High-toughness and high-entropy alloy with inverse gradient structure and preparation method of high-toughness and high-entropy alloy

Abstract

The invention relates to a high-toughness high-entropy alloy with an inverse gradient structure and a preparation method of the high-toughness high-entropy alloy, and belongs to the technical field of high-entropy alloy preparation. The high-entropy alloy chilled plate with set chemical components is obtained, and the set chemical components comprise Ni, Co, Cr, Al and Ti; the high-entropy alloy chilled plate is subjected to sectional type heat treatment, so that the grain size of the high-entropy alloy chilled plate is in a decreasing trend from the surface to the inner core and is decreased to the nanoscale from the micron scale, and the high-toughness high-entropy alloy with the reverse gradient structure is obtained; wherein the sectional type heat treatment comprises heat treatment of a heating section, an aging section with set temperature and set pressure and a cooling section which are arranged in sequence. According to the embodiment of the invention, the high-entropy alloy chilled plate is subjected to aging treatment under the set pressure and the set temperature, dynamic recrystallization of the high-entropy alloy chilled plate can be achieved, the purpose of refining grains is achieved, the decreasing effect of heat transfer is intensified, and therefore the high-entropy alloy of an inverse gradient structure is obtained.

Description

Technical Field

[0001] This application relates to the technical field of high-entropy alloy preparation, and particularly relates to a high-strength, tough and high-entropy alloy with an inverse gradient structure and a preparation method thereof. Background Art

[0002] Multi-principal element high-entropy alloys with equiatomic or near-equiatomic ratios have attracted great attention in the materials field due to their novel design concept and comprehensive mechanical and functional properties. The high mixing entropy enables them to form simple solid-solution structures, such as face-centered cubic (FCC), body-centered cubic (BCC), or hexagonal close-packed (HCP) structures. Among them, single-phase FCC-structured high-entropy alloys have excellent ductility and strain hardening ability, high wear resistance and corrosion resistance, good radiation resistance, excellent damage tolerance, and excellent low-temperature properties, etc. However, these single-phase FCC-structured high-entropy alloys with coarse grains have insufficient yield strength, which is less than 400 MPa under general environmental conditions, severely limiting their engineering applications. Currently, heterogeneous microstructures composed of gradient grain sizes, nano-clusters, multi-phases, etc. can also endow high-entropy alloys with excellent properties similar to those of traditional heterogeneous-structured metallic materials (with an excellent combination of strength and ductility). The gradient structure is a promising heterogeneous structure that makes an important contribution to the trade-off between the strength and ductility of materials.

[0003] Currently, the materials with gradient structures are mainly prepared by surface treatment methods, such as laser shot peening, dry spraying + temperature inverse gradient sintering method, ultrasonic surface rolling, etc. However, these methods are either complex in process or have high equipment requirements. Although materials with gradient structures can be successfully prepared, they are restricted by problems such as high cost, low efficiency, limited product size, and experimental difficulties. Summary of the Invention

[0004] This application provides a high-strength, tough and high-entropy alloy with an inverse gradient structure and a preparation method thereof to solve the following technical problems: providing a preparation method for a high-strength, tough and high-entropy alloy with an inverse gradient structure.

[0005] In the first aspect, this application provides a preparation method for a high-strength, tough and high-entropy alloy with an inverse gradient structure, and the method includes:

[0006] Obtaining a cold-rolled plate of high-entropy alloy with a set chemical composition, where the set chemical composition includes Ni, Co, Cr, Al, and Ti;

[0007] Performing segmented heat treatment on the cold-rolled plate of high-entropy alloy so that the grain size of the cold-rolled plate of high-entropy alloy shows a decreasing trend from the surface to the core, decreasing from the micron level to the nano level, to obtain a high-strength, tough and high-entropy alloy with an inverse gradient structure; wherein, the segmented heat treatment includes: heat treatment of a heating section, an aging section with a set temperature and a set pressure, and a cooling section arranged in sequence.

[0008] Optionally, the set pressure is 2 GPa to 6 GPa; and / or,

[0009] the set temperature is 1000 °C to 1100 °C.

[0010] Optionally, the time of the aging stage is 0.5 h to 2 h.

[0011] Optionally, in the set chemical composition, in terms of atomic fraction, the content of Ni is 33% to 36%, the content of Co is 33% to 36%, the content of Cr is 22% to 25%, and the total content of Al and Ti is 6% to 10%.

[0012] Optionally, the set chemical composition satisfies the following relationship: a / b > 3, where a = [Ni] / [Co] and b = [Al] / [Ti];

[0013] In the formula, [Ni] represents the atomic fraction of Ni, [Co] represents the atomic fraction of Co, [Al] represents the atomic fraction of Al, and [Ti] represents the atomic fraction of Ti.

[0014] Optionally, the heating rate in the heating stage is 120 °C / min to 180 °C / min; and / or,

[0015] the cooling rate in the cooling stage is 200 °C / min to 250 °C / min.

[0016] Optionally, obtaining the high-entropy alloy cold hard plate with the set chemical composition includes:

[0017] subjecting the high-entropy alloy ingot with the set chemical composition to solution treatment;

[0018] subjecting the solution-treated high-entropy alloy ingot to segmented cold rolling to obtain a high-entropy alloy cold hard plate with the set chemical composition; wherein, the segmented cold rolling includes: cold rolling of a first rolling stage, a solution treatment stage, and a second rolling stage arranged in sequence.

[0019] Optionally, the process parameters of the solution treatment include: temperature of 1150 °C to 1200 °C, time of 1 h to 2 h; and / or,

[0020] the process parameters of the solution treatment stage include: temperature of 1150 °C to 1200 °C, time of 1 h to 2 h; and / or,

[0021] the rolling speed of the cold rolling is 80 mm / s to 100 mm / s; and / or,

[0022] the reduction per pass of the cold rolling is 0.1 mm to 0.2 mm.

[0023] Optionally, the high-strength, high-toughness, high-entropy alloy with an inverse gradient structure satisfies at least one of the following properties: the tensile strength is greater than 1500 MPa, the fracture elongation is greater than 15%, and the Vickers hardness is greater than 350 HV.

[0024] In a second aspect, the present application provides a high-strength, high-toughness, high-entropy alloy with an inverse gradient structure, which is prepared by the method according to any one of the first aspects.

[0025] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0026] The preparation method of the high-strength, high-toughness, high-entropy alloy with an inverse gradient structure provided by the embodiment of the present application includes: obtaining a cold-rolled hard plate of a high-entropy alloy with a set chemical composition, where the set chemical composition includes Ni, Co, Cr, Al, and Ti; performing segmented heat treatment on the cold-rolled hard plate of the high-entropy alloy so that the grain size of the cold-rolled hard plate of the high-entropy alloy shows a decreasing trend from the surface to the core, decreasing from the micron level to the nanometer level, to obtain a high-strength, high-toughness, high-entropy alloy with an inverse gradient structure; where the segmented heat treatment includes: heat treatment in a sequentially set heating section, an aging section with a set temperature and a set pressure, and a cooling section. The cold-rolled hard plate of the high-entropy alloy with a set chemical composition is subjected to segmented heat treatment. Among them, the heating section can heat the surface of the cold-rolled hard plate of the high-entropy alloy; the cooling section can promote the retention of the inverse gradient structure; the aging section with a set temperature and a set pressure can realize the recrystallization of the cold-rolled hard plate of the high-entropy alloy, and at the same time, the set pressure can cause the cold-rolled hard plate of the high-entropy alloy to deform and intensify the decreasing effect of heat transfer from the surface to the center, so that the grain size of the alloy decreases from the micron level of the soft surface to the nanometer level of the hard core, which is in good agreement with the microhardness distribution; the synergistic effect of the set temperature and the set pressure can realize the dynamic recrystallization of the cold-rolled hard plate of the high-entropy alloy, so as to achieve the purpose of refining the grains and intensifying this thermal effect, and further obtain a high-strength, high-toughness, high-entropy alloy with an inverse gradient structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1Schematic flow chart of a preparation method of a high-strength, high-toughness and high-entropy alloy with an inverse gradient structure provided in Embodiment 1 of the present application;

[0030] Figure 2 Scanning electron microscope image of a high-strength, high-toughness and high-entropy alloy with an inverse gradient structure provided in Embodiment 1 of the present application;

[0031] Figure 3 Electron backscatter diffraction pattern of a high-strength, high-toughness and high-entropy alloy with an inverse gradient structure provided in Embodiment 1 of the present application;

[0032] Figure 4 Scanning electron microscope image of a high-strength, high-toughness and high-entropy alloy with an inverse gradient structure provided in Comparative Example 1 of the present application;

[0033] Figure 5 Inverse gradient distribution diagram of the Vickers hardness of the high-strength, high-toughness and high-entropy alloy with an inverse gradient structure provided in Embodiment 1 and Comparative Example 1 of the present application along the radial direction. Detailed implementation manners

[0034] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0035] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0036] In this application, unless otherwise specified, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the attached drawings. Additionally, in the description of this application's specification, the terms "comprising", "including", etc. mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural.

[0037] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in this application can all be obtained through market purchases or can be prepared by existing methods.

[0038] In a first aspect, this application provides a preparation method for a high-strength, high-toughness, and high-entropy alloy with an inverse gradient structure. Figure 1 It is a schematic flow chart of a preparation method for a high-strength, high-toughness, and high-entropy alloy with an inverse gradient structure provided by an embodiment of this application; please refer to Figure 1 , and the method includes:

[0039] S1. Obtain a cold hard plate of a high-entropy alloy with a set chemical composition, and the set chemical composition includes Ni, Co, Cr, Al, and Ti;

[0040] High-entropy alloys generally refer to alloys composed of five or more main elements. In high-entropy alloys, multiple elements are in a "high-entropy" state and jointly affect the properties of the alloy. According to the definition of entropy, the higher the degree of disorder of the system, the greater the entropy value. In high-entropy alloys, the mixing of multiple elements greatly increases the degree of disorder of atomic arrangement, having a relatively high mixing entropy, which is an important feature that distinguishes high-entropy alloys from traditional alloys and is also one of the important reasons for their unique properties. In the embodiments of this application, in this multi-principal-element alloy system, when multiple elements (Ni, Co, Cr, Al, and Ti) are mixed to form a solid solution, a relatively high mixing entropy will be generated. The atomic sizes and chemical properties of elements such as Ni, Co, Cr, Al, and Ti are different. When they jointly form an alloy, it will cause severe lattice distortion. The presence of multiple principal elements makes atomic diffusion in the alloy complex and sluggish.

[0041] Ni and Co have a face-centered cubic (FCC) structure. They can solid-solution strengthen the matrix in the alloy, improving the strength and toughness of the alloy. When Cr dissolves in the alloy matrix, it will produce a solid-solution strengthening effect, increasing the strength and hardness of the alloy. Al and Ti can form intermetallic compounds with other elements or improve the strength and hardness of the alloy through solid-solution strengthening. Especially at high temperatures, they can form some stable strengthening phases, such as γ' phase (Ni 3 3 3 Al, Ni

[0042] Ti, etc.). These strengthening phases can effectively hinder the movement of dislocations, improving the high-temperature strength and creep properties of the alloy.

[0043] In some embodiments, in the set chemical composition, in terms of atomic fraction, the content of Ni is 33% - 36%, the content of Co is 33% - 36%, the content of Cr is 22% - 25%, and the total content of Al and Ti is 6% - 10%.

[0044] The content of Ni can be 33% - 36%, the content of Co can be 33% - 36%, the content of Cr can be 22% - 25%, and the total content of Al and Ti can be 6% - 10%. Reasonable design of the atomic fractions of Ni, Co, Cr, Al, and Ti can enable the high-entropy alloy cold hard plate and the subsequent high-strength and high-toughness high-entropy alloy with an inverse gradient structure to have excellent mechanical properties. Exemplarily, the content of Ni can be 33, 34, 35, 36%, etc., the content of Co can be 33, 34, 35, 36%, etc., the content of Cr can be 22%, 23%, 24%, 25%, etc., and the total content of Al and Ti can be 6%, 7%, 8%, 9%, 10%, etc.

[0045] In some embodiments, the set chemical composition satisfies the following relationship: a / b > 3, where a = [Ni] / [Co] and b = [Al] / [Ti];

[0046] In the formula, [Ni] represents the atomic fraction of Ni, [Co] represents the atomic fraction of Co, [Al] represents the atomic fraction of Al,

[0047] [Ti] represents the atomic fraction of Ti.

[0048] In some embodiments, obtaining the high-entropy alloy cold hard plate with a set chemical composition includes:

[0049] Perform solution treatment on the high-entropy alloy ingot with the described set chemical composition;

[0050] Perform segmented cold rolling on the solution-treated high-entropy alloy ingot to obtain a cold hard plate of high-entropy alloy with a set chemical composition; wherein, the segmented cold rolling includes: cold rolling in a first rolling section, a solution treatment section, and a second rolling section arranged in sequence.

[0051] Before step S1, it also includes: Melting: Put the proportioned raw materials Ni, Co, Cr, Al, and Ti into a copper crucible, introduce argon gas, and after all are melted, gently stir to remove the oxide layer and impurities on the surface of the molten liquid, and then quickly cast it into a copper mold to form an ingot.

[0052] "Obtain a cold hard plate of high-entropy alloy with a set chemical composition" can specifically include: Solution treatment: Place the high-entropy alloy ingot in a tube furnace for heat preservation, and then quench it to room temperature, so that the alloy is in a fully solid solution state; Cold rolling: First deform the high-entropy alloy ingot by rolling (first rolling section) to a thickness of about 8 mm, then perform solution treatment (solution treatment section) by heat preservation in a tube furnace, take it out and quench it to room temperature with water; Perform multi-pass rolling (second rolling section) at room temperature to roll the sheet thickness to 1.6 - 2.5 mm, and the total reduction rate is 70% - 80%.

[0053] In some embodiments, the process parameters of the solution treatment include: temperature is 1150°C - 1200°C, time is 1 h - 2 h; and / or,

[0054] The process parameters of the solution treatment section include: temperature is 1150°C - 1200°C, time is 1 h - 2 h; and / or,

[0055] The rolling speed of the cold rolling is 80 mm / s - 100 mm / s; and / or,

[0056] The reduction per pass of the cold rolling is 0.1 mm - 0.2 mm.

[0057] In the embodiments of the present application, solution treatment is a heat treatment process for metal materials. Through solution treatment, various phases in the alloy can be fully dissolved, thereby improving the mechanical properties of the alloy. During the processing of metal materials, such as casting, forging, and welding, residual stresses will be generated. Solution treatment can homogenize the internal organizational structure of the metal, effectively eliminate these residual stresses, and reduce the possibility of deformation or cracking of the parts due to stress concentration during use. Solution treatment can improve the cutting and cold working properties of metal materials. Therefore, after solution treatment, the hardness and strength distribution of the metal are more uniform, making it easier to obtain good surface quality and dimensional accuracy during processing.

[0058] The solution treatment temperature can be 1150°C to 1200°C, and the time can be 1 h to 2 h, which can make the alloying elements of the high-entropy alloy ingot in a completely miscible state, forming a uniform solid solution. And for the subsequent solution treatment section of cold rolling, the temperature can be 1150°C to 1200°C, and the time can be 1 h to 2 h, which can eliminate the work hardening phenomenon generated during the first rolling section and make the alloying elements in the high-entropy alloy ingot after the first rolling in a completely miscible state, thus providing conditions for the subsequent second rolling section. Exemplarily, the temperatures of this solution treatment and the solution treatment section of cold rolling can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, etc. The time can be 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2.0 h, etc.

[0059] Cold rolling is a rolling process carried out below the recrystallization temperature of the metal material. During cold rolling, the metal material is subjected to the pressure of the rolling rolls and undergoes plastic deformation, and its internal grain structure is elongated, broken, and refined, thereby increasing the strength and hardness of the metal and improving its surface quality and dimensional accuracy at the same time. The rolling speed of cold rolling can be 80 mm / s to 100 mm / s, and the reduction per pass of cold rolling can be 0.1 mm to 0.2 mm. It can achieve the deformation effect of the ingot and reduce the working efficiency, and avoid cracking of the ingot during the rolling process. Exemplarily, the rolling speed can be 80 mm / s, 85 mm / s, 90 mm / s, 95 mm / s, 100 mm / s, etc.; the reduction per pass can be 0.1 mm, 0.12 mm, 0.14 mm, 0.16 mm, 0.2 mm, etc.

[0060] S2. Perform segmented heat treatment on the high-entropy alloy cold hard plate so that the grain size of the high-entropy alloy cold hard plate shows a downward trend from the surface to the core, decreasing from the micron level to the nanometer level, to obtain a high-strength and high-toughness high-entropy alloy with an inverse gradient structure; wherein, the segmented heat treatment includes: a heat treatment of a heating section, an aging section with a set temperature and a set pressure, and a cooling section arranged in sequence.

[0061] The high-entropy alloy cold hard plate with a set chemical composition is subjected to segmented heat treatment. Among them, the heating section can heat the surface of the high-entropy alloy cold hard plate; the cooling section can promote the retention of the inverse gradient structure; the aging section with a set temperature and a set pressure can achieve the recrystallization of the high-entropy alloy cold hard plate. At the same time, the set pressure can cause the high-entropy alloy cold hard plate to deform and intensify the decreasing effect of heat transfer, reducing the grain size of the alloy from the micron level of the soft surface to the nanometer level of the hard inner core, which is in good agreement with the microhardness distribution; the synergistic effect of the set temperature and the set pressure can achieve the dynamic recrystallization of the high-entropy alloy cold hard plate, so as to achieve the purpose of refining grains and intensify the decreasing effect of heat transfer, and then obtain a high-strength and high-toughness high-entropy alloy with an inverse gradient structure.

[0062] In some embodiments, the set pressure is 2 GPa to 6 GPa; and / or,

[0063] The set temperature is 1000 °C to 1100 °C.

[0064] In some embodiments, the time of the aging section is 0.5 h to 2 h.

[0065] Due to the high-pressure effect intensifying the decreasing effect of heat transfer, on the surface of the alloy, the heat transfer received is relatively strong, and the activity of atoms is relatively strong. In this case, the diffusion of atoms and the movement of dislocations are more active, making the recrystallization process easier to proceed, thus forming micron-sized grains with relatively large sizes. These regions have relatively low hardness and are manifested as soft surfaces. As the depth into the alloy increases, the decreasing effect of heat transfer gradually intensifies, and the activity of atoms under high pressure also decreases accordingly. At this time, the movement and interaction of dislocations are restricted to a certain extent, and the nucleation and growth processes of new grains are more difficult, resulting in smaller grain sizes. In the region of the hard inner core, the grain size is reduced to the nanometer level. Due to the higher grain boundary ratio of nanometer-sized grains, the strengthening effect of grain boundaries on the material is significantly enhanced, making the hardness of this part of the region increase significantly. This gradual change in grain size from the surface to the inside just coincides with the distribution of microhardness, that is, the microhardness of the soft phase on the surface is relatively low, while the microhardness of the hard phase inside is relatively high, thus forming an inverse gradient structure.

[0066] In the embodiments of the present application, due to the decreasing effect of heat transfer, the high pressure intensifies this thermal effect to obtain an inverse gradient structure, and its grain size decreases from the micron level (more than several hundred microns) of the soft surface to the nanometer level (tens to several hundred nanometers) of the hard core, which is in good agreement with the microhardness distribution. The set pressure can be 2 GPa to 6 GPa. The cold deformation caused by the high pressure increases the dislocation density inside the alloy, provides more nucleation sites for recrystallization, realizes grain refinement, and at the same time the pressure intensifies the thermal effect caused by the sample thickness, which is conducive to realizing the inverse gradient structure. If the set pressure is higher than 6 GPa, it may cause excessive deformation of the sample and reduce the thermal effect; if the set pressure is lower than 2 GPa, it is difficult to achieve the internal deformation effect of the alloy, and thus more nucleation sites cannot be provided. Exemplarily, the set pressure can be 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, etc.

[0067] The set temperature can be 1000 °C to 1100 °C, and the time of the aging section can be 0.5 h to 2 h, effectively capturing the recrystallized and non-recrystallized states of the alloy, realizing full recrystallization of the alloy, and thus obtaining excellent mechanical properties. The appropriate time of the aging section can inhibit the abnormal grain growth of the alloy, give sufficient time for alloy recrystallization and precipitation phase precipitation, and thus improve the mechanical properties of the alloy. On the surface of the alloy, due to the relatively strong thermal effect, the atomic activity ability is high, and the recrystallization process is relatively fast, and new equiaxed grains can be quickly formed. These grains are relatively large in size under appropriate temperature and time conditions, reaching the micron level, forming a soft surface region. As the depth into the alloy increases, the thermal effect gradually decays, and the recrystallization process is relatively slow. Under the conditions that the set temperature can be 1000 °C to 1100 °C and the time of the aging section can be 0.5 h to 2 h, the atomic diffusion and migration are relatively difficult, making the newly formed grain size smaller and gradually transitioning to the nanometer level, thus constructing an inverse gradient structure from micron-level grains on the soft surface to nanometer-level grains in the hard core. Exemplarily, the set temperature can be 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1040 °C, 1050 °C, 1060 °C, 1070, 1080, 1090 °C, 1100 °C, etc., and the time can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, etc.

[0068] In some embodiments, the heating rate of the heating section is 120 °C / min to 180 °C / min; and / or, the cooling rate of the cooling section is 200 °C / min to 250 °C / min.

[0069] In the embodiment of the present application, the heating rate in the heating stage can be 120 °C / min to 180 °C / min, which is beneficial to the uniform heating of the surface of the high-entropy alloy cold hard plate. The prior heating of the surface can trigger an inverse temperature gradient between the surface and the interior, which may affect the subsequent formation of the inverse gradient structure. Exemplarily, the heating rate in this heating stage can be 120 °C / min, 130 °C / min, 140 °C / min, 150 °C / min, 160 °C / min, 170 °C / min, 180 °C / min, etc.; the cooling rate in the cooling stage can be 150 °C / min to 200 °C / min, which can fully promote the retention of the inverse gradient structure. Rapid cooling can fix the inverse gradient structure formed in the aging stage and prevent the formed structure from changing due to atomic diffusion and tissue transformation during the cooling process. An appropriate cooling rate can ensure the stability of the internal tissue structure of the material, thereby retaining the excellent properties obtained through the previous treatment. Exemplarily, the cooling rate in this cooling stage can be 200 °C / min, 210 °C / min, 220 °C / min, 230 °C / min, 240 °C / min, 250 °C / min, etc. This cooling stage can be water cooling.

[0070] In some embodiments, the high-strength and high-toughness high-entropy alloy with an inverse gradient structure satisfies at least one of the following properties: the tensile strength is greater than 1500 MPa, the elongation at break is greater than 15%, and the Vickers hardness is greater than 350 HV.

[0071] The preparation method of a high-strength and high-toughness high-entropy alloy with an inverse gradient structure provided by the embodiment of the present application has the following advantages:

[0072] 1. Conduct heat treatment in the aging stage under a set temperature and a set pressure to realize the recrystallization of the high-entropy alloy cold hard plate. During this process, new non-distorted grains nucleate and grow in the deformed tissue, replacing the original deformed grains. At the same time, the existence of the set pressure causes the alloy cold hard plate to deform, and the dislocation movement intensifies, which not only promotes the progress of recrystallization but also changes the energy state inside the alloy, intensifying the decreasing effect of heat transfer. This combined effect causes the grain size of the alloy to gradually decrease from the micron level on the soft surface to the nanometer level on the hard inner core, and it fits well with the microhardness distribution. That is, the surface is relatively soft but has a certain toughness, while the interior has a higher hardness, forming the structural characteristics of an inverse gradient. This structure is beneficial to improving the overall strength and toughness of the material.

[0073] 2. The combined action of the set temperature and set pressure realizes the dynamic recrystallization of the high-entropy alloy cold hard plate. During the dynamic recrystallization process, under the combined driving of heat and pressure, dislocations continuously proliferate, move, and interact with each other, and new grains continuously nucleate and grow. This dynamic recrystallization process effectively refines the grains, further reducing the grain size of the material, thereby improving the mechanical properties such as the strength and toughness of the material. At the same time, the pressure exacerbates the decreasing effect of heat transfer, contributing to obtaining a non-uniform structure, achieving the combination of soft and hard tissues, further optimizing the properties of the alloy, and finally obtaining a high-strength and high-toughness high-entropy alloy material with an inverse gradient structure.

[0074] In a second aspect, the present application provides a high-strength and high-toughness high-entropy alloy with an inverse gradient structure, which is prepared by the method according to any one of the first aspect.

[0075] This high-strength and high-toughness high-entropy alloy with an inverse gradient structure is realized based on the preparation method of the high-strength and high-toughness high-entropy alloy with an inverse gradient structure. The specific steps of the preparation method of the high-strength and high-toughness high-entropy alloy with an inverse gradient structure can refer to the above embodiments. Since this high-strength and high-toughness high-entropy alloy with an inverse gradient structure adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated one by one here.

[0076] The following further elaborates the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0077] Example 1

[0078] A preparation method of a high-strength and high-toughness high-entropy alloy with an inverse gradient structure includes:

[0079] Smelting: Put pure metals Ni (purity 99.99%), Co (purity 99.99%), Cr (purity 99.99%), Al (purity 99.99%), and Ti (purity 99.99%) into an arc melting furnace. After sealing, evacuate and fill with argon. The melting temperature is about 2000°C or higher. After all are melted, gently stir to remove the oxide layer and impurities on the surface of the melt, and then quickly cast it into a copper mold to form an ingot. Among them, in terms of atomic fraction, the content of Ni is 35%, the content of Co is 34%, the content of Cr is 23%, the content of Al is 1%, and the content of Ti is 7%; a / b is 7.2, where a = [Ni] / [Co] and b = [Al] / [Ti];

[0080] Solution treatment: Place the alloy ingot in an air furnace at 1200 °C and hold for 2 hours. After removal, water quench to room temperature;

[0081] Cold rolling: First, roll the round ingot to a thickness of about 8 mm, then perform solution treatment by holding in an air furnace at 1200 °C for 2 hours. After removal, water quench to room temperature; Carry out cold rolling, perform room-temperature rolling on a rolling mill at a speed of 100 mm / s, with the reduction per pass being 0.1 mm to 0.2 mm. After multiple passes of rolling, roll the sheet thickness to 1.6 mm, with a total reduction rate of 80%, to obtain a high-entropy alloy cold hard sheet.

[0082] Heat treatment: Perform segmented heat treatment on the high-entropy alloy cold hard sheet to obtain a high-strength, high-toughness high-entropy alloy with an inverse gradient structure; Among them, the segmented heat treatment includes: heat treatment of a heating section, an aging section with a set temperature and a set pressure, and a cooling section arranged in sequence. The heating rate of the heating section is 160 °C / min; the set temperature is 1100 °C, the set pressure is 4 GPa, the time of the aging section is 1 h, water cool to room temperature in the cooling section, and the cooling rate of the cooling section is 220 °C / min.

[0083] Comparative Example 1

[0084] Based on the disclosed content of Example 1, the difference between Comparative Example 1 and Example 1 lies in: atmospheric pressure heat treatment.

[0085] Perform mechanical property tests on the high-strength, high-toughness high-entropy alloy with an inverse gradient structure prepared in Example 1 and Comparative Example 1. Please refer to Table 1.

[0086] Table 1 Mechanical properties of the high-strength, high-toughness high-entropy alloy with an inverse gradient structure

[0087] Serial number Tensile strength Mpa Yield strength Mpa Elongation at break % Vickers hardness Example 1 1550 1500 16 371 Comparative example 1 750 1150 41 310

[0088] As can be seen from Table 1, the high-strength, high-toughness high-entropy alloy with an inverse gradient structure prepared in Example 1 has excellent comprehensive mechanical properties. Figure 2 This is the scanning electron microscope image of a high-strength, high-toughness high-entropy alloy with an inverse gradient structure provided in Example 1 of this application; Figure 3 This is the electron backscatter diffraction pattern of a high-strength, high-toughness high-entropy alloy with an inverse gradient structure provided in Example 1 of this application; Please refer to Figures 2 - 3 , indicating that the alloy prepared in Example 1 undergoes complete recrystallization; The high-entropy alloy with an inverse gradient structure is obtained in Example 1; It has a structure that gradually changes from coarse grains to ultrafine grains from the surface to the center. Figure 4 This is the scanning electron microscope image of a high-strength, high-toughness high-entropy alloy with an inverse gradient structure provided in Comparative Example 1 of this application; Please refer to Figure 4, indicating that the alloy prepared in Comparative Example 1 is fully recrystallized and the equiaxed grains grow uniformly. The high-strength, high-toughness high-entropy alloy with an inverse gradient structure provided in Example 1 and Comparative Example 1 was tested using a microhardness tester, Figure 5 is the inverse gradient distribution diagram of the Vickers hardness along the radial direction of the high-strength, high-toughness high-entropy alloy with an inverse gradient structure provided in Example 1 and Comparative Example 1 of the present application; please refer to Figure 5 , indicating that the hardness of the alloy prepared in Example 1 shows a trend of low surface hardness and high core hardness; the hardness of the alloy prepared in Comparative Example 1 shows a stable trend and is lower than that of Example 1. High-pressure heat treatment inhibits grain growth, thereby promoting the improvement of alloy properties. The alloy after high-pressure treatment has high Vickers strength. Heat treatment at 1100 °C under high pressure and high temperature promotes the complete recrystallization of the high-entropy alloy, and at the same time, due to the decreasing effect of heat transfer, a high-entropy alloy with an inverse gradient structure is prepared, which is beneficial to improving the mechanical properties of the high-entropy alloy.

[0089] One or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0090] (1) The deformation heat treatment method combining long-time high-temperature solid solution, cold rolling deformation, and short-time high-temperature and high-pressure aging is adopted in the embodiments of the present application. While realizing room-temperature cold rolling of the alloy, the grains are significantly refined, achieving good strength-ductility matching, and having the characteristics of energy saving, high efficiency, and low cost;

[0091] (2) The embodiments of the present application perform high-temperature aging under high pressure, realizing recrystallization annealing and increasing the nucleation sites through deformation at the same time, achieving the purpose of refining the grains of the alloy;

[0092] (3) The embodiments of the present application utilize the decreasing effect of high pressure on heat transfer to prepare a high-entropy alloy with an inverse gradient structure, achieving the purpose of preparing a complex inverse gradient tissue structure by a simple process with low cost.

[0093] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a high-strength and high-toughness high-entropy alloy with an inverse gradient structure, the method comprising: Obtaining a high entropy alloy chilled plate having a set chemical composition, wherein the set chemical composition includes Ni, Co, Cr, Al and Ti; The high entropy alloy cold-hardened plate is subjected to a segmented heat treatment so that the grain size of the high entropy alloy cold-hardened plate decreases from the surface to the core, from the micron level to the nanometer level, so as to obtain a high-strength and tough high entropy alloy with an inverse gradient structure; wherein the segmented heat treatment includes: a heating section, an aging section with a set temperature and a set pressure, and a cooling section heat treatment which are sequentially arranged.

2. The method according to claim 1, characterized in that The set pressure is 2 GPa to 6 GPa; and / or, The set temperature is 1000°C to 1100°C.

3. The method according to claim 2, characterized in that The time of the aging period is 0.5h to 2h.

4. The method according to any one of claims 1 to 3, characterized in that: In the set chemical composition, in terms of atomic fraction, the content of Ni is 33% to 36%, the content of Co is 33% to 36%, the content of Cr is 22% to 25%, and the sum of the content of Al and the content of Ti is 6% to 10%.

5. The method according to claim 4, characterized in that The set chemical composition satisfies the following relationship: a / b>3, where a=[Ni] / [Co], b=[Al] / [Ti]; In the formula, [Ni] represents the atomic fraction of Ni, [Co] represents the atomic fraction of Co, [Al] represents the atomic fraction of Al, and [Ti] represents the atomic fraction of Ti.

6. The method according to claim 1, characterized in that The heating rate of the heating section is 120°C / min to 180°C / min; and / or, The cooling rate of the cooling section is 200°C / min to 250°C / min.

7. The method according to claim 1, characterized in that The method of obtaining a high entropy alloy chilled plate having a set chemical composition comprises: subjecting a high entropy alloy ingot having the set chemical composition to a solid solution treatment; The high entropy alloy ingot after solid solution treatment is subjected to segmented cold rolling to obtain a high entropy alloy chilled plate with a set chemical composition; wherein the segmented cold rolling includes: cold rolling of a first rolling segment, a solid solution treatment segment, and a second rolling segment arranged in sequence.

8. The method according to claim 7, characterized in that The process parameters of the solution treatment include: a temperature of 1150° C. to 1200° C. and a time of 1 h to 2 h; and / or, The process parameters of the solution treatment stage include: temperature of 1150°C to 1200°C, time of 1h to 2h; and / or, The cold rolling speed is 80 mm / s to 100 mm / s; and / or, The reduction amount of each cold rolling pass is 0.1 mm to 0.2 mm.

9. The method according to claim 1, characterized in that: The high-strength and high-toughness high-entropy alloy with an inverse gradient structure satisfies at least one of the following properties: a tensile strength greater than 1500 MPa, an elongation at break greater than 15%, and a Vickers hardness greater than 350 HV.

10. A high-strength and high-toughness high-entropy alloy with an inverse gradient structure, wherein the high-strength and high-toughness high-entropy alloy with an inverse gradient structure is prepared by the method described in any one of claims 1 to 9.

Images