CN113046585B - Preparation method and application of high-entropy alloy for extremely cold environment - Google Patents

Preparation method and application of high-entropy alloy for extremely cold environment Download PDF

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CN113046585B
CN113046585B CN202110287194.8A CN202110287194A CN113046585B CN 113046585 B CN113046585 B CN 113046585B CN 202110287194 A CN202110287194 A CN 202110287194A CN 113046585 B CN113046585 B CN 113046585B
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entropy alloy
molten metal
cocrfenimn
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CN113046585A (en
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王泽�
秦青丰
王云壮
夏少华
孙志娟
苏冬梅
张波
吴振华
杨晓红
叶霞
李小平
雷卫宁
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Jiangsu University of Technology
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C1/00Making non-ferrous alloys
    • C22C1/02Making non-ferrous alloys by melting
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C30/00Alloys containing less than 50% by weight of each constituent
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24Nitriding

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Abstract

The invention discloses a preparation method and application of a high-entropy alloy for an extremely cold environment. (1) Mixing cobalt, chromium, iron, nickel and manganese according to atomic percentage to obtain mixed metal powder; (2) melting the mixed metal powder into molten metal; (3) coating a lubricant in the mold in the deposition cavity, and introducing inert gas after drying; (4) injecting molten metal into a molten metal bag, introducing inert gas, and performing atomization deposition on the molten metal in a mold to obtain a high-entropy alloy ingot; (5) placing the high-entropy alloy ingot in a vacuum heating furnace for heat treatment and water cooling; (6) then, carrying out hot extrusion on the high-entropy alloy ingot to obtain a high-entropy alloy bar; (7) removing oxide skin on the surface of the high-entropy alloy bar; (8) and then placing the high-entropy alloy bar in a vacuum nitriding device, introducing mixed gas of argon and nitrogen for nitriding treatment, and forming a nitriding layer on the surface of the high-entropy alloy bar to obtain the high-entropy alloy for the extremely cold environment. The application comprises the following steps: the obtained high-entropy alloy is used as polar region mining and drilling equipment.

Description

Preparation method and application of high-entropy alloy for extremely cold environment
Technical Field
The invention relates to the technical field of high-entropy alloys, in particular to a preparation method and application of a high-entropy alloy for an extremely cold environment.
Background
In recent years, with the continuous promotion of industrialization and the rising of population, the energy demand is continuously increased, and the global energy shortage is caused by excessive production of energy in land, offshore and deep sea areas. The human exploration range for energy sources gradually expands towards the south pole circle and the north pole circle. The arctic is recognized by scientists as a region for storing future energy, and development of oil and gas resources has been conducted centering on countries adjacent to the arctic circle. Steel materials for mining and drilling in polar regions have a high tendency to fracture at low temperatures under the action of long-term alternating stress, and are more likely to undergo brittle fracture when becoming brittle. In recent years, scientific research works are carried out on a large scale in south and north pole areas in China, and the lowest temperature of the environment reaches minus 80 ℃. Therefore, while the strength of steel is improved, a certain low-temperature toughness and plasticity is required to be ensured, the existing material is difficult to effectively meet the use requirement, and a metal material with toughness and fatigue fracture characteristics at extremely low temperature is urgently needed.
Disclosure of Invention
The invention aims to provide a preparation method of a high-entropy alloy for extremely cold environments.
The invention is realized by the following technical scheme:
a preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: mixing elemental cobalt powder, elemental chromium powder, elemental iron powder, elemental nickel powder and elemental manganese powder according to the atomic percent of the high-entropy alloy to obtain mixed metal powder;
(2) smelting: melting the mixed metal powder to obtain molten metal;
(3) coating a lubricant: coating a lubricant in a circular mould on a workbench in a deposition cavity, and introducing inert gas after drying to form a protective atmosphere;
(4) deposition: injecting the molten metal into a molten metal bag, introducing inert gas, and performing atomization deposition on the molten metal in the mold to obtain a CoCrFeNiMn high-entropy alloy ingot;
(5) homogenizing: placing the CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace for heat treatment, and then cooling by water;
(6) hot extrusion: carrying out hot extrusion on the homogenized CoCrFeNiMn high-entropy alloy ingot to obtain a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing the oxide skin on the surface of the CoCrFeNiMn high-entropy alloy bar;
(8) nitriding treatment: and placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen to carry out high-temperature nitriding treatment, and forming a nitride layer on the surface of the CoCrFeNiMn high-entropy alloy bar to obtain the CoCrFeNiMn high-entropy alloy for the extremely cold environment.
Further, the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese in step (1) are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese was 99.9%.
Further, smelting in the step (2): and (3) adding the mixed metal powder into a crucible smelting furnace of the spray deposition equipment to be melted at 1500-1600 ℃ to obtain molten metal.
Further, the lubricant in the step (3) is aqueous colloidal graphite, DFY-1 type fat-based paint or spindle oil; the inert gas is argon, and the flow rate of the argon is 80-100 sccm.
Further, step (4) deposits: and (3) injecting the molten metal into a molten metal bag, introducing argon gas of 0.9-1.2MPa, atomizing the molten metal through a nozzle with the diameter of phi 3 +/-0.05 mm, and atomizing and depositing the molten metal in a circular mold to obtain the CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80 cm.
Further, the step (5) of homogenization treatment: placing the CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at the temperature of 900-1100 ℃ for heat treatment for 6-12 hours; the water cooling temperature is 0-20 ℃.
Further, step (6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at the temperature of 800-900 ℃ for 8-10 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 10-20, and the extrusion speed is 1-3 mm/s; obtaining the CoCrFeNiMn high-entropy alloy bar.
Further, descaling in the step (7): removing 1-1.5mm of oxide skin on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe.
Further, the temperature of the nitriding treatment in the step (8) is 500-; the flow rate of the argon gas is 40-100sccm, and the flow rate ratio of the argon gas to the nitrogen gas is 1: (0.2-1); the thickness of the nitride layer is 2-3 mm.
The high-entropy alloy prepared by the preparation method is used as steel for mining and drilling equipment in polar regions.
The invention has the beneficial effects that:
the CoCrFeNiMn high-entropy alloy for the extremely cold environment prepared by the method has uniform and compact structure, fine crystal grains with the grain diameter of about 20-30 mu m, increased grain boundary density after the crystal grains are refined, the grain boundary can effectively block dislocation motion, and the compact structure has few defects, so that the prepared CoCrFeNiMn high-entropy alloy has high tensile strength. In addition, the stacking fault energy of CoCrFeNiMn is reduced along with the temperature under the low-temperature condition, the deformation mechanism of the alloy is transformed, the dislocation slip is transformed into the twinning process, and the occurrence of cold brittle fracture caused by dislocation plugging is avoided, so that the alloy has high low-temperature toughness. The preparation method is completed by the spray forming and nitriding technology, the production efficiency is high, large-size alloy billets can be obtained by large-scale production, and the prepared high-entropy alloy bars have high-hardness surfaces and high low-temperature toughness and can be used for steel for polar region mining and drilling equipment. According to the preparation method, before nitriding treatment, the surface of the CoCrFeNiMn high-entropy alloy bar is turned by a large amount to remove an oxidation layer, so that nitrogen atoms are favorably dissolved into the alloy in a solid manner; in addition, the high-entropy alloy contains manganese with higher atomic percentage, and the manganese is beneficial to the nitrogen atoms to be dissolved into the alloy in a solid mode, so that a thicker nitriding layer can be formed, and the hardness and the low-temperature toughness of the obtained alloy are further improved.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: uniformly mixing simple substance powder of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder; the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese is 99.9%;
(2) smelting: adding the mixed metal powder into a crucible smelting furnace of spray deposition equipment to be melted at 1500 ℃ to obtain molten metal;
(3) coating a lubricant: coating aqueous colloidal graphite lubricant in a circular mould on a workbench in a deposition cavity, drying, and introducing high-purity argon to form protective atmosphere; and the argon flow is 100 sccm;
(4) deposition: injecting the molten metal into a molten metal bag, introducing high-purity argon gas of 1.2MPa, atomizing the molten metal through a nozzle with the diameter of phi 3mm, and atomizing and depositing the molten metal in a circular mold to obtain a CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80 cm;
(5) homogenizing: placing the obtained CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at 1000 ℃ for heat treatment for 12 hours, and then placing the alloy ingot in water at 20 ℃ for cooling;
(6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at 800 ℃ for 8 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 10, and the extrusion speed is 3 mm/s; thus obtaining a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing oxide skin with the thickness of 1.0mm on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen, and performing nitriding treatment at 600 ℃ for 12 hours to form a nitriding layer on the surface of the CoCrFeNiMn high-entropy alloy bar so as to obtain a CoCrFeNiMn high-entropy alloy for an extremely cold environment; and the flow rate of introduced argon is 40sccm, and the flow ratio of argon to nitrogen is 1: 0.2.
and (3) testing: the surface hardness of the extremely cold environment CoCrFeNiMn high-entropy alloy obtained in the example 1 is measured to be 8GPa by a hardness meter; the tensile strength measured by a tensile test at liquid nitrogen (-196 ℃) was 802MPa, and the elongation was 68%; therefore, the high-entropy alloy prepared by the invention has good elongation at extremely low temperature and good low-temperature toughness.
The application comprises the following steps: the CoCrFeNiMn high-entropy alloy prepared by the invention has a high-hardness surface and high low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions.
Example 2
A preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: uniformly mixing simple substance powder of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder; the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese is 99.9%;
(2) smelting: adding the mixed metal powder into a crucible smelting furnace of a spray deposition device to be melted at 1550 ℃ to obtain molten metal;
(3) coating a lubricant: coating aqueous colloidal graphite lubricant in a circular mould on a workbench in a deposition cavity, drying, and introducing high-purity argon to form protective atmosphere; and the argon flow is 80 sccm;
(4) deposition: injecting the molten metal into a molten metal bag, introducing high-purity argon gas of 1.1MPa, atomizing the molten metal through a nozzle with the diameter of phi 3.05mm, and atomizing and depositing the molten metal in a circular mold to obtain a CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80 cm;
(5) homogenizing: placing the obtained CoCrFeNiMn high-entropy alloy ingot in a 950 ℃ vacuum heating furnace for heat treatment for 10 hours, and then placing the ingot in 15 ℃ water for cooling;
(6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at 900 ℃ for 8 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 15, and the extrusion speed is 2 mm/s; thus obtaining a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing oxide skin with the thickness of 1.2mm on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen, and performing nitriding treatment for 8 hours at 500 ℃ to form a nitriding layer on the surface of the CoCrFeNiMn high-entropy alloy bar so as to obtain a CoCrFeNiMn high-entropy alloy for an extremely cold environment; and the flow rate of introduced argon is 60sccm, and the flow ratio of argon to nitrogen is 1: 0.4.
and (3) testing: the surface hardness of the extremely cold environment CoCrFeNiMn high-entropy alloy obtained in the above example 2 was measured by a hardness tester to be 10.2 GPa; tensile strength was 799MPa and elongation 70% as measured by a tensile test at liquid nitrogen (-196 ℃); therefore, the high-entropy alloy prepared by the invention has good elongation at extremely low temperature and good low-temperature toughness.
The application comprises the following steps: the CoCrFeNiMn high-entropy alloy prepared by the invention has a high-hardness surface and high low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions.
Example 3
A preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: uniformly mixing simple substance powder of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder; the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese is 99.9%;
(2) smelting: adding the mixed metal powder into a crucible smelting furnace of spray deposition equipment to be melted at 1580 ℃ to obtain molten metal;
(3) coating a lubricant: coating DFY-1 type grease-based coating lubricant in a circular mould on a workbench in a deposition cavity, and introducing high-purity argon after drying to form a protective atmosphere; and the argon flow is 100 sccm;
(4) deposition: injecting the molten metal into a molten metal bag, introducing high-purity argon of 0.9MPa, atomizing the molten metal through a nozzle with the diameter of phi 2.95mm, and atomizing and depositing the molten metal in a circular mold to obtain a CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80 cm;
(5) homogenizing: placing the obtained CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at 900 ℃ for heat treatment for 8 hours, and then placing the alloy ingot in water at 10 ℃ for cooling;
(6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at 850 ℃ for 8 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 20, and the extrusion speed is 2 mm/s; obtaining a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing oxide skin with the thickness of 1.5mm on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen, and performing nitriding treatment for 2 hours at 1000 ℃, forming a nitriding layer on the surface of the CoCrFeNiMn high-entropy alloy bar, and obtaining the CoCrFeNiMn high-entropy alloy for the extremely cold environment; and the flow rate of introduced argon is 80sccm, and the flow ratio of argon to nitrogen is 1: 0.6.
and (3) testing: the surface hardness of the extremely cold environment CoCrFeNiMn high-entropy alloy obtained in example 3 was measured by a hardness tester to be 11.98 GPa; the tensile strength measured by a tensile test at liquid nitrogen (-196 ℃) was 801MPa, and the elongation was 68%; therefore, the high-entropy alloy prepared by the invention has good elongation at extremely low temperature and good low-temperature toughness.
The application comprises the following steps: the CoCrFeNiMn high-entropy alloy prepared by the invention has a high-hardness surface and high low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions.
Example 4
A preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: uniformly mixing simple substance powder of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder; the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese is 99.9%;
(2) smelting: adding the mixed metal powder into a crucible smelting furnace of spray deposition equipment to be melted at 1600 ℃ to obtain molten metal;
(3) coating a lubricant: coating spindle oil in a circular mould on a workbench in a deposition cavity, drying, and introducing high-purity argon to form a protective atmosphere; and the argon flow is 90 sccm;
(4) deposition: the molten metal is added into a molten metal bag, high-purity argon gas with the pressure of 1.0MPa is introduced, the molten metal is atomized through a nozzle with the diameter of phi 3.0mm, and the molten metal is atomized and deposited in a circular mold, so that a CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80cm can be obtained;
(5) homogenizing: placing the obtained CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at 1100 ℃ for heat treatment for 6 hours, and then placing the alloy ingot in water at 5 ℃ for cooling;
(6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at 900 ℃ for 8 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 10, and the extrusion speed is 3 mm/s; thus obtaining a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing oxide skin with the thickness of 1.3mm on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen, and performing nitriding treatment for 5 hours at 800 ℃ to form a nitriding layer on the surface of the CoCrFeNiMn high-entropy alloy bar so as to obtain a CoCrFeNiMn high-entropy alloy for an extremely cold environment; and the flow rate of introduced argon is 100sccm, and the flow ratio of argon to nitrogen is 1: 0.8.
and (3) testing: the surface hardness of the extremely cold environment CoCrFeNiMn high-entropy alloy obtained in example 4 was measured by a hardness tester to be 12.2 GPa; the tensile strength was 804MPa and the elongation was 69% as measured by a tensile test at liquid nitrogen (-196 ℃); therefore, the high-entropy alloy prepared by the invention has good elongation at extremely low temperature and good low-temperature toughness.
The application comprises the following steps: the CoCrFeNiMn high-entropy alloy prepared by the invention has a high-hardness surface and high low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions.
Example 5
A preparation method of a high-entropy alloy for an extremely cold environment comprises the following steps:
(1) powder preparation: uniformly mixing elemental powders of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder; the atomic percentages of the cobalt, the chromium, the iron, the nickel, and the manganese are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese is 99.9%;
(2) smelting: adding the mixed metal powder into a crucible smelting furnace of spray deposition equipment to be melted at 1500 ℃ to obtain molten metal;
(3) coating a lubricant: coating aqueous colloidal graphite lubricant in a circular mould on a workbench in a deposition cavity, drying, and introducing high-purity argon to form protective atmosphere; and the argon flow is 100 sccm;
(4) deposition: the molten metal is added into a molten metal bag, high-purity argon of 1.2MPa is introduced, the molten metal is atomized through a nozzle with the diameter of phi 3.0mm, and the molten metal is atomized and deposited in a circular mold, so that a CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80cm can be obtained;
(5) homogenization treatment: placing the obtained CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at 1050 ℃ for heat treatment for 9 hours, and then placing the ingot in water at 20 ℃ for cooling;
(6) hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at 800 ℃ for 9 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 10, and the extrusion speed is 3 mm/s; thus obtaining a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing oxide skin with the thickness of 1.1mm on the surface of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen, and performing nitriding treatment for 8 hours at 700 ℃ to form a nitriding layer on the surface of the CoCrFeNiMn high-entropy alloy bar so as to obtain a CoCrFeNiMn high-entropy alloy for an extremely cold environment; and the flow rate of introduced argon is 50sccm, and the flow ratio of argon to nitrogen is 1: 1.
and (3) testing: the surface hardness of the extremely cold environment CoCrFeNiMn high-entropy alloy obtained in example 5 was measured by a hardness tester to be 12.1 GPa; tensile strength of 805MPa and elongation of 70% as measured by a tensile test at liquid nitrogen (-196 ℃); therefore, the high-entropy alloy prepared by the invention has good elongation at extremely low temperature and good low-temperature toughness.
The application comprises the following steps: the CoCrFeNiMn high-entropy alloy prepared by the invention has a high-hardness surface and high low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions.
From the test results of the above examples 1-5, it can be seen that the CoCrFeNiMn high-entropy alloy prepared by the preparation method of the invention has excellent mechanical properties such as hardness, tensile strength and low-temperature toughness, and can be used as steel for mining and drilling equipment in polar regions. The above-mentioned preferred embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention. Obvious variations or modifications of the present invention are within the scope of the present invention.

Claims (8)

1. A preparation method of a high-entropy alloy for an extremely cold environment is characterized by comprising the following steps:
(1) powder preparation: mixing simple substance powder of cobalt, chromium, iron, nickel and manganese according to the atomic percentage of the high-entropy alloy to obtain mixed metal powder;
(2) smelting: melting the mixed metal powder to obtain molten metal;
(3) coating a lubricant: coating a lubricant in a mould in the deposition cavity, drying and introducing inert gas to form a protective atmosphere;
(4) deposition: injecting the molten metal into a molten metal bag, introducing inert gas, and performing atomization deposition on the molten metal in the mold to obtain a CoCrFeNiMn high-entropy alloy ingot;
(5) homogenizing: placing the CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace for heat treatment, and then cooling by water;
(6) hot extrusion: carrying out hot extrusion on the homogenized CoCrFeNiMn high-entropy alloy ingot to obtain a CoCrFeNiMn high-entropy alloy bar;
(7) descaling: removing the oxide skin on the surface of the CoCrFeNiMn high-entropy alloy bar;
(8) nitriding treatment: placing the CoCrFeNiMn high-entropy alloy bar subjected to descaling in a vacuum nitriding device, introducing mixed gas of argon and nitrogen for high-temperature nitriding treatment, and forming a nitride layer on the surface of the CoCrFeNiMn high-entropy alloy bar to obtain a high-entropy alloy for an extremely cold environment;
the temperature of the nitriding treatment in the step (8) is 500-; the flow rate of the argon gas is 40-100sccm, and the flow rate ratio of the argon gas to the nitrogen gas is 1: (0.2-1); the thickness of the nitride layer is 2-3 mm;
the high-entropy alloy is used as a material for polar region mining and drilling equipment.
2. A method for preparing a high entropy alloy for extremely cold environments as claimed in claim 1, wherein the atomic percentages of the cobalt, the chromium, the iron, the nickel and the manganese in step (1) are 1: 1: 1: 1: 1; the purity of the cobalt, the chromium, the iron, the nickel and the manganese was 99.9%.
3. The preparation method of the high-entropy alloy for the extremely cold environment according to claim 1, wherein the step (2) is to smelt: and (3) adding the mixed metal powder into a crucible smelting furnace of the spray deposition equipment to be melted at 1500-1600 ℃ to obtain molten metal.
4. A method for preparing a high-entropy alloy for extremely cold environments as claimed in claim 1, wherein the lubricant in step (3) is aqueous colloidal graphite, DFY-1 type fat-based paint or spindle oil; the inert gas is argon, and the flow rate of the argon is 80-100 sccm.
5. A method for preparing a high-entropy alloy for extremely cold environments according to claim 1, wherein the deposition in the step (4): and (3) injecting the molten metal into a molten metal bag, introducing argon gas of 0.9-1.2MPa, atomizing the molten metal through a nozzle with the diameter of phi 3 +/-0.05 mm, and atomizing and depositing the molten metal in a circular mold to obtain the CoCrFeNiMn high-entropy alloy ingot with the size of phi 50cm multiplied by 80 cm.
6. A method for preparing a high-entropy alloy for an extremely cold environment according to claim 1, wherein the homogenization treatment in the step (5): placing the CoCrFeNiMn high-entropy alloy ingot in a vacuum heating furnace at the temperature of 900-1100 ℃ for heat treatment for 6-12 hours; the water cooling temperature is 0-20 ℃.
7. A method for preparing a high-entropy alloy for an extremely cold environment according to claim 1, wherein the step (6) of hot extrusion: preheating the homogenized CoCrFeNiMn high-entropy alloy ingot at the temperature of 800-900 ℃ for 8-10 hours, and then carrying out hot extrusion, wherein the extrusion ratio is 10-20, and the extrusion speed is 1-3 mm/s; obtaining the CoCrFeNiMn high-entropy alloy bar.
8. The method for preparing the high-entropy alloy for the extremely cold environment according to claim 1, wherein the descaling in the step (7): and removing 1-1.5mm of surface oxide skin of the CoCrFeNiMn high-entropy alloy bar by using a numerical control lathe.
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