A method for preparing a high-temperature oxidation-resistant composite coating on the surface of a light-weight high-strength alloy

Abstract

The present application belongs to the technical field of intermetallic compound coating, and particularly relates to a method for preparing a high-temperature oxidation resistant composite coating on the surface of a light-weight high-strength alloy, characterized in that the method comprises surface degreasing, sand blasting, plasma spraying, electric arc spraying and heat treatment. The present application has the beneficial effects that the coating is well combined with the substrate, the joint between the coating and the substrate is free of pores and cracks, the bonding strength between the coating and the substrate is above 38 MPa, and the overall porosity of the coating is not higher than 5%. After vacuum heat treatment, the coating on the substrate is a pure Ni layer and a Ni-Al intermetallic compound layer. Vacuum heat treatment causes in-situ reaction at the Ni / Al interface, and finally makes Al completely consumed. The upper coating is an in-situ generated Ni-Al intermetallic compound layer and a part of the pure Ni layer which is not completely reacted after vacuum heat treatment. The composite coating has better bonding strength, lower porosity and better high-temperature oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of lightweight high-strength alloy surface coating technology, and particularly relates to a method for preparing a high-temperature oxidation-resistant composite coating on the surface of a lightweight high-strength alloy. Background Technology

[0002] Lightweight, high-strength alloys are widely used in aerospace, automotive, and shipbuilding industries, including titanium and titanium alloys, aluminum and aluminum alloys, titanium-aluminum alloys, and aluminum-magnesium alloys. Titanium and titanium alloys are frequently used in aerospace engine components, aircraft compressor discs, and marine internal combustion engine parts. However, high-temperature titanium alloys are designed for operation at temperatures between 400°C and 600°C. When the operating temperature exceeds 400°C, atmospheric oxygen atoms readily react with the titanium alloy, forming rutile titanium oxide on its surface. This titanium oxide is highly susceptible to detachment, leading to oxidation of the matrix and reducing the overall performance of the titanium alloy, thus limiting its application in high-temperature environments.

[0003] Since oxidation often occurs on the substrate surface, preparing a high-temperature resistant coating on the surface of titanium and titanium alloys can effectively improve their resistance to high-temperature oxidation. Preparing a high-temperature anti-oxidation coating on the surface of titanium and titanium alloys can achieve the effect of resisting high-temperature oxidation without affecting the substrate microstructure.

[0004] Invention patent CN114075665A discloses a NiSiAlY coating on a titanium alloy surface and its preparation method. This process uses cold spraying technology to prepare a 500-900 μm NiSiAlY coating on the titanium alloy surface. The prepared parts are then annealed to improve adhesion strength, reduce porosity, and thus enhance the high-temperature oxidation resistance of the titanium alloy. However, the annealed coating still has high porosity, and there are pores between the NiSiAlY coating and the substrate, which may still lead to substrate oxidation.

[0005] Invention patent CN110144541A discloses a high-temperature titanium alloy thermal barrier coating material and its preparation method. A Ti48Al2Cr2Nb binder layer is prepared on the surface of an IMI834 alloy substrate by supersonic flame spraying. An 8YSZ layer is then prepared on the binder layer as a working layer to improve its high-temperature oxidation resistance. However, Cr, Nb, and YSZ are expensive, and the thermal expansion coefficients of 8YSZ and the Ti48Al2Cr2Nb binder layer differ significantly. Therefore, there are still many pores at the interface between the binder layer and the working layer, affecting the coating's performance at high temperatures. Furthermore, there are also many pores between the binder layer and the substrate.

[0006] As can be seen from the existing technologies, to improve the high-temperature oxidation resistance of titanium and titanium alloys, coatings are mostly prepared by adding non-metallic elements or ceramic phases to metallic elements. These coatings tend to have high porosity and are not dense, making them susceptible to oxygen atom intrusion and substrate oxidation with prolonged oxidation time. Furthermore, the presence of pores at the coating-substrate interface can easily lead to coating detachment. Additionally, the coating composition often includes some expensive metals, resulting in high costs. Currently, there are few publicly available reports on how to improve the high-temperature oxidation resistance of titanium and titanium alloys, reduce coating costs, and simultaneously achieve coatings with fewer pores and air pockets while maintaining good bonding strength. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a high-temperature resistant oxide composite coating on the surface of a lightweight, high-strength alloy, overcoming the shortcomings of the prior art. This method prepares a high-temperature resistant oxide composite coating on the surface of titanium and titanium alloys, achieving low cost, low porosity, and high bonding strength. It forms a protective high-temperature resistant oxide film on the surface of the part, preventing oxygen from entering the interior of the coating structure. The coating provides complete protection for the substrate, with no surface peeling, and effectively isolates oxygen and slows down oxidation.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing a high-temperature resistant oxidation composite coating on the surface of a lightweight, high-strength alloy, characterized by comprising surface degreasing, sandblasting roughening, plasma spraying, arc spraying, and vacuum heat treatment, with the specific operation steps as follows:

[0010] 1) Surface degreasing: Remove oil stains from the surface of the parts to be treated using sodium hydroxide alkaline cleaning solution;

[0011] 2) Sandblasting roughening: Use 180-200 mesh white corundum abrasive to sandblast the surface of the part. The sandblasting angle is 80°-90°, the compressed air pressure is 0.60MPa-0.65MPa, and the sandblasting distance is 100mm-150mm until the surface has a rough silver-gray luster.

[0012] 3) Plasma spraying: A NiCrAlY underlayer is prepared on the roughened surface of the part after sandblasting. The plasma spraying process parameters are: welding current 600A~650A, voltage 38V~44V, and NiCrAlY underlayer thickness 45~55mm. An intermediate layer is prepared on the NiCrAlY underlayer using pure Ni powder, with a pure Ni intermediate layer thickness of 230~255μm. The plasma spraying process parameters are: welding current 600A~650A, voltage 39V~44V; NiCrAlY underlayer and... The spraying speed of the intermediate layer is 400-500 mm / min, the spraying distance is 150 mm to 200 mm, the powder output of the powder feeding pipe is 8 mg / s to 12 mg / s, the powder feeder speed is 0.55 rad / min to 0.7 rad / min, the powder feeding gas is argon, the powder feeding gas flow rate is 38 psi to 42 psi, the protective gas is argon, the protective gas flow rate is 42 psi to 46 psi, and the combustion-supporting gas is hydrogen, with a gas flow rate of 8 psi to 12 psi.

[0013] 4) Arc Spraying: Using aluminum wire with a diameter of Φ2.0mm and a purity of 99.5%–99.7% as the spraying raw material, arc spraying is performed on the surface of the parts after plasma spraying. The spraying distance is 100mm–150mm, the wire feed speed is 3m / min–4m / min, the current I = 130A–150A, the voltage U = 30–35V, the compressed gas pressure is 0.65MPa–0.75MPa, and the compressed gas flow rate is 1.6m³ / min. 3 / min~2.0m 3 / min, spraying time 50s~90s;

[0014] 5) Vacuum heat treatment: Parts after plasma and arc composite thermal spraying are subjected to vacuum heat treatment at a temperature of 660℃~700℃ for 15h~25h, with a vacuum degree of 5.0×10⁻⁶. -2 Pa ~ 7.0 × 10 -3 Pa.

[0015] In step 1), the mass percentage of sodium hydroxide alkaline washing solution is 4.0% to 5.0%, and the soaking time is 3.0 min to 5.0 min at a temperature of 60℃ to 70℃.

[0016] In step 2), in order to make the coating and the substrate have better bonding strength, it is necessary to control the surface roughness after sandblasting. The surface roughness of the sample after sandblasting is Ra5.0μm~Ra6.0μm. After sandblasting, the sand particles adhering to the surface are blown off with compressed air.

[0017] In step 3), the particle size of the NiCrAlY powder used for the NiCrAlY base coat plasma spraying is 300-400 mesh, and the powder material is spherical powder.

[0018] In step 3), the particle size of the pure Ni powder used for plasma spraying is 300 mesh to 400 mesh, the powder material is spherical powder, and the Ni purity is 99.7% to 99.9%.

[0019] In step 3), the metal powder for plasma spraying is preheated and dried in a drying oven before plasma spraying. The drying temperature is 50℃~80℃ and the drying time is 2h~6h.

[0020] In step 4), the Al wire used for arc spraying is fed by gear clamping, and the clamping pressure of the wire feeding fixture is adjusted to 0.5-0.6 MPa before spraying.

[0021] The heating rate during the vacuum heat treatment in step 5) is 10℃ / min to 15℃ / min, and the furnace is cooled after the vacuum heat treatment.

[0022] After the vacuum heat treatment in step 5), the porosity of the coating on the surface of the part is not higher than 5%. After oxidation at a high temperature of 800℃~900℃ for 100h~150h, the coating does not fail and the substrate is not oxidized.

[0023] The lightweight high-strength alloy is any one of titanium and titanium alloys, aluminum and aluminum alloys, titanium-aluminum alloys, and aluminum-magnesium alloys.

[0024] The surface roughness after sandblasting is a crucial technical parameter in this invention, as it is a key factor in achieving bonding between the thermal spray coating and the substrate. After sandblasting, the resulting surface is a homogeneous, grayish-white metal surface, roughened to the point where the coating can "anchor" itself. This surface is also free of oil, grease, contaminants, rolled iron scale, rust, corrosion, oxides, paint, and other foreign matter. As the surface roughness Ra increases, the bonding strength also improves, but the degree of improvement decreases after exceeding 10 μm. Compressed air can be used to clean the surface, with optimal results achieved at a surface roughness of Ra 5.0 μm to Ra 6.0 μm.

[0025] Another key point of this invention is that since the material used in plasma spraying is powder and the plasma spraying equipment is an internal powder feeder, it prevents the NiCrAlY powder and pure Ni powder from being too sticky during the spraying process, which could lead to powder blockage or the generation of large molten droplets during the spraying process. Before spraying, the metal powder is preheated and dried in a drying oven at a temperature of 50°C to 80°C for 2 hours to 6 hours.

[0026] The third key aspect of this invention is vacuum heat treatment. The main purpose is to melt Al, allowing for in-situ reaction at the Ni / Al interface to form an intermetallic compound. During the formation of the intermetallic compound layer after Al melting, the porosity of the coating is further reduced; therefore, the heating rate should not be too fast. The heating rate is 10°C / min to 15°C / min, and the vacuum level is controlled at 5.0 × 10⁻⁶. -2 Pa ~ 7.0 × 10 -3 Pa. After vacuum heat treatment, the coating is cooled in the furnace. This furnace cooling is to ensure that the cooling rate is not too fast, as an excessively fast cooling rate can lead to increased porosity or other defects in the composite coating during the cooling process.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1) The coating prepared by the present invention has good bonding with the substrate, the overall porosity of the coating is not higher than 5%, and there are no pores or cracks at the bonding point between the coating and the substrate. The bonding strength between the coating and the substrate is above 38 MPa.

[0029] 2) After vacuum heat treatment, the coating on the substrate consists of a pure Ni layer and a Ni-Al intermetallic compound layer. Vacuum heat treatment causes an in-situ reaction at the Ni / Al interface, ultimately leading to the complete consumption of Al. The upper coating layer is a Ni-Al intermetallic compound layer generated in-situ after vacuum heat treatment. This composite coating exhibits better high-temperature resistance than a pure Al coating and better bonding strength, lower porosity, and better high-temperature oxidation resistance than a directly prepared sprayed Ni-Al intermetallic compound coating.

[0030] 3) Both NiAl phase and α-Al2O3 have good high-temperature oxidation resistance. Among them, NiAl3 in the coating after vacuum heat treatment is Al-rich phase. The Al in the Al-rich phase reacts with oxygen in the atmosphere and undergoes secondary Al combination to generate Al2O3 with good oxidation resistance. The dense α-Al2O3 layer generated on the surface will block the invasion of oxygen atoms, thus playing a perfect role in isolating oxygen and slowing down oxidation. Attached Figure Description

[0031] Figure 1 The image shows the cross-sectional microstructure of the composite coating under an electron microscope in Embodiment 1 of this invention.

[0032] Figure 2 The image shows the XRD pattern of the Ni / Al composite coating after high-temperature oxidation in Example 1 of this invention.

[0033] Figure 3 This is the high-temperature oxidation weight gain curve of the Ni / Al composite coating in Example 1 of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.

[0036] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0037] Example 1

[0038] This invention discloses a method for preparing a high-temperature resistant oxidation composite coating on the surface of a lightweight, high-strength alloy, comprising surface degreasing, sandblasting roughening, plasma spraying, arc spraying, and vacuum heat treatment. The specific operation steps are as follows:

[0039] 1) Surface degreasing: Remove oil stains from the surface of the parts to be treated with sodium hydroxide alkaline cleaning solution; the mass percentage of sodium hydroxide alkaline cleaning solution is 4.0% to 5.0%, and immersion is carried out at a temperature of 60℃ to 70℃ for 3.0 min to 5.0 min. The parts to be treated are 100mm×100mm titanium plates (grade TA1) with a thickness of 3mm.

[0040] 2) Sandblasting roughening: Use 180-200 mesh white corundum abrasive to sandblast the surface of the part. The sandblasting angle is 80°-90°, the compressed air pressure is 0.60MPa-0.65MPa, and the sandblasting distance is 100mm-150mm until the surface shows a rough silver-gray luster. The surface roughness of the sample after sandblasting is Ra5.0μm-Ra6.0μm. After sandblasting, use compressed air to blow away the sand particles adhering to the surface.

[0041] 3) Plasma spraying: A NiCrAlY underlayer is prepared on the roughened surface of the part after sandblasting. The plasma spraying process parameters are: welding current 600A-650A, voltage 38V-44V, and NiCrAlY underlayer thickness 45-55mm. An intermediate layer is prepared on the NiCrAlY underlayer using pure Ni powder. The plasma spraying process parameters are: welding current 600A-650A, voltage 39V-44V. The spraying speed for both the NiCrAlY underlayer and intermediate layer is 400-500mm / min, and the spraying distance is 150mm. The powder feeding pipes are all 200mm in diameter, with a powder output of 8mg / s-12mg / s. The powder feeder speed is 0.55rad / min-0.7rad / min. Argon is used for powder feeding, with a flow rate of 38psi-42psi. Argon is used for protective gas, with a flow rate of 42psi-46psi. Hydrogen is used for combustion, with a flow rate of 8psi-12psi. The NiCrAlY powder used for the NiCrAlY undercoat plasma spraying has a particle size of 300-400 mesh and is spherical. The pure Ni powder used for plasma spraying has a particle size of 300-400 mesh and is spherical, with a Ni purity of 99.7%-99.9%. Before plasma spraying, the metal powder for plasma spraying is preheated and dried in a drying oven at 50℃-80℃ for 2-6 hours.

[0042] 4) Arc Spraying: Using aluminum wire with a diameter of Φ2.0mm and a purity of 99.5%–99.7% as the spraying raw material, arc spraying is performed on the surface of the parts after plasma spraying. The pure Al layer thickness is 230–255μm; the spraying distance is 100mm–150mm, the wire feed speed is 3m / min–4m / min, the current I = 130A–150A, the voltage U = 30–35V, the compressed gas is 0.65MPa–0.75MPa, and the compressed gas flow rate is 1.6m³ / min. 3 / min~2.0m 3 The spraying speed is 50s to 90s. The Al wire used for arc spraying is fed by gear clamping. Before spraying, the clamping pressure of the wire feeding fixture is adjusted to 0.5-0.6MPa.

[0043] 5) Vacuum heat treatment: Parts after plasma and arc composite thermal spraying are subjected to vacuum heat treatment at a temperature of 660℃~700℃ for 15h~25h. The heating rate during vacuum heat treatment is 10℃ / min~15℃ / min, and the vacuum level is controlled at 5.0×10⁻⁶. -2 Pa ~ 7.0 × 10 -3Pa, after vacuum heat treatment, is cooled in the furnace. After vacuum heat treatment, the porosity of the coating on the surface of the part is not higher than 5%. After oxidation at a high temperature of 800℃~900℃ for 100h~150h, the coating does not fail and the substrate is not oxidized.

[0044] See Figure 1 The image shows the cross-section of the composite coating after vacuum heat treatment, observed under a scanning electron microscope. It is evident that the coating exhibits good adhesion to the substrate after the above processing. The coating porosity, measured using Image software, is approximately 3.51%, exhibiting a typical thermal spray coating structure. The coating and substrate have good adhesion, with no pores or cracks at the interface. The NiCrAlY underlayer thickness is 53 μm, the Ni intermediate layer thickness is 113 μm, and the Ni-Al intermetallic compound layer thickness is 344 μm. The coating and substrate are mechanically bonded, with a bonding strength of 42.5 MPa.

[0045] Furthermore, there are no pores or cracks at the interface between the coating and the substrate, and the bonding strength between the coating and the substrate is above 38 MPa. Energy dispersive spectroscopy (EDS) and XRD analysis revealed that the Ni-Al intermetallic compound layer consists of NiAl3 and Ni2Al3 layers from top to bottom, with an unreacted pure Ni coating beneath the compound layers. This will provide a sufficient Ni source for the subsequent formation of a higher melting point Ni-Al intermetallic compound layer during high-temperature oxidation.

[0046] See Figure 2 The image shows the XRD pattern of the Ni / Al composite coating after heating at 900℃ for 150 h. It can be seen that the Ni / Al composite coating after vacuum heat treatment and high-temperature oxidation contains both α-Al₂O₃ and NiAl phases. In the Al-rich NiAl₃ phase formed after vacuum heat treatment, Al atoms in the NiAl₃ phase react with atmospheric oxygen atoms through secondary Al combination to generate Al₂O₃, which has good oxidation resistance. A dense α-Al₂O₃ layer is formed on the surface, thus preventing oxygen atom intrusion. The remaining Ni layer after vacuum heat treatment can provide a Ni source for the subsequent formation of the NiAl phase. The NiAl phase has a high melting point, and both α-Al₂O₃ and NiAl phases have excellent high-temperature oxidation resistance.

[0047] See Figure 3 The samples were heated at 900℃ for 150 hours. Weight gain curves were plotted for different time periods based on the weight gain data. The oxidation weight gain curve was a relatively gentle parabola. Before 20 hours, the composite coated parts showed a slight weight gain. Later, after the formation of an Al2O3 thermal barrier layer on the outermost layer, oxidation gradually slowed down. The entire process conformed to a parabolic law, indicating that the coating has good anti-oxidation effect. After 150 hours, the coating still effectively protected the substrate, with no surface peeling, demonstrating its excellent oxygen isolation and oxidation-reducing effect.

[0048] Example 2

[0049] The part to be processed is a 100mm×100mm titanium alloy (grade TC4) with a thickness of 3mm.

[0050] The specific steps for preparing a high-temperature resistant oxide composite coating on its surface are as follows:

[0051] 1) Immerse the test plate in a 4.5% sodium hydroxide alkaline cleaning solution, heat the alkaline cleaning solution to 70°C, and immerse for 4.0 minutes to remove the grease from the surface of the parts.

[0052] 2) The TC4 titanium alloy surface was sandblasted using 200-mesh white corundum abrasive grains. The angle between the sandblasting nozzle and the titanium plate surface was 85°, the compressed air pressure was 0.63 MPa, and the sandblasting distance was 130 mm. After sandblasting, the surface roughness of the test sample was Ra 5.5 μm. Subsequently, the adhering sand particles on the surface were blown away using compressed air at the same pressure in an air compressor. Before spraying, the metal powder for plasma spraying was preheated and dried in a drying oven at 70℃ for 5 hours.

[0053] 3) The base coat was prepared using 350-mesh NiCrAlY powder. The NiCrAlY powder composition (mass fraction) was 21.7% Cr, 11.0% Al, 1.2% Y, 0.5% Ti, with the remainder being Ni. The plasma spraying process parameters were: welding current 620A, arc voltage 38V, spraying speed 400mm / min, spraying distance 180mm, powder output from the powder feeder 10.33mg / s, argon as the powder feed gas with a flow rate of 40psi, argon as the shielding gas with a flow rate of 45psi, and hydrogen as the combustion-supporting gas with a flow rate of 10psi. The base coat was prepared using 350-mesh pure Ni powder with a Ni content of 99.9% by mass. The plasma spraying process parameters are as follows: welding current 650A, arc voltage 40V, spraying speed 400mm / min, spraying distance 160mm, powder output from the powder feeding pipe 9.83mg / s, powder feeding gas is argon with a flow rate of 40psi, shielding gas is argon with a flow rate of 45psi, and combustion-supporting gas is hydrogen with a flow rate of 10psi.

[0054] 4) Use 99.60% aluminum wire with a diameter of Φ2.0mm as the raw material for arc spraying. Adjust the clamping pressure of the wire feeding mechanism gears. After the wire feeding system feeds the wire at a uniform and stable speed with consistent speeds on both sides, proceed with arc spraying. The spraying distance is 130mm, the wire feeding speed is 3m / min, the current I = 140A, the voltage U = 32V, the compressed gas is 0.7MPa, and the flow rate is guaranteed to be 1.8m³ / min. 3The spraying speed was 1 min, and the spraying time was 1 min. Scanning electron microscopy revealed that the coating was firmly bonded to the titanium substrate without any separation. The base layer thickness was 50 μm, the intermediate pure Ni layer was 200 μm, and the surface pure Al layer was 250 μm.

[0055] 5) Subsequently, vacuum heat treatment was performed at 680℃ for 20 hours, with a heating rate of 12℃ / min and the vacuum degree controlled at 6.0×10⁻⁶. -2 Pa, after vacuum heat treatment, is cooled in the furnace.

[0056] After the above processing, the porosity was measured to be 3.55%, the NiCrAlY underlayer thickness was 50 μm, the Ni intermediate layer thickness was 116 μm, the Ni-Al intermetallic compound layer thickness was 332 μm, and the coating-substrate bonding strength was 40.7 MPa. After oxidation at 900℃ for 150 h, the coating did not fail. After 150 h, the coating still provided excellent protection to the substrate, with no surface peeling, effectively isolating oxygen and slowing down oxidation.

[0057] Example 3

[0058] The part to be treated was a 100mm × 100mm TiAl alloy (grade Ti / Al50) with a thickness of 3mm, and other parameters were the same as in Example 2. The porosity was measured to be 3.99%. The NiCrAlY underlayer thickness was 49μm, the Ni intermediate layer thickness was 119μm, the aluminum layer thickness was 363μm, and the coating-substrate bonding strength was 39.8MPa. After oxidation at 900℃ for 150h, the coating did not fail, the part was not oxidized, and the coating still provided protection for the part.

[0059] Example 4

[0060] The part to be treated was a 100mm × 100mm aluminum alloy (grade 7075) with a thickness of 3mm, and other parameters were the same as in Example 2. After the above process, the porosity was measured to be 4.27%, the NiCrAlY underlayer thickness was 51μm, the Ni intermediate layer thickness was 109μm, the Ni-Al intermetallic compound layer thickness was 372μm, and the coating-substrate bonding strength was 41.3MPa. After oxidation at 800℃ for 200h, the coating did not fail, the part was not oxidized, and the coating still provided protection for the part.

[0061] Example 5

[0062] The part to be treated was a 100mm × 100mm aluminum alloy (grade 6061) with a thickness of 3mm, and other parameters were the same as in Example 2. After the above process, the porosity was measured to be 3.91%, the NiCrAlY underlayer thickness was 52μm, the Ni intermediate layer thickness was 125μm, the Ni-Al intermetallic compound layer thickness was 357μm, and the coating-substrate bonding strength was 39.6MPa. After oxidation at 800℃ for 200h, the coating did not fail, the part was not oxidized, and the coating still provided protection for the part.

[0063] 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 oxidation-resistant composite coating on the surface of a lightweight, high-strength alloy, characterized in that, The process includes surface degreasing, sandblasting roughening, plasma spraying, arc spraying, and vacuum heat treatment. The specific operating steps are as follows: 1) Surface degreasing: Remove oil stains from the surface of the parts to be treated using sodium hydroxide alkaline cleaning solution; 2) Sandblasting roughening: Use 180-200 mesh white corundum abrasive to sandblast the surface of the part. The sandblasting angle is 80°-90°, the compressed air pressure is 0.60MPa-0.65MPa, and the sandblasting distance is 100mm-150mm until the surface has a rough silver-gray luster. 3) Plasma spraying: A NiCrAlY underlayer is prepared on the roughened surface of the part after sandblasting. The plasma spraying process parameters are: welding current 600A~650A, voltage 38V~44V, and NiCrAlY underlayer thickness 45~55μm; an intermediate layer is prepared on the NiCrAlY underlayer using pure Ni powder, with a pure Ni intermediate layer thickness of 230~255μm; the plasma spraying process parameters are: welding current 600A~650A, voltage 39V~44V; the NiCrAlY underlayer and... The spraying speed of the intermediate layer is 400-500 mm / min, the spraying distance is 150-200 mm, the powder output of the powder feeding pipe is 8 mg / s-12 mg / s, the powder feeder speed is 0.55 rad / min-0.7 rad / min, the powder feeding gas is argon, the powder feeding gas flow rate is 38 psi-42 psi, the protective gas is argon, the protective gas flow rate is 42 psi-46 psi, and the combustion-supporting gas is hydrogen, with a gas flow rate of 8 psi-12 psi. 4) Arc Spraying: Using aluminum wire with a purity of 99.5%–99.7% as the spraying raw material, arc spraying is performed on the surface of the parts after plasma spraying. The spraying distance is 100mm–150mm, the wire feed speed is 3m / min–4m / min, the current I = 130A–150A, the voltage U = 30–35V, the compressed gas pressure is 0.65MPa–0.75MPa, and the compressed gas flow rate is 1.6m³ / min. 3 / min~2.0m 3 / min, spraying time 50s~90s; 5) Vacuum heat treatment: Parts after plasma and arc composite thermal spraying are subjected to vacuum heat treatment at a temperature of 660℃~700℃ for 15h~25h, with a vacuum degree of 5.0×10⁻⁶. -2 Pa ~ 7.0 × 10 -3 Pa; In step 1), the sodium hydroxide alkaline washing solution has a mass percentage of 4.0% to 5.0%, and is immersed at a temperature of 60°C to 70°C for 3.0 min to 5.0 min. In step 2), the surface roughness of the sample after sandblasting is Ra5.0μm~Ra6.0μm, and the sand particles adhering to the surface are blown off with compressed air after sandblasting. In step 3), the particle size of the NiCrAlY powder used for the NiCrAlY base coat plasma spraying is 300 mesh to 400 mesh, and the powder material is spherical powder. In step 3), the particle size of the pure Ni powder used for plasma spraying is 300 mesh to 400 mesh, the powder material is spherical powder, and the Ni purity is 99.7% to 99.9%. In step 3), the metal powder for plasma spraying is preheated and dried in a drying oven before plasma spraying. The drying temperature is 50℃~80℃ and the drying time is 2h~6h. After the vacuum heat treatment in step 5), the porosity of the coating on the surface of the part is not higher than 5%. After oxidation at a high temperature of 800℃~900℃ for 100h~150h, the coating does not fail and the substrate is not oxidized. The heating rate during the vacuum heat treatment in step 5) is 10℃ / min~15℃ / min, and the part is cooled with the furnace after the vacuum heat treatment. The lightweight high-strength alloy is any one of titanium and titanium alloys, aluminum and aluminum alloys, titanium-aluminum alloys, and aluminum-magnesium alloys.

2. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a lightweight high-strength alloy according to claim 1, characterized in that, In step 4), the Al wire used for arc spraying is fed by gear clamping, and the clamping pressure of the wire feeding fixture is adjusted to 0.5-0.6 MPa before spraying.

Images