Cr purity of 99.9% in both targets. The operating temperature was 480℃. The specific preparation method included: S1. Place the metal substrate 10 in the coating equipment, start the chromium target, adjust the power of the chromium target to 800kW, and simultaneously introduce nitrogen and inert gas, controlling the flow rate of the inert gas to be 0.48 of the total flow rate of nitrogen and inert gas, so as to form a bonding layer 20 on the surface of the metal substrate 10.

[0035] S2. Start the aluminum-chromium alloy target material. Gradually adjust the power of the aluminum-chromium alloy target material from 0 to 100 kW and the power of the chromium target material from 800 kW to 650 kW. Adjust the flow rate of the inert gas to 0.45~0.55 of the total flow rate of nitrogen and inert gas, so as to form the first functional layer 31 on the surface of the bonding layer 20 away from the metal substrate 10.

[0036] S3. The power of the aluminum-chromium alloy target is gradually adjusted from 100 kW to 400 kW, and the power of the chromium target is gradually adjusted from 650 kW to 400 kW. The flow rate of the inert gas is adjusted to 0.55~0.65 of the total flow rate of nitrogen and inert gas, so as to form the second functional layer 32 on the surface of the first functional layer 31 away from the bonding layer 20.

[0037] S4. The power of the aluminum-chromium alloy target is gradually adjusted from 400 kW to 800 kW, and the power of the chromium target is gradually adjusted from 400 kW to 100 kW. The flow rate of the inert gas is adjusted to 0.60~0.70 of the total flow rate of nitrogen and inert gas, so as to form a third functional layer 33 on the surface of the second functional layer 32 away from the first functional layer 31.

[0038] S4. Turn off the chromium target, the power of the aluminum-chromium alloy target is 800 kW, and adjust the flow rate of the inert gas to 0.65 of the total flow rate of nitrogen and inert gas, so as to form an outer layer 40 on the surface of the third functional layer 33 opposite to the second functional layer 32.

[0039] The metal part 100 is obtained by the above steps. The metal part 100 includes a metal substrate 10, a bonding layer 20, a gradient layer 30, and an outer layer 40. The bonding layer 20 covers the surface of the metal substrate 10, contains chromium nitride, and has a thickness of 50 nm to 100 nm. The gradient layer 30 includes a first functional layer 31, a second functional layer 32, and a third functional layer 33 stacked sequentially. The first functional layer 31 contains chromium nitride and aluminum chromium nitride, and has a thickness of 300 nm to 500 nm. The second functional layer 32 contains aluminum chromium nitride, and has a thickness of 300 nm to 500 nm. The third functional layer 33 contains aluminum chromium nitride and chromium nitride, and has a thickness of 300 nm to 400 nm. An outer layer 40 covers the surface of the third functional layer 33 opposite to the second functional layer 32. The outer layer 40 contains aluminum chromium nitride and has a thickness of 400 nm to 500 nm. In the first functional layer 31, N1 / M1 is 0.7 to 0.85. In the second functional layer 32, N2 / M2 is 0.40 to 0.45. In the third functional layer 33, N3 / M3 is 0.35 to 0.40. In the outer layer 40, N4 / M4 is 0.30 to 0.35.

[0040] Comparative Example 1 Comparative Example 1 provides a metallic material comprising a substrate, a first layer, a second layer, and a surface layer, wherein the substrate is made of the same material as the metallic substrate of Example 1. The first layer covers the surface of the substrate, the second layer covers the surface of the first layer opposite to the substrate, and the surface layer covers the surface of the second layer opposite to the first layer. The first layer is chromium nitride, the second layer is aluminum chromium nitride, and the surface layer is AlCrSiN.

[0041] Performance testing The metal parts of Example 1 and the metal material of Comparative Example 1 were subjected to high-temperature performance tests as follows: Both the metal parts of Example 1 and the metal material of Comparative Example 1 were heated to 650°C in a high-temperature furnace and kept at a constant temperature for 2 hours, 10 hours, and 24 hours. Their appearance was observed under atmospheric conditions, and the surface roughness of both was measured using the same white light interferometer. The comparison results are shown in Table 1.

[0042] Table 1 As shown in Table 1, the metal part provided in this application maintained its normal surface color after 24 hours of high-temperature testing, with no obvious discoloration or pitting, indicating good high-temperature stability. Furthermore, the surface roughness did not increase significantly after prolonged high-temperature testing. In contrast, Comparative Example 1, after the same high-temperature test, showed a significant discoloration and pitting. Simultaneously, the surface roughness of Comparative Example 1 increased sharply from 28 nm to 52 nm, a nearly 86% increase, indicating poor high-temperature resistance.

[0043] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A metal part, characterized in that, include: Metal substrate; A bonding layer is formed by covering the surface of the metal substrate. A gradient layer includes a first functional layer, a second functional layer, and a third functional layer stacked sequentially. The first functional layer covers the surface of the bonding layer opposite to the metal substrate, the second functional layer covers the surface of the first functional layer opposite to the bonding layer, and the third functional layer covers the surface of the second functional layer opposite to the first functional layer. The outer layer covers the surface of the third functional layer that is opposite to the second functional layer.

2. The metal part as described in claim 1, characterized in that, The bonding layer includes chromium nitride, the first functional layer includes chromium nitride and aluminum chromium nitride, the second functional layer includes aluminum chromium nitride, the third functional layer includes aluminum chromium nitride and chromium nitride, and the outer layer includes aluminum chromium nitride.

3. The metal part as described in claim 1, characterized in that, In the first functional layer, the atomic content of chromium is N1, and the sum of the atomic contents of chromium and aluminum is M1, with N1 / M1 being 0.70~0.85; in the second functional layer, the atomic content of chromium is N2, and the sum of the atomic contents of chromium and aluminum is M2, with N2 / M2 being 0.40~0.45; in the third functional layer, the atomic content of chromium is N3, and the sum of the atomic contents of chromium and aluminum is M3, with N3 / M3 being 0.35~0.

40.

4. The metal part as described in claim 1, characterized in that, In the outer layer, the atomic content of chromium is N4, and the sum of the atomic contents of chromium and aluminum is M4, with N4 / M4 being 0.30~0.

35.

5. The metal part as described in claim 1, characterized in that, The thickness of the bonding layer is 50nm~100nm, and the thickness of the outer layer is 400nm~500nm.

6. The metal part as described in claim 1, characterized in that, The thickness of the first functional layer is 300nm~500nm, the thickness of the second functional layer is 300nm~500nm, and the thickness of the third functional layer is 300nm~400nm.

7. A coating method for a metal part as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Provide metal substrates; A bonding layer is formed on the surface of the metal substrate; A gradient layer is formed on the surface of the bonding layer opposite to the metal substrate; An outer layer is formed on the surface of the gradient layer that is opposite to the bonding layer; The gradient layer comprises a first functional layer, a second functional layer, and a third functional layer stacked sequentially. The first functional layer covers the surface of the bonding layer opposite to the metal substrate, the second functional layer covers the surface of the first functional layer opposite to the bonding layer, and the third functional layer covers the surface of the second functional layer opposite to the first functional layer.

8. The coating method for metal parts as described in claim 7, characterized in that, The step of "forming a bonding layer on the surface of the metal substrate" includes: in a coating equipment, starting a chromium target with a power of 790kW to 810kW, and simultaneously introducing nitrogen and an inert gas, wherein the flow rate of the inert gas is 0.47 to 0.49 of the total gas flow rate.

9. The coating method for metal parts as described in claim 8, characterized in that, The step of "forming an outer layer on the surface of the gradient layer away from the bonding layer" includes: in the coating equipment, starting an aluminum-chromium alloy target with a power of 800kW~900kW, and simultaneously introducing nitrogen and inert gas, wherein the flow rate of the inert gas is 0.60~0.70 of the total gas flow rate.

10. The coating method for metal parts as described in claim 8, characterized in that, The step of "forming a gradient layer on the surface of the bonding layer away from the metal substrate" includes a first stage, a second stage, and a third stage in sequence, wherein... The first stage includes: simultaneously starting a chromium target and an aluminum-chromium alloy target in the coating equipment, adjusting the power of the chromium target to 650kW to 800kW, adjusting the power of the aluminum-chromium alloy target to 50kW to 100kW, and simultaneously introducing nitrogen and inert gas, wherein the flow rate of the inert gas is 0.48 to 0.56 of the total gas flow rate; The second stage includes: adjusting the power of the chromium target to 400kW to 650kW, adjusting the power of the aluminum-chromium alloy target to 100kW to 400kW, and adjusting the flow rate of the inert gas to 0.55 to 0.65 of the total gas flow rate; The third stage includes: adjusting the power of the chromium target to 100kW to 400kW, adjusting the power of the aluminum-chromium alloy target to 400kW to 800kW, and adjusting the flow rate of the inert gas to 0.60 to 0.70% of the total gas flow rate.

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