A corrosion and wear resistant CoCrNiMo-based composite coating and a preparation method and application thereof

Abstract

The application discloses a kind of anticorrosive wear-resistant CoCrNiMo base composite coating, it is characterized in that, by the following atomic percentage of metal powder and ceramic powder are mixed to be prepared: 29.5-31% Co metal powder, 4.7-25% Cr metal powder, 29.5-31% Ni metal powder, 5.5-25% Mo metal powder, 5.5-8% Nb metal powder and 1.8-2% B4C ceramic powder powder.The application uses Co, Cr, Ni, Mo and Nb metal powder and B4C ceramic powder as raw material, by optimizing the ratio between metal powder and ceramic powder and using laser cladding process to form CoCrNiMo base composite coating on substrate, the coating has the advantages of high hardness, good wear resistance, strong corrosion resistance and good pitting resistance, realizes the synergistic enhancement of corrosion resistance and wear resistance, provides new ideas for the performance improvement of high-strength steel in actual service environment.

Description

Technical Field

[0001] This invention relates to the field of alloy coating technology, specifically to a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, its preparation method, and its application. Background Technology

[0002] 300M ultra-high strength steel, due to its excellent mechanical properties and fatigue resistance, is widely used in structural components such as landing gear. During actual service, 300M steel frequently undergoes takeoff and landing operations, making it susceptible to corrosion and wear, seriously threatening service safety. To address this issue, preparing functional coatings on the surface of 300M steel has become the preferred solution. The service environment of 300M ultra-high strength steel places higher demands on the performance of the coating, requiring a balance between corrosion resistance and wear resistance. High entropy alloys (HEAs) exhibit excellent hardness and mechanical properties due to their grain refinement strengthening, solid solution strengthening, and second-phase strengthening effects. The high concentration of transition metal elements in HEAs can significantly improve their corrosion resistance. Therefore, preparing high entropy alloy coatings on the surface of high-strength steel is expected to achieve a synergistic enhancement of corrosion resistance and wear resistance, providing a new approach to improving the performance of high-strength steel in actual service environments. Laser cladding has an extremely high cooling rate during processing, which can effectively suppress component segregation, refine grains, and improve the solubility limit of elements. Laser cladding produces coatings with a smaller heat-affected zone, offering advantages in preparing wear-resistant, corrosion-resistant, and oxidation-resistant coatings. Combining laser cladding technology with high-entropy alloys to fully leverage the strengths of both has become a popular research direction in surface modification in recent years.

[0003] Currently, the design of high-entropy alloy coatings mainly follows the "cocktail effect" strategy, introducing other elements into the CoCrNi-based high-entropy alloy system for regulation. Cr and Mo, as key alloying elements in the passivation system, can form a dense passivation film on the coating surface, significantly improving its corrosion resistance. Preliminary studies have revealed the synergistic effects of Cr and Mo on the microstructure and corrosion performance of high-entropy alloy coatings, but research on how to regulate the proportions of Cr, Mo, and other metals to achieve both high wear resistance and high corrosion resistance, as well as their passivation and pitting corrosion behavior, remains limited. Summary of the Invention

[0004] To address the problems of existing technologies, this invention prepares a CoCrNiMo-based composite coating with high hardness, good wear resistance, strong corrosion resistance, and good pitting corrosion resistance by adjusting the Cr / Mo ratio and using a laser cladding process.

[0005] The primary objective of this invention is to provide a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, which is prepared by mixing metal powder and ceramic powder in the following atomic percentages: 29.5-31% Co metal powder, 4.7-25% Cr metal powder, 29.5-31% Ni metal powder, 5.5-25% Mo metal powder, 5.5-8% Nb metal powder, and 1.8-2% B4C ceramic powder.

[0006] The second objective of this invention is to provide a method for preparing a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, the method comprising the following steps: S1 weighs out Co, Cr, Ni, Mo and Nb metal powders and B4C ceramic powder in sequence according to atomic percentage, mixes them evenly, and obtains the first mixed powder; S2 Place the first mixed powder in a planetary ball mill and ball mill it in anhydrous ethanol medium, and then place it in a vacuum drying oven to dry it to obtain the second mixed powder. S3 The second mixed powder is pre-uniformly spread on the surface of the pretreated substrate and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer; Under the protection of argon gas, S4 uses a semiconductor fiber laser to perform laser cladding on a pre-placed powder layer, forming a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, namely CoCr x NiMo 30-x Nb6 / B4C coating.

[0007] Specifically, the purity of the Co, Mo, and Nb metal powders in step S1 is ≥99.9 wt%; the purity of the Cr and Ni metal powders is ≥99.5 wt%; and the purity of the B4C metal powder is ≥98 wt%.

[0008] Specifically, the ball milling process in step S2 takes 4-6 hours; the particle size of each metal powder in the second mixed powder is 45-55 μm.

[0009] Specifically, the drying temperature in step S2 is 50-60℃, and the drying time is 20-26h.

[0010] Specifically, the thickness of the pre-placed powder layer in step S3 is 2 mm.

[0011] Specifically, the method for obtaining the pretreated substrate in step S3 includes: processing 300M steel into strips of fixed size using wire cutting technology, and polishing the surface of the strips of steel with 180# and 400# sandpaper in sequence to remove the oxide layer, thereby obtaining the pretreated substrate.

[0012] Specifically, the process parameters for the laser melting process in step S4 are: laser power 1.2-1.4kW, scanning speed 300mm / min, spot diameter 3mm, and overlap rate 25-30%; the flow rate of the argon gas is 15L / min.

[0013] The third objective of this invention is to provide an application of the aforementioned corrosion-resistant and wear-resistant CoCrNiMo-based composite coating in the fields of surface strengthening or repair of aerospace, automotive, shipbuilding, or industrial equipment.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: (1) This invention uses Co, Cr, Ni, Mo and Nb metal powders and B4C ceramic powder as raw materials. By optimizing the ratio between the metal powders and ceramic powders and using a laser cladding process, a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating is formed on the substrate, namely Cr x NiMo 30-x The Nb6 / B4C coating has the advantages of high hardness, good wear resistance, strong corrosion resistance and good pitting corrosion resistance, achieving synergistic enhancement of corrosion resistance and wear resistance, and providing a new approach to improving the performance of high-strength steel in actual service environments.

[0015] (2) This invention employs a laser cladding process to prepare the coating, which effectively suppresses component segregation, refines grain size, and improves the solubility limit of elements. Simultaneously, the high-energy laser beam achieves excellent metallurgical bonding between the coating and the substrate. The heat-affected zone of the laser-clad coating is small, offering significant advantages in preparing wear-resistant, corrosion-resistant, and oxidation-resistant coatings. Furthermore, CoCr... x NiMo 30-x The preparation method of Nb6 / B4C coating is simple, easy to operate, fast, low in cost, and easy to automate. It ensures that the actual coating composition is close to the design composition and does not require complex equipment. It has significant economic benefits in the field of laser cladding preparation of high-entropy alloy coatings.

[0016] (3) In this invention, other metallic elements are introduced into the CoCrNiMo-based high-entropy alloy system and the composition ratio is optimized and controlled to form Cr x NiMo 30-x Nb6 / B4C coating. B4C ceramic powder is introduced, which possesses high hardness, thermal stability, and good reactivity. Under the action of a high-energy laser cladding beam, it undergoes thermal decomposition, releasing the active elements B and C. B and C react with the metallic elements in the alloy system to form reinforcing phases such as metal borides and carbides, achieving indirect in-situ reaction enhancement. This, in turn, alters the microstructure and phase structure of the coating, improving its hardness and wear resistance.

[0017] (4) The corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared by the present invention controls the microstructure and strengthening phase by optimizing the composition ratio. The coating mainly enriches Co and Ni to form FCC as the main phase, and also enriches Mo, Nb, B and C to form the second phase, namely BCC and Laves phase. The FCC phase is a plastic matrix, while the BCC structure has higher hardness. The Laves phase has extremely high hardness, strength and good creep / wear resistance. In addition, B and C react with the metal elements in the alloy system to form metal carbides, which further improve the hardness performance of the coating through precipitation strengthening.

[0018] (5) In this invention, the outer layer of the passivation film on the coating surface is mainly composed of hydroxides rich in Cr and Mo, while the inner layer is mainly composed of Cr oxides; the outer layer has a loose structure, while the inner layer has a dense structure. By optimizing the atomic ratio of Cr and Mo and controlling the Cr-Mo composition ratio, the high chromium and low molybdenum composition forms a dense chromium-rich passivation film, which improves the corrosion resistance and critical pitting temperature of the coating, making the prepared coating exhibit better anti-pitting performance. Attached Figure Description

[0019] Figure 1 X-ray diffraction (XRD) comparison patterns of the coatings prepared in Examples 1-5 of this invention; Figure 2 (a) Cr5Mo prepared in Example 1 of the present invention 25 SEM images and EDS elemental distribution maps of the coating; Figure 2 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 SEM images of the coating at different resolutions; Figure 2 (b3) is the Cr prepared in Example 2 of this invention. 10 Mo 20 EDS energy dispersive spectroscopy analysis of the coating; Figure 2 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15 SEM images of the coating at different resolutions; Figure 2 (c3) is the Cr prepared in Example 3 of this invention. 15 Mo 15 EDS elemental distribution diagram of the coating; Figure 2 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 SEM images of the coating at different resolutions; Figure 2 (d3) is the Cr prepared in Example 4 of this invention. 20 Mo 10 EDS elemental distribution diagram of the coating; Figure 2(e1-e2) refers to the Cr prepared in Example 5 of this invention. 25 EDS elemental distribution diagram of Mo5 coating; Figure 3 (a1-a2) are Cr5Mo prepared in Example 1 of this invention. 25 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (e1-e2) refers to the Cr prepared in Example 5 of this invention. 25 Microscopic morphology and voltaic potential diagram of Mo5 coating; Figure 4 (a) is a curve showing the change in microhardness along the thickness direction of the coatings prepared in Examples 1-5 of the present invention; Figure 4 (b) is a diagram showing the average microhardness of the coatings prepared in Examples 1-5 of the present invention; Figure 4 (c) is an indentation diagram at the interface between the coating prepared in Example 1 of the present invention and the substrate; Figure 4 (d) is an indentation diagram at the interface between the coating prepared in Example 5 of the present invention and the substrate; Figure 5 (a) Nyquist plots of the coatings prepared in Examples 1-5 of the present invention in 0.1 M H2SO4; Figure 5 (b) is a Bode plot of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 5 (c) is the equivalent circuit diagram of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 5 (d) is the potentiodynamic polarization curve of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 6 (a) is the OCP curve of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6 (b) Nyquist plots of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6 (c) Bode plots of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6(d) Equivalent circuit elements of the coatings prepared in Examples 1-5 of this invention in 3.5% NaCl solution. R 1. CPE The graph showing the changing pattern of 1; Figure 6 (e) Equivalent circuit elements of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution. R 2. CPE 2. R p The diagram showing the changing patterns; Figure 6 (f) is a diagram showing the thickness of the passivation film formed on the coatings prepared in Examples 1-5 of the present invention in a 3.5% NaCl solution; Figure 6 (g) is the potentiodynamic polarization curve of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 7 (a1-a2) are Cr5Mo prepared in Example 1 of this invention. 25 SEM images of the surface morphology and CLSM features of the topography of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15 Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (e1-e2) refers to the Cr prepared in Example 5 of this invention. 25 Surface morphology and topographic features of Mo5 coating after polarization curve testing in 3.5% NaCl solution; Figure 8 (a1-a3) are Cr5Mo prepared in Example 1 of this invention. 25 Fractional content analysis of Cr, Mo and O elements in different valence states in the passivation film formed on the coating; Figure 8 (b1-b3) are Cr prepared in Example 2 of this invention. 10 Mo 20 Fractional content analysis of Cr, Mo and O elements in different valence states in the passivation film formed on the coating; Figure 8 (c1-c3) are Cr prepared in Example 2 of this invention.15 Mo 15 Fractional content analysis of Cr, Mo and O elements in various chemical states in the passivation film formed on the coating; Figure 8 (d1-d3) Cr prepared in Example 4 of this invention 20 Mo 10 A graph showing the fractional content of Cr, Mo, and O elements in different valence states in the passivation film formed on the coating. Figure 8 (e1-e3) are Cr prepared in Example 5 of this invention. 25 A graph showing the fractional content of Cr, Mo, and O elements in different valence states in the passivation film formed on the Mo5 coating; Figure 9 (a) Cr5Mo prepared in Example 1 of the present invention 25 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (b) Cr prepared in Example 2 of the present invention 10 Mo 20 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (c) Cr prepared in Example 3 of the present invention 15 Mo 25 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (d) is the Cr prepared in Example 4 of this invention. 20 Mo 10 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (e) is the Cr prepared in Example 5 of the present invention. 25 OCP diagrams of Mo5 coatings at different temperatures in 3.5% NaCl solution; Figure 10 The image shows the potentiostatic test results of the coatings prepared in Examples 1-5 of this invention in a 3.5% NaCl solution. Detailed Implementation Plan The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 S1 weighs out 31% Co, 5% Cr, 31% Ni, 25% Mo, and 6% Nb metal powder and 2% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder; wherein, the purity of Co, Mo, and Nb metal powder is ≥99.9 wt%; the purity of Cr and Ni metal powder is ≥99.5 wt%; and the purity of B4C metal powder is ≥98 wt%. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 6 h, and then dried in a vacuum drying oven at 50°C for 24 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 50 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.4 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, namely CoCr5NiMo. 25 Nb6 / 2%B4C composite coating.

[0021] The actual composition of the corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared according to the method of Example 1 is approximately Co. 29.97 Cr 4.79 Ni 29.87 Mo 24.61 Nb 6.68 / 1.86%B4C, denoted as Cr5Mo 25 coating.

[0022] Example 2 S1 weighs out 31% Co, 10% Cr, 31% Ni, 20% Mo, 6% Nb metal powder and 2% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 4 h, and then dried in a vacuum drying oven at 60°C for 20 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 55 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.2 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 25%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 10 NiMo 20 Nb6 / 2%B4C coating.

[0023] The corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared according to the method in Example 2 has an actual composition approximately equal to Co. 29.86 Cr 9.86 Ni 30.02 Mo 20.56 Nb 6.35 / 1.9%B4C, denoted as Cr 10 Mo 20 coating.

[0024] Example 3 S1 weighs out 31% Co, 15% Cr, 31% Ni, 15% Mo, 6% Nb metal powder and 2% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled for 5 hours in anhydrous ethanol medium at a speed of 60 r / min, and then dried in a vacuum drying oven at 55°C for 26 hours to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 45 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.3 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 15 NiMo 15 Nb6 / 2%B4C coating.

[0025] The corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared according to the method in Example 3 has an actual composition approximately equal to Co. 29.86 Cr 9.86 Ni 30.02 Mo 20.56 Nb 6.35 / 1.9%B4C, denoted as Cr 15 Mo 15 coating.

[0026] Example 4 S1 weighs out 31% Co, 20% Cr, 31% Ni, 10% Mo, 6% Nb metal powder and 2% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 6 h, and then dried in a vacuum drying oven at 50°C for 24 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 50 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.4 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 20 NiMo 10 Nb6 / 2%B4C coating.

[0027] The corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared according to the method in Example 4 has an actual composition approximately equal to Co. 29.82 Cr 19.99 Ni 30.46 Mo9Nb 7.69 / 1.84%B4C, denoted as Cr 20 Mo 10 coating.

[0028] Example 5 S1 weighs out 31% Co, 25% Cr, 31% Ni, 5% Mo and 6% Nb metal powder and 2% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 6 h, and then dried in a vacuum drying oven at 50°C for 24 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 50 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.4 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 25 NiMo5Nb6 / 2%B4C coating.

[0029] The corrosion-resistant and wear-resistant CoCrNiMo-based composite coating prepared according to the method in Example 5 has an actual composition approximately equal to Co. 30.93 Cr2 4.64Ni 30.53 Mo 5.24 Nb 5.68 / 1.99%B4C, denoted as Cr 25 Mo5 coating.

[0030] Example 6 S1 weighs out 29.5% Co, 15% Cr, 29.5% Ni, 15% Mo, 8% Nb metal powder and 1.8% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 6 h, and then dried in a vacuum drying oven at 50°C for 24 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 50 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.4 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 15 NiMo 15 Nb6 / 1.8%B4C coating.

[0031] Example 7 S1 weighs out 30% Co, 15% Cr, 30% Ni, 15% Mo, 7% Nb metal powder and 1.9% B4C ceramic powder according to atomic percentage, and mixes all powders evenly to obtain the first mixed powder. S2 The first mixed powder is placed in a planetary ball mill, and cemented carbide grinding balls are added at a ball-to-powder ratio of 8:1. The mixture is ball-milled in anhydrous ethanol medium at a speed of 60 r / min for 6 h, and then dried in a vacuum drying oven at 50°C for 24 h to obtain the second mixed powder. The particle size of each metal powder in the second mixed powder is 50 μm. S3 uses wire cutting technology to process 300M steel into strip-shaped samples with dimensions of 100mm×10mm×5mm. The surface is polished with 180# and 400# sandpaper to remove the oxide layer and expose the metallic luster, thus obtaining a pretreated matrix. The second mixed powder is pre-evenly spread on the surface of the pretreated matrix and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer with a thickness of 2mm. Under the protection of argon gas at a flow rate of 15 L / min, S4 employs a semiconductor fiber laser with the following process parameters: laser power 1.4 kW, scanning rate 300 mm / min, spot diameter 3 mm, and overlap rate 30%. A pre-placed powder layer is then laser-clad to form a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, i.e., CoCr... 15 NiMo 15 Nb6 / 1.9%B4C coating.

[0032] Structural characterization The coatings prepared in the embodiments of the present invention were sequentially sanded with sandpaper ranging from 400# to 5000# until the surface was smooth and uniform. The phase composition of the coatings prepared in the embodiments of the present invention was analyzed by XRD. Figure 1 These are XRD comparison patterns of the coatings prepared in Examples 1-5 of this invention; Figure 1 It can be seen that the coating prepared in the examples mainly consists of a face-centered cubic (FCC) structure as the main phase. With increasing Cr content and decreasing Mo content, the proportion of the FCC phase gradually increases, while the volume fraction of the second phase gradually decreases. The second phase includes a body-centered cubic (BCC) structure, a hexagonal close-packed Laves phase, and a phase composed of (Mo, Nb). 23 Metal carbides composed of (B,C)6 and (Co,Cr)2(B,C). The Cr prepared in Example 5 of this invention... 25 The Mo5 coating achieves a single FCC phase structure. The aforementioned phase transformation behavior can be attributed to the atomic size effect of the alloying elements: the atomic radii of Mo and Nb are much larger than those of Co, Cr, and Ni, easily inducing lattice distortion and promoting the formation of BCC and Laves phases. The second phase is uniformly distributed in the matrix, forming a significant second-phase strengthening effect and improving the coating hardness. The FCC phase is a ductile matrix, while the BCC structure has higher hardness, and the Laves phase combines extremely high hardness, strength, and good creep / wear resistance. Furthermore, metal carbides further enhance the coating's hardness performance through precipitation strengthening.

[0033] The microstructure and elemental distribution of the coatings prepared in the examples were observed using a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) instrument. Figure 1 X-ray diffraction (XRD) comparison patterns of the coatings prepared in Examples 1-5 of this invention; Figure 2(a) Cr5Mo prepared in Example 1 of the present invention 25 SEM images and EDS elemental distribution maps of the coating; Figure 2 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 SEM images of the coating at different resolutions; Figure 2 (b3) is the Cr prepared in Example 2 of this invention. 10 Mo 20 EDS energy dispersive spectroscopy analysis of the coating; Figure 2 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15 SEM images of the coating at different resolutions; Figure 2 (c3) is the Cr prepared in Example 3 of this invention. 15 Mo 15 EDS elemental distribution diagram of the coating; Figure 2 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 SEM images of the coating at different resolutions; Figure 2 (d3) is the Cr prepared in Example 4 of this invention. 20 Mo 10 EDS elemental distribution diagram of the coating; Figure 2 (e1-e2) refers to the Cr prepared in Example 5 of this invention. 25 EDS elemental distribution map of Mo5 coating; by Figure 2 It can be seen that the microstructure of the coating changes significantly with the change of Cr and Mo content. Based on the EDS line scan and area scan results, the Cr5Mo prepared in Examples 1-3... 25 Cr 10 Mo 20 and Cr 15 Mo 15 A second phase enriched with Mo, Nb, B, and C elements was formed in the coating, corresponding to (Mo, Nb) in the XRD pattern. 23 (B,C)6. This type of second phase has a regular morphology, while the matrix is ​​enriched in Co, Cr, Ni, and Fe. During high-speed laser cladding, due to the limited atomic diffusion time, the Cr content in the second phase does not reach the concentration corresponding to free energy equilibrium, resulting in Cr depletion in this region. In contrast, the Cr prepared in Examples 4-5... 20 Mo 10 and Cr 25The Mo5 coating exhibits a typical dendritic structure with a uniform Cr distribution. Co and Ni are enriched in the dendritic regions, forming an FCC solid solution; while Mo, Nb, B, and C are enriched in the interdendritic regions, forming metal carbides and the Laves phase. Due to the larger atomic radii of Mo and Nb, they are displaced to the interdendritic regions after exceeding the solubility limit of the FCC matrix, resulting in enrichment. Simultaneously, B and C are also preferentially enriched in the interdendritic regions, which can be attributed to their more negative enthalpy of mixing with Mo and Nb, forming more stable intermetallic compounds. Furthermore, small amounts of B and C react with Co and Cr to form the (Co,Cr)4(B,C) phase. These results indicate that during laser cladding, B4C particles decompose, react with metal elements to form metal carbides, and produce a significant second-phase strengthening effect, thereby greatly improving the microhardness and mechanical properties of the coating.

[0034] After the coating prepared in the embodiments of the present invention was finely polished with silicone polishing liquid, the surface morphology and Volta potential distribution were tested in air using atomic force microscopy (AFM). Figure 3 (a1-a2) are Cr5Mo prepared in Example 1 of this invention. 25 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 Microscopic morphology and voltaic potential diagram of the coating; Figure 3 (e1-e2) are the microscope morphology and volt-potential diagram of the Cr25Mo5 coating prepared in Example 5 of the present invention; Figure 3 The atomic force microscopy (AFM) morphology and Volta potential distribution of the coatings prepared in Examples 1-5 are shown. Figure 3 It can be seen that in AFM measurement, when the probe tip is set to zero potential, the results show that the Volta potential in the second phase region is generally lower than that in the matrix region, meaning that corrosion reaction is more likely to occur in the low potential region. Figure 3 The potential distributions of two different regions are clearly shown. This is evident in the Cr5Mo prepared in Examples 1-3. 25 Cr 10 Mo 20 With Cr 15 Mo 15In the coating, the second phase is randomly distributed in the matrix and is sparse in the interdendritic region. As the Mo content decreases, the size and area fraction of the second phase in the coating significantly decrease. In the Cr prepared in Examples 4-5... 20 Mo 10 With Cr 25 In the Mo5 coating, the matrix exhibits a typical dendritic distribution, while the second phase is mainly located in the interdendritic region. The Volta potential of the dendritic region is higher than that of the interdendritic region, indicating that the second phase preferentially dissolves as an anode in the corrosion reaction, thereby protecting the FCC matrix phase.

[0035] Performance testing The coatings prepared in Examples 1-5 were tested for hardness along the thickness direction using a Vickers microhardness tester, with an indentation spacing of 100 μm. Each depth was tested at least three times to ensure data repeatability. Figure 4 (a) is a curve showing the change in microhardness along the thickness direction of the coatings prepared in Examples 1-5 of the present invention; Figure 4 (b) is a diagram showing the average microhardness of the coatings prepared in Examples 1-5 of the present invention; Figure 4 (c) is an indentation diagram at the interface between the coating prepared in Example 1 of the present invention and the substrate; Figure 4 (d) is an indentation diagram at the interface between the coating prepared in Example 5 of the present invention and the substrate; Figure 4 (ab) shows the microhardness variation curves and average microhardness values ​​of the coating along its thickness. The hardness near the coating / substrate interface is slightly lower than that of the 300M steel substrate. This may be due to: a deviation of the composition in this region from the designed high-entropy alloy ratio; grain growth or soft phase formation caused by the heat input of laser cladding; and potential defects or residual stress in the interface region. The Vickers hardness of the substrate exceeds 500 HV. 0.2 It exhibits a significantly higher hardness level than conventional stainless steel or titanium alloys. Cr5Mo prepared in Examples 1-4 25 Cr 10 Mo 20 Cr 15 Mo 15 and Cr 20 Mo 10 The average microhardness of the coatings all exceeded 1000 HV. 0.2 It is approximately twice the size of the matrix. The Cr prepared in Example 5... 25 The average microhardness of the Mo5 coating decreased slightly to 953.4 HV. 0.2 The hardness distribution curves of the five coatings showed no significant fluctuations, indicating that the reinforcing phase was uniformly distributed in the FCC matrix. Figure 4As shown in (cd), the indentation size at the coating-substrate interface is significantly smaller than that of the substrate, and no cracks were found around the indentation, indicating that the coating possesses both high hardness and good toughness. Introducing 2 at.% B4C into the coating induces the precipitation of various metal carbides in the matrix and interdendritic regions. The second phase exhibits a micron-scale dispersed distribution with different crystallographic characteristics, forming an effective reinforcing phase carrier. Its strengthening mechanism mainly suppresses plastic deformation through dislocation shearing, significantly improving the strength and hardness of the coating.

[0036] The corrosion-resistant and wear-resistant CoCrNiMo-based composite coatings prepared in Examples 1-5 were welded to copper wires to form working electrodes, which were then encapsulated with epoxy resin, leaving only a 5mm × 10mm exposed area. For high-temperature electrochemical testing, E44 epoxy resin and ethylenediamine were used as curing agents to prevent softening at high temperatures. All tests were performed using an AUTOLAB PGSTAT 302N electrochemical workstation with a three-electrode system: the working electrode was the corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, the reference electrode was a saturated calomel electrode (SCE), and the auxiliary electrode was a platinum electrode. The corrosive media were 0.1 M H2SO4 and 3.5% NaCl solution, respectively. Except for the critical pitting temperature test, all other experiments were conducted in a 25°C constant temperature water bath. The test procedure included: open circuit potential (OCP) test, electrochemical impedance spectroscopy (EIS) test, and potentiodynamic polarization curve test. Before the OCP test, the working electrode was subjected to -1V (SCE) cathodic polarization for 3 minutes to unify its surface state, followed by a 3600-second OCP test. EIS testing was conducted immediately after OCP stabilization, with a test frequency range of 100 kHz to 10 mHz and a perturbation voltage of 20 mV. ZSimpWin software was used to fit the EIS data to obtain the capacitance and resistance information of the passivation film. The scan rate for the potentiodynamic polarization curve was 0.5 mV / s, and the anolyte current density reached 5 mA / cm². 2 That is, it ends. Figure 5 (a) Nyquist plots of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 5 (b) is a Bode plot of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 5 (c) is the equivalent circuit diagram of the coatings prepared in Examples 1-5 of the present invention in 0.1M H2SO4; Figure 5 (d) shows the potentiodynamic polarization curves of the coatings prepared in Examples 1-5 of this invention in 0.1M H2SO4; the Nyquist spectra of the coatings all exhibit a compressed semi-circular shape, reflecting the charge transfer process on the surface of the non-uniform passivation film. With increasing Cr content and decreasing Mo content, the radius of the capacitance arc gradually increases, indicating improved corrosion resistance. Among them, Cr... 25The Mo5 coating exhibits the largest capacitance arc radius and modulus, demonstrating optimal corrosion resistance. The corrosion resistance of the coating is closely related to the charge transfer resistance. In this embodiment, the R2 value is positively correlated with the capacitance arc radius. The Cr prepared in Example 5... 25 The R2 of the Mo5 coating is much larger than R1, which plays a decisive role in the polarization resistance. In addition, the n1 values ​​are all higher than 0.80, indicating that the coating surface has good density and can effectively prevent the penetration of corrosive ions. Figure 5 (d) shows the potentiodynamic polarization curves of the coatings in 0.1M H2SO4 solution. All five coatings exhibit a significant passivation trend. Examples 3-5 show the Cr... 15 Mo 15 Cr 20 Mo 10 With Cr 25 The polarization curves of the Mo5 coatings exhibit a stable passivation region without a significant activation-passivation transition, indicating that a passivation film can spontaneously form at its respective corrosion potential. Cr plays a crucial role in the formation and growth of this passivation film. The overpassivation potentials of the five coatings are roughly similar, corresponding to the dissolution potential of Cr2O3. Within the passivation region, surface dissolution and oxide film formation are in dynamic equilibrium. As the potential shifts positively, elements such as Cr and Mo cease continuous dissolution and instead form dense oxide films (such as Cr2O3 and MoO2) to achieve surface passivation, with their dissolution rate significantly decreasing and remaining at a low level. When the potential further increases to the overpassivation region, the oxide film undergoes chemical dissolution or electrochemical decomposition, leading to a renewed increase in current density. At 0.4V... SCE In the examples 1-5, the passivation current densities of the five coatings prepared, from highest to lowest, are: Cr5Mo 25 >Cr 10 Mo 20 >Cr 15 Mo 15 >Cr 20 Mo 10 >Cr 25 Mo5, as seen in the Cr prepared in Example 5 25 The Mo5 coating exhibits the best corrosion resistance, as shown in Example 1 with Cr5Mo. 25 The coating is the worst.

[0037] To further investigate the coating in Cl-rich environments - In terms of performance in the environment, this embodiment of the invention uses a 3.5% NaCl solution to evaluate its corrosion behavior and localized corrosion resistance. Figure 6 (a) is the OCP curve of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6 (b) Nyquist plots of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6 (c) Bode plots of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution; Figure 6 (d) Equivalent circuit elements of the coatings prepared in Examples 1-5 of this invention in 3.5% NaCl solution. R 1. CPE The graph showing the changing pattern of 1; Figure 6 (e) Equivalent circuit elements of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution. R 2. CPE 2. R p The diagram showing the changing patterns; Figure 6 (f) is a diagram showing the thickness of the passivation film formed on the coatings prepared in Examples 1-5 of the present invention in a 3.5% NaCl solution; Figure 6 (g) is the potentiodynamic polarization curve of the coatings prepared in Examples 1-5 of the present invention in 3.5% NaCl solution. Figure 6 (a) The open-circuit potential (OCP) curve of the coating in 3.5% NaCl solution for 3600 s. The results show that as the Cr content increases and the Mo content decreases, the OCP gradually shifts positively, indicating that the corrosion resistance of the coating is significantly improved, that is, a higher OCP value corresponds to a lower corrosion tendency. After 3600 s, the OCP tends to stabilize, indicating that a stable steady-state condition has been established at the coating / electrolyte interface. Figure 6 (bc) shows the Nyquist and Bode plots of the coating in 3.5% NaCl solution, respectively. The equivalent circuit used for fitting is the same as... Figure 6 (c) In the mid-frequency region, the Bode plots of the coatings all exhibit broad peak phase angles between 70° and 90°, and the modulus-frequency plots show a linear slope of approximately -1, indicating that the coating surface possesses typical capacitive behavior. Fitting results show that the resistance of the inner passivation film is generally higher than that of the outer passivation film, especially in the Cr prepared in Example 4. 20 Mo 10 Compared with the Cr prepared in Example 5 25 This is more pronounced in the Mo5 coating, indicating that the coating forms a double-layer passivation film structure of "porous outer layer + dense inner layer". The five coatings... R The small variation in the 1 value indicates that the outer membrane structures are all quite similar. R The low 1 value may be related to the poor stability of the hydroxide formed by Cr and Mo, resulting in a looser outer film. Figure 6 (de) shows R 1. CPE 1. R 2. CPE 2 with polarization resistor R p The fitting results show that...R The trend of p does not correspond to R 1 is consistent with, but with R The consistency in 2 indicates that the protective capability of the passivation film is mainly determined by the inner layer. For the inner passivation film, as the Cr content increases and the Mo content decreases, n 2 values ​​and R The gradually increasing value of 2 indicates that the compactness of the passivation film gradually increases. Specifically, Cr... 25 Mo5 coating n 2 is 0.99, which is close to the state of an ideal capacitor. R The value of 2 is significantly higher than that of other coatings, indicating that a dense and stable passivation film has been formed on its surface. Figure 6 (g) shows the potentiodynamic polarization curve of the coating in 3.5% NaCl solution. With increasing Cr content and decreasing Mo content, the polarization curve shifts significantly to the left, indicating a positive shift in corrosion potential and a decrease in corrosion current density, suggesting a significant improvement in the coating's corrosion resistance. The polarization curve exhibits typical passivation characteristics, indicating the formation of a protective passivation film on the coating surface. Further analysis revealed that Cr is the key factor affecting the corrosion resistance of the HEA coating. Cr easily accumulates on the alloy surface, forming a dense and stable oxide film mainly composed of Cr2O3, effectively blocking the contact between the corrosive medium and the metal substrate, significantly reducing the corrosion rate. With increasing Cr content, the passivation film forms more easily and becomes more stable, leading to a positive shift in corrosion potential, a decrease in current density, and enhanced corrosion resistance. In contrast, while Mo also improves corrosion performance, its mechanism is different. Mo mainly functions by increasing the density and pitting resistance of the passivation film. In reducing media, Mo can accumulate at passivation film defects, playing a repairing and strengthening role. It should be noted that the overpassivation potential of the coating generally decreases with increasing Cr content, indicating that Cr plays a dominant role in improving corrosion resistance, while increasing Mo content can increase the overpassivation potential and expand the passivation region. Therefore, a high Cr and low Mo composition (Cr prepared in Example 5) is suitable. 25 The Mo5 coating exhibits superior corrosion resistance.

[0038] Figure 7 (a1-a2) are Cr5Mo prepared in Example 1 of this invention. 25 SEM images of the surface morphology and CLSM features of the topography of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (b1-b2) are Cr prepared in Example 2 of this invention. 10 Mo 20 Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (c1-c2) represents the Cr prepared in Example 3 of this invention. 15 Mo 15Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (d1-d2) Cr prepared in Example 4 of this invention 20 Mo 10 Surface morphology and topographic features of the coating after polarization curve testing in 3.5% NaCl solution; Figure 7 (e1-e2) refers to the Cr prepared in Example 5 of this invention. 25 Surface morphology and topographic features of Mo5 coating after polarization curve testing in 3.5% NaCl solution; Figure 7 SEM and CLSM images of the coatings prepared in Examples 1-5 after polarization testing in 3.5% NaCl solution are shown. Different degrees of corrosion morphology are observed on the sample surfaces. The second phase in the coating is randomly distributed within the matrix, resulting in a potential difference between the two, which in turn induces galvanic corrosion. Cr5Mo 25 The corrosion was most severe in the coating. Compared to the Cr5Mo prepared in Example 1... 25 Compared to the coating prepared in Example 4, the Cr coating... 20 Mo 10 And the Cr prepared in Example 5 25 The corrosion morphology of Mo5 coatings differs. For example... Figure 7 As shown in (a1-c1), corrosion mainly concentrates at the interface between the second phase and the matrix phase (around the regular rhomboid area in the figure), meaning the second phase with lower potential is more prone to corrosion. This is also the case for the Cr prepared in Example 2. 10 Mo 20 And the Cr prepared in Example 3 15 Mo 15 The main causes of passivation film failure in coatings. (Combined) Figure 2 and Figure 3 It can be seen that the Cr prepared in Example 4 20 Mo 10 Compared with the Cr prepared in Example 5 25 The Mo5 coating exhibits a typical dendritic structure, and its corrosion morphology is also basically similar. The second phase is enriched in the interdendritic regions, which have a lower potential and thus become preferential rusting areas, the main sites leading to localized failure of the passivation film. Due to the Cr prepared in Example 4... 20 Mo 10 And the Cr prepared in Example 5 25 The phase distribution in the Mo5 coating is more uniform, with relatively less second phase, so its corrosion morphology tends to be more uniform corrosion.

[0039] Under constant temperature of 25°C, the coatings prepared in Examples 1-5 were immersed in 3.5% NaCl solution for 24 hours to form passivation films on their surfaces. Subsequently, X-ray photoelectron spectroscopy (XPS) was used to analyze the composition, elemental composition, and chemical state of the passivation films. Test parameters included: monochromatic Al Kα radiation, power 150 W, spot diameter 500 μm, and C1s (284.8 eV) as the binding energy calibration standard. The sputtering rate was 0.02 nm / s, and data were acquired every 20 seconds for a total of 8 times. XPS PEAK 4.1 software was used for data fitting and quantitative analysis. Figure 8 (a1-a3) are Cr5Mo prepared in Example 1 of this invention. 25 Fractional content analysis of Cr, Mo and O elements in different valence states in the passivation film formed on the coating; Figure 8 (b1-b3) are Cr prepared in Example 2 of this invention. 10 Mo 20 Fractional content analysis of Cr, Mo and O elements in different valence states in the passivation film formed on the coating; Figure 8 (c1-c3) are Cr prepared in Example 2 of this invention. 15 Mo 15 Fractional content analysis of Cr, Mo and O elements in various chemical states in the passivation film formed on the coating; Figure 8 (d1-d3) Cr prepared in Example 4 of this invention 20 Mo 10 A graph showing the fractional content of Cr, Mo, and O elements in different valence states in the passivation film formed on the coating. Figure 8 (e1-e3) are Cr prepared in Example 5 of this invention. 25 A graph showing the fractional content of Cr, Mo, and O elements in different valence states in the passivation film formed on the Mo5 coating.

[0040] Cr 2p 3 / 2 The spectrum shows three peak positions: metallic Cr, Cr₂O₃, and Cr(OH)₃. Surface analysis results show that the outermost layer is mainly Cr(OH)₃, while the metallic Cr signal originates from the substrate coating. The study indicates that Cr(OH)₃ exhibits a porous microstructure, making it difficult to effectively suppress Cl₂. - Penetration limits its anti-corrosion effect; while Cr2O3, with its dense and stable structure, is a key barrier to improve the material's corrosion resistance. With prolonged sputtering time, the passivation film gradually transitions from Cr(OH)3 to a Cr2O3-dominated inner layer, the latter possessing superior protective performance. The thickness of the outer Cr(OH)3 layer can be inferred from the disappearance time of its peak in XPS. The thickness increases with Cr content... 10 Mo 20 Rise to Cr 25The sputtering time required for the Mo5,Cr(OH)3 signal to disappear decreased from 120 s to 60 s, indicating that the outer porous film gradually thinned, suggesting that the inner Cr2O3 enrichment region plays a dominant role in the overall corrosion resistance. Metallic Mo and Mo2O3 are visible in the Mo 3d spectrum. 4+ with Mo 6+ The spin-orbit coupling peak. Mo in the initial sputtering stage. 6+ The proportion was relatively high at first, then gradually decreased. 6+ Located on the surface of the passivation film, from Mo 4+ It can effectively resist oxidation by Cl. - Induced pitting corrosion. Metallic Mo primarily originates from the alloy matrix. 4+ It is mainly present in the inner passivation film. Mo's high standard electrode potential gives it high stability in the metallic state, further enhancing the long-term protective capability of the passivation film. The O element signal can be deconvolved into O. 2- OH - It exists in three forms: adsorbed H2O, bound water, and soluble H2O. Bound water signals can be detected in the initial sputtering stage. Bound water effectively captures dissolved metal ions, promoting the formation of a new passivation film and thus improving corrosion resistance.

[0041] The critical pitting temperature (CPT) test employed potentiostatic technology, with the following procedure: The HEA-coated sample was immersed in a 3.5 wt% NaCl solution as the working electrode. After the anodic current density (OCP) stabilized, a constant potential (+0.2V relative to OCP) was applied, and the temperature was linearly increased from 5°C to 90°C at a rate of 1°C / min. The change in anodic current density was monitored in real time. When the current density suddenly increased and continued to rise, pitting corrosion occurred, and the corresponding temperature was the critical pitting temperature. After completing 3600 seconds of OCP testing at different temperatures, capacitance measurements were performed at a fixed frequency of 1 kHz, an AC voltage of 10 mV, and a step size of 25 mV, with the scan direction from anode to cathode. A high scan rate was used during the test to "freeze" the film thickness and defect structure, allowing only the electronic structure to respond to voltage changes. Figure 9 (a) Cr5Mo prepared in Example 1 of the present invention 25 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (b) Cr prepared in Example 2 of the present invention 10 Mo 20 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (c) Cr prepared in Example 3 of the present invention 15 Mo 25 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (d) is the Cr prepared in Example 4 of this invention. 20 Mo10 OCP diagrams of the coating at different temperatures in 3.5% NaCl solution; Figure 9 (e) is the Cr prepared in Example 5 of the present invention. 25 OCP curves of Mo5 coatings in 3.5% NaCl solution at different temperatures. In the later stages of the test, all curves tended to stabilize. However, at 80°C and 90°C, the Cr5Mo prepared in Example 1 showed... 25 The OCP curve of the coating showed slight fluctuations; the Cr prepared in Example 2 10 Mo 20 The coating also exhibited similar fluctuations at 90°C. This phenomenon is attributed to the dynamic evolution of the passivation film during corrosion and repassivation at high temperatures. In the embodiments of the invention, the negative shift trend of OCP is dominant, indicating that Cl... - Enhanced dissolution effect dominates passivation behavior. Cr prepared in Example 5 25 The Mo5 coating exhibits the smallest negative OCP shift, possibly due to the stronger resistance of its dense passivation film to Cl. - It is closely related to penetration ability. Figure 10 Potentiostatic test graphs of the coatings prepared in Examples 1-5 of this invention in 3.5% NaCl solution are shown to reveal their critical pitting temperature (CPT) behavior. As the Cr content gradually increases from 5 at.% to 25 at.%, the Mo content decreases accordingly, and the CPT and electrochemical behavior show a clear composition-dependent relationship. Low Cr / high Mo coating (Cr5Mo prepared in Example 1) 25 The coating did not exhibit significant CPT in the 5–90°C range, and the anolyte current density increased linearly, approaching 1000 μA / cm². This is due to the formation of a MoO₂-based passivation film on its surface. While this film can suppress metastable pitting corrosion, its overall passivation behavior is poor. Medium Cr / Mo ratio coatings (Cr 10 Mo 20 To Cr 20 Mo 10 A current density inflection point appears in the temperature range of 35–55°C, reflecting the competitive oxidation and structural phase transformation of the Cr2O3-MoO2 composite film, but metastable pitting corrosion can still occur at high temperatures. 15 Mo 15 The coating exhibits a significant CPT jump near 83°C, and its passivation film possesses dielectric relaxation characteristics of a bilayer structure and rapid repassivation capability. Meanwhile, the high Cr / low Mo coating (Cr... 25The current density of the Mo5 coating remained consistently low at 60–90 μA / cm² throughout the entire test temperature range, without exhibiting CPT (cutting-point pitting). This is because the Cr-rich passivation film on the surface, combined with the catalytic passivation effect of Mo, formed a supersaturated protective film, exhibiting excellent resistance to pitting corrosion. In 3.5% NaCl solution, the corrosion resistance of the coating depended on the dynamic balance between the formation, rupture, and repassivation mechanisms of the passivation film. EIS and XPS results revealed that the coating formed a typical bilayer structure: an outer porous film mainly composed of Cr(OH)3 and an inner dense film mainly composed of Cr2O3. Although the protective effect of Cr(OH)3 was relatively weak, the inner Cr2O3 layer effectively prevented Cl- from forming. - Permeation is a key barrier for coatings to resist localized corrosion; Mo plays a multi-dimensional role in the formation kinetics of the passivation film, significantly improving the film formation efficiency and stability. XPS results show that the passivation film surface is dominated by Mo. 6+ Mainly, derived from Mo 4+ In the rapid oxidation process at the metal / electrolyte interface, the MoO3 formed in this stage can inhibit further metal dissolution. With prolonged sputtering time, the Mo valence state changes from Mo... 6+ Gradually transforming into Mo 4+ The latter exists stably within the membrane layer. The inner Cr2O3 layer acts as a diffusion barrier, preventing oxidant penetration, while Mo... 4+ This can serve as a reserve resource for the self-healing of the coating. This mechanism, through Cr promoting oxidation nucleation and Mo regulating valence state stability, significantly enhances the passivation initiation efficiency and self-healing ability of the coating in a chloride ion environment, thereby improving the overall corrosion resistance and long-term stability.

[0042] In summary, this invention investigated the effects of Cr and Mo content on corrosion and wear resistance of CoCrNiMo-based composite coatings, i.e., CoCr... x NiMo 30-x The influence of CoCr on the microstructure and corrosion behavior of the Nb6 / B4C coating. Results show that CoCr... x NiMo 30- x The phase composition of the Nb6 / 2%B4C coating includes an FCC phase and precipitated phases, among which the precipitated phases are (Mo, Nb). 23 (B,C)6, (Co,Cr)2(B,C) and Laves phases. The main strengthening mechanisms are precipitation strengthening and solid solution strengthening. The microhardness of the coating is approximately twice that of the substrate. The Cr5Mo prepared in Example 1 was subjected to treatment in 0.1 mol / L H2SO4 solution and 3.5% NaCl solution. 25 The coating exhibited the worst corrosion resistance, while the Cr prepared in Example 5... 25The Mo5 coating exhibits the best corrosion resistance. The outer layer of the passivation film prepared in the embodiments of this invention is mainly composed of hydroxides rich in chromium and molybdenum, while the inner layer is mainly composed of chromium oxides; the outer layer has a loose structure, while the inner layer has a dense structure, thus exhibiting high corrosion resistance. This invention alters the composition of the passivation film by adjusting the Cr-Mo ratio, and studies the optimal ratio for both corrosion resistance and critical pitting temperature. It was found that the high-chromium, low-molybdenum Cr5 coating prepared in Example 5... 25 The composition of Mo5 can form a dense chromium-rich passivation film, exhibiting superior resistance to pitting corrosion.

[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, characterized in that, It is prepared by mixing metal powder and ceramic powder in the following atomic percentages: 29.5-31% Co metal powder, 4.7-25% Cr metal powder, 29.5-31% Ni metal powder, 5.5-25% Mo metal powder, 5.5-8% Nb metal powder and 1.8-2% B4C ceramic powder. The preparation method of the corrosion-resistant and wear-resistant CoCrNiMo-based composite coating includes the following steps: S1 weighs out Co, Cr, Ni, Mo and Nb metal powders and B4C ceramic powder in sequence according to atomic percentage, mixes them evenly, and obtains the first mixed powder; S2 Place the first mixed powder in a planetary ball mill and ball mill it in anhydrous ethanol medium, and then place it in a vacuum drying oven to dry it to obtain the second mixed powder. S3 The second mixed powder is pre-uniformly spread on the surface of the pretreated substrate and compacted and flattened by mechanical extrusion to obtain a pre-placed powder layer; Under the protection of argon gas, S4 uses a semiconductor fiber laser to perform laser cladding on a pre-placed powder layer, forming a corrosion-resistant and wear-resistant CoCrNiMo-based composite coating, namely CoCr x NiMo 30-x Nb6 / B4C coating; The ball milling process in step S2 takes 4-6 hours; the particle size of each metal powder in the second mixed powder is 45-55 μm.

2. The composite coating according to claim 1, characterized in that, The purity of the Co, Mo, and Nb metal powders mentioned in step S1 is ≥99.9wt%; the purity of the Cr and Ni metal powders is ≥99.5wt%; and the purity of the B4C ceramic powder is ≥98wt%.

3. The composite coating according to claim 1, characterized in that, The drying temperature in step S2 is 50-60℃, and the drying time is 20-26h.

4. The composite coating according to claim 1, characterized in that, The thickness of the pre-placed powder layer in step S3 is 2 mm.

5. The composite coating according to claim 1, characterized in that, The method for obtaining the pretreated substrate in step S3 includes: processing 300M steel into strips of fixed size using wire cutting technology, and polishing the surface of the strips of steel with 180# and 400# sandpaper in sequence to remove the oxide layer, thereby obtaining the pretreated substrate.

6. The composite coating according to claim 1, characterized in that, The process parameters for laser cladding in step S4 are: laser power 1.2-1.4kW, scanning speed 300mm / min, spot diameter 3mm, and overlap rate 25-30%.

7. The composite coating according to claim 1, characterized in that, The flow rate of the argon gas in step S4 is 15 L / min.

8. The application of the composite coating as described in claim 1 in the field of surface strengthening or repair of aerospace, automotive, marine or industrial equipment.

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