A Cr-rich nanoprecipitate multiphase precipitation-strengthened high-entropy alloy and preparation method thereof

Abstract

The present invention belongs to the technical field of alloy preparation, and specifically discloses a multiphase precipitation-strengthened high entropy alloy of Cr-rich nano-precipitates and a preparation method thereof. The multiphase precipitation-strengthened high entropy alloy of Cr-rich nano-precipitates is prepared by vacuum suspension induction melting. 0.5 Cr 0.9 FeNi 2.5 Si 0.25 The alloy was heat treated at different temperatures (750℃-1200℃) to improve the microhardness and mechanical properties by regulating the microstructure and phase structure, thereby obtaining a multiphase precipitation-strengthened high-entropy alloy with optimal comprehensive mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy preparation, in particular to a Cr-rich nano-precipitate multiphase precipitation-strengthened high-entropy alloy and a preparation method thereof. Background Art

[0002] In recent years, high-entropy alloys (HEAs) have garnered significant attention due to their unique combination of properties. HEAs are defined as being composed of at least five primary elements, with the atomic percentage of each element ranging from 5% to 35%. Compared to conventional alloys, HEAs exhibit distinct characteristics such as high entropy, severe lattice distortion, hysteretic diffusion, and the cocktail effect. Their exceptional properties have led many researchers to investigate and develop HEAs as future high-performance structural materials. Generally, strength and ductility at room temperature are two fundamental properties of structural materials. However, previous studies have observed a trade-off between strength and ductility in single-phase HEAs. Single-phase body-centered cubic (BCC) HEAs exhibit high strength but low ductility, while single-phase face-centered cubic (FCC) HEAs exhibit the opposite properties. Compared to single-phase HEAs, dual-phase or multi-phase HEAs with unique microstructures exhibit balanced strength-ductility properties because the synergistic effects of the dual-phase or multi-phase structure can significantly enhance their properties. Outstanding performance can be achieved by engineering the composite microstructures of nanoprecipitates in dual-phase or multi-phase non-equimolar ratio high-entropy alloys.

[0003] In addition, metal elements are the main components of non-equimolar high entropy alloys, but the research on the addition of non-metallic elements to these alloys is relatively insufficient. The addition of non-metallic elements can significantly improve the mechanical properties of equimolar or near-equimolar high entropy alloys. Among them, Si doping has attracted attention because of its ability to improve mechanical properties through solid solution strengthening, dislocation strengthening and secondary phase strengthening. The appropriate Si content has little effect on ductility and successfully improves the strength and hardness of high entropy alloys. However, in some cases, when the Si content exceeds the threshold, the ductility decreases. Therefore, it is worth studying how to overcome the trade-off between strength and ductility by incorporating an appropriate Si content into non-equimolar multiphase high entropy alloys. In addition, it is well known that the mechanical properties of alloys (including high entropy alloys) may be affected by defects generated during the smelting process. Heat treatment can eliminate some defects, promote the formation of precipitates, or regulate the volume fraction and distribution of each phase in the high entropy alloy without changing the chemical composition of the alloy. Therefore, by designing and preparing a non-equimolar multiphase Al 0.5 CrFeNi 2.5 Si 0.25The high-entropy alloy was then heat treated. It is necessary to study how to use heat treatment to eliminate some defects in the alloy, and at the same time further improve the compression properties of the alloy through microstructural control. It is also necessary to conduct relevant experimental tests to prove that the compressive strength, yield strength, and plasticity of the alloy are improved, thereby obtaining a high-entropy alloy with better overall performance. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a Cr-rich nano-precipitate multiphase precipitation strengthened high entropy alloy and a preparation method thereof.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The first object of the present invention is to provide a Cr-rich nano-precipitate multiphase precipitation strengthened high entropy alloy, which is composed of the following components in the following molar ratios: Al 0.5 Cr 0.9 FeNi 2.5 Si 0.25 .

[0007] A second object of the present invention is to provide a method for preparing a Cr-rich nano-precipitate multiphase precipitation-strengthened high entropy alloy, comprising the following steps:

[0008] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weigh Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and clean the raw materials;

[0009] 2) Vacuum suspension induction melting: Place the raw materials in a vacuum suspension induction melting furnace, evacuate the furnace, and repeatedly melt them multiple times under an inert gas atmosphere, followed by cooling in the furnace to obtain a high entropy alloy;

[0010] 3) Heat treatment: The high entropy alloy is annealed at 750° C. to 1200° C. for 1 hour, and then quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high entropy alloy with Cr-rich nano-precipitates.

[0011] Furthermore, the cleaning treatment of the raw materials in step 1) is: acid washing each raw material with a sulfuric acid aqueous solution with a volume fraction of 10%.

[0012] Furthermore, the vacuum suspension induction melting furnace in step 2) is evacuated to 10 -3 level, and flush twice with inert gas until it is fully filled with inert gas.

[0013] Furthermore, in the step 2), during the vacuum suspension induction melting furnace smelting, the power is set from low to high to 100KW-150KW-200KW, with each adjustment time interval of 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes.

[0014] Furthermore, in step 2), the product is cooled to a temperature between 100-150° C. and then taken out of the furnace.

[0015] Furthermore, the annealing treatment in step 3) is as follows: the high entropy alloy is vacuum sealed in a quartz tube and placed in a box-type resistance furnace (SX-4-10M), and the heat treatment temperatures are set to 750°C, 850°C, 1050°C, and 1200°C, respectively. After the heat treatment holding time is 1 hour, water cooling is performed.

[0016] Preferably, the inert gas is argon.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a multiphase precipitation-strengthened high entropy alloy of Cr-rich nano-precipitates, which has a novel alloy component ratio and is smelted in a vacuum induction furnace to ensure the uniformity of the alloy and effectively avoid the problems of alloy oxidation and burning. 0.5 CrFeNi 2.5 Si 0.25The high-entropy alloy exhibits a bright surface with a distinct metallic luster and a uniformly distributed microstructure. The main phases are FCC and BCC, distributed in the interdendritic and dendritic regions. With increasing annealing temperature, the proportion of the BCC phase gradually increases from approximately 21.68% to 40.73%, while the proportion of the FCC phase decreases from 78.32% to 59.27%. The increasing proportion of the BCC region contributes to improved strength. Nanoindentation hardness testing of the annealed high-entropy alloy at 1200°C reveals that the hardness of the FCC region is approximately 3.872 GPa, while the hardness of the BCC region is approximately 8.853 GPa, approximately 2.3 times that of the FCC region. The hardness of the σ precipitates near the grain boundaries is approximately 5.575 GPa. After heat treatment, changes in the volume fraction and size of the Cr-rich nanostructures within the BCC matrix result in precipitation strengthening and grain refinement. Furthermore, during deformation, the dendritic regions composed of Cr-rich and σ phases within the BCC matrix act as a hard phase, while nearly spherical Cr-rich precipitates are uniformly dispersed within the BCC matrix, resulting in performance far superior to that of a single brittle BCC phase. The nano- and submicron-sized σ precipitates effectively strengthen the high-entropy alloy without causing significant plasticity loss, while the interdendritic FCC / L12 phase acts as a soft phase. The synergistic effect of these two phases during deformation improves the compression properties, resulting in enhanced compression performance. When the alloy is in cast state, its compressive strength is 2267MPa and its plasticity is 14.8%; when the annealing temperature is 750℃, the strength is 2288MPa and the plasticity is 14.9%; when the annealing temperature is 850℃, the strength is 2367MPa and the plasticity is 17.4%; when the annealing temperature is 1050℃, the strength is 2431MPa and the plasticity is 21.2%; when the annealing temperature is 1200℃, the strength is 2584MPa and the plasticity is 23.4%.

[0019] The present invention adopts vacuum suspension induction melting method to design and prepare Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy. The alloy is heat treated at different temperatures (750℃850℃, 1050℃ and 1200℃) to improve the mechanical properties by regulating the microstructure and phase structure. 0.5 CrFeNi 2.5 Si 0.25 The high entropy alloy exhibits a dendritic microstructure. L12 nanoparticles are distributed in the FCC matrix, while Cr-rich nanoparticles and strip-like σ phase are distributed in the BCC matrix. 0.5 CrFeNi 2.5 Si 0.25HEAs are primarily characterized by a dual-phase (FCC and BCC) structure, with nano- and micro-sized precipitates distributed within the FCC and BCC matrices, respectively. With increasing annealing temperature (750°C-1200°C), the proportion of the BCC matrix containing Cr-rich nanoparticles and lamellar σ phase increases. Simultaneously, the Cr-rich nanoparticles gradually refine. After heat treatment at 1050°C and 1200°C, some σ phase dissolves. The shift in precipitate phases at different heat treatment temperatures leads to a strengthening mechanism that overcomes the trade-off between compressive strength and ductility. While strength is enhanced, ductility is also improved. Annealing at 750°C-1200°C increases compressive strength from 2288 MPa to 2584 MPa, while ductility increases from 14.9% to 23.4%. As the annealing temperature increases from 750°C to 1200°C, the proportion of BCC collective regions increases due to element diffusion. When the temperature is higher than 1050°C, some strip-shaped σ phase precipitates disappear in the BCC region. During annealing, the size of the nanoscale Cr-rich phase gradually decreases. As the annealing temperature increases, precipitation strengthening and grain refinement occur due to changes in the microstructure and phase ratio. At the same time, during compression deformation, the dendritic region composed of BCC, Cr-rich, and σ phase acts as a hard phase, while the ordered FCC / L12 phase between the dendrites acts as a soft phase. The synergistic effect of the dendrite and interdendritic microstructures helps improve compressive properties. Therefore, both compressive strength and plasticity are improved after heat treatment. Furthermore, a high-entropy alloy with optimal comprehensive mechanical properties is obtained after vacuum suspension induction melting at 1200°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The Si addition content designed for the present invention is the calculation result.

[0021] Figure 2 Comparative Example 1: As-cast Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, Al alloy heat treated at different temperatures in Examples 1 to 4 0.5 CrFeNi 2.5 Si 0.25 XRD diffraction patterns of high entropy alloys (750℃, 850℃, 1050℃ and 1200℃).

[0022] Figure 3 The optical microscope and thermal field electron backscatter diffraction patterns of comparative example 1 and embodiments 1 to 4 of the present invention; wherein a and f are cast Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloys, b and g are Al heat-treated at 750℃ 0.5 CrFeNi 2.5Si 0.25 High entropy alloy, c and h are Al heat treated at 850℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, d and i are Al heat treated at 1050℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, e and j are Al heat-treated at 1200℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, k is Al in cast and heat treated (750℃, 850℃, 1050℃ and 1200℃) 0.5 CrFeNi 2.5 Si 0.25 Results of the ratio change of FCC and BCC in high entropy alloys.

[0023] Figure 4 The thermal field scanning electron microscope morphology and organization diagram of comparative example 1 and embodiments 1 to 4 of the present invention; a and f are cast Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloys, b and g are Al heat-treated at 750℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, c and h are Al heat treated at 850℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, d and i are Al heat treated at 1050℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, e and j are Al heat-treated at 1200℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy, (k)-(o) are the EDS characterization results of Al0.5CrFeNi2.5Si0.25 high entropy alloy as-cast, heat-treated at 750℃, 850℃, 1050℃, and 1200℃, respectively.

[0024] Figure 5 Al of Comparative Example 1 and Examples 1 to 4 of the present invention 0.5 CrFeNi 2.5 Si 0.25Transmission images and element distribution of high-entropy alloys: (a) and (f) as-cast; (b) and (g) 750°C; (c) and (h) 850°C; (d) and (i) 1050°C; (e) and (j) 1200°C, (k) magnified image of strip-like precipitates at 1200°C; (l) nanoscale precipitates, (m) FCC cubic precipitates.

[0025] Figure 6 Al of Comparative Example 1 and Examples 1 to 4 of the present invention 0.5 CrFeNi 2.5 Si 0.25 Compressive stress-strain curve of high entropy alloy.

[0026] Figure 7 Al of Comparative Example 1 and Examples 1 to 4 of the present invention 0.5 CrFeNi 2.5 Si 0.25 Thermal field scanning image of high entropy alloy (a) nanoindentation test; (b) annealing at 1200℃-Al 0.5 CrFeNi 2.5 Si 0.25 Hardness of high-entropy alloy; (c) hardness at different points; (d) load-displacement curve measured by nanoindentation.

[0027] Figure 8 Al of Comparative Example 1 and Examples 1 to 4 of the present invention 0.5 CrFeNi 2.5 Si 0.25 Thermal field scanning images of the fracture surface of a high-entropy alloy: (a)-(c) as-cast; (d)-(f) 750℃; (g)-(i) 850℃; (j)-(l) 1050℃; (m)-(o) 1200℃. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] Example 1

[0030] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weighing Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and pickling each raw material with a 10% by volume sulfuric acid aqueous solution;

[0031] 2) Vacuum suspension induction melting: Place the raw materials into a vacuum suspension induction melting furnace and evacuate to 10 -3The power is set from low to high to 100KW-150KW-200KW, and the time interval of each adjustment is 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes. The smelting is repeated many times, and the furnace is cooled to between 100-150℃ and then taken out of the furnace to obtain a high entropy alloy.

[0032] 3) Heat treatment: The high-entropy alloy was vacuum-sealed in a quartz tube and placed in a box-type resistance furnace (SX-4-10M). The heat treatment temperature was set at 750°C. After the heat treatment holding time was 1 hour, the alloy was quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high-entropy alloy with Cr-rich nanoprecipitates.

[0033] Example 2

[0034] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weighing Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and pickling each raw material with a 10% by volume sulfuric acid aqueous solution;

[0035] 2) Vacuum suspension induction melting: Place the raw materials into a vacuum suspension induction melting furnace and evacuate to 10 -3 The power is set from low to high to 100KW-150KW-200KW, and the time interval of each adjustment is 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes. The smelting is repeated many times, and the furnace is cooled to between 100-150℃ and then taken out of the furnace to obtain a high entropy alloy.

[0036] 3) Heat treatment: The high-entropy alloy was vacuum-sealed in a quartz tube and placed in a box-type resistance furnace (SX-4-10M). The heat treatment temperature was set at 850°C. After the heat treatment holding time was 1 hour, the alloy was quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high-entropy alloy with Cr-rich nanoprecipitates.

[0037] Example 3

[0038] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weighing Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and pickling each raw material with a 10% by volume sulfuric acid aqueous solution;

[0039] 2) Vacuum suspension induction melting: Place the raw materials into a vacuum suspension induction melting furnace and evacuate to 10 -3The power is set from low to high to 100KW-150KW-200KW, and the time interval of each adjustment is 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes. The smelting is repeated many times, and the furnace is cooled to between 100-150℃ and then taken out of the furnace to obtain a high entropy alloy.

[0040] 3) Heat treatment: The high-entropy alloy was subjected to vacuum heat treatment at 1050°C. The sample was vacuum-sealed in a quartz tube and placed in a box-type resistance furnace (SX-4-10M). The heat treatment temperature was set at 1050°C. After the heat treatment holding time was 1 hour, the sample was quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high-entropy alloy with Cr-rich nanoprecipitates.

[0041] Example 4

[0042] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weighing Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and pickling each raw material with a 10% by volume sulfuric acid aqueous solution;

[0043] 2) Vacuum suspension induction melting: Place the raw materials into a vacuum suspension induction melting furnace and evacuate to 10 -3 The power is set from low to high to 100KW-150KW-200KW, and the time interval of each adjustment is 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes. The smelting is repeated many times, and the furnace is cooled to between 100-150℃ and then taken out of the furnace to obtain a high entropy alloy.

[0044] 3) Heat treatment: The high-entropy alloy was vacuum-sealed in a quartz tube and placed in a box-type resistance furnace (SX-4-10M). The heat treatment temperature was set at 1200°C. After the heat treatment holding time was 1 hour, the alloy was quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high-entropy alloy with Cr-rich nanoprecipitates.

[0045] Comparative Example 1

[0046] 1) Raw material preparation: according to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weighing Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9%, and pickling each raw material with a 10% by volume sulfuric acid aqueous solution;

[0047] 2) Vacuum suspension induction melting: Place the raw materials into a vacuum suspension induction melting furnace and evacuate to 10 -3The power is set from low to high to 100KW-150KW-200KW, and the time interval for each adjustment is 5 minutes. After the raw material is melted, it is smelted at 150KW for 15 minutes. The smelting is repeated many times, and the furnace is cooled to between 100-150℃ and then taken out of the furnace to obtain a high entropy alloy.

[0048] The multiphase precipitation-strengthened high-entropy alloys of Cr-rich nanoprecipitates prepared in Examples 1 to 4 and the high-entropy alloy prepared in Comparative Example 1 were tested respectively:

[0049] The microstructure of the as-cast and annealed alloys was examined using an optical microscope (OM, Axio Observer, ZEISS) and a field emission scanning electron microscope (FE-SEM, GeminiSEM300). The chemical composition of the alloy was determined using energy dispersive spectroscopy (EDS, EDS, X80, Oxford, UK). The distribution and fraction of the phases were analyzed using electron backscatter diffraction (EBSD). The microstructure was observed using a high-resolution transmission electron microscope (TEM, JEM-2100). The hardness test was performed using a nanoindenter (Nano IndenterXP, MTS, US). The compression samples were cut from the center of the alloy into small cylinders with a diameter of 4 mm and a height of 6 mm and were tested using a CSS55100 universal materials testing machine at room temperature at a speed of 1.0×10 -3 s -1 At least three samples were tested to ensure the reliability of the results.

[0050] Depend on Figure 1 It can be seen that in order to study the addition of Si content, various thermodynamic parameters were calculated to predict the Al 0.5 CrFeNi 2.5 Si x Phase formation and stability of high entropy alloys. Equations (1)-(6) can be used to predict the phase composition of high entropy alloys:

[0051]

[0052] Where (VEC)i is the VEC of the i-th element, ci is the atomic percentage, n represents the number of constituent elements, ci and cj represent the atomic percentages of the i-th and j-th constituent elements, R (8.314 J mol -1 K -1 ) is the ideal gas constant. VEC values ​​between 6.87 and 8 indicate that the mixed BCC and FCC phases are stable. The alloy tends to form the following solid solution phase: 11≤ΔS mix ≤19.5(kJ / mol),-22≤ΔH mix≤7(kJ / mol),Ω≥1.1 and 0≤δ≤6.6 Therefore, in this work, the Si content was selected as 0.25 mol to form Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloy.

[0053] Depend on Figure 2 It can be seen that the phase structure evolution at different annealing temperatures. 0.5 CrFeNi 2.5 Si 0.25 High entropy alloys are composed of FCC / L12, BCC and σ phases. Although the phase structure does not change significantly before and after annealing, the intensity of the FCC / L12 and BCC diffraction peaks changes significantly. Figure 2 As shown in (b), the intensities of the FCC / L12 and BCC diffraction peaks show slight changes as the annealing temperature increases from 750°C to 1050°C. After annealing at 1200°C, the intensity of the BCC diffraction peak increases, while the diffraction peak of the FCC / L12 phase shows a weakening trend. The change in the diffraction peak intensity indicates that the relative proportions of the BCC and FCC phases have changed.

[0054] Depend on Figure 3 The morphology of the as-cast and annealed high-entropy alloys at 750°C, 850°C, 1050°C, and 1200°C is shown. The microstructure consists of light gray (FCC) and dark gray (BCC) regions. Compared to the as-cast alloy, there is no apparent coarsening trend in the microstructure of the different regions as the heat treatment temperature increases from 750°C to 1050°C. However, after annealing at 1200°C, the alloy's microstructure exhibits significant coarsening. Figure 3 (f)-(j) show the Al 0.5 CrFe 2.5 Si 0.25 Phase distribution diagram of high entropy alloy, showing that the light gray area corresponds to FCC phase structure, and the dark gray area corresponds to BCC phase structure. The ratio of FCC and BCC has changed significantly. Figure 3 As shown in Figure (k), with increasing vacuum levitation induction melting temperature, the proportion of the BCC phase gradually increases from approximately 21.68% to 40.73%, while the proportion of the FCC phase decreases from 78.32% to 59.27%, which is consistent with the XRD results. Furthermore, EDS results indicate that Fe and Cr are enriched in the ID region, while Ni and Al are concentrated in the DR region. However, with increasing annealing temperature, Si is uniformly enriched in the DR region and then segregates at the DR region boundary.

[0055] Depend on Figure 4As can be seen from (a)-(e) and (f)-(j), the DR region shows a large number of micron-sized stripe precipitates and nano-sized precipitates in the BCC matrix. As the heat treatment temperature increases, the distribution and size of the stripe precipitates show obvious changes. For the cast alloys at 750℃ and 850℃ and the annealed alloys, most of the DR region is composed of stripe precipitates and nano-sized precipitates. When the temperature exceeds 1050℃, as shown in Figure 4 As shown in (d)-(e) and (i)-(j), nano-scale precipitates were only observed in some DR regions. This indicates that after heat treatment at 1050℃, part of the strip-like precipitates dissolved. Figure 4 (k)-(o) EDS results show that the stripe-like precipitates contain more Cr, Fe, and Si elements in the DR region, while the ID region is rich in Ni, Cr, and Fe elements in the FCC matrix.

[0056] Depend on Figure 5 It can be seen that the DR and ID regions were analyzed by transmission. As shown in Figures (a)-(e) and (k), the stripe-like precipitates in the DR region are σ phases, which are rich in Cr, Fe and Si elements. Figure 5 As shown in (f)-(j) and (l), spherical nano-sized precipitates are also observed to be Cr-rich (BCC) phases. As the temperature increases, the size of the Cr-rich (BCC) phase tends to decrease. Figure 5 As shown in (m), cubic L12 nanoparticles are uniformly distributed in the FCC matrix in the inner diameter region. The L12 phase is rich in Ni and Al. Therefore, the alloy consists of a strip-like σ phase and a Cr-rich nanoscale phase in the BCC matrix, and cubic L12 nanoparticles in the FCC matrix. With the increase of heat treatment temperature, the proportion of the DR zone (σ phase and Cr-rich phase in the BCC matrix) increases, while the proportion of the ID zone (L12 / FCC) gradually decreases. Compared with the samples treated at 750℃-1050℃, the phase ratio and microstructure of the alloy changed most significantly before and after heat treatment at 1200℃. With the increase of temperature, Al 0.5 CrFeNi 2.5 Si 0.25 Si in high-entropy alloys may cause significant chemical segregation and affect phase stability due to differences in atomic size and mixing enthalpy with other constituent elements. The atomic radii of Si, Al, Cr, Fe, and Ni are 117 pm, 143 pm, 128 pm, 126 pm, and 124 pm, respectively. The mixing enthalpies of Si-Al, Si-Cr, Si-Fe, and Si-Ni are -19 kJ mol, respectively. -1 、-37KJ mol -1 、-35KJ mol -1 and -19 kJ mol -1During the annealing process, the ratio of the phase structure can change. With the increase of heat treatment temperature (1050℃-1200℃), some strip-shaped σ phase precipitates disappear in the DR region because part of the σ phase dissolves in the BCC matrix during heat treatment.

[0057] Depend on Figure 6 It can be seen that the Al annealed at different temperatures 0.5 CrFeNi 2.5 Si 0.25 True compressive stress-strain curve of high entropy alloy. Figure 6 (b) shows the cast Al 0.5 CrFeNi 2.5 Si 0.25 The ultimate compressive strength of the high entropy alloy is about 2267MPa, and the fracture strain is about 14.8%. As the heat treatment temperature increases, the ultimate compressive strength increases from 2288MPa to 2584MPa, and the plasticity increases from 14.9% to 23.4%. At the same time, the yield strength of the heat-treated high entropy alloy is higher than that of the cast high entropy alloy. For alloys heat-treated at 750℃ and 850℃, the yield strength increases with the increase of strength and strain. For alloys annealed at 1050℃ and 1200℃, the yield strength first decreases and then increases. Al 0.5 CrFeNi 2.5 Si 0.25 High-entropy alloys exhibit the highest yield strength, approximately 1083 MPa, after heat treatment at 850°C. The main factors contributing to the improved properties of these alloys after heat treatment are as follows. First, heat treatment accelerates atomic diffusion, which eliminates some casting defects. Simultaneously, this process leads to changes in the alloy's microstructure and phase composition. The increasing proportion of BCC regions contributes to the increased strength.

[0058] Depend on Figure 7 Nanoindentation hardness testing of the 1200°C alloy after heat treatment revealed that the hardness of the ID zone (point 18) was approximately 3.872 GPa, while the hardness of the DR zone (point 44) was approximately 8.853 GPa, approximately 2.3 times that of the ID zone. The hardness of the σ precipitate phase near the grain boundary (point 67) was approximately 5.575 GPa. Therefore, the DR zone and the σ precipitate phase significantly strengthened the alloy. The fluctuation in yield strength may be due to the partial dissolution of the σ phase after 1050°C. With increasing temperature, the ultimate fracture strain also gradually increased. The dissolution of the σ precipitate phase is conducive to the improvement of plasticity. In addition, with increasing heat treatment temperature, the refinement of the chromium-rich phase in the DR zone produces a fine grain strengthening effect. This also has a positive impact on the compression properties.

[0059] Depend on Figure 8 It can be seen that Al0.5 CrFeNi 2.5 Si 0.25 Fracture morphology of high entropy alloy after casting and heat treatment. Figure 8 As shown in (c), (f), (i) and (l), vein-like patterns and obvious molten droplets were observed on the fracture surface under high magnification. Figure 8 As shown in (b), (e), (h), and (k), cleavage steps and slip features are also observed on the fracture surface. The alloy heat-treated at 1200°C exhibits more slip features, indicating enhanced plasticity. The alloy annealed at 1200°C did not fracture directly. This sample cracked along a direction inclined by approximately 39° to the loading direction. It also exhibits the same fracture characteristics.

[0060] The present invention designs a multi-phase Al 0.5 CrFeNi 2.5 Si 0.25 High entropy alloys, the evolution of microstructure and phase structure of alloys at different heat treatment temperatures (750℃-1200℃) were systematically studied. The results show that the Al 0.5 CrFeNi 2.5 Si 0.25 The high entropy alloy exhibits a dendritic structure. Cubic L12 nanoparticles are distributed in the FCC matrix, while Cr-rich nanoparticles and strip-shaped σ phase are distributed in the BCC matrix. As the heat treatment temperature increases from 750℃ to 1200℃, the proportion of the BCC region increases due to element diffusion. When the temperature is higher than 1050℃, some strip-shaped σ phase precipitates disappear in the BCC region. During the heat treatment, the size of the Cr-rich phase tends to decrease. With the increase of heat treatment temperature, the ultimate compressive strength and plasticity after heat treatment are improved due to precipitation strengthening and grain refinement caused by changes in microstructure and phase structure. In addition, the synergistic effect of dendrite and interdendritic microstructure during deformation is conducive to improving the compressive properties. Dendrites composed of BCC, Cr-rich and σ phase act as hard phases, while the ordered FCC / L12 phase between dendrites acts as soft phase. Therefore, Al after heat treatment at 1200℃ 0.5 CrFeNi 2.5 Si 0.25 High entropy alloys can simultaneously improve the strength and plasticity of alloys.

[0061] Therefore, a multiphase precipitation-strengthened high-entropy alloy with Cr-rich nanoprecipitates can be obtained after heat treatment at 1200 °C to obtain the best comprehensive mechanical properties.

[0062] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A multiphase precipitation-strengthened high entropy alloy of Cr-rich nanoprecipitates, characterized in that: It is composed of the following components in the following molar ratios: Al 0.5 Cr 0.9 FeNi 2.5 Si 0.25 .

2. A method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 1, characterized in that: The following steps are involved: 1) Raw material preparation: According to the molar ratio of Al 0.5 CrFeNi 2.5 Si 0.25 Weigh Al, Cr, Fe, Ni, and Si raw materials with a purity higher than 99.9% and clean them; 2) Vacuum suspension induction melting: Place the raw materials in a vacuum suspension induction melting furnace, evacuate the furnace, and repeatedly melt them multiple times in an inert gas atmosphere. Cool the furnace to obtain a high-entropy alloy. 3) Heat treatment: The high entropy alloy is annealed at 750°C-1200°C for 1 hour and then quenched and cooled to room temperature to obtain a multiphase precipitation-strengthened high entropy alloy with Cr-rich nano-precipitates.

3. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2, characterized in that: The cleaning treatment of the raw materials in step 1) is: acid washing the raw materials with a sulfuric acid aqueous solution having a volume fraction of 10%.

4. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2, characterized in that: The vacuum suspension induction melting furnace in step 2) is evacuated to 10 -3 level, and flush twice with inert gas until it is fully filled with inert gas.

5. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2, characterized in that: During the vacuum suspension induction melting furnace melting in step 2), the power is set from low to high to 100KW-150KW-200KW, with each adjustment interval of 5 minutes. After the raw material is completely melted, the melting is carried out at 150KW for 15 minutes.

6. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2, characterized in that: In step 2), the product is cooled to between 100-150° C. and then removed from the furnace.

7. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2, characterized in that: The annealing treatment in step 3) is as follows: the high entropy alloy is vacuum sealed in a quartz tube and then placed in a box-type resistance furnace, the heat treatment temperature is set to 750° C., 850° C., 1050° C. or 1200° C., the heat treatment holding time is 1 hour, and then water cooling is performed.

8. The method for preparing a multiphase precipitation-strengthened high-entropy alloy of Cr-rich nanoprecipitates according to claim 2 or 4, characterized in that: The inert gas is argon.

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