A low-expansion, oxidation-resistant iron-nickel alloy substrate and a method for making the same

Abstract

The application relates to the technical field of plating, and discloses a low-expansion oxidation-resistant iron-nickel alloy base material and a preparation method thereof; the method comprises the following operation steps: in the scheme, an iron-nickel alloy base material is sequentially subjected to embedding aluminizing, micro-arc oxidation, coating of aluminum composite sol and temperature rising solidification to obtain the low-expansion oxidation-resistant iron-nickel alloy base material; wherein the iron-nickel alloy base material itself has the low-expansion characteristic, but the oxidation resistance is poor; if a ceramic layer is directly arranged on the surface of the iron-nickel alloy base material, the oxidation resistance can be improved, but the low-expansion characteristic of the material is reduced; in order to solve the problem, in the scheme, a transition layer is formed by embedding aluminizing to improve the combination of the micro-arc oxidation layer and the oxidation-resistant layer, and modified macrocyclic polysiloxane is added to raw materials of the micro-arc oxidation layer and the oxidation-resistant layer; the temperature is controlled to make the modified macrocyclic polysiloxane be converted into amorphous silicon dioxide at high temperature, and the thermal expansion of aluminum oxide is balanced.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a low-expansion, oxidation-resistant iron-nickel alloy substrate and its preparation method. Background Technology

[0002] Due to their excellent magnetic and mechanical properties, iron-nickel alloys are widely used in high-end fields such as aerospace, electronic packaging, and precision instruments. Among them, low-expansion iron-nickel alloys (such as Invar alloys) have extremely low coefficients of thermal expansion near room temperature, but their high-temperature oxidation resistance is generally insufficient. Traditional iron-nickel alloys are prone to react with oxygen and water vapor in high-temperature environments, and the oxide layer formed on the surface is loose and easy to fall off, resulting in a reduction in the performance of the substrate.

[0003] Existing technologies mainly improve performance by increasing the content of antioxidant elements such as Cr, but this often significantly alters the phase composition of the alloy, deteriorating its low expansion characteristics and even inducing harmful ordered phase transformations.

[0004] In summary, the preparation of a low-expansion, oxidation-resistant iron-nickel alloy substrate is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a low-expansion, oxidation-resistant iron-nickel alloy substrate and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate includes the following steps:

[0008] Step 1: The iron-nickel alloy substrate is placed in a diffusion agent and aluminized to form a transition layer, thus obtaining iron-nickel alloy substrate A;

[0009] Step 2: Place the iron-nickel alloy substrate A in an electrolyte for micro-arc oxidation to form a micro-arc oxidation layer, thus obtaining the iron-nickel alloy substrate B;

[0010] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, heat and cure to form an anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate.

[0011] In a more optimized configuration, the thickness of the transition layer is 15-20 μm, the thickness of the micro-arc oxidation layer is 20-30 μm, and the thickness of the antioxidant layer is 5-10 μm.

[0012] In a more optimized form, the raw materials of the penetrant include the following components: by mass, 40-50 parts aluminum powder, 1-2 parts activator, and 10-12 parts alumina.

[0013] In a more optimized form, the electrolyte raw materials include the following components: 5~8 g / L sodium silicate, 3~5 g / L boric acid, 2~4 g / L sodium hexametaphosphate, and 2 g / L macrocyclic polysiloxane modified graphene.

[0014] A more optimized method for preparing the macrocyclic polysiloxane-modified graphene is as follows: (1) Tetramethyltetravinylcyclotetrasiloxane, ferric chloride, deionized water, and acetone are mixed uniformly and stirred at 85-95°C for 18-22 hours. After cooling to room temperature, the mixture is post-treated to obtain macrocyclic vinyl polysiloxane; (2) Macrocyclic vinyl polysiloxane, methanol, and Karstedt catalyst are mixed uniformly and heated to 50-60°C under a nitrogen atmosphere. Trimethoxyhydrosilane is added and stirred for 8-10 hours. Activated carbon is added and stirred for 30-40 minutes. The mixture is cooled to room temperature to obtain modified macrocyclic polysiloxane; (3) Reduced graphene oxide is added to a methanol aqueous solution and mixed. Modified macrocyclic polysiloxane is added. Acetic acid is added and the pH is adjusted to 4-5. The mixture is stirred at 40-50°C for 4-6 hours, washed until neutral, and dried to obtain macrocyclic polysiloxane-modified graphene.

[0015] In a more optimized form, the raw materials for the modified macrocyclic polysiloxane include the following components: by mass, 12-18 parts tetramethyltetravinylcyclotetrasiloxane, 0.2-0.4 parts ferric chloride, 1.2-1.7 parts deionized water, and 15-20 parts acetone; the raw materials for the multifunctional modified macrocyclic polysiloxane include the following components: by mass, 4-6 parts cyclovinyl polysiloxane, 1.5-2 parts trimethoxyhydrosilane, 0.7-1 part tetramethyldihydrodisiloxane, and 0.07-0.12 parts Karstedt catalyst;

[0016] The raw materials for the macrocyclic polysiloxane-modified graphene include the following components: by mass, 1-2 parts of reduced graphene oxide, 0.5-1 parts of modified macrocyclic polysiloxane, and 10-20 parts of methanol aqueous solution.

[0017] In this scheme, tetramethyltetravinylcyclotetrasiloxane undergoes cationic ring-opening polymerization under ferric chloride catalysis. After the Si-O bond of the cyclosiloxane breaks, linear segments are formed, which are then rearranged intramolecularly to form a macrocyclic structure, retaining the vinyl functional group, to obtain macrocyclic vinyl polysiloxane. After the vinyl (C=C bond) on the macrocyclic polysiloxane is activated by the Karstedt catalyst, the Si-H bonds in trimethoxysilane and tetramethyldihydrodisiloxane undergo an addition reaction, adding to both ends of the activated C=C bond, thereby forming a new Si-C bond and introducing siloxane to obtain modified macrocyclic polysiloxane. The trimethoxysilyl group in the modified macrocyclic polysiloxane undergoes hydrolysis in methanol aqueous solution to generate Si-OH groups. Acidic conditions (pH 4~5) promote the condensation of Si-OH with the hydroxyl groups (-OH) on the surface of reduced graphene oxide to obtain macrocyclic polysiloxane modified graphene.

[0018] In the procedure, 5 parts of graphene oxide are added to 100 parts of deionized water, ultrasonically exfoliated (to obtain graphene oxide), 4 parts of hydrazine hydrate (reducing agent) are added and mixed evenly, and refluxed at 90°C for 20 hours to obtain reduced graphene oxide; parts are by weight.

[0019] A more optimized method for preparing the aluminum composite sol is as follows: aluminum nitrate is added to deionized water and mixed, ammonia is added to adjust the pH to 9-10, the mixture is filtered, washed until neutral, nitric acid solution is added to adjust the pH to 3.7-4.5, modified macrocyclic polysiloxane-methanol aqueous solution is added, and the mixture is stirred at 50-55°C and aged to obtain the aluminum composite sol.

[0020] In a more optimized form, the raw materials for the aluminum composite sol include the following components: by mass, 18-20 parts aluminum nitrate, 4-6 parts modified macrocyclic polysiloxane, and 40-50 parts deionized water.

[0021] In a more optimized form, the iron-nickel alloy substrate comprises the following components: 35.5~36.5wt% Ni, 2~3% Mo, 0.7~1% Ti, 0.3~0.5% Mn, 0.1~0.20% Cr, C≤0.015%, Si≤0.25%, P≤0.008%, S≤0.005%, with the balance being Fe.

[0022] The optimized process conditions for the embedding and aluminizing are: vacuum atmosphere, temperature 700~750℃;

[0023] The micro-arc oxidation process conditions are: current density of 2~4 A / dm³. 2 Frequency 500~1000Hz, duty cycle 10%~30%;

[0024] The process conditions for the heating and curing are as follows: keep at 60~80℃ for 3~5 hours, heat up to 200~300℃ at a rate of 1~2℃ / min for 1~2 hours, continue to heat up to 400℃~500℃ and keep at 1~2 hours, and heat up to 600~700℃ and keep at 2~3 hours.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] In this scheme, the iron-nickel alloy substrate is sequentially subjected to aluminizing, micro-arc oxidation, spin coating of aluminum composite sol, and temperature curing to obtain a low-expansion oxidation-resistant iron-nickel alloy substrate.

[0027] Among them, the iron-nickel alloy substrate itself has low expansion characteristics, but poor oxidation resistance; and when the iron-nickel alloy is directly bonded to the ceramic layer, the large difference in the coefficient of thermal expansion can easily lead to coating cracking and affect the low expansion of the iron-nickel alloy substrate. In order to solve this problem, the solution is to form Fe-Al alloy on the surface of the iron-nickel alloy by embedding aluminizing as a transition layer to relieve thermal stress; the transition layer can improve the bonding force between the micro-arc oxidation layer and the iron-nickel alloy substrate and prevent the coating from falling off.

[0028] Furthermore, during the micro-arc oxidation process, the Al in the transition layer will further participate in the oxidation reaction, so that the Al element in the micro-arc oxidation layer and the Al composition in the transition layer will continuously transition, resulting in a strong metallurgical bond between the two layers, thereby improving the oxidation resistance.

[0029] Furthermore, the micro-arc oxidation layer is a ceramic layer, which, although hard, is brittle. The transition layer, being an intermetallic compound, possesses a certain degree of toughness, buffering the thermal stress generated during micro-arc oxidation, reducing interfacial cracks, and enhancing bonding stability. During subsequent temperature-curing processes, the micro-arc oxidation layer exhibits high brittleness, leading to coating cracks and failure, and also increasing thermal expansion. To address this issue, the proposed solution incorporates cyclic polysiloxane-modified graphene into the electrolyte.

[0030] Reduced graphene oxide is a low-expansion material whose layered structure provides basic toughness in the micro-arc oxidation layer, and introduces cyclic polysiloxane flexible chains on the surface of reduced graphene oxide. This improves dispersibility and synergistically alleviates the brittleness of the micro-arc oxidation layer, reducing the generation and propagation of cracks. After micro-arc oxidation, pores are generated on the surface. In this scheme, cyclic polysiloxanes are added to aluminum sol to obtain aluminum composite sol, which serves as a sealing agent. This reduces porosity while alleviating shrinkage stress during heating and curing, reducing crack generation, and thus improving oxidation resistance.

[0031] During the curing process of aluminum sol, tiny pores remain. Cyclic polysiloxanes can penetrate into these pores. By controlling the temperature during the curing process, the cyclic polysiloxanes are transformed into amorphous silica, forming an Al2O3-SiO2 interwoven network, which reduces the porosity of the coating. In addition, Al2O3 itself has excellent oxidation resistance, but its density is insufficient. Amorphous silica derived from organic precursors has good oxidation resistance and low expansion. Together with reduced graphene oxide, it can effectively alleviate the expansion of Al2O3, synergistically improve oxidation resistance, reduce the risk of brittle cracking under high temperature cycling, and extend the sealing life.

[0032] Furthermore, the proposed method first macrocyclizes tetramethyltetravinylcyclotetrasiloxane to increase its molecular weight. This prevents the low molecular weight siloxanes prepared from tetramethyltetravinylcyclotetrasiloxane with trimethoxyhydrosilane and tetramethyldihydrodisiloxane from having high reactivity and rapidly crosslinking and gelling during high-temperature curing, which would affect the coating performance. Macrocyclization requires increasing the high-temperature curing time to allow the polysiloxane sufficient time to flow between layers, improving adhesion, reducing defects such as cracks and pores, and enabling the antioxidant layer to more stably block oxygen from contacting the iron-nickel alloy substrate, thus significantly enhancing the substrate's high-temperature oxidation resistance. Detailed Implementation

[0033] 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.

[0034] In the following specific embodiments, the parts are by weight. In this embodiment, it should be noted that there are no special restrictions on the purchase manufacturers of all the raw materials involved in this invention. Exemplary examples include: tetramethyltetravinylcyclotetrasiloxane (CAS number 2554-06-5); ferric chloride (CAS number 7705-08-0); trimethoxysilane (CAS number 2487-90-3); tetramethyldihydrodisiloxane (CAS number 3277-26-7); ammonium chloride (activator) (CAS number 12125-02-9); aluminum powder with an average particle size of 300 mesh; alumina with an average particle size of 200 mesh; sodium silicate (CAS number 1344-09-8); boric acid (CAS number 10043-35-3); and sodium hexametaphosphate (CAS number 10124-56-8).

[0035] In the following examples, the composite sol was prepared as follows: 18 parts of aluminum nitrate were added to 45 parts of deionized water and mixed. Ammonia water was added to adjust the pH to 9.3. The mixture was filtered, washed until neutral, and nitric acid solution (2M concentration) was added to adjust the pH to 4. Modified macrocyclic polysiloxane-methanol aqueous solution (6 parts of modified macrocyclic polysiloxane were added to 80wt% methanol aqueous solution) was added. The mixture was stirred at 50°C for 4 hours and aged for 3 hours to obtain aluminum composite sol.

[0036] Example 1: A method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate, comprising the following steps:

[0037] Pre-preparation: The preparation method of macrocyclic polysiloxane modified graphene is as follows: (1) 16 parts of tetramethyltetravinylcyclotetrasiloxane, 0.3 parts of ferric chloride, 1.7 parts of deionized water and 20 parts of acetone are mixed evenly and stirred at 90°C for 20 hours. After cooling to room temperature, n-hexane is added and mixed. The solid is removed by filtration. The filtrate is washed with methanol several times to remove the solvent and obtain macrocyclic vinyl polysiloxane; (2) 5 parts of macrocyclic vinyl polysiloxane, 40 parts of methanol and 0.08 parts of Karstedt catalyst are mixed evenly and heated to 50°C under nitrogen atmosphere. 1.5 parts of trimethoxyhydrosilane and 1 part of tetramethyldihydrodisiloxane are added and stirred for 8 hours. The temperature is raised to 80°C and activated carbon is added and stirred for 30 minutes. After cooling to room temperature, the solid is removed by filtration and the filtrate is evaporated by rotary evaporation to obtain modified macrocyclic polysiloxane;

[0038] (3) Two parts of reduced graphene oxide were added to 15 parts of methanol aqueous solution (methanol accounted for 80 wt% of the methanol aqueous solution), and one part of modified macrocyclic polysiloxane was added; acetic acid was added to adjust the pH to 4.5, and the mixture was stirred at 50°C for 6 hours. After washing until neutral, the mixture was dried to obtain cyclic polysiloxane-modified graphene.

[0039] The raw materials for the penetrant include the following components: by mass, 40 parts aluminum powder, 2 parts activator, and 10 parts alumina;

[0040] The electrolyte raw materials include the following components: 6 g / L sodium silicate, 4 g / L boric acid, 3 g / L sodium hexametaphosphate, and 2 g / L cyclic polysiloxane modified graphene.

[0041] Step 1: Place the iron-nickel alloy substrate in a diffusion agent and embed it in an aluminizing agent at 750°C under a vacuum atmosphere to form a 15μm thick transition layer, thus obtaining iron-nickel alloy substrate A;

[0042] Step 2: Place the iron-nickel alloy substrate A in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 20μm thick micro-arc oxidation layer, resulting in iron-nickel alloy substrate B.

[0043] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 4 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 5μm thick anti-oxidation layer, and obtaining a low-expansion anti-oxidation iron-nickel alloy substrate.

[0044] Example 2, a method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate, includes the following steps:

[0045] Pre-preparation: The preparation method of cyclic polysiloxane modified graphene is as follows: (1) 16 parts of tetramethyltetravinylcyclotetrasiloxane, 0.3 parts of ferric chloride, 1.7 parts of deionized water and 20 parts of acetone are mixed evenly and stirred at 90°C for 20 hours. After cooling to room temperature, n-hexane is added and mixed. The solid is removed by filtration. The filtrate is washed with methanol several times to remove the solvent and obtain macrocyclic vinyl polysiloxane; (2) 5 parts of macrocyclic vinyl polysiloxane, 40 parts of methanol and 0.08 parts of Karstedt catalyst are mixed evenly and heated to 50°C under nitrogen atmosphere. 1.5 parts of trimethoxyhydrosilane and 1 part of tetramethyldihydrodisiloxane are added and stirred for 8 hours. The temperature is raised to 80°C and activated carbon is added and stirred for 30 minutes. After cooling to room temperature, the solid is removed by filtration and the filtrate is evaporated by rotary evaporation to obtain modified macrocyclic polysiloxane;

[0046] (3) Two parts of reduced graphene oxide were added to 15 parts of methanol aqueous solution (methanol accounted for 80 wt% of methanol aqueous solution), and one part of modified macrocyclic polysiloxane was added; acetic acid was added to adjust the pH to 4.5, and the mixture was stirred at 50°C for 6 hours. The mixture was washed until neutral and dried to obtain cyclic polysiloxane modified graphene.

[0047] The raw materials for the penetrant include the following components: by mass, 40 parts aluminum powder, 2 parts activator, and 10 parts alumina;

[0048] The electrolyte raw materials include the following components: 6 g / L sodium silicate, 4 g / L boric acid, 3 g / L sodium hexametaphosphate, and 2 g / L cyclic polysiloxane modified graphene.

[0049] Step 1: Place the iron-nickel alloy substrate in a diffusion agent and embed it in an aluminizing agent at 750°C under a vacuum atmosphere to form a 15μm thick transition layer, thus obtaining iron-nickel alloy substrate A;

[0050] Step 2: Place the iron-nickel alloy substrate A in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 20μm thick micro-arc oxidation layer, resulting in iron-nickel alloy substrate B.

[0051] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 4 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 10μm thick anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate.

[0052] Example 3: A method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate, comprising the following steps:

[0053] Pre-preparation: The preparation method of cyclic polysiloxane modified graphene is as follows: (1) 16 parts of tetramethyltetravinylcyclotetrasiloxane, 0.3 parts of ferric chloride, 1.7 parts of deionized water and 20 parts of acetone are mixed evenly and stirred at 90°C for 20 hours. After cooling to room temperature, n-hexane is added and mixed. The solid is removed by filtration. The filtrate is washed with methanol several times to remove the solvent and obtain macrocyclic vinyl polysiloxane; (2) 5 parts of macrocyclic vinyl polysiloxane, 40 parts of methanol and 0.08 parts of Karstedt catalyst are mixed evenly and heated to 50°C under nitrogen atmosphere. 1.5 parts of trimethoxyhydrosilane and 1 part of tetramethyldihydrodisiloxane are added and stirred for 8 hours. The temperature is raised to 80°C and activated carbon is added and stirred for 30 minutes. After cooling to room temperature, the solid is removed by filtration and the filtrate is evaporated by rotary evaporation to obtain modified macrocyclic polysiloxane;

[0054] (3) Two parts of reduced graphene oxide were added to 15 parts of methanol aqueous solution (methanol accounted for 80 wt% of methanol aqueous solution), and one part of modified macrocyclic polysiloxane was added; acetic acid was added to adjust the pH to 4.5, and the mixture was stirred at 50°C for 6 hours. The mixture was washed until neutral and dried to obtain cyclic polysiloxane modified graphene.

[0055] The raw materials for the penetrant include the following components: by mass, 40 parts aluminum powder, 2 parts activator, and 10 parts alumina;

[0056] The electrolyte raw materials include the following components: 6 g / L sodium silicate, 4 g / L boric acid, 3 g / L sodium hexametaphosphate, and 2 g / L cyclic polysiloxane modified graphene.

[0057] Step 1: Place the iron-nickel alloy substrate in a diffusion agent and embed it in an aluminizing agent at 750°C under a vacuum atmosphere to form a 15μm thick transition layer, thus obtaining iron-nickel alloy substrate A;

[0058] Step 2: Place the iron-nickel alloy substrate A in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 20μm thick micro-arc oxidation layer, resulting in iron-nickel alloy substrate B.

[0059] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 4 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 7μm thick anti-oxidation layer, and obtaining a low-expansion anti-oxidation iron-nickel alloy substrate.

[0060] Comparative Example 1 is based on Example 2, but without aluminizing; the remaining operating steps are the same.

[0061] Step 1: Place the iron-nickel alloy substrate in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 7μm thick micro-arc oxidation layer, resulting in an iron-nickel alloy substrate A.

[0062] Step 2: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 5 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 10μm thick anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate.

[0063] Comparative Example 2 is based on Example 2, except that reduced graphene oxide is added directly to the electrolyte; the remaining operation steps are the same.

[0064] Pre-preparation: The raw materials for the electrolyte include the following components: 6 g / L sodium silicate, 4 g / L boric acid, 3 g / L sodium hexametaphosphate, and 2 g / L reduced graphene oxide;

[0065] Step 1: Place the iron-nickel alloy substrate in a diffusion agent and embed it in an aluminizing agent at 750°C under a vacuum atmosphere to form a 15μm thick transition layer, thus obtaining iron-nickel alloy substrate A;

[0066] Step 2: Place the iron-nickel alloy substrate A in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 20μm thick micro-arc oxidation layer, resulting in iron-nickel alloy substrate B.

[0067] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 4 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 10μm thick anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate.

[0068] Comparative Example 3 is based on Example 2, but the tetramethyltetravinylcyclotetrasiloxane was not macrocyclized; the remaining operating steps were the same.

[0069] Pre-preparation: The preparation method of cyclic polysiloxane modified graphene is as follows: (1) 5 parts tetramethyltetravinylcyclotetrasiloxane, 40 parts methanol, and 0.08 parts Karstedt catalyst are mixed evenly. Under a nitrogen atmosphere, the temperature is raised to 50°C, 1.5 parts trimethoxysilane and 1 part tetramethyldihydrodisiloxane are added and stirred for 8 hours. The temperature is raised to 80°C, activated carbon is added and stirred for 30 minutes. The temperature is cooled to room temperature, the solid is removed by filtration, and the filtrate is evaporated by rotary evaporation to obtain multifunctional modified cyclic siloxane oligomers.

[0070] (3) Two parts of reduced graphene oxide were added to a methanol aqueous solution and mixed. One part of multifunctional modified cyclosiloxane oligomer was added. Acetic acid was added to adjust the pH to 4.5. The mixture was stirred at 50°C for 6 hours, washed until neutral, and dried to obtain cyclosiloxane oligomer modified graphene.

[0071] The electrolyte raw materials include the following components: 6 g / L sodium silicate, 4 g / L boric acid, 3 g / L sodium hexametaphosphate, and 2 g / L cyclosiloxane oligomer modified graphene.

[0072] Step 1: Place the iron-nickel alloy substrate in a diffusion agent and embed it in an aluminizing agent at 750°C under a vacuum atmosphere to form a 15μm thick transition layer, thus obtaining iron-nickel alloy substrate A;

[0073] Step 2: Place the iron-nickel alloy substrate A in the electrolyte and set the current density to 3A / dm³. 2 Micro-arc oxidation was performed at a frequency of 800Hz and a duty cycle of 30% to form a 20μm thick micro-arc oxidation layer, resulting in iron-nickel alloy substrate B.

[0074] Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, keep it at 80℃ for 4 hours, raise the temperature to 300℃ at a rate of 2℃ / min for 1 hour, continue to raise the temperature to 400℃ and keep it at 1.5 hours, raise the temperature to 650℃ and keep it at 2.5 hours for curing, forming a 10μm thick anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate.

[0075] Test: (1) The low-expansion anti-oxidation iron-nickel alloy substrates prepared in Examples 1-3 were cut into 30mm×15mm pieces, weighed, and then placed at 750℃ with air introduced from bottom to top for constant temperature oxidation for 30 hours. After cooling, they were weighed and the oxidation weight gain (g / m) was calculated. 2 ·h);

[0076] Table 1

[0077]

[0078] Conclusion: Comparative Example 1, based on Example 1, did not involve aluminizing, making it difficult to form a uniform micro-arc oxidation layer on the iron-nickel alloy substrate surface, and the layer thickness formed within the same micro-arc oxidation time decreased, thus leading to a decrease in the performance of Comparative Example 1. Comparative Example 2, based on Example 1, directly added reduced graphene oxide to the electrolyte, resulting in the reduced graphene oxide lacking polysiloxane modification, making it prone to agglomeration, and causing an uneven micro-arc oxidation layer, which affected the bonding with the antioxidant layer, thus leading to a decrease in antioxidant properties.

[0079] Comparative Example 3 is based on Example 1, but the tetramethyltetravinylcyclotetrasiloxane was not macrocyclic; this made the conversion of the cyclosiloxane oligomer to nonstatic silica at high temperature faster, but it still retained the aluminized transition layer and the synergistic effect of siloxane and graphene, which had a certain protective effect, so the change in antioxidant properties was not significant.

[0080] (2) The coefficient of thermal expansion of Example 2 and the iron-nickel alloy substrate at 25-200℃ was measured by a dilatometer;

[0081] Table 2

[0082]

[0083] Conclusion: Modified macrocyclic polysiloxane forms amorphous silicon dioxide at high temperature, which, together with reduced graphene oxide, can effectively balance the expansion of the alumina ceramic layer, so that the low-expansion, oxidation-resistant iron-nickel alloy substrate is not much different from that of iron-nickel alloy substrate.

[0084] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate, characterized in that: The following steps are included: Step 1: The iron-nickel alloy substrate is placed in a diffusion agent and aluminized to form a transition layer, thus obtaining iron-nickel alloy substrate A; Step 2: Place the iron-nickel alloy substrate A in an electrolyte for micro-arc oxidation to form a micro-arc oxidation layer, thus obtaining the iron-nickel alloy substrate B; Step 3: Coat the surface of the iron-nickel alloy substrate B with aluminum composite sol, heat and cure to form an anti-oxidation layer, and obtain a low-expansion anti-oxidation iron-nickel alloy substrate; The electrolyte contains the following components: 5-8 g / L sodium silicate, 3-5 g / L boric acid, 2-4 g / L sodium hexametaphosphate, and 2 g / L macrocyclic polysiloxane modified graphene. The preparation method of the macrocyclic polysiloxane modified graphene is as follows: by mass fraction, (1) 12-18 parts of tetramethyltetravinylcyclotetrasiloxane, 0.2-0.4 parts of ferric chloride, 1.2-1.7 parts of deionized water and 15-20 parts of acetone are mixed evenly, stirred at 85-95°C for 18-22 hours, cooled to room temperature, added n-hexane and mixed, filtered to remove solids, the filtrate is washed several times with methanol to remove solvent, and macrocyclic vinyl polysiloxane is obtained; (2) Methanol, 4-6 parts of macrocyclic vinyl polysiloxane, and 0.07-0.12 parts of Karstedt catalyst are mixed evenly. Under a nitrogen atmosphere, the mixture is heated to 50-60°C, and 1.5-2 parts of trimethoxysilane and 0.7-1 parts of tetramethyldihydrodisiloxane are added. The mixture is stirred for 8-10 hours. After heating, activated carbon is added and the mixture is stirred for 30-40 minutes. The mixture is cooled to room temperature, filtered to remove the solid, and the filtrate is evaporated by rotary evaporation to obtain the modified macrocyclic polysiloxane. (3) 1-2 parts of reduced graphene oxide are added to 10-20 parts of methanol aqueous solution and mixed. 0.5-1 parts of modified macrocyclic polysiloxane are added. Acetic acid is added to adjust the pH to 4-5. The mixture is stirred at 40-50°C for 4-6 hours, washed until neutral, and dried to obtain macrocyclic polysiloxane modified graphene.

2. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The thickness of the transition layer is 15~20μm, the thickness of the micro-arc oxidation layer is 20~30μm, and the thickness of the antioxidant layer is 5~10μm.

3. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The raw materials of the infiltrator include the following components: by mass, 40-50 parts aluminum powder, 1-2 parts activator, and 10-12 parts alumina.

4. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The aluminum composite sol is prepared by adding aluminum nitrate to deionized water and mixing, adding ammonia to adjust the pH to 9-10, filtering, washing until neutral, adding nitric acid solution to adjust the pH to 3.7-4.5, adding modified macrocyclic polysiloxane-methanol aqueous solution, stirring at 50-55℃, aging, and obtaining aluminum composite sol.

5. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The raw materials for the aluminum composite sol include the following components: by mass, 18-20 parts aluminum nitrate, 4-6 parts modified macrocyclic polysiloxane, and 40-50 parts deionized water.

6. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The iron-nickel alloy substrate comprises the following components: 35.5~36.5wt% Ni, 2~3% Mo, 0.7~1% Ti, 0.3~0.5% Mn, 0.1~0.20% Cr, C≤0.015%, Si≤0.25%, P≤0.008%, S≤0.005%, with the balance being Fe.

7. The method for preparing a low-expansion, oxidation-resistant iron-nickel alloy substrate according to claim 1, characterized in that: The process conditions for the embedding and aluminizing are: vacuum atmosphere, temperature 700~750℃; The micro-arc oxidation process conditions are: current density of 2~4 A / dm³. 2 Frequency 500~1000Hz, duty cycle 10%~30%; The process conditions for the heating and curing are as follows: keep at 60~80℃ for 3~5 hours, heat up to 200~300℃ at a rate of 1~2℃ / min for 1~2 hours, continue to heat up to 400℃~500℃ and keep at 1~2 hours, and heat up to 600~700℃ and keep at 2~3 hours.

8. A low-expansion, oxidation-resistant iron-nickel alloy substrate is prepared by a method according to any one of claims 1 to 7.

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