A crconi alloy with dislocation-short-range-order composite defect structure and a preparation method thereof

Abstract

The application belongs to the technical field of metal material strengthening and surface protection, and particularly relates to a CrCoNi alloy with dislocation-short-range order composite defect structure and a preparation method thereof. The CrCoNi alloy is subjected to high-pressure heat treatment, and the high-pressure heat treatment process parameters are regulated to simultaneously construct a high-density dislocation and short-range order composite defect structure in the CrCoNi alloy, so that the CrCoNi alloy with the dislocation-short-range order composite defect structure is obtained. The high-density dislocation and short-range order composite defect structure is introduced into the CrCoNi entropy alloy, excellent synergy of strength, plasticity and corrosion resistance is realized, and the engineering applicability and service reliability of the CrCoNi alloy under extreme environments are significantly improved. The preparation strategy has good universality and can be extended to other metal structural material systems, and provides a new technical approach for synergistically optimizing multiple properties through composite defect engineering.

Description

Technical Field

[0001] This invention belongs to the field of metal material strengthening and surface protection technology, specifically relating to a CrCoNi alloy with a dislocation-short-range ordered composite defect structure and its preparation method. Background Technology

[0002] The design concept of multi-principal element alloys (MPEAs) breaks the constraints of traditional alloy composition design by dissolving multiple elements in a single crystal structure, providing a multi-dimensional parameter space for the control of microstructure and macroscopic properties. Medium-entropy alloys, as an important branch of MPEAs, are typically composed of 3 to 4 principal elements in near-equiatomic ratios, with a mixing entropy of 1R to 1.5R. Due to their unique high-entropy effect, lattice distortion effect, and diffusion hysteresis effect, medium-entropy alloys possess superior strength and toughness potential compared to traditional alloys.

[0003] Among numerous medium-entropy alloys, equiatomic-ratio CrCoNi medium-entropy alloys exhibit comprehensive advantages such as high strength, high fracture toughness, good corrosion resistance, and radiation resistance due to the intrinsic ductility of their face-centered cubic structure, making them important candidate materials for structural components under extreme conditions. However, with the increasing demands on material performance in extreme environments—for example, spacecraft structures needing to withstand high loads and impacts simultaneously, and marine engineering components requiring both corrosion resistance and deformation resistance—the existing synergistic level of strength, toughness, and corrosion resistance in CrCoNi medium-entropy alloys can no longer meet the practical application requirements under high loads and extreme environments.

[0004] Traditional processing modification methods generally strengthen materials but often struggle to maintain both ductility and corrosion resistance. For example, constant-diameter angular extrusion and cumulative rolling introduce local shear strain, effectively increasing dislocation density based on the Bailey-Hirsch relationship. The resulting grain refinement from severe deformation generates numerous grain boundaries, synergistically improving the alloy's strength and plasticity. However, this strengthening strategy has inherent drawbacks: high dislocation density regions are prone to stress concentration, while local shear bands can become preferential pathways for crack initiation and propagation, increasing the material's brittle fracture tendency. Furthermore, dislocation nuclei, as high-energy regions, are more likely to become corrosion initiation sites in corrosive media, further weakening the alloy's overall corrosion resistance.

[0005] Heat treatment, a common material modification method, can achieve a certain degree of synergistic optimization of material strength and plasticity by controlling atomic diffusion and phase transformation behavior. However, while eliminating internal stress, this process often leads to a significant decrease in dislocation density, thereby weakening the material's strength. Furthermore, excessive precipitates not only reduce the material's plasticity but also induce micro-galvanic corrosion due to the electrochemical difference between the precipitates and the matrix, adversely affecting the material's corrosion resistance.

[0006] Therefore, existing improved processes cannot effectively balance the strength, toughness, and corrosion resistance of CrCoNi alloys, making it difficult to meet the high-performance requirements of structural materials in extreme environments such as aerospace and marine engineering. Summary of the Invention

[0007] This invention addresses the technical problem that existing improved processes cannot effectively balance the strength, toughness, and corrosion resistance of CrCoNi alloys. It provides a high-performance CrCoNi alloy preparation process based on the thermo-field coupling construction of a dislocation-short-range ordered composite defect structure. This invention utilizes high temperature and high pressure synergistically to construct a high-density dislocation and short-range ordered composite defect structure in CrCoNi alloys, thereby obtaining CrCoNi alloys with high strength, ductility, and excellent corrosion resistance.

[0008] This invention employs high-pressure heat treatment on CrCoNi alloys, controlling the process parameters to simultaneously construct high-density dislocations and short-range ordered (SRO) structures within the alloy. The introduction of SRO structures alters dislocation motion, reducing stacking fault energy and significantly improving the strength-ductility balance of the alloy. Simultaneously, SROs modify Cr atom occupancy in the CrCoNi alloy, promoting the aggregation of Cr-O-Cr units and facilitating the formation of a CrCoNi oxide film, thus endowing the material with superior corrosion resistance. This achieves excellent synergy between strength, ductility, and corrosion resistance in a medium-entropy CrCoNi alloy, significantly enhancing its engineering applicability and service reliability in extreme environments.

[0009] The first objective of this invention is to provide a method for preparing a CrCoNi alloy with a dislocation-short-range ordered composite defect structure, comprising the following steps: The CrCoNi alloy was subjected to high-pressure heat treatment at 3GPa~5GPa and 600℃~865℃ to simultaneously construct a high-density dislocation and short-range ordered composite defect structure in the matrix, so that the Cr-O-Cr units aggregated to form a CrCoNi oxide film, thus obtaining a CrCoNi alloy with a dislocation-short-range ordered composite defect structure.

[0010] Preferably, the high-pressure heat treatment is performed at a pressure of 5 GPa and a temperature of 600 °C. Pressure, as a crucial thermodynamic parameter, directly alters the Gibbs free energy of a phase, significantly influencing the diffusion and nucleation rates of melting elements in the alloy, thus providing a possibility for comprehensive performance improvement. Under constant temperature conditions, the Gibbs free energy of a phase increases with increasing pressure, which promotes the formation of new phases with smaller molar volumes. The SRO structure reduces the lattice constant of the CrCoNi medium-entropy alloy; therefore, theoretically, high-pressure heat treatment can promote the formation of SRO structures in CrCoNi alloys. High temperature and pressure induce atomic rearrangement, causing changes in atomic occupancy and lattice distortion, thus promoting SRO formation. Furthermore, increased pressure can stabilize dislocation density by suppressing atomic diffusion; this characteristic provides an effective way to address the strength loss caused by dislocation annihilation and recombination during heat treatment.

[0011] Meanwhile, the shear stress induced by the high temperature and high pressure environment exceeds the critical strength for dislocation nucleation, causing a large number of dislocations to multiply and slide, forming dense dislocations. Dislocation entanglement hinders dislocation movement, and the small-angle grain boundaries formed by the recombination of high-density dislocations effectively improve the strength of the CrCoNi alloy. High temperature and high pressure promote atomic rearrangement, causing changes in atomic occupancy, resulting in lattice distortion and promoting the formation of SROs. While maintaining a high dislocation density, the introduction of short-range ordered structures alters dislocation movement, reduces stacking fault energy, and significantly improves the strength-ductility matching of the alloy; at the same time, the short-range ordered structures change the occupancy of Cr atoms in the CrCoNi alloy, promote the aggregation of Cr-O-Cr units, promote the formation of CrCoNi oxide film, and endow the material with superior corrosion resistance.

[0012] Preferably, the high-pressure heat treatment time is 2 hours. During the high-pressure heat treatment, as the temperature increases, the migration ability of Cr, Co, and Ni atoms is significantly enhanced, and their rapid diffusion and rearrangement provide the necessary kinetic conditions and thermodynamic driving force for the formation of short-range ordered structures. When the pressure reaches 5 GPa, the generated shear stress exceeds the critical strength for dislocation nucleation, inducing a large number of dislocation nucleations and proliferations, creating favorable conditions for the stable existence of high-density dislocations.

[0013] Preferably, the heating rate of the high-pressure heat treatment is 100℃ / min.

[0014] Preferably, the specific preparation method of CrCoNi alloy is as follows: Cr, Co, and Ni in equimolar ratio are melted and cast into alloy ingots; the alloy ingots are homogenized and then rolled to obtain raw metal parts; the raw metal parts are heat-treated and water-cooled to obtain CrCoNi alloy.

[0015] Preferably, the homogenization treatment temperature is 1000℃~1200℃ and the time is 4h.

[0016] Preferably, the heat treatment temperature is 900℃~1000℃ and the time is 1 hour.

[0017] Preferably, the total deformation during the rolling process is controlled to be 50%.

[0018] The second objective of this invention is to provide a CrCoNi medium-entropy alloy with a dislocation-short-range ordered composite defect structure, wherein the CrCoNi medium-entropy alloy with the dislocation-short-range ordered composite defect structure is prepared by the above-described preparation method.

[0019] Compared with the prior art, the present invention has the following technical effects: This invention employs high-pressure heat treatment on CrCoNi alloys, controlling the process parameters to simultaneously construct high-density dislocations and SRO structures. The introduction of SROs alters dislocation motion, reducing stacking fault energy and significantly improving the strength-ductility balance of the alloy. Simultaneously, the short-range ordered structure alters Cr atom occupancy in the CrCoNi alloy, promoting the aggregation of Cr-O-Cr units and the formation of a dense Cr2O3 oxide film, thus endowing the material with superior corrosion resistance. This achieves excellent synergy between strength, ductility, and corrosion resistance in the CrCoNi alloy, significantly improving its engineering applicability and service reliability in extreme environments.

[0020] Compared with traditional processes, this invention achieves superior comprehensive properties in the alloy by constructing a dislocation-short-range ordered composite defect structure: yield strength is increased from 326 MPa to 564 MPa, tensile strength from 800 MPa to 880 MPa, elongation at break from 69.4% to 72.3%, and self-corrosion current density is reduced from 3.608 μA / cm² to 1.109 μA / cm². 2 .

[0021] The preparation strategy of this invention has good universality and can be extended to other metal structural material systems, providing a new technical approach for synergistically optimizing multiple properties through composite defect engineering. Attached Figure Description

[0022] Figure 1Microstructure characterization diagrams of the CrCoNi alloys with dislocation-short-range ordered composite defect structures prepared in Examples 1 and 2, and the CrCoNi alloy prepared in Comparative Example 1. (a) is the nanobeam selected area electron diffraction (SEG) pattern of Example 1 along the

[112] zone axis; (b) is the nanobeam selected area electron diffraction (SEG) pattern of Comparative Example 2 along the

[112] zone axis; (c) is the nanobeam selected area electron diffraction (SEG) pattern of Comparative Example 1 along the

[112] zone axis; (d) is the transmission electron microscope (TEM) bright-field image of Example 1; (e) is the TEM bright-field image of Comparative Example 2; (f) is the TEM bright-field image of Comparative Example 1; and (g) is the intensity distribution diagram of SRO in Example 1.

[0023] Figure 2 The elemental distribution of the energy dispersive X-ray spectrum of the CrCoNi alloy with dislocation-short-range ordered composite defect structure prepared in Example 1 is shown in the figure; where (a) is Cr, (b) is Co, and (c) is Ni.

[0024] Figure 3 The stress-strain curves of the CrCoNi alloy with dislocation-short-range ordered composite defect structure prepared in Example 1 and the CrCoNi alloy prepared in Comparative Example 1 are shown.

[0025] Figure 4 Potential dynamic polarization curves of the CrCoNi alloy with dislocation-short-range ordered composite defect structure prepared in Example 1 and the CrCoNi alloy prepared in Comparative Example 1. Detailed Implementation

[0026] It should be noted that Short Range Order (SRO) is a nanoscale chemical ordering phenomenon commonly found in various alloy systems, including multi-principal alloys, titanium-based alloys, and nickel-based alloys. SRO can significantly regulate the microscopic deformation mechanism and corrosion behavior of alloys: mechanically, SRO effectively enhances material strength and optimizes the strength-ductility match by increasing lattice resistance, altering dislocation motion, and reducing stacking fault energy; in terms of corrosion resistance, the presence of SRO alters atomic occupancy, facilitating the formation of uniformly distributed passivation film nucleation sites, promoting the formation and stabilization of continuous and dense passivation films, while simultaneously inhibiting the penetration of corrosive media along grain and phase boundaries, thus delaying the occurrence and development of localized corrosion. Therefore, introducing SRO structures has become one of the effective strategies for synergistically improving the mechanical properties and corrosion resistance of metallic materials.

[0027] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0028] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0029] The parameters of the raw materials used in the following examples are as follows: The purity of Cr is ≥99.99%; the purity of Co is ≥99.99%; the purity of Ni is ≥99.99%.

[0030] Example 1 A method for preparing a CrCoNi alloy with a dislocation-short-range ordered composite defect structure includes the following steps: Step 1: Preparation of CrCoNi alloy: Cr, Co and Ni are mixed in an equimolar ratio and melted by electric arc melting to obtain a melt. After the mixture is completely melted, melting is stopped and the melt is poured to obtain an alloy ingot. To ensure the uniformity of composition, the melting is repeated at least 4 times.

[0031] The alloy ingot was placed in a muffle furnace and held at 1200℃ for 4 hours for homogenization treatment. It was then cooled to room temperature with the furnace to obtain the as-cast alloy.

[0032] The cast alloy is rolled in a vertical direction, and the total deformation is controlled to be 50% to obtain the rolled alloy.

[0033] The rolled alloy was placed in a muffle furnace and held at 900℃ for 1 hour for solution treatment. After the holding time was completed, it was immediately subjected to water quenching to obtain the CrCoNi alloy.

[0034] Step 2: Prepare a CrCoNi alloy with a dislocation-short-range ordered composite defect structure: The molybdenum sheet, graphite sleeve, boron nitride sheet, and boron nitride crucible were dried at 60°C, and the hollow block was baked at 480°C for 12 hours to remove moisture.

[0035] The CrCoNi medium-entropy alloy was machined into ∅8mm×12mm CrCoNi cylindrical specimens using wire electrical discharge machining (EDM) technology. The surface of the CrCoNi cylindrical specimens was then polished to 2000 grit using silicon carbide sandpaper to effectively remove the oxide layer and defects on the surface of the CrCoNi cylindrical specimens.

[0036] The sample was assembled in the following order: a CrCoNi cylindrical specimen, a dried molybdenum sheet, a dried boron nitride sheet, a dried boron nitride crucible, a dried graphite sleeve, and a conductive steel cap. The assembled sample was then placed inside a hollow block. The hollow block was placed in a six-anvil cubic high-pressure device, and high-pressure heat treatment was performed using a pressure-temperature coupled loading mode. A constant load of 5 GPa was applied to the sample. After the pressure sensor reading stabilized, a temperature field was applied at a heating rate of 100 °C / min. When the temperature reached the preset value of 600 °C, the temperature was switched to isothermal holding for 2 hours. After the holding period, a cooling program was executed. The entire process was maintained at a pressure of 5 GPa, resulting in a CrCoNi alloy with a dislocation-short-range ordered composite defect structure.

[0037] Example 2 A method for preparing a CrCoNi alloy with a dislocation-short-range ordered composite defect structure is basically the same as the preparation method in Example 1, except that the high-pressure heat treatment temperature is 775℃.

[0038] Example 3 A method for preparing a CrCoNi alloy with a dislocation-short-range ordered composite defect structure is basically the same as the preparation method in Example 1, except that the high-pressure heat treatment temperature is 865℃.

[0039] Comparative Example 1 A method for preparing a CrCoNi alloy includes the following steps: Cr, Co, and Ni are mixed in an equimolar ratio to obtain a mixture; an electric arc melt is then used to obtain a melt. After the mixture is completely melted, the melting is stopped and the melt is poured to obtain an alloy ingot. To ensure compositional uniformity, the melting process is repeated at least four times.

[0040] The alloy ingot was placed in a muffle furnace and held at 1200℃ for 4 hours for homogenization treatment. It was then cooled to room temperature with the furnace to obtain the as-cast alloy.

[0041] The cast alloy is rolled in a vertical direction, and the total deformation is controlled to be 50% to obtain the rolled alloy.

[0042] The rolled alloy was placed in a muffle furnace and held at 900℃ for 1 hour for solution treatment. After the holding time was completed, it was immediately subjected to water quenching to obtain the CrCoNi alloy.

[0043] Comparative Example 2 A method for preparing a modified CrCoNi alloy includes the following steps: The preparation method is basically the same as that in Example 1. The difference from Example 1 is:

[0044] The high-pressure heat treatment was performed at room temperature.

[0045] Experimental test: 1. Microscopic morphological characterization.

[0046] like Figure 1 As shown in (a) of the diagram, the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1 can be seen in the zone axis electron diffraction pattern

[112] as indicated by the arrow. { The appearance of superlattice diffraction spots at position 11 indicates that a clear short-range ordered structure has been formed in the CrCoNi alloy with dislocation-short-range ordered composite defect structure. Figure 1 (g) further provides a quantitative analysis of the corresponding SRO diffraction intensity. In contrast, Figure 1 As shown in (b) of Comparative Example 2, the electron diffraction pattern of the CrCoNi alloy only shows Bragg spots with a conventional face-centered cubic structure, and no SRO diffraction signal was observed. Figure 1 As shown in (c), the microstructure of the CrCoNi alloy in Comparative Example 1 is also a single face-centered cubic structure, without any short-range ordering characteristics. This indicates that Example 1 achieved the introduction of a short-range ordered structure under specific temperature and pressure conditions.

[0047] like Figure 1 As shown in (d) of Example 1, the CrCoNi alloy with a dislocation-short-range ordered composite defect structure exhibits a high-density dislocation distribution on its surface, accompanied by obvious dislocation entanglement and pinning phenomena, further verifying the inhibitory effect of the short-range ordered structure on dislocation movement. In contrast, Figure 1 As shown in (e) in Comparative Example 2, the surface dislocation density of the modified CrCoNi alloy is significantly reduced and the distribution is relatively sparse. Figure 1 As shown in (f), no obvious dislocation structure was observed on the surface of the CrCoNi alloy in Comparative Example 1. This indicates that Example 1 achieved the formation of high-density dislocations under specific temperature and pressure conditions, and SRO played a significant pinning role on the dislocations.

[0048] This indicates that the original CrCoNi alloy surface lacks obvious dislocation structure and short-range ordered structure. After room temperature high-pressure treatment, the CrCoNi alloy in Comparative Example 1 still shows no short-range ordered characteristics, and the dislocation density is low and sparsely distributed. However, under the high-pressure heat treatment conditions of Example 1, high-density dislocations can be generated. This shows that the high-pressure process can maintain the stability of dislocations, and short-range order plays a pinning role for dislocations.

[0049] like Figure 2As shown, significant chemical composition fluctuations and uneven elemental distribution were observed in the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1. This result provides direct evidence for the existence of the short-range ordered structure and the resulting compositional fluctuations. Therefore, Example 1 of this invention formed a high-density dislocation-short-range ordered composite defect structure under specific temperature and pressure conditions.

[0050] 2. Mechanical property testing.

[0051] Mechanical properties were tested on the CrCoNi alloys with dislocation-short-range ordered composite defect structures prepared in Examples 1-3 and the CrCoNi alloy prepared in Comparative Example 1. Tensile specimens were prepared along the rolling direction of the sheet metal using wire electrical discharge machining (EDM), and the sample surfaces were polished with 1200-grit SiC sandpaper to ensure smoothness. Room temperature tensile tests were performed on an Instron 3369 electronic universal testing machine with a strain rate set to 1 × 10⁻⁶. -3 ·s -1 .

[0052] Table 1. Mechanical property data of CrCoNi alloys prepared in Examples 1-3 and Comparative Example 1 from Figure 3 As shown in Table 1, the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1 has a yield strength of 564 MPa and an ultimate tensile strength of 880 MPa; the CrCoNi alloy prepared in Comparative Example 1 has a yield strength of 326 MPa and an ultimate tensile strength of 800 MPa. Compared with the CrCoNi alloy, the strength of the modified CrCoNi alloy with a dislocation-short-range ordered composite defect structure after high-pressure heat treatment is significantly improved. The strain of the CoCrNi alloy prepared in Comparative Example 1 is 69.4%, while the strain of the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1 is 72.3%, an increase of 4.18%. This indicates that Example 1 of the present invention achieves a simultaneous improvement in the strength and plasticity of the CrCoNi alloy by constructing a high-density dislocation and a high-density short-range ordered structure.

[0053] 3. Electrochemical testing.

[0054] The electrochemical performance of the CrCoNi alloy with dislocation-short-range ordered composite defect structure prepared in Example 1 and the CrCoNi alloy prepared in Comparative Example 1 were tested using the following methods: Electrochemical measurements of the CrCoNi alloys prepared in Example 1 and Comparative Example 1 were performed at room temperature using a three-electrode electrochemical workstation in 0.1 M H₂SO₄ solution. The working electrode was a 10 mm × 10 mm CrCoNi medium-entropy alloy, the counter electrode was a 15 mm × 15 mm platinum sheet, and the reference electrode was a mercurous sulfate electrode. The measurements were taken from -1.0 V at a scan rate of 0.25 mV / s. SCE The anodic current density was scanned to reach 1 mA·cm. -2 Potential dynamic polarization.

[0055] like Figure 4 As shown, compared to the CrCoNi alloy prepared in Comparative Example 1, the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1 has a self-corrosion potential of -0.645V. SCE The self-corrosion potential of the CrCoNi alloy prepared in Comparative Example 1 is -0.664V. SCE The self-corrosion current of the CrCoNi alloy with a dislocation-short-range ordered composite defect structure prepared in Example 1 was 1.109 μA / cm, which was reduced by 2.86%. 2 The self-corrosion current of the CrCoNi alloy prepared in Comparative Example 1 was 3.608 μA / cm. 2 This reduces the corrosion resistance by 69.26%. This demonstrates that Embodiment 1 of the present invention improves the corrosion resistance of the CrCoNi medium-entropy alloy by constructing a high-density dislocation and a high-density short-range ordered structure.

[0056] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If these modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a CrCoNi alloy with a dislocation-short-range ordered composite defect structure, characterized in that, Includes the following steps: The CrCoNi alloy was subjected to high-pressure heat treatment at 3GPa~5GPa and 600℃~865℃ to simultaneously construct a dislocation and short-range ordered composite defect structure in the CrCoNi alloy, so that the Cr-O-Cr units aggregated and formed a Cr2O3 oxide film, thus obtaining a CrCoNi alloy with a dislocation-short-range ordered composite defect structure. The high-pressure heat treatment time is 1 hour to 3 hours; The specific preparation method of CrCoNi alloy is as follows: Cr, Co and Ni in equimolar ratio are melted and cast into alloy ingots; the alloy ingots are homogenized and then rolled to obtain raw metal parts; the raw metal parts are solution treated and water-cooled to obtain CrCoNi alloy. The homogenization temperature is 1000℃~1200℃; The solution treatment temperature is 800℃~1000℃; The total deformation during rolling is controlled at 50%.

2. The method for preparing the CrCoNi alloy with a dislocation-short-range ordered composite defect structure according to claim 1, characterized in that, The heating rate for high-pressure heat treatment is 100℃ / min.

3. A CrCoNi alloy with a dislocation-short-range ordered composite defect structure, characterized in that, The CrCoNi alloy with dislocation-short-range ordered composite defect structure is prepared by the preparation method of the CrCoNi alloy with dislocation-short-range ordered composite defect structure as described in claim 1 or 2.

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