High-durability composite spark plug electrode material and preparation method and application thereof

Abstract

This application discloses a high-durability composite spark plug electrode material, its preparation method, and its application. It belongs to the technical field of spark plug electrode material preparation. The electrode material of this invention consists of a core layer and a surface composite layer. The core layer is a dispersion-strengthened alloy with iridium as the matrix, doped with rare earth oxides and refractory metals, possessing high-temperature strength, creep resistance, and a short melting point. The surface composite layer is a gradient functional material, consisting of a transition layer, an intermediate functional layer, and a surface nanolayer from the inside out. This invention achieves a strong metallurgical bond and a smooth transition of performance between the core layer and the surface composite layer through the synergistic design of the core layer components, the optimization of the multi-layer gradient structure of the surface composite layer, and the use of a special preparation process. This significantly improves resistance to electrical erosion and chemical corrosion, reduces ignition voltage, ensures the ignition stability and durability of the engine under extreme operating conditions, improves combustion efficiency, and achieves increased power and reduced fuel consumption.

Description

Technical Field

[0001] This invention relates to the field of spark plug electrode material preparation technology, and more specifically to a high-durability composite spark plug electrode material, its preparation method, and its application. Background Technology

[0002] As a core component of the ignition system in gasoline and natural gas engines, the performance of spark plugs directly determines the engine's starting characteristics, power output, fuel economy, and emissions. The electrodes, as critical components of the spark plug, operate in extremely harsh environments: they must withstand instantaneous pulse voltages of tens of thousands of volts, periodic high-temperature combustion gas impacts exceeding 2000°C, and chemical corrosion from additives in fuel and lubricating oil (such as lead, sulfur, and phosphorus compounds). With modern engine technology evolving towards higher compression ratios, turbocharging, and lean combustion, even more stringent requirements are placed on the durability, ignition reliability, and lifespan of spark plugs.

[0003] To address this challenge, high-performance spark plugs commonly use precious metals such as platinum and iridium as electrode materials. Platinum electrodes offer excellent oxidation resistance and chemical corrosion resistance, but their relatively low melting point (approximately 1768°C) limits their resistance to electrolytic corrosion at high temperatures, making them susceptible to arc erosion and lifespan reduction under extreme conditions. Iridium electrodes, on the other hand, possess extremely high melting points (approximately 2454°C) and hardness, exhibiting superior resistance to electrolytic corrosion. However, their oxidation resistance is weaker at high temperatures, and they are more sensitive to certain specific chemical corrosions.

[0004] Existing technologies attempt to combine the advantages of different materials through composite structures. Common solutions include welding precious metal (such as platinum or iridium) tips onto nickel-based or ordinary alloy electrodes, or coating the electrode substrate with a single precious metal coating. However, these solutions have significant limitations: First, the weld interface is prone to becoming a structural weak point under long-term thermal cycling loads in the engine, leading to the failure of the precious metal tip; second, there is a mismatch in physical properties (such as the coefficient of thermal expansion) between the single surface coating and the substrate material, which is prone to cracking or even peeling under thermal stress, and its function is singular, unable to simultaneously meet multiple requirements such as resistance to electrolytic corrosion, corrosion resistance, and ignition promotion.

[0005] A deeper problem lies in the inherent defects of existing composite electrode materials in terms of material system design, interlayer structure optimization, and bonding methods:

[0006] Insufficient performance of core layer materials: Most solutions still use nickel-based alloys or single precious metals, whose high-temperature strength and creep resistance are insufficient to support the electrode to maintain geometric stability under long-term extreme heat loads, resulting in electrode deformation and gap changes, which affect ignition accuracy.

[0007] The surface functional layer design is simple: it is usually just a single layer of platinum or iridium coating, lacking a gradient design for different functional requirements such as interface bonding, host corrosion resistance, and surface catalysis, and cannot systematically solve the multi-mode failure problem of electrodes.

[0008] The interlayer bonding interface is fragile: the core layer and the surface layer are mostly mechanically bonded or simply metallurgically bonded, with a clear interface and obvious performance abrupt changes, which can easily become the source of failure under thermal shock and mechanical vibration.

[0009] Limited by the manufacturing process: It relies heavily on traditional processes such as welding and infiltration, making it difficult to achieve precise control of composition and microstructure, as well as strong metallurgical bonding between layers and smooth transition of properties.

[0010] Therefore, how to effectively solve the above problems and develop a new generation of spark plug electrode materials that combine ultra-long durability, excellent ignition stability and significant engine benefits is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0011] In view of this, the present invention develops a high-durability composite spark plug electrode material, its preparation method and application, overcoming the shortcomings of the prior art. Through the synergistic optimization design of the core layer and the surface composite layer, this material has excellent high-temperature strength, resistance to electro-erosion, resistance to chemical corrosion and stable low ignition voltage characteristics.

[0012] To solve the above-mentioned technical problems, this application adopts the following technical solution:

[0013] The primary objective of this application is to provide a high-durability composite spark plug electrode material, wherein the electrode material comprises a core layer and a surface composite layer covering the core layer.

[0014] The core layer is composed of the following components by mass percentage: iridium (Ir): 85.0%~92.0%, rare earth oxides: 3.0%~8.0%, refractory metals: 5.0%~10.0%, wherein the rare earth oxides are at least one of Y2O3 and La2O3, and the refractory metals are at least one of W and Re;

[0015] The surface composite layer is a gradient functional layer with continuously changing composition and structure from the inside to the outside, and includes at least:

[0016] The transition layer adjacent to the core layer is a Pt-Rh alloy, with an Rh content of 5%~15wt%.

[0017] The intermediate functional layer located outside the transition layer is a high-purity Pt or a Pt-Ir alloy with a Pt content greater than 95wt%.

[0018] The outermost surface nanolayer is a nanocrystalline Pt or Pt alloy coating with a grain size of 20~100 nanometers.

[0019] The high-durability composite spark plug electrode material of this invention adopts a composite structure of "strong core + gradient functional surface". This structure is not a simple double-layer superposition, but a carefully designed whole with gradient performance.

[0020] Core layer: As the carrier of the electrodes, its core functions are to provide structural support, conductivity, and high-temperature resistance. This invention abandons the use of a single precious metal or nickel-based alloy and innovatively designs an iridium-based dispersion-strengthened alloy.

[0021] Substrate selection: Iridium (Ir), with its extremely high melting point and excellent strength and hardness, is used as the substrate to ensure that the electrode does not deform or melt under extreme high temperatures.

[0022] Dispersion-strengthening phase: A specific ratio of rare earth oxides (such as Y₂O₃, La₂O₃) and refractory metals (such as W, Re) are uniformly dispersed in the iridium matrix. The rare earth oxide particles effectively pin grain boundaries, hindering grain growth and dislocation movement at high temperatures, significantly improving the material's recrystallization temperature and creep resistance. The solid solution of refractory metals W and Re further strengthens the iridium matrix. This synergistic effect of "rare earth oxide dispersion strengthening" and "refractory metal solid solution strengthening" allows the core layer to maintain good electrical conductivity while achieving unprecedented high-temperature mechanical properties, which cannot be achieved with a single material or simple alloy.

[0023] Surface composite layer: As a functional layer that comes into direct contact with the combustion environment, its design goal is to resist electrochemical corrosion, reduce ignition voltage, and achieve reliable bonding with the core layer. This invention breaks through the single-coating approach and designs a three-layer gradient functional surface composite layer.

[0024] Transition layer: In direct contact with the core layer, it is made of Pt-Rh alloy. The addition of Rh improves the high-temperature resistance of platinum, and its coefficient of thermal expansion is between that of the iridium-based alloy in the core layer and the outer platinum layer. It can effectively buffer the stress caused by thermal mismatch and achieve a strong metallurgical bond with the core layer.

[0025] Intermediate functional layer: Composed of high-purity Pt or a Pt-Ir alloy with high Pt content. Platinum has excellent resistance to oxidation and chemical corrosion, effectively resisting the erosion of harmful components in fuel. This layer is the primary corrosion barrier.

[0026] Surface nanolayer: The outermost layer is a nanocrystalline Pt or Pt alloy layer. Nanocrystalline materials have extremely high specific surface area and activity, which can significantly reduce the adsorption and ionization energy of gases, thereby effectively reducing the voltage required for ignition. At the same time, the dense nanostructure can further enhance corrosion resistance.

[0027] As a preferred technical solution, in the core layer, the particle size of the rare earth oxide is 0.5~2.0 micrometers, and it is uniformly dispersed in the iridium matrix.

[0028] As a preferred technical solution, the total thickness of the surface composite layer is 1 / 10 to 1 / 5 of the diameter or thickness of the core layer, wherein the thickness of the transition layer accounts for 20% to 30% of the total thickness of the surface composite layer, the thickness of the intermediate functional layer accounts for 50% to 60%, and the thickness of the surface nanolayer accounts for 10% to 20%.

[0029] As a preferred technical solution, the Pt alloy of the surface nanolayer is one of Pt-Ni alloy and Pt-Ru alloy, and the total content of alloying elements does not exceed 5wt%.

[0030] The ingenuity of this invention lies not only in the selection of materials for each layer, but also in the innovation of their combination method.

[0031] Thickness ratio optimization: The total thickness of the surface composite layer is kept in the optimal ratio (1 / 10~1 / 5) to the diameter / thickness of the core layer, which ensures sufficient thickness of the functional layers while avoiding internal stress problems and increased costs caused by excessively thick coatings. The thickness ratio of each sublayer has also been optimized to ensure the effective performance of its respective function.

[0032] Gradient transition: From the core layer to the outermost layer, the material composition (Ir -> PtRh -> Pt -> nano Pt) and properties (high strength -> high toughness / bonding -> high corrosion resistance -> high catalytic activity) are continuous and smoothly gradual, avoiding abrupt changes in performance, minimizing interfacial stress, and improving bonding reliability and thermal shock resistance.

[0033] Interface bonding enhancement: Through a specific preparation process (see below), a high-strength bond is achieved between layers, mainly through diffusion metallurgy. The interface is blurred, elements diffuse into each other, and the bonding strength is much higher than that of mechanical bonding or welding.

[0034] Another object of this application is to provide: a method for preparing the high-durability composite spark plug electrode material as described above, comprising the following steps:

[0035] S1: Core layer preparation: Iridium powder, rare earth oxide powder, and refractory metal powder are mixed by high-energy ball milling according to the formula to obtain a uniform composite powder; the composite powder is loaded into a mold and cold isostatically pressed to obtain a green blank; the green blank is placed in an inert atmosphere at 1800℃~2200℃ for pressure sintering to obtain a dense iridium-based alloy core layer blank.

[0036] S2: Core layer pretreatment: The sintered iridium-based alloy core layer blank is surface cleaned and machined to the predetermined size, then surface roughened by sandblasting, and ultrasonically cleaned and dried;

[0037] S3: Preparation of transition layer and intermediate functional layer: The transition layer and intermediate functional layer are prepared by sequentially spraying supersonic plasma spraying technology onto the surface of the pretreated core layer.

[0038] Preparation of transition layer: Using Pt-Rh alloy powder as the spraying material, by adjusting the plasma power and powder feeding rate, a metallurgically bonded Pt-Rh alloy transition layer is formed on the surface of the core layer.

[0039] Preparation of intermediate functional layer: On the transition layer, switch to high-purity Pt or Pt-Ir alloy powder and continue spraying to form a dense intermediate functional layer;

[0040] S4: Nanocrystalline surface treatment: Using pulsed electrodeposition technology, the electrode with transition layer and intermediate functional layer obtained in step S3 is used as the cathode. Electrodeposition is carried out in an electrolyte containing platinum salt. By controlling the pulse current density, frequency and duty cycle, a surface nanolayer with nanocrystalline structure is deposited on the outermost layer.

[0041] S5: Post-treatment: The deposited electrode material is annealed at 800℃~1000℃ in a vacuum or inert atmosphere to eliminate internal stress and promote further diffusion of interlayer elements, thereby strengthening the bonding force.

[0042] As a preferred technical solution, in step S1, the ball-to-material ratio of the high-energy ball mill is 10:1, the rotation speed is 300~400rpm, and the time is 4~8h; the pressure of the pressure sintering is 30~50MPa, and the pressure sintering time is 2~4h.

[0043] As a preferred technical solution, in step S3, the parameters for supersonic plasma spraying are: plasma power of 40~60kW, spraying distance of 100~150mm, powder feeding rate of 30~50g / min, and protective gas of a mixture of argon and hydrogen.

[0044] As a preferred technical solution, in step S4, the parameters of pulse electrodeposition are: average current density of 0.5~2.0A / dm², pulse frequency of 100~1000 Hz, duty cycle of 10%~30%, and electrolyte temperature of 50℃~70℃.

[0045] This invention employs a unique composite preparation process, which has the following technical effects:

[0046] Core layer preparation: A powder metallurgy method combining high-energy ball milling and pressure sintering was employed. High-energy ball milling ensures atomic-level uniform mixing of all component powders (especially nano / submicron rare earth oxides). Pressure sintering, performed at temperatures far below the melting point of iridium, achieves densification, preventing excessive grain growth and ensuring effective dispersion strengthening.

[0047] Surface composite layer preparation: A combination of supersonic plasma spraying and pulsed electrodeposition techniques is used.

[0048] Plasma spraying can generate extremely high temperatures, causing Pt-Rh and Pt powders to melt and impact the core layer surface at high speed, forming a dense and metallurgically bonded transition layer and intermediate functional layer.

[0049] Pulse electrodeposition, by precisely controlling the electrocrystallization process, can obtain a dense, fine-grained nanocrystalline surface layer on an already formed, flat surface. Compared to conventional electroplating, this method offers better adhesion and higher coating quality.

[0050] Post-processing: The final vacuum annealing is a crucial step. It not only eliminates the internal stress generated during the preparation process, but also promotes the further interdiffusion of interlayer elements, making the interface more blurred, the bonding stronger, and forming a whole with a smoother performance transition.

[0051] Another object of this application is to provide a spark plug in which the center electrode and / or side electrode are made of the above-described high-durability composite spark plug electrode material or a high-durability composite spark plug electrode material prepared by the above-described method.

[0052] Another object of this application is to provide the application of the spark plug in a gasoline engine, a natural gas engine or an aircraft engine, wherein the application of the spark plug can reduce the ignition voltage, improve the ignition stability and durability under extreme operating conditions, and help improve combustion efficiency.

[0053] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) Non-obviousness of material composition: The use of dispersion-strengthened iridium-based alloys in the spark plug core layer, and the synergistic strengthening mechanism of rare earth oxides and refractory metals, solves the problem of insufficient high-temperature strength of single noble metals, which is the first of its kind in this field. The surface layer adopts a multi-layer gradient functional design, especially the outermost nanocrystalline catalytic layer, which creatively applies the cutting-edge concepts of materials science (nanotechnology, gradient functional materials) to solve the specific failure problem of spark plug electrodes. The technical means exceed the conventional understanding of those skilled in the art.

[0055] (2) Optimization and Synergistic Effect of Structural Combination: This invention is not a simple stacking of materials, but rather achieves optimal matching and performance synergy between the "strong and tough core" and the "functional surface" through transition layer design, thickness ratio control, and gradient composition variation. The core layer ensures overall strength and stability, while the gradient surface layers address the three major challenges of bonding, corrosion, and ignition. This systematic structural optimization brings about a "1+1>2" effect, with overall performance far exceeding the simple superposition of the performance of each layer.

[0056] (3) Excellent overall performance:

[0057] Extremely high durability: The high-temperature creep resistance of the core layer prevents electrode deformation; the excellent corrosion resistance of the surface layer extends lifespan; and the robust gradient bonding interface prevents interlayer peeling. Combined, these features result in spark plug lifespan more than twice that of ordinary platinum spark plugs.

[0058] Excellent ignition performance: The nanocrystalline surface layer effectively reduces the ignition voltage (by 15%-20%), improving ignition reliability, especially under cold start and lean combustion conditions.

[0059] Engine benefits: Stable ignition and lower voltage requirements help improve combustion efficiency, thereby achieving a slight increase in engine power and a reduction in fuel consumption.

[0060] (4) Innovation of the preparation process: The three processes of powder metallurgy, thermal spraying and pulse electrodeposition are organically combined to successfully prepare composite electrode materials with complex gradient structures. The process route is ingeniously designed and solves the problem of forming high-performance materials.

[0061] In summary, this invention represents a comprehensive innovation in material selection, structural design, and manufacturing process. Its technical solution is not a simple improvement on existing technologies, but rather brings unexpected technical effects. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example

[0063] S1. Core Layer Preparation: Iridium powder (91wt%) with an average particle size of 5μm, Y2O3 powder (4wt%) with an average particle size of 1μm, and tungsten powder (5wt%) with an average particle size of 3μm were taken. The three were mixed in a specific ratio and placed in a high-energy ball mill. Alcohol was used as the medium, the ball-to-powder ratio was 10:1, and the milling speed was 350 rpm for 6 hours. The slurry was removed, dried, and sieved. It was then placed into a rubber mold and cold isostatically pressed (200 MPa pressure) to form the core layer. The green blank was placed in a vacuum hot-pressing sintering furnace and sintered at 1950℃ and 40 MPa pressure under argon protection for 3 hours. After furnace cooling, a dense iridium-based alloy rod was obtained, which was then wire-cut into cylinders with a diameter of 1.0 mm as the core layer blank.

[0064] S2. Core layer pretreatment: The core layer blank is subjected to surface sandblasting (using 100-mesh corundum sand), then ultrasonically cleaned with acetone and alcohol for 15 minutes each, and dried.

[0065] S3. Preparation of transition and intermediate layers:

[0066] Transition layer spraying: Using Pt-Rh alloy powder (particle size 15-45μm) with Rh content of 10wt%, supersonic plasma spraying equipment is used with the following parameters: power 45kW, main gas Ar flow rate 50SLPM, auxiliary gas H2 flow rate 10SLPM, spraying distance 120mm, powder feeding rate 40g / min, to form a transition layer with a thickness of about 20μm on the surface of the core layer.

[0067] Spraying the intermediate functional layer: Immediately switch to high-purity Pt powder (particle size 15-45μm), keep other parameters basically unchanged, and continue spraying on the transition layer to form a dense intermediate functional layer with a thickness of about 60μm.

[0068] S4. Electrodeposition of surface nanolayer: The above workpiece is used as the cathode and placed in a platinum sulfamate electrolyte at a temperature of 60°C. A pulse power supply is used with an average current density of 1.0 A / dm², a pulse frequency of 500 Hz, and a duty cycle of 20%. Electrodeposition is carried out for 30 minutes to obtain a nanocrystalline platinum layer with a thickness of about 20 μm and a grain size of about 50 nm on the outermost layer, i.e., the surface nanolayer.

[0069] S5. Post-processing: The workpiece is annealed in a vacuum furnace at 900℃ for 1 hour and then cooled in the furnace to finally obtain a composite electrode material with a total diameter of about 1.2 mm. Example

[0070] S1. Core Layer Preparation: Iridium powder (85wt%) with an average particle size of 5μm, Y₂O₃ powder (5wt%) with an average particle size of 1μm, and tungsten powder (10wt%) with an average particle size of 3μm were mixed in a specific ratio and placed in a high-energy ball mill. Alcohol was used as the medium, the ball-to-particle ratio was 10:1, and the milling speed was 330 rpm for 4 hours. The slurry was removed, dried, sieved, and then placed into a rubber mold for cold isostatic pressing (200 MPa). The green blank was placed in a vacuum hot-pressing sintering furnace and sintered at 1800℃ and 30 MPa under argon protection for 2 hours. After furnace cooling, a dense iridium-based alloy rod was obtained, which was then wire-cut into cylinders with a diameter of 1.0 mm as the core layer blank.

[0071] S2. Core layer pretreatment: The core layer blank is subjected to surface sandblasting (using 100-mesh corundum sand), then ultrasonically cleaned with acetone and alcohol for 15 minutes each, and dried.

[0072] S3. Preparation of transition and intermediate layers:

[0073] Transition layer spraying: Using Pt-Rh alloy powder (particle size 15-45μm) with Rh content of 5wt%, supersonic plasma spraying equipment is used with the following parameters: power 40kW, main gas Ar flow rate 50SLPM, auxiliary gas H2 flow rate 10SLPM, spraying distance 100mm, powder feeding rate 30g / min, to form a transition layer with a thickness of about 30μm on the surface of the core layer.

[0074] Spraying intermediate functional layer: Immediately switch to Pt-Ir alloy powder (particle size 15-45μm), keep other parameters basically unchanged, and continue to spray on the transition layer to form a dense intermediate functional layer with a thickness of about 50μm.

[0075] S4. Electrodeposition of surface nanolayer: The above workpiece is used as the cathode and placed in a platinum sulfamate electrolyte at a temperature of 50°C. A pulse power supply is used with an average current density of 0.5 A / dm², a pulse frequency of 100 Hz, and a duty cycle of 10%. Electrodeposition is carried out for 30 minutes to obtain a nanocrystalline platinum layer with a thickness of about 20 μm and a grain size of about 25 nm on the outermost layer, i.e., the surface nanolayer.

[0076] S5. Post-processing: The workpiece is annealed in a vacuum furnace at 800℃ for 1 hour and then cooled in the furnace to finally obtain a composite electrode material with a total diameter of about 1.2 mm. Example

[0077] S1. Core Layer Preparation: Iridium powder (90wt%) with an average particle size of 5μm, Y₂O₃ powder (5wt%) with an average particle size of 1μm, and tungsten powder (5wt%) with an average particle size of 3μm were mixed in a specific ratio and placed in a high-energy ball mill. Alcohol was used as the medium, the ball-to-particle ratio was 10:1, and the milling speed was 400 rpm for 8 hours. The slurry was removed, dried, sieved, and then placed into a rubber mold for cold isostatic pressing (200 MPa). The green blank was placed in a vacuum hot-pressing sintering furnace and sintered at 2200℃ and 50 MPa under argon protection for 4 hours. After furnace cooling, a dense iridium-based alloy rod was obtained, which was then wire-cut into cylinders with a diameter of 1.0 mm as the core layer blank.

[0078] S2. Core layer pretreatment: The core layer blank is subjected to surface sandblasting (using 100-mesh corundum sand), then ultrasonically cleaned with acetone and alcohol for 15 minutes each, and dried.

[0079] S3. Preparation of transition and intermediate layers:

[0080] Transition layer spraying: Using Pt-Rh alloy powder (particle size 15-45μm) with Rh content of 15wt%, supersonic plasma spraying equipment is used with the following parameters: power 60kW, main gas Ar flow rate 50SLPM, auxiliary gas H2 flow rate 10SLPM, spraying distance 150mm, powder feeding rate 50g / min, a transition layer with a thickness of about 25μm is formed on the surface of the core layer.

[0081] Spraying the intermediate functional layer: Immediately switch to high-purity Pt powder (particle size 15-45μm), keep other parameters basically unchanged, and continue spraying on the transition layer to form a dense intermediate functional layer with a thickness of about 55μm.

[0082] S4. Electrodeposition of surface nanolayer: The above workpiece is used as the cathode and placed in a chloroplatinic acid electrolyte with nickel sulfate added at a temperature of 70°C. A pulse power supply is used with an average current density of 2.0 A / dm², a pulse frequency of 1000 Hz, and a duty cycle of 30%. Electrodeposition is carried out for 30 minutes to obtain a nanocrystalline platinum layer with a thickness of about 20 μm and a grain size of about 100 nm on the outermost layer, i.e., the surface nanolayer.

[0083] S5. Post-processing: The workpiece is annealed in a vacuum furnace at 1000℃ for 1 hour and then cooled in the furnace to finally obtain a composite electrode material with a total diameter of about 1.2 mm. Example

[0084] S1. Core layer preparation: The composition was adjusted to Ir 88wt%, La2O3 5wt%, Re 7wt%, and the preparation process was the same as in Example 1. Finally, it was processed into a sheet-like core layer blank with a thickness of 0.8mm.

[0085] S2. Core layer preprocessing: Same as in Example 1.

[0086] S3. Preparation of transition layer and intermediate layer: The transition layer uses Pt-Rh alloy powder (Rh content is 8wt%), with a spraying thickness of about 20μm; the intermediate functional layer uses Pt-Ir alloy powder (Ir content is 3wt%), with a spraying thickness of about 60μm.

[0087] S4. Electrodeposition of surface nanolayer: Parameters are the same as in Example 1, deposition time is 20 minutes, and a surface nanolayer with a thickness of about 20 μm is obtained.

[0088] S5. Post-processing: Same as in Example 1.

[0089] The electrode is made of pure iridium (99.9% purity) with a diameter of 1.0 mm.

[0090] It uses a commercially available high-performance platinum spark plug (its center electrode is a nickel-based alloy welded platinum tip).

[0091] The electrode materials of Examples 1-4 and Comparative Example 1 were made into standard samples and tested on a self-made electro-erosion test bench. The spark plug discharge conditions (discharge voltage 30kV, frequency 100Hz, ambient temperature 800℃) were simulated and the test was conducted continuously for 100h. The results are shown in Table 1.

[0092] Table 1. High-temperature electrolytic corrosion results for different groups

[0093]

[0094] Results Analysis: The extremely harsh working environment of spark plugs was simulated to test the materials' resistance to electrical erosion. As shown in Table 1, the diameter loss of Examples 1-4 was less than 1 / 5 of that of Comparative Example 1, proving that their resistance to electrical erosion was significantly superior and their durability greatly improved. Comparative Example 1 suffered severe surface damage, while the gradient composite structure of Examples 1-4 effectively resisted arc erosion, with the core functional layer remaining intact, demonstrating excellent damage tolerance.

[0095] Spark plugs made with the materials of Examples 1-4 (invention group) and commercial platinum spark plugs of Comparative Example 2 (control group) were installed on the same model of 1.5L turbocharged gasoline engine for durability bench testing. Test conditions included high speed and high load, idling, and hot / cold cycles, with a cumulative running time of 1000 hours. Ignition voltage and misfire rate were recorded during the test, and electrode gap wear was measured after the test. The experimental results are shown in Table 2.

[0096] Table 2. Durability test results of spark plugs prepared from different groups

[0097]

[0098] Results analysis:

[0099] The initial ignition voltage of all the spark plugs of the present invention (Examples 1-4) was significantly lower than that of Comparative Example 2 (16.5 kV). This directly demonstrates the effectiveness of the electrode material of the present invention, especially its surface nanocrystalline layer, in reducing ignition voltage, which is beneficial for engine cold starts and energy saving.

[0100] Durability advantage: After 1000 hours of rigorous testing, the ignition voltage of Comparative Example 2 increased by 1.7 kV (from 16.5 kV to 18.2 kV), an increase of approximately 10.3%. In contrast, the voltage increase in each embodiment of the present invention is minimal (Example 1 increased by only 0.9 kV, an increase of approximately 6.2%).

[0101] An increase in ignition voltage typically stems from electrode corrosion, increased gap due to wear, and deterioration of surface condition. The significant voltage increase in Comparative Example 2 indicates severe electrode wear. The superior stability of the electrode voltage in this invention is attributed to the robust iridium alloy core layer providing structural support, and the excellent resistance to electrolytic and chemical corrosion of the gradient functional surface layer, effectively maintaining the stability of the electrode gap and surface morphology.

[0102] The electrode gap wear in Comparative Example 2 was as high as 0.25 mm, while the wear in all embodiments of this invention was controlled below 0.09 mm, less than 36% of that in Comparative Example 2. Electrode gap wear is a key indicator determining spark plug life. A wear of 0.25 mm usually exceeds the allowable limit, requiring spark plug replacement. The extremely low wear of this invention directly translates into an ultra-long service life. This is mainly attributed to: Core layer: a high-melting-point, high-strength iridium-based dispersion-reinforced alloy, resisting electrolytic corrosion and deformation at high temperatures; Surface composite layer: the protection of a platinum-rhodium alloy transition layer and a platinum intermediate layer, delaying the wear of the core material.

[0103] To quantitatively evaluate the improvement effect of the spark plug of this invention on the actual engine performance, comparative example 2 (commercial platinum spark plug) and the example (spark plug of the composite electrode material of this invention) were installed on the same 1.5L turbocharged gasoline engine that meets the China VI emission standard. Standardized external characteristic tests and universal characteristic tests were performed on the engine bench. The test environment temperature was controlled at 25±2℃, and the same batch of commercially available 95-octane gasoline was used.

[0104] The test results are as follows:

[0105] (1) External characteristic test results (full load performance):

[0106] Under full engine load (100% throttle opening), from idle to rated speed, the engine equipped with spark plugs made from the electrode material of Example 1 showed increased output torque across the entire speed range. At the commonly used maximum torque point of 3000 rpm, the torque value increased from 250.5 N·m in Comparative Example 2 to 254.3 N·m, an absolute increase of 3.8 N·m and a relative increase of approximately 1.53%. This indicates that more stable ignition helps the combustion process complete closer to top dead center, releasing more effective work. Meanwhile, the engines equipped with spark plugs made from the electrode materials of Examples 2, 3, and 4 also showed better torque values ​​at the commonly used maximum torque point of 3000 rpm, at 253.9 N·m, 254.2 N·m, and 254.0 N·m, respectively, compared to Comparative Example 2.

[0107] (2) Universal characteristic test results (economic efficiency under all operating conditions):

[0108] In universal characteristic tests covering all commonly used engine speeds and loads, the spark plug of Example 1 exhibited a more significant economic advantage: in the engine's most frequently used operating range (2000-4000 rpm, average effective pressure 0.4-0.8 MPa), the average effective fuel consumption rate (BSFC) of the engine equipped with the spark plug of Example 1 was 235.5 g / kWh, a reduction of 5.1 g / kWh compared to the average of 240.6 g / kWh in Comparative Example 2, representing a decrease of approximately 2.1%. This means that lower fuel consumption can be achieved in daily driving. Meanwhile, the spark plugs prepared with electrode materials of Examples 2, 3, and 4 also showed better average effective fuel consumption rates (BSFC) than Comparative Example 2, with average values ​​of 235.5 g / kWh, 235.8 g / kWh, and 235.6 g / kWh, respectively.

[0109] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0110] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-durability composite spark plug electrode material, characterized in that, The electrode material consists of a core layer and a surface composite layer covering the core layer. The core layer is composed of the following components by mass percentage: iridium (Ir): 85.0%~92.0%, rare earth oxides: 3.0%~8.0%, refractory metals: 5.0%~10.0%, wherein the rare earth oxides are at least one of Y2O3 and La2O3, and the refractory metals are at least one of W and Re; In the core layer, the rare earth oxides have a particle size of 0.5 to 2.0 micrometers and are uniformly dispersed in the iridium matrix; The surface composite layer is a gradient functional layer with continuously changing composition and structure from the inside to the outside, and includes at least: The transition layer adjacent to the core layer is a Pt-Rh alloy, with an Rh content of 5%~15wt%. The intermediate functional layer located outside the transition layer is a high-purity Pt or a Pt-Ir alloy with a Pt content greater than 95wt%. The coefficient of thermal expansion of the transition layer is between that of the core layer and the outer platinum layer; The outermost surface nanolayer is a nanocrystalline Pt or Pt alloy coating with a grain size of 20~100 nanometers. The surface nanolayer is used to reduce the voltage required for ignition.

2. The high-durability composite spark plug electrode material according to claim 1, characterized in that, in, The total thickness of the surface composite layer is 1 / 10 to 1 / 5 of the diameter or thickness of the core layer, the thickness of the transition layer accounts for 20% to 30% of the total thickness of the surface composite layer, the thickness of the intermediate functional layer accounts for 50% to 60%, and the thickness of the surface nanolayer accounts for 10% to 20%.

3. The high-durability composite spark plug electrode material according to claim 1, characterized in that, The Pt alloy of the surface nanolayer is one of Pt-Ni alloy and Pt-Ru alloy, and the total content of alloying elements does not exceed 5wt%.

4. A method for preparing the high-durability composite spark plug electrode material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Core layer preparation: Iridium powder, rare earth oxide powder, and refractory metal powder are mixed by high-energy ball milling according to the formula to obtain a uniform composite powder; the composite powder is loaded into a mold and cold isostatically pressed to obtain a green blank; the green blank is placed in an inert atmosphere at 1800℃~2200℃ for pressure sintering to obtain a dense iridium-based alloy core layer blank. S2: Core layer pretreatment: The sintered iridium-based alloy core layer blank is surface cleaned and machined to the predetermined size, then surface roughened by sandblasting, and ultrasonically cleaned and dried; S3: Preparation of transition layer and intermediate functional layer: The transition layer and intermediate functional layer are prepared by sequentially spraying supersonic plasma spraying technology onto the surface of the pretreated core layer. Preparation of transition layer: Using Pt-Rh alloy powder as the spraying material, by adjusting the plasma power and powder feeding rate, a metallurgically bonded Pt-Rh alloy transition layer is formed on the surface of the core layer. Preparation of intermediate functional layer: On the transition layer, switch to high-purity Pt or Pt-Ir alloy powder and continue spraying to form a dense intermediate functional layer; S4: Nanocrystalline surface treatment: Using pulsed electrodeposition technology, the electrode with transition layer and intermediate functional layer obtained in step S3 is used as the cathode. Electrodeposition is carried out in an electrolyte containing platinum salt. By controlling the pulse current density, frequency and duty cycle, a surface nanolayer with nanocrystalline structure is deposited on the outermost layer. S5: Post-treatment: The deposited electrode material is annealed at 800℃~1000℃ in a vacuum or inert atmosphere to eliminate internal stress and promote further diffusion of interlayer elements, thereby strengthening the bonding force.

5. The method according to claim 4, characterized in that, In step S1, the ball-to-material ratio of the high-energy ball mill is 10:1, the rotation speed is 300~400 rpm, and the time is 4~8 h; the pressure of the pressure sintering is 30~50 MPa, and the pressure sintering time is 2~4 h.

6. The method according to claim 4, characterized in that, In step S3, the parameters for supersonic plasma spraying are: plasma power of 40~60kW, spraying distance of 100~150mm, powder feeding rate of 30~50g / min, and protective gas of a mixture of argon and hydrogen.

7. The method according to claim 4, characterized in that, In step S4, the parameters for pulse electrodeposition are: average current density of 0.5~2.0 A / dm², pulse frequency of 100~1000 Hz, duty cycle of 10%~30%, and electrolyte temperature of 50℃~70℃.

8. A spark plug, characterized in that, Its center electrode and / or side electrode are made of the high-durability composite spark plug electrode material as described in any one of claims 1-3 or the high-durability composite spark plug electrode material prepared by the method as described in any one of claims 5-7.

9. The application of the spark plug according to claim 8 in a gasoline engine, a natural gas engine, or an aircraft engine, characterized in that, Using this spark plug can reduce ignition voltage, improve ignition stability and durability under extreme conditions, and help improve combustion efficiency.

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