High-temperature high-strength oxidation-resistant niobium alloy and preparation method thereof

Abstract

The application discloses a high-temperature high-strength antioxidant niobium alloy and a preparation method thereof, relates to the technical field of high-temperature alloy thermal protection, and the antioxidant niobium alloy comprises a niobium alloy base body and an antioxidant coating on the surface of the niobium alloy base body, wherein the antioxidant coating at least comprises a % RE m TaO n +(100-a) % (Nb, X) Si2 phase, X represents Mo and Ta. The preparation method comprises the following steps: proportioning Nb, Mo, Ta and rare earth elements, smelting to obtain a niobium alloy ingot, and then performing silicon infiltration treatment on the niobium alloy ingot and a permeation agent powder to obtain the antioxidant niobium alloy. The niobium alloy has excellent high-temperature antioxidant capacity and meets the high-temperature and long-time application requirements.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy thermal protection technology, specifically to a high-temperature, high-strength, oxidation-resistant niobium alloy and its preparation method. Background Technology

[0002] Niobium and its alloys possess excellent characteristics such as high melting point, good plasticity, moderate density, high high-temperature strength, and good corrosion resistance, making them important candidate materials for the manufacture of key components such as aerospace engine shields, combustion chambers, and attitude control nozzles. They have broad application prospects in aerospace, nuclear industry, and metallurgical industry. However, niobium alloys have poor oxidation resistance. When niobium oxidizes, it mainly forms Nb₂O₅, which increases in volume and generates large internal stresses in the oxide film, easily leading to oxide film rupture. Therefore, this oxide film is not protective, severely limiting the use of niobium alloys as high-temperature materials in oxidizing environments.

[0003] To improve the high-temperature oxidation resistance of niobium, it can be alloyed or an anti-oxidation coating can be prepared on its surface.

[0004] Improving the oxidation resistance of nitrogen (Nb) through alloying primarily involves adding alloying elements to the Nb matrix to modify the Nb oxidation product (Nb₂O₅), thereby improving the oxide film properties and reducing the oxidation rate. Appropriate alloying treatment can influence the crystal defect structure and volume ratio of Nb₂O₅, altering the diffusion characteristics of the oxide layer and thus reducing the oxygen diffusion rate. It can also improve the creep resistance and strength of the oxide film, alleviate internal stress, and reduce crack formation. Furthermore, it can densify the oxide film surface, reduce porosity, and block oxygen diffusion into the matrix.

[0005] Antioxidant coating is a method of preparing an antioxidant coating on the surface of a substrate. Among them, silicide coatings have been the most studied and are the most widely used high-temperature antioxidant coating system for refractory metal surfaces. However, according to the current research status at home and abroad, the following drawbacks still exist: (1) catastrophic oxidation occurs in oxygen-containing environments above 600℃; (2) the thermal expansion coefficients of the coating and the substrate are mismatched, resulting in poor thermal shock resistance; (3) SiO2 has a certain fluidity at high temperatures, and the coating is not strong enough to resist gas erosion.

[0006] The research and development trend of niobium and its alloys is to simultaneously possess excellent oxidation resistance, thermal shock resistance, and gas erosion resistance over a wider operating temperature range. However, there is currently no mature method to solve all of these problems at the same time. Summary of the Invention

[0007] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a high-temperature, high-strength, oxidation-resistant niobium alloy and its preparation method.

[0008] The technical solution of the present invention is as follows:

[0009] A high-temperature, high-strength, oxidation-resistant niobium alloy comprises: a niobium alloy substrate and an oxidation-resistant coating on its surface, wherein the oxidation-resistant coating contains at least a% RE m TaO n +(100-a)%(Nb,X)Si2 phase, where X represents Mo and Ta.

[0010] As a preferred embodiment of the present invention, the niobium alloy matrix comprises the following components: 10-30 wt% Mo, 5-20 wt% Ta, 0.0-5.0 wt% rare earth elements, and the balance being Nb.

[0011] As a preferred embodiment of the present invention, the antioxidant coating has a two-layer structure, with the outer layer containing at least a% RE. m TaO n +(100-a)%(Nb,X)Si2 phase, the inner layer contains at least (Nb,X)5Si3 phase.

[0012] As a preferred embodiment of the present invention, the thickness of the antioxidant coating is 100-300 μm.

[0013] This invention also discloses a method for preparing a high-temperature, high-strength, oxidation-resistant niobium alloy, comprising the following steps:

[0014] S1: Nb, Mo, Ta and rare earth elements are mixed in proportion and smelted to obtain niobium alloy ingots;

[0015] S2: Weigh out a certain amount of silicon powder, sodium fluoride powder, sodium fluorosilicate powder, alumina powder and yttrium oxide powder in proportion, mix them well, and obtain the infiltration agent powder;

[0016] S3: The niobium alloy ingot obtained in S1 and the carburizing agent powder obtained in S2 are loaded into a crucible, sealed, and then placed in a tube furnace for silicon diffusion treatment.

[0017] As a preferred embodiment of the present invention, in step S1, the melting is carried out by at least one of vacuum electron beam melting, vacuum suspension melting and vacuum consumable melting.

[0018] As a preferred embodiment of the present invention, the niobium alloy ingot is further subjected to the following pretreatment: the niobium alloy ingot is cut into blocks by the center line, and then subjected to grinding, polishing, cleaning and drying in sequence.

[0019] As a preferred embodiment of the present invention, in step S2, the infiltrator powder is prepared by ball milling and mixing the following raw materials in the indicated mass fractions: 15-25% silicon powder, 2-6% sodium fluoride powder, 1-3% sodium fluorosilicate powder, 1-5% yttrium oxide powder, and the remainder being alumina powder.

[0020] As a preferred embodiment of the present invention, in step S3, the sealing is performed using a slurry prepared from Al2O3 powder and high-temperature silica sol.

[0021] As a preferred embodiment of the present invention, in step S3, the silicon infiltration process specifically involves heating the tubular furnace to 1000-1200°C under an argon protective atmosphere and holding it at that temperature for 5-30 hours, followed by cooling the furnace.

[0022] This invention has at least one of the following beneficial effects:

[0023] (1) The present invention uses a matrix alloying method to prepare niobium alloys, which have a certain high-temperature oxidation resistance. During high-temperature oxidation, a dense oxide film with self-healing ability can be generated on the alloy surface, which protects the alloy and meets the requirements of high-temperature, short-time and high-reliability applications.

[0024] (2) This invention employs a combination of matrix alloying and surface modification, along with a method that combines alloying and multilayer structure modification of silicide coatings to prepare a%RE. m TaO n Niobium alloys protected by a +(100-a)%(Nb,X)Si2 coating exhibit excellent high-temperature oxidation resistance, meeting the requirements for high-temperature and long-term applications.

[0025] (3) This invention alloys the substrate and simultaneously prepares a composite coating on its surface, reducing the difference in the coefficients of thermal expansion between the two and forming a dense coating with good interfacial bonding, thereby improving the coating's thermal shock resistance; a%RE is prepared on the surface of the niobium alloy by embedding and infiltration method. m TaO n The +(100-a)%(Nb,X)Si2 coating is dense and uniform, with a tight bond to the substrate. The SiO2 protective film formed on the alloy surface during oxidation has high viscosity, thus improving the material's resistance to erosion.

[0026] (4) This invention has the advantages of simple process, convenient operation, low cost, high yield and high efficiency. It is suitable for industrial promotion and application and has important practical value for the preparation of high temperature hot end components in aerospace, nuclear industry and metallurgical industry. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the protective oxide layer formed on the surface of the niobium alloy substrate prepared in Example 1 of the present invention after oxidation in an atmospheric environment for 15 minutes;

[0028] Figure 2 The image shows the surface microstructure of the niobium alloy with an antioxidant coating prepared in Example 4 of this invention.

[0029] Figure 3This is a cross-sectional view of the niobium alloy with an anti-oxidation coating prepared in Example 4 of the present invention after oxidation in an atmospheric environment for 7 hours. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0031] Example 1

[0032] In this embodiment, the specific implementation steps are as follows:

[0033] Step 1, Preparation of niobium alloy: Weigh the corresponding raw materials according to the ratio of 69.9wt% Nb, 20wt% Mo, 10wt% Ta, and 0.1wt% RE, and repeatedly melt them 5 times at 2700℃ by suspension melting to obtain niobium alloy.

[0034] Step 2, Sample preparation: Cut a 6×10×30mm sample from the substrate obtained in Step 1 using wire cutting. Grind and polish the sample in sequence with 80#, 120#, 240#, 600#, 800#, 1000#, 1500# and 2000# silicon carbide sandpaper. After ultrasonic cleaning in anhydrous ethanol for 5 minutes, dry the sample.

[0035] Step 3, Self-oxidation resistance assessment: The polished sample underwent an 18-minute, 1600℃ oxy-acetylene flame high-temperature oxidation test (using a stable oxy-acetylene flame as the heat source, the flame was directed at a 90° angle onto the circular sample to ablate the material). The oxygen-acetylene mixing ratio was controlled between 1.25 and 1.30 during the experiment. After the experiment, the oxide film on the sample surface was dense and intact, with no peeling, and the sample weight increased by 0.39%. After oxidation, a dense oxide film was formed on the sample surface, the cross-section of which is shown below. Figure 1 As shown, this indicates that the alloy exhibits excellent erosion resistance and superior high-temperature oxidation resistance.

[0036] Example 2

[0037] In this embodiment, the specific implementation steps are as follows:

[0038] Step 1, Preparation of niobium alloy: Weigh the corresponding raw materials according to the ratio of 63.4wt% Nb, 20wt% Mo, 15wt% Ta, 0.5wt% Zr, and 0.1wt% RE, and obtain the niobium alloy by electron beam melting (repeated melting 5 times at 2700℃).

[0039] Step 2, Sample preparation: Cut a 6×10×30mm sample from the substrate obtained in Step 1 using wire cutting. Grind and polish the sample in sequence with 80#, 120#, 240#, 600#, 800#, 1000#, 1500# and 2000# silicon carbide sandpaper. After ultrasonic cleaning in anhydrous ethanol for 5 minutes, dry the sample.

[0040] Step 3, Self-oxidation resistance assessment: The polished sample was subjected to a high-temperature oxidation test at 1600℃ in an oxy-acetylene flame for 18 minutes, with the oxygen-acetylene mixing ratio controlled between 1.25 and 1.30 during the test. After the test, the oxide film on the sample surface was dense and intact, with no peeling, and the sample weight increased by 0.53%. This indicates that the alloy exhibits excellent erosion resistance and excellent high-temperature oxidation resistance.

[0041] Example 3

[0042] In this embodiment, the specific implementation steps are as follows:

[0043] Step 1, Preparation of niobium alloy:

[0044] The raw materials were weighed according to the ratio of 69.9wt% Nb, 20wt% Mo, 10wt% Ta and 0.1wt% RE, and the niobium alloy was obtained by suspension melting (repeated melting 5 times at 2700℃).

[0045] Step 2, Preparation of Antioxidant Coating: an a% RE coating is prepared on the surface of the alloy obtained in Step 1. m TaO n +(100-a)%(Nb,X)Si2 anti-oxidation coating.

[0046] Small pieces of 6×10×30mm were cut from the substrate obtained in step one by wire cutting. They were then successively sanded and polished with silicon carbide sandpaper of grades 80#, 120#, 240#, 600#, 800#, 1000#, 1500# and 2000#. After ultrasonic cleaning in anhydrous ethanol for 5 minutes, they were dried.

[0047] Silicon powder, sodium fluoride powder, sodium fluorosilicate powder, yttrium oxide powder, and alumina powder were mixed in a certain proportion and then ball-milled at 120 rpm for 4 hours using a planetary ball mill to obtain a penetrant powder. The powder contained 20 wt% silicon powder, 4 wt% sodium fluoride powder, 2 wt% sodium fluorosilicate powder, 3 wt% yttrium oxide powder, and 71 wt% alumina powder, with each component having a purity of not less than 99.0%.

[0048] After loading the infiltrating agent into an alumina crucible, the previously polished and dried substrate is embedded in the infiltrating agent powder. The crucible is then covered and sealed with a slurry made of Al2O3 powder and high-temperature silica sol in a mass ratio of 4:1. The sealed crucible is placed in a tube furnace and heated to 1150°C under an argon atmosphere for 10 hours to complete the silicon infiltration process and obtain a% RE. m TaO n +(100-a)%(Nb,X)Si2 anti-oxidation coating;

[0049] Step 3, High-temperature test: The silicon-diffused sample was placed in a muffle furnace and subjected to an oxidation resistance test at 1300℃ for 7 hours. The sample was removed from the muffle furnace, weighed, and put back at 1, 2, 3, 5, and 7 hours (thermal and cold cycling). Each time the sample was removed, the oxide film on the surface was dense and intact, with no peeling and good morphology. The oxidation weight gain rate at 7 hours was 0.28%, indicating that the alloy exhibits excellent thermal shock resistance and excellent high-temperature oxidation resistance.

[0050] Example 4

[0051] In this embodiment, the specific implementation steps are as follows:

[0052] Step 1, Preparation of niobium alloy:

[0053] The appropriate raw materials were weighed according to the ratio of 63.4wt% Nb, 20wt% Mo, 15wt% Ta, 0.5wt% Zr, and 0.1wt% RE, and niobium alloy was obtained by electron beam melting.

[0054] Step 2, Preparation of Antioxidant Coating: an a% RE coating is prepared on the surface of the alloy obtained in Step 1. m TaO n +(100-a)%(Nb,X)Si2 anti-oxidation coating;

[0055] Cut small pieces of 10×10×5mm from the substrate obtained in step one by wire cutting. Grind and polish them step by step with silicon carbide sandpaper of grades 80#, 120#, 240#, 600#, 800#, 1000#, 1500# and 2000#. After ultrasonic cleaning in anhydrous ethanol for 5 minutes, dry them.

[0056] Silicon powder, sodium fluoride powder, sodium fluorosilicate powder, yttrium oxide powder, and alumina powder were mixed in a certain proportion and then ball-milled at 120 rpm for 4 hours using a planetary ball mill to obtain a penetrant powder. The powder contained 20 wt% silicon powder, 4 wt% sodium fluoride powder, 2 wt% sodium fluorosilicate powder, 3 wt% yttrium oxide powder, and 71 wt% alumina powder, with each component having a purity of not less than 99.0%.

[0057] After loading the diluent into an alumina crucible, the previously polished and dried substrate is embedded in the diluent powder. The crucible is then covered and sealed with a slurry made of Al2O3 powder and high-temperature silica sol in a mass ratio of 4:1. The sealed crucible is placed in a tube furnace and heated to 1150°C for 20 hours under an argon atmosphere to complete the silicon infiltration process and obtain a% RE. m TaO n +(100-a)%(Nb,X)Si2 anti-oxidation coating.

[0058] The surface microstructure of the coating obtained in step two is shown below. Figure 2 The coating is dense and does not peel off;

[0059] Step 3, High-Temperature Testing: The silicon-infiltrated sample was placed in a muffle furnace and subjected to a 7-hour oxidation resistance test at 1300℃ in an atmospheric environment. The sample was removed from the muffle furnace, weighed, and returned at hours 1, 2, 3, 5, and 7 (thermal cycling). The surface oxide film was dense and intact, with no peeling. The oxidation weight gain at hour 7 was 0.37%. The cross-section of the oxidized coating is shown below. Figure 3 As shown, after 7 hours of oxidation, the coating thickness is 218 μm, and it has a two-layer structure, consisting of an outer layer and an inner layer approximately 19 μm thick. This indicates that the alloy exhibits excellent thermal shock resistance and superior high-temperature oxidation resistance.

[0060] The test temperatures for Examples 1-4 were 1300℃ and 1600℃, respectively, far exceeding the initial temperature of 600℃ in the mid-temperature zone. The samples in these examples remained intact at these temperatures, thus solving the problem of catastrophic oxidation occurring above the mid-temperature zone. In Examples 1 and 2, during the high-temperature oxidation experiment in an oxy-acetylene flame at 1600℃, the flame velocity was extremely high, yet the sample morphology remained intact without peeling, demonstrating excellent erosion resistance. Examples 3 and 4 underwent a 7-hour static oxidation experiment at 1300℃, with the samples being removed from the muffle furnace, weighed, and returned at the 1st, 2nd, 3rd, 5th, and 7th hours, respectively. This means the samples experienced multiple thermal cycles, i.e., thermal shock, yet the samples still maintained their morphology, indicating excellent thermal shock resistance.

[0061] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of the present invention.

Claims

1. A high-temperature, high-strength, oxidation-resistant niobium alloy, characterized in that, include: An anti-oxidation coating on a niobium alloy substrate and its surface, wherein the anti-oxidation coating has a two-layer structure, and the outer layer contains at least a% RE m TaO n +(100-a)% (Nb, X)Si2 phase, the inner layer contains at least (Nb,X)5Si3 phase, where X represents Mo and Ta; The niobium alloy matrix comprises the following components: 10–30 wt% Mo, 5–20 wt% Ta, 0.0–5.0 wt% rare earth elements, with the balance being Nb; The method for preparing the niobium alloy includes the following steps: S1: Nb, Mo, Ta and rare earth elements are mixed in proportion and smelted to obtain niobium alloy ingots; S2: Weigh out a certain amount of silicon powder, sodium fluoride powder, sodium fluorosilicate powder, alumina powder and yttrium oxide powder in proportion, mix them well, and obtain the infiltration agent powder; S3: After loading the infiltrating agent powder into an alumina crucible, bury the niobium alloy ingot in the infiltrating agent powder, cover the crucible, and seal it with a slurry made of Al2O3 powder and high-temperature silica sol at a mass ratio of 4:1; place the sealed crucible in a tube furnace tube, heat it to 1000-1200℃ under an argon atmosphere, hold it at that temperature for 5-30 hours, and then cool it with the furnace to complete the silicon infiltration process and obtain a%RE. m TaO n +(100-a)% (Nb, X)Si2 anti-oxidation coating; In step S2, the infiltrator powder is prepared by ball milling and mixing the following raw materials in the following mass fractions: 15-25% silicon powder, 2-6% sodium fluoride powder, 1-3% sodium fluorosilicate powder, 1-5% yttrium oxide powder, and the balance being alumina powder.

2. The high-temperature, high-strength, oxidation-resistant niobium alloy according to claim 1, characterized in that, The thickness of the antioxidant coating is 100-300 μm.

3. A method for preparing a high-temperature, high-strength, oxidation-resistant niobium alloy as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Nb, Mo, Ta and rare earth elements are mixed in proportion and smelted to obtain niobium alloy ingots; S2: Weigh out a certain amount of silicon powder, sodium fluoride powder, sodium fluorosilicate powder, alumina powder and yttrium oxide powder in proportion, mix them well, and obtain the infiltration agent powder; S3: After loading the infiltrating agent powder into an alumina crucible, bury the niobium alloy ingot in the infiltrating agent powder, cover the crucible, and seal it with a slurry made of Al2O3 powder and high-temperature silica sol at a mass ratio of 4:1; place the sealed crucible in a tube furnace tube, heat it to 1000-1200℃ under an argon atmosphere, hold it at that temperature for 5-30 hours, and then cool it with the furnace to complete the silicon infiltration process and obtain a%RE. m TaO n +(100-a)% (Nb, X)Si2 anti-oxidation coating; In step S2, the infiltrator powder is prepared by ball milling and mixing the following raw materials in the following mass fractions: 15-25% silicon powder, 2-6% sodium fluoride powder, 1-3% sodium fluorosilicate powder, 1-5% yttrium oxide powder, and the balance being alumina powder.

4. The method for preparing a high-temperature, high-strength, oxidation-resistant niobium alloy according to claim 3, characterized in that, In step S1, the melting is carried out using at least one of vacuum electron beam melting, vacuum suspension melting, and vacuum consumable melting.

5. The method for preparing a high-temperature, high-strength, oxidation-resistant niobium alloy according to claim 3, characterized in that, The niobium alloy ingot also undergoes the following pretreatment: the niobium alloy ingot is wire-cut into blocks, and then sequentially subjected to grinding, polishing, cleaning and drying.

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