A nano-precipitate strengthening hydrogen embrittlement resistant medium-entropy alloy and a preparation method thereof

Abstract

The application belongs to the technical field of medium-entropy alloys, and particularly relates to a nano-precipitated phase reinforced hydrogen embrittlement resistant medium-entropy alloy and a preparation method thereof. The medium-entropy alloy with high dispersion distribution of nano-scale L12 phase precipitation is obtained through electric arc melting, homogenization treatment, cold rolling and aging treatment, the strength and toughness of the medium-entropy alloy are matched, the hydrogen embrittlement resistance of the medium-entropy alloy during service is greatly improved, and the comprehensive performance of the material, such as the material strengthening and hydrogen embrittlement resistance, is improved, which has far-reaching significance.

Description

Technical Field

[0001] This invention relates to the field of medium-entropy alloy technology, specifically to a medium-entropy alloy with nano-precipitated phase reinforcement to resist hydrogen embrittlement and its preparation method. Background Technology

[0002] With the advancement of major industries such as aerospace and defense, as well as the development of hydrogen energy, the development of new alloy materials with high strength, high toughness, resistance to hydrogen embrittlement, and corrosion resistance is urgently needed. As research on medium-entropy alloys deepens, their unique properties, including high strength and high ductility, have gradually attracted attention. However, hydrogen embrittlement has long been a bottleneck restricting the industrial application of medium-entropy alloys, often leading to catastrophic consequences. Summary of the Invention

[0003] To address the problems existing in the prior art, the main objective of this invention is to propose a nano-precipitated phase-reinforced medium-entropy alloy resistant to hydrogen embrittlement and its preparation method.

[0004] According to one aspect of the present invention, the present invention provides the following technical solution:

[0005] A nano-precipitated phase-reinforced medium-entropy alloy for resisting hydrogen embrittlement comprises, by mass percentage: Co 33.30–34.30%; Ni 33.20–34.20%; Cr 29.45–30.45%; Ti 1.30–1.90%; Al 0.65–1.05%; B 0.04–0.06%; with the balance being unavoidable impurities.

[0006] As a preferred embodiment of the medium-entropy alloy for hydrogen embrittlement resistance reinforced by nano-precipitates described in this invention, the microstructure of the medium-entropy alloy comprises an FCC solid solution structure composed of equiatomic proportions of Co, Cr, Ni, and small amounts of Al and Ti, and nano-sized L12 precipitates dispersed in the matrix. Co, Cr, and Ni are the main elements constituting the medium-entropy alloy, forming a face-centered cubic (FCC) solid solution structure in equiatomic proportions, thus providing good plasticity and toughness. Al forms L12-type nano-sized precipitates with other elements in the alloy, significantly improving the alloy's strength. Ti can form stable TiC with Al, helping to fix C in the alloy, preventing carbide precipitation, and thus maintaining the alloy's homogeneity. Trace amounts of B atoms tend to segregate at grain boundaries, enhancing the cohesive force at grain boundaries, thereby improving the alloy's resistance to hydrogen embrittlement. Furthermore, the segregation of B can reduce the diffusion rate of hydrogen at grain boundaries, reducing stress concentration of hydrogen at grain boundaries, thereby reducing the nucleation and propagation of hydrogen-induced cracks.

[0007] As a preferred embodiment of the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy described in this invention, the average size of the nano-sized L12 precipitate is 17.5–27.0 nm.

[0008] As a preferred embodiment of the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy of the present invention, the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy has a yield strength ≥780MPa, ductility ≥39.0%, hydrogen embrittlement sensitivity index ≤4.5% after 24h hydrogen pre-charging, and hydrogen embrittlement sensitivity index ≤9.5% after 72h hydrogen pre-charging.

[0009] According to another aspect of the present invention, the present invention provides the following technical solution:

[0010] A method for preparing a nano-precipitated phase-reinforced, hydrogen-embrittlement-resistant medium-entropy alloy includes the following steps:

[0011] S1. Raw materials are selected according to the composition of medium-entropy alloy, and medium-entropy alloy ingots are obtained by arc melting in an argon atmosphere.

[0012] S2. The elemental distribution of the ingot is controlled through homogenization treatment.

[0013] S3. The ingot is rolled into sheet metal using a cold rolling process;

[0014] S4. The plate is subjected to heat treatment by solution treatment and aging treatment to obtain a medium entropy alloy with nano-precipitated phase reinforcement and resistance to hydrogen embrittlement.

[0015] As a preferred embodiment of the preparation method of a nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy according to the present invention, in step S1, the ingot obtained by arc melting is flipped and remelted at least 5 times to ensure uniform element distribution.

[0016] As a preferred embodiment of the preparation method of the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy of the present invention, in step S2, the homogenization treatment temperature is 1200±50℃ and the homogenization treatment time is 3±0.2h.

[0017] As a preferred embodiment of the preparation method of the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy of the present invention, wherein: in step S3, rolling reduces the thickness of the blocky medium-entropy alloy ingot by 50±5%.

[0018] In a preferred embodiment of the preparation method of the nano-precipitated phase-reinforced anti-hydrogen embrittlement medium-entropy alloy according to the present invention, step S4 includes the following steps:

[0019] S41. The plate is heated to 1000±50℃ and held for 1±0.05h to achieve solid solution treatment, which dissolves the second phase particles that may exist in the alloy, promotes the uniform distribution of elements, and reduces the grain size.

[0020] S42. The solution-treated board is aged at 800±50℃ for 5±0.3h to ensure sufficient precipitation of L12 phase particles.

[0021] S43. The aged plate is water-quenched for rapid cooling to fix the microstructure generated by the heat treatment and prevent phase transformation or particle coarsening during the cooling process.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention proposes a medium-entropy alloy with nano-precipitated phase reinforcement to resist hydrogen embrittlement and its preparation method. The medium-entropy alloy with highly dispersed nano-scale L12 phase precipitation is obtained by arc melting, homogenization treatment, cold rolling and aging treatment. This achieves a balance between strength and toughness in the medium-entropy alloy and significantly improves the hydrogen embrittlement resistance of the material during service. This has profound significance for improving the comprehensive performance of the material, such as strengthening and resistance to hydrogen embrittlement. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 The size and distribution of the diffuse L12 phase in the samples of Example 1 and Comparative Example 1 of this invention are statistically analyzed and shown under a transmission electron microscope.

[0026] Figure 2 The mechanical properties of the samples from Example 1 and Comparative Example 1 of this invention are shown in the diagram.

[0027] Figure 3 The above are the desorption peak (TDS) diagrams of the samples from Example 1 and Comparative Example 1 after hydrogen charging.

[0028] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention proposes a nano-precipitated phase-reinforced medium-entropy alloy for hydrogen embrittlement resistance and its preparation method. Introducing a precipitated phase is an effective method for preventing hydrogen embrittlement, and the academic community has achieved some results in the research of precipitated phases. The L12 phase, as a precipitated phase, has a coherent interface with the matrix, effectively hindering dislocation movement and improving the alloy's yield strength. Simultaneously, it promotes dislocation accumulation during tensile testing, thereby increasing the alloy's ultimate tensile strength. Furthermore, the L12 phase can trap hydrogen atoms in the alloy matrix, thereby reducing the concentration of diffusible hydrogen in the alloy and helping to reduce hydrogen-induced stress concentration and the risk of hydrogen embrittlement. Therefore, the L12 phase plays a crucial role in improving the performance of medium-entropy alloys, not only improving the alloy's strength and toughness but also significantly enhancing its resistance to hydrogen embrittlement, which is of great significance for the alloy's application in harsh environments. The segregation of boron atoms at grain boundaries alters hydrogen diffusion behavior and stress concentration, while the precipitation of the L12 phase directly reduces the risk of hydrogen embrittlement by trapping hydrogen atoms. The combination of these two factors provides the alloy with superior resistance to hydrogen embrittlement. Therefore, the process design of nano-precipitated phase-reinforced medium-entropy alloys for hydrogen embrittlement resistance based on the above concepts is particularly important. Highly dispersed nanoscale L12 phase precipitation was obtained through electric arc melting and a series of homogenization treatments, followed by cold rolling and aging treatments, in order to achieve a balance between alloy strength and toughness and significantly improve the material's resistance to hydrogen embrittlement during service. This has profound significance for improving the material's comprehensive properties, such as strengthening and resistance to hydrogen embrittlement.

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0032] Example 1

[0033] A method for preparing a nano-precipitated phase-reinforced, hydrogen-embrittlement-resistant medium-entropy alloy includes the following steps:

[0034] S1, based on medium-entropy alloys (CoCrNi) 96 Al 1.8 Ti 1.8 B 0.4 The composition (by mass percentage, including: Co 33.87%; Ni 33.74%; Cr 29.88%; Ti 1.58%; Al 0.88%; B 0.05%, with the balance being unavoidable impurities) is as follows: raw materials are used to obtain medium-entropy alloy ingots through arc melting in an argon atmosphere; the ingots obtained by arc melting are flipped and remelted 5 times to ensure uniform element distribution.

[0035] S2. The element distribution of the ingot is controlled by homogenization treatment; the homogenization treatment temperature is 1200℃ and the homogenization treatment time is 3h.

[0036] S3. The ingot is rolled into a sheet using a cold rolling process; rolling reduces the thickness of the blocky medium-entropy alloy ingot by 50%.

[0037] S4. The plate is subjected to heat treatment by solution treatment and aging treatment. The plate is heated to 1000℃ and held for 1 hour to achieve solution treatment. After solution treatment, the plate is aged at 800℃ for 5 hours. After aging treatment, the plate is water quenched to obtain a medium entropy alloy with nano-precipitated phase strengthening and resistance to hydrogen embrittlement.

[0038] Comparative Example 1

[0039] The difference from Example 1 is that no aging process is performed in step S4.

[0040] Figure 1 A series of microscopic images were used to demonstrate the microstructure of CoCrNi-based medium-entropy alloys under different treatment conditions:

[0041] Figure 1 Image a is a BF image: a bright-field image under a transmission electron microscope, showing the microstructure of sample 1 (ATB-S).

[0042] Figure 1 Image b is an HRTEM image: a high-resolution transmission electron microscope image that further magnifies the details of the alloy in Comparative Example 1.

[0043] Figure 1 In the middle, 'c' stands for SAED: Selected Area Electron Diffraction mode, used to determine crystal structure and orientation.

[0044] Figure 1 In the middle, d is a HAADF image: a high-angle annular dark field image, which specifically shows the distribution of L12 particles in the alloy of Example 1 sample (ATB-SA), as well as an inset of the particle size distribution;

[0045] Figure 1 In the middle, e represents STEM-EDS: scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, which shows the distribution of L12 particles and elements in the FCC matrix;

[0046] Figure 1 f in the middle represents SAED: The selected area electron diffraction mode of the sample in Example 1 is shown again, proving the existence of L12 particles;

[0047] Figure 1 In the middle, g represents HRTEM: a high-resolution image of L12 particles in the alloy sample of Example 1;

[0048] Figure 1 The middle h represents the interface structure: it shows the interface between the L12 particle and the FCC matrix, demonstrating a fully coherent structure.

[0049] In the sample of Example 1, a large number of diffusely distributed nanoscale L12 precipitates were observed by transmission electron microscopy (TEM). These L12 phases exhibited a very fine and uniform size distribution, with an average particle size of 22.2 ± 4.5 nm. These particles were clearly visible in high-angle annular dark-field (HAADF) images, and high-resolution transmission electron microscopy (HRTEM) images confirmed the existence of a completely coherent interface between them and the face-centered cubic (FCC) matrix. This coherent interface indicates that the lattice mismatch between the L12 particles and the matrix is ​​very small, which helps to improve the strength of the alloy without introducing additional stress concentration, thus not reducing the toughness of the material.

[0050] Figure 2 The mechanical property diagrams for the samples of Example 1 and Comparative Example 1 show a comparison of the mechanical properties of the sample of Example 1 and the sample of Comparative Example 1 (without aging treatment):

[0051] Figure 2 In the middle, a represents the engineering stress-strain curve: showing the stress-strain behavior of the alloys of Comparative Example 1 and Example 1 after no hydrogen pre-charging and after 24 h and 72 h of hydrogen pre-charging;

[0052] Figure 2 In the middle, b is the true stress-strain curve: it further demonstrates the relationship between true stress and true strain under the same conditions;

[0053] Figure 2 In the middle, c represents the strain hardening rate curve, which shows the change in strain hardening rate of the two alloys during the tensile process.

[0054] The sample of Example 1 exhibited a significantly improved yield strength of approximately 780.8 MPa, far exceeding the yield strength of the sample of Comparative Example 1 (approximately 386.5 MPa). Furthermore, the ductility of the sample of Example 1 was 39.5%, compared to 60.7% for the sample of Comparative Example 1, representing a decrease of only 35.9%. This significant strengthening effect is attributed to the dispersion strengthening effect of the L12 particles. Notably, although the strength of the sample of Example 1 was improved, its hydrogen embrittlement susceptibility index (IHE) did not increase, contrary to the trend in conventional materials where increased strength is typically accompanied by increased hydrogen embrittlement susceptibility. This result indicates that the strength of alloys can be improved without sacrificing resistance to hydrogen embrittlement through optimized aging treatment to introduce L12 particles.

[0055] Figure 3 The TDS (Total Desorption Discharge) peaks of the samples from Example 1 and Comparative Example 1 after hydrogen precharging are shown, illustrating the hydrogen desorption behavior of the samples from Example 1 and Comparative Example 1 after hydrogen precharging treatment:

[0056] Figure 3In Figure 'a', the TDS curves are shown, illustrating the TDS analysis results of the alloys from Comparative Example 1 and Example 1 after 72 hours of hydrogen pre-charging, using a heating rate of 100 °C / h.

[0057] Figure 3 In Figure b, the TDS spectrum decomposition and fitting of the sample from Example 1 is shown: The TDS spectrum of the alloy from Example 1 was decomposed to identify hydrogen release peaks at different temperatures, which helps to understand the hydrogen capture ability of different trap sites.

[0058] After 72 hours of hydrogen pre-charging, the hydrogen capture capacity of the sample in Example 1 was 18.5 ppm, which was much lower than the 28.8 ppm of the sample in Comparative Example 1. Furthermore, a high-temperature desorption peak related to L12 particles appeared at 191 °C, indicating a decrease in the hydrogen diffusion rate in the material. This suggests that the L12 particles effectively captured hydrogen, reduced hydrogen diffusion in the alloy, and lowered the risk of hydrogen embrittlement.

[0059] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A nano-precipitate strengthened, hydrogen embrittlement resistant medium entropy alloy, characterized in that, The alloy comprises, in percentage by mass: Co 33.30-34.30%; Ni 33.20-34.20%; Cr 29.45-30.45%; Ti 1.30-1.90%; Al 0.65-1.05%; B 0.04-0.06%, and the balance is inevitable impurities; the microstructure of the medium-entropy alloy is an FCC solid solution structure of Co, Cr, Ni and a small amount of Al and Ti, and a nanoscale L12 precipitated phase dispersed in the matrix, the average size of the nanoscale L12 precipitated phase being 17.5-27.0 nm; The yield strength of the nanoscale precipitated phase strengthened hydrogen embrittlement resistant medium-entropy alloy is greater than or equal to 780 MPa, the ductility is greater than or equal to 39.0%, the hydrogen embrittlement sensitivity index is less than or equal to 4.5% after 24 hours of hydrogen pre-charging, and the hydrogen embrittlement sensitivity index is less than or equal to 9.5% after 72 hours of hydrogen pre-charging.

2. A method of producing the nano precipitate-strengthened, hydrogen embrittlement resistant, medium-entropy alloy of claim 1, characterized in that, The method comprises the following steps: S1, taking raw materials according to the composition of the medium-entropy alloy, and obtaining a medium-entropy alloy ingot by arc melting in an argon atmosphere; S2, controlling element distribution by homogenizing treatment of the ingot; S3, rolling the ingot by a cold rolling process to obtain a plate; S4, quenching and tempering heat treatment of the plate by solid solution treatment and aging treatment to obtain a nanoscale precipitated phase strengthened hydrogen embrittlement resistant medium-entropy alloy.

3. The method of manufacturing nano precipitate strengthened anti- hydrogen embrittlement medium entropy alloy according to claim 2, characterized in that, In the step S1, the ingot obtained by arc melting is turned over and re-melted for at least 5 times to ensure uniform distribution of elements.

4. The method for preparing a nano-precipitated phase-reinforced, hydrogen-embrittlement-resistant intermediate-entropy alloy according to claim 2, characterized in that, In the step S2, the homogenizing treatment temperature is 1200±50℃, and the homogenizing treatment time is 3.0±0.2h.

5. The method of manufacturing nano precipitate strengthened anti- hydrogen embrittlement medium entropy alloy as claimed in claim 2, wherein, In the step S3, the rolling reduces the thickness of the bulk medium-entropy alloy ingot by 50±5%.

6. The method of manufacturing nano precipitate strengthened anti- hydrogen embrittlement medium entropy alloy as claimed in claim 2, wherein, The step S4 comprises the following steps: S41, heating the plate to 1000±50℃ for 1±0.05h to realize solid solution treatment; S42, aging treatment of the plate after solid solution treatment at 800±50℃ for 5±0.3h; S43, water quenching of the plate after aging treatment to obtain a nanoscale precipitated phase strengthened hydrogen embrittlement resistant medium-entropy alloy.

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