A method for preparing a tensile specimen of a CoFeNi medium-entropy alloy under a deep undercooling condition

Abstract

This invention provides a method for preparing tensile specimens of CoFeNi medium-entropy alloy under deep supercooling conditions. The deep supercooling process of this method is carried out using a high-frequency induction heating device and a combination of melt immersion and cyclic superheating. During the melting process, the alloy raw materials are placed sequentially in a quartz crucible from bottom to top according to their melting points, with glass cleaning agents added to the bottom and top layers. During melting, the vertical movement of the quartz crucible along the central axis of the high-frequency induction coil and the heating temperature of the high-frequency induction coil are controlled to sequentially melt and coat the alloy surface with the glass cleaning agent, melt the Ni metal raw material, and melt the remaining metal raw materials. After the alloy liquid is thoroughly mixed, it is cooled and solidified. This heating and cooling solidification process is repeated until a supercooling of 205K is achieved, producing a CoFeNi medium-entropy alloy ingot that meets the dimensions required for tensile testing. This invention features an easily controllable solidification process, mature technology, and minimal component loss.

Description

Technical Field

[0001] This application belongs to the field of alloy preparation technology, and in particular relates to a method for preparing tensile specimens of CoFeNi medium-entropy alloy under deep supercooling conditions. Background Technology

[0002] Medium-entropy alloys are alloys composed of three elements in equimolar or near-equimolar ratios. Their compositional characteristics give them high strength and hardness, good wear resistance, high resistivity, excellent corrosion resistance and magnetic properties, and good hydrogen storage performance, which has aroused great interest in these alloy systems.

[0003] CoFeNi is a single-phase disordered solid solution alloy with an FCC crystal structure, exhibiting low yield strength. Currently, most studies use arc melting to prepare CoFeNi alloy ingots, which easily leads to coarse grains, negatively impacting the alloy's mechanical properties and limiting its application as a structural material. Compared to equilibrium solidification processes like arc melting, rapid solidification can significantly reduce the generation of microstructural defects and refine grains. For many years, the dendritic growth and solidification mechanism of alloys under deep supercooling conditions have received widespread attention from researchers, and the thermodynamic and kinetic theories of molten metals under deep supercooling rapid solidification conditions are relatively mature. A literature search revealed Chinese Patent Publication No. CN103643063 A, patent titled "Solidation Method for Obtaining Stable Supercooling of 210–430K in Multi-element Alloys." This patent uses a combination of molten glass purification, temperature control, and glass purification agent to achieve deep supercooling solidification of multi-element alloys, obtaining button alloy ingots with a mass of 30 / 120g. However, the dimensions still do not meet the requirements for tensile mechanical testing. The patent, published by the Chinese Patent Office (CN1552544A), is titled "Method for Preparing Oriented Alloy Materials by In-situ Deep Supercooling." This patent proposes a method for preparing oriented alloys by combining molten glass purification and cyclic superheating. During the preparation process, the alloy in the first quartz tube needs to be leaked into the second quartz tube after reaching the softening point, resulting in a certain scrap rate. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing tensile specimens of CoFeNi medium-entropy alloy under deep supercooling conditions, thereby solving the problem of insufficient height of tensile specimens.

[0005] This invention is implemented as follows: a method for preparing a CoFeNi medium-entropy alloy tensile specimen under deep supercooling conditions. The deep supercooling process of the alloy is carried out by a high-frequency induction heating device and a combination of melt immersion and cyclic superheating. In the melting process, each alloy raw material is placed into a quartz crucible in order of melting point from high to low, and a glass cleaning agent is added to the bottom and top layers of the alloy raw materials. During melting, the vertical movement of the quartz crucible along the central axis of the high-frequency induction coil and the heating temperature of the high-frequency induction coil are controlled to sequentially melt and coat the alloy surface with the glass cleaning agent, melt the Ni metal raw material, and melt the remaining metal raw materials. After the alloy liquid is fully mixed, it is cooled and solidified, and the heating and cooling solidification are repeated until a supercooling of 205K is obtained, thus preparing a CoFeNi medium-entropy alloy ingot that meets the tensile test dimensions.

[0006] The present invention is further characterized in that the preparation method includes the following steps:

[0007] Step 1, Ingredient Preparation: Using the elemental substances as raw materials, weigh each metal element according to the molar percentage of each element in the CoFeNi entropy alloy Co:Fe:Ni = 1:1:1, and prepare the raw materials.

[0008] Step 2, Feeding: Select a cylindrical quartz crucible with an open top, and put the prepared raw materials into the quartz crucible in sequence. When placing the raw materials, according to their melting points, they should be placed into the quartz crucible from bottom to top in the order of glass cleaner, Fe, Co, Ni, glass cleaner.

[0009] Step 3, Adjusting the crucible position: Use an electric actuator to control the quartz crucible to move vertically up and down along the central axis of the high-frequency induction coil, so that the contact surface between the glass cleaning agent and the Ni element in the upper part of the quartz crucible is in the effective heating position in the vertical direction of the high-frequency induction coil;

[0010] Step 4: Vacuuming: After closing the vacuum chamber door, turn on the chiller to evacuate the vacuum level inside the vacuum arc furnace chamber to 10. -3 After reaching Pa or above, close the evacuation valve, open the inlet valve, and backfill the cavity with high-purity argon gas to 0.5 standard atmospheres, then close the inlet valve.

[0011] Step 5: Heat the alloy to 1073-1173℃ using a high-frequency induction coil, observe the softening of the glass cleaner using a high-speed CCD, and hold for 1 minute to allow the glass cleaner to melt and coat the alloy surface.

[0012] Step 6: Heat to 1400-1500℃, then hold for 1 minute to ensure that all Ni metal is melted;

[0013] Step 7: Heat to 1650-1850℃, control the electric push rod device to move the quartz crucible upward, melt the Co and Fe metal elements through high-frequency induction heating and heat conduction between the metals, stop moving the quartz crucible after all the metals have melted, keep it at the temperature for 2 minutes, use electromagnetic stirring to fully mix the alloy liquid, turn off the high frequency and cool and solidify.

[0014] Step 8: Observe the temperature curve collected by the infrared probe, and turn on the high frequency to continue heating when the temperature drops to 850-900℃;

[0015] Step 9: Rapidly heat to 1650-1850℃ and hold for 1 minute, then turn off the high-frequency circuit and allow it to cool and solidify;

[0016] Step 10: Repeat steps 8 and 9 until a supercooling of 205K is achieved. After cooling for 3 hours, remove the cylindrical CoFeNi alloy sample with uniform composition.

[0017] The invention is further characterized in that the quartz crucible used has the following specifications: inner diameter: 16mm, outer diameter: 20mm, height: 100mm, and the addition height of the alloy raw material is 4 / 5 of the height of the quartz crucible.

[0018] The present invention is further characterized in that the total amount of alloy raw materials is 60g and the total amount of glass cleaner used is 9-10g.

[0019] The invention is further characterized in that one end of the electric actuator of the electric actuator device is connected to a crucible base made of boron nitride, the quartz crucible is placed on the crucible base, and the electric actuator device is electrically connected to an external control switch for adjustment to control the quartz crucible to move up and down along the central axis of the high-frequency induction coil.

[0020] A further feature of this invention is that the length of the obtained cylindrical CoFeNi alloy sample reaches more than 30 mm.

[0021] A further feature of this invention is that the glass cleaning agent used is glass with Na2O·CaO·6SiO2 as its main component.

[0022] This invention employs melt immersion flotation technology as a deep undercooling preparation method. It utilizes the method of immersing the alloy melt in a purifying agent to achieve rapid deep undercooling solidification of the liquid alloy. The solidification process is easy to control, the technology is mature, and component loss is minimal. During sample preparation, a cylindrical quartz crucible is used. A pusher device controls the up-and-down movement of the quartz crucible containing the raw material to ensure the melting and purification of the metal raw material and the occurrence of a large degree of undercooling. This allows for the acquisition of large-size CoFeNi alloy samples that meet the dimensional requirements for in-situ tensile testing.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the quartz crucible and sample loading used in the deep supercooling test.

[0026] Figure 2 This is a schematic diagram of the cutting dimensions of a tensile specimen of the CoFeNi alloy with a supercooling degree of 205K prepared in Example 1.

[0027] Figure 3 This is a stress-strain curve of the CoFeNi alloy with a supercooling of 205K prepared in Example 1 at room temperature. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0029] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the specific implementation methods, structural features and effects of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0030] This invention provides a method for preparing a CoFeNi medium-entropy alloy tensile specimen under deep supercooling conditions. The deep supercooling process of this preparation method is carried out by a high-frequency induction heating device and a combination of melt immersion and cyclic superheating. In the melting process, each alloy raw material is placed into a quartz crucible in order of melting point from high to low. Glass purifying agent is added to the bottom and top layers of the alloy raw materials. During melting, the vertical movement of the quartz crucible along the central axis of the high-frequency induction coil and the heating temperature of the high-frequency induction coil are controlled to sequentially melt and coat the alloy surface with the glass purifying agent, melt the Ni metal raw material, and melt the remaining metal raw materials. After the alloy liquid is fully mixed, it is cooled and solidified. The heating and cooling solidification are repeated until a supercooling of 205K is obtained, thus preparing a CoFeNi medium-entropy alloy ingot that meets the tensile test dimensions.

[0031] Example 1: Preparation of tensile specimens of CoFeNi medium-entropy alloy under deep supercooling conditions

[0032] The specific steps are as follows:

[0033] Step 1, Ingredient Preparation: Using the elemental substances as raw materials, weigh out each metal element according to the molar percentage of each element in the CoFeNi entropy alloy Co:Fe:Ni = 1:1:1, and prepare 60g of raw materials; the metal elements used are metal particles corresponding to Co, Fe, and Ni elements respectively.

[0034] Step 2, Material Placement: Select a cylindrical quartz crucible with an open top. The specifications of the quartz crucible are: inner diameter: 16mm, outer diameter: 20mm, height: 100mm. Place the prepared raw materials into the quartz crucible in sequence. When placing the raw materials, according to their melting points, place them into the quartz crucible from bottom to top in the order of glass purifier, Fe, Co, Ni, and glass purifier again. The bottom layer of the quartz crucible should be a 5mm thick layer of glass purifier, with a total amount of 9-10g. The height of the alloy raw materials should be 4 / 5 of the height of the quartz crucible. Optionally, the glass purifier used should be a glass with Na2O·CaO·6SiO2 as its main component. After the glass purifier melts completely, it can completely cover the metal raw materials.

[0035] Step 3: Adjusting the crucible position: Use an electric actuator to control the vertical movement of the quartz crucible along the central axis of the high-frequency induction coil. To ensure complete melting of the raw material and achieve a large degree of supercooling, place the upper part of the quartz crucible, where the purifying agent contacts the Ni element, at the center of the high-frequency coil in the vertical direction. This ensures that the upper part of the quartz crucible, where the glass purifying agent contacts the Ni element, is in an effective heating position in the vertical direction of the high-frequency induction coil. Figure 1 This is a schematic diagram of a quartz crucible and sample loading to ensure effective heating. One end of the electric actuator is connected to a boron nitride crucible base, on which the quartz crucible is placed. The electric actuator is electrically connected to an external control switch to control the quartz crucible to move up and down along the central axis of the high-frequency induction coil.

[0036] Step 4: Vacuuming: After closing the vacuum chamber door, turn on the chiller to evacuate the vacuum level inside the vacuum arc furnace chamber to 10. -3 After reaching Pa or above, close the evacuation valve, open the inlet valve, and backfill the cavity with high-purity argon gas to 0.5 standard atmospheres, then close the inlet valve.

[0037] Step 5: Heat the alloy to 1073-1173℃ using a high-frequency induction coil, observe the softening of the glass cleaner using a high-speed CCD, and hold the temperature for 1 minute to allow the glass cleaner to melt and coat the alloy surface; this heating process ensures that the cleaner melts and coats the top Ni metal material, preventing it from oxidizing upon contact with air.

[0038] Step 6: Heat to 1400-1500℃, some Ni metal particles will begin to melt and flow downwards, then hold for 1 minute to ensure that all Ni metal is melted;

[0039] Step 7: Heat to 1650-1850℃. The liquid Ni begins to flow downwards under the influence of gravity, covering the Co metal raw material. The temperature around the Co metal rises due to thermal radiation and heat conduction, accelerating the melting of the Co metal raw material. Control the electric push rod device to move the quartz crucible upwards. Melt the Co and Fe metal elements through high-frequency induction heating and heat conduction between the metals until all the metals are melted. Stop moving the quartz crucible and hold it at this temperature for 2 minutes. Use electromagnetic stirring to fully mix the alloy liquid. Turn off the high frequency and allow it to cool and solidify.

[0040] Step 8: Observe the temperature curve collected by the infrared probe, and turn on the high frequency to continue heating when the temperature drops to 850-900℃;

[0041] Step 9: Rapidly heat to 1650-1850℃ and hold for 1 minute, then turn off the high-frequency circuit and allow it to cool and solidify;

[0042] Step 10: Repeat steps 8 and 9 until a supercooling of 205K is achieved. After cooling for 3 hours, remove the cylindrical CoFeNi alloy sample with uniform composition. The final product is a cylindrical CoFeNi medium-entropy alloy ingot with a diameter of 15.5 mm and a height of 37 mm, which meets the requirements for tensile test specimen dimensions. Figure 2 This is a schematic diagram showing the cutting dimensions of the tensile specimen of the CoFeNi alloy with an undercooling of 205K prepared in this embodiment. It can be used as a reference. Figure 2 The ingot is processed as shown. Figure 3 The stress-strain curve of the prepared CoFeNi alloy with an undercooling of 205K at room temperature is shown. The yield strength is 129 MPa and the elongation at break is 40.6%.

[0043] This invention employs melt immersion flotation technology as a deep undercooling preparation method. It utilizes the method of immersing the molten alloy in a purifying agent to achieve rapid deep undercooling solidification of the liquid alloy. The solidification process is easy to control, the technology is mature, and component loss is minimal. The molten purifying agent removes impurities through interfacial physical interactions with the liquid alloy, while simultaneously using interfacial chemical reactions to passivate heterogeneous nucleation and isolate the sample from the container wall to eliminate nucleation catalysis. During sample preparation, a cylindrical quartz crucible is used. A pusher device controls the up-and-down movement of the quartz crucible containing the raw material to ensure the melting and purification of the metal raw material and the occurrence of significant undercooling, thus obtaining large-sized CoFeNi alloy samples that meet the dimensional requirements for in-situ tensile testing. Because the obtained CoFeNi alloy samples meet the size requirements for tensile testing, it facilitates the study of the intrinsic mechanism between its mechanical properties and undercooling. Furthermore, this invention effectively solves the problem of alloy sample height, resulting in an extremely low scrap rate.

[0044] In this embodiment of the invention, a cylindrical quartz crucible with an inner diameter of 16 mm, an outer diameter of 20 mm, and a height of 100 mm is selected to hold the metal raw material. The height of the metal raw material reaches 4 / 5 of the height of the quartz crucible, and the high-frequency induction coil cannot completely cover the raw material to be heated. To ensure that the raw material is completely melted and a large degree of supercooling is obtained, an electric pusher device is used to place the uppermost metal raw material in the quartz crucible at the center of the high-frequency induction coil, and the smelting is carried out to obtain a cylindrical ingot. The use of this size of quartz crucible is due to two considerations: firstly, considering the required size of the tensile sample, its height must be at least 30 mm; secondly, the difficulty of obtaining a large degree of supercooling for large-volume alloys increases. Therefore, the size of the quartz crucible must ensure that a large degree of supercooling is obtained while melting an ingot of a suitable height. In addition, because of its transparency and good light transmittance, the quartz crucible provides great real-time performance and accuracy for high-speed CCD monitoring and infrared thermometer measurement of melt temperature.

[0045] The reason why this invention uses glass with Na2O·CaO·6SiO2 as the main component is that the softening point of the glass purifier is around 1100K, which is lower than the melting point of each element in the alloy. This makes it easy for the purifier to coat the alloy surface. At the same time, the purifier does not react with the elements in the alloy, but has a good adsorption capacity and can react with the oxides or hydroxides of each element to achieve a good purification effect. Moreover, the purifier has good light transmittance, which facilitates temperature collection.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a tensile specimen of a CoFeNi medium-entropy alloy under deep supercooling conditions, characterized in that, The alloy undercooling process described in the preparation method is carried out using a high-frequency induction heating device and a combination of melt immersion and cyclic superheating. During the melting process, the alloy raw materials are first placed into a quartz crucible in descending order of melting point, with glass cleaning agent added to the bottom and top layers. During melting, the vertical movement of the quartz crucible along the central axis of the high-frequency induction coil and the heating temperature of the high-frequency induction coil are controlled to sequentially melt and coat the alloy surface with the glass cleaning agent, melt the Ni metal raw material, and melt the remaining metal raw materials. After the alloy liquid is fully mixed, it is cooled and solidified, and the heating and cooling solidification process is repeated until a supercooling of 205K is achieved, producing a CoFeNi medium-entropy alloy ingot that meets the tensile test dimensions. Specifically, the process includes the following steps: Step 1, Ingredient Preparation: Using the elemental substances as raw materials, weigh each metal element according to the molar percentage of each element in the CoFeNi entropy alloy Co:Fe:Ni = 1:1:1, and prepare the raw materials. Step 2, Feeding: Select a cylindrical quartz crucible with an open top, and put the prepared raw materials into the quartz crucible in sequence; when placing the raw materials, according to their melting points, they should be placed into the quartz crucible from bottom to top in the order of glass purifier, Fe, Co, Ni, glass purifier. Step 3, Adjusting the crucible position: Use an electric actuator to control the quartz crucible to move vertically up and down along the central axis of the high-frequency induction coil, so that the contact surface between the glass cleaning agent and the Ni element in the upper part of the quartz crucible is in the effective heating position in the vertical direction of the high-frequency induction coil; Step 4: Vacuuming: After closing the vacuum chamber door, turn on the chiller to evacuate the vacuum level inside the vacuum arc furnace chamber to 10. -3 After reaching Pa or above, close the evacuation valve, open the inlet valve, and backfill the cavity with high-purity argon gas to 0.5 standard atmospheres, then close the inlet valve. Step 5: Heat the alloy to 1073-1173℃ using a high-frequency induction coil, observe the softening of the glass cleaner using a high-speed CCD, and hold for 1 minute to allow the glass cleaner to melt and coat the alloy surface. Step 6: Heat to 1400-1500℃, then hold for 1 minute to ensure that all Ni metal is melted; Step 7: Heat to 1650-1850℃, control the electric push rod device to move the quartz crucible upward, melt the Co and Fe metal elements through high-frequency induction heating and heat conduction between the metals, stop moving the quartz crucible after all the metals have melted, keep it at the temperature for 2 minutes, use electromagnetic stirring to fully mix the alloy liquid, turn off the high frequency and cool and solidify. Step 8: Observe the temperature curve collected by the infrared probe, and turn on the high frequency to continue heating when the temperature drops to 850-900℃; Step 9: Rapidly heat to 1650-1850℃ and hold for 1 minute, then turn off the high-frequency circuit and allow it to cool and solidify; Step 10: Repeat steps 8 and 9 until a supercooling of 205K is achieved. After cooling for 3 hours, remove the cylindrical CoFeNi alloy sample with uniform composition.

2. The method for preparing CoFeNi medium-entropy alloy tensile specimens under deep supercooling conditions according to claim 1, characterized in that, The quartz crucible used has the following specifications: inner diameter: 16mm, outer diameter: 20mm, height: 100mm. The alloy raw material is added to a height of 4 / 5 of the quartz crucible.

3. The method for preparing a CoFeNi medium-entropy alloy tensile specimen under deep supercooling conditions according to claim 1, characterized in that, The total amount of alloy raw materials is 60g, and the total amount of glass cleaner used is 9-10g.

4. The method for preparing a CoFeNi medium-entropy alloy tensile specimen under deep supercooling conditions according to claim 1, characterized in that, One end of the electric actuator of the electric actuator device is connected to a crucible base made of boron nitride. The quartz crucible is placed on the crucible base. The electric actuator device is electrically connected to an external control switch for adjustment to control the quartz crucible to move up and down along the central axis of the high-frequency induction coil.

5. The method for preparing a CoFeNi medium-entropy alloy tensile specimen under deep supercooling conditions according to claim 1, characterized in that, The length of the obtained cylindrical CoFeNi alloy sample reached over 30 mm.

6. The method for preparing CoFeNi medium-entropy alloy tensile specimens under deep supercooling conditions according to any one of claims 1-5, characterized in that, The glass cleaner used is glass with Na2O·CaO·6SiO2 as its main component.

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