High-temperature nitriding method using nitride dispersion strengthened cobalt-based superalloy

Abstract

The application relates to a high-temperature nitriding preparation method of a cobalt-based high-temperature alloy by using nitride dispersion reinforcement, and belongs to the technical field of dispersion reinforcement materials. The cobalt-based high-temperature alloy profile is placed in a high-temperature nitriding furnace, the inner cavity of the nitriding furnace is vacuumized, the cobalt-based high-temperature alloy profile is in a vacuum environment, then argon is filled into the inner cavity of the nitriding furnace, and the temperature is raised to a set temperature of 1100-1200 DEG C; then a mixed gas atmosphere of nitrogen and argon is introduced into the inner cavity of the nitriding furnace, the flow speed is 80-120 mL / min, the cobalt-based high-temperature alloy profile is subjected to nitriding treatment in the furnace for a certain time, and after the high-temperature nitriding process is completed, the temperature is cooled to room temperature at a cooling rate of 20-40 DEG C / min. The method is aimed at cobalt-based high-temperature alloy wire or plate, high-temperature nitriding treatment is carried out in a mixed gas atmosphere of nitrogen and argon, stable nitrides are formed in the alloy organization to play a dispersion reinforcement role, and the problem that the strength of the cobalt-based high-temperature alloy is relatively low can be effectively solved.

Description

Technical Field

[0001] This invention relates to a high-temperature nitriding preparation method for cobalt-based superalloys using nitride dispersion strengthening, belonging to the field of dispersion strengthening materials technology. Background Technology

[0002] Brush seals are a type of contact-type dynamic sealing technology with excellent sealing performance developed in recent years. Their leakage rate is 1 / 5 to 1 / 10 that of traditional labyrinth seals, and they are widely used in high-end equipment such as aero engines and gas turbines. A brush seal assembly consists of tightly packed, high-rigidity, high-temperature alloy wires welded to a low-expansion alloy brush shank. The brush wire bundle is the key to the performance of the brush seal. Brush wire materials are divided into two types: ① metallic materials such as nickel-based and cobalt-based high-temperature alloys; ② non-metallic materials such as aramid fiber brush wires. Compared with non-metallic brush wire materials, metallic brush wire materials have a wider service environment range and are easier to apply; therefore, metallic brush wire materials are usually chosen. To improve weldability, the brush seal wire is made of cobalt-based high-temperature alloys to replace the traditional nickel-based high-temperature alloys. Compared with nickel-based high-temperature alloys, cobalt-based high-temperature alloys have a higher elastic modulus and better weldability, but lower strength. Therefore, dispersion strengthening methods (intrinsic nitrides) need to be introduced into the cobalt-based high-temperature alloys to improve high-temperature strength, specific stiffness, etc., thereby increasing the wear resistance and long-term safe service life of the brush wires.

[0003] Nitriding is a common method for improving the strength, hardness, wear resistance, and corrosion resistance of materials. Currently, nitriding research both domestically and internationally focuses on gas nitriding and ion nitriding, with temperatures ranging from 400 to 700°C. Ammonia decomposition is often used as the nitriding atmosphere. However, existing technologies for improving the mechanical properties of cobalt-based superalloys encounter the following problems: ① Low nitriding temperature. For cobalt-based superalloys, nitrogen atoms have extremely low solid solubility in cobalt, making it impossible to form stable nitrides at nitriding temperatures of 400–700°C; ② Insufficient nitriding layer depth. The face-centered cubic crystal structure of cobalt-based superalloys results in dense atomic packing, hindering nitrogen atom diffusion and making nitriding difficult, leading to insufficient nitriding layer depth; ③ Problems with nitriding gas composition. Currently, hydrogen is mostly used in nitriding processes, which can easily cause safety issues if not handled properly, limiting the effectiveness of nitriding. Therefore, based on these problems, a novel nitriding process is needed to obtain high-performance cobalt-based superalloys. Summary of the Invention

[0004] To address the technical challenges of low strength in cobalt-based superalloys, this invention aims to provide a high-temperature nitriding method for preparing cobalt-based superalloys using nitride dispersion strengthening. This method utilizes endogenous nitrides to supplement dispersion strengthening and proposes a method for preparing endogenous nitrides through high-temperature nitriding treatment. This method solves the problems of cobalt-based superalloys failing to generate stable nitrides and insufficient nitriding layer depth during traditional nitriding processes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-temperature nitriding method for preparing cobalt-based superalloys using nitride dispersion strengthening includes the following steps:

[0007] (1) Cobalt-based high-temperature alloy profiles

[0008] Cobalt-based high-temperature alloy profiles were prepared using traditional processes. Their nominal chemical composition, by mass percentage, was: Cr 24–28%, Fe 20–23%, Ni 5–10%, C 0.05–0.15%, Al 0.3–0.4%, with the remainder being Co.

[0009] (2) High-temperature nitriding treatment

[0010] The cobalt-based superalloy profile is placed in a high-temperature nitriding furnace. The furnace cavity is evacuated to place the cobalt-based superalloy profile in a vacuum environment. Argon gas is then introduced into the furnace cavity, and the temperature is initially increased to the set temperature of 1100–1200°C at a heating rate of 40–60°C / min. Subsequently, a nitrogen and argon mixture is introduced into the furnace cavity at a flow rate of 80–120 mL / min. The cobalt-based superalloy profile undergoes nitriding treatment in the furnace for a certain period of time. After the high-temperature nitriding process is completed, it is cooled to room temperature at a cooling rate of 20–40°C / min.

[0011] In the high-temperature nitriding preparation method of cobalt-based superalloys using nitride dispersion strengthening, in step (1), the typical dimensions of the cobalt-based superalloy profile are as follows: a plate with a thickness of 1.8 to 2.2 mm and a wire with a diameter of Φ0.1 to 0.2 mm.

[0012] In the high-temperature nitriding preparation method of cobalt-based superalloy strengthened by nitride dispersion, in step (1), the cobalt-based superalloy profile has an equiaxed grain structure with an average grain diameter of 30-50 μm, and is composed of MC-type carbides and austenitic matrix. By volume percentage, MC-type carbides account for 1.24-1.98%, and the remainder is austenitic matrix.

[0013] In the high-temperature nitriding preparation method for strengthening cobalt-based superalloys using nitride dispersion, in step (2), the nitriding treatment time is 1 to 24 hours and the nitriding layer depth is 100 to 800 μm.

[0014] The high-temperature nitriding preparation method for cobalt-based high-temperature alloys using nitride dispersion strengthening, in step (2), in the mixed atmosphere of nitrogen and argon, by volume percentage, nitrogen is 55-95% and argon is 5-45%, and the volume purity of both nitrogen and argon is above 90%.

[0015] In the high-temperature nitriding preparation method for cobalt-based superalloys strengthened by nitride dispersion, step (2) describes the following performance indicators of the nitride-dispersion strengthened cobalt-based superalloy after high-temperature nitriding: surface microhardness is 300-500 Hv. 0.1 The wear rates under loads of 5N and 15N were 0.5–1.5 × 10⁻⁶, respectively. -5 mm 3 ·N -1 ·m -1 and 2~4×10 -5 mm 3 ·N -1 ·m -1 The yield strengths at room temperature and 600℃ are 500–700 MPa and 150–300 MPa, respectively.

[0016] The design concept of this invention is:

[0017] By using a high-temperature nitriding process to disperse nitrides as reinforcing phases within a cobalt-based superalloy, the strength, hardness, and wear resistance of the superalloy are significantly improved. The introduction of the nitride reinforcing phase has specific effects: on the one hand, it hinders the movement of intragranular dislocations, forming an intragranular strengthening mechanism, thereby increasing the hardness and yield strength of the cobalt-based superalloy; on the other hand, the reinforcing phase has extremely high stability, increasing the service temperature of the cobalt-based superalloy during service. Ultimately, a cobalt-based superalloy with high strength, high wear resistance, and good long-term safe service performance is obtained.

[0018] Compared with the prior art, the features and beneficial effects of the present invention are as follows:

[0019] 1. The method of the present invention can form endogenous nitrides inside the microstructure of cobalt-based superalloys. These endogenous nitrides are small in size and dispersed in distribution. Compared with intermetallic compounds and carbides, the endogenous nitrides have higher thermodynamic stability.

[0020] 2. This invention uses a higher temperature for high-temperature nitriding treatment (temperature not lower than 1000℃). The higher nitriding temperature can accelerate the nitriding rate, so that the N in the alloy has a sufficiently high saturation rate, increase the nitrogen concentration on the surface of the nitrided layer, and more effectively promote the dispersion and distribution of endogenous nitrides and obtain a nitrided layer of sufficient thickness within a reasonable time.

[0021] 3. The present invention introduces a nitrogen and argon mixed atmosphere into the nitriding furnace, which is safer. In addition, a high-performance vacuum pump composed of mechanical pump and molecular pump is added to minimize the reaction between the material placed in the furnace and oxygen in the air, thereby changing the original properties of the material.

[0022] 4. The nitride dispersion-strengthened cobalt-based superalloy prepared using the method of the present invention exhibits significantly improved strength and wear resistance. Attached Figure Description

[0023] Figure 1 This is a typical microstructure of a cobalt-based superalloy.

[0024] Figure 2 Cross-sectional view of the nitrided layer of a cobalt-based superalloy after high-temperature nitriding treatment. Detailed Implementation

[0025] In its specific implementation, this invention proposes a high-temperature nitriding preparation method for cobalt-based superalloys strengthened by nitride dispersion, comprising the following steps:

[0026] 1. Cobalt-based high-temperature alloy profiles

[0027] Cobalt-based superalloy profiles are prepared using traditional processes. The nominal chemical composition (mass percentage) is: Cr 26%, Fe 21.6%, Ni 8%, C 0.1%, Al 0.35%, with the remainder being Co. Typical profile dimensions are as follows: plates with a thickness of 2 mm, or wires with a diameter of Φ0.15 mm.

[0028] 2. High-temperature nitriding treatment

[0029] The cobalt-based superalloy profile sample was placed inside a high-temperature nitriding furnace. The furnace cavity was evacuated to create a vacuum environment for the sample. Argon gas was then introduced into the furnace cavity, and the temperature was raised to the set temperature at a rate of 50°C / min. Subsequently, a nitrogen-argon mixture with a specific ratio was introduced into the furnace cavity at a flow rate of 100 mL / min. The sample underwent nitriding treatment in the furnace for a certain period. After the high-temperature nitriding process was completed, the sample was cooled to room temperature at a rate of 30°C / min.

[0030] 3. Dispersion-strengthened cobalt-based superalloy profiles

[0031] Microstructure and performance testing were conducted on high-temperature nitrided cobalt-based superalloy profiles to determine the depth of the nitrided layer, which significantly improved hardness, wear resistance, and strength.

[0032] The present invention will now be described in detail with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments:

[0033] Example 1:

[0034] In this embodiment, the preparation process steps of the nitride dispersion strengthened cobalt-based superalloy are as follows:

[0035] 1. Cobalt-based superalloy profiles are prepared using processes such as vacuum induction melting, electroslag remelting, forging, hot and cold deformation, and heat treatment. The nominal chemical composition (mass percentage) is: Cr 26%, Fe 21.6%, Ni 8%, C 0.1%, Al 0.35%, with the remainder being Co. Typical profile dimensions are as follows: plates with a thickness of 2 mm, or wires with a diameter of Φ0.15 mm.

[0036] like Figure 1 As shown, the cobalt-based superalloy prepared by the above method has an equiaxed grain structure with an average grain diameter of about 40 μm; it is composed of MC-type carbides and an austenitic matrix, with MC-type carbides accounting for 1.24 to 1.98% by volume and the remainder being an austenitic matrix.

[0037] 2. High-Temperature Nitriding Treatment. The cobalt-based superalloy profile sample was placed in a high-temperature nitriding furnace. The furnace cavity was evacuated to create a vacuum environment. Argon gas was then introduced into the furnace cavity, and the temperature was initially raised to 1200°C at a rate of 50°C / min. Subsequently, a mixed atmosphere of 95% N₂ + 5% Ar was introduced into the furnace cavity at a flow rate of 100 mL / min for 3 hours. After the high-temperature nitriding process was completed, the sample was cooled to room temperature at a rate of 30°C / min. The nitrided layer depth was approximately 375 μm, with fine and uniformly distributed granular nitride reinforcing phases forming within the grains. The size of the nitride reinforcing phase was 1–2 μm, and the volume percentage of the nitride reinforcing phase was 2.00–2.50%.

[0038] The nitride dispersion-strengthened cobalt-based superalloy obtained by the above method, tested using a KB30SRFA micro Vickers hardness tester according to GB / T 4340.1-2009 Metallic Materials - Vickers Hardness Test - Part 1: Test Methods, showed an increase in microhardness compared to the unnitrided alloy. The surface microhardness increased from 230 Hv. 0.1 Increased to 335Hv 0.1 The tribological characteristics of the nitrided layer were determined using a UMT-2 multifunctional tribological testing machine and compared with those of the unnitrided sample. The upper sample was a Φ4mm Si3N4 ball, and the lower samples were a cobalt-based superalloy and a nitride-dispersion-strengthened cobalt-based superalloy sample after high-temperature nitriding. A reciprocating motion mode was used with a frequency of 2Hz, loading forces of 5N and 15N, a working time of 30 minutes, and a total friction stroke of 72m. The wear rate of the cobalt-based superalloy under loads of 5N and 15N was calculated to be 14.6 × 10⁻⁶. -5 mm 3 ·N -1·m -1 and 8.8×10 -5 mm 3 ·N -1 ·m -1 The wear rate of nitride dispersion strengthened cobalt-based superalloys under loads of 5N and 15N is 1.3×10⁻⁶. -5 mm 3 ·N -1 ·m -1 and 2.7×10 -5 mm 3 ·N -1 ·m -1 Comparative studies showed that, under the same load, the wear resistance of nitride-dispersion strengthened cobalt-based superalloys after high-temperature nitriding was significantly improved.

[0039] Example 2:

[0040] In this embodiment, the preparation process steps of the nitride dispersion strengthened cobalt-based superalloy are as follows:

[0041] The cobalt-based superalloy was obtained using the same process as in Example 1, except for the high-temperature nitriding process parameters: the cobalt-based superalloy profile sample was placed upright in a high-temperature nitriding furnace, and the furnace cavity was evacuated to create a vacuum environment. Argon gas was then introduced into the furnace cavity, and the temperature was initially increased to 1200°C at a rate of 50°C / min. Subsequently, a mixed atmosphere of 55% N2 + 45% Ar was introduced into the furnace cavity by volume percentage at a flow rate of 100 mL / min for 10 hours. After the high-temperature nitriding process was completed, the sample was cooled to room temperature at a rate of 30°C / min.

[0042] like Figure 2 As shown, the nitride dispersion strengthened cobalt-based superalloy prepared after high-temperature nitriding treatment has a nitriding layer depth of about 670 μm. Fine and uniformly distributed granular nitride strengthening phases are formed in the crystal, with a size of 1 to 2 μm and a volume percentage of 6.50 to 7.00%.

[0043] The nitride dispersion-strengthened cobalt-based superalloy obtained by the above method, tested using a KB30SRFA micro Vickers hardness tester according to GB / T 4340.1-2009 Metallic Materials - Vickers Hardness Test - Part 1: Test Methods, showed an increase in microhardness compared to the unnitrided alloy. The surface microhardness increased from 230 Hv. 0.1 Increased to 420Hv 0.1Using a Zwick Z100 tensile testing machine, the mechanical properties were tested according to GB / T 228.1-2010 Metallic materials, tensile testing—Part 1: Test at room temperature and GB / T 228.2-2015 Metallic materials, tensile testing—Part 2: Test at high temperature. The nitride dispersion strengthened cobalt-based superalloy after high-temperature nitriding showed improved performance compared to the unnitrided alloy. The yield strength at room temperature increased from 302 MPa to 570 MPa, and the yield strength at 600℃ increased from 138 MPa to 197 MPa.

[0044] The results show that the method of the present invention is effective in solving the problem of relatively low strength of cobalt-based superalloy wires or plates by using high-temperature nitriding treatment in a mixed atmosphere of nitrogen and argon to form stable nitrides in the alloy structure and exert a dispersion strengthening effect.

Claims

1. A method for preparing cobalt-based superalloys using nitride dispersion strengthening at high temperatures, characterized in that, Includes the following steps: (1) Cobalt-based high-temperature alloy profiles Cobalt-based high-temperature alloy profiles were prepared using traditional processes. Their nominal chemical composition, by mass percentage, was: Cr 24-28%, Fe 20-23%, Ni 5-10%, C 0.05-0.15%, Al 0.3-0.4%, with the remainder being Co. (2) High-temperature nitriding treatment A cobalt-based superalloy profile is placed inside a high-temperature nitriding furnace. The furnace cavity is evacuated to create a vacuum environment for the profile. Argon gas is then introduced into the furnace cavity, and the temperature is initially increased to a set temperature of 1100–1200 °C at a rate of 40–60 °C / min. A nitrogen-argon mixture is then introduced into the furnace cavity at a flow rate of 80–120 mL / min. The profile undergoes nitriding treatment for a certain period. After the high-temperature nitriding process, the profile is cooled to room temperature at a rate of 20–40 °C / min. The high-temperature nitriding process disperses nitrides as reinforcing phases within the cobalt-based superalloy, improving its strength, hardness, and wear resistance. The size of the nitride reinforcing phase is 1–2 μm. In step (2), the nitriding treatment time is 1 to 24 hours and the nitriding layer depth is 100 to 800 μm; in step (2), the nitrogen and argon mixed atmosphere is 55 to 95% by volume percentage and 5 to 45% by volume percentage, and the volume purity of nitrogen and argon is above 90%. In step (1), the dimensions of the cobalt-based high-temperature alloy profile are as follows: a plate with a thickness of 1.8~2.2 mm, or a wire with a diameter of Φ0.1~0.2 mm; In step (1), the cobalt-based high-temperature alloy profile has an equiaxed grain structure with an average grain diameter of 30~50 μm. It is composed of MC-type carbides and an austenitic matrix. By volume percentage, the MC-type carbides account for 1.24~1.98%, and the remainder is an austenitic matrix. In step (2), the performance indicators of the nitride dispersion-strengthened cobalt-based superalloy after high-temperature nitriding are as follows: the surface microhardness is 300~500 H. v 0.1 The wear rates under loads of 5 N and 15 N were 0.5~1.5×10⁻⁶, respectively. -5 mm 3 ·N -1 ·m -1 and 2~4×10 -5 mm 3 ·N -1 ·m -1 The yield strengths at room temperature and 600 ℃ are 500~700 MPa and 150~300 MPa, respectively.

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