Electric arc spraying / argon arc cladding high-temperature-resistant alloy coating and preparation method thereof

Abstract

The invention relates to the technical field of composite coatings, in particular to an electric arc spraying / argon arc cladding high-temperature-resistant alloy coating and a preparation method thereof. According to the method, the WC88-Co12 base coat is sprayed on the surface of the titanium alloy matrix by adopting an electric arc spraying technology, so that the binding force of Ti-Al-xNb-Y and the titanium alloy matrix is improved, and meanwhile, the high-temperature oxidation resistance of the coating is enhanced by the base coat; and Ti, Al, Nb and Y metal powder is cladded on the surface of the base layer through the argon arc cladding technology, the Ti-Al-xNb-Y coating is prepared, and the high-temperature oxidation resistance of the surface of the titanium alloy is improved. According to the WC88-Co12 / Ti-Al-10Nb-Y composite coating and the preparation method thereof, the process conditions are controlled, the composite coating is free of defects, the coating and a base body are in good metallurgical bonding, and in a constant-temperature oxidation test at 800 DEG C / 100 h, the unit oxidation weight increment of the prepared WC88-Co12 / Ti-Al-10Nb-Y coating is 22.73 mg / cm < 2 > and is only 0.63 times of the unit oxidation weight increment of the base body.

Description

Technical Field

[0001] This invention relates to the field of composite coating technology, and in particular to an arc spraying / argon arc cladding high-temperature resistant alloy coating and its preparation method. Background Technology

[0002] With the continuous development of my country's industrial technology, the development of new structural materials and surface protective coating technologies with high comprehensive performance, low resource consumption, and strong competitive advantages has become the mainstream direction of industrial technology development in various countries. Titanium and titanium alloys possess excellent properties such as high specific strength, excellent corrosion resistance, and good toughness. These superior mechanical properties enable titanium and titanium alloys to be widely used in aerospace, chemical, and biomedical industries. Compared with nickel-based superalloys currently used in the aerospace industry, titanium alloys have a lower density. If high-temperature titanium alloys can be developed to meet the performance requirements of engine components under high-temperature conditions, this will significantly improve engine thrust and further expand the application of titanium alloys in the aerospace field. While titanium alloys themselves have excellent mechanical properties, they have weak fatigue resistance, are prone to oxidation at high temperatures, and experience adhesive wear when in contact with metals, affecting the service life and safety of titanium alloy structural components. Especially in practical industrial applications, titanium alloy structural components generate high temperatures during operation and friction, leading to rapid oxidation of the surface of the titanium alloy structural components, which affects the performance of the titanium alloy and reduces the service life of the titanium alloy workpiece. Therefore, improving the high-temperature oxidation resistance of titanium alloys is a key issue in expanding the application range of titanium alloys. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide an arc spraying / argon arc cladding high-temperature resistant alloy coating and its preparation method. This invention significantly improves the high-temperature oxidation resistance of titanium alloy surfaces by preparing a high-temperature resistant alloy coating on the surface of the titanium alloy substrate.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a high-temperature resistant alloy coating by electric arc spraying / argon arc cladding, comprising the following steps: An arc spraying process is performed on the surface of a titanium alloy substrate to form a WC-Co coating; the welding wire used for the arc spraying uses WC88-Co12 powder as the flux core; the conditions for the arc spraying include: a spraying voltage of 25V, a current of 50A, and a wire feed speed of 25.54mm / s; or, a spraying voltage of 37V, a current of 50-110A, and a wire feed speed of 25.54-55.67mm / s. After coating the WC-Co coating surface with cladding powder, argon arc cladding is performed to form a Ti-Al-xNb-Y coating, thus obtaining the arc spraying / argon arc cladding high-temperature alloy coating; where x=0-15, and x is the mass fraction; The cladding powder is a mixture of Ti, Al, Nb, and Y; by mass percentage, the cladding powder comprises 0.8% Y, 60% Al, 0-15% Nb, and the balance Ti. The conditions for argon arc cladding include: cladding current of 110-120A, gas flow rate of 10-15L / min, welding speed of 150-230mm / min, and when the cladding current is 120A, the welding speed is 150mm / min.

[0005] Preferably, the cladding powder comprises, by mass percentage, 0.8% Y, 60% Al, 10% Nb, and the balance Ti.

[0006] Preferably, the spraying distance of the arc spraying is 80-120mm.

[0007] Preferably, the diameter of the welding wire is 1.0 mm.

[0008] Preferably, the outer sheath of the welding wire is stainless steel.

[0009] Preferably, the thickness of the arc spray coating is 200-350 μm.

[0010] Preferably, the coating thickness of the cladding powder is 1-1.5 mm.

[0011] Preferably, before the arc spraying, the titanium alloy substrate is further subjected to sandblasting.

[0012] Preferably, before coating, the cladding powder is mixed with water glass.

[0013] The present invention provides an arc spraying / argon arc cladding high-temperature alloy coating prepared by the preparation method described above, comprising a WC-Co coating and a Ti-Al-xNb-Y coating stacked on the surface of a titanium alloy substrate, wherein x=0-15 and x is a mass fraction.

[0014] Compared with the prior art, the present invention has the following beneficial effects. This invention employs arc spraying technology to apply a WC88-Co12 underlayer to the surface of a titanium alloy substrate, improving the adhesion between the Ti-Al-xNb-Y coating and the titanium alloy substrate. Simultaneously, the WC88-Co12 underlayer enhances the coating's resistance to high-temperature oxidation. Then, argon arc cladding technology is used to clad Ti, Al, Nb, and Y metal powders onto the underlayer surface, preparing a Ti-Al-xNb-Y coating, further improving the titanium alloy surface's resistance to high-temperature oxidation. By controlling the process conditions, this invention achieves a defect-free composite coating with excellent metallurgical bonding between the coating and the substrate.

[0015] Furthermore, this invention investigated the effects of arc spraying and argon arc cladding technology parameters on the macroscopic morphology and high-temperature oxidation resistance of the composite coating. By controlling the parameters of arc spraying and argon arc cladding, the prepared composite coating exhibited better macroscopic formation and good metallurgical bonding between the coating and the substrate.

[0016] This invention improves the high-temperature oxidation resistance of coatings by modifying the Nb content based on the Ti-Al-Y alloy system. The final result is a WC88-Co12 / Ti-Al-10Nb-Y composite coating, exhibiting optimal high-temperature oxidation resistance. In a isothermal oxidation test at 800℃ for 100h, the weight gain per unit oxidation layer was 22.73 mg / cm³. 2 It is only 0.63 times the unit weight gain of the matrix due to oxidation. Attached Figure Description

[0017] Figure 1 Spraying samples under different spraying process parameters; Figure 2 The macroscopic surface of the WC-Co coating of specimens P1 to P9 underwent thermal shock tests at 600℃, 700℃ and 800℃. Figure 3 The oxidation kinetics curves of the substrate and the WC-Co coating of samples P1 to P9 at 800℃ / 100h are shown. Figure 4 The XRD patterns of the WC-Co coating on sample P7 before and after oxidation are shown. Figure 5 The surface morphology of the WC-Co coating on sample P7 is shown in the SEM image. Figure 6 Surface scanning EDS energy dispersive spectroscopy analysis of the WC-Co coating of sample P7; Figure 7 The oxidation cross-section and EDS energy spectrum of the WC-Co coating on sample P7 are shown. Figure 8 For cladding coatings under different argon arc cladding process parameters; Figure 9 The cross-sectional morphology of the cladding layer under different argon arc cladding process parameters; Figure 10 The oxidation kinetics curves of Ti-Al-Y coatings on TC4 substrate and samples R1 to R9 are shown. Figure 11 XRD patterns of sample R7 before and after oxidation; Figure 12 SEM images of the oxidized surface of sample R7 after being oxidized at 800℃ for 100h at different magnifications; Figure 13 Surface scan image of the Ti-Al-Y coating prepared for sample R7; Figure 14Surface line scan composition of the Ti-Al-Y coating prepared for sample R7; Figure 15 XRD pattern of WC-Co / Ti-Al-xNb-Y alloy coating; Figure 16 Microstructure of WC-Co / Ti-Al-xNb-Y coating; Figure 17 The microstructure of the middle part of the WC-Co / Ti-Al-xNb-Y coating; Figure 18 Microstructure and EDS energy dispersive spectroscopy analysis of WC-Co / Ti-Al-10Nb-Y; Figure 19 XRD pattern of WC-Co / Ti-Al-xNb-Y alloy coating; Figure 20 The surface macroscopic morphology of WC-Co / Ti-Al-xNb-Y alloy after oxidation for 20h, 50h and 100h; Figure 21 The SEM morphology of the WC-Co / Ti-Al-0Nb-Y alloy coating at different magnifications; Figure 22 SEM morphology of WC-Co / Ti-Al-5Nb-Y alloy coating at different magnifications; Figure 23 SEM morphology of WC-Co / Ti-Al-10Nb-Y alloy coating at different magnifications; Figure 24 SEM morphology of WC-Co / Ti-Al-15Nb-Y alloy coating at different magnifications; Figure 25 Surface scanning EDS analysis of WC-Co / Ti-Al-10Nb-Y alloy coating; Figure 26 The cross-sectional morphology and composition curves of the WC-Co / Ti-Al-xNb-Y alloy coating are shown. Figure 27 Oxidation kinetics curves of WC-Co / Ti-Al-xNb-Y alloy coating; Figure 28 The fitting curve of lnΔw - lnt between the substrate and the WC-Co / Ti-Al-xNb-Y alloy coating; Figure 29 Piecewise linear fitting was performed on the substrate and the WC-Co / Ti-Al-xNb-Y coating. Detailed Implementation

[0018] This invention provides a method for preparing a high-temperature resistant alloy coating by electric arc spraying / argon arc cladding, comprising the following steps: A WC-Co coating is formed by arc spraying on the surface of a titanium alloy substrate; the welding wire used for arc spraying uses WC88-Co12 powder as the flux core. After coating the WC-Co coating surface with cladding powder, argon arc cladding is performed to form a Ti-Al-xNb-Y coating, thus obtaining the arc spraying / argon arc cladding high-temperature alloy coating; where x=0-15, and x is the mass fraction; The cladding powder is a mixture of Ti, Al, Nb and Y; by mass percentage, the cladding powder comprises 0.8% Y, 60% Al, 0-15% Nb and the balance Ti.

[0019] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0020] This invention involves arc spraying on the surface of a titanium alloy substrate to form a WC-Co coating.

[0021] This invention does not have any special requirements for the titanium alloy matrix; any titanium alloy matrix well-known in the art is acceptable. In the embodiments of this invention, the titanium alloy matrix is ​​specifically TC4 titanium alloy.

[0022] Before arc spraying, the titanium alloy substrate is preferably sandblasted. There are no special requirements for the sandblasting process; any sandblasting method well-known in the art can be used. Sandblasting increases the surface roughness of the substrate material, allowing for a better mechanical bond between the spraying material and the substrate during subsequent spraying. In an embodiment of the invention, an RH-1212A-F sandblasting machine is used at a gas pressure of 0.7 MPa to sandblast the material surface, with corundum as the sandblasting material. Prior to sandblasting, the invention preferably also includes degreasing and decontamination treatment of the titanium alloy substrate. In an embodiment of the invention, this is specifically achieved by grinding with a grinding wheel and degreasing and decontaminating the surface of the titanium alloy substrate with anhydrous ethanol.

[0023] In this invention, the welding wire used for arc spraying uses WC88-Co12 powder as the core. The diameter of the welding wire is preferably 1.0 mm; the outer sheath of the welding wire is preferably stainless steel. This invention does not have special requirements for the preparation process of the welding wire; a preparation process well-known in the art can be used. In an embodiment of this invention, WC88-Co12 powder is weighed, thoroughly ground, and then machine-rolled into a welding wire with a diameter of 1.0 mm. In this invention, the WC88-Co12 powder is obtained by mixing WC and Co in a mass ratio of 88:12. Before use, this invention preferably dries the welding wire. In this invention, the drying temperature is preferably 50°C, and the drying time is preferably 5 hours.

[0024] In this invention, the conditions for arc spraying include: a spraying voltage of 25V, a current of 50A, and a wire feed speed of 25.54mm / s; or, a spraying voltage of 37V, a current of 50-110A, and a wire feed speed of 25.54-55.67mm / s; the most preferred option is: a spraying voltage of 25V, a current of 50A, and a wire feed speed of 25.54mm / s. The spraying distance for arc spraying is 80-120mm, and in specific embodiments, it can be 80, 90, 100, 110, or 120mm. By controlling the conditions of arc spraying, this invention can improve the bonding ability between the coating and the titanium alloy substrate and prevent the coating from peeling off when subjected to high temperatures.

[0025] In this invention, the thickness of the arc spray coating is preferably 200-350 μm, and in specific embodiments it can be 200, 230, 250, 280, 300, 320 or 350 μm.

[0026] After forming the WC-Co coating, the present invention coats the WC-Co coating surface with cladding powder and then performs argon arc cladding to form a Ti-Al-xNb-Y coating, thereby obtaining the arc spraying / argon arc cladding high-temperature alloy coating; where x=0-15, and x is the mass fraction.

[0027] In this invention, the cladding powder is a mixed powder of Ti, Al, Nb, and Y; by mass percentage, the cladding powder comprises 0.8% Y, 60% Al, 0-15% Nb, and the balance Ti. In specific embodiments, the Nb content in the cladding powder can be 0%, 3%, 5%, 8%, 10%, 12%, or 15%, with 10% being the most preferred.

[0028] In this invention, the coating thickness of the cladding powder is preferably 1-1.5 mm. Before coating, it is preferable to mix the cladding powder with water glass. There are no special requirements for the amount of water glass used; it can be mixed to a paste-like consistency. The purpose of adding water glass is to ensure that the alloy powder maintains a set thickness and shape, uniformly covering the substrate surface, and does not scatter during subsequent handling or cladding.

[0029] In this invention, the conditions for argon arc cladding include: a cladding current of 110-120A, a gas flow rate of 10-15L / min, and a welding speed of 150-230mm / min, wherein when the cladding current is 120A, the welding speed is 150mm / min. In a specific embodiment, the conditions for argon arc cladding can be a cladding current of 110A, a welding speed of 150, 180, 200, 220, or 230mm / min, and a gas flow rate of 10, 11, 12, 13, 14, or 15L / min. As the most preferred embodiment, the welding current is 110A, the welding speed is 230mm / min, and the gas flow rate is 12L / min.

[0030] By controlling the argon arc cladding conditions within the aforementioned range, this invention ensures that the Ti-Al-xNb-Y coating exhibits excellent high-temperature oxidation resistance. In this invention, x corresponds to the Nb content in the cladding powder.

[0031] The present invention provides an arc spraying / argon arc cladding high-temperature alloy coating prepared by the preparation method described above, comprising a WC-Co coating and a Ti-Al-xNb-Y coating stacked on the surface of a titanium alloy substrate, wherein x=0-15 and x is a mass fraction.

[0032] This invention employs arc spraying technology to coat a titanium alloy substrate with a WC88-Co12 underlayer, improving the adhesion between Ti-Al-xNb-Y and the titanium alloy substrate. Simultaneously, the WC88-Co12 underlayer enhances the coating's resistance to high-temperature oxidation. Then, argon arc cladding technology is used to clad Ti, Al, Nb, and Y metal powders onto the underlayer surface, preparing a Ti-Al-xNb-Y coating, further improving the titanium alloy surface's resistance to high-temperature oxidation. The results of the examples demonstrate that the high-temperature alloy coating prepared by this invention possesses excellent resistance to high-temperature oxidation.

[0033] The following detailed description, in conjunction with embodiments, illustrates the high-temperature resistant alloy coating and its preparation method provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0034] Optimization Experiment During the coating preparation process, the quality of the coating is affected by many factors. In order to obtain a composite coating with the best forming quality and the best high-temperature oxidation resistance, it is necessary to determine the optimal electric arc spraying and argon arc cladding process parameters. This test case studies the electric arc spraying and argon arc cladding process parameters.

[0035] 1. Coating phase structure analysis and performance testing methods 1.1 Phase Structure Analysis of the Coating (1) Sample preparation After the coating was cladding completed, a DK7725 CNC wire EDM machine was used to cut the cladding specimens into sizes of 15 mm × 10 mm × 10 mm and 25 mm × 25 mm × 10 mm. The front and back 5 mm of the specimens were not used for performance testing and were avoided as much as possible. The coating cross-section and surface were smoothed with metallographic sandpaper for subsequent testing.

[0036] X-ray diffraction (XRD) is an important part of phase analysis. When preparing the sample, the cladding layer is sanded smooth with sandpaper to make the coating clean and neat before XRD testing can be performed.

[0037] For Zeiss metallographic specimens, the cut specimen cross-section needs to be successively polished with 400#, 600#, 800#, 1000#, 1500#, and 2000# sandpaper. The polished specimen is then polished on an LP-2C metallographic polishing machine until it is mechanically polished to a mirror finish with no obvious scratches under an optical microscope. Etching is then performed using an etchant (hydrofluoric acid: nitric acid = 1:3). The specimen cross-section is wiped with an alcohol-soaked cotton swab dipped in the etchant until etching is complete. The specimen cross-section is then cleaned with anhydrous ethanol and dried. The coating morphology can then be observed under an optical microscope and a scanning electron microscope.

[0038] The high-temperature oxidation test requires immersing the cut and polished sample in a beaker filled with anhydrous ethanol for ultrasonic cleaning. After ultrasonic cleaning, the sample is dried in a 100℃ drying oven for 1 hour. After drying, the original weight is measured and recorded using a balance with a measurement accuracy of 0.0001 mg. The length, width, and height of the sample are recorded using a screw positioner with an accuracy of 0.001 mm, and the oxidation area is calculated.

[0039] (2) X-ray diffraction test The experiment used a DX-2700B X-ray diffractometer to conduct X-ray diffraction tests on the Ti-Al-Nb-Y alloy coating. Cu was used as the cathode target, the diffraction wavelength was 1.5406 Å, and the parameters of the X-ray diffractometer were as follows: tube voltage 40 kV, tube current 30 mA, diffraction angle 10 °~90 °, and scanning speed 4 ° / min. The obtained diffraction patterns were screened and compared using MDI Jade 6 software to obtain the corresponding phase information.

[0040] (3) Characterization of coating structure The microstructure of the Ti-Al-xNb-Y alloy coating was observed using an optical microscope (Zeiss Lab.A1) and a Hitachi SU500 scanning electron microscope, and the microstructure of the coating cross section and the oxide layer of the coating and the substrate were characterized by surface scanning microscopy.

[0041] 1.2 Performance Testing Methods (1) Analysis of high-temperature oxidation behavior A box-type resistance furnace was used to conduct a 100-hour isothermal oxidation test at 800℃ on the samples. Before the oxidation test, the dimensions of the samples were measured with vernier calipers and the surface area was calculated. The oxidized samples were placed in an alumina crucible. Before the high-temperature oxidation experiment began, the samples and the container were weighed together using an electronic balance with a measurement accuracy of 0.0001 mg, and the original weight was recorded. Next, the samples oxidized at different times were weighed together with the crucible. They were taken out and weighed at 1h, 3h, 6h, and 10h after the start of oxidation, and then weighed every 5h until 50h. In the next 50h, the samples were taken out at 10h intervals and weighed together with the crucible. The unit oxidation weight gain for different time periods was calculated based on the oxidation area and the weight gain at different oxidation times. The phase composition and oxidation morphology of the oxide film on the surface of the oxidized samples were analyzed using XRD diffraction and SEM. Ni plating was performed on the oxidized cross-section using a chemical Ni plating process. The oxide film thickness and cross-sectional structure of the samples after 100h of oxidation were analyzed using SEM and surface scanning.

[0042] 2. Determination of Arc Spraying Process Parameters 2.1 Supersonic Arc Spraying Supersonic arc spraying is a relatively advanced thermal spraying technology. Its working principle involves connecting two identical or different metal conductors, ensuring the positive and negative terminals of the DC power supply are insulated. The angle between the two conductors is ideally 45°, and a wire feeder moves the two welding wires at a certain speed. When the two welding wires come into contact and a short circuit occurs, the heat source is activated, heating the two materials to a molten state. Under the influence of high-speed gas, the atomized metal droplets impact the sandblasted material, forming an alloy coating. The spraying experiment used an SX-600 supersonic spraying system. A 1.0mm diameter flux-cored welding wire was prepared from WC-Co powder using a stainless steel sheath and dried in a 50℃ drying oven for 5 hours before use. Before arc spraying the TC4 substrate material, the surface of the substrate material was degreased and cleaned with anhydrous ethanol. To increase the adhesion and bonding strength between the coating and the substrate surface, the TC4 titanium alloy strip was sandblasted using an RH-1212A-F sandblasting machine at a gas pressure of 0.7 MPa. The sandblasting material was corundum. Sandblasting increased the surface roughness of the substrate material, ensuring a good mechanical bond between the coating material and the substrate during subsequent spraying. After sandblasting, arc spraying was performed. An SX-600 supersonic arc spraying system was used, and spraying experiments were conducted according to the designed process parameters. The coating thickness was 300 μm. The designed process parameters are shown in Table 1. The effects of spraying voltage, spraying current, and wire feed speed on the coating microstructure were mainly discussed. Under the same airflow conditions, the optimal process parameters were determined by adjusting the spraying voltage, spraying current, and wire feed speed and analyzing the coating microstructure and properties.

[0043] Table 1. Arc Spraying Parameters

[0044] 2.2 Macroscopic morphology of the sample Figure 1 The coating surfaces of the sprayed samples under different spraying process parameters are shown in Table 1. Figure 1 It can be observed that, under constant spraying voltage and current, the coating becomes smoother, denser, and better bonded to the surface as the wire feed speed decreases. Similarly, when the wire feed speed is constant, an increase in voltage and current also results in a smoother and denser coating. This is because a decrease in wire feed speed or an increase in spraying voltage and current increases the melting degree of the alloy powder particles in the wire, reducing the porosity of the coating and making the surface of the sprayed coating denser.

[0045] Overall observation and comparison revealed numerous particles and tiny pores on the surface. The analysis suggests that an excessively high wire feeding speed or insufficient voltage and current would reduce or prevent the alloy powder from melting properly, directly resulting in an increase in particles and tiny pores on the coating surface.

[0046] 2.3 Thermal shock test Nine sets of samples prepared according to the parameters in Table 1 were each cut into three pieces measuring 25 mm × 25 mm × 10 mm. Using a KSL-1100X box-type resistance furnace, the temperatures were adjusted to 600℃, 700℃, and 800℃ respectively. The nine sets of samples were subjected to a cycle of heating for 10 minutes at different temperatures followed by water cooling, then heating for 10 minutes again, and finally water cooling, to achieve high-temperature impact resistance testing. During the thermal shock test, a large thermal stress gradient was generated at the interface between the sprayed coating and the substrate. Therefore, when the mechanical bonding between the sprayed coating and the titanium alloy surface was poor, coating peeling occurred. Furthermore, due to the linear expansion coefficient of TC4 alloy being 10.5 × 10⁻⁶, the coating may peel off. -6 K, while the coefficient of linear expansion of tungsten-cobalt cemented carbide is typically 5 × 10⁻⁶. -6 K~7×10 -6 K, therefore, the coefficient of linear expansion of the coating obtained by arc spraying that is mechanically bonded to the TC4 substrate is significantly different from that of the TC4 substrate, making it more susceptible to temperature-induced peeling. Figure 2 In the middle (a), (b), and (c), the macroscopic morphology of the sample after 4 cycles at 600℃, 700℃, and 800℃, respectively, is shown after air cooling for 1 hour.

[0047] Through observation Figure 2 It can be seen that the samples prepared with parameters P1, P2, and P7 showed no cracks or peeling on the coating surface under high-temperature impact conditions of 600℃, 700℃, and 800℃, indicating that the coating has excellent thermal shock resistance. The sample prepared with parameter P8 also did not show cracks or peeling under the high-temperature impact condition of 600℃, but as the impact temperature increased, small cracks appeared under the high-temperature cyclic impact condition of 700℃, and larger cracks appeared under the high-temperature cyclic impact condition of 800℃, indicating that the coating of sample P8 has weak adhesion. The samples prepared with parameters P4, P5, and P6 produced large cracks under the three-temperature thermal shock conditions, while P3 and P9 peeled off directly.

[0048] Experimental results show that the cladding layers prepared with the nine process parameters exhibit significant differences in high-temperature resistance. The coatings prepared with parameters P1, P2, and P7 demonstrate good resistance to high-temperature environments, showing no visible damage even after 1 hour of air cooling. Conversely, the coatings prepared with parameters P3, P4, P5, P6, and P9 show weaker high-temperature resistance due to insufficient adhesion between the coating and the substrate at high temperatures compared to the thermal stress generated.

[0049] 2.4 Isothermal Oxidation Experiment Figure 3The oxidation kinetics curves of WC-Co high-temperature resistant coatings and TC4 titanium alloy substrates prepared with nine different spraying parameters at 800℃ are shown in the figure. As can be seen from the figure, the oxidation of the coating surface becomes more pronounced with time at 800℃, and the oxidation curve continuously rises. After 100 hours of oxidation at 800℃, the unit oxidation weight gain for the nine parameters was 24.98 mg / cm³. 2 24.29 mg / cm 2 31.86 mg / cm 2 22.58 mg / cm 2 24.21 mg / cm 2 22.39 mg / cm 2 18.39 mg / cm 2 23.92 mg / cm 2 21.21 mg / cm 2 The oxidation weight gain relative to the matrix was 0.82 times, 0.80 times, 1.05 times, 0.74 times, 0.80 times, 0.74 times, 0.60 times, 0.79 times, and 0.70 times that of the matrix, respectively. Comparative analysis shows that the oxidation weight gain of samples prepared with different process parameters varies. Except for the sample prepared with parameter P3, the samples prepared with other parameters showed good resistance to high-temperature oxidation. The sample prepared with parameter P7 had the best resistance to high-temperature oxidation and had better oxidation resistance than TC4 titanium alloy.

[0050] 2.5 Phase structure analysis of coatings before and after oxidation XRD analysis was performed on the surface of the P7 coating of the sample before oxidation. The diffraction pattern is as follows: Figure 4 As shown in the diagram, the diffraction pattern reveals that the sprayed coating primarily contains the WC phase, along with small amounts of Co, W₂C, and Co₃W₃C phases. The WC phase mainly originates from the sprayed WC-Co powder and is the main component phase of the coating. The small amount of W₂C phase is produced by the reaction 2WC + O₂ → W₂C + CO₂WC under the high-temperature conditions of supersonic arc spraying. Co, WC, and O₂ undergo the following reaction at high temperatures: 3Co + 3WC + O₂ → Co₃W₃C + 2CO. Therefore, Co and WC in the sprayed material undergo intermetallic combination reactions during arc spraying to form metastable Co₃W₃C. The main products after oxidation are WO₃, CoWO₄, and WC. The figure shows that the diffraction peaks of WO₃ and CoWO₄ oxides exhibit relatively high diffraction intensities. This is because, with the change in the isothermal oxidation time at 800℃, WC decomposes into W and C on the coating surface under high-temperature conditions, while W combines with Co and O to form oxides.

[0051] 2.6 Oxidation Morphology Analysis / Oxidation Cross Section Figure 5The surface morphology of the WC-Co coating prepared for arc spraying parameter P7 after being held at 800℃ for 100 h at different magnifications is shown below: (a) 200x, (b) 500x, (c) 1000x, and (d) 4000x. The oxidized coating surface remained largely intact, with no obvious peeling or cracks. The coating structure maintained good integrity and density. Compared to before oxidation, the surface morphology and physical phases of the coating changed significantly, with numerous black oxide spots, peeling, and wrinkling observed on the surface. (Combined with...) Figure 6 EDS surface scan results, Figure 6 In the images, (a) surface scan, (b) element content, and (c) element distribution show that the oxidized coating surface is composed of O, C, a small amount of Co, and trace amounts of W, with a relatively uniform element distribution and no obvious enrichment. According to EDS surface scan composition table 2, O accounts for 74.39% of the surface oxides. Combined with the XRD analysis after oxidation, the oxides are mainly WO3 and CoWO4.

[0052] Table 2. Surface Scan EDS Composition Table

[0053] Figure 7 The cross-sectional morphology and composition analysis of the WC-Co coating prepared for P7 arc spraying process parameters after oxidation at 800℃ for 100 h are shown in (a) cross-sectional morphology and (b) cross-sectional elemental distribution. The coating mainly contains four elements: W, C, Co, and O. A very small oxygen diffusion zone was observed beneath the coating, indicating that the oxide layer thickness is approximately 60 μm, and the interior of the coating is not oxidized. This is because the outermost coating structure is not dense enough, allowing O atoms to easily erode the coating surface, thus facilitating oxidation. The interior of the coating remains consistent with its structure before oxidation, without oxygen erosion. Oxygen-rich areas sometimes appear at the interface between the alloy coating and the TC4 titanium alloy substrate. This is due to oxygen pores caused by limitations in the spraying technology; however, these pores are closed and discontinuous and do not affect the coating's oxidation resistance.

[0054] The following conclusions can be drawn from the above characterization results: the optimal arc spraying process parameters are a spraying voltage of 25V, a spraying current of 50A, a spraying distance of 100mm, and a wire feed speed of 25.54mm / s, under which the coating surface is the smoothest; in the thermal shock test at 800℃, the coating surface showed no blistering, peeling, or cracking tendency; in the isothermal oxidation test at 800℃+100h, the unit oxidation increase was only 18.39 mg / cm³. 2The concentration of WC in the coating is 0.6 times that of the TC4 matrix. Before oxidation, the coating mainly contains WC phase, as well as small amounts of Co, W2C, and Co3W3C phases. After oxidation, the main products are WO3, CoWO4, and WC. The surface of the oxidized coating is basically intact, with no obvious peeling or cracks. The coating structure still maintains good integrity and density. Compared with the unoxidized coating, the surface morphology and physical phases of the coating have changed significantly. A large number of black oxide spots are distributed on the surface of the coating, and peeling and wrinkling occur. Combined with EDS, the surface of the oxidized coating is composed of O, C, a small amount of Co, and trace amounts of W. The elemental distribution is relatively uniform without obvious enrichment. The oxidation cross-section and EDS show that the coating structure is mainly composed of four elements: W, C, Co, and O. The oxygen diffusion zone below the coating is very small. As a result, the continuous oxide layer on the surface only occurs within 60 μm of the coating surface and does not extend into the coating interior.

[0055] 3. Determination of Argon Arc Cladding Process Parameters 3.1 Argon Arc Cladding Process This experiment employed cladding technology to achieve a good metallurgical bond between the alloy powder and the substrate. The designed process parameters are shown in Table 3. The main discussion focuses on the effects of welding current and welding speed on the microstructure of the cladding coating. Under the same gas flow conditions, the optimal process parameters were determined by adjusting the welding current and welding speed and analyzing the microstructure and properties of the coating after isothermal oxidation experiments.

[0056] In the experiment of adjusting the argon arc cladding process parameters on the surface of TC4 titanium alloy, a Ti-Al-Y alloy powder with a fixed composition and a mass fraction ratio of 39.2:60:0.8 was used. The powder was accurately weighed using an AB265-S analytical balance with an accuracy of 0.1 mg. The weighed alloy powder was then placed in a grinding jar and ball-milled in an XQM-2 vertical planetary ball mill using a wet grinding method for 90 min at a ball-to-powder ratio of 2:1:1, resulting in a uniformly mixed pre-coated powder. The mixed alloy powder was then dried in a drying oven for 60 min at 80℃. Using water glass, the uniformly mixed alloy powder was evenly coated onto the TC4 titanium alloy surface, which had been degreased and cleaned with anhydrous ethanol and then sandblasted to remove rust. The thickness of the alloy powder layer was approximately 1 mm. This experiment used a MagicWave3000FuzzyG / W / Z argon arc welding machine to conduct a cladding experiment according to the designed process parameters.

[0057] Table 3 Process Parameter Design

[0058] 3.2 Macroscopic morphology of the sample Figure 8The cladding coatings are shown in Table 3 under different argon arc cladding process parameters. Figure 8 It can be observed that, at a constant welding speed, the cladding coating becomes relatively smoother and the surface of the cladding layer becomes more even with an increase in welding current. This is because the increase in welding current raises the temperature of the molten pool, resulting in a longer interaction time between the cladding layer and the substrate, allowing the alloy powder to flow and diffuse more fully, thus obtaining a smooth and even coating surface. When the welding current is the same, the surface of the cladding layer becomes smoother and more even with an increase in welding current. Figure 8 Observations reveal that the width of the cladding layer decreases with increasing welding speed. This is because at lower welding speeds, the interaction time between the heat source and the alloy powder and the substrate is longer, intensifying the melting of the base material and increasing the dilution rate of the cladding layer, resulting in a wider cladding zone. Conversely, at higher welding speeds, the heat input is relatively reduced, leading to a narrower weld bead. Therefore, while maintaining good cladding quality, the scanning speed can be appropriately increased to reduce the width of the heat-affected zone.

[0059] 3.3 Dilution rate of cladding layer Figure 9 To illustrate the cross-sectional morphology of the cladding layer under nine different process parameters, a low dilution rate was obtained by adjusting the heat input through changes in the argon arc cladding process parameters. A lower dilution rate can give the cladding layer excellent properties such as wear resistance and corrosion resistance, thereby directly affecting the overall performance of the cladding coating. The dilution rate under different process parameters was calculated by measuring the substrate melting depth (h) and the cladding layer height (H) and using the dilution rate formula (1). The results are shown in Table 4.

[0060] η= Formula (1) Table 4 Coating Dilution Rate

[0061] Metallurgical microscope analysis of cross-sectional morphology Figure 9 It can be observed that the melt width decreases with increasing welding speed; on the other hand, the dilution rate decreases with increasing welding speed, while the coating height does not show a significant regular change. Under the nine sets of process parameters, when the welding current is 110A and the welding speed is 230mm / min, the coating dilution rate is relatively low at 53.77%.

[0062] 3.4 Oxidation kinetic curves The oxidation kinetics curve of TC4 titanium alloy substrate and Ti-Al-Y coating after isothermal oxidation at 800℃ for 100h is shown below. Figure 10 As shown, the oxidation of the TC4 titanium alloy substrate becomes increasingly pronounced as the oxidation process continues, with the oxidation weight gain curve exhibiting a continuous upward trend. The unit oxidation weight gain of the alloy coatings prepared with the nine cladding parameters was 31.76 mg / cm³. 233.99 mg / cm 2 34.48 mg / cm 2 36.19 mg / cm 2 33.90 mg / cm 2 27.42 mg / cm 2 23.62 mg / cm 2 24.83 mg / cm 2 28.23 mg / cm 2 Among them, the samples prepared with parameters R6, R7, R8, and R9 all showed less weight gain per unit oxidation than the matrix, exhibiting good resistance to high-temperature oxidation. The sample with parameter R7 showed the best resistance to high-temperature oxidation, demonstrating superior oxidation resistance compared to TC4 titanium alloy.

[0063] Overall, the oxidation weight gain curve at 800℃ can be divided into three stages: rapid oxidation growth in the initial stage (0h-20h), slower growth in the middle stage (20h-45h), and a relatively stable growth after 45h. This indicates that the initial oxide film structure is relatively dense and has good antioxidant properties. However, as the isothermal oxidation process continues, the originally formed oxide film cracks, exposing the inner coating surface, which is then further oxidized.

[0064] 3.5 Phase structure analysis of coatings before and after oxidation The sample R7, which exhibits the best high-temperature resistance, was selected. XRD analysis was performed on the surface of the sample coating. The diffraction pattern of R7 before the high-temperature oxidation experiment is shown below. Figure 11 As shown in the diagram, the diffraction pattern reveals that the coating before oxidation mainly consists of TiAl and a small amount of Ti3Al. After oxidation, the coating surface is mainly composed of an oxide layer consisting of a mixed oxide of TiO2 and Al2O3.

[0065] 3.6 Oxidation Morphology Analysis / Oxidation Cross Section Figure 12 The SEM images of sample R7 after being oxidized at 800℃ for 100 h at different magnifications are shown in Table 5. (a) 500x, (b) 1000x, (c) 2000x, and (d) 4000x. Combined with surface scanning analysis, Table 5 shows that at 800℃, the percentage of O atoms is 65.94%, while the percentage of Al atoms is only 16.97%. XRD phase analysis of the oxidized surface indicates that the phases are Al2O3 and TiO2. Figure 12 As shown, at a temperature of 800℃, the oxides uniformly cover the surface of the matrix material. It can be seen that the generated oxide particles are densely distributed on the surface and have a small particle size. This is observed in conjunction with the scanning image in Composition Table 5. Figure 13It can be observed that the composition ratio of Ti and Al is not significantly different. The reason for this small difference in composition ratio is that the diffusion rate of Ti atoms is greater than that of Al atoms. Therefore, the growth rate of TiO2 is greater than that of Al2O3.

[0066] Table 5. Surface scan composition of Ti-Al-Y coatings prepared with parameter R7

[0067] Further observation was conducted on the oxidation cross-section and EDS scan results of the Ti-Al-Y coating after isothermal oxidation at 800℃ for 100 h. The results are shown in [Figure number missing]. Figure 14 Among them, (a) cross-sectional morphology, and (b) cross-sectional element distribution. From Figure 12 and Figure 14 It can be seen that the oxide film peels off at 800℃, exposing the oxide layer and newly oxidized parts. Combined with XRD and EDS analysis (Table 6), the oxide film at this point mainly consists of TiO2 and a small amount of Al2O3. Thermodynamic analysis shows that this is because the Gibbs free energy required to produce TiO2 and Al2O3 is similar, leading to their simultaneous formation in the initial stage of oxidation. However, oxidation kinetics studies indicate that the formation rate of TiO2 is higher than that of Al2O3, resulting in a layered oxide film after oxidation. In summary, after oxidizing at 800℃ for 100 hours, the oxide film on the coating surface exhibits cracking and peeling. The unit oxidation weight gain curve shows a rapid upward trend, with the outermost TiO2 oxide film peeling off, and the Al2O3 oxide film in the middle of the coating also cracking. The bottommost mixed TiO2 and Al2O3 oxide film is exposed to high temperature conditions.

[0068] Table 6. Surface line scan composition of Ti-Al-Y coatings prepared with parameter R7

[0069] Conclusion: The optimal argon arc cladding process parameters are a cladding current of 110 A, a gas flow rate of 12 L / min, and a cladding speed of 230 mm / min. Under these conditions, the coating surface is the smoothest; the coating dilution rate is relatively low at 53.77%; and in the isothermal oxidation test at 800℃ for 100 h, the unit oxidation increase is only 23.62 mg / cm³. 2 The content of TC4 matrix is ​​0.77. Before oxidation, the coating mainly consists of TiAl and a small amount of Ti3Al. After oxidation, the surface of the coating mainly consists of Al2O3 and TiO2. The morphology of the oxidized surface is mainly fine and dispersed particles in an irregular block shape. Combined with the XRD phase analysis of the oxidized surface, it can be known that it is Al2O3 and TiO2. Based on the morphology of the oxidized cross section and EDS, the surface layer of the oxide film is TiO2, the middle layer is Al2O3, and the lower layer is a mixed layer of TiO2 and Al2O3.

[0070] Examples 1-4 S1: Sandblasting treatment is performed on the TC4 titanium alloy matrix material; Specifically, the experiment used TC4 titanium alloy as the substrate, the main components of which are shown in Table 7 below. Before the experiment, the TC4 titanium alloy was cut into cuboid samples of 100mm × 15mm × 10mm. After cutting, the samples were ground with a grinding wheel, and the surface of the substrate material was degreased and cleaned with anhydrous ethanol to increase the adhesion and bonding strength between the coating and the substrate material surface. Following this, the TC4 titanium alloy strips were sandblasted using an RH-1212A-F sandblasting machine at a gas pressure of 0.7 MPa. The sandblasting material was corundum. Sandblasting increased the surface roughness of the substrate material to ensure a good mechanical bond between the coating material and the substrate during subsequent spraying.

[0071] Table 7. Composition of TC4 titanium alloy (wt.%)

[0072] S2: Determine the arc spraying powder: Select W, C, and Co alloying elements as the main components of the first layer of arc spraying; Determine the argon arc cladding powder: Select Ti, Al, Nb, and Y elements as the main components of the second layer of argon arc cladding; S3: Design the alloy element ratio of W, C, and Co for the spraying material; design the alloy element ratio of Ti-Al-xNb-Y, and weigh the alloy powder with the corresponding element ratio, where x = 0, 5, 10, 15, and x is the mass fraction.

[0073] Specifically, S301: The mass fraction of the spraying material elements is WC:Co = 88:12; In the Ti-Al-xNb-Y alloy system, the mass fraction ratio of Nb among the four elements is a variable. The Ti-Al-xNb-Y alloy powder is shown in Table 8, weighed using an AB265-S analytical balance.

[0074] Table 8. Mass fraction (wt.%) of alloy powders in Examples 1-4

[0075] S4: Pre-treatment of alloy powder before use; Specifically, S401: Weigh out the mixed powder of WC88-Co12 alloy elements and grind it thoroughly. Then, use a machine to roll it into a welding wire with a diameter of 1.0 mm. The outer sheath of the wire is stainless steel.

[0076] S402: Use a drying oven to dry the WC88-Co12 welding wire at 50°C for 5 hours, and then use a supersonic arc spraying device to spray the sandblasted TC4 titanium alloy surface.

[0077] S403: Weigh different masses of Ti-Al-xNb-Y alloy element mixed powder, grind it, place it in a petri dish, add an appropriate amount of water glass and mix thoroughly.

[0078] S404: The uniformly mixed Ti-Al-xNb-Y alloy element powder is evenly coated onto the surface of the WC88-Co12 coating prepared by arc spraying to form a powder preform layer.

[0079] S405: Let the prefabricated layer rest naturally for 24 hours, then place it in a drying oven at 100℃ for 2 hours for later use.

[0080] S5: WC88-Co12 alloy powder was arc-sprayed onto the sandblasted TC4 titanium alloy substrate surface. The spraying voltage was 25V, the spraying current was 50A, the spraying distance was 100mm, and the wire feed speed was 25.54mm / s. The spraying thickness was 200μm. Then, Ti-Al-xNb-Y alloy powder was argon-arc cladding. The powder thickness was 1-1.5mm, the cladding current was 110A, the gas flow rate was 12L / min, and the cladding speed was 230mm / min, thus preparing a WC-Co / Ti-Al-xNb-Y high-temperature resistant alloy coating.

[0081] High-temperature oxidation experiments were conducted on the WC-Co / Ti-Al-xNb-Y alloy coatings prepared in Examples 1-4. The phase composition of the coatings before and after oxidation was compared and analyzed for different Nb contents. The data on the weight gain of the coatings after oxidation were collected and analyzed to prepare oxidation kinetic curves. The cross-section and surface structure of the prepared alloy coating oxide film were characterized using SEM scanning electron microscopy and EDS energy dispersive spectroscopy. The phase composition of the generated oxide film was analyzed using X-ray diffraction to determine the optimal Nb content ratio.

[0082] 1. Phase structure analysis of the coating before oxidation Figure 15 The XRD diffraction pattern of the WC-Co / Ti-Al-xNb-Y alloy coating is shown. Figure 15It is known that the main phases of the alloy coating are TiAl, Ti3Al, TiC, Ti2AlC, WC, and Co3W3C. The diffraction pattern shows that the WC diffraction peak is not strong, indicating that WC is decomposed at high temperature during cladding. The decomposed elements C and W diffuse and migrate through the stirring of the heat source. Because TiC has a high melting point and low Gibbs free energy required for its formation, the C atoms decomposed from WC during cladding will first react with Ti atoms in the coating to form TiC. The generated TiC will then react with the generated TiAl during the subsequent cladding process to form the ternary compound Ti2AlC. Therefore, under high C content, the intensity of the characteristic diffraction peaks of TiC and Ti2AlC gradually increases, indicating the coexistence of TiC and Ti2AlC in the cladding layer.

[0083] 2. Microstructure Figure 16 Metallographic micrographs of cross-sections of the WC-Co / Ti-Al-xNb-Y alloy coatings are shown, including (a) WC-Co / Ti-Al-0Nb-Y, (b) WC-Co / Ti-Al-5Nb-Y, (c) WC-Co / Ti-Al-10Nb-Y, and (d) WC-Co / Ti-Al-15Nb-Y. Overall observation reveals that the Ti-Al-xNb-Y alloy coating has a dense and uniform microstructure, with a clear boundary between the coating and the substrate. The cladding layer is tightly bonded to the substrate, exhibiting a bright white bonding area. The overall bonding between the cladding layer and the substrate is excellent, with no cracks, pores, or other defects observed, demonstrating good metallurgical bonding.

[0084] Figure 17The images show the metallographic structure of the central part of the WC-Co / Ti-Al-xNb-Y alloy coating, including (a) WC-Co / Ti-Al-0Nb-Y, (b) WC-Co / Ti-Al-5Nb-Y, (c) WC-Co / Ti-Al-10Nb-Y, and (d) WC-Co / Ti-Al-15Nb-Y. The coating consists of dendritic crystals and diffusely distributed black particles. When the Nb content is 0%, the dendritic structure is relatively coarse; with the addition of Nb, the coating structure changes significantly, and the size of the particles gradually decreases. In the WC-Co / Ti-Al-0Nb-Y coating, the dendritic trunks are relatively long and arranged in a somewhat disordered manner. As shown in the figure, when the Nb content is increased to 5%, the WC-Co / Ti-Al-5Nb-Y alloy coating exhibits a dendritic structure, with the dendrites contacting the surrounding dendrites to form a closed, basket-like morphology. When the Nb content is increased to 10%, the dendritic structure in the WC-Co / Ti-Al-10Nb-Y alloy coating is refined. Because Nb has a high melting point, the alloy undercooling increases during solidification, leading to increased dendrite growth rate and dendrite refinement. As the dendrites refine, their morphology transforms into fine equiaxed crystals. This is because, with continued compositional undercooling, Nb's larger atomic radius makes it easily repelled by other atoms. As the Nb content increases, grain growth is hindered, causing the grains to grow uniformly in all directions, forming equiaxed crystals.

[0085] Compared to simply cladding Ti-Al-xNb-Y alloy coatings, performing arc spraying followed by cladding can mitigate thermal stress, reduce the impact of sudden performance changes, and improve the quality of the cladding layer. In this case, due to the slow changes in composition and structure, the properties of the alloy coating also change slowly, significantly reducing the performance difference between the cladding layer and the substrate material. Furthermore, the addition of WC-Co can further refine the grain size.

[0086] Figure 18 The microstructure and energy dispersive spectroscopy (EDS) of the WC-Co / Ti-Al-10Nb-Y alloy coating are shown. (a) and (b) are microstructures at different magnifications, and (c) is the EDS of the sample point in (b). The petal-shaped material in the figure (spectral density) is shown. Figure 1 The position shown in the table (Table 9) shows that the ratio of Ti to C atoms at this point is approximately 1:1. Based on the X-ray diffraction pattern, the substance is TiC.

[0087] Table 9. EDS energy dispersive spectroscopy analysis of the microstructure of WC-Co / Ti-Al-10Nb-Y

[0088] 4.3 Phase Structure Analysis of the Coating After High-Temperature Oxidation Figure 19 The XRD diffraction pattern of the WC-Co / Ti-Al-xNb-Y alloy coating after isothermal oxidation at 800℃ for 100 h is shown. Analysis of the product after the same alloy coating was oxidized at 800℃ for 100 h reveals that the WC-Co / Ti-Al-xNb-Y alloy coating ultimately forms a mixed oxide layer of TiO2 and Al2O3, with small amounts of WO3 and CoWO4. Although the mixed oxide film produced during oxidation is composed of Al2O3 and TiO2, the ratio of Al2O3 peak intensity to TiO2 peak intensity increases as the mass fraction of Nb increases from 0% to 10%. Compared to the pure Ti-Al-xNb-Y alloy coating, the WC-Co / Ti-Al-xNb-Y alloy coating exhibits a slower oxidation rate, further improving its resistance to high-temperature oxidation. The intensity of the Al2O3 diffraction peak in the WC-Co / Ti-Al-10Nb-Y alloy coating is greater than that in the WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings, indicating that the proportion of Al2O3 in the WC-Co / Ti-Al-10Nb-Y alloy coating is higher than that in the WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings.

[0089] 4.4 Surface morphology of oxide film after high-temperature oxidation Figure 20 The macroscopic surface morphology of WC-Co / Ti-Al-xNb-Y alloy after oxidation at 800℃ for 20h, 50h, and 100h is shown in (a) 20h, (b) 50h, and (c) 100h. After 20h oxidation, the WC-Co / Ti-Al-xNb-Y alloy coating surface is covered with a complete oxide film, which is well bonded to the coating and no cracking is observed (e.g., Figure 20 As shown in (a); after 50 hours of oxidation, the oxide film formed on the alloy surface remained stable, with no obvious oxide film peeling, and the oxide film morphology on the coating surface was intact (as shown in (a)). Figure 20 As shown in (b); after oxidizing for 100 hours, no obvious peeling of the oxide film on the alloy surface was observed (as shown in the figure). Figure 20 As shown in (c), the oxide film at this time has good adhesion.

[0090] Figures 21 to 24The images show the microstructures of the oxide films formed on the surfaces of WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, WC-Co / Ti-Al-10Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings after being oxidized at 800℃ for 100 hours. (a) is magnified 4000 times, and (b) is magnified 1000 times. Observation revealed that the oxides on the alloy coating surface consisted of plate-like and rod-like oxides. Because the Nb content varied, the specific morphology of the oxides formed on the coating surface after high temperature differed. With the continuous increase of Nb content, the surface density of the oxide film formed under high temperature conditions became increasingly apparent.

[0091] Depend on Figure 23 It can be seen that the WC-Co / Ti-Al-10Nb-Y alloy coating oxidized for 100 hours has a surface oxide composition consisting of plate-like and rod-like oxides, while the WC-Co / Ti-Al-0Nb-Y alloy coating (such as...) Figure 21 WC-Co / Ti-Al-5Nb-Y alloy coating (such as...) Figure 22 (as shown) and WC-Co / Ti-Al-15Nb-Y alloy coating (such as...) Figure 24 As shown, after 100 hours of oxidation, plate-like oxides formed on the surface of the WC-Co / Ti-Al-xNb-Y alloy coating, and no other obvious oxide shapes were observed. After 100 hours of oxidation, the average diameters of the blocky oxides on the surface of the WC-Co / Ti-Al-xNb-Y alloy coating were approximately 2.5 μm, 2 μm, 2 μm, and 3 μm, respectively.

[0092] A comparative analysis of the WC-Co / Ti-Al-xNb-Y alloy coating and the Ti-Al-xNb-Y alloy coating reveals that, with the same Nb mass fraction, the alloy coating formed by arc-spraying WC-Co followed by Ti-Al-xNb-Y cladding exhibits a denser oxide film after 100 hours of isothermal oxidation at 800℃ compared to the Ti-Al-xNb-Y alloy coating clad alone. This indicates that the W, C, and Co elements introduced by arc spraying further refine the oxide film grains. The resulting dense oxide film hinders oxygen diffusion, reduces the oxidation rate, and further enhances the high-temperature oxidation resistance of the alloy coating.

[0093] Similar to the oxidation process of the Ti-Al-xNb-Y alloy coating, after isothermal oxidation at 800℃ for 100 h, the oxide on the surface of the alloy coating consists of blocky and rod-shaped oxides. Post-oxidation scanning analysis of the WC-Co / Ti-Al-10Nb-Y alloy coating is shown below. Figure 25The table shows (a) surface scan, (b) elemental content, and (c) elemental distribution. The surface scan EDS composition (Table 10) combined with XRD analysis shows that the oxide film surface is filled with a mixture of TiO2 and Al2O3. The presence of C may be due to the presence of TiC on the surface, and no Nb oxide was detected on the surface, suggesting that Nb oxide may not be visible on the surface. (Based on surface scan...) Figure 25 It can be seen that the main elements such as Ti, Al, Nb, W, and C in the coating exhibit a diffuse distribution. These elements do not show obvious enrichment. This is because the addition of rare earth element Y accelerates the flow rate of molten droplets during cladding, making the internal structure of the alloy coating more uniform, thereby improving the microstructure of the coating and further enhancing the adhesion of the oxide film formed by the alloy coating.

[0094] Table 10 Composition of WC-Co / Ti-Al-10Nb-Y Alloy Coating

[0095] 4.5 Cross-sectional morphology of oxide film after high-temperature oxidation Figure 26 The images show the cross-sectional morphology and composition curves of the WC-Co / Ti-Al-xNb-Y alloy coating. (a) and (b) represent the WC-Co / Ti-Al-0Nb-Y alloy coating, (c) and (d) represent the WC-Co / Ti-Al-5Nb-Y alloy coating, (e) and (f) represent the WC-Co / Ti-Al-10Nb-Y alloy coating, and (g) and (h) represent the WC-Co / Ti-Al-15Nb-Y alloy coating. Figure 26 It can be seen that the thickness of the oxide film on the surface of the WC-Co / Ti-Al-0Nb-Y alloy coating is about 20 μm; the thickness of the oxide film on the surface of the WC-Co / Ti-Al-5Nb-Y alloy coating is about 25 μm; the thickness of the oxide film on the surface of the WC-Co / Ti-Al-10Nb-Y alloy coating is about 19 μm; and the thickness of the oxide film on the surface of the WC-Co / Ti-Al-15Nb-Y alloy coating is about 22 μm. It can be observed that there is an oxygen diffusion region with a thickness of 2~10 μm under the oxide film of the WC-Co / Ti-Al-xNb-Y alloy coating.

[0096] The composition curves show that the surface layers of the WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings are predominantly TiO2-based mixed oxides. However, the outermost layer of the oxide film on the WC-Co / Ti-Al-10Nb-Y alloy coating is a mixed oxide layer dominated by Al2O3. This Al2O3-based mixed oxide layer effectively inhibits oxygen diffusion. Below the outermost oxide film is a TiO2 oxide layer. This is because the preferential formation of Al2O3 on the surface results in a Ti-rich and Al-poor state in the next outermost layer, which is predominantly TiO2. Below this next outermost layer is a mixed oxide layer composed of Al2O3 and TiO2. Due to the higher Al2O3 content in the mixed oxide layer, the layer below it exhibits a Ti-rich and Al-poor elemental distribution, leading to a TiO2-rich oxide layer. Ultimately, the oxide film forms a multi-layered structure.

[0097] 4.6 Oxidation Kinetics Figure 27 The oxidation kinetics curves of the WC-Co / Ti-Al-xNb-Y alloy coating and substrate after oxidation at 800℃ for 100 h are shown. With increasing temperature, the oxidation curves show a linear upward trend over time, then tend towards a relatively stable weight gain trend. The unit oxidation weight gain of the WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, WC-Co / Ti-Al-10Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings after oxidation at 800℃ for 100 h is 25.92 mg / cm³, respectively. 2 26.45 mg / cm 2 22.73 mg / cm 2 29.03 mg / cm 2 The oxidative weight gain was less than that of the matrix (36.01 mg / cm³). 2Among the various alloys, WC-Co / Ti-Al-10Nb-Y exhibited the best high-temperature oxidation resistance, with a unit oxidation weight gain of only 0.63 times that of the substrate. The WC-Co / Ti-Al-xNb-Y alloy coating demonstrated excellent high-temperature oxidation resistance, and the improvement in high-temperature resistance became more pronounced with increasing Nb content, showing the best improvement when 10% Nb content was added. Under constant-temperature oxidation conditions of 800℃ for 100 hours, the WC-Co / Ti-Al-xNb-Y alloy coating showed a significantly lower unit oxidation weight gain compared to the Ti-Al-xNb-Y alloy coating, indicating a further improvement in high-temperature oxidation resistance. This suggests that spraying the WC-Co coating followed by cladding can further reduce the oxidation rate of the alloy coating, thereby improving its high-temperature oxidation resistance. Analysis... Figure 27 The oxidation kinetic curves show that the oxidation rate of the coating is relatively high from 0h to 15h, while the rate of weight gain per unit of oxidation slows down from 35h to 100h. This is because the oxidation process at different stages is affected by different oxidation factors.

[0098] The substrate and WC-Co / Ti-Al-xNb-Y alloy coating were analyzed using Origin software. - The data from the curve were subjected to regression linear fitting. Based on the oxidation kinetic curve, the linear fitting was divided into three segments: 0h-15h, 15-35h, and 35h-100h. Figure 28 Among them, (a) the substrate, (b) the WC-Co / Ti-Al-0Nb-Y alloy coating, (c) the WC-Co / Ti-Al-5Nb-Y alloy coating, (d) the WC-Co / Ti-Al-10Nb-Y alloy coating, and (e) the WC-Co / Ti-Al-15Nb-Y alloy coating. Through Figure 28 The power exponents of the oxidation kinetic curves of coatings with different Nb contents and time periods were obtained, as shown in Table 11.

[0099] Table 11 Power exponent n of oxidation kinetic curves

[0100] The n values ​​of both the substrate and the WC-Co / Ti-Al-xNb-Y alloy coating are between 1 and 2, so the WC-Co / Ti-Al-xNb-Y substrate and coating approximately follow a linear weight gain pattern. This was confirmed using Origin software. The data from the curve were subjected to regression linear fitting. Based on the oxidation kinetic curve, the linear fitting was divided into three segments: 0h-15h, 1165h, and 35h-100h. Figure 29Among them, (a) the substrate, (b) the WC-Co / Ti-Al-0Nb-Y alloy coating, (c) the WC-Co / Ti-Al-5Nb-Y alloy coating, (d) the WC-Co / Ti-Al-10Nb-Y alloy coating, and (e) the WC-Co / Ti-Al-15Nb-Y alloy coating.

[0101] The slope K of the fitted curve represents the rate of oxidative weight gain, obtained by... Figure 29 The oxidation rate constants are shown in Table 12. The oxidation rates K of WC-Co / Ti-Al-0Nb-Y, WC-Co / Ti-Al-5Nb-Y, WC-Co / Ti-Al-10Nb-Y, and WC-Co / Ti-Al-15Nb-Y alloy coatings after isothermal oxidation at 800℃ for 100h at different time periods are also shown. p All of them are lower than the oxidation rate constant of the matrix, and the oxidation weight gain rate decreases with the continuous addition of Nb.

[0102] Among them, the alloy coating with 10 wt.% Nb content has the lowest parabolic oxidation rate constant and the best high-temperature oxidation resistance. Observation of the oxidation rate constant table shows that as the Nb content continues to be added, the parabolic oxidation rate constant of the WC-Co / Ti-Al-15Nb-Y alloy coating begins to rise, indicating that the higher Nb content at this time has begun to accelerate the oxidation of the alloy coating, thus accelerating the oxidation of the coating and reducing the coating's high-temperature oxidation resistance.

[0103] Table 12 Parabolic oxidation rate constant K p

[0104] Similarly, observations show that the oxidation rate of the WC-Co / Ti-Al-xNb-Y alloy coating is significantly lower than that of the Ti-Al-xNb-Y alloy coating. This indicates that the prior preparation of the WC-Co coating by arc spraying followed by argon arc cladding can reduce the oxidation rate of the alloy coating. Furthermore, the addition of W, C, and Co elements to the WC-Co coating is more effective in reducing the oxidation rate than adding Nb alone during cladding. It can be concluded that the overall weight gain of the samples after the prior arc spraying of WC-Co is relatively small, indicating that the addition of WC-Co enhances the coating's resistance to high-temperature oxidation.

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant alloy coating by electric arc spraying / argon arc cladding, characterized in that, Includes the following steps: A WC-Co coating is formed by arc spraying on the surface of a titanium alloy substrate. The welding wire used in the arc spraying uses WC88-Co12 powder as the flux core; the conditions for arc spraying include: spraying voltage of 25V, current of 50A, and wire feed speed of 25.54mm / s; or, spraying voltage of 37V, current of 50-110A, and wire feed speed of 25.54-55.67mm / s; After coating the WC-Co coating surface with cladding powder, argon arc cladding is performed to form a Ti-Al-xNb-Y coating, thus obtaining the arc spraying / argon arc cladding high-temperature alloy coating; where x=0-15, and x is the mass fraction; The cladding powder is a mixture of Ti, Al, Nb, and Y; by mass percentage, the cladding powder comprises 0.8% Y, 60% Al, 0-15% Nb, and the balance Ti. The conditions for argon arc cladding include: cladding current of 110-120A, gas flow rate of 10-15L / min, welding speed of 150-230mm / min, and when the cladding current is 120A, the welding speed is 150mm / min.

2. The preparation method according to claim 1, characterized in that, The cladding powder comprises, by mass percentage, 0.8% Y, 60% Al, 10% Nb, and the balance Ti.

3. The preparation method according to claim 1, characterized in that, The spraying distance for the arc spraying is 80-120mm.

4. The preparation method according to claim 1, characterized in that, The diameter of the welding wire is 1.0 mm.

5. The preparation method according to claim 1 or 3, characterized in that, The outer sheath of the welding wire is made of stainless steel.

6. The preparation method according to claim 1, characterized in that, The thickness of the arc spray coating is 200-350 μm.

7. The preparation method according to claim 1 or 2, characterized in that, The coating thickness of the cladding powder is 1-1.5 mm.

8. The preparation method according to claim 1, characterized in that, Before the arc spraying, the titanium alloy substrate is also subjected to sandblasting treatment.

9. The preparation method according to claim 1, characterized in that, Before coating, the cladding powder is mixed with water glass.

10. The high-temperature resistant alloy coating prepared by the preparation method according to any one of claims 1 to 9, characterized in that, This includes WC-Co coatings and Ti-Al-xNb-Y coatings layered and distributed on the surface of a titanium alloy substrate, where x = 0-15 and x is the mass fraction.

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