High-temperature wear-resistant crack-free cobalt-based alloy coating as well as preparation method and application thereof

Abstract

The invention discloses a high-temperature wear-resistant crack-free cobalt-based alloy coating as well as a preparation method and application thereof, and the high-temperature wear-resistant crack-free cobalt-based alloy coating is prepared according to the following steps: (1) respectively and accurately weighing spherical Co powder, Cr powder, W powder and C powder according to a stoichiometric equation Co0. 665Cr0. 3W0. 02 C0. 015, and (2) putting the weighed powder into a ball milling tank for ball milling, so that the powder is uniformly mixed, and then drying, sieving, drying and storing; (3) 5NiCrMo steel is selected as a base material, a sand mill is used for polishing the surface of the base material so as to remove surface oxide skin until a bright surface is exposed, and oil stains on the surface are removed; and (4) a laser directional energy deposition method in laser additive manufacturing is used for continuously depositing the crack-free cobalt-based alloy coating with high temperature resistance, wear resistance and no cracks one by one. No metallurgical defect exists, and the wear-resisting property is excellent at high temperature.

Description

Technical Field

[0001] This invention relates to the field of cobalt-based alloy technology, specifically to a high-temperature wear-resistant and crack-free cobalt-based alloy coating, its preparation method, and its application. Background Technology

[0002] High-temperature wear-resistant materials are core materials for extreme operating conditions such as aero-engines, gas turbines, and nuclear power plants. Their performance directly affects the service life and reliability of key components (such as turbine blades, high-temperature sealing rings, and molds). Currently, commonly used high-temperature wear-resistant materials mainly include nickel-based superalloys, cobalt-based alloys, cemented carbides, and cermets. However, with the increasing demands of modern industry for power density and efficiency, traditional materials are showing increasingly obvious limitations in high-temperature (>500°C) environments. Nickel-based superalloys (such as Inconel 718 and Hastelloy X) mainly rely on the γ' phase (Ni3Al) for strengthening, exhibiting excellent strength and oxidation resistance below 700°C; however, when the temperature is further increased to 800–1000°C, oxidation softening and grain boundary weakening problems easily occur. Materials represented by WC-Co cemented carbides and TiC-Ni cermets have extremely high hardness at room temperature (>1500 HV), but their high-temperature performance is limited by factors such as binder phase failure, oxidation, and thermal shock. In addition, Fe-Ni alloys (such as Fe-50Ni Invar alloy) are often used in high-temperature seals due to their low cost and small coefficient of thermal expansion, but their wear resistance, hardness and oxidation resistance under high-temperature conditions are insufficient.

[0003] Laser Additive Manufacturing (LAM) uses high-energy lasers as a heat source to form materials layer by layer, overcoming the limitations of traditional manufacturing technologies and exhibiting significant advantages in many aspects. This technology offers extremely high design freedom, enabling the direct forming of complex geometric components with lightweight cavities, biomimetic topologies, or functional integration features. Simultaneously, its material utilization rate typically exceeds 90%, significantly reducing the waste of expensive metal materials. Combined with its short-cycle, mold-free, and flexible production characteristics, it can effectively shorten R&D cycles and reduce the cost of small-batch customized products. Thanks to the high energy density of lasers, this technology can precisely melt difficult-to-machine materials such as titanium alloys and nickel-based superalloys, achieving microstructural densification and optimized mechanical properties. Furthermore, this technology also possesses strong potential for composite manufacturing. Among these technologies, laser-directed energy deposition (L-DED) stands out. It can precisely deposit materials onto designated areas, making it ideal for repairing damage, restoring dimensions, and strengthening surfaces (such as preparing wear-resistant coatings) of high-value critical components (e.g., aero-engine blades, turbine disks). This not only extends component lifespan but also significantly reduces resource consumption and waste generation. This capability allows additive manufacturing technology to transcend the simple realm of "manufacturing," extending into "remanufacturing" and "functional enhancement," aligning with the principles of green and sustainable development. Overall, laser additive manufacturing technologies, represented by L-DED, are becoming one of the core driving forces propelling high-end manufacturing towards personalization, high performance, and sustainability in the Industry 4.0 era. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the first objective of this invention is to provide a method for preparing a high-temperature wear-resistant and crack-free cobalt-based alloy coating, the second objective is to provide the high-temperature wear-resistant and crack-free cobalt-based alloy coating prepared therefrom, and the third objective is to provide its application.

[0005] To achieve the first objective mentioned above, the present invention provides the following technical solution: a method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating, characterized by the following steps:

[0006] (1) According to the stoichiometric formula Co 0.665 Cr 0.3 W 0.02 C 0.015 Accurately weigh out spherical Co, Cr, W, and C powders respectively.

[0007] (2) Place the weighed powder into a ball mill jar for ball milling to make the powder mix evenly, then dry, sieve, and store in a dry place;

[0008] (3) Select 5NiCrMo steel as the base material, use a sand mill to grind the surface of the base material to remove the surface oxide scale until the bright surface is exposed, and remove the surface oil.

[0009] (4) Using the laser directional energy deposition method in laser additive manufacturing, dry powder is placed in the powder feeding tank of the laser system, and high-purity Ar gas is used to send the powder to the circular spot laser head for melting and deposition, and a crack-free, high-temperature wear-resistant, crack-free cobalt-based alloy coating is continuously deposited.

[0010] In the above scheme: in step (1), the particle size of Co, Cr, W and C powder is 50-150 μm and the purity is ≥ 99.5%.

[0011] In the above scheme: in step (2), the material is sieved through a 100-200 mesh sieve.

[0012] In the above scheme: in step (3), the oil stains on the surface of 5NiCrMo steel are cleaned with alcohol and then air-dried.

[0013] In the above scheme: the laser model is RC-LMS-6000-R fiber laser, the laser power P is 1500-1800W, the scanning rate v is 8-12mm / s, the circular spot diameter is 3mm, and the defocusing amount is 35mm.

[0014] In the above scheme: the laser power is 1600W and the scanning rate v is 10mm / s.

[0015] A high-temperature wear-resistant and crack-free cobalt-based alloy coating is prepared by a method described above.

[0016] The application of the aforementioned high-temperature wear-resistant, crack-free cobalt-based alloy coating in the manufacture of high-temperature wear-resistant materials. These include core materials for extreme operating conditions such as aero-engines, gas turbines, and nuclear power plants. Examples include high-temperature sealing rings for aero-engines, protective coatings for gas turbine blades, and critical components in extreme environments such as deep-sea drilling tools.

[0017] Cobalt-based alloys hold an important position due to their excellent high-temperature strength and outstanding oxidation and corrosion resistance. This invention uses cobalt as the matrix and adds chromium, tungsten, and carbon to form a microstructure combining solid solution strengthening and carbide strengthening, resulting in superior comprehensive performance under extreme high-temperature and wear conditions. Its excellent high-temperature performance stems from a unique synergistic strengthening mechanism of "cobalt-based solid solution + high-hardness carbides." The cobalt matrix provides good high-temperature toughness and thermal stability, while the dispersed chromium, tungsten, and carbides act as hard reinforcing phases, significantly improving the material's wear resistance and load-bearing capacity at high temperatures. Thanks to this microstructure design, the alloy maintains excellent wear resistance, oxidation resistance, and corrosion resistance even above 800°C.

[0018] This invention utilizes laser-directed energy deposition (LDED) technology in laser additive manufacturing to prepare an alloy free of metallurgical defects and cracks. No subsequent heat treatment is required, resulting in an deposited alloy coating exhibiting excellent wear resistance at high temperatures.

[0019] The Co-Cr-WC alloy coating of this invention exhibits excellent wear resistance at both room temperature and high temperature. The average coefficient of friction at room temperature decreases from 0.78 for the substrate to 0.55. The alloy shows shallower wear depth and narrower wear track width over a wide temperature range, with the wear rate at room temperature decreasing from 8.89 × 10⁻⁶ for the substrate. -6 mm 3 / N·m decreased to 5.62×10 -6 mm 3 / N·m, at 800℃, the wear rate is 749.74×10⁻⁶ N·m. -6 mm 3 / N·m decreased to 20.3×10 -6 mm 3 / N·m. Attached Figure Description

[0020] Figure 1 Morphology (a), particle size statistics (b), and macroscopic morphology (c) of the coating prepared by laser-directed energy deposition for the mixed powder of Co, Cr, W, and C.

[0021] Figure 2 The microstructures of the coatings prepared under 12 different laser process parameters are shown.

[0022] Figure 3 The image shows the XRD pattern of the coating (a) and the SEM image of the coating-substrate bonding area (b).

[0023] Figure 4 The images shown are the SEM-SE image (c), SEM-BSE image (d), and elemental surface scan (e) of the coating.

[0024] Figure 5 The IPF diagram (a), phase composition diagram (b), grain size statistics (c), KAM diagram (d), and pole diagram (e) of the coating are shown.

[0025] Figure 6 Microhardness of different samples (a) and their corresponding hardness test indentations (b).

[0026] Figure 7The friction coefficient, wear cross section, 3D image and SEM image of the wear track between the substrate and the coating at room temperature are shown. (a1) Friction coefficient of the substrate, (a2) Cross section curve of the wear track of the substrate, (a3) ​​Morphology of the wear track of the substrate, (a4-a6) SEM images of the wear track of the substrate; (b1) Friction coefficient of the coating, (b2) Cross section curve of the wear track of the coating, (b3) Morphology of the wear track of the coating, (b4-b6) SEM images of the wear track of the coating.

[0027] Figure 8 The friction coefficient, wear cross section, 3D image and SEM image of the wear track between the substrate and the coating at 800℃ are shown. (a1) Friction coefficient of substrate, (a2) Cross section curve of wear track of substrate, (a3) ​​Wear track morphology of substrate, (a4-a6) SEM images of wear track of substrate; (b1) Friction coefficient of coating, (b2) Cross section curve of wear track of coating, (b3) Wear track morphology of coating, (b4-b6) SEM images of wear track of coating.

[0028] Figure 9 This compares the wear rates of the substrate and coating at different temperatures.

[0029] Figure 10 XPS images of the substrate and coating samples after wear tests at room temperature and 800℃. a1-a4: Elemental spectra of the substrate surface after room temperature wear, representing Si, O, Fe, and Ni, respectively; b1-b4: Elemental spectra of the substrate surface after wear at 800℃, representing Si, O, Fe, and Ni, respectively; c1-c6: Elemental spectra of the coating surface after room temperature wear, representing Si, O, Co, Cr, Ni, and Fe, respectively; d1-d6: Elemental spectra of the coating surface after wear at 800℃, representing Si, O, Co, Cr, Ni, and Fe, respectively.

[0030] Figure 11 This diagram illustrates the wear behavior of the coating at 800℃. Stages: Unworn (a), Initial oxide film damage (b), Oxide film self-repair (c). Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] (1) Powder selection: according to the stoichiometric formula Co 0.665 Cr 0.3 W 0.02 C 0.015 Spherical Co, Cr, W, and C powders were accurately weighed. The selected Co, Cr, W, and C alloy powders were spherical with a size of 50-150 μm and a purity of ≥ 99.5%.

[0034] (2) Place the weighed powder into a ball mill jar for ball milling to make the powder mix evenly. Then dry it in a vacuum drying oven at 60°C, pass it through a 100-200 sieve, and store it dry.

[0035] (3) Substrate selection: Magnetic 5NiCrMo steel with a diameter of 105mm and a thickness of 10mm was selected as the substrate. The oxide scale on the surface of the substrate was removed by a grinding wheel until a bright surface was exposed to prevent the formation of holes in the lower part of the sample during the deposition process. The surface oil was cleaned with alcohol and dried with a hair dryer for later use.

[0036] (4) Sample preparation: Using the laser-directed energy deposition method in laser additive manufacturing, the dried powder was placed in the powder feeding tank of the laser powder feeding system. High-purity argon gas with a purity of 99.999% was used to transport the powder raw material to the substrate. At the same time, the laser beam was focused to form a small molten pool, and the powder was gradually deposited on the substrate through a zigzag path to form a crack-free planar sample. Laser power P=1500W, 1600W, 1700W, 1800W, scanning rate v=8mm / s, 10mm / s, 12mm / s, circular spot diameter 3mm, powder filling speed 2r / min, defocusing amount 35mm, and coating thickness 1.5mm were selected for the experiment. A total of 12 sets of process parameters were tested.

[0037] (5) High temperature wear test: Co-Cr-WC alloy samples without metallurgical defects were prepared into 25mm×10mm×5mm friction wear test specimens by wire cutting. The HT-1000 high temperature friction wear tester was used to conduct experiments at room temperature and 800℃ respectively. The high temperature test was conducted by heating the furnace to 800℃ and then conducting friction wear. The load was 10N and the rotation speed was 1000rpm. The friction wear performance of laser-directed energy deposition cobalt-based alloy at room temperature and 800℃ was studied.

[0038] Figure 1 The figures show the morphology, particle size distribution, and macroscopic morphology of the coatings prepared by laser-directed energy deposition (LDED) of a mixed powder of Co, Cr, W, and C. As can be seen from the figures, the raw powder exhibits uniform spherical shape with an average particle size of approximately 100 μm. No obvious defects such as peeling, cracks, nodules, or nodules were observed in the coatings prepared by LDED, indicating that the samples prepared under these process parameters have good surface morphology.

[0039] Figure 2 The images show the microstructure of coatings prepared under 12 different laser process parameters. It can be seen that, except for the 1600W & 10mm / s process, the coatings prepared under other processes all exhibited obvious pores or cracks due to the mismatch in laser energy input.

[0040] from Figure 3It can be seen that the main phase of the Co-Cr-WC alloy coating prepared by laser-directed energy deposition is the FCC phase, and the SEM image shows that the coating and the substrate exhibit good metallurgical bonding.

[0041] Figure 4 SEM images show that the microstructure of the Co-Cr-WC alloy coating consists of dendritic and cellular crystals. Elemental surface scans and the elemental distribution between and within dendrites clearly reveal the presence of Cr, W, and C-rich granular second-phase particles in the coating, possibly carbides of types such as M23C6, M7C3, and MC.

[0042] from Figure 5 It can be seen that the coating grains are columnar with a small amount of cellular grains, and the color corresponds to the standard polar triangle. The phase distribution and grain boundary distribution diagram shows that the FCC phase accounts for 99.8%, while carbides account for only 0.2%, which is consistent with the XRD results. The average grain size is approximately 35 μm. The intragranular stress distribution is uniform, with slight residual stress at the grain boundaries, and no stress concentration is observed within the surface coating. <100> , <110> , <111> The pole figures in three directions are visible <100> The presence of regions with high intensity along the direction indicates that the grain orientation in the coating is mainly along... <100> Directional growth is a common texture in materials prepared by laser deposition.

[0043] Figure 6 The microhardness of different samples and their corresponding hardness test indentations are shown. It can be seen that the hardness of the substrate is approximately 529 HV. 0.2 After being worn at room temperature and 800°C, the voltage drops to 546 HV. 0.2 and 252 HV 0.2 The coating has a hardness of approximately 435 HV. 0.2 After wear at room temperature and 800°C, the values ​​are 478 HV respectively. 0.2 and 427 HV 0.2 The size of the indentation is a direct reflection of the material's microhardness. Hardness is significantly affected by both dissolved atoms and precipitated phases, both of which can enhance material strength by hindering dislocation movement. The hardness of the substrate decreased significantly after being worn at 800℃. This is because the lower bainite structure of the substrate underwent tempering and partial austenitization during the high-temperature wear test.

[0044] Figure 7 The friction coefficients, wear cross-sections, 3D images of the wear tracks, and SEM images of the wear tracks are shown for the substrate and coating at room temperature. The average friction coefficients for the substrate and coating are approximately 0.78 and 0.55, respectively. Comparison of the 3D surface morphology of the wear tracks reveals that the wear tracks on the coating are smaller, but exhibit slight peeling; while the wear tracks on the substrate are wider and deeper, indicating more severe wear behavior. Based on the wear profile area, the wear rates of the substrate and coating at room temperature are calculated to be 8.89 × 10⁻⁶, respectively. -6mm 3 / N·m and 5.62×10 -6 mm 3 / N·m. Observation and elemental analysis of the wear trajectory using SEM, combined with the elemental distribution in Table 1, indicate that the wear mechanism of the substrate at room temperature is a mixed mechanism of abrasive wear, oxidative wear, and adhesive wear, while the wear mechanism of the coating at room temperature is mainly adhesive wear, accompanied by abrasive wear and oxidative wear.

[0045] Table 1 Figure 7 Chemical composition at corresponding points

[0046]

[0047] Figure 8 The friction coefficient, wear cross-section, 3D image of the wear track, and SEM image of the wear track are shown for the substrate and coating at 800℃. The average friction coefficients of the substrate and coating are stable at approximately 0.43 and 0.53, respectively. The wear rates of the substrate and coating at high temperature are calculated from the profile area of ​​the wear track cross-section at 800℃ to be 749.74 × 10⁻⁶. -6 mm 3 / N·m and 20.3×10 -6 mm 3 / N·m. Obvious grooves and material peeling are visible on the substrate surface. Based on the elemental distribution in Table 2, the wear mechanism of the substrate at 800℃ is a combination of oxidative wear, abrasive wear, and adhesive wear. The wear mechanism of the coating at 800℃ is mainly oxidative wear, accompanied by a certain degree of abrasive wear and slight adhesive wear. In summary, due to the low coefficient of friction of the coating at room temperature, and its lower wear rate and smaller wear track depth over a wide temperature range, it exhibits superior wear resistance under both room temperature and high temperature conditions.

[0048] Table 2 Figure 8 Chemical composition at corresponding points

[0049]

[0050] Figure 9 This section compares the wear rates of the substrate and coating at different temperatures. After RT wear, the wear rates of the substrate and coating were 8.89 × 10⁻⁶. -6 mm 3 / N·m and 5.62×10 -6 mm 3 / N·m, the wear rates of the substrate and coating after high-temperature wear at 800℃ were 749.74×10. -6 mm 3 / N·m and 20.3×10 -6 mm 3 / N·m。 At RT and 800℃, the wear resistance of the coating is improved by about 0.6 times and 36 times compared with the substrate, respectively. The wear resistance of the coating is significantly improved at high temperature.

[0051] Figure 10 XPS images of the substrate and coating samples after wear tests at room temperature and 800°C. Both the substrate and coating exhibit common characteristics after high-temperature wear at 800°C: the elemental peaks present at room temperature disappear, indicating that the oxidation degree of the worn surface is intensified at 800°C. For the substrate: at room temperature, the sample surface mainly consists of FeO, Fe2O3, and Si. 4+ It consists of a small amount of elemental compounds; at high temperatures, the Fe content does not change significantly, while the proportion of Si decreases. The surface composition of the coated sample mainly includes Si. 4+ The surface contains CoO, Fe3O4, Cr2O3, and trace amounts of elemental elements. After being worn at 800℃, the main component of the surface is Si. 4+ CoO, FeO and Cr2O3.

[0052] Figure 11 This diagram illustrates the wear behavior of the coating at 800℃. Before wear, a continuous oxide layer rich in Co, Fe, and Cr forms on the coating surface at high temperatures. Once wear begins, this oxide layer provides protection. Under cyclic stress, cracks initiate at defects beneath the surface due to stress concentration. However, the fine, dispersed carbides in the coating pin grain boundaries, effectively hindering crack propagation; therefore, the worn surface undergoes only slight plastic deformation. The fresh surface exposed during friction rapidly forms a secondary oxide layer identical to the primary oxide layer, continuing to protect the underlying material.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating, characterized in that, Prepare according to the following steps: (1) According to the stoichiometric formula Co 0.665 Cr 0.3 W 0.02 C 0.015 Accurately weigh out spherical Co, Cr, W, and C powders respectively. (2) Place the weighed powder into a ball mill jar for ball milling to make the powder mix evenly, then dry, sieve, and store in a dry place; (3) Select 5NiCrMo steel as the base material, use a sand mill to grind the surface of the base material to remove the surface oxide scale until the bright surface is exposed, and remove the surface oil. (4) Using the laser directional energy deposition method in laser additive manufacturing, dry powder is placed in the powder feeding tank of the laser system, and high-purity Ar gas is used to send the powder to the circular spot laser head for melting and deposition, and a crack-free, high-temperature wear-resistant, crack-free cobalt-based alloy coating is continuously deposited.

2. The method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating according to claim 1, characterized in that: In step (1), the particle size of Co, Cr, W and C powders is 50-150 μm and the purity is ≥ 99.5%.

3. The method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating according to claim 2, characterized in that: In step (2), the sample is sieved through a 100-200 mesh sieve.

4. The method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating according to claim 3, characterized in that: In step (3), the oil stains on the surface of 5NiCrMo steel are cleaned with alcohol and then air-dried.

5. The method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating according to claim 4, characterized in that: The laser model is RC-LMS-6000-R fiber laser, with a laser power P of 1500-1800W, a scanning rate v of 8-12mm / s, a circular spot diameter of 3mm, and a defocusing amount of 35mm.

6. The method for preparing a high-temperature wear-resistant, crack-free cobalt-based alloy coating according to claim 5, characterized in that: The laser power is 1600W and the scanning rate v is 10mm / s.

7. A high-temperature wear-resistant, crack-free cobalt-based alloy coating prepared by the method of any one of claims 1-6.

8. The application of the high-temperature wear-resistant, crack-free cobalt-based alloy coating of claim 7 in the manufacture of high-temperature wear-resistant materials.

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