Metal connector material suitable for SOFC (Solid Oxide Fuel Cell) electric pile and preparation method of metal connector material

Abstract

The invention discloses a metal connector material suitable for an SOFC (Solid Oxide Fuel Cell) electric pile and a preparation method of the metal connector material, and belongs to the technical field of solid oxide fuel cells. The metal connector material suitable for the SOFC electric pile takes Fe-Cr ferrite alloy as a matrix and comprises the following components in percentage by mass: 20%-30% of Cr, 2%-5% of Al, 0.5%-2.0% of Mn, 0.1%-1.0% of Ti, 0.05%-0.5% of rare earth elements and the balance of Fe and inevitable impurities. The metal connector material suitable for the SOFC electric pile has excellent oxidation resistance, conductivity and thermal expansion matching performance in a high-temperature oxidation environment of 600-1000 DEG C, and is suitable for being used as an interconnection component of the SOFC electric pile.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid oxide fuel cell, and particularly relates to a metal connector material suitable for SOFC stack and a preparation method thereof. BACKGROUND

[0002] Solid oxide fuel cell (SOFC) is a kind of high-efficiency and low-emission electrochemical power generation device, and its operating temperature is usually 600-1000℃. In the flat-plate SOFC, the anode, the electrolyte and the cathode are stacked to form a single cell, and the single cells are connected by the connector to form a multi-layer stack, and finally the glass seal is used to prevent the leakage of the gas in the system, so as to realize high power. The connector of the flat-plate SOFC is usually made of metal material (the resistance is lower and the strength is higher than that of ceramic), but there is also a ceramic connector.

[0003] The metal connector is responsible for electrically connecting the single cells, separating the fuel gas and the oxidant gas, and bearing the thermal cycle and the mechanical load in the SOFC stack. The ideal connector material needs to have high-temperature oxidation resistance, low surface resistance, matched coefficient of thermal expansion (CTE) with the ceramic electrolyte (such as yttria-stabilized zirconia ceramic, YSZ, CTE≈10.5×10 -6 K -1 6 / ℃) and long-term stability.

[0004] At present, the Fe-Cr-based ferritic stainless steel (such as Crofer 22 APU) is widely used in the field of connector due to its low cost and good oxidation resistance. However, it has the following defects: (1) Cr volatilization: the Cr2O3 oxidation layer is decomposed to generate CrO3 or CrO2(OH)2 at high temperature, and the volatilization rate is about 0.05g / m 2 ·h~0.1g / m 2 ·h, which will pollute the cathode (such as LaMnO3 cathode material, LSM) and reduce the catalytic activity.

[0005] (2) Resistance increase: the Cr2O3 has poor conductivity, and the surface resistance increases to 50mΩ·cm 2 ~70mΩ·cm 2 after 1000 hours, thereby reducing the efficiency of the stack.

[0006] (3) CTE mismatch: the CTE of the traditional Fe-Cr alloy is 13×10 -6 K -1 ~14×10 -6 K -1 , which is quite different from that of YSZ, and will cause thermal stress concentration and interface peeling.

[0007] Although the existing improved methods (such as adding Al or surface coating) have achieved some results, the excessive Al content will reduce the electrical conductivity, the surface coating process is complex and easy to peel off, and it is difficult to balance the performance and cost. SUMMARY

[0008] The purpose of the present application is to provide a metal connector material suitable for SOFC stacks and a preparation method thereof, which can solve the technical problems of the existing Fe-Cr-based connector materials, such as serious Cr volatilization at high temperature, surface resistance increase, and thermal expansion coefficient mismatch with ceramic components.

[0009] To achieve the above purpose, the present application provides a metal connector material suitable for SOFC stacks, which comprises the following mass percentage components: Cr 20%~30%, Al 2%~5%, Mn 0.5%~2.0%, Ti 0.1%~1.0%, rare earth elements 0.05%~0.5%, and the balance of Fe and impurities. Among them, the rare earth elements are La and / or Y, and the total content of impurities is <0.05%.

[0010] Further, it comprises the following mass percentage components: Cr 25%~28%, Al 3%~4%, Mn 1.0%~1.5%, Ti 0.5%~0.8%, rare earth elements 0.1%~0.3%, and the balance of Fe and unavoidable impurities.

[0011] The present application also provides a preparation method of a metal connector material suitable for SOFC stacks, which comprises the following steps: After mixing the components by mass percentage, sequentially perform cleaning treatment, drying treatment and vacuum induction melting treatment to obtain a melt; Pour the melt into a mold preheated to a target temperature for casting, and then cool to obtain an alloy ingot; Sequentially perform heat treatment and forming treatment on the alloy ingot, and the metal connector material suitable for SOFC stacks is obtained. Among them, the forming treatment is rolling treatment or powder metallurgy treatment.

[0012] Further, the solvent for ultrasonic cleaning is ethanol, the drying temperature is 70°C~90°C, and the drying time is 1h~3h.

[0013] Further, the parameters of the vacuum induction melting include: The vacuum degree is 10 -4 Pa~10 -3 Pa, the melting temperature is 1500°C~1600°C, the melting power is 20kW~30kW, the holding time is 30min~60min, and the stirring frequency is 45Hz~60Hz.

[0014] Further, the vacuum induction melting process is performed by introducing argon gas at a rate of 0.1L / min to 0.2L / min.

[0015] Further, the target temperature is 300℃ to 500℃, the cooling rate is 5℃ / s to 10℃ / s, and the cooling time is 120s to 240s.

[0016] Further, the heat treatment process comprises: placing the alloy ingot in a tube furnace, heating to 900℃ to 1100℃ in an argon atmosphere, annealing for 2h to 4h, cooling at a rate of 1℃ / min to 3℃ / min, and cooling for 120s to 240s. The oxygen content in the argon atmosphere is less than 10ppm.

[0017] Further, the rolling process comprises hot rolling and cold rolling, wherein the hot rolling temperature is 800℃ to 1000℃, and the cold rolling temperature is room temperature; and the thickness of the material after the rolling process is 0.5mm to 2.0mm.

[0018] Further, the powder metallurgy process specifically comprises: atomizing the powder to a particle size of 20μm to 50μm, then pressing and forming under a pressure of 9.0MPa to 11.0MPa, and then sintering and forming at a temperature of 1200℃ to 1400℃.

[0019] In summary, the present application has the following advantages: The present application provides a material that can replace traditional Crofer 22APU, has strong oxidation resistance, excellent electrical conductivity, and a matching thermal expansion coefficient, takes Fe-Cr ferrite alloy as a matrix, reduces Cr volatilization and ion conduction through an Al2O3 protective layer, and is supplemented by rare earth elements to optimize electrical conductivity and stability, so that the CTE of the connector is closer to YSZ, and the comprehensive performance is significantly improved, thereby solving the technical problems of Fe-Cr-based connector materials in the prior art, such as serious Cr volatilization at high temperatures, increased surface resistance, and mismatched thermal expansion coefficient with ceramic components. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A comparison chart of the oxidation resistance performance of the metal connector material prepared in the embodiment of the present application and a conventional Fe-Cr alloy suitable for SOFC stacks; Figure 2 A graph of the thermal expansion coefficient of the metal connector material prepared in the embodiment of the present application and YSZ and Crofer 22APU as a function of temperature suitable for SOFC stacks; Figure 3 A comparison chart of the ion conductivity of the metal connector material prepared in the embodiment of the present application and YSZ and Crofer 22APU suitable for SOFC stacks. DETAILED DESCRIPTION

[0021] The principles and features of the present application are described below in connection with embodiments, which are presented only for illustrative purposes and not for limiting the scope of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturers. The reagents or instruments not mentioned by the manufacturers are all conventional products that can be obtained by commercial purchase.

[0022] In a first aspect, the present application provides a metal connector material for SOFC stack, comprising the following mass percentage components: Cr 20%~30%, Al 2%~5%, Mn 0.5%~2.0%, Ti 0.1%~1.0%, rare earth elements 0.05%~0.5%, and the balance of Fe and impurities. Wherein the rare earth elements are La and / or Y, and the total content of impurities is <0.05%.

[0023] In the metal connector material of the present application, Cr can form a Cr2O3 oxidation layer at high temperature to provide oxidation protection; the formation of Al2O3 can enhance the oxidation resistance, especially to form a continuous protective layer under the Cr2O3 layer; the addition of Mn can help the system to form a spinel structure, improving the electrical conductivity of the connector; Ti is usually used as a stabilizer, which plays a role in refining the grain size and improving the strength of the connector material; rare earth elements such as La or Y are usually used to improve the adhesion of the oxidation layer and refine the grain size. In addition to their respective roles, Cr and Al also have a synergistic effect to form a double-layer oxidation layer, with Cr2O3 as the outer layer and Al2O3 as the inner layer, which protects the substrate and reduces the growth rate of the oxidation layer. The addition of rare earth elements can prevent the volatilization of Cr by pinning the grain boundaries, while also playing a role in refining the grain size with Ti, further improving the mechanical properties of the material. Mn forms a conductive spinel structure with Cr, which can reduce the contact resistance. In addition, impurity control is also important for the present application, and a total content of less than 0.05% can reduce the formation of harmful phases, such as sulfur and phosphorus impurities, which can reduce the toughness and high-temperature performance of the material. The formula in the present application file optimizes the high-temperature oxidation resistance, electrical conductivity, thermal expansion matching, and mechanical strength of the connector material through the synergy of multiple elements, while controlling impurities to improve the stability of the material. The roles of the elements are complementary, forming a multi-level protection mechanism, which is especially suitable for the harsh working environment of SOFC stacks.

[0024] Specifically, the metal connector material of the present application file takes Fe-Cr ferrite alloy as the matrix, Cr forms Cr2O3 to provide basic oxidation resistance; Al generates dense Al2O3 layer (thickness 1 μm~2 μm) to inhibit oxygen diffusion in cooperation with Cr2O3; Mn promotes the formation of MnCr2O4 spinel to reduce the Cr evaporation rate to about 60%~80%; Ti refines the grain (20 μm~30 μm) to enhance the adhesion of the oxidation layer; La / Y inhibits the growth of the oxidation layer through grain boundary segregation to improve the electrical conductivity and stability of the connector material. Compared with the traditional ferrite Crofer 22 APU high-temperature alloy, the present application reduces Cr evaporation and ion conduction through the Al2O3 protective layer, forms a unique structure of Al2O3 and MnCr2O4 composite oxidation layer, and improves the electrical conductivity and stability through rare earth elements, so that the CTE is closer to YSZ, and the comprehensive performance is significantly improved. Unlike the prior art, the Al content is lower than that of the traditional high Al alloy, endogenous Al2O3 is formed, and Cr evaporation is inhibited in cooperation with MnCr2O4 (reduced by 60%~80%), balancing the oxidation resistance and electrical conductivity; at the same time, multiple elements are used in cooperation, Ti is used to refine the grain, and La / Y is used to improve the stability. Finally, the metal connector material suitable for SOFC stack provided by the present application has a thermal expansion coefficient of 11×10 -6 K -1 ~12×10 -6 K -1 , and an ion conductivity of 10 -15 S / cm.

[0025] In some optional embodiments of the present application, the metal connector material suitable for SOFC stack includes the following mass percentage components: Cr 25%~28%, Al 3%~4%, Mn 1.0%~1.5%, Ti 0.5%~0.8%, rare earth elements 0.1%~0.3%, and the balance of Fe and unavoidable impurities.

[0026] In the most preferred embodiment of the present application, the metal connector material for SOFC stack comprises the following mass percentage components: Cr 25%, Al 3%, Mn 1.0%, Ti 0.5%, La 0.1%, and the balance of Fe and inevitable impurities. Under this proportion, a Cr-Al dual-phase oxide layer structure, i.e., a Cr2O3-Al2O3 composite oxide layer, can be formed, and 25% Cr can ensure the rapid formation of a continuous Cr2O3 layer on the surface, and 3% Al can promote the formation of Al2O3 in the inner layer, both of which can synergistically control the oxidation weight gain at 1000°C. The phase transition can also be inhibited, and the Cr content is precisely controlled below the critical point of σ phase formation (~26%), avoiding the embrittlement of FeCr phase at high temperature. 0.1% La segregates at the grain boundary to form LaCrO3 nanoparticles, which can inhibit grain growth, block the outward diffusion of Cr, and also improve the adhesion of the oxide layer. 1.0% Mn promotes the formation of MnCr2O4 spinel structure in the oxide layer, reducing the oxygen diffusion coefficient, and 0.5% Ti can fix the interstitial atoms to prevent Cr 23 C6 precipitation.

[0027] In a second aspect, based on the overall inventive concept, the present application provides a preparation method of the above-mentioned metal connector material for SOFC stack, comprising the following steps: (1) After mixing the components according to mass percentage, sequentially performing cleaning treatment, drying treatment and vacuum induction melting treatment, a melt is obtained; (2) The melt is injected into a mold preheated to a target temperature for casting, and then cooled to complete solidification to obtain an alloy ingot; (3) The alloy ingot is sequentially subjected to heat treatment and forming treatment, and the metal connector material for SOFC stack is obtained; Wherein the forming treatment is rolling treatment or powder metallurgy treatment.

[0028] In the present application, high-purity metals are used for raw material preparation, and ethanol ultrasonic cleaning and drying are performed to ensure the purity of the raw materials and reduce impurity interference. If the purity of the materials is insufficient, unexpected phases or impurities may appear in the final alloy, thereby affecting the electrical conductivity and oxidation resistance of the alloy material. Ultrasonic cleaning can effectively remove surface contaminants, and drying can avoid water residue. Vacuum induction melting is used, high vacuum can reduce oxidation, and Ar gas protection can further prevent oxidation. The temperature is controlled at 1500°C-1600°C, which can ensure complete melting of the metal while avoiding excessive volatilization, and the holding time is controlled to ensure uniform composition. If the vacuum degree is not enough, oxide inclusions may be produced; if the temperature is too high, elements may volatilize; if the temperature is too low, complete melting cannot be achieved, and the composition is not uniform. During the casting process, preheating the mold and the cooling rate are critical. Preheating the mold can reduce thermal stress and prevent cracking; applying a ZrO2 coating can prevent the metal from reacting with the mold; the cooling rate affects the size of the grains, and rapid cooling can refine the grains and improve mechanical properties. If the mold is not preheated enough, it may cause excessive internal stress in the casting, resulting in cracks. Slow cooling rate may result in coarse grains, affecting the strength. During the heat treatment process, the annealing temperature and time, as well as the cooling rate, all affect the results of the present application. Annealing can eliminate internal stress, uniformize the structure, and adjust the grain structure. Insufficient temperature and time may result in residual stress or uneven structure, and excessive temperature or time may cause excessive grain growth, reducing material performance. Controlling the cooling rate affects the precipitation of phases, too fast may produce residual stress, and too slow may precipitate unfavorable phases. The processing in the present application can choose rolling or powder metallurgy forming. Rolling is a combination of hot rolling and cold rolling, hot rolling is performed at high temperature, which can reduce the product deformation resistance and improve plasticity, but excessive temperature may cause oxidation or grain coarsening, and too low temperature may cause processing difficulty. Cold rolling can increase the strength and hardness of the product, but excessive deformation may cause cracks, and the choice of deformation amount in the present application also needs to balance the strength and ductility.

[0029] In summary, after cleaning the raw materials (removing surface oxides), the melting process can ensure low gas inclusion, uniform melting process (controlling the composition of the melt by stirring frequency) can ensure the dendrite spacing of the solidification structure (directional solidification molding by mold), and controlling the solidification cooling rate can ensure uniform deformation during rolling. That is, through the process closed loop of pure melting-structure regulation-interface engineering, the present application can realize the cross-scale optimization of material performance, and meet the stringent requirements of SOFC stack on connector materials.

[0030] In some optional embodiments of the present application, the purity of the raw material is >99.9%, the solvent for ultrasonic cleaning is ethanol, the drying temperature is 70°C-90°C, and the drying time is 1h-3h.

[0031] In the above scheme, the use of high-purity raw materials (Fe≥99.95%, Cr≥99.9%, etc.) can reduce the grain boundary embrittlement caused by impurity elements (such as S, P<50ppm) and inhibit the risk of Cr2O3 oxide layer cracking (thermal cycle life increased to >5000h). Rare earth elements La / Y (≥99.95%) refine the grain size (grain size <20μm) through the "active element effect" and improve the high-temperature strength of the product (tensile strength >80MPa at 1000℃). If the purity of the raw material is insufficient, for example, Fe purity <99.9%, impurities Ni, Cu will form low-melting-point eutectic phases (such as Fe-Ni, melting point 1450℃), which will cause cracks during later smelting. After ethanol ultrasonic cleaning and drying at 70℃~90℃, the ultrasonic cavitation effect (40kHz) can remove surface oxides and organic contaminants; low-temperature drying can avoid metal pre-oxidation. If the ethanol ultrasonic cleaning is not thorough, residual oil will cause CO bubbles to be generated during the smelting process (porosity >3%).

[0032] In some optional embodiments of the present application, the parameters of the vacuum induction melting include: a vacuum degree of 10 -4 Pa~10 -3 Pa, a melting temperature of 1500℃~1600℃, a smelting power of 20kW~30kW, a holding time of 30min~60min, and a stirring frequency of 45Hz~60Hz.

[0033] In the above scheme, the vacuum degree is in the range of 10 -4 Pa~10 -3 Pa, which can inhibit metal oxidation and reduce Al2O3 inclusions. Insufficient vacuum degree will increase the dissolved oxygen in the melt, form Cr2O3 particles and reduce the electrical conductivity. The melting temperature is controlled at 1500℃~1600℃, which is higher than the Fe-Cr liquidus line (≈1480℃), which can ensure that the raw materials are completely melted and the element distribution is uniform. If the temperature exceeds 1600℃, Al and Mn elements will be volatilized and lost, resulting in a decrease in oxidation resistance.

[0034] In some optional embodiments of the present application, argon gas is also introduced at a rate of 0.1L / min~0.2L / min during the vacuum induction melting process. This rate range can form a dynamic protective gas curtain to prevent the melt from absorbing gas. If the introduction rate is too low, the melt surface will absorb gas, which will cause porosity and thus reduce the material density.

[0035] In some optional embodiments of the present application, the target temperature is 300℃~500℃, the cooling rate is 5℃ / s~10℃ / s, the cooling time is 120s~240s, and the target temperature after cooling is 300℃~500℃, which is convenient for subsequent annealing.

[0036] In the above scheme, the mold is preferably a graphite mold, and a ZrO2 isolation layer needs to be applied inside the mold. The mold is preheated at 300-500℃, which can reduce thermal stress (stress value < 50 MPa) and prevent casting cracks. If the preheating temperature is lower than 300℃, the alloy solidification shrinkage will be blocked, resulting in shrinkage holes. If the cooling rate is too high (> 10℃ / s), non-equilibrium phases may be generated, resulting in an increase in cold rolling cracking rate. The application of the ZrO2 isolation layer can prevent C pollution (C content < 0.03%) and avoid the formation of Cr3C2 brittle phase.

[0037] In some optional embodiments of the present application, the heat treatment process includes: placing the alloy ingot in a tube furnace, heating to 900-1100℃ in an argon atmosphere, annealing for 2-4h, and cooling at a rate of 1-3℃ / min. The oxygen content in the argon atmosphere is <10ppm.

[0038] In the above scheme, the annealing temperature of 900-1100℃ can promote recrystallization and eliminate work hardening. If the annealing temperature is too high, it will cause abnormal grain growth and reduce the fatigue life of the product. The cooling rate of 1-3℃ / min can control the precipitation of C6 carbide and maintain the creep resistance. If the cooling rate is too fast, it will form network carbide and reduce the electrical conductivity. 23 C6 carbide precipitation, maintain creep resistance, if the cooling rate is too fast, will form network carbide reduce electrical conductivity.

[0039] In some optional embodiments of the present application, the rolling process includes hot rolling and cold rolling, wherein the hot rolling temperature is 800-1000℃, and the deformation amount is 50-70%; the cold rolling temperature is room temperature, and the deformation amount is 20-30%, and the thickness of the material after the rolling process is 0.5-2.0mm.

[0040] In the above scheme, the mechanism of hot rolling is: dynamic recrystallization to refine the grain and improve the high temperature strength; the mechanism of cold rolling is: to introduce dislocation strengthening to improve the room temperature hardness. Therefore, if the hot rolling temperature is too high (> 1000℃), the surface oxide skin will thicken, increasing the subsequent processing loss.

[0041] In some optional embodiments of the present application, the powder metallurgy process specifically includes: atomizing the powder to a particle size of 20-50 μm, compression molding at a pressure of 9.0-11.0 MPa, and then sintering at 1200-1400 °C. The rolling process of the present application can adopt a combination of cold rolling and hot rolling technology, or a powder metallurgy technology. The powder metallurgy technology can maximize the reduction of alloy composition segregation, eliminate coarse and uneven casting structures, and easily realize the compounding of various types of materials, fully exerting the respective characteristics of each component material. If the rolling process adopts powder metallurgy, the material utilization rate can be improved. Powder metallurgy can improve the material utilization rate from 60-70% in traditional rolling to more than 95%, and is particularly suitable for batch production of complex-shaped connectors. If the rolling process adopts powder metallurgy, the microstructure will be homogenized, and atomized powder can eliminate the dendritic segregation of traditional casting; a uniform oxidation layer is formed during the sintering process (1200-1400 °C), improving the oxidation resistance (1000 °C oxidation weight gain reduction of 30%). If the rolling process adopts powder metallurgy, the mechanical property regulation is more flexible, and through powder grading and sintering process optimization, high strength and high electrical conductivity can be achieved simultaneously. If the rolling process adopts a combination of cold rolling and hot rolling, the relative density of the rolled material is higher, and the oxidation layer stability is better during long-term high-temperature service. Through multi-pass rolling, a Goss texture can be generated in a specific direction, improving the electrical conductivity in a specific direction and better adapting to the current path design of SOFC stacks.

[0042] The above technical solutions of the present application will be described in detail below in conjunction with specific embodiments.

[0043] Embodiment 1 The present embodiment provides a preparation method of a metal connector material suitable for SOFC stacks, comprising the following steps: (1) The raw materials are weighed according to the following mass percentages: Cr (purity ≥ 99.9%) 25%, Al (purity ≥ 99.99%) 3%, Mn (purity ≥ 99.9%) 1%, Ti (purity ≥ 99.9%) 0.5%, La (purity ≥ 99.95%) 0.1%, and the balance is Fe (purity ≥ 99.95%).

[0044] (2) The raw materials are mixed and then ultrasonically cleaned with ethanol for 5 min, and then dried at 80 °C for 2 hours.

[0045] (3) The dried raw materials are placed in an alumina crucible, and a vacuum degree of 10 -3 Pa is set, and a melt is obtained by vacuum induction melting at a temperature of 1550 °C, with a melting power of 20 kW and a time of 40 min. Argon is introduced during the vacuum induction melting process at a rate of 0.1 L / min, with a purity of ≥ 99.999%, and the stirring frequency of the vacuum induction melting is 50 Hz.

[0046] (4) The melt is injected into a preheated graphite mold coated with a zirconium dioxide isolation layer, the preheating temperature is 400°C, the cooling rate is 8°C / s, and the alloy ingot is completely solidified after 150s, with a size of 100mmx50mmx20mm.

[0047] (5) The alloy ingot is placed in a tube furnace, argon is introduced to make the oxygen content less than 10ppm, the argon introduction rate is 0.5L / min. After heating to 1000°C, annealing for 3 hours, cooling at a rate of 2°C / min.

[0048] (6) The heat-treated material is hot-rolled at a temperature of 800°C, with a deformation of 50%, then cold-rolled at room temperature, with a deformation of 30%, and the thickness of the cold-rolled material is 1mm.

[0049] Example 2 The present embodiment provides a preparation method of a metal connector material suitable for SOFC stacks, comprising the following steps: (1) The high-purity raw materials are weighed according to the following mass percentage: Cr (purity ≥ 99.9%) 28%, Al (purity ≥ 99.99%) 4%, Mn (purity ≥ 99.9%) 1.5%, Ti (purity ≥ 99.9%) 0.8%, Y (purity ≥ 99.95%) 0.2%, and the balance is Fe (purity ≥ 99.95%).

[0050] (2) The raw materials are mixed and ultrasonically cleaned with ethanol for 5min, and then dried at 80°C for 2 hours.

[0051] (3) The dried raw materials are placed in an alumina crucible, the vacuum degree is set to 10 -3 Pa, vacuum induction melting is carried out at a temperature of 1500°C to obtain a melt, the melting power is set to 20kW, the holding time is set to 40min, argon is introduced during vacuum induction melting, the argon introduction rate is 0.1L / min, the purity is ≥ 99.999%, and the stirring frequency of vacuum induction melting is 50Hz.

[0052] (4) The melt is injected into a preheated graphite mold coated with a zirconium dioxide isolation layer, the preheating temperature is 400°C, the cooling rate is 8°C / s, and the alloy ingot is completely solidified after 3min, with a size of 100mmx50mmx20mm.

[0053] (5) The alloy ingot is placed in a tube furnace, argon is introduced to make the oxygen content less than 10ppm, the argon introduction rate is 0.5L / min. After heating to 1050°C, annealing for 3 hours, cooling at a rate of 2°C / min.

[0054] (6) The material after heat treatment is powder metallurgy, the atomized powder is 50 μm, then it is pressed to 1.5 mm thickness at 10 MPa, and then sintered at 1250 °C for 2 hours to obtain a material with a density of ≥98%.

[0055] Example 3 The present embodiment provides a preparation method of a metal connector material suitable for SOFC stacks, comprising the following steps: (1) The high-purity raw materials are weighed according to the following mass percentage: Cr (purity ≥ 99.9%) 30%, Al (purity ≥ 99.99%) 5%, Mn (purity ≥ 99.9%) 2%, Ti (purity ≥ 99.9%) 1%, Y (purity ≥ 99.95%) 0.2%, and the balance is Fe (purity ≥ 99.95%).

[0056] (2) The raw materials are mixed and ultrasonically cleaned with ethanol for 5 min, and then dried at 80 °C for 2 hours.

[0057] (3) The dried raw materials are placed in an alumina crucible, the vacuum degree is set to 10 -4 Pa, the temperature is set to 1580 °C for vacuum induction melting to obtain a melt, the melting power is set to 30 kW, the holding time is set to 60 min, argon is introduced during vacuum induction melting, the introduction rate of argon is 0.2 L / min, the purity is ≥ 99.999%, and the stirring frequency of vacuum induction melting is 50 Hz.

[0058] (4) The melt is poured into a preheated graphite mold coated with a zirconium dioxide isolation layer, the preheating temperature is 450 °C, the cooling rate is 10 °C / s, and the alloy ingot is completely solidified after cooling for 4 minutes, the size of the alloy ingot is 100 mm x 50 mm x 20 mm.

[0059] (5) The alloy ingot is placed in a tube furnace, argon is introduced to make the oxygen content less than 10 ppm, the introduction rate of argon is 0.5 L / min. After heating to 1100 °C, annealing for 4 hours, and cooling at a rate of 3 °C / min.

[0060] (6) The material after heat treatment is hot rolled at a temperature of 900 °C with a deformation of 70%, and then cold rolled at room temperature with a deformation of 20%, the thickness of the material after cold rolling is 0.5 mm.

[0061] Comparative Example Ferritic Crofer 22 APU is a high-temperature alloy mainly used as a ceramic metal interconnect material for solid oxide fuel cells (SOFC). Its elemental content is iron (Fe), chromium (Cr) and aluminum (Al), among which iron is the main element with the highest proportion. Its thermal expansion coefficient (also known as thermal expansion coefficient) refers to the ratio of the change in length of a material to its initial length when the temperature changes. Since Crofer 22 APU is an iron-based alloy, its thermal expansion coefficient is similar to that of other iron-based alloys.

[0062] Experimental Example (1) Oxidation weight gain test: heated in a 1000℃ muffle furnace for 1000 hours in an air atmosphere, and weighed (with an accuracy of 0.01mg); (2) Surface resistance: high-temperature resistivity was measured by four-probe method at 800℃, and tested after the formation of the oxidation layer.

[0063] (3) Thermal expansion coefficient: tested by Netzsch DIL 402 dilatometer, temperature range 20℃-1000℃, heating rate set to 5℃ / min.

[0064] (4) Ionic conductivity: impedance spectrum analysis, temperature range 600℃-1000℃, oxygen partial pressure set to 0.21atm.

[0065] The above four tests were performed on the metal interconnector material suitable for SOFC stacks produced by Examples 1-2 and the traditional ferritic Crofer 22 APU high-temperature alloy, and the results are shown in Table 1 and Figures 1-3 .

[0066]

[0067] It can be seen that the metal interconnector material prepared in the embodiments of the present application has excellent oxidation resistance, and the oxidation weight gain rate is ≤0.1mg / cm 2 after 1000 hours of oxidation in 1000℃ air, and the oxidation layer thickness is 3μm-5μm; the metal interconnector material prepared in the embodiments of the present application also has excellent electrical conductivity, and the surface resistance after 1000 hours is ≤20mΩ·cm 2 ; the thermal expansion coefficient of the metal interconnector material prepared in the embodiments of the present application is 11×10 -6 K -1 -12×10 -6 K -1 , close to YSZ, and the thermal stress is reduced by 80%; the metal interconnector material prepared in the embodiments of the present application has low ionic conductivity and high mechanical strength, among which the room temperature tensile strength is not less than 500MPa, and the tensile strength at 800℃ is not less than 300MPa.

[0068] ByFigure 1 It can be seen that the metal connector material prepared by the embodiment of the application for the SOFC stack has an oxidation weight gain rate from 0 hour to 1000 hours in the air environment at 1000℃, and the weight gain rate is lower than 0.1mg / cm 2 .

[0069] From Figure 2 It can be seen that the change of the thermal expansion coefficient in the range of 20℃~1000℃, the thermal expansion coefficient of the metal connector material prepared by the embodiment of the application increases from 11×10 -6 K -1 to 12×10 -6 K -1 , close to 10.5×10 - 6 K -1 of YSZ, and better than 13.5×10 -6 K -1 ~14.0×10 -6 K -1 .

[0070] From Figure 3 It can be seen that in the range of 600℃~1000℃, the ionic conductivity of the metal connector material of the embodiment of the application is about 10 -15 S / cm, lower than 10 -14 S / cm of the ferritic Crofer 22 APU, and far lower than 10 -2 S / cm of YSZ, which proves that the isolation performance of the metal connector material is excellent.

[0071] Figure 2 And Figure 3 YSZ is included in the comparison of the CTE change with temperature and the ionic conductivity of the metal connector material of the embodiment of the application and Crofer 22 APU: because the thermal expansion coefficient (CTE), chemical compatibility and interface stability of the two are closely related, the metal connector is in direct contact or indirect contact with the YSZ electrolyte through the electrode layer (such as LSM cathode), forming an interface. The CTE of the metal connector of the application is closer to YSZ than the traditional Crofer 22 APU high-temperature alloy, which can reduce the interface thermal stress.

[0072] Although the specific embodiments of the application are described in detail, it should not be understood as limiting the scope of protection of the application. Various modifications and variations made by those skilled in the art within the scope described in the claims are still within the scope of protection of the patent.

Claims

1. A metal connector material suitable for SOFC stack, characterized in that: It includes the following components by mass percentage: Cr 20%~30%, Al 2%~5%, Mn 0.5%~2.0%, Ti 0.1%~1.0%, rare earth elements 0.05%~0.5%, and the balance is Fe and impurities; The rare earth elements are La and / or Y, and the total impurity content is less than 0.05%.

2. The metal connector material suitable for SOFC stack according to claim 1, characterized in that: It includes the following components in mass percentage: Cr 25%~28%, Al 3%~4%, Mn 1.0%~1.5%, Ti 0.5%~0.8%, rare earth elements 0.1%~0.3%, and the balance is Fe and impurities.

3. A method for preparing a metal connector material suitable for SOFC stacks according to claim 1 or 2, characterized in that: The following steps are involved: After mixing the components according to mass percentage, washing, drying and vacuum induction melting are sequentially performed to obtain a melt; The melt is poured into a mold preheated to a target temperature for casting, and then cooled to obtain an alloy ingot; The alloy ingot is subjected to heat treatment and forming treatment in sequence to obtain; The forming process is rolling or powder metallurgy.

4. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The solvent for ultrasonic cleaning is ethanol, the drying temperature is 70° C. to 90° C., and the drying time is 1 h to 3 h.

5. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The parameters of the vacuum induction melting include: Vacuum degree is 10 -4 Pa~10 -3 Pa, melting temperature is 1500℃~1600℃, melting power is 20kW~30kW, holding time is 30min~60min, and stirring frequency is 45Hz~60Hz.

6. The method for preparing a metal connector material suitable for SOFC stack according to claim 5, characterized in that: During the vacuum induction melting process, argon gas is introduced at a rate of 0.1 L / min to 0.2 L / min.

7. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The target temperature is 300° C. to 500° C., the cooling rate is 5° C. / s to 10° C. / s, and the cooling time is 120s to 240s.

8. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The heat treatment process comprises: placing the alloy ingot in a tube furnace, heating to 900° C. to 1100° C. in an argon atmosphere, annealing for 2 h to 4 h, and cooling at a rate of 1° C. / min to 3° C. / min; The oxygen content in the argon atmosphere is less than 10 ppm.

9. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The rolling process includes hot rolling and cold rolling, wherein the hot rolling temperature is 800° C. to 1000° C., and the cold rolling temperature is room temperature. The thickness of the material after the rolling process is 0.5 mm to 2.0 mm.

10. The method for preparing a metal connector material suitable for SOFC stack according to claim 3, characterized in that: The powder metallurgy process specifically includes: atomizing the powder to a particle size of 20 μm to 50 μm, pressing and molding under a pressure of 9.0 MPa to 11.0 MPa, and then sintering at 1200° C. to 1400° C.

Images