A method for preparing a self-propagating combustion synthesis melt-cast high entropy alloy

Abstract

The present invention specifically discloses a method for preparing a self-propagating combustion synthesis molten-cast high-entropy alloy, comprising the following steps: mixing and drying pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder, and titanium oxide powder, and then adding pure aluminum powder to obtain a mixture; compacting the mixture into a prefabricated block, placing an igniter on the surface of the prefabricated block; igniting the igniter to cause the prefabricated block to undergo a self-propagating combustion synthesis reaction to obtain a high-entropy alloy solution; and cooling the high-entropy alloy solution to obtain a high-entropy alloy block. The preparation method provided by the present invention utilizes the exothermic reaction between pure aluminum powder and a variety of metal oxides, and has a fast reaction speed, high efficiency, low cost, and can reduce energy consumption.

Description

Technical Field

[0001] The invention relates to the field of high entropy alloy preparation, and in particular to a method for preparing a self-propagating combustion synthesis molten-cast high entropy alloy. Background Art

[0002] For metal materials, the design concept of traditional alloys is to obtain excellent performance by appropriately adding a small amount of other elements based on one or two main elements. For example, the widely used steel materials are carbon steel, stainless steel and tool steel formed by adding other alloy elements of different contents with Fe as the single main element. The toughness of the alloy can be significantly improved by adding an appropriate amount of Mo element to titanium alloy, and the strength can be improved by adding a certain amount of Zn element to aluminum alloy. In the past two hundred years, many material systems such as copper alloys, aluminum alloys, titanium alloys, magnesium alloys and superalloys for high temperature fields have been designed and developed based on this traditional alloy concept, providing important material support for the progress of human society.

[0003] High-entropy alloys (HEAs) are a new alloy system proposed in the past decade for innovative alloy design. Different from the traditional alloy design strategy of single element-based alloy materials, high-entropy alloys are composed of 5 or more metal elements in equiatomic or nearly equiatomic ratios, with the atomic fraction of each component between 5% and 35%, and a simple solid solution phase with a mixing entropy greater than 1.61R (R is the gas constant).

[0004] The emergence of high entropy alloys has broken through the traditional metal material design concept of alloys with a single main element, allowing alloy design to expand from the corners of the phase diagram to the middle, greatly expanding the field of alloy design and arousing great interest in the field of materials at home and abroad. In recent years, research on high entropy alloys has gradually become an international hotspot in the field of materials. The main research has extended from the phase formation mechanism and criteria of high entropy alloys, preparation methods, alloy systems, and from atoms to microstructures and then to macroscopic properties, from mechanical properties (from room temperature to related fields of high and low temperature conditions) to other properties, and from applied basic scientific explorations such as coatings and weldability to rapidly expand to applied research fields such as aerospace, advanced nuclear energy, bioengineering, advanced equipment manufacturing, and defense industry.

[0005] At present, the main preparation methods of high entropy alloys include vacuum melting to prepare blocks, mechanical alloying to prepare powders, laser cladding to prepare coatings, and electrochemical deposition to prepare thin films, among which vacuum arc melting and mechanical alloying are the mainstream multi-principal alloy preparation methods. These preparation methods require the use of high-purity raw materials and complex process control devices during the preparation process, resulting in high preparation costs for high entropy alloys and difficulty in forming parts with complex shapes.

[0006] Therefore, developing a high-entropy alloy with fast reaction speed, high efficiency and low cost is an urgent problem to be solved by technicians in this field. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a high entropy alloy by self-propagating combustion synthesis and molten casting, which has fast reaction speed, high efficiency, low cost and can reduce energy consumption.

[0008] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0009] The first aspect of the present invention provides a method for preparing a high entropy alloy by self-propagating combustion synthesis and melt-casting, comprising the following steps:

[0010] Pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder and titanium oxide powder are mixed and dried, and then pure aluminum powder is added to obtain a mixture;

[0011] compacting the mixture into a prefabricated block, and placing an igniter on the surface of the prefabricated block;

[0012] Ignite the igniter to cause the prefabricated block to undergo a self-propagating combustion synthesis reaction to obtain a high entropy alloy solution;

[0013] The high entropy alloy solution is cooled to obtain a high entropy alloy block.

[0014] In the present invention, aluminum powder and pure iron powder are added simultaneously as diluents for the self-propagating combustion synthesis reaction, and the chemical composition of the high entropy alloy is adjusted by the diluents. The addition of diluents can reduce the severity of the self-propagating combustion synthesis reaction and adjust the chemical composition of the high entropy alloy.

[0015] In the present invention, pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder and titanium oxide powder are mixed and dried to volatilize water and eliminate other volatile substances. The remaining aluminum powder is added after drying to avoid explosion during the drying process.

[0016] In the present invention, firstly, boron nitride is sprayed in a water-cooled copper mold, then an alumina crucible is assembled and fixed with the water-cooled copper mold, and placed in a resistance heating furnace to dry the mold, the mold drying temperature is controlled at 50-100°C, the mold drying time is controlled at 1-5h, and then the water-cooled copper mold is placed in water for circulation cooling and a uniformly mixed mixture is prepared to be placed in the alumina crucible. Then the mixture is compacted to form a prefabricated block, and an igniter is placed on the surface of the compacted prefabricated block. Thereafter, the igniter is ignited to rapidly ignite the mixture to generate a self-propagating combustion synthesis reaction, and a high entropy alloy solution is obtained in the self-propagating combustion exothermic process, and the high entropy alloy solution is rapidly cooled in the water-cooled copper mold to obtain a high entropy alloy block.

[0017] In the present invention, the exothermic reaction between aluminum powder and various metal oxide powders, i.e., the aluminothermic reaction method, is used to melt and cast a high entropy alloy block. A high entropy alloy block can be obtained in a short time. Combined with the process of assembling a fixed alumina crucible on the upper part of a water-cooled copper casting mold, a short-process preparation of a high entropy alloy block material can be achieved, with fast reaction speed, short production process time, large amount of energy saving, maximum utilization of chemical energy in the reaction, and rapid molding and other process advantages. In this process, metal oxides are used to effectively prevent oxidation or burning of pure metal elements, and no high vacuum or inert gas protection device is required, thereby significantly improving the alloy preparation cost.

[0018] Furthermore, the self-propagating combustion synthesis reaction time is 20-50 s, and the reaction time is related to the mass of the reaction mixture, for example, it can be 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, or 50 s.

[0019] Furthermore, the mass ratio of the pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder, titanium oxide powder and aluminum powder is (2-15): (25-32): (4-8): (1-13): (1-3): (4-10).

[0020] Furthermore, the igniter is pure magnesium powder, which is ignited by tungsten wire, high-energy electric flame ignition, pulse plasma, etc.

[0021] Furthermore, the mass ratio of the igniter to the mixture is 1:10-1:30, for example, 1:10, 1:20, or 1:30.

[0022] Furthermore, the igniter is spread on the surface of the prefabricated block or in powder form.

[0023] Furthermore, when the igniter is spread on the surface of the prefabricated block, the thickness of the igniter is 1 to 3 mm, for example, 1 mm, 2 mm, or 3 mm.

[0024] Furthermore, when the igniter is in powder form and spread on the surface of the prefabricated block, the particle size of the powder is 10 to 200 μm, for example, 10 μm, 50 μm, 100 μm, 150 μm, or 200 μm.

[0025] Furthermore, the drying temperature is 80-120°C, for example, 80°C, 85°C, 90°C, 95°C, 105°C, 110°C, 115°C, or 120°C.

[0026] Furthermore, the relative density of the prefabricated block is 50-75%, for example, 50%, 55%, 60%, 65%, 70%, 75%, and the relative density refers to the ratio of the density of the prefabricated block to the density of the reference material under cold isostatic pressing (99%).

[0027] Further, the mass fraction of aluminum in the high entropy alloy block prepared by the above method is 5.5-9.5%, for example, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%; the mass fraction of iron is 16.9-26.9%, for example, 16.9%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5%, 20.0%, 20.5%, 21.0%, 21.5%, 22.0%, 22.5%, 23.0%, 23.5%, 24.0%, 24.5%, 25.0%, 25.5%, 26.0%, 26.5%, 26.9%. The content of aluminum and iron can be adjusted according to the chemical composition of the high entropy alloy.

[0028] The second aspect of the present invention provides a high entropy alloy block Ni prepared by the above preparation method (20.9-49.6) Fe (16.9-26.9) Co (16.9-26.9) Cr (6.9-15.9) Al (5.5-9.5) Ti (3.9-10.9) .

[0029] In the present invention, the mass fraction of Ni in the high entropy alloy block is 20.9-49.6%, the mass fraction of Fe is 16.9-26.9%, the mass fraction of Co is 6.9-15.9%, the mass fraction of Al is 5.5-9.5%, and the mass fraction of Ti is 3.9-10.9%.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention provides a method for preparing a high entropy alloy by self-propagating combustion synthesis and melt-casting, which has fast reaction speed, high efficiency and low cost.

[0032] 2. The present invention provides a method for preparing a high entropy alloy, in which a high entropy alloy is melt-casted through an exothermic reaction between pure aluminum powder and a variety of metal oxide powders. The raw materials are easily available and have stable properties. The preparation conditions do not require high vacuum or protective atmosphere. The process and equipment are simple, the pollution is small, and the phase interface is clean. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Alumina crucible for the mixture.

[0034] Figure 2 It is a water-cooled copper mold.

[0035] Figure 3 The alumina crucible for assembling and fixing is assembled and fixed with the water-cooled copper casting mold.

[0036] Figure 4It is a high entropy alloy block formed by high entropy alloy liquid in a water-cooled copper mold.

[0037] Figure 5 This is a metallographic (OM) photograph of the high entropy alloy prepared in Example 1. DETAILED DESCRIPTION

[0038] In order to make the content of the present invention easier to understand, the technical scheme of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited thereto. All technologies realized based on the above content of the present invention are included in the scope that the present invention is intended to protect. Unless otherwise specified, the raw materials and reagents used in the examples are all commercially available products. The reagents, instruments or operating procedures not recorded herein are all contents that can be routinely determined by a person of ordinary skill in the art.

[0039] Embodiment 1:

[0040] The process for preparing high entropy alloy by self-propagating combustion synthesis in this embodiment is as follows:

[0041] Step 1:

[0042] The reaction raw materials were prepared with pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), titanium oxide powder (TiO2) and aluminum powder (Al) in a mass ratio of 3:27:5:2:1:5.

[0043] Mix pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), and titanium oxide powder (TiO2) and stir and mix thoroughly, dry (drying temperature is 100°C), add aluminum powder (Al) and mix again to make the raw materials uniform by self-propagating combustion synthesis, in order to avoid explosion during the drying process;

[0044] Step 2: spray boron nitride in the water-cooled copper mold, then place the alumina crucible on the top of the water-cooled copper mold for assembly and fixation, and then place the mold in a resistance heating furnace for drying. The mold temperature is controlled at 60°C, and then the water-cooled copper mold is placed in water for circulation cooling and the mixed mixture is prepared to be placed in the alumina crucible;

[0045] Step 3: placing the mixture stirred and dried in step 1 in the alumina crucible obtained in step 2, and then compacting it to form a prefabricated block with a certain density (relative density 60%), and placing pure magnesium powder on the surface of the compacted prefabricated block, with the mass ratio of pure magnesium powder to the mixture being 1:20;

[0046] Step 4: Use a magnesium rod or tungsten wire to ignite pure magnesium powder. The ignition of pure magnesium quickly ignites the mixture, and a high-entropy alloy liquid is obtained during the exothermic process of the self-propagating combustion synthesis reaction. The alloy liquid is quickly cooled in a water-cooled copper mold to obtain a high-entropy alloy block. The self-propagating combustion synthesis reaction time is 30s. The high-entropy alloy Ni is obtained by melting and casting through the self-propagating combustion synthesis reaction. 32.8 Fe 21.9 Co 21.9 Cr 10.9 Al 7.5 Ti 5.0 .

[0047] The method for preparing the self-propagating combustion synthesis melt-cast high entropy alloy of this embodiment has fast reaction speed, high efficiency and low cost. At the same time, the prepared high entropy alloy is a high entropy alloy melt-cast by exothermic reaction between pure aluminum powder and various metal oxide powders, the raw materials are easy to obtain and have stable properties, the preparation conditions do not require high vacuum or protective atmosphere, the process and equipment are simple, the pollution is small, and the phase interface is clean.

[0048] Embodiment 2:

[0049] Step 1:

[0050] The reaction raw materials were prepared with pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), titanium oxide powder (TiO2) and aluminum powder (Al) in a mass ratio of 6:20:4:3:1:10.

[0051] Mix pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), and titanium oxide powder (TiO2) and stir and mix thoroughly, dry (drying temperature is 100°C), add aluminum powder (Al) and mix again to make the raw materials uniform by self-propagating combustion synthesis, in order to avoid explosion during the drying process;

[0052] The rest is the same as Example 1.

[0053] High entropy alloy Ni was obtained by melting and casting through self-propagating combustion synthesis reaction 25 Fe 18 Co 18 Cr 18 Al 10 Ti4.

[0054] Embodiment 3:

[0055] Step 1:

[0056] The reaction raw materials were prepared with pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), titanium oxide powder (TiO2) and aluminum powder (Al) in a mass ratio of 2.8:25:5:2:1:6.

[0057] Mix pure iron powder (Fe), cobalt oxide powder (Co2O3), nickel oxide powder (NiO), chromium oxide powder (Cr2O3), and titanium oxide powder (TiO2) and stir and mix thoroughly, dry (drying temperature is 100°C), add aluminum powder (Al) and mix again to make the raw materials uniform by self-propagating combustion synthesis, in order to avoid explosion during the drying process;

[0058] The rest is the same as Example 1.

[0059] High entropy alloy Ni was obtained by melting and casting through self-propagating combustion synthesis reaction 30 Fe 20 Co 20 Cr 15 Al8Ti7.

[0060] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a self-propagating combustion synthesis melt-cast high entropy alloy, characterized in that: The following steps are involved: Pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder and titanium oxide powder are mixed, dried at 80-120° C., and then pure aluminum powder is added to obtain a mixture; the mass ratio of the pure iron powder, cobalt oxide powder, nickel oxide powder, chromium oxide powder, titanium oxide powder and aluminum powder is (2-15): (25-32): (4-8): (1-13): (1-3): (4-10); The mixture is placed in an alumina crucible and compacted into a prefabricated block, and an igniter is placed on the surface of the prefabricated block; the igniter is pure magnesium powder; the mass ratio of the igniter to the mixture is 1:10-1:30; the igniter is spread on the surface of the prefabricated block or spread on the surface of the prefabricated block in the form of powder, the thickness of the igniter spread on the surface of the prefabricated block is 1-3 mm, and the particle size of the powder when the igniter is spread on the surface of the prefabricated block in the form of powder is 10-200 μm; Ignite the igniter to cause the prefabricated block to undergo a self-propagating combustion synthesis reaction, the reaction time being 20 to 50 seconds, to obtain a high entropy alloy melt; The high entropy alloy melt is cooled in a water-cooled copper mold to obtain a high entropy alloy block.

2. The preparation method according to claim 1, characterized in that: The relative density of the prefabricated block is 50-75%.

3. A high entropy alloy block, characterized in that: The high entropy alloy block is prepared based on the preparation method according to any one of claims 1 to 2; the mass fraction of aluminum element in the high entropy alloy block is 5.5-9.5%, and the mass fraction of iron element is 16.9-26.9%.

4. A high entropy alloy bulk Ni （20.9-49.6） Fe （16.9-26.9） Co （16.9-26.9） Cr （6.9-15.9） Al （5.5-9.5） Ti （3.9-10.9） , characterized in that, The preparation method is based on any one of claims 1 to 2.

Images