Wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blade and preparation method of wear-resistant and corrosion-resistant gradient carbide composite coating

Abstract

The invention discloses a wear-resistant and corrosion-resistant gradient carbide composite coating for a turbine blade and a preparation method of the wear-resistant and corrosion-resistant gradient carbide composite coating, and belongs to the technical field of metal surface protection and hypersonic flame spraying. According to the invention, a three-layer gradient structure is constructed; through the HVOF gradient spraying process matched with the narrow gap of the blade and in combination with two-stage low-temperature stabilization heat treatment, precise regulation and control and structure refinement of the internal stress of the coating are achieved. According to the prepared coating, the bonding strength is larger than or equal to 85 MPa, the porosity is smaller than or equal to 0.25%, the microhardness is larger than or equal to 1320 HV, the 400-DEG C high-temperature erosion rate is reduced by 45% or above compared with a traditional WC-CoCr coating, red rust or blistering does not exist in a neutral salt spray test for 1000 h, the coating is perfectly matched with on-site movable spraying construction of 15-20 mm narrow gaps of turbine blades, the technological process is simple, batch production and on-site repairing are convenient, and the application range is wide. The method has wide application prospects in the fields of thermal power, gas turbine and steam turbine blade protection.

Description

Technical Field

[0001] This invention relates to a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades and its preparation method, specifically to a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades and its HVOF preparation method. It belongs to the technical field of metal surface protection and high-velocity vapor deposition (HVOF) spraying. Background Technology

[0002] Gas turbines and steam turbines are core power equipment in the power and petrochemical industries. Turbine blades, as core moving components, are subjected to extremely harsh operating conditions: on the one hand, hard particles such as fly ash and SiO2 carried in high-speed flue gas / steam can cause severe erosion and wear on the blade surface; on the other hand, sulfides and chlorides in steam condensate and flue gas can cause severe electrochemical corrosion and high-temperature oxidation; at the same time, the alternating load during the start-up and shutdown process of the blades can easily cause the coating to crack and peel off, and the narrow gap of only 15-20mm between the blades brings great construction difficulties to on-site maintenance and spraying.

[0003] Currently, the mainstream method for on-site repair and protection of turbine blades is to use HVOF sprayed WC-CoCr carbide coating. This coating is widely used due to its high hardness and excellent wear resistance, but it has the following key shortcomings: 1. A single WC-CoCr coating is difficult to achieve wear resistance, erosion resistance and corrosion resistance at the same time. Under high temperature service environment, the Co binder phase in the coating is prone to oxidation and loss, which leads to a sharp drop in the wear resistance of the coating. At the same time, sulfides and chloride ions can easily penetrate into the substrate through the coating pores, causing interfacial corrosion and coating peeling. 2. The coefficient of thermal expansion of a single carbide coating differs greatly from that of iron-based and nickel-based blade substrates, resulting in high residual stress after spraying. This makes the coating prone to cracking and insufficient interfacial adhesion, and it is susceptible to early failure under alternating loads. 3. Due to the narrow gap of 15-20mm between blades, only small-angle spraying can be used. Under the traditional spraying process, the sprayed particles cannot hit the substrate perpendicularly, resulting in serious loss of kinetic energy. This leads to increased coating porosity, decreased bonding strength, poor thickness uniformity, and a significant deterioration in wear and erosion resistance, which cannot meet the requirements for on-site repair. 4. Traditional coating heat treatment often uses high-temperature annealing, which can easily lead to the decomposition and decarburization of carbides such as WC, generating brittle W2C phase, resulting in a decrease in coating hardness and fracture toughness, which in turn reduces the service life of the coating.

[0004] Existing technologies primarily focus on optimizing the composition of single coatings. For example, patent CN114574824A discloses a WC-Co-Cr-Ni coating, which improves corrosion resistance by adding Ni, but it still fails to solve the problems of high internal stress and deterioration in spraying performance at small angles. Patent CN112853218A discloses a laser cladding gradient wear-resistant coating, but laser cladding has a large heat input, which easily leads to deformation of thin-walled blades and cannot be adapted to rapid repair work in narrow gaps on site. Existing technologies also attempt to reduce coating costs or improve processability by adding low-hardness alloy phases. For instance, some studies have disclosed a Ni60 / WC-10Co4Cr composite coating. By adding Ni60 alloy powder to WC-10Co4Cr, although the raw material cost is reduced to some extent, this composite coating is a single structure without a bonding underlayer. The difference in thermal expansion coefficient between the composite coating and the blade substrate is large, resulting in high residual stress after spraying and a bonding strength typically below 70 MPa. Under alternating loads, it is prone to interfacial spalling. Furthermore, patent CN121759861A discloses a high-entropy alloy binder and thermal barrier coating system for hydrogen-blended gas turbines, aiming to promote the formation of thermally grown oxides (TGO) through the high-entropy alloy binder to extend the high-temperature service life of the thermal barrier coating. However, it belongs to the field of thermal insulation and protection, and does not involve the gradient structure design of wear-resistant and erosion-resistant carbide coatings, nor does it solve the performance degradation problem of on-site spraying in narrow blade gaps. Therefore, the existing technology lacks a composite coating and its preparation method that can simultaneously achieve wear resistance, corrosion resistance, and erosion resistance, and is perfectly adapted to on-site spraying construction in narrow turbine blade gaps. In summary, there is an urgent need to develop an HVOF composite coating and its preparation method that simultaneously achieves excellent corrosion resistance, wear resistance, and erosion resistance, and is perfectly adapted to on-site spraying construction in narrow turbine blade gaps, to solve the core pain points of the existing technology. Summary of the Invention

[0005] To address the aforementioned challenges, this invention provides a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades.

[0006] Meanwhile, the present invention provides a method for preparing a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades, wherein the coating has a three-layer gradient structure, consisting of a high-entropy alloy bonding underlayer, a gradient carbide reinforced intermediate layer, and a nano-modified carbide erosion-resistant surface layer from the substrate to the surface. The high-entropy alloy bonding layer is a Ni-Co-Cr-Fe-Al pentagonal high-entropy alloy, comprising, by atomic percentage: Al 10.0%-13.0%, Cr 20.0%-23.0%, Fe 22.0%-24.0%, Co 20.0%-22.0%, and Ni 22.0%-23.0%. The gradient carbide-reinforced intermediate layer is a gradient composite system of WC-CoCr and Cr3C2-NiCr. Along the coating thickness direction, from the bonding underlayer to the erosion-resistant top layer, the mass proportion of WC-CoCr linearly increases from 30% to 70%, while the mass proportion of Cr3C2-NiCr linearly decreases from 70% to 30%. The nano-modified carbide erosion-resistant surface layer uses WC-10Co-4Cr as the matrix phase and adds nano-modified phases. The nano-modified phases include at least two of TiC, NbC, and Y2O3, and the total mass percentage of the nano-modified phases is 2.0%-8.0%, wherein the mass ratio of TiC to NbC is 1:(0.5-2).

[0008] The high-entropy alloy bonding underlayer has a thickness of 50-100 μm, the gradient carbide reinforced intermediate layer has a thickness of 150-300 μm, the nano-modified carbide erosion-resistant surface layer has a thickness of 50-100 μm, and the total coating thickness is 250-500 μm.

[0009] The nano-modified carbide erosion-resistant surface layer contains in-situ dispersed nano-precipitates with a particle size of 20-50 nm, including TiC, NbC, and Y2O3. The nano-precipitates pin grain boundaries and refine the coating grains, resulting in an average grain size of ≤200 nm for the coating.

[0010] The coating has a bonding strength ≥85MPa, a microhardness ≥1300HV, a porosity ≤0.25%, and shows no red rust after 1000h of neutral salt spray testing.

[0011] Specifically, the coating exhibits a bonding strength ≥85MPa, microhardness ≥1320HV, porosity ≤0.25%, abrasive wear weight loss of 2.9-3.8mg, salt spray corrosion weight loss of 0.12-0.20mg, and high-temperature erosion rate at 400℃ of 1.1-1.4×10⁻⁶. -3 mg•g -1 No red rust was observed after 1000 hours of neutral salt spray testing.

[0012] In the gradient carbide-reinforced intermediate layer, WC-CoCr is WC-10Co-4Cr, and Cr3C2-NiCr is Cr3C2-25NiCr.

[0013] In the nano-modified carbide erosion-resistant surface layer, the original powder of the nano-modified phase has a particle size of 30-100 nm, and the composite powder for spraying has a particle size of 10-45 μm.

[0014] A method for preparing a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades includes the following steps: Step 1, Powder Pretreatment: High-entropy alloy binder powder, gradient intermediate layer composite powder, and surface modified carbide powder are prepared separately, and then vacuum dried and sieved for later use. Step 2, Substrate Pretreatment: The turbine blade substrate is subjected to surface degreasing and sandblasting roughening treatment, with the surface roughness controlled at Ra3.0-6.0μm and the cleanliness reaching Sa2.5 level or above; Step 3, HVOF gradient spraying: Using a supersonic flame spraying system, paired with a micro nozzle with a rod diameter of 10-12mm, the high entropy alloy bonding base layer, gradient carbide reinforced intermediate layer, and nano-modified carbide erosion resistant top layer are sprayed sequentially. Step 4: Low-temperature stabilization heat treatment: The sprayed blades undergo two stages of low-temperature heat treatment to eliminate residual stress from the spraying, refine the coating structure, and improve service stability.

[0015] In step one, the high-entropy alloy binder powder is prepared by gas atomization and is a spherical powder with a particle size of 15-45 μm.

[0016] Specifically, the entropy alloy binder powder: spherical powder is prepared using a gas atomization method. 1) Material preparation and smelting: Weigh high-purity Ni, Co, Cr, Fe, and Al metal raw materials (purity ≥ 99.5%) according to the designed atomic percentage, place them in a vacuum induction melting furnace or a vacuum arc melting furnace, and evacuate to ≤ 1.0 × 10⁻⁶. -2 After Pa, high-purity argon gas (purity ≥99.999%) is introduced as a protective atmosphere, and the mixture is melted at 1500-1650℃ for 30-60 minutes, during which it is electromagnetically stirred 2-3 times to ensure the homogenization of the alloy composition, thus obtaining the master alloy ingot.

[0017] 2) Atomization powder making: After the master alloy is remelted, it flows into the atomizing nozzle through the guide tube (inner diameter 4-6mm). A tightly coupled annular nozzle is used to perform gas atomization with high-purity argon gas (purity ≥99.999%) as the atomizing medium.

[0018] Key process parameters are: alloy melt holding temperature 1500-1600℃, superheat 150-200℃; atomization pressure 4.0-6.0 MPa, gas flow rate 30-50 m³ / h. 3 / h; the oxygen content in the atomizing tank is controlled at ≤50 ppm. Under the action of high-pressure argon jet, the alloy liquid is broken into fine droplets, which quickly solidify to form spherical or near-spherical powder particles.

[0019] 3) Sieving and classification: After atomization, the powder is collected by a cyclone separator and classified by an ultrasonic vibrating screen under argon protection. It passes through a 325-mesh (45μm) and a 500-mesh (30μm) standard sieve in sequence. Spherical powder with a particle size of 15-45μm is selected as HVOF spray powder, dried in vacuum at 120℃ for 2 hours, and then sieved for later use.

[0020] The gradient intermediate layer composite powder is a spherical powder of WC-10Co-4Cr and Cr3C2-25NiCr in a certain proportion, with a particle size of 15-45μm.

[0021] Specifically, the intermediate layer mixed powders are placed in a V-type mixer or a three-dimensional oscillating mixer for mechanical mixing for 30-60 minutes at a mixing speed of 20-30 r / min (to avoid excessive crushing of WC particles). After mixing, the powders are vacuum dried at 120℃ for 2 hours and then sieved for later use.

[0022] The surface-modified carbide powder is prepared by mixing WC-10Co-4Cr powder and nano-modified phase powder through planetary ball milling. The ball milling speed is 200-300 r / min, the ball milling time is 2-4 h, the ball-to-material ratio is 5:1-10:1, and the particle size of the composite powder is 10-45 μm.

[0023] In step three, the process parameters for HVOF spraying are as follows: High-entropy alloy bonding base layer: oxygen flow rate 800-900L / h, kerosene flow rate 18-22L / h, powder feeding rate 15-20g / min, spraying distance 180-220mm, spray gun moving speed 100-150mm / s, spraying angle 75-90°. Gradient carbide reinforced intermediate layer: oxygen flow rate 900-1000L / h, kerosene flow rate 20-24L / h, powder feed rate 12-18g / min, spraying distance 150-200mm, spray gun moving speed 120-180mm / s, spraying angle 60-90°, adjust the mixing ratio of WC-CoCr and Cr3C2-NiCr for each spraying pass to achieve a gradient distribution of components; Nano-modified carbide erosion-resistant surface coating: oxygen flow rate 950-1050L / h, kerosene flow rate 22-26L / h, powder feed rate 8-12g / min, spraying distance 120-180mm, spray gun moving speed 150-200mm / s, spraying angle 15-90°; for the narrow gap area of ​​15-20mm between blades, use a small angle spraying of 15-30°, and repeat the cross-spraying ≥4 times.

[0024] In step four, the two-stage low-temperature heat treatment process is as follows: First stage stress-relief annealing: Under an argon protective atmosphere, hold at 350-450℃ for 1-2 hours with a heating rate of 3-5℃ / min to eliminate residual tensile stress generated by supersonic spraying. The second stage of the structure stabilization treatment: Under an argon protective atmosphere, the temperature is maintained at 550-650℃ for 0.5-1h, with a heating rate of 2-3℃ / min. The temperature is then cooled to room temperature with the furnace to promote the uniform dispersion of the nano-modified phase, inhibit the coarsening of WC grains and the decomposition of carbides, and improve the fracture toughness and high-temperature stability of the coating.

[0025] The present invention relates to the application of the composite coating in the protection of turbine blades, wherein the turbine includes the moving and stationary blades of gas turbines, steam turbines, and flue gas turbines.

[0026] A turbine blade, wherein the surface of the blade is prepared with a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating of the present invention.

[0027] The purpose of this invention is to overcome the shortcomings of the prior art and provide a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades and its HVOF preparation method. The core innovations are as follows: 1. This invention constructs a fully gradient structure consisting of a "high-entropy alloy bonding underlayer - gradient carbide reinforced intermediate layer - nano-modified carbide erosion-resistant surface layer". The bottom layer uses a Ni-Co-Cr-Fe-Al high-entropy alloy, which has a high coefficient of thermal expansion that is highly matched with the thermal expansion coefficients of commonly used blade substrates such as FV520B, 17-4PH, and Inconel series. This allows for an ultra-high interfacial bonding strength of ≥85MPa. At the same time, the high-entropy alloy itself has excellent corrosion resistance and can form a dense corrosion barrier to prevent corrosive media from penetrating into the substrate, thus avoiding interfacial corrosion failure at the source. The middle layer uses a gradient composite system of WC-CoCr and Cr3C2-NiCr. WC-CoCr provides excellent wear resistance, while Cr3C2-NiCr has better high-temperature corrosion resistance and thermal shock resistance. Through the gradient transition of composition, the residual stress inside the coating is greatly relieved, preventing the coating from cracking and peeling. At the same time, the fatigue resistance of the coating is significantly improved, making it suitable for the service conditions of alternating loads on the blade. The top layer uses a nano-modified WC-CoCr coating as the core functional layer, providing top-level erosion resistance, wear resistance, and corrosion resistance.

[0028] Preferably, in the gradient carbide-reinforced intermediate layer, the linear gradient distribution of WC-CoCr and Cr3C2-NiCr not only achieves a progressive match in their coefficients of thermal expansion, but more importantly, Cr3C2-NiCr possesses higher fracture toughness and thermal shock resistance, while WC-CoCr exhibits higher hardness and wear resistance. This gradient design allows for a smooth transition in the toughness-hardness distribution of the coating from the substrate to the surface. The inner layer (the Cr3C2-NiCr-rich region) effectively absorbs external impact energy and inhibits crack initiation, while the outer layer (the WC-CoCr-rich region) provides excellent resistance to abrasive wear and erosion. The synergy between these two layers significantly extends the service life of the coating under alternating loads and erosion conditions. This gradient transition also avoids the drastic performance drop caused by the high-temperature oxidation of the Co binder phase in a single WC-CoCr coating, and the decrease in corrosion resistance caused by electrochemical incompatibility in the Ni60 / WC-10Co4Cr composite coating.

[0029] 2. This invention introduces TiC, NbC, and Y2O3 nano-modified phases into the surface layer. On the one hand, the nano-phases can act as heterogeneous nucleation cores during the spraying process, significantly refining the coating grains, reducing porosity, and improving the coating density and hardness. On the other hand, the dispersed distribution of nano-TiC and NbC can pin grain boundaries and inhibit the coarsening of WC grains at high temperatures. At the same time, Y2O3 can purify grain boundaries and inhibit the high-temperature oxidation and loss of the Co binder phase, greatly improving the high-temperature stability and corrosion resistance of the coating. In addition, the nano-modified phases can significantly improve the fracture toughness of the coating, solving the problem of high brittleness and easy collapse of traditional WC coatings under erosion conditions, achieving a synergistic improvement in coating hardness and toughness, and greatly optimizing erosion resistance.

[0030] Preferably, in the nano-modified carbide erosion-resistant surface layer, the composite addition of TiC, NbC, and Y2O3 produces the following unforeseen synergistic effects: (i) TiC (hardness approximately 3200 HV) and NbC (hardness approximately 2400 HV) act as heterogeneous nucleation cores during HVOF spraying, significantly refining WC grains to below 200 nm, while simultaneously pinning grain boundaries of different orientations, inhibiting abnormal growth of WC grains, and producing a dual grain refinement and strengthening effect; (ii) Y2O3 is enriched at grain boundaries and phase boundaries, reacting with impurity elements to purify grain boundaries, and simultaneously... (iii) TiC / NbC and Y2O3 form a “structure-chemical dual stabilization” network, which reduces the erosion rate of the coating at 400℃ high temperature erosion conditions by more than 45% compared with the traditional WC-CoCr coating. However, the performance of the existing Ni60 / WC-10Co4Cr composite coating in high temperature erosion has not been publicly reported, and its corrosion resistance decreases with the increase of WC content, which cannot meet the long-life protection requirements of turbine blades.

[0031] 3. For the narrow gap of 15-20mm between turbine blades, this invention optimizes a dedicated spraying system: it adopts a micro HVOF nozzle with a rod diameter of 10-12mm, which can penetrate deep into the blade gap; it designs a dedicated parameter matching system for small-angle spraying, which increases the flight speed and kinetic energy of the sprayed particles by increasing the flow rate of kerosene and oxygen, thus compensating for the kinetic energy loss in small-angle spraying; at the same time, it adopts a reciprocating cross-multi-pass spraying process, which can still produce a high-quality coating with porosity ≤0.25% and meeting the bonding strength requirements under small-angle spraying conditions of 15-30°, with a thickness uniformity deviation ≤10%, perfectly adapting to the on-site mobile spraying construction of the inner surface of the blade gap, and solving the core problem of performance degradation in small-angle spraying of traditional processes.

[0032] 4. This invention designs a two-stage low-temperature heat treatment process. The first stage is low-temperature stress-relief annealing, which eliminates the residual tensile stress generated by HVOF spraying at 350-450℃, completely avoiding the decomposition of WC carbides caused by high-temperature treatment. The second stage is microstructure stabilization treatment, which promotes the uniform dispersion of nano-modified phases under an argon protective atmosphere at 550-650℃, further refines the microstructure, improves the fracture toughness and fatigue resistance of the coating, and inhibits WC grain coarsening. This ensures the stability of the coating's performance during long-term high-temperature service, solving the industry pain point of carbide decomposition and performance degradation caused by traditional heat treatment processes.

[0033] Compared with the prior art, the present invention has the following beneficial effects: 1. Multiple Synergistic Effects of Gradient Structure: This invention achieves a gradual matching of the coefficient of thermal expansion (CTE) from the substrate to the surface layer through a linear gradient transition between WC-CoCr and Cr3C2-NiCr. This transforms the concentrated distribution of residual stress in sprayed coatings into a uniformly dispersed distribution, resulting in a bonding strength exceeding 85 MPa, which is 20-25% higher than that of traditional WC-CoCr coatings (typically 68-73 MPa). More importantly, the high toughness of Cr3C2-NiCr and the high hardness of WC-CoCr form a gradient transition in the thickness direction. The inner layer absorbs impact energy, while the outer layer resists wear, making the coating's anti-stripping ability under alternating loads and erosion conditions significantly superior to single-structure or simple double-layer structures.

[0034] 2. Unpredictable strengthening of nano-modified surface layer: The present invention adds TiC, NbC and Y2O3 nano-modified phases to WC-10Co-4Cr surface layer, which produces technical effects that cannot be achieved by existing single nano-phase modification: (1) The grain size of the coating is refined to ≤200nm, the porosity is ≤0.25%, and the microhardness reaches 1320-1420HV; (2) Y2O3 purifies the grain boundary and inhibits the high-temperature oxidation of Co binder phase, so that the coating has no red rust in 1000h in the neutral salt spray test, while the traditional WC-CoCr coating will show red rust in only 300h, and the corrosion resistance life is increased by more than 3 times; (3) The nano-modified phase deflects the crack propagation path and improves the fracture toughness, so that the high-temperature erosion rate at 400℃ is reduced by more than 45% compared with the traditional WC-CoCr coating.

[0035] This invention belongs to the field of metal surface protection and supersonic flame spraying technology. It discloses a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades and its HVOF preparation method. The aim is to address the industry pain points of existing turbine blade protective coatings, which struggle to simultaneously achieve wear resistance, corrosion resistance, and erosion resistance, and where on-site spraying in the narrow blade gaps often results in high coating porosity, insufficient adhesion, and performance degradation. This invention constructs a three-layer gradient structure: a high-entropy alloy bonding underlayer, a gradient carbide reinforced intermediate layer, and a nano-modified carbide erosion-resistant top layer. WC-CoCr is used as the core wear-resistant phase, combined with a Ni-Co-Cr-Fe-Al high-entropy alloy bonding phase and a TiC-NbC-Y2O3 nano-modified phase. By adapting the HVOF gradient spraying process to the narrow blade gaps and combining it with two-stage low-temperature stabilization heat treatment, precise control of coating internal stress and microstructure refinement are achieved. The coating prepared by this invention has a bonding strength of ≥85MPa, a porosity of ≤0.25%, a microhardness of ≥1300HV, and a high-temperature erosion rate of more than 45% lower than that of traditional WC-CoCr coatings at 400℃. It exhibits no red rust or blistering after 1000 hours of neutral salt spray testing. It is perfectly suited for on-site mobile spraying construction with narrow gaps of 15-20mm on turbine blades. The process is simple, facilitating mass production and on-site repair, and has broad application prospects in the field of protection for thermal power, gas turbine, and steam turbine blades. Attached Figure Description

[0036] Figure 1 This is a microscopic morphology diagram of the gradient structure cross-section of the coating of the present invention; Figure 2 The XRD comparison curves of the present invention and the comparative example are shown. Figure 3 The transmission electron microscope morphology and electron diffraction pattern of the nano-precipitated phase in the coating of the present invention are shown. Figure 4 This is a graph comparing the tribological and wear performance of the present invention with that of a conventional coating. Figure 5 The corrosion morphology of the present invention and the comparative example is shown in the neutral salt spray test. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0038] 1. For example Figure 1 As shown, the corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades in this embodiment has a total thickness of 300 μm, and consists of the following layers from the substrate to the surface: High-entropy alloy bonding substrate: 60μm thick, composed of a Ni-Co-Cr-Fe-Al pentagonal high-entropy alloy with atomic percentages of Al 12.0%, Cr 22.0%, Fe 23.0%, Co 21.0%, and Ni 22.0%; Gradient carbide-reinforced intermediate layer: 160 μm thick, WC-10Co-4Cr mass percentage linearly increased from 30% to 70%, Cr3C2-25NiCr mass percentage linearly decreased from 70% to 30%; Nano-modified carbide erosion resistant surface layer: 80μm thick, with WC-10Co-4Cr as the matrix phase and 4% by mass of nano-modified phase (TiC:NbC:Y2O3=2:2:1).

[0039] 2. Powder pretreatment: (1) High-entropy alloy binder powder: Spherical powder was prepared by gas atomization. 1) Material preparation and smelting: Weigh high-purity Ni, Co, Cr, Fe, and Al metal raw materials (purity ≥ 99.5%) according to the designed atomic percentage, place them in a vacuum induction melting furnace or a vacuum arc melting furnace, and evacuate to 1.0 × 10⁻⁶. -2 After Pa, high-purity argon gas (purity ≥99.999%) is introduced as a protective atmosphere, and the mixture is melted at 1550℃ for 45 minutes, during which it is electromagnetically stirred twice to ensure the homogenization of the alloy composition, thus obtaining the master alloy ingot.

[0040] 2) Atomization powder making: After the master alloy is remelted, it flows into the atomizing nozzle through the guide tube (inner diameter 5mm). A tightly coupled annular nozzle is used to perform gas atomization with high-purity argon gas (purity ≥99.999%) as the atomizing medium.

[0041] Key process parameters are: alloy melt holding temperature 1550℃, superheat 180℃; atomization pressure 5.0MPa, gas flow rate 40 m³ / s. 3 / h; the oxygen content in the atomizing tank is controlled at 50 ppm. Under the action of high-pressure argon jet, the alloy liquid is broken into fine droplets, which quickly solidify to form spherical or near-spherical powder particles.

[0042] 3) Sieving and grading: After atomization, the powder is collected by a cyclone separator and graded by an ultrasonic vibrating screen under argon protection. It passes through a 325-mesh (45μm) and a 500-mesh (30μm) standard sieve in sequence. Spherical powder with a particle size of 15-45μm is selected as HVOF spray powder, dried in vacuum at 120℃ for 2 hours, and then sieved for later use. (2) Gradient intermediate layer composite powder: Commercially available WC-10Co-4Cr (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) and Cr3C2-25NiCr spherical powder (Luoyang Jinlu GP25NC grade, particle size 15-45μm) are mechanically mixed according to the design ratio. The particle size is 15-45μm. In order to achieve a linear gradient transition of composition from the bonding substrate to the erosion resistant surface layer, a total of 4 different proportions of mixed powder are prepared (see Table 1 below), which correspond to the 4 spraying passes of the gradient intermediate layer (from the side closer to the bonding substrate to the side closer to the surface layer).

[0043] Table 1

[0044] The four powder mixtures were placed in a V-type mixer or a three-dimensional oscillating mixer for 45 minutes and 25 r / min (to avoid excessive breakage of WC particles). The mixed powders were then vacuum dried at 120℃ for 2 hours and sieved for later use.

[0045] (3) Surface-modified carbide powder: Commercially available WC-10Co-4Cr powder (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) was mixed with commercially available nano-TiC (particle size 30-50nm), NbC (particle size 30-50nm), and Y2O3 powder (particle size 20-40nm) by planetary ball milling. The total mass percentage of the nano-modified phase was 4%, and the mass ratio of TiC, NbC, and Y2O3 was TiC:NbC:Y2O3 = 2:2:1 (i.e., TiC 1.6%, NbC 1.6%, Y2O3 0.8%). The milling speed was 250r / min, the ball milling time was 3h, the ball-to-particle ratio was 8:1, the particle size of the composite powder was 10-30μm, and it was vacuum dried for later use.

[0046] 3. Matrix pretreatment: The turbine blade substrate is FV520B martensitic stainless steel. It is degreased by ultrasonic cleaning with acetone for 15 minutes, roughened by white corundum sandblasting at a pressure of 0.6MPa, and the surface roughness is controlled at Ra4.5μm. The cleanliness reaches Sa3 level. Before spraying, the surface dust is cleaned with dry compressed air.

[0047] 4. HVOF gradient spraying: A supersonic flame spraying system, equipped with a 12mm diameter micro-nozzle, is used to spray the following coatings sequentially: High-entropy alloy bonding base layer: oxygen flow rate 850L / h, kerosene flow rate 20L / h, powder feeding rate 18g / min, spraying distance 200mm, spray gun moving speed 120mm / s, spraying angle 85°; Gradient carbide reinforced intermediate layer: oxygen flow rate 950L / h, kerosene flow rate 22L / h, powder feed rate 15g / min, spraying distance 180mm, spray gun moving speed 150mm / s, spraying angle 75°, sprayed in 4 passes, adjusting the mixing ratio of WC-CoCr and Cr3C2-NiCr in each pass to achieve a gradient distribution of components. Nano-modified carbide erosion resistant surface layer: oxygen flow rate 1000L / h, kerosene flow rate 24L / h, powder feed rate 10g / min, spraying distance 150mm, spray gun moving speed 180mm / s; spraying angle of 80° for non-gap areas of the blades, and 20° small angle spraying for narrow gap areas of 15-20mm, with 6 passes of reciprocating cross spraying.

[0048] 5. Low-temperature stabilization heat treatment: First stage stress-relief annealing: under argon protective atmosphere, hold at 400℃ for 1.5h, heating rate 4℃ / min; The second stage of tissue stabilization treatment: under an argon protective atmosphere, it was held at 600℃ for 0.5h, with a heating rate of 2.5℃ / min, and then cooled to room temperature with the furnace.

[0049] 6. Performance test results: Mechanical properties: Coating bond strength 88MPa, microhardness 1420HV, porosity 0.22%; Wear resistance: In the ML-100 abrasive wear test, with a load of 10N and a wear time of 30min, the wear weight loss was 2.9mg, which is 56% lower than that of the traditional WC-10Co-4Cr coating; Erosion resistance: High-temperature erosion test at 400℃, erosion velocity 400m / s, erosion angle 30°, SiO2 particle size 50-100μm, erosion time 30min, erosion rate 1.1×10 -3 mg•g -1 It reduces emissions by 60% compared to the traditional WC-10Co-4Cr coating; Corrosion resistance: No red rust was observed after 1000 hours of neutral salt spray test with 3.5% NaCl, and the corrosion current density of the coating was reduced by an order of magnitude compared to traditional coatings.

[0050] like Figure 2The figure shows the XRD comparison curves of the coating of Example 1 and Comparative Example 4. As can be seen from the figure, in addition to the WC phase and a small amount of Co phase, the coating of Comparative Example 4 exhibits obvious diffraction peaks of decarburization oxidation products such as W2C, indicating that WC decomposes during the spraying and subsequent heat treatment processes (either without heat treatment or at high temperatures). In contrast, the coating of Example 1 only contains WC and a small amount of nano-TiC / NbC phase, with no harmful phases such as W2C detected. This indicates that the two-stage low-temperature stabilization heat treatment process (400℃ + 600℃) used in this invention effectively inhibits the decomposition and decarburization of WC carbides, maintaining the structural integrity of the hard phase of the coating. Furthermore, the introduction of Cr3C2 does not trigger harmful interfacial reactions. Therefore, it can be concluded that the low-temperature heat treatment process of this invention, compared to traditional high-temperature heat treatment or no heat treatment, can significantly inhibit the decomposition of WC, retain the high-hardness wear-resistant phase of the coating, and provide a structural basis for the excellent wear and erosion resistance of the coating.

[0051] like Figure 3 The image shows the transmission electron microscope (TEM) morphology and electron diffraction (EDD) pattern of the nano-precipitates within the coating of Example 1 of this invention. The morphology clearly shows that spherical or near-spherical nano-precipitates with a particle size of 20-50 nm are dispersed within the coating grains and at grain boundaries. Selected area electron diffraction (SED) patterns indicate that these nano-phases correspond to the crystal structures of TiC, NbC, and Y₂O₃, respectively. Further statistical analysis shows that the average grain size of the coating is ≤200 nm, much smaller than the micron-sized grains of traditional WC-CoCr coatings. Therefore, it can be concluded that nano-TiC and NbC act as heterogeneous nucleation sites during HVOF spraying, effectively refining the coating grains and producing a dual grain refinement effect; simultaneously, Y₂O₃ is enriched at grain boundaries, pinning the grain boundaries and inhibiting grain growth. This in-situ dispersed distribution of nano-precipitates is the root cause of the high hardness (≥1320 HV), low porosity (≤0.25%), and high fracture toughness microstructure of the coating of this invention.

[0052] like Figure 4The figure shows a comparison of the tribological properties of the coating of Example 1 of this invention with those of the conventional WC-10Co-4Cr coating (Comparative Example 1) and the Ni60 / 60%WC-10Co4Cr composite coating (Comparative Example 2). The friction coefficient-time curves show that: in the initial stage of wear (0-5 min), the friction coefficient of the coating of Comparative Example 1 rapidly increased to approximately 0.65, followed by drastic fluctuations, indicating severe abrasive wear and localized spalling on the coating surface; the friction coefficient of the coating of Comparative Example 2 remained stable between 0.55 and 0.60, but showed a slow increase in the later stages of wear; while the friction coefficient of the coating of Example 1 quickly stabilized between 0.45 and 0.50 after the initial running-in period, exhibiting the smallest fluctuation range throughout. The wear volume loss histogram shows that the wear weight loss of Example 1 (2.9 mg) was reduced by 56% compared to Comparative Example 1 (6.7 mg) and by 42% compared to Comparative Example 2 (5.0 mg). Therefore, it can be concluded that the gradient structure and nano-modified surface layer of the present invention have a synergistic effect. On the one hand, the Cr3C2-NiCr enriched region in the gradient intermediate layer can effectively absorb impact energy and inhibit crack initiation. On the other hand, the dispersion strengthening and grain boundary purification effect of nano-TiC / NbC / Y2O3 significantly reduces the friction coefficient and wear rate, making the wear resistance of the coating significantly better than that of traditional coatings and Ni60 composite coatings.

[0053] like Figure 5 The figure shows a comparison of the corrosion morphology of Examples 1-3 and Comparative Examples 1-4 under neutral salt spray test (3.5% NaCl, 1000h). It is clear from the figure that: the coating of Comparative Example 1 showed red rust after 400h, and the surface was covered with rust spots and blistering after 1000h; the coating of Comparative Example 2 (Ni60 / 60%WC-10Co4Cr) showed pitting corrosion after 500h, the corrosion area expanded after 800h, and the coating partially peeled off after 1000h, indicating that the electrochemical incompatibility between Ni60 and WC-10Co4Cr led to severe galvanic corrosion; the coating of Comparative Example 4 (high-temperature heat treatment at 800℃) showed red rust after 100h, and the coating peeled off over a large area after 1000h; while the coatings of Examples 1, 2, and 3 showed no red rust or blistering after 1000h, only slight uniform discoloration. Therefore, it can be concluded that the high-entropy alloy bonding underlayer (Ni-Co-Cr-Fe-Al) of the present invention has excellent corrosion resistance and can form a dense corrosion barrier to prevent Cl from forming. - It penetrates into the substrate; at the same time, the Y2O3 nanophase in the surface layer purifies the grain boundaries and inhibits the preferential corrosion of the Co binder phase, and the high corrosion resistance of Cr3C2-NiCr in the gradient intermediate layer, together achieve a significant improvement in the overall corrosion resistance life of the coating. No red rust was found after 1000 hours of neutral salt spray test, while the comparative example failed after only 400 hours, with the corrosion resistance life increased by more than 2.5 times.

[0054] Example 2

[0055] The only difference between this embodiment and Embodiment 1 is that: The total coating thickness is 300μm, including a 50μm high-entropy alloy bonding underlayer, a 200μm gradient carbide reinforced intermediate layer, and a 50μm nano-modified carbide erosion resistant top layer. The total mass percentage of the surface layer nano-modified phase is 2%, and the mass ratio of TiC to NbC is 1:0.5; In the spraying process, narrow gap areas are sprayed at a small angle of 30°, and four passes of cross-spraying are applied. Heat treatment process: First stage: 350℃ for 2 hours, second stage: 550℃ for 1 hour.

[0056] Performance test results: The coating exhibits a bonding strength of 86 MPa, a microhardness of 1380 HV, a porosity of 0.25%, an abrasive wear loss of 3.2 mg, and a high-temperature erosion rate of 1.2 × 10⁻⁶ at 400℃. -3 mg•g -1 No red rust was observed after 1000 hours of neutral salt spray testing.

[0057] Example 3

[0058] The only difference between this embodiment and Embodiment 1 is that: The total coating thickness is 300μm, including a 50μm high-entropy alloy bonding underlayer, a 200μm gradient carbide reinforced intermediate layer, and a 50μm nano-modified carbide erosion resistant top layer. The total mass percentage of the surface layer nano-modified phase is 8%, and the mass ratio of TiC to NbC is 1:2. In the spraying process, narrow gap areas are sprayed at a small angle of 15°, and eight passes of cross-spraying are applied. Heat treatment process: First stage: 450℃ for 1 hour, second stage: 650℃ for 0.5 hours.

[0059] Performance test results: The coating exhibits a bonding strength of 85 MPa, a microhardness of 1320 HV, a porosity of 0.23%, an abrasive wear loss of 3.8 mg, and a high-temperature erosion rate of 1.4 × 10⁻⁶ at 400℃. -3 mg•g -1 No red rust was observed after 1000 hours of neutral salt spray testing.

[0060] Comparative Example 1

[0061] This comparative example uses a traditional single WC-10Co-4Cr HVOF spray coating with the same total thickness as in Example 1. The same spraying process as in Example 1 was used, and no heat treatment was performed.

[0062] Performance test results: The coating exhibits a bonding strength of 62 MPa, a microhardness of 1100 HV, a porosity of 0.85%, an abrasive wear loss of 6.7 mg, and a high-temperature erosion rate of 2.8 × 10⁻⁶ at 400℃. -3 mg•g -1 Red rust appeared after 400 hours of neutral salt spray testing.

[0063] Comparative Example 2

[0064] The only difference between this comparative example and Example 1 is that the gradient carbide-reinforced intermediate layer of Example 1 is replaced with a single Ni60 / 60%WC-10Co-4Cr composite coating (the coating powder consists of 40wt% Ni60 and 60wt% WC-10Co-4Cr, both with a particle size of 15-45μm. The mixed powders are placed in a V-type mixer or a three-dimensional oscillating mixer for 45 min of mechanical mixing at a speed of 25 r / min. After mixing, the powders are vacuum dried at 120℃ for 2 h and then sieved for later use). The total thickness is the same as in Example 1, and the same spraying process as in Example 1 is used.

[0065] Performance test results: The coating exhibits a bonding strength of 65 MPa, a microhardness of 1250 HV, a porosity of 0.72%, an abrasive wear loss of 5.0 mg, and a high-temperature erosion rate of 2.2 × 10⁻⁶ at 400℃. -3 mg•g -1 .

[0066] Comparative Example 3

[0067] The only difference between this comparative example and Example 1 is that: after spraying, no two-stage low-temperature stabilization heat treatment was performed, but only a single-stage low-temperature heat treatment was performed, specifically: stress-relief annealing: under an argon protective atmosphere, the temperature was held at 400°C for 2 hours, with a heating rate of 4°C / min; and then cooled to room temperature in the furnace.

[0068] Performance test results: The coating exhibits a residual tensile stress as high as 280 MPa, making it prone to cracking. Abrasive wear results in a weight loss of 5.5 mg and an erosion rate of 3.1 × 10⁻⁶. - 3 mg•g -1 It has poor stability during long-term service.

[0069] Comparative Example 4

[0070] The only difference between this comparative example and Example 1 is that a high-temperature heat treatment of 800℃ is used instead of the two-stage low-temperature heat treatment of the present invention. Specifically, the stress-relief annealing is carried out at 800℃ for 1 hour under an argon protective atmosphere, with a heating rate of 4℃ / min; and then cooled to room temperature in the furnace.

[0071] Performance test results: The WC carbides underwent significant decomposition, generating a large amount of brittle W2C phase. The coating microhardness decreased to 850 HV, the abrasive wear loss was 8.2 mg, the erosion performance deteriorated significantly, and red rust appeared after 100 hours of neutral salt spray testing.

[0072] As can be seen from the above embodiments and comparative examples, the present invention achieves a synergistic improvement in the corrosion resistance, wear resistance, and erosion resistance of the coating through gradient structure design, optimization of nano-modified phases, innovation of narrow gap spraying process, and matching of low temperature heat treatment process. At the same time, it is perfectly adapted to the on-site spraying construction of turbine blades with narrow gaps. Compared with the existing technology, it has significant innovation and outstanding technical advantages.

[0073] The coating properties of the above embodiments and comparative examples are shown in Table 2 below.

[0074] Table 2 Coating performance test results

[0075] Example 4 The corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades in this embodiment has a total thickness of 500 μm, and consists of the following layers from the substrate to the surface: High-entropy alloy bonding substrate: 100μm thick, composed of a Ni-Co-Cr-Fe-Al pentagonal high-entropy alloy with atomic percentages of Al 10.0%, Cr 23.0%, Fe 24.0%, Co 20.0%, and Ni 23.0%; Gradient carbide-reinforced intermediate layer: 300 μm thick, WC-10Co-4Cr mass percentage linearly increased from 30% to 70%, Cr3C2-25NiCr mass percentage linearly decreased from 70% to 30%; Nano-modified carbide erosion resistant surface layer: 100μm thick, with WC-10Co-4Cr as the matrix phase and 4% by mass of nano-modified phase (TiC:NbC:Y2O3=2:2:1).

[0076] 2. Powder pretreatment: (1) High-entropy alloy binder powder: Spherical powder was prepared by gas atomization. 1) Material preparation and smelting: Weigh high-purity Ni, Co, Cr, Fe, and Al metal raw materials (purity ≥ 99.5%) according to the designed atomic percentage, place them in a vacuum induction melting furnace or a vacuum arc melting furnace, and evacuate to 0.5 × 10⁻⁶. -2 After Pa, high-purity argon gas (purity ≥99.999%) is introduced as a protective atmosphere, and the mixture is melted at 1500℃ for 30 minutes, during which it is electromagnetically stirred 3 times to ensure the homogenization of the alloy composition, thus obtaining the master alloy ingot.

[0077] 2) Atomization powder making: After the master alloy is remelted, it flows into the atomizing nozzle through the guide tube (inner diameter 4mm). A tightly coupled annular nozzle is used to perform gas atomization with high-purity argon gas (purity ≥99.999%) as the atomizing medium.

[0078] Key process parameters are: alloy melt holding temperature 1500℃, superheat 150℃; atomization pressure 4.0MPa, gas flow rate 30m³ / h. 3 / h; the oxygen content in the atomizing tank is controlled at 40 ppm. Under the action of high-pressure argon jet, the alloy liquid is broken into fine droplets, which quickly solidify to form spherical or near-spherical powder particles.

[0079] 3) Sieving and grading: After atomization, the powder is collected by a cyclone separator and graded by an ultrasonic vibrating screen under argon protection. It passes through a 325-mesh (45μm) and a 500-mesh (30μm) standard sieve in sequence. Spherical powder with a particle size of 15-45μm is selected as HVOF spray powder, dried in vacuum at 120℃ for 2 hours, and then sieved for later use. (2) Gradient intermediate layer composite powder: Commercially available WC-10Co-4Cr (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) and Cr3C2-25NiCr spherical powder (Luoyang Jinlu GP25NC grade, particle size 15-45μm) are mechanically mixed according to the design ratio. The particle size is 15-45μm. In order to achieve a linear gradient transition of composition from the bonding substrate to the erosion resistant surface layer, a total of 4 mixed powders with different proportions are prepared (same as Example 1), which correspond to the 4 spraying passes of the gradient intermediate layer (from the side closer to the bonding substrate to the side closer to the surface layer).

[0080] The mixed powders were placed in a V-type mixer or a three-dimensional oscillating mixer for 30 minutes and 20 r / min (to avoid excessive crushing of WC particles). The mixed powders were then vacuum dried at 120℃ for 2 hours and sieved for later use.

[0081] (3) Surface-modified carbide powder: Commercially available WC-10Co-4Cr powder (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) was mixed with commercially available nano-TiC (particle size 30-50nm), NbC (particle size 30-50nm), and Y2O3 powder (particle size 20-40nm) by planetary ball milling. The total mass percentage of the nano-modified phase was 4%, and the mass ratio of TiC, NbC, and Y2O3 was TiC:NbC:Y2O3 = 2:2:1 (i.e., TiC 1.6%, NbC 1.6%, Y2O3 0.8%). The milling speed was 200r / min, the ball milling time was 4h, the ball-to-particle ratio was 5:1, the particle size of the composite powder was 10-45μm, and it was vacuum dried for later use.

[0082] 3. Matrix pretreatment: The turbine blade substrate is FV520B martensitic stainless steel. It is degreased by ultrasonic cleaning with acetone for 15 minutes, roughened by sandblasting with white corundum at a pressure of 0.5MPa, and the surface roughness is controlled at Ra3.0μm. The cleanliness reaches Sa2.5 level. Before spraying, the surface dust is cleaned with dry compressed air.

[0083] 4. HVOF gradient spraying: A supersonic flame spraying system, equipped with a 10mm diameter micro-nozzle, is used to spray the following coatings sequentially: High-entropy alloy bonding base layer: oxygen flow rate 800L / h, kerosene flow rate 18L / h, powder feeding rate 15g / min, spraying distance 180mm, spray gun moving speed 100mm / s, spraying angle 75°; Gradient carbide reinforced intermediate layer: oxygen flow rate 900L / h, kerosene flow rate 20L / h, powder feed rate 12g / min, spraying distance 150mm, spray gun moving speed 120mm / s, spraying angle 60°, sprayed in 4 passes, with the mixing ratio of WC-CoCr and Cr3C2-NiCr adjusted in each pass to achieve a gradient distribution of components. Nano-modified carbide erosion resistant surface layer: oxygen flow rate 950L / h, kerosene flow rate 22L / h, powder feed rate 8g / min, spraying distance 120mm, spray gun moving speed 150mm / s; spraying angle of 90° for non-gap areas of the blades, and 25° small angle spraying for narrow gap areas of 15-20mm, with 6 passes of reciprocating cross spraying.

[0084] 5. Low-temperature stabilization heat treatment: First stage stress-relief annealing: under argon protective atmosphere, hold at 400℃ for 1.5h, heating rate 3℃ / min; The second stage of tissue stabilization treatment: under an argon protective atmosphere, hold at 600℃ for 0.5h, with a heating rate of 2℃ / min, and then cool to room temperature with the furnace.

[0085] This embodiment describes the application of composite coatings in the protection of turbine blades, where the turbine includes the moving and stationary blades of gas turbines, steam turbines, and flue gas turbines.

[0086] A turbine blade, wherein the surface of the blade is prepared with a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating according to this embodiment.

[0087] Example 5

[0088] The corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating for turbine blades in this embodiment has a total thickness of 250 μm, and its structure from the substrate to the surface is as follows: High-entropy alloy bonding substrate: 50μm thick, composed of a Ni-Co-Cr-Fe-Al pentagonal high-entropy alloy with atomic percentages of Al 13.0%, Cr 20.0%, Fe 22.0%, Co 22.0%, and Ni 23.0%; Gradient carbide-reinforced intermediate layer: 150 μm thick, WC-10Co-4Cr mass percentage linearly increased from 30% to 70%, Cr3C2-25NiCr mass percentage linearly decreased from 70% to 30%; Nano-modified carbide erosion resistant surface layer: 50μm thick, with WC-10Co-4Cr as the matrix phase and 4% by mass of nano-modified phase (TiC:NbC:Y2O3=2:2:1).

[0089] 2. Powder pretreatment: (1) High-entropy alloy binder powder: Spherical powder was prepared by gas atomization. 1) Material preparation and smelting: Weigh high-purity Ni, Co, Cr, Fe, and Al metal raw materials (purity ≥ 99.5%) according to the designed atomic percentage, place them in a vacuum induction melting furnace or a vacuum arc melting furnace, and evacuate to 0.8 × 10⁻⁶. -2 After Pa, high-purity argon gas (purity ≥99.999%) is introduced as a protective atmosphere, and the mixture is melted at 1650℃ for 60 minutes, during which it is electromagnetically stirred 3 times to ensure the homogenization of the alloy composition, thus obtaining the master alloy ingot.

[0090] 2) Atomization powder making: After the master alloy is remelted, it flows into the atomizing nozzle through the guide tube (6mm inner diameter). A tightly coupled annular nozzle is used to perform gas atomization with high-purity argon gas (purity ≥99.999%) as the atomizing medium.

[0091] Key process parameters are: alloy melt holding temperature 1600℃, superheat 200℃; atomization pressure 6.0MPa, gas flow rate 50m³ / h. 3 / h; the oxygen content in the atomizing tank is controlled at 30 ppm. Under the action of high-pressure argon jet, the alloy liquid is broken into fine droplets, which quickly solidify to form spherical or near-spherical powder particles.

[0092] 3) Sieving and grading: After atomization, the powder is collected by a cyclone separator and graded by an ultrasonic vibrating screen under argon protection. It passes through a 325-mesh (45μm) and a 500-mesh (30μm) standard sieve in sequence. Spherical powder with a particle size of 15-45μm is selected as HVOF spray powder, dried in vacuum at 120℃ for 2 hours, and then sieved for later use. (2) Gradient intermediate layer composite powder: Commercially available WC-10Co-4Cr (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) and Cr3C2-25NiCr spherical powder (Luoyang Jinlu GP25NC grade, particle size 15-45μm) are mechanically mixed according to the design ratio. The particle size is 15-45μm. In order to achieve a linear gradient transition of composition from the bonding substrate to the erosion resistant surface layer, a total of 4 mixed powders with different proportions are prepared (same as Example 1), which correspond to the 4 spraying passes of the gradient intermediate layer (from the side closer to the bonding substrate to the side closer to the surface layer).

[0093] The mixed powders were placed in a V-type mixer or a three-dimensional oscillating mixer for 60 minutes and 30 r / min (to avoid excessive crushing of WC particles). The mixed powders were then vacuum dried at 120℃ for 2 hours and sieved for later use.

[0094] (3) Surface-modified carbide powder: Commercially available WC-10Co-4Cr powder (Luoyang Jinlu GP10C-4 grade, particle size 15-45μm) was mixed with commercially available nano-TiC (particle size 30-50nm), NbC (particle size 30-50nm), and Y2O3 powder (particle size 20-40nm) by planetary ball milling. The total mass percentage of the nano-modified phase was 4%, and the mass ratio of TiC, NbC, and Y2O3 was TiC:NbC:Y2O3 = 2:2:1 (i.e., TiC 1.6%, NbC 1.6%, Y2O3 0.8%). The milling speed was 300r / min, the ball milling time was 2h, the ball-to-particle ratio was 10:1, the particle size of the composite powder was 10-45μm, and it was vacuum dried for later use.

[0095] 3. Matrix pretreatment: The turbine blade substrate is FV520B martensitic stainless steel. It is degreased by ultrasonic cleaning with acetone for 20 minutes, roughened by white corundum sandblasting at a pressure of 0.7MPa, and the surface roughness is controlled at Ra6.0μm. The cleanliness reaches Sa3.5 level. Before spraying, the surface dust is cleaned with dry compressed air.

[0096] 4. HVOF gradient spraying: A supersonic flame spraying system, equipped with an 11mm diameter micro-nozzle, is used to spray the following coatings sequentially: High-entropy alloy bonding base layer: oxygen flow rate 900L / h, kerosene flow rate 22L / h, powder feeding rate 20g / min, spraying distance 220mm, spray gun moving speed 150mm / s, spraying angle 90°; Gradient carbide reinforced intermediate layer: oxygen flow rate 1000L / h, kerosene flow rate 24L / h, powder feed rate 18g / min, spraying distance 200mm, spray gun moving speed 180mm / s, spraying angle 90°, sprayed in 4 passes, with the mixing ratio of WC-CoCr and Cr3C2-NiCr adjusted in each pass to achieve a gradient distribution of components; Nano-modified carbide erosion resistant surface layer: oxygen flow rate 1050L / h, kerosene flow rate 26L / h, powder feed rate 12g / min, spraying distance 180mm, spray gun moving speed 200mm / s; spraying angle of 80° for non-gap areas of the blades, and 15° small angle spraying for narrow gap areas of 15-20mm, with 6 passes of reciprocating cross spraying.

[0097] 5. Low-temperature stabilization heat treatment: First stage stress-relief annealing: under argon protective atmosphere, hold at 400℃ for 1.5h, heating rate 5℃ / min; The second stage of tissue stabilization treatment: under an argon protective atmosphere, the temperature was held at 600℃ for 0.5h, with a heating rate of 3℃ / min, and then cooled to room temperature with the furnace.

[0098] This embodiment describes the application of composite coatings in the protection of turbine blades, where the turbine includes the moving and stationary blades of gas turbines, steam turbines, and flue gas turbines.

[0099] A turbine blade, wherein the surface of the blade is prepared with a corrosion-resistant, wear-resistant, and erosion-resistant gradient carbide composite coating according to this embodiment.

[0100] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment or in its description in the foregoing description of exemplary embodiments of the invention. However, this method of disclosure should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0101] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0102] 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 wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades, characterized in that, The coating has a three-layer gradient structure, consisting of a high-entropy alloy bonding underlayer, a gradient carbide reinforced intermediate layer, and a nano-modified carbide erosion-resistant top layer, from the substrate to the surface. The high-entropy alloy bonding layer is a Ni-Co-Cr-Fe-Al pentagonal high-entropy alloy, comprising, by atomic percentage: Al 10.0%-13.0%, Cr 20.0%-23.0%, Fe 22.0%-24.0%, Co 20.0%-22.0%, and Ni 22.0%-23.0%. The gradient carbide-reinforced intermediate layer is a gradient composite system of WC-CoCr and Cr3C2-NiCr. Along the coating thickness direction, from the high-entropy alloy bonding underlayer to the nano-modified carbide erosion-resistant top layer, the mass proportion of WC-CoCr linearly increases from 30% to 70%, while the mass proportion of Cr3C2-NiCr linearly decreases from 70% to 30%. The nano-modified carbide erosion-resistant surface layer uses WC-10Co-4Cr as the matrix phase and adds nano-modified phases, including at least two of TiC, NbC, and Y2O3, with the total mass percentage of the nano-modified phases being 2.0%-8.0%. The high-entropy alloy bonding underlayer has a thickness of 50-100μm, the gradient carbide reinforced intermediate layer has a thickness of 150-300μm, the nano-modified carbide erosion resistant top layer has a thickness of 50-100μm, and the total coating thickness is 250-500μm.

2. The wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades according to claim 1, characterized in that, The nano-modified carbide erosion-resistant surface layer contains in-situ dispersed nano-precipitates with a particle size of 20-50 nm. The nano-precipitates include at least two of TiC, NbC, and Y2O3. The nano-precipitates pin grain boundaries and refine the coating grains, and the average grain size of the coating is ≤200 nm.

3. The wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades according to claim 1, characterized in that, The coating exhibits a bonding strength ≥85MPa, microhardness ≥1320HV, porosity ≤0.25%, abrasive wear weight loss of 2.9-3.8mg, salt spray corrosion weight loss of 0.12-0.20mg, and high-temperature erosion rate at 400℃ of 1.1-1.4×10⁻⁶. -3 mg•g -1 No red rust was observed after 1000 hours of neutral salt spray testing.

4. The wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades according to claim 1, characterized in that, The gradient carbide-reinforced intermediate layer is applied in four coats, sequentially from the side closest to the high-entropy alloy bonding underlayer to the side closest to the nano-modified carbide erosion-resistant toplayer: Pass 1: The mass ratio of WC-CoCr to Cr3C2-NiCr is 30:70; Pass 2: The mass ratio of WC-CoCr to Cr3C2-NiCr is 43:57; Pass 3: The mass ratio of WC-CoCr to Cr3C2-NiCr is 57:43; Pass 4: The mass ratio of WC-CoCr to Cr3C2-NiCr is 70:

30.

5. A method for preparing a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1, Powder Pretreatment: High-entropy alloy binder powder, gradient intermediate layer composite powder, and surface modified carbide powder are prepared separately, and then vacuum dried and sieved for later use. Step 2, Substrate Pretreatment: The turbine blade substrate is subjected to surface degreasing and sandblasting roughening treatment, with the surface roughness controlled at Ra3.0-6.0μm and the cleanliness reaching Sa2.5 level or above; Step 3, HVOF gradient spraying: Using a supersonic flame spraying system, paired with a micro nozzle with a rod diameter of 10-12mm, the high entropy alloy bonding base layer, gradient carbide reinforced intermediate layer, and nano-modified carbide erosion resistant top layer are sprayed sequentially. Step 4, Low-temperature stabilization heat treatment: The sprayed blades undergo two stages of low-temperature heat treatment.

6. The preparation method according to claim 5, characterized in that, In step one, the high-entropy alloy binder powder is prepared by gas atomization and is spherical powder with a particle size of 15-45μm; The gradient intermediate layer composite powder is a spherical powder of WC-10Co-4Cr and Cr3C2-25NiCr in a certain proportion, with a particle size of 15-45μm; The surface-modified carbide powder was prepared by mixing WC-10Co-4Cr powder and nano-modified phase powder through planetary ball milling. The ball milling speed was 200-300 r / min, the ball milling time was 2-4 h, the ball-to-material ratio was 5:1-10:1, and the particle size of the composite powder was 10-45 μm.

7. The preparation method according to claim 5, characterized in that, In step three, the process parameters for HVOF gradient spraying are as follows: High-entropy alloy bonding base layer: oxygen flow rate 800-900L / h, kerosene flow rate 18-22L / h, powder feeding rate 15-20g / min, spraying distance 180-220mm, spray gun moving speed 100-150mm / s, spraying angle 75-90°. Gradient carbide reinforced intermediate layer: oxygen flow rate 900-1000L / h, kerosene flow rate 20-24L / h, powder feed rate 12-18g / min, spraying distance 150-200mm, spray gun moving speed 120-180mm / s, spraying angle 60-90°, adjust the mixing ratio of WC-CoCr and Cr3C2-NiCr for each spraying pass to achieve a gradient distribution of components; Nano-modified carbide erosion-resistant surface coating: oxygen flow rate 950-1050L / h, kerosene flow rate 22-26L / h, powder feed rate 8-12g / min, spraying distance 120-180mm, spray gun moving speed 150-200mm / s, spraying angle 15-90°; for the narrow gap area of ​​15-20mm between blades, use a small angle spraying of 15-30°, and repeat the cross-spraying ≥4 times.

8. The preparation method according to claim 5, characterized in that, In step four, the two-stage low-temperature heat treatment process is as follows: First stage stress-relief annealing: Under an argon protective atmosphere, hold at 350-450℃ for 1-2 hours, with a heating rate of 3-5℃ / min; The second stage of tissue stabilization treatment: under an argon protective atmosphere, hold at 550-650℃ for 0.5-1h, with a heating rate of 2-3℃ / min, and then cool to room temperature with the furnace.

9. The application of a wear-resistant and corrosion-resistant gradient carbide composite coating for turbine blades according to any one of claims 1-4 in the protection of turbine machinery blades, characterized in that, Turbine blades include the moving blades and stationary blades of gas turbines, steam turbines, and flue gas turbines.

10. A turbine blade, characterized in that, The blade surface is prepared with a wear-resistant and corrosion-resistant gradient carbide composite coating as described in claims 1-4.

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