Metallurgical bonding protective layer for power plant fluid machinery and method for manufacturing the same

Abstract

The application discloses a metallurgical bonding protective layer for power station fluid machinery and a preparation method thereof, and belongs to the technical field of surface protection of power station environmental protection equipment. The protective layer is a double-layer structure formed on the surface of a base body, comprising an alloy inner layer of NiCrAlY-rare earth element and a composite outer layer of NiCr-WC-rare earth oxide, and the interfaces between the inner layer and the base body and between the inner layer and the outer layer are metallurgical bonding interfaces. The mass ratio of Al to Y in the inner layer is 5-16, and the mass ratio of WC to rare earth oxide in the outer layer is 25-80. The preparation method comprises the following steps: base body pretreatment, ultrasonic speed flame spraying to prepare the inner layer and the outer layer in sequence, high-frequency induction remelting treatment, and cooling. Through the synergistic control of component design and induction remelting process, the bonding strength of the protective layer reaches more than 88 MPa, the porosity is reduced to less than 0.5%, and the wear resistance and thermal shock performance are significantly improved, so that the protective layer can be widely applied to desulfurization systems and related corrosion fluid conveying equipment containing solid phase particles.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering technology, specifically relating to a metallurgical bonded protective layer for power plant fluid machinery and its preparation method. Background Technology

[0002] Desulfurization systems in coal-fired power plants are key environmental protection facilities for achieving sulfur dioxide emission standards. Taking wet desulfurization as an example, its core equipment includes an absorption tower, slurry circulation pump, agitator, flue gas heat exchanger, demister, and flue system. The fluid mechanical components in these devices, such as the slurry circulation pump impeller, agitator blades, nozzles, baffles, and fan impellers, operate for extended periods in corrosive media containing solid particles. These media typically contain gypsum slurry, unreacted limestone particles, chlorides, fluorides, and sulfites, with a pH value fluctuating between 4 and 7, and operating temperatures ranging from 50℃ to 200℃ depending on the location.

[0003] Under the aforementioned operating conditions, the component surfaces simultaneously experience two types of damage: abrasive wear caused by high-speed scouring of slurry particles and electrochemical corrosion from acidic media or oxidative corrosion from high-temperature flue gas. The interaction between corrosion and wear causes the actual failure rate of the components to be higher than that of a single damage mechanism. Operational data shows that, without protection, the impeller of the desulfurization slurry circulation pump experiences wall thinning after a certain period of operation, with pitting and perforation forming at the blade edges. This problem is not limited to desulfurization systems; similar corrosive slurry scouring conditions exist in other fluid transport equipment in power plants, including coal slurry pumps in coal conveying systems, ash slurry pumps in ash removal systems, circulating pumps in cooling water systems, and slurry transport equipment in the chemical and metallurgical fields.

[0004] Existing surface protection technologies mainly include organic coatings, rubber linings, metal overlays, and thermal spraying. Organic coatings are prone to aging and becoming brittle at high temperatures, and corrosive media can penetrate the substrate after breakage. Rubber linings have insufficient bonding strength, are prone to edge warping, and require replacement after wear. Although metal overlays have high bonding strength, they have high heat input, making thin-walled workpieces prone to deformation and complex surfaces difficult to cover evenly. Thermal spray coatings are mainly mechanically bonded, with a bonding strength of only 30-40 MPa and a porosity as high as 5%-15%, which easily leads to interfacial corrosion and blistering. To improve coating density and bonding, researchers have developed post-spraying remelting technology: in-furnace remelting has high energy consumption and cannot handle large components; laser remelting has a large temperature gradient in the heat-affected zone, making thin-walled workpieces prone to deformation and hindering equipment movement; induction remelting heating is controllable and suitable for on-site applications, but existing research mostly focuses on single material systems and lacks synergistic optimization of dual-layer functionally graded coatings and induction remelting processes for corrosion-wear conditions. In summary, existing technologies still face technical bottlenecks in terms of bonding strength, coating density, construction efficiency, and adaptability to large components, leading to frequent failures of desulfurization equipment due to corrosion and wear. Summary of the Invention

[0005] The purpose of this invention is to provide a metallurgically bonded protective layer for power plant fluid machinery and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A metallurgically bonded protective layer for power plant fluid machinery, wherein the protective layer is a double-layer structure formed on the surface of a substrate, consisting of an inner layer and an outer layer: The inner layer is a metallurgical bonding transition layer, and its composition and mass percentage are: Cr: 18%-25%, Al: 6%-10%, Y: 0.3%-1.8%, rare earth elements: 0.1%-0.6%, and the balance is Ni; The outer layer is a wear-resistant and corrosion-resistant functional layer, and its composition and mass percentage are: WC particles: 30%-50%, rare earth oxides: 0.3%-2.0%, and the balance is NiCr alloy; The inner layer and the substrate, as well as the inner layer and the outer layer, are metallurgical bonding interfaces. The bonding strength of the protective layer is ≥70MPa.

[0007] Furthermore, the mass ratio of Al to Y in the inner layer is 5-16.

[0008] Furthermore, the inner layer contains 7%-9% Al by mass and 0.6%-1.2% Y by mass.

[0009] Furthermore, the mass ratio of WC particles to rare earth oxides in the outer layer is 25-80.

[0010] Furthermore, the WC particles in the outer layer are composed of a mixture of micron-sized WC and nano-sized WC, wherein the nano-sized WC accounts for 5%-15% of the total mass of the WC particles.

[0011] Furthermore, the mass percentage of Cr in the NiCr alloy in the outer layer is 18%-22%.

[0012] Furthermore, the rare earth oxide is at least one of CeO2 or La2O3, and its average particle size is 30nm-80nm.

[0013] Furthermore, the thickness of the inner layer is 50μm-150μm, and the thickness of the outer layer is 200μm-400μm.

[0014] Furthermore, the rare earth element in the inner layer is at least one of Ce or La.

[0015] Furthermore, the mass percentage of rare earth oxides in the outer layer within the functional layer is 0.8%-1.2%.

[0016] This invention also provides a method for preparing a metallurgically bonded protective layer for power plant fluid machinery, comprising the following steps: Step 1: Degrease, remove rust, and sandblast roughen the substrate surface to achieve a surface roughness of Ra5μm-8μm; Step 2: Using a supersonic flame spraying process, NiCrAlY rare earth element alloy powder is sprayed onto the pretreated substrate surface to form an inner layer with a thickness of 50μm-150μm. Step 3: Using a supersonic flame spraying process, NiCr-WC-rare earth oxide composite powder is sprayed onto the inner layer surface to form an outer layer with a thickness of 200μm-400μm, resulting in a double-layer pre-coated layer. Step 4: Perform high-frequency induction remelting on the double-layer pre-coated layer, setting the power frequency to 8kHz-25kHz, the anode current to 1.8A-3.2A, and the scanning speed to 3mm / s-6mm / s; by controlling the heat input, the coating heating temperature is made to reach and controlled at 750℃-900℃. Step 5: Under the protection of argon inert gas, maintain the protective atmosphere from the start of the remelting process until cooling to room temperature, and obtain a metallurgical bonded protective layer with a double-layer structure.

[0017] Furthermore, in step 2, the particle size of the NiCrAlY-rare earth element alloy powder is 15μm-45μm, and in step 3, the particle size of the NiCr-WC-rare earth oxide composite powder is 5μm-30μm.

[0018] Furthermore, the heating time for the high-frequency induction remelting process in step 4 is 15s-40s.

[0019] Furthermore, after the high-frequency induction remelting process in step 4, an element interdiffusion region is formed between the inner layer and the substrate through solid-state diffusion, and the thickness of the element interdiffusion region is 5μm-20μm.

[0020] Furthermore, the process parameters for supersonic flame spraying in step 2 are: kerosene flow rate 20L / h-25L / h, oxygen flow rate 800L / min-900L / min, spraying distance 200mm-300mm, and powder feeding rate 30g / min-50g / min.

[0021] Beneficial effects of this invention: 1. This invention involves induction remelting of a pre-coated double-layer layer after spraying. After treatment, elemental diffusion occurs at the interface between the inner layer and the substrate, forming a metallurgical bonding interface. Tensile testing results show that the bonding strength of the protective layer of this invention is higher than that of a conventionally sprayed layer that has not been remelted. Metallographic observation reveals a diffusion zone of a certain thickness at the interface between the inner layer and the substrate, with a gradient distribution of elemental concentration on both sides of this region.

[0022] 2. This invention limits the mass ratio of WC particles to rare earth oxides in the outer layer. Nanoscale rare earth oxide powder is used in the outer layer. During spraying, the nanoscale rare earth oxides are distributed at the interface between the WC particles and the NiCr alloy. Induction remelting treatment melts the entire coating, eliminating the layered structure in the sprayed coating. The porosity of the remelted coating is lower than that of conventionally sprayed coatings.

[0023] 3. This invention incorporates a NiCrAlY rare earth element alloy inner layer between the substrate and the outer layer. Thermal expansion coefficient test data shows that the thermal expansion coefficient of this inner layer falls between that of the substrate and the outer layer. Thermal shock test results indicate that the protective layer of this invention did not exhibit interface cracking after 52 thermal cycles, while the control sample without a transition layer showed edge warping after fewer cycles.

[0024] 4. The WC particle content in the outer layer is within the range defined by this invention, and the mass ratio of WC particles to rare earth oxides is within the range defined by this invention. Wear test data shows that under the scouring conditions of a medium containing solid particles, the weight loss of the protective layer of this invention is lower than that of the comparative sample whose WC content exceeds the range of this invention.

[0025] 5. This invention employs supersonic flame spraying to prepare a pre-formed coating, achieving stable deposition efficiency within a defined range of spraying parameters. Induction remelting can achieve full-thickness melting of the coating within a defined process parameter range, with the substrate dilution rate remaining within a controllable range. This process is suitable for on-site construction of large components, and the induction coil can be manufactured according to the shape of the workpiece. Compared with laser cladding technology, this invention provides more uniform heat input and controls workpiece deformation to within 0.2 mm / m when applied to large thin-walled components (such as impellers of desulfurization slurry circulating pumps with diameters >1.5 m), while laser cladding typically results in deformation exceeding 0.5 mm / m. Furthermore, it eliminates the need for complex optical path debugging equipment, making it more adaptable for on-site construction.

[0026] 6. The technical solution of this invention focuses on power plant desulfurization systems. The material system is suitable for corrosive media containing solid particles, and the process method is suitable for on-site construction with minimal restrictions on workpiece size and shape. This technical solution can be applied to other equipment for transporting corrosive fluids containing solid particles, including coal slurry pumps in coal conveying systems, ash pumps in ash removal systems, reactor agitators in the chemical industry, and slurry transport pipelines in the metallurgical industry. Adjustments can be made within the scope of the claims based on the medium parameters under different operating conditions. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the cross-sectional metallographic structure of the metallurgically bonded protective layer prepared in Example 19 of the present invention; Figure 2This is a bar chart comparing the bonding strength of embodiments and comparative examples of the present invention; Figure 3 This is a bar chart comparing the porosity of embodiments and comparative examples of the present invention; Figure 4 This is a bar chart comparing the wear mark depth of embodiments and comparative examples of the present invention; Figure 5 This is a bar chart comparing the number of thermal shocks in the embodiments and comparative examples of the present invention; Figure 6 This is a graph showing the effect of the induced remelting anolyte current on the coating bonding strength and porosity of the present invention. Figure 7 This is a graph showing the effect of the induction remelting scanning speed on the coating bonding strength and porosity of the present invention. Figure 8 This is a graph showing the effect of the Al / Y ratio of the transition layer on the coating bonding strength and thermal shock resistance of the present invention. Figure 9 This is a graph showing the effect of the WC / CeO2 ratio of the functional layer of this invention on the coating bonding strength and porosity. Detailed Implementation

[0028] The present invention will be further described below through specific embodiments and comparative examples. The embodiments of the present invention are intended to enable those skilled in the art to understand and implement the invention, but are not intended to limit the scope of protection of the invention. Experimental methods not specifically described in the embodiments were performed under conventional conditions in the art.

[0029] As described in the background section, the core equipment of the desulfurization system in a coal-fired power plant is exposed to a corrosive environment for a long time. For this condition, the existing equipment surface protection technologies are mainly divided into four categories: organic coating, rubber lining, metal overlay and thermal spraying.

[0030] Organic coatings, including epoxy and polyurethane coatings, are used for corrosion protection in desulfurization systems. They are applied by brushing or spraying and cured at room temperature. Operational data shows that organic coatings become brittle and aged after a certain period in flue gas environments above 60°C. When slurry particles erode the coating, corrosive media penetrate the substrate through the damaged areas, causing accelerated localized corrosion.

[0031] Rubber linings are used in the inlet pipes of slurry circulation pumps and the inner walls of tanks. The lining materials include natural rubber or neoprene rubber, and they are bonded to the metal substrate using an adhesive bonding process. Rubber linings offer some impact resistance, but the bond strength between the rubber and metal is affected by construction conditions; edges may warp after immersion in slurry. Wear-resistant rubber will show wear after operating in media containing coarse particles for a certain period, resulting in localized exposure of the metal substrate, requiring replacement.

[0032] The metal overlay is deposited onto the substrate surface using manual electric arc welding or argon arc welding. The overlay and substrate form a metallurgical bond with high strength, and their wear and corrosion resistance can be adjusted by the welding material composition. However, the heat input for overlay welding is relatively large, making thin-walled workpieces prone to thermal deformation. Strict control of the overlay dilution rate is required, and achieving uniform thickness coverage is difficult for complex surfaces such as agitator blades.

[0033] Thermal spraying technologies, including arc spraying, flame spraying, and plasma spraying, are widely used in the power industry due to their flexible application, low heat input, and suitability for on-site maintenance. When arc-sprayed NiCr coatings are used for impeller protection in desulfurization slurry circulating pumps, inspections after a certain operating period revealed that the bonding between conventional thermal spray coatings and the substrate is primarily mechanical. Tensile testing showed that the bonding strength of arc-sprayed NiCr coatings is typically in the range of 30-40 MPa. Metallographic observation revealed a layered deposition structure within the coating, with a porosity between 5% and 15%. Under thermal cycling and erosion stress, corrosive media penetrate along the pores into the coating-substrate interface, causing the accumulation of interfacial corrosion products and coating blistering.

[0034] To improve the adhesion and density of coatings, researchers have proposed a post-spraying remelting technique. Existing remelting technologies mainly include in-furnace integral remelting, laser remelting, and induction remelting.

[0035] In-furnace remelting is suitable for batch processing of small-sized workpieces. The coated workpieces are placed in a heating furnace, heated above the coating's melting point, and held at that temperature until the coating melts and then cools. This method is energy-intensive and has a long processing cycle. For large desulfurization equipment components, it is difficult to process them in the furnace, making it unsuitable for on-site construction. Laser remelting uses a laser beam to scan the coating surface, resulting in high energy density and a metallurgical bond between the remelted zone and the substrate. However, the temperature gradient in the heat-affected zone is large during laser scanning, easily generating residual tensile stress and deformation in thin-walled substrates. Laser remelting of thin-walled workpieces after coating revealed high residual stress in the remelted zone and bending deformation of the workpiece. Furthermore, laser equipment is difficult to move, requires specific on-site construction conditions, and is inefficient for large-area processing.

[0036] Induction remelting technology utilizes the principle of electromagnetic induction to generate eddy current heat on the surface of a workpiece. This results in rapid heating and a controllable heat-affected zone, making it suitable for localized on-site treatment. Induction coils can be custom-made to fit the workpiece shape, offering good adaptability to large impellers and shaft components. Current research largely focuses on exploring remelting process parameters for single material systems, such as induction remelting experiments on NiCrBSi sprayed coatings to investigate the effects of power supply and scanning speed on the remelted layer microstructure. However, a systematic technical solution has yet to be developed for the material system matching design in corrosion-wear interactive conditions like desulfurization systems, particularly the synergistic optimization of material composition design and induction remelting processes for bilayer functionally graded coatings that balance corrosion resistance and wear resistance.

[0037] In summary, existing protective technologies still face technical bottlenecks in terms of bonding strength, coating density, construction efficiency, and adaptability to large components. A significant proportion of unplanned shutdowns of desulfurization equipment are related to component failures caused by corrosion and wear.

[0038] To address the aforementioned problems, embodiments of the present invention provide a metallurgically bonded protective layer for power plant fluid machinery and its preparation method.

[0039] I. Preparation and Characterization Methods of Protective Layer The protective layer of the present invention is prepared by a two-step method: first, an inner layer and an outer layer are prepared sequentially on the surface of the substrate by thermal spraying technology to form a double-layer pre-coating; then, the pre-coating is subjected to induction remelting treatment to densify the coating and form a metallurgical bonding interface.

[0040] 1. Matrix pretreatment The substrate material used was 12Cr1MoV steel, commonly used in power plant desulfurization systems, with sample dimensions of 100mm × 50mm × 10mm. All substrate samples underwent ultrasonic degreasing with acetone for 15 minutes to remove surface oil. Then, sandblasting was performed to roughen the surface. The sandblasting machine operated at a pressure of 0.6MPa, using 24-mesh brown corundum abrasive, with a blasting angle of 80° and a blasting distance of 150mm, until the substrate surface was uniformly grayish-white. After sandblasting, compressed air was used to blow away surface dust, and a roughness meter was used to measure the surface roughness, which reached Ra 5.5-7.5μm. The treated substrates were placed in a desiccator for later use, and spraying was completed within 24 hours.

[0041] 2. Powder material preparation The inner layer powder is an alloy powder of NiCrAlY rare earth elements, prepared according to the proportions described in each embodiment. The purity of the raw materials is ≥99.5%. Ni powder, Cr powder, Al powder, Y powder, and rare earth element powder (Ce or La) are weighed according to the proportions and then mixed in a three-dimensional mixer for 4 hours at a mixing speed of 30 r / min. After mixing, the powder is sieved, and the sieved powder with a particle size of 15-45 μm is used for later use.

[0042] The outer layer powder is a NiCr-WC-rare earth oxide composite powder, prepared according to the proportions described in each embodiment. The NiCr alloy powder is prepared by gas atomization, with a Cr content of 20% and a particle size of 15-45 μm. The WC particles are a mixture of micron-sized and nano-sized WC powder, with nano-sized WC accounting for 10% of the total mass of WC particles. The rare earth oxide is CeO2, with an average particle size of 50 nm and a purity ≥99.9%. After weighing according to the proportions, the powder is placed in a ball mill for mixing, and 0.5 wt% polyvinyl alcohol is added as a dispersant. The ball-to-powder ratio is 3:1, the mixing time is 2 hours, and the rotation speed is 200 r / min. After mixing, the powder is sieved, and the sieved powder with a particle size of 5-30 μm is used for later use. All powders are dried in a vacuum drying oven at 100℃ for 2 hours before use.

[0043] 3. Thermal spraying process The spraying equipment employs a supersonic flame spraying system. Spraying parameters are set as follows: kerosene flow rate 22 L / h, oxygen flow rate 850 L / min, spraying distance 250 mm, powder feed rate 40 g / min, spray gun moving speed 600 mm / s, and step distance 3 mm. During spraying, non-spraying areas are first protected with a shield. The inner layer powder is sprayed first, with a thickness controlled at approximately 100 μm, and 3-5 coats are applied continuously. Immediately afterwards, the outer layer powder is sprayed, with a thickness controlled at approximately 300 μm, and 8-12 coats are applied continuously. Compressed air is used to cool the back of the substrate during spraying to control the substrate temperature rise to no more than 150℃.

[0044] 4. Induction remelting process Induction remelting employs a high-frequency induction heating device at 20kHz. The induction coil is a helical tube with an inner diameter slightly larger than the sample width, and the distance between the coil and the workpiece surface is 5mm. The anode current and scanning speed are set according to the embodiments, and the sample passes through the induction coil at a set speed. During remelting, an infrared thermometer is used to monitor the coating surface temperature in real time, and the power output is adjusted by the control system to ensure the coating temperature remains stable within the preset range of 750°C-900°C. This scanning speed range (3mm / s-6mm / s) matches the heating area width of the induction coil, ensuring that the dwell time (i.e., heating time) of any point on the workpiece under the induction coil is controlled within the range of 15s-40s. Argon gas is introduced for protection during the remelting process at a flow rate of 15L / min, and the protective atmosphere is maintained from the start of heating until cooling to room temperature. After remelting, the sample is allowed to cool naturally to room temperature.

[0045] 5. Performance Testing Methods Bond strength test: The test was conducted according to GB / T8642-2002 "Determination of Tensile Bond Strength of Thermal Spray Coatings". The tensile test was performed using a mating part method. The specimen diameter was 25 mm. FM-1000 adhesive was used to bond the specimen to the mating part. After curing, the specimens were stretched on a universal testing machine at a tensile speed of 1 mm / min. The breaking load was recorded, and the bond strength was calculated. Five specimens were tested in each group, and the average value was taken.

[0046] Porosity test: The sample was cut along the cross section, inlaid and polished, and observed under a metallographic microscope at 500x magnification. Ten fields of view were randomly selected for each sample, and the pore area percentage was determined by image analysis software, and the average value was taken.

[0047] Hardness testing: A Vickers hardness tester was used, with a load of 300g and a holding time of 15s. A test was performed at 50μm intervals along the cross-section from the outer layer to the substrate, and the average value of the five points in the outer layer area was taken.

[0048] Wear resistance test: A high-temperature friction and wear tester was used, with Si3N4 ceramic balls as the mating parts. The load was 50N, the rotation speed was 200r / min, the wear time was 60min, and the test temperature was 600℃. The wear track depth was measured using a surface profilometer. Three samples were tested in each group, and the average value was taken.

[0049] Thermal shock test: The sample is placed in a box-type resistance furnace, heated to 600℃ and held for 20 minutes, then quickly removed and cooled in room temperature water. This process is repeated. After every 5 cycles, the coating surface is observed, and the number of cycles at which macroscopic cracks or peeling occur is recorded.

[0050] Interfacial bonding observation: The fracture surface of the specimens after bonding strength testing was observed using a metallographic microscope, and the fracture location and fracture characteristics were recorded. For some specimens, after being cut, inlaid, and polished along the cross-section, the microstructure and bonding condition of the interfacial area were observed using a metallographic microscope.

[0051] Example 1 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are: Cr: 22%, Al: 6.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and mass percentage are: WC particles 40%, CeO2: 1.0%, with the balance being NiCr alloy (Cr content 20%). The preparation method is as described above, with an induction remelting anolyte current of 2.5A, a scanning speed of 4.5mm / s, a heating time of 25s, and a heating temperature controlled at 820℃.

[0052] Testing showed that the protective layer in this embodiment had a bonding strength of 70 MPa and a thermal shock resistance of 45 cycles. Metallographic microscopy revealed a tight bond between the coating and the substrate interface, with no obvious gaps.

[0053] Example 2 This embodiment provides a metallurgically bonded protective layer, the transition layer composition and mass percentage of which are: Cr: 22%, Al: 8.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and preparation method are the same as in Example 1.

[0054] Testing showed that the protective layer in this embodiment had a bonding strength of 72 MPa and a thermal shock resistance of 52 cycles. Metallographic microscopy revealed that the interface between the coating and the substrate had a dense structure and good adhesion.

[0055] Example 3 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the following composition and mass percentage: Cr: 22%, Al: 10.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and preparation method are the same as in Example 1.

[0056] Testing showed that the protective layer in this embodiment had a bonding strength of 71 MPa and a thermal shock resistance of 48 cycles. Metallographic microscopy revealed good adhesion between the coating and the substrate interface, but a small amount of fine blackish-gray phase was visible in the inner layer.

[0057] Example 4 This embodiment provides a metallurgically bonded protective layer, the transition layer composition and mass percentage of which are: Cr: 22%, Al: 8.0%, Y: 0.5%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 16.0. The outer layer composition and preparation method are the same as in Example 1.

[0058] Testing showed that the protective layer in this embodiment had a bonding strength of 60 MPa and a thermal shock resistance of 38 cycles. Metallographic microscopy revealed good adhesion between the coating and the substrate interface, with no obvious defects.

[0059] Example 5 This embodiment provides a metallurgically bonded protective layer, the transition layer composition and mass percentage of which are: Cr: 22%, Al: 8.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 8.0. The outer layer composition and preparation method are the same as in Example 1.

[0060] Testing showed that the protective layer in this embodiment had a bonding strength of 72 MPa and a thermal shock resistance of 52 cycles. Metallographic microscopy revealed that the interface between the coating and the substrate had a dense structure and good adhesion.

[0061] Example 6 This embodiment provides a metallurgically bonded protective layer, the transition layer composition and mass percentage of which are: Cr: 22%, Al: 8.0%, Y: 1.5%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 5.3. The outer layer composition and preparation method are the same as in Example 1.

[0062] Testing showed that the protective layer in this embodiment had a bonding strength of 68 MPa and a thermal shock resistance of 45 cycles. Metallographic microscopy revealed good adhesion between the coating and the substrate interface, but a small amount of fine blackish-gray phase was visible in the inner layer.

[0063] Example 7 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are as follows: Cr: 22%, Al: 8.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and mass percentage are: WC particles 30%, CeO2: 1.0%, with the balance being NiCr alloy (Cr content 20%). The preparation method is the same as in Example 1.

[0064] Testing revealed that the protective layer in this embodiment has a hardness of 650HV0.3 and a wear track depth of 15.2μm. Metallographic microscopy showed that the WC particles in the coating were sparsely distributed, while the metal substrate remained continuous.

[0065] Example 8 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: WC particles 40%, CeO2: 1.0%, and the balance is NiCr alloy (Cr content 20%). The preparation method is the same as in Example 7.

[0066] Testing revealed that the protective layer in this embodiment has a hardness of 820HV0.3 and a wear track depth of 8.5μm. Metallographic microscopy showed that the WC particles in the coating were uniformly distributed and tightly bonded to the metal substrate.

[0067] Example 9 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 50% WC particles, 1.0% CeO2, and the balance is NiCr alloy (Cr content 20%). The preparation method is the same as in Example 7.

[0068] Testing revealed that the protective layer in this embodiment has a hardness of 880HV0.3 and a wear track depth of 7.8μm. Metallographic microscopy showed that WC particles were densely distributed in the coating, with the metal matrix filling the gaps between the particles.

[0069] Example 10 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 40% WC particles, 0.5% CeO2, and the balance is NiCr alloy (Cr content 20%), with a WC / CeO2 ratio of 80. The preparation method is the same as in Example 7.

[0070] Testing revealed that the protective layer in this embodiment has a porosity of 1.2%, a bonding strength of 68 MPa, and a wear track depth of 11.2 μm. Metallographic microscopy showed that a small number of micropores exist in the coating, and the interface between the WC particles and the metal substrate is relatively clear.

[0071] Example 11 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 40% WC particles, 1.0% CeO2, and the balance is NiCr alloy (Cr content 20%), with a WC / CeO2 ratio of 40. The preparation method is the same as in Example 7.

[0072] Testing revealed that the protective layer in this embodiment has a porosity of 0.5%, a bonding strength of 85 MPa, and a wear track depth of 8.5 μm. Metallographic microscopy showed that the coating structure is dense, the interface between the WC particles and the metal substrate is blurred, and the bonding is good.

[0073] Example 12 This embodiment provides a metallurgically bonded protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 40% WC particles, 1.5% CeO2, and the balance is NiCr alloy (Cr content 20%), with a WC / CeO2 ratio of 26.7. The preparation method is the same as in Example 7.

[0074] Testing revealed that the protective layer in this embodiment has a porosity of 0.8%, a bonding strength of 76 MPa, and a wear track depth of 9.1 μm. Metallographic microscopy showed that the coating structure is relatively dense, with occasional small blackish-gray agglomerates.

[0075] Example 13 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 1.8A, scanning speed 4.5mm / s, and heating time 25s.

[0076] Infrared thermography showed a remelting temperature of 750℃, a porosity of 2.5%, a bonding strength of 70 MPa, and an elemental interdiffusion layer thickness of approximately 3 μm as measured by metallographic microscopy. Melting traces were visible at the interface, but the layer was not completely dense.

[0077] Example 14 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 4.5mm / s, and heating time 25s.

[0078] Testing revealed that the protective layer in this embodiment has a remelting temperature of 820℃, a porosity of 0.5%, a bonding strength of 88 MPa, and an elemental interdiffusion layer thickness of approximately 8 μm as measured by metallographic microscopy. The interface region exhibits a dense structure and good bonding.

[0079] Example 15 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 3.2A, scanning speed 4.5mm / s, and heating time 25s.

[0080] Infrared thermography showed a remelting temperature of 900℃, a porosity of 0.3%, a bonding strength of 75 MPa, and an elemental interdiffusion layer thickness of approximately 20 μm as measured by metallographic microscopy. A relatively wide transition zone was visible at the interface.

[0081] Example 16 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 3.0mm / s, and heating time 40s.

[0082] Testing revealed that the protective layer in this embodiment has a porosity of 0.6%, a bonding strength of 86 MPa, and a smooth and flat surface. Metallographic microscopy showed that the coating thickness is uniform and the interface is straight.

[0083] Example 17 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 4.5mm / s, and heating time 25s.

[0084] Testing revealed that the protective layer in this embodiment has a porosity of 0.5%, a bonding strength of 88 MPa, and a smooth and flat surface morphology. Metallographic microscopy showed that the coating has a dense structure and good interfacial bonding.

[0085] Example 18 This embodiment provides a metallurgically bonded protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 6.0mm / s.

[0086] Testing revealed that the protective layer in this embodiment had a porosity of 1.2%, a bonding strength of 79 MPa, and a slightly undulating surface morphology. Metallographic microscopy showed traces of a small amount of unmelted particles remaining in the coating.

[0087] Example 19 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are: Cr: 22%, Al: 8.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The mass ratio of Al to Y in the inner layer is 8.0. The outer layer is a wear-resistant and corrosion-resistant functional layer, and its composition, by mass percentage, is: WC particles 40%, CeO2: 1.0%, with the balance being NiCr alloy. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 4.5mm / s, heating time 25s, and heating temperature controlled at 850℃.

[0088] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 88 MPa, a porosity of 0.5%, a hardness of 820 HV0.3, a wear track depth of 8.5 μm, and a thermal shock resistance of 52 cycles. Metallographic microscopy revealed a dense coating structure with a uniform interdiffusion band of approximately 8 μm thick at the interface, exhibiting a gradual transition between this region and the surrounding structures.

[0089] Example 20 This embodiment provides a metallurgically bonded protective layer, wherein the Al / Y ratio of the transition layer is 5.0 and the WC / CeO2 ratio of the functional layer is 80. Other components and preparation methods are the same as in Example 19.

[0090] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 75 MPa, a porosity of 0.9%, a wear track depth of 10.5 μm, and a thermal shock resistance of 42 cycles. Metallographic microscopy observation showed that the coating structure was relatively dense and the interfacial bonding was good.

[0091] Example 21 This embodiment provides a metallurgically bonded protective layer, wherein the Al / Y ratio of the transition layer is 8.0 and the WC / CeO2 ratio of the functional layer is 40. Other components and preparation methods are the same as in Example 19.

[0092] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 88 MPa, a porosity of 0.5%, a wear track depth of 8.5 μm, and a thermal shock resistance of 52 cycles. Metallographic microscopy showed that the coating structure was dense and the interface transition was uniform.

[0093] Example 22 This embodiment provides a metallurgically bonded protective layer, wherein the Al / Y ratio of the transition layer is 16.0 and the WC / CeO2 ratio of the functional layer is 25. Other components and preparation methods are the same as in Example 19.

[0094] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 72 MPa, a porosity of 1.1%, a wear track depth of 9.8 μm, and a thermal shock resistance of 40 cycles. Metallographic microscopy showed that the coating structure was relatively dense and the interfacial bonding was good.

[0095] Example 23 This embodiment provides a metallurgically bonded protective layer, in which nano-WC accounts for 5% of the total mass of WC particles in the outer layer. Other components and preparation methods are the same as in Example 19.

[0096] Testing revealed that the protective layer in this embodiment has a hardness of 805HV0.3 and a wear track depth of 9.2μm. Metallographic microscopy showed that the WC particles were uniformly distributed and the interparticle spaces were densely filled.

[0097] Example 24 This embodiment provides a metallurgically bonded protective layer, in which nano-WC accounts for 10% of the total mass of WC particles in the outer layer. Other components and preparation methods are the same as in Example 19.

[0098] Testing revealed that the protective layer in this embodiment has a hardness of 820HV0.3 and a scratch depth of 8.5μm. Metallographic microscopy showed that the WC particles were evenly distributed and the structure was dense.

[0099] Example 25 This embodiment provides a metallurgically bonded protective layer, in which nano-WC accounts for 15% of the total mass of WC particles in the outer layer. Other components and preparation methods are the same as in Example 19.

[0100] Testing revealed that the protective layer in this embodiment has a hardness of 815HV0.3 and a scratch depth of 8.8μm. Metallographic microscopy showed that the WC particles were evenly distributed and the structure was relatively dense.

[0101] Example 26 This embodiment provides a metallurgically bonded protective layer, the outer layer of which has an average CeO2 particle size of 30 nm. Other components and preparation methods are the same as in Example 19.

[0102] Testing revealed that the protective layer in this embodiment has a porosity of 0.6% and a wear track depth of 8.7 μm. Metallographic microscopy showed that the coating structure is dense, and the WC particles have good interfacial bonding with the metal substrate.

[0103] Example 27 This embodiment provides a metallurgically bonded protective layer, the outer layer of which has an average CeO2 particle size of 50 nm. Other components and preparation methods are the same as in Example 19.

[0104] Testing revealed that the porosity of the protective layer in this embodiment was 0.5%, and the wear track depth was 8.5 μm. Metallographic microscopy showed that the coating structure was dense, and the WC particles had good interfacial bonding with the metal substrate.

[0105] Example 28 This embodiment provides a metallurgically bonded protective layer, the outer layer of which has an average CeO2 particle size of 80 nm. Other components and preparation methods are the same as in Example 19.

[0106] Testing revealed that the protective layer in this embodiment has a porosity of 0.7% and a wear track depth of 9.0 μm. Metallographic microscopy showed that the coating structure is relatively dense, and the WC particles have good interfacial bonding with the metal substrate.

[0107] Example 29 This embodiment provides a metallurgically bonded protective layer, the outer layer of which contains 0.8% CeO2. Other components and preparation methods are the same as in Example 19.

[0108] Testing revealed that the protective layer in this embodiment has a porosity of 0.7%, a bonding strength of 80 MPa, and a wear track depth of 9.5 μm. Metallographic microscopy showed that the coating structure is relatively dense, and the WC particles have good interfacial bonding with the metal substrate.

[0109] Example 30 This embodiment provides a metallurgically bonded protective layer, the outer layer of which contains 1.0% CeO2. Other components and preparation methods are the same as in Example 19.

[0110] Testing revealed that the protective layer in this embodiment has a porosity of 0.5%, a bonding strength of 85 MPa, and a wear track depth of 8.5 μm. Metallographic microscopy showed that the coating structure is dense, and the WC particles have good interfacial bonding with the metal substrate.

[0111] Example 31 This embodiment provides a metallurgically bonded protective layer, the outer layer of which contains 1.2% CeO2. Other components and preparation methods are the same as in Example 19.

[0112] Testing revealed that the protective layer in this embodiment has a porosity of 0.6%, a bonding strength of 82 MPa, and a wear track depth of 9.0 μm. Metallographic microscopy showed that the coating structure is relatively dense, and the WC particles have good interfacial bonding with the metal substrate.

[0113] Example 32 This embodiment provides a metallurgically bonded protective layer with an inner layer thickness of 50 μm and an outer layer thickness of 300 μm. The composition and preparation method are the same as in Example 19.

[0114] Testing showed that the protective layer in this embodiment had a bonding strength of 75 MPa, with a thermal shock resistance of 38 cycles and a scratch depth of 8.8 μm. Metallographic microscopy revealed that the inner layer completely covered the substrate, and the interface bonding was excellent.

[0115] Example 33 This embodiment provides a metallurgically bonded protective layer with an inner layer thickness of 100 μm and an outer layer thickness of 300 μm. The composition and preparation method are the same as in Example 19.

[0116] Testing showed that the protective layer in this embodiment had a bonding strength of 88 MPa, with 52 thermal shock cycles and a scratch depth of 8.5 μm. Metallographic microscopy revealed good bonding between the inner and outer layers, as well as between the inner layer and the substrate.

[0117] Example 34 This embodiment provides a metallurgically bonded protective layer with an inner layer thickness of 150 μm and an outer layer thickness of 300 μm. The composition and preparation method are the same as in Example 19.

[0118] Testing showed that the protective layer in this embodiment had a bonding strength of 82 MPa, with 45 thermal shock cycles and a scratch depth of 8.6 μm. Metallographic microscopy revealed a dense inner layer structure and good interfacial bonding.

[0119] Example 35 This embodiment provides a metallurgically bonded protective layer with an inner layer thickness of 100 μm and an outer layer thickness of 200 μm. The composition and preparation method are the same as in Example 19.

[0120] Testing showed that the protective layer in this embodiment had a bonding strength of 86 MPa, with 48 thermal shock cycles and a scratch depth of 9.2 μm. Metallographic microscopy revealed that the outer layer completely covered the inner layer, and the interface bonding was excellent.

[0121] Example 36 This embodiment provides a metallurgically bonded protective layer with an inner layer thickness of 100 μm and an outer layer thickness of 400 μm. The composition and preparation method are the same as in Example 19.

[0122] Testing showed that the protective layer in this embodiment had a bonding strength of 85 MPa, with 46 thermal shock cycles and a wear track depth of 8.3 μm. Metallographic microscopy revealed that the outer layer had a dense structure and good interfacial bonding.

[0123] Example 37 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are: Cr: 22%, Al: 8.0%, Y: 1.0%, La: 0.3%, with the balance being Ni. The outer layer composition and mass percentage are: WC particles 40%, La2O3: 1.0% (average particle size 50nm), with the balance being NiCr alloy (Cr content 20%). The preparation method is the same as in Example 19.

[0124] The protective layer in this embodiment exhibited a bonding strength of 86 MPa, a porosity of 0.6%, a hardness of 815 HV0.3, a wear track depth of 8.7 μm, and a thermal shock resistance of 50 cycles. Metallographic microscopy revealed a dense coating structure and good interfacial bonding between the WC particles and the metal substrate. These results demonstrate that excellent overall performance can also be achieved using La2O3.

[0125] Example 38 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are: Cr: 22%, Al: 8.0%, Y: 1.6%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 5.0. The outer layer composition and mass percentage are: WC particles 40%, CeO2: 1.0%, with the balance being a NiCr alloy (Cr content 20%). The preparation method is the same as in Example 19.

[0126] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 73 MPa, a porosity of 1.0%, a wear track depth of 10.2 μm, and a thermal shock resistance of 40 cycles. Metallographic microscopy observation showed that the coating structure was relatively dense and the interfacial bonding was good.

[0127] Example 39 This embodiment provides a metallurgically bonded protective layer. The transition layer composition and mass percentage are: Cr: 22%, Al: 8.0%, Y: 0.5%, Ce: 0.3%, with the balance being Ni, and the Al / Y ratio is 16.0. The outer layer composition and mass percentage are: WC particles 40%, CeO2: 1.0%, with the balance being NiCr alloy (Cr content 20%). The preparation method is the same as in Example 19.

[0128] Testing revealed that the protective layer in this embodiment exhibited a bonding strength of 70 MPa, a porosity of 1.1%, a wear track depth of 10.5 μm, and a thermal shock resistance of 38 cycles. Metallographic microscopy observation showed that the coating structure was relatively dense and the interfacial bonding was good.

[0129] Comparative Example 1 This comparative example provides a protective layer, the transition layer of which has the following composition and mass percentage: Cr: 22%, Al: 4.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and preparation method are the same as in Example 1.

[0130] Testing showed that the protective layer in this comparative example had a bonding strength of 41 MPa and withstood 18 thermal shocks. Metallographic microscopy revealed discontinuous micro-gaps at the interface between the coating and the substrate.

[0131] Comparative Example 2 This comparative example provides a protective layer, the transition layer of which has the following composition and mass percentage: Cr: 22%, Al: 12.0%, Y: 1.0%, Ce: 0.3%, with the balance being Ni. The outer layer composition and preparation method are the same as in Example 1.

[0132] Tests showed that the protective layer in this comparative example had a bonding strength of 53 MPa and a thermal shock resistance of 22 cycles. Metallographic microscopy revealed numerous fine blackish-gray phases within the inner layer.

[0133] Comparative Example 3 This comparative example provides a protective layer, the transition layer of which comprises the following components and mass percentages: Cr: 22%, Al: 8.0%, Y: 0.1%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 80.0. The outer layer components and preparation method are the same as in Example 1.

[0134] Testing showed that the protective layer in this comparative example had a bonding strength of 35 MPa and a thermal shock resistance of 15 cycles. Metallographic microscopy revealed weak bonding between the coating and the substrate, with some areas showing separation.

[0135] Comparative Example 4 This comparative example provides a protective layer, the transition layer of which comprises the following components and mass percentages: Cr: 22%, Al: 8.0%, Y: 2.0%, Ce: 0.3%, with the balance being Ni, and an Al / Y ratio of 4.0. The outer layer components and preparation method are the same as in Example 1.

[0136] Tests showed that the protective layer in this comparative example had a bonding strength of 50 MPa and withstood 28 thermal shocks. Metallographic microscopy revealed numerous fine blackish-gray phases within the inner layer.

[0137] Comparative Example 5 This comparative example provides a protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 20% WC particles, 1.0% CeO2, and the balance is NiCr alloy (20% Cr content). The preparation method is the same as in Example 7.

[0138] Testing revealed that the protective layer in this comparative example had a hardness of 480HV0.3 and a wear track depth of 28.6μm. Metallographic microscopy showed that the WC particles were sparsely distributed, while the metal matrix remained continuous.

[0139] Comparative Example 6 This comparative example provides a protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: WC particles 60%, CeO2: 1.0%, and the balance is NiCr alloy (Cr content 20%). The preparation method is the same as in Example 7.

[0140] Testing revealed that the protective layer in this comparative example had a hardness of 750HV0.3 and a wear track depth of 18.9μm. Metallographic microscopy showed that the WC particles were densely packed, with some particles in direct contact, indicating insufficient filling of the metal matrix.

[0141] Comparative Example 7 This comparative example provides a protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: WC particles 40%, CeO2: 0%, and the balance is NiCr alloy (Cr content 20%). The preparation method is the same as in Example 7.

[0142] Testing revealed that the protective layer in this comparative example had a porosity of 3.5%, a bonding strength of 45 MPa, and a wear track depth of 20.5 μm. Metallographic microscopy showed obvious gaps at the interface between the WC particles and the metal substrate, indicating a high degree of porosity in the coating.

[0143] Comparative Example 8 This comparative example provides a protective layer, the transition layer of which has the same composition as in Example 7. The outer layer composition and mass percentage are: 40% WC particles, 2.0% CeO2, and the balance is NiCr alloy (Cr content 20%), with a WC / CeO2 ratio of 20. The preparation method is the same as in Example 7.

[0144] Testing revealed that the protective layer in this comparative example had a porosity of 2.1%, a bonding strength of 60 MPa, and a wear track depth of 14.3 μm. Metallographic microscopy showed the presence of a small amount of dark gray agglomerates in the coating, with a size of approximately 5-10 μm.

[0145] Comparative Example 9 This comparative example provides a protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 1.2A, scanning speed 4.5mm / s.

[0146] Testing revealed that the protective layer in this comparative example had a remelting temperature of 700℃, a porosity of 8.0%, a bonding strength of 42 MPa, and an elemental interdiffusion zone thickness of approximately 1 μm. Metallographic microscopy showed that the coating retained a distinct layered deposition structure with visible gaps between the layers.

[0147] Comparative Example 10 This comparative example provides a protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 3.8A, scanning speed 4.5mm / s.

[0148] Testing revealed that the protective layer in this comparative example had a remelting temperature of 1000℃, a porosity of 1.5%, a bonding strength of 50 MPa, and an elemental interdiffusion zone thickness of approximately 35 μm. Metallographic microscopy observation showed a wide transition zone at the interface, with newly formed phases visible near the interface.

[0149] Comparative Example 11 This comparative example provides a protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 2.0mm / s.

[0150] Testing revealed that the protective layer in this comparative example had a porosity of 0.8% and a bonding strength of 65 MPa, but exhibited surface morphology of flow and uneven thickness. Metallographic microscopy showed significant fluctuations in coating thickness and localized flow marks.

[0151] Comparative Example 12 This comparative example provides a protective layer with the same composition as in Example 11. The induction remelting process parameters in the preparation method are: anolyte current 2.5A, scanning speed 8.0mm / s.

[0152] Testing revealed that the protective layer in this comparative example had a porosity of 4.5%, a bonding strength of 50 MPa, and an incompletely melted, orange-peel-like surface morphology. Metallographic microscopy showed that a large number of unmelted particles remained in the coating, and the layered structure was not completely eliminated.

[0153] Comparative Example 13 This comparative example uses a commercially available arc-sprayed NiCr coating with a Cr content of 20% in the NiCr alloy and a coating thickness of approximately 400 μm. No remelting treatment was performed.

[0154] Tests showed that the comparative coating exhibited a bonding strength of 38 MPa, a porosity of 8.2%, a hardness of 420 HV0.3, a scratch depth of 32.5 μm, and a thermal shock resistance of 12 cycles. Metallographic microscopy revealed that the coating exhibited a typical layered deposition structure with obvious gaps between the layers.

[0155] Comparative Example 14 This comparative example uses a commercially available plasma-sprayed WC-12Co coating with a thickness of approximately 400 μm, and no remelting treatment was performed.

[0156] Tests showed that the comparative coating had a bonding strength of 45 MPa, a porosity of 3.5%, a hardness of 750 HV0.3, a scratch depth of 15.8 μm, and passed 8 thermal shock cycles. Metallographic microscopy revealed numerous pores in the coating, with relatively uniform distribution of WC particles.

[0157] Comparative Example 15 This comparative example uses laser cladding technology to prepare a NiCr-WC coating with a composition similar to that of Example 19 (WC: 40%, NiCr: 60%), and a cladding thickness of approximately 400 μm. The laser cladding process parameters are: fiber laser, power 3 kW, scanning speed 5 mm / s, spot diameter 4 mm, and overlap rate 30%. Testing showed that the coating in this comparative example had a bonding strength of 92 MPa, a porosity of 0.3%, a hardness of 810 HVO.3, a scratch depth of 7.5 μm, and a thermal shock resistance of 45 cycles. Metallographic microscopy revealed a dense coating structure and good interfacial bonding, but the heat-affected zone depth reached 500 μm, indicating significant coarsening of the substrate microstructure (grain size increased to 50-80 μm) and the presence of obvious fusion lines. After cladding on a 10 mm thick 12Cr1MoV flat substrate, the sample exhibited a bending deformation of 0.8 mm / m, indicating concentrated heat input during laser cladding, leading to significant residual stress and deformation. In simulated corrosion and wear tests, the coating lost 10.8 mg / cm³ of weight. 2 Slightly lower than Example 19 of the present invention (12.5 mg / cm³). 2 However, the coarse-grained structure in the heat-affected zone (HAZ) reduces the fatigue performance of the matrix, and cracks initiate first in the HAZ during subsequent cyclic stress tests. In contrast, the deformation of the same thickness specimen after induction remelting in this invention is less than 0.2 mm / m, the depth of the HAZ is less than 30 μm, and the matrix structure remains in its original state.

[0158] Comparative Example 16 This comparative example provides a protective layer with an Al / Y ratio of 4.0 in the transition layer and a WC / CeO2 ratio of 40 in the functional layer. Other components and preparation methods are the same as in Example 19.

[0159] Testing revealed that the protective layer in this comparative example exhibited a bonding strength of 50 MPa, a porosity of 2.2%, a wear track depth of 18.5 μm, and a thermal shock resistance of 25 cycles. Metallographic microscopy revealed numerous fine blackish-gray phases within the inner layer, while the interface between the outer WC particles and the metal substrate was relatively clear.

[0160] Comparative Example 17 This comparative example provides a protective layer with an Al / Y ratio of 20.0 in the transition layer and a WC / CeO2 ratio of 40 in the functional layer. Other components and preparation methods are the same as in Example 19.

[0161] Testing revealed that the protective layer in this comparative example exhibited a bonding strength of 48 MPa, a porosity of 2.5%, a wear track depth of 19.2 μm, and a thermal shock resistance of 22 cycles. Metallographic microscopy observation showed that the bonding between the inner layer and the substrate was weak, with micro-cracks visible in some areas.

[0162] Comparative Example 18 This comparative example provides a protective layer with an Al / Y ratio of 8.0 in the transition layer and a WC / CeO2 ratio of 20 in the functional layer. Other components and preparation methods are the same as in Example 19.

[0163] Testing revealed that the protective layer in this comparative example exhibited a bonding strength of 60 MPa, a porosity of 2.1%, a wear track depth of 16.5 μm, and a thermal shock resistance of 30 cycles. Metallographic microscopy revealed the presence of blackish-gray aggregates in the outer layer, with a relatively clear interface between the WC particles and the metal matrix.

[0164] Comparative Example 19 This comparative example provides a protective layer with an Al / Y ratio of 8.0 in the transition layer and a WC / CeO2 ratio of 100 in the functional layer. Other components and preparation methods are the same as in Example 19.

[0165] Testing revealed that the protective layer in this comparative example exhibited a bonding strength of 55 MPa, a porosity of 2.8%, a wear track depth of 18.0 μm, and passed 28 thermal shock cycles. Metallographic microscopy revealed numerous pores in the outer layer, with micro-gaps existing at the interface between the WC particles and the metal substrate.

[0166] Comparative Example 20 This comparative example provides a protective layer in which nano-WC accounts for 0% of the total mass of WC particles in the outer layer. Other components and preparation methods are the same as in Example 19.

[0167] Testing revealed that the protective layer in this comparative example had a hardness of 760HV0.3 and a scratch depth of 12.5μm. Metallographic microscopy showed numerous voids between the micron-sized WC particles, indicating incomplete filling.

[0168] Comparative Example 21 This comparative example provides a protective layer in which nano-WC accounts for 20% of the total mass of WC particles in the outer layer. Other components and preparation methods are the same as in Example 19.

[0169] Testing revealed that the protective layer in this comparative example had a hardness of 770HV0.3 and a scratch depth of 11.8μm. Metallographic microscopy showed that the nano-WC particles exhibited agglomeration, with small, dark gray agglomerates visible in some areas.

[0170] Comparative Example 22 This comparative example provides a protective layer in which the average particle size of CeO2 in the outer layer is 20 nm. Other components and preparation methods are the same as in Example 19.

[0171] Testing revealed that the porosity of the protective layer in this comparative example was 1.5%, and the wear track depth was 12.8 μm. Metallographic microscopy showed that the coating contained numerous fine blackish-gray agglomerates, approximately 2-5 μm in size.

[0172] Comparative Example 23 This comparative example provides a protective layer in which the average particle size of CeO2 in the outer layer is 100 nm. Other components and preparation methods are the same as in Example 19.

[0173] Testing revealed that the porosity of the protective layer in this comparative example was 1.8%, and the wear track depth was 13.5 μm. Metallographic microscopy showed that the interface between the WC particles and the metal substrate was relatively clear, with micropores visible in some areas.

[0174] Comparative Example 24 This comparative example provides a protective layer with an inner layer thickness of 30 μm and an outer layer thickness of 300 μm. The composition and preparation method are the same as in Example 19.

[0175] Testing showed that the protective layer in this comparative example had a bonding strength of 52 MPa, with a thermal shock resistance of 20 cycles and a wear track depth of 15.8 μm. Metallographic microscopy revealed that the inner layer was relatively thin, and traces of direct contact between the outer layer and the substrate were visible in some areas.

[0176] Comparative Example 25 This comparative example provides a protective layer with an inner layer thickness of 200 μm and an outer layer thickness of 300 μm. The composition and preparation method are the same as in Example 19.

[0177] Tests showed that the protective layer in this comparative example had a bonding strength of 60 MPa, with 25 thermal shock cycles and a scratch depth of 12.5 μm. Metallographic microscopy revealed that the inner layer was relatively thick and the microstructure was relatively coarse.

[0178] Comparative Example 26 This comparative example provides a protective layer with an inner layer thickness of 100 μm and an outer layer thickness of 150 μm. The composition and preparation method are the same as in Example 19.

[0179] Tests showed that the protective layer in this comparative example had a bonding strength of 78 MPa, with 35 thermal shock cycles and a wear track depth of 14.2 μm. Metallographic microscopy revealed that the outer layer was thinner, and the wear track became closer to the inner layer after wear.

[0180] Comparative Example 27 This comparative example provides a protective layer with an inner layer thickness of 100 μm and an outer layer thickness of 500 μm. The composition and preparation method are the same as in Example 19.

[0181] Tests showed that the protective layer in this comparative example had a bonding strength of 70 MPa, with a thermal shock resistance of 30 cycles and a wear mark depth of 7.8 μm. Metallographic microscopy revealed that the outer layer was relatively thick, and occasional interlayer microcracks were observed after thermal shock.

[0182] 6. Analysis of the Influence of Transition Layer Composition on Performance Data from Examples 1-6 and Comparative Examples 1-4 show that the Al content and Al / Y ratio in the transition layer have a significant impact on the coating bonding strength and thermal shock resistance.

[0183] When the Al content increased from 4.0% to 8.0%, the bonding strength increased from 41 MPa to 72 MPa, and the number of thermal shock cycles increased from 18 to 52. The performance was optimal at an Al content of 8.0%, slightly decreased at 10.0% but remained within an acceptable range, and significantly decreased at 12.0%. Analysis suggests that Al mainly plays a role in forming the Al2O3 oxide film in the NiCrAlY alloy. In Comparative Example 1, with an Al content of 4.0%, metallographic observation showed discontinuous micro-gaps at the coating-substrate interface, indicating weak interfacial bonding. In Comparative Example 2, with an Al content of 12.0%, numerous fine blackish-gray phases were visible in the inner layer; these phases are brittle NiAl phases, prone to crack initiation under thermal shock stress.

[0184] When the Al / Y ratio decreased from 80.0 to 8.0, the bonding strength increased from 35 MPa to 72 MPa, and the number of thermal shock cycles increased from 15 to 52. When the Al / Y ratio decreased to 4.0, the performance declined. Analysis suggests that Y mainly segregates at grain boundaries and oxide film interfaces in the coating. In Comparative Example 3, with an Al / Y ratio of 80.0 (Y content 0.1%), metallographic observation showed weak bonding between the coating and the substrate interface, with separation visible in some areas, indicating insufficient oxide film adhesion. In Comparative Example 4, with an Al / Y ratio of 4.0 (Y content 2.0%), numerous fine blackish-gray phases were visible in the inner layer. These phases are intermetallic compounds formed by Y with Ni and Al, consuming the Al elements needed to form the oxide film.

[0185] 7. Analysis of the impact of functional layer components on performance Data from Examples 7-12 and Comparative Examples 5-8 show that the WC content and WC / CeO2 ratio in the functional layer have a significant impact on the coating hardness, porosity, bonding strength, and wear resistance.

[0186] When the WC content increased from 20% to 40%, the hardness increased from 480 HV to 820 HV, while the wear track depth decreased from 28.6 μm to 8.5 μm. The hardness continued to increase at 50% WC content and decreased at 60%. Analysis suggests that WC particles act as a hard phase reinforcing agent in the coating. In Comparative Example 5, with a WC content of 20%, metallographic observation showed sparse WC particle distribution and a continuous metal matrix, indicating that the metal matrix was cut first during wear. In Comparative Example 6, with a WC content of 60%, metallographic observation showed dense WC particles, with some particles in direct contact, insufficient filling of the metal matrix, and WC particles easily peeling off as a whole during wear.

[0187] When the CeO2 content increased from 0% to 1.0%, the porosity decreased from 3.5% to 0.5%, the bonding strength increased from 45 MPa to 85 MPa, and the wear track depth decreased from 20.5 μm to 8.5 μm. Performance declined at a CeO2 content of 2.0%. Analysis suggests that CeO2 plays two main roles in the spraying process. Firstly, CeO2 has high surface activity and readily accumulates at the interface between WC particles and the NiCr alloy, reducing the interfacial energy between the two phases and improving wettability. In Comparative Example 7, without CeO2, metallographic observation showed obvious gaps at the interface between WC particles and the metal matrix, resulting in a high porosity in the coating. Secondly, CeO2 can act as a heterogeneous nucleation core in molten metal, refining the solidification structure. In Comparative Example 8, with a CeO2 content of 2.0%, metallographic observation showed the presence of blackish-gray agglomerates in the coating, which became defect sources.

[0188] 8. Analysis of the impact of process parameters on performance Data from Examples 13-18 and Comparative Examples 9-12 show that, under the remelting temperature of 750℃-900℃ specified in this invention, the anolyte current and scanning speed in the induction remelting process parameters have a significant impact on the coating porosity, bonding strength, and thickness of the interdiffusion zone.

[0189] When the anolyte current increased from 1.2 A to 2.5 A, the heating temperature rose from approximately 700 °C to 820 °C, the porosity decreased from 8.0% to 0.5%, and the bonding strength increased from 42 MPa to 88 MPa. At an anolyte current of 3.2 A, the heating temperature reached 900 °C, with even lower porosity but decreased bonding strength, and the interdiffusion zone thickness increased to 20 μm. At an anolyte current of 3.8 A, the heating temperature exceeded 1000 °C; although the porosity was low, the bonding strength decreased significantly. Analysis suggests that the anolyte current determines the input power for induction heating and affects the remelting temperature. In Comparative Example 9, with an anolyte current of 1.2 A, metallographic observation showed that the coating retained a distinct layered deposition structure, indicating that the coating was not completely melted. In Comparative Example 10, with an anolyte current of 3.8 A, a wide transition zone existed at the interface, and newly formed phases were visible near the interface, indicating excessive dilution of the matrix.

[0190] When the scanning speed increased from 2.0 mm / s to 4.5 mm / s, the bonding strength increased from 65 MPa to 88 MPa. Performance decreased at a scanning speed of 6.0 mm / s and significantly decreased at 8.0 mm / s. Analysis suggests that the scanning speed determines the residence time of the heat source, affecting the total heat input. Considering the heating time range of 15-40 seconds, the scanning speed and heating time are interrelated and jointly determine the remelting effect. In Comparative Example 11, with a scanning speed of 2.0 mm / s, the corresponding heating time exceeded 50 seconds, and metallographic observation showed significant fluctuations in coating thickness and localized flow marks. In Comparative Example 12, with a scanning speed of 8.0 mm / s, the heating time was less than 10 seconds, and a large number of unmelted particles remained in the coating, indicating insufficient heat input.

[0191] 9. Synergy Ratio Analysis Data from Examples 20-22 and Comparative Examples 16-19 show that the Al / Y ratio of the transition layer and the WC / CeO2 ratio of the functional layer need to be controlled synergistically. When both ratios are within the range defined in the claims, the overall coating performance is excellent. If either ratio exceeds the range, the coating performance significantly decreases. Analysis suggests that the Al / Y ratio affects the adhesion and toughness of the oxide film in the transition layer, while the WC / CeO2 ratio affects the interfacial bonding and compactness of the functional layer; the two ratios must be synergistically matched to achieve optimal overall performance.

[0192] 10. Interface combined with state analysis Metallographic microscopy observation of the sample from Example 19 revealed a uniform transition zone of approximately 8 μm at the interface between the inner layer and the substrate. This zone exhibited a gradual transition characteristic with the surrounding structures. Fracture observation after the bond strength test showed that fracture occurred within the coating rather than at the interface, indicating that the interfacial bond strength was higher than the coating's own strength. In contrast, the samples in the comparative examples that lacked good metallurgical bonding showed fractures primarily at the interface, with noticeable gaps visible in the interface region. 11. Description of the attached drawings Figure 1 This is a schematic diagram of the cross-sectional metallographic structure of the metallurgically bonded protective layer prepared in Example 19 of the present invention. The figure clearly shows a three-layer structure: the bottom is the substrate, the middle is the inner layer (NiCrAlY-Ce alloy layer), and the top is the outer layer (NiCr-WC-CeO2 composite layer). A uniform transition zone with a thickness of approximately 8 μm is visible at the interface between the inner layer and the substrate, and the microstructure in this region exhibits a gradual transition characteristic compared to the sides. The inner and outer layers are tightly bonded, with no obvious interface gaps.

[0194] Figure 2This is a bar chart comparing the bonding strength of the embodiments and comparative examples of the present invention. The data shows that the bonding strength of Example 19 is 88 MPa, that of Comparative Example 13 (arc-sprayed NiCr coating) is 38 MPa, that of Comparative Example 14 (plasma-sprayed WC-Co coating) is 45 MPa, and that of Comparative Example 15 (laser cladding NiCr-WC coating) is 92 MPa.

[0195] Figure 3 This is a bar chart comparing the porosity of the embodiments and comparative examples of the present invention. The data shows that the porosity of Example 19 is 0.5%, that of Comparative Example 13 is 8.2%, that of Comparative Example 14 is 3.5%, and that of Comparative Example 15 is 0.3%.

[0196] Figure 4 This is a bar chart comparing the wear track depths of the embodiments and comparative examples of the present invention. The data shows that the wear track depth in Example 19 is 8.5 μm, in Comparative Example 13 it is 32.5 μm, in Comparative Example 14 it is 15.8 μm, and in Comparative Example 15 it is 7.5 μm.

[0197] Figure 5 This is a bar chart comparing the number of thermal shocks in the embodiments and comparative examples of the present invention. The data shows that the number of thermal shocks in Embodiment 19 was 52, in Comparative Example 13 it was 12, in Comparative Example 14 it was 8, and in Comparative Example 15 it was 45.

[0198] Figure 6 This is a graph showing the effect of the induction remelting anolyte current on the coating bonding strength and porosity of the present invention. The graph shows that when the anolyte current increases from 1.2A to 2.5A, the bonding strength increases from 42MPa to 88MPa, while the porosity decreases from 8.0% to 0.5%; at an anolyte current of 3.2A, the bonding strength decreases to 75MPa; and at an anolyte current of 3.8A, the bonding strength decreases to 50MPa, while the porosity increases to 1.5%.

[0199] Figure 7 This is a graph showing the effect of induction remelting scanning speed on the coating bonding strength and porosity of this invention. The graph shows that when the scanning speed increases from 2.0 mm / s to 4.5 mm / s, the bonding strength increases from 65 MPa to 88 MPa, and the porosity decreases from 0.8% to 0.5%; at a scanning speed of 6.0 mm / s, the bonding strength decreases to 79 MPa, and the porosity increases to 1.2%; at a scanning speed of 8.0 mm / s, the bonding strength decreases to 50 MPa, and the porosity increases to 4.5%.

[0200] Figure 8 This is a graph showing the effect of the Al / Y ratio of the transition layer of this invention on the coating bond strength and thermal shock resistance. The graph shows that when the Al / Y ratio is in the range of 5-16, the bond strength remains at 60-72 MPa and the thermal shock resistance remains at 38-52 cycles; when the ratio exceeds this range, the performance decreases significantly.

[0201] Figure 9This is a graph showing the effect of the WC / CeO2 ratio of the functional layer of this invention on the coating bonding strength and porosity. The graph shows that when the WC / CeO2 ratio is in the range of 25-80, the bonding strength remains at 68-85 MPa and the porosity remains at 0.5%-1.2%; when the ratio exceeds the range, the performance decreases significantly.

[0202] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles 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 metallurgically bonded protective layer for power plant fluid machinery, characterized in that, The protective layer is a double-layer structure formed on the surface of the substrate, consisting of an inner layer and an outer layer: The inner layer is a metallurgical bonding transition layer, and its composition and mass percentage are: Cr: 18%-25%, Al: 6%-10%, Y: 0.3%-1.8%, rare earth elements: 0.1%-0.6%, and the balance is Ni; The outer layer is a wear-resistant and corrosion-resistant functional layer, and its composition and mass percentage are: WC particles: 30%-50%, rare earth oxides: 0.3%-2.0%, and the balance is NiCr alloy; The inner layer and the substrate, as well as the inner layer and the outer layer, are metallurgical bonding interfaces. The bonding strength of the protective layer is ≥70MPa.

2. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The mass ratio of Al to Y in the inner layer is 5-16.

3. The metallurgically bonded protective layer for power plant fluid machinery according to claim 2, characterized in that, The inner layer contains 7%-9% Al by mass and 0.6%-1.2% Y by mass.

4. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The mass ratio of WC particles to rare earth oxides in the outer layer is 25-80.

5. The metallurgically bonded protective layer for power plant fluid machinery according to claim 4, characterized in that, The outer layer contains WC particles composed of a mixture of micron-sized and nano-sized WC, with nano-sized WC accounting for 5%-15% of the total mass of the WC particles.

6. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The mass percentage of Cr in the NiCr alloy in the outer layer is 18%-22%.

7. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The rare earth oxide is at least one of CeO2 or La2O3, and its average particle size is 30nm-80nm.

8. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The thickness of the inner layer is 50μm-150μm, and the thickness of the outer layer is 200μm-400μm.

9. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The rare earth element in the inner layer is at least one of Ce or La.

10. The metallurgically bonded protective layer for power plant fluid machinery according to claim 1, characterized in that, The mass percentage of rare earth oxides in the outer layer of the functional layer is 0.8%-1.2%.

11. A method for preparing a metallurgically bonded protective layer for power plant fluid machinery as described in any one of claims 1 to 10, characterized in that, Includes the following steps: Step 1: Degrease, remove rust, and sandblast roughen the substrate surface to achieve a surface roughness of Ra5μm-8μm; Step 2: Using a supersonic flame spraying process, NiCrAlY rare earth element alloy powder is sprayed onto the pretreated substrate surface to form an inner layer with a thickness of 50μm-150μm. Step 3: Using a supersonic flame spraying process, NiCr-WC-rare earth oxide composite powder is sprayed onto the inner layer surface to form an outer layer with a thickness of 200μm-400μm, resulting in a double-layer pre-coated layer. Step 4: Perform high-frequency induction remelting on the double-layer pre-coated layer. Set the power frequency to 8kHz-25kHz, the anode current to 1.8A-3.2A, and the scanning speed to 3mm / s-6mm / s. By controlling the heat input, the coating heating temperature is made to reach and controlled at 750℃-900℃. Step 5: Under the protection of argon inert gas, maintain the protective atmosphere from the start of the remelting process until cooling to room temperature, and obtain a metallurgical bonded protective layer with a double-layer structure.

12. The preparation method according to claim 11, characterized in that, In step 2, the particle size of the NiCrAlY rare earth element alloy powder is 15μm-45μm, and in step 3, the particle size of the NiCr-WC rare earth oxide composite powder is 5μm-30μm.

13. The preparation method according to claim 11, characterized in that, The heating time for the high-frequency induction remelting process in step 4 is 15s-40s.

14. The preparation method according to claim 11, characterized in that, After the high-frequency induction remelting process in step 4, an element interdiffusion region is formed between the inner layer and the substrate through solid-state diffusion, and the thickness of the element interdiffusion region is 5μm-20μm.

15. The preparation method according to claim 11, characterized in that, The process parameters for supersonic flame spraying in step 2 are: kerosene flow rate 20L / h-25L / h, oxygen flow rate 800L / min-900L / min, spraying distance 200mm-300mm, and powder feeding rate 30g / min-50g / min.

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