A refractory medium-entropy alloy of Mo-Ti-Cr-Si system and a preparation method thereof

Abstract

The application belongs to the technical field of high-temperature materials, and more particularly relates to a Mo-Ti-Cr-Si refractory medium-entropy alloy and a preparation method thereof; the medium-entropy alloy is composed of Mo, Ti, Cr and Si, and the addition amount of Si is 1% to 3% according to atomic percentage; in the medium-entropy alloy, the addition amount of Mo is 32.4% to 33%, the addition amount of Ti is 32.3% to 33%, and the addition amount of Cr is 32.3% to 33%. The Mo-Ti-Cr-Si refractory medium-entropy alloy provided by the application can reduce the density of the alloy by Ti element, can improve the high-temperature oxidation resistance of the alloy by Cr element, and can further promote the generation of a passivation film by adding a small amount of Si element; the alloy provided by the application has better oxidation resistance than some existing refractory high-entropy / medium-entropy alloys, and can overcome the common problem of catastrophic oxidation of the refractory alloy system.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature materials technology, and more specifically, relates to a Mo-Ti-Cr-Si refractory medium-entropy alloy and its preparation method. Background Technology

[0002] High-temperature structural materials are fundamental to innovation and development in fields such as aerospace and weaponry. For example, nickel-based superalloys are widely used in the aerospace industry due to their high specific strength, good ductility, excellent creep resistance, outstanding structural stability, and resistance to hot corrosion. However, because their melting point is only around 1280℃, they can only withstand limited ambient temperatures, which cannot fully meet the development requirements of future advanced aircraft. Therefore, developing high-temperature structural materials with higher temperature resistance is extremely crucial.

[0003] In recent years, high-entropy / medium-entropy alloys have attracted widespread attention from researchers. This type of alloy is a novel alloy that breaks through the traditional alloy design concept. It is typically alloyed from multiple main elements in equal or near-equal atomic ratios, with each main element having an atomic fraction ranging from 5% to 35%. Furthermore, its high mixing entropy makes it prone to forming simple solid solutions rather than intermetallic compounds. Its high melting point and high strength also give it enormous application potential in the field of high-temperature structural materials.

[0004] However, refractory high-entropy / medium-entropy alloys have the drawback of poor oxidation resistance at medium and high temperatures. In particular, they are prone to catastrophic oxidation, which transforms dense bulk materials into loose powders, thus limiting their practical application in engineering. Summary of the Invention

[0005] In view of this, the present invention proposes a Mo-Ti-Cr-Si refractory medium-entropy alloy and its preparation method, aiming to solve the problem of poor high-temperature oxidation resistance of existing refractory high-entropy / medium-entropy alloys.

[0006] The technical solution of this invention is implemented as follows:

[0007] In a first aspect, the present invention provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, wherein the medium-entropy alloy is composed of Mo, Ti, Cr and Si, and the amount of Si added is 1% to 3% by atomic percentage.

[0008] Specifically, molybdenum is a refractory metal that ensures the high-temperature strength of the alloy; titanium has good strength, low density, and good corrosion resistance, which can improve the mechanical properties and corrosion resistance of the alloy; chromium is a common high-temperature alloying element that can improve the oxidation resistance and corrosion resistance of the alloy; silicon can improve the thermal stability and oxidation resistance of the alloy. The above elements work synergistically in the Mo-Ti-Cr-Si system of refractory medium-entropy alloys to jointly improve the high-temperature performance of the alloy, especially its oxidation resistance.

[0009] The mixture of Mo, Ti, and Cr elements exhibits high high-temperature stability. Ti reduces alloy density, while Cr forms a dense oxide layer on the alloy surface, improving the oxidation resistance of medium-entropy alloys. Furthermore, the addition of Si enhances the stability and density of the oxide layer, reduces oxide defects, and further improves the alloy's oxidation resistance. Specifically, Si reacts chemically with oxygen to form a SiO2 layer. SiO2 possesses good thermal stability and is not easily volatilized, effectively isolating the alloy matrix from oxygen and improving oxidation resistance. Simultaneously, the SiO2 formed at high temperatures is typically glassy and possesses a certain degree of fluidity, allowing it to spread uniformly on the alloy surface, improving the density and uniformity of the oxide layer, effectively reducing the oxidation rate, and enhancing the alloy's oxidation resistance.

[0010] The addition of 1% to 3% Si can improve the oxidation resistance of medium-entropy alloys while avoiding the formation of excessive brittle metal silicides that could affect their mechanical properties. If the Si content is too high, it will lead to an increase in the formation of metal silicides, which may reduce the alloy's plasticity and toughness, causing it to become brittle.

[0011] Based on the above technical solutions, preferably, in the medium entropy alloy, the amount of Mo added is 32.4% to 33%, the amount of Ti added is 32.3% to 33%, and the amount of Cr added is 32.3% to 33% by atomic percentage.

[0012] By using Mo-Ti-Cr refractory medium-entropy alloys composed of Mo, Ti, and Cr elements in (near) equal atomic ratios, the high-temperature stability and oxidation resistance of the alloy can be improved through the severe lattice distortion and entropy increase effect of the medium-entropy alloy. However, excessively high or low content may prevent the formation of the solid solution phase unique to medium-entropy alloys, thus affecting the alloy's performance.

[0013] Secondly, the present invention provides a method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy, comprising the following steps:

[0014] S1. Using pure metals and non-metallic elements as raw materials, the raw materials are weighed and proportioned according to the atomic percentage of medium-entropy alloys;

[0015] S2. Mo-Ti-Cr-Si alloy ingots were prepared by vacuum arc melting.

[0016] S3. The Mo-Ti-Cr-Si alloy ingot prepared in step S2 is subjected to high-temperature homogenization annealing to obtain a Mo-Ti-Cr-Si refractory medium-entropy alloy.

[0017] Based on the above technical solutions, preferably, in step S1, the raw materials include Mo strips with a purity of 99.95 wt.%, Ti sheets with a purity of 99.995 wt.%, Cr blocks with a purity of 99.98 wt.%, and Si blocks with a purity of 99.999 wt.%.

[0018] Based on the above technical solutions, preferably, step S2 specifically includes: first, preparing a Mo-Ti pre-alloy ingot by vacuum arc melting, then adding Cr for vacuum arc melting, and finally adding Si for vacuum arc melting to obtain a Mo-Ti-Cr-Si alloy ingot.

[0019] Specifically, since the melting point of Mo is much higher than that of other alloying elements, preparing a Mo-Ti pre-alloyed solid solution first can effectively lower the alloy melting point, which is beneficial for the subsequent addition of Cr and Si. Then, Cr and Si are added in steps, and after each melting step, the element loss is confirmed by weighing and then remelted to replenish the losses, ensuring that the alloy composition meets the target composition design and promoting the formation of a medium-entropy alloy solid solution phase structure. During vacuum arc melting, Si easily reacts with oxygen to form oxides, leading to Si loss, reducing the actual Si content, and affecting the alloy microstructure and properties. Therefore, Si is added last to reduce the oxidation reaction of Si and ensure that the Si content meets the design requirements.

[0020] Based on the above technical solution, preferably, in step S2, the vacuum arc melting is performed by first evacuating the vacuum to a vacuum degree of 3×10. -3 ~5×10 -3 Pa, introduce protective gas at 0.04-0.06 MPa, control the voltage of the vacuum arc melting furnace to 550V, the current to 10-16A, and the melting time for each melting session to 15-20 minutes.

[0021] By drawing a vacuum and introducing a protective gas, the mixing of impurities such as oxygen and nitrogen during the alloy melting process can be effectively reduced, thereby ensuring the purity and quality of the alloy. By controlling the voltage and current of the vacuum arc melting furnace, the energy input during the melting process can be adjusted to ensure the stability of the alloy melting temperature, which is beneficial to the uniform mixing of alloy components and the control of the melting process.

[0022] Based on the above technical solutions, preferably, the vacuum arc melting further includes turning the alloy melt over after it has cooled, and then continuing the vacuum arc melting. Each time the alloy raw material is completely melted, it is held for 3 to 5 minutes, and the melting is repeated ≥ 4 times.

[0023] Specifically, multiple melting and flipping processes help to achieve a more uniform mixing of the elements in the alloy. Because the water-cooled copper mold is at a low temperature during melting, the lower part of the alloy ingot is also at a low temperature, resulting in some alloying elements not being fully melted. Flipping during the melting process promotes the dissolution of each element and improves the chemical homogeneity of the alloy ingot.

[0024] Based on the above technical solutions, preferably, the vacuum arc melting further includes weighing the mass change of each element in the alloy before and after each melting, replenishing the elements that have lost mass, and then melting again until the mass of each element in the obtained alloy ingot meets the alloy composition ratio of the formulation.

[0025] By weighing the mass changes of each element in the alloy, we can understand the loss of each element during the smelting process, and then replenish the elements that have lost mass to ensure that the final composition of the alloy meets the design requirements.

[0026] Based on the above technical solutions, the preferred high-temperature homogenization annealing treatment specifically includes: heating the Mo-Ti-Cr-Si alloy ingot obtained in step S2, raising the temperature from 25-27°C to 1200°C at a heating rate of 8-12°C / min; then raising the temperature from 1200°C to 1300°C at a heating rate of 4-6°C / min, holding the temperature at 1300°C for 22-26 hours, and then furnace cooling to 25-27°C.

[0027] Specifically, since alloys expand thermally at high temperatures, multi-stage heating can reduce the accumulation of thermal stress. At the same time, a slower heating rate can reduce sudden temperature differences between the inside and outside of the alloy during the heating process, avoiding deformation and cracks caused by temperature changes. Multi-stage heating can also avoid thermal overshoot caused by excessively fast heating rates, ensuring the stability of the heat treatment temperature.

[0028] Based on the above technical solution, preferably, in step S3, before the high-temperature homogenization annealing treatment, a vacuum of 3×10 is further included. -3 ~5×10 -3 Pa, an inert gas is introduced, wherein the atmospheric pressure of the inert gas is 0.02 to 0.04 MPa.

[0029] The Mo-Ti-Cr-Si refractory medium-entropy alloy and its preparation method of the present invention have the following advantages over the prior art:

[0030] (1) The Mo-Ti-Cr-Si refractory medium-entropy alloy provided by this invention uses Ti to reduce the alloy density, Cr to improve the high-temperature oxidation resistance, and a small amount of Si to further promote the formation of a passivation film. The Si content does not exceed 3 at.%, preventing the formation of excessive metal silicides that could affect the alloy's mechanical properties. Compared to some existing refractory high-entropy / medium-entropy alloys, the alloy of this invention exhibits better oxidation resistance and overcomes the common problem of catastrophic oxidation in refractory alloy systems. Furthermore, the refractory medium-entropy alloy provided by this invention has a simple composition, does not contain expensive rare metal elements, and has a lower cost.

[0031] (2) The Mo-Ti-Cr-Si refractory medium-entropy alloy prepared by vacuum arc melting in this invention has a BCC solid solution structure with accurate composition and stable structure. Compared with powder metallurgy, this preparation process greatly improves production efficiency, introduces fewer impurity elements, and has good repeatability.

[0032] (3) This invention, through the design of the purity of raw materials and the vacuum degree, protective gas purity, and protective gas atmosphere pressure during arc melting, can effectively protect the alloy from oxidation during the preparation process. While ensuring that the raw materials are fully melted and undergo metallurgical reactions, it can effectively avoid raw material loss, resulting in a final alloy with accurate composition and few impurities. At the same time, in response to the characteristics of uneven as-cast structure and compositional segregation of alloys, it proposes to use a homogenization heat treatment method to reduce the degree of compositional segregation.

[0033] (4) The Mo-Ti-Cr-Si refractory medium-entropy alloy designed and prepared in this invention does not undergo catastrophic oxidation in atmospheric conditions at 800℃, exhibiting excellent oxidation resistance. Oxidation performance tests show that the total weight loss of this alloy after 24 hours of oxidation at 800℃ in atmospheric conditions is less than 11 mg / cm³. 2 This invention breaks through the application bottleneck of high-temperature oxidation of this type of alloy, and the material has broad application prospects in aerospace, marine and other fields. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is an electron microscope image of the Mo-Ti-Cr-Si medium-entropy alloy prepared in Example 1 of the present invention;

[0036] Figure 2This is a diagram showing the morphological changes of the Mo-Ti-Cr-Si medium-entropy alloy prepared in Example 1 of this invention after cyclic oxidation at 800℃.

[0037] Figure 3 The oxidation kinetics curves are shown for the refractory medium-entropy alloys prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 1% by atomic percentage. Its preparation method includes the following steps:

[0041] (1) Prepare Mo with a purity of 99.95%, Ti with a purity of 99.995%, Cr with a purity of 99.98%, and Si with a purity of 99.999%. First, use sandpaper to remove the oxide layer on the surface, then perform ultrasonic cleaning in anhydrous ethanol and dry it. The total mass of the alloy ingot is designed to be 25g. The mass ratio is converted according to the atomic ratio of 33%Mo-33%Ti-33%Cr-1%Si. Then, according to the calculation results, accurately weigh the Mo, Ti, Cr and Si in the raw materials with a balance to obtain them for subsequent electric arc melting.

[0042] (2) Place the prepared raw materials into a vacuum arc melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 After Pa, argon gas is introduced into the vacuum chamber until the chamber pressure reaches 0.05 MPa. The raw material is then subjected to arc melting. At the start of melting, after successful arc ignition, the melting current is slowly adjusted, melting the titanium ingot two or three times to purify the gas inside the furnace. After arc ignition on the titanium ingot, the tungsten electrode is moved to the raw material station at the minimum current. The current is initially set to 10 A to slightly melt the upper layer of raw material, then increased to 16 A to melt all the raw material into a molten body. After the molten body solidifies, a flipping rod is used to flip the solidified button ingot, and the melting is repeated more than four times to obtain the alloy ingot. The melting sequence is as follows: first, a Mo-Ti pre-alloy ingot is prepared by vacuum arc melting; then Cr is added for vacuum arc melting; finally, Si is added for vacuum arc melting to obtain the Mo-Ti-Cr-Si as-cast alloy.

[0043] (3) Then place the Mo-Ti-Cr alloy ingot into a high-temperature heat treatment furnace, close all valves in the furnace, and evacuate to a vacuum level of 3×10⁻⁶. -3 After Pa, argon gas was introduced into the chamber to a pressure of 0.04 MPa. The heat treatment process was programmed and set as follows: segmented heating was adopted, with a heating rate of 10℃ / min from room temperature (25℃) to 1200℃, and a heating rate of 5℃ / min from 1200℃ to 1300℃. After heating to 1300℃, the temperature was held for 24 hours. During the heat treatment process, the argon gas pressure was maintained at 0.04 MPa by controlling the relevant valves. After the holding period, the furnace was cooled to room temperature and removed to obtain the Mo-Ti-Cr-Si medium-entropy alloy.

[0044] Example 2

[0045] This embodiment provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 32.6%, Ti: 32.7%, Cr: 32.7%, and Si: 2% by atomic percentage. The specific preparation method is as follows:

[0046] (1) Prepare Mo with a purity of 99.95%, Ti with a purity of 99.995%, Cr with a purity of 99.98%, and Si with a purity of 99.999%. First, use sandpaper to remove the oxide layer on the surface, then perform ultrasonic cleaning in anhydrous ethanol and dry it. The total mass of the alloy ingot is designed to be 25g. Calculate the mass ratio according to the atomic ratio of Mo 32.6%, Ti 32.7%, Cr 32.7%, and Si 2%. Then, accurately weigh the Mo, Ti, Cr, and Si in the raw materials according to the calculation results using a balance for subsequent use in electric arc melting.

[0047] (2) Place the prepared raw materials into a vacuum arc melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 After Pa, argon gas is introduced into the vacuum chamber until the chamber pressure reaches 0.05 MPa. The raw material is then subjected to arc melting. At the start of melting, after successful arc ignition, the melting current is slowly adjusted, melting the titanium ingot two or three times to purify the gas inside the furnace. After arc ignition on the titanium ingot, the tungsten electrode is moved to the raw material station at the minimum current. The current is initially set to 10 A to slightly melt the upper layer of raw material, then increased to 16 A to melt all the raw material into a molten body. After the molten body solidifies, a flipping rod is used to flip the solidified button ingot, and the melting is repeated more than four times to obtain the alloy ingot. The melting sequence is as follows: first, a Mo-Ti pre-alloy ingot is prepared by vacuum arc melting; then Cr is added for vacuum arc melting; finally, Si is added for vacuum arc melting to obtain the Mo-Ti-Cr-Si as-cast alloy.

[0048] (3) Place the obtained as-cast alloy into a high-temperature resistance furnace, close all valves in the furnace, and evacuate to a vacuum level of 3×10⁻⁶. -3After Pa, argon gas was introduced into the chamber to a pressure of 0.04 MPa. The heat treatment process was programmed with the following settings: a heating rate of 10 °C / min from room temperature to 1200 °C, a heating rate of 5 °C / min from 1200 °C to 1300 °C, and a holding time of 24 hours after reaching 1300 °C. During the heat treatment process, the argon gas pressure was maintained at 0.04 MPa by controlling relevant valves. After the holding time, the furnace was cooled to room temperature and removed to obtain a Mo-Ti-Cr-Si medium-entropy alloy.

[0049] Example 3

[0050] This embodiment provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 32.4%, Ti: 32.3%, Cr: 32.3%, and Si: 3% by atomic percentage. The specific preparation method is as follows:

[0051] (1) Prepare Mo with a purity of 99.95%, Ti with a purity of 99.995%, Cr with a purity of 99.98%, and Si with a purity of 99.999%. First, use sandpaper to remove the oxide layer on the surface, then perform ultrasonic cleaning in anhydrous ethanol and dry it. The total mass of the alloy ingot is designed to be 25g. Calculate the mass ratio according to the atomic ratio of Mo 32.4%, Ti 32.3%, Cr 32.3%, and Si 3%. Then, accurately weigh the Mo, Ti, Cr, and Si in the raw materials according to the calculation results using a balance to obtain them for subsequent electric arc melting.

[0052] (2) Place the prepared raw materials into a vacuum arc melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 After Pa, argon gas is introduced into the vacuum chamber until the chamber pressure reaches 0.05 MPa. The raw material is then subjected to arc melting. At the start of melting, after successful arc ignition, the melting current is slowly adjusted, melting the titanium ingot two or three times to purify the gas inside the furnace. After arc ignition on the titanium ingot, the tungsten electrode is moved to the raw material station at the minimum current. The current is initially set to 10 A to slightly melt the upper layer of raw material, then increased to 16 A to melt all the raw material into a molten body. After the molten body solidifies, a flipping rod is used to flip the solidified button ingot, and the melting is repeated more than four times to obtain the alloy ingot. The melting sequence is as follows: first, a Mo-Ti pre-alloy ingot is prepared by vacuum arc melting; then Cr is added for vacuum arc melting; finally, Si is added for vacuum arc melting to obtain the Mo-Ti-Cr-Si as-cast alloy.

[0053] (3) Then place the Mo-Ti-Cr-Si as-cast alloy into a high-temperature resistance furnace, close all valves in the furnace, and evacuate to a vacuum level of 3×10⁻⁶. -3After Pa, argon gas was introduced into the chamber to a pressure of 0.04 MPa. The heat treatment process was programmed and set as follows: the heating rate was 10℃ / min from room temperature to 1200℃, and the heating rate was 5℃ / min from 1200℃ to 1300℃. After heating to 1300℃, the temperature was held for 24 hours. During the heat treatment process, the argon gas pressure was maintained at 0.04 MPa by controlling the relevant valves. After the holding period, the furnace was cooled to room temperature and removed to obtain the Mo-Ti-Cr-Si medium-entropy alloy.

[0054] Example 4

[0055] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 2% by atomic percentage. The specific preparation method is the same as in Example 2, except that in step (3), the obtained as-cast alloy is placed in a high-temperature resistance furnace, all valves of the furnace are closed, and a vacuum of 3×10⁻⁶ is drawn. -3 After Pa, argon gas was introduced into the chamber to a pressure of 0.02 MPa. The heat treatment process was programmed with the following settings: a heating rate of 8 °C / min from room temperature to 1200 °C, a heating rate of 4 °C / min from 1200 °C to 1300 °C, and a holding time of 22 hours after reaching 1300 °C. During the heat treatment process, the argon gas pressure was maintained at 0.02 MPa by controlling relevant valves. After the holding time was completed, the furnace was cooled to room temperature and removed to obtain a Mo-Ti-Cr-Si medium-entropy alloy.

[0056] Example 5

[0057] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 3% by atomic percentage. The specific preparation method is the same as in Example 3, except that in step (3), the Mo-Ti-Cr-Si as-cast alloy is placed in a high-temperature resistance furnace, all valves of the furnace are closed, and a vacuum of 4×10⁻⁶ is drawn. -3 After Pa, argon gas was introduced into the chamber to a pressure of 0.04 MPa. The heat treatment process was programmed and set as follows: the heating rate was 12℃ / min from room temperature to 1200℃, and the heating rate was 6℃ / min from 1200℃ to 1300℃. After heating to 1300℃, the temperature was held for 26 hours. During the heat treatment process, the argon gas pressure was maintained at 0.04 MPa by controlling the relevant valves. After the holding period, the furnace was cooled to room temperature and removed to obtain the Mo-Ti-Cr-Si medium-entropy alloy.

[0058] Comparative Example 1

[0059] This comparative example provides a Mo-Ti-Cr refractory medium-entropy alloy, with Mo: 33.34%, Ti: 33.33%, and Cr: 33.33% by atomic percentage, which includes the following steps:

[0060] (1) Prepare Mo with a purity of 99.95%, Ti with a purity of 99.995%, and Cr with a purity of 99.98%. First, use sandpaper to remove the oxide layer on the surface, then perform ultrasonic cleaning in anhydrous ethanol and dry it. The total mass of the alloy ingot is designed to be 25g. Calculate the mass ratio according to the atomic ratio of Mo 33.34%, Ti 33.33%, and Cr 33.33%. Then, accurately weigh the Mo, Ti, and Cr in the raw materials according to the calculation results using a balance for subsequent use in electric arc melting.

[0061] (2) Place the prepared raw materials into a vacuum arc melting furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 After Pa, argon gas is introduced into the vacuum chamber until the chamber pressure reaches 0.05 MPa. The raw material is then subjected to arc melting. At the start of melting, after successful arc ignition on the titanium ingot, the melting current is slowly adjusted, melting the ingot two or three times to purify the furnace gas. After arc ignition on the titanium ingot, the tungsten electrode is moved to the raw material station at the minimum current. The current is initially set to 10 A to slightly melt the upper layer of raw material, then increased to 16 A to melt all the raw material into a molten body. After the molten body solidifies, a flipping rod is used to flip the solidified button ingot, and the melting is repeated more than four times to obtain the alloy ingot. The melting sequence is as follows: first, a Mo-Ti pre-alloy ingot is prepared by vacuum arc melting; then, Cr is added and vacuum arc melting is performed to obtain the as-cast alloy Mo-Ti-Cr.

[0062] (3) The Mo-Ti-Cr alloy ingot is then placed in a high-temperature heat treatment furnace. All valves in the furnace are closed, and a vacuum of 3×10⁻³ Pa is applied. Argon gas is then introduced until the chamber pressure reaches 0.03 MPa. The heat treatment process is programmed as follows: the heating rate from room temperature to 1200℃ is 10℃ / min, and the heating rate from 1200℃ to 1300℃ is 5℃ / min. After reaching 1300℃, the temperature is held for 24 hours. During the heat treatment process, the argon gas pressure is maintained at 0.03 MPa by controlling the relevant valves. After the holding period, the ingot is cooled to room temperature with the furnace and removed to obtain the Mo-Ti-Cr annealed alloy.

[0063] Comparative Example 2

[0064] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 1% by atomic percentage. The specific preparation method is the same as in Example 1, except that in step (2), the melting order is to add Mo, Ti, Cr and Si to a vacuum arc melting furnace at the same time for vacuum arc melting to obtain the as-cast alloy Mo-Ti-Cr-Si.

[0065] Comparative Example 3

[0066] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 30%, Ti: 33%, Cr: 33%, and Si: 4% by atomic percentage. The specific preparation method is the same as in Example 1.

[0067] Comparative Example 4

[0068] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 1% by atomic percentage. The specific preparation method is the same as in Example 1, except that in step (3), the temperature is raised to 1300℃ and then held for 18 hours.

[0069] Comparative Example 5

[0070] This comparative example provides a Mo-Ti-Cr-Si refractory medium-entropy alloy, with Mo: 33%, Ti: 33%, Cr: 33%, and Si: 1% by atomic percentage. The specific preparation method is the same as in Example 1, except that the heat treatment in step (3) is not carried out in stages. The heat treatment process is from room temperature (25℃) to 1300℃, with a heating rate of 10℃ / min and a holding time of 24h.

[0071] Performance testing

[0072] The alloy ingot was cut into rectangular samples of 4mm×5mm×8mm using wire cutting. The surfaces of the samples were then polished to ensure cleanliness and flatness. An oxidation temperature of 800℃ was selected, and the oxidation time was 24 hours. Before the oxidation test, the mass and surface area of ​​the sample were measured. The rectangular sample was then suspended in a corundum crucible using a 0.1mm diameter platinum wire. The crucible was placed in a constant-temperature furnace. After the set oxidation time, the crucible was removed, air-cooled to room temperature, and the mass of the sample was measured to obtain the oxidation weight loss of the alloy. The refractory medium-entropy alloys prepared in the examples and comparative examples were subjected to high-temperature oxidation tests. The test results are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] Figure 1 The image shows a scanning electron microscope (SEM) image of the medium-entropy alloy prepared in Example 1. As can be seen from the image, the alloy forms a medium-entropy solid solution matrix, in which a small amount of Ti-rich phase and Cr-rich phase are sporadically distributed.

[0077] Figure 2 The changes in morphology of the refractory medium-entropy alloy prepared in Example 1 after cyclic oxidation at 800°C are shown. Figure 2a is the morphology after oxidation at 800℃ for 0.5h. Figure 2 b is the morphology image after oxidation at 800℃ for 6 hours. Figure 2 c is the morphology image after oxidation at 800℃ for 12 hours. Figure 2 d shows the morphology after oxidation at 800℃ for 18 hours. Figure 2 Figure e shows the morphology after oxidation at 800℃ for 24 hours. As can be seen from the figure, the appearance of the sample hardly changed after cyclic oxidation at 800℃ for 0.5h, 6h, 12h, 18h and 24h, no catastrophic oxidation occurred, and a dense dark oxide layer was formed on the surface, which has excellent antioxidant properties.

[0078] Figure 3 The oxidation kinetics curves of the medium-entropy alloys prepared in Examples 1-3 and Comparative Example 1 after oxidation at 800℃ for 24 hours are shown. As can be seen from the figures, the oxidation kinetic curves of the refractory medium-entropy alloys prepared in Examples 1-3 after oxidation at 800℃ for 24 hours basically conform to a parabolic law. The mass change of Example 1 after 24 hours of oxidation is approximately 10.45 mg / cm³. 2 In Example 2, the mass change after 24 hours of oxidation was approximately 9.35 mg / cm³. 2 In Example 3, the mass change after 24 hours of oxidation was approximately 8.35 mg / cm³. 2 Its oxidation resistance is superior to most refractory high-entropy / medium-entropy alloys currently available; while the oxidation kinetics curve of the refractory medium-entropy alloy prepared in Comparative Example 1 basically conforms to a parabolic law, but its oxidation rate is significantly higher than that of the three examples, with a mass change of approximately 13.70 mg / cm³ after 24 hours of oxidation. 2 The oxidation resistance of this comparative example is significantly greater than that of the three examples, indicating that the oxidation resistance of this comparative example is inferior to that of the three examples. It can be seen that the addition of Si can significantly improve the oxidation resistance of the Mo-Ti-Cr refractory medium-entropy alloy.

[0079] As shown in Table 1, comparing Examples 1 to 5, it is evident that the refractory medium-entropy alloy prepared by the technical solution of this invention does not undergo catastrophic oxidation in atmospheric conditions at 800°C, and the total weight loss after 24 hours of oxidation is less than 11 mg / cm³. 2 It possesses excellent antioxidant properties; comparing Example 1 with Comparative Example 1, it can be seen that adding Si can significantly improve the antioxidant properties of the Mo-Ti-Cr refractory medium-entropy alloy; comparing Example 1 with Comparative Example 2, it can be seen that the melting sequence also affects the antioxidant properties of the alloy; comparing Example 1 with Comparative Example 3, it can be seen that when the proportion of Si exceeds the range defined in this application, it will affect the antioxidant properties of the alloy; comparing Example 1 with Comparative Examples 4 and 5, it can be seen that the heating method and holding time during heat treatment will affect the antioxidant properties of the prepared medium-entropy alloy.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Mo-Ti-Cr-Si refractory medium-entropy alloy, characterized in that: The medium-entropy alloy is composed of Mo, Ti, Cr and Si. By atomic percentage, the amount of Si added is 1% to 3%, the amount of Mo added is 32.4% to 33%, the amount of Ti added is 32.3% to 33%, and the amount of Cr added is 32.3% to 33%.

2. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 1, characterized in that: Includes the following steps, S1. Using pure metals and non-metallic elements as raw materials, the raw materials are weighed and proportioned according to the atomic percentage of medium-entropy alloys; S2. Mo-Ti-Cr-Si alloy ingots were prepared by vacuum arc melting. S3. The Mo-Ti-Cr-Si alloy ingot prepared in step S2 is subjected to high-temperature homogenization annealing to obtain a Mo-Ti-Cr-Si refractory medium-entropy alloy.

3. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 2, characterized in that: In step S1, the raw materials include Mo strips with a purity of 99.95 wt.%, Ti sheets with a purity of 99.995 wt.%, Cr blocks with a purity of 99.98 wt.%, and Si blocks with a purity of 99.999 wt.%.

4. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 2, characterized in that: Step S2 specifically includes: first, preparing a Mo-Ti pre-alloy ingot through vacuum arc melting, then adding Cr and performing vacuum arc melting, and finally adding Si and performing vacuum arc melting to obtain a Mo-Ti-Cr-Si alloy ingot.

5. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 4, characterized in that: In step S2, the vacuum arc melting process involves first evacuating the vacuum to a degree of 3 × 10⁻⁶. -3 ~5×10 -3 Pa, introduce protective gas at 0.04~0.06 MPa, control the voltage of the vacuum arc melting furnace to 550V, the current to 10~16A, and the melting time for each melting session to 15~20min.

6. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 5, characterized in that: The vacuum arc melting process also includes turning the molten alloy over after it has cooled down, and then continuing the vacuum arc melting process. Each time the alloy raw material is completely melted, it is held for 3 to 5 minutes, and the melting process is repeated ≥ 4 times.

7. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 6, characterized in that: The vacuum arc melting process also includes weighing the mass change of each element in the alloy before and after each melting, replenishing the elements that have lost mass, and melting again until the mass of each element in the resulting alloy ingot meets the alloy composition ratio specified in the formula.

8. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 2, characterized in that: In step S3, the high-temperature homogenization annealing treatment specifically includes: heating the Mo-Ti-Cr-Si alloy ingot obtained in step S2, raising the temperature from 25~27℃ to 1200℃ at a heating rate of 8~12℃ / min; then raising the temperature from 1200℃ to 1300℃ at a heating rate of 4~6℃ / min, holding the temperature at 1300℃ for 22~26h, and then furnace cooling to 25~27℃.

9. The method for preparing a Mo-Ti-Cr-Si refractory medium-entropy alloy as described in claim 8, characterized in that: In step S3, before the high-temperature homogenization annealing treatment, a vacuum of 3×10⁻⁶ is also included. -3 ~5×10 -3 Pa, an inert gas is introduced, and the atmospheric pressure of the inert gas is 0.02~0.04 MPa.

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