A Cr-Fe-Mn-Ni-Al series high specific strength multi-scale structure high entropy alloy and preparation method thereof

Abstract

The present invention belongs to the technical field of metal materials, and particularly relates to a Cr-Fe-Mn-Ni-Al series high-specific-strength multi-scale structure high-entropy alloy and a preparation method thereof. The general formula of the alloy is Cr a Mn b Fe c Ni d Al e , a, b, c, d, e are molar ratios, a+b+c+d+e=100%. The present invention also discloses a method for preparing a high-specific-strength high-entropy alloy with a multi-scale structure, comprising distributing high-purity raw materials, evacuating and filling a certain amount of high-purity argon gas, and performing multiple arc melting to obtain the desired alloy. The alloy of the present invention has the characteristics of low density, high high-temperature hardness and high high-temperature specific strength. The higher the Al content, the higher the high-temperature strength and specific strength, which is better than the traditional Inconel 718 nickel-based alloy, and provides selection support for new high-temperature structural materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and in particular relates to a Cr-Fe-Mn-Ni-Al series high-entropy alloy with high specific strength and multi-scale structure and a preparation method thereof. Background Art

[0002] The development and application of low-density, high-specific-strength materials are crucial to the development of industries such as aerospace and rail transportation. At present, traditional lightweight alloy materials, such as aluminum alloys and magnesium alloys, have been widely used. Although such materials have low density, their strength is often not high, and it is difficult to meet the growing demand for harsh service environments, such as high temperature, high pressure, corrosion, wear and other harsh environments. Nickel-based high-temperature alloys are known for their excellent high-temperature strength and are often used in the manufacture of aircraft engines. However, due to the high density of nickel-based high-temperature alloys (8.2g / cm 3 ) increases the weight of the aircraft and limits the increase in thrust-to-weight ratio. At present, as my country increases its exploration and development of deep space, deep sea and polar regions, the requirements for equipment service performance have greatly increased, and materials with higher comprehensive performance are often required. Low-density, high-specific strength materials designed based on traditional alloy design concepts have reached a bottleneck.

[0003] In recent years, the introduction of high entropy alloys has broken the traditional design concept of a single principal element in alloys. This type of alloy forms a simple structured solid solution based on multiple principal elements, which represents a new alloy design concept. The biggest feature of high entropy alloys is that they have long-range structural order and chemical disorder, and they exhibit unique effects, including high entropy effect, slow diffusion effect, severe lattice distortion, and cocktail effect. These characteristics make high entropy alloys exhibit many excellent comprehensive properties, such as (FeCoNi) with both high strength and plasticity. 86 Al7Ti7 alloy, high strength and corrosion resistant CoNiV alloy, high strength and wear resistant (TiNbZr) 75 Ag 25 Alloys, etc. The design concept of high entropy alloys has greatly broadened the design scope of alloys and provided new ideas for the development and design of new low-density, high-specific strength materials. Using the design concept of high entropy alloys with multiple principal elements, a low-density, high-specific strength alloy that can be used under complex working conditions is developed, which has practical significance for the development of aerospace, rail transportation and other fields. Summary of the invention

[0004] The purpose of the present invention is to provide a Cr-Mn-Fe-Ni-Al series high specific strength high entropy alloy with a multi-scale structure and a preparation method thereof, in order to address the problems that the current traditional magnesium alloys, aluminum alloys and other light alloys have low strength, while the nickel-based and iron-based alloys have high density and low specific strength. The alloy has the characteristics of low density, high high temperature hardness, high high temperature specific strength and good softening resistance.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A Cr-Fe-Mn-Ni-Al system high specific strength multi-scale structure high entropy alloy, the general formula of the alloy is Cr a Mn b Fe c Ni d Al e , wherein a, b, c, d and e are molar ratios, 10%≤a≤40%, 10%≤b≤40%, 10%≤c≤40%, 10%≤d≤40%, 10%≤e≤30%, and a+b+c+d+e=100%;

[0007] The preparation method thereof comprises the following specific steps:

[0008] (1) Selecting granular alloy raw materials of chromium, manganese, iron, nickel, and aluminum, each raw material is ultrasonically cleaned for 5 to 10 minutes to remove impurities adsorbed on the surface, and before mixing, the molar ratio of the alloy components in the designed general formula is converted into mass percentage, and weighed according to mass percentage;

[0009] (2) the raw materials processed in step (1) are distributed in the order of density from low to high and from bottom to top, so as to ensure that the low-density alloy floats up and the high-density alloy sinks during the smelting process. The density difference thus formed can make the alloy solution more uniform to a certain extent;

[0010] (3) Close the furnace and evacuate the vacuum. When the vacuum reaches 3×10 -3 Pa~5×10 -3 When the pressure is 0.05 MPa, high-purity argon gas of 0.05 MPa is filled in for protection, and the current is gradually increased for smelting. The alloy ingot is turned over and smelted repeatedly for more than 6 times to ensure the uniformity of the smelting of the alloy sample. Finally, the cast alloy sample is obtained by cooling with the furnace.

[0011] Preferably, in step (1), each alloy raw material selected is an industrial grade pure raw material with a purity of 99.9wt%.

[0012] Preferably, in step (3), the current is increased to 300-400A for melting, maintained for one minute, and then turned over for melting, each time maintained for at least 1 minute, and the melting is repeated five to six times.

[0013] Preferably, e=16.7%, a+b+c+d=83.3%, and a=b=c=d.

[0014] Finally, the phase and microstructure of the cast alloy sample prepared in step (3) were characterized by XRD and SEM, hardness was tested by a high temperature hardness tester, and high temperature compression performance was tested by a thermal simulation tester. It was determined that the present invention is a Cr-Mn-Fe-Ni-Al series high specific strength high entropy alloy with a multi-scale structure.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] (1) The Cr-Mn-Fe-Ni-Al series high-entropy alloy of the present invention has a scientific and reasonable element combination. Since the elemental properties and structures of Co, Cr, Fe, Mn, and Ni are similar, they can be mutually dissolved to form a multi-principal alloy with a simple structure, which is often used as the basic element of the high-entropy alloy. The present invention abandons the expensive and high-density Co element, increases the specific gravity of the Mn and Cr elements with lower density, controls the ratio of Fe and Ni elements, and the ratio reaches more than 20%, which can ensure the formation of a low-density solid solution structure. The Al element has a negative mixing enthalpy with other transition metal elements, and is easy to form a B2 phase with Ni. Al has a large atomic radius. The lattice mismatch of different phases can be regulated by regulating the Al content, thereby obtaining B2 phases of different scales. At the same time, the addition of Al and Cr elements can also improve the high-temperature oxidation resistance of the alloy.

[0017] (2) The Cr-Mn-Fe-Ni-Al high specific strength high entropy alloy of the present invention has precipitation phases with multiple scale distributions, a coherent B2 phase, and other intermetallic compound phases with non-coherent structures. There are multiple strengthening mechanisms during the deformation process. At the same time, precipitation phases of various sizes also play a certain inhibitory role in the formation and expansion of cracks.

[0018] (3) The Cr-Mn-Fe-Ni-Al high-strength high-entropy alloy of the present invention has a greater density advantage than traditional iron-based and nickel-based alloys. The alloy density of the system is measured to be 7.1 g / cm 3 The high entropy alloy of this system has excellent room temperature and high temperature mechanical properties, and its specific yield strength at room temperature, 400℃ and 600℃ is as high as 178MPa / (g / cm 3 )、156MPa / (g / cm 3 )、96MPa / (g / cm 3 ), which is superior to traditional Inconel 718 nickel-based alloy.

[0019] (4) The Cr-Mn-Fe-Ni-Al series high specific strength high entropy alloy of the present invention can be directly obtained by vacuum melting, without the need for subsequent deformation treatment and heat treatment, and the preparation method is simple and has strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the XRD diagram of the cast state obtained in Examples 1, 2 and 3 of the present invention;

[0021] Figure 2 The cast alloy Al of Example 1 of the present invention 16.7 (CrFeMnNi) 83.3 SEM image (a) and high temperature compression true stress-true strain curve (b);

[0022] Figure 3 The cast alloy Al of Example 2 of the present invention 14.9 (CrFeMnNi) 85.1 SEM image (a) and high temperature compression true stress-true strain curve (b);

[0023] Figure 4 The cast alloy Al in Example 3 of the present invention 11.1 (CrFeMnNi) 88.9 SEM image (a) and high temperature compression true stress-true strain curve (b). DETAILED DESCRIPTION

[0024] The accompanying drawings are only for illustrative purposes; it should be understood that the embodiments mentioned below are only used to explain the present invention, in order to facilitate the description of the present invention and simplify the description, and therefore, should not be understood as limiting the present invention.

[0025] The principles and features of the present invention are described below in conjunction with the examples, which are only used to explain the present invention and are not used to limit the scope of the present invention. If the specific conditions are not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially. Other technical methods not described adopt the existing technology.

[0026] The present invention will be further described below with reference to the embodiments:

[0027] Example 1

[0028] This embodiment discloses a Cr-Mn-Fe-Ni-Al series high specific strength high entropy alloy, the general formula of the alloy is Cr a Mn b Fe c Ni d Al e , designed according to atomic percentage, e = 16.7%, a + b + c + d = 83.3%, and a = b = c = d = 20.8%, that is, the alloy composition is Al 16.7 (CrFeMnNi) 83.3 , and its preparation method is:

[0029] Before mixing, the atomic percentage of Al 16.7 (CrFeMnNi) 83.3 The high entropy alloy is converted into mass percentage, and the required cast alloy is determined to be 100g. The required pure aluminum is 7.128g, pure chromium is 17.108g, pure iron is 18.375g, pure manganese is 18.076g, and pure nickel is 19.312g, totaling 100g. The purity of each alloy raw material selected reaches 99.9wt%. The raw materials are ultrasonically cleaned in alcohol for 10 minutes to remove impurities adsorbed on the surface. The cleaned raw materials are weighed according to the calculated mass and marked.

[0030] The prepared alloy raw materials are placed in the copper crucible in the order of density from low to high and from bottom to top (Al, Cr, Mn, Fe, Ni). After the furnace is loaded, the furnace is closed and vacuumed. When the vacuum degree reaches 3×10 -3 Pa, fill with 0.05MPa high-purity argon gas for protection, and then strike the arc. After the arc is struck, gradually increase the current to 300A~400A for melting. Melt for one minute, turn the alloy ingot over and then melt for at least one minute, then turn it over again, and repeat the melting for more than six times to ensure the uniformity of the melting of the alloy sample. Finally, cool it in the furnace to obtain the cast alloy sample.

[0031] The multi-scale high entropy alloy of this embodiment is composed of BCC phase and B2 phase. Figure 1 As shown, the B2 phase has a dual size distribution: a lath-shaped p-B2 phase (about 5 μm long and 400 nm wide) and a spherical s-B2 phase (about 400 nm in diameter). Figure 2 (a) shows. The density of the alloy is 6.736 g / cm 3 The compressive yield strength at room temperature, 400℃, 600℃, 800℃ and 1000℃ are 1200MPa, 1050MPa, 650MPa, 255MPa and 78MPa, respectively, and the specific yield strength is 178MPa / (g / cm 3 )、156MPa / (g / cm 3 )、96MPa / (g / cm 3 )、38MPa / (g / cm 3 )、12MPa / (g / cm 3 ),like Figure 2 (b) as shown.

[0032] Example 2

[0033] This embodiment discloses a Cr-Mn-Fe-Ni-Al series high specific strength high entropy alloy, the general formula of the alloy is Cr a Mn b Fec Ni d Al e , designed according to atomic percentage, e = 14.9%, a + b + c + d = 85.1%, and a = b = c = d, that is, the alloy composition is Al 14.9 (CrFeMnNi) 85.1 , and its preparation method is:

[0034] Before mixing, the atomic percentage of Al 14.9 (CrFeMnNi) 85.1 The high entropy alloy is converted into mass percentage, and the required cast alloy is determined to be 100g. The required pure aluminum is 6.282g, pure chromium is 17.307g, pure iron is 18.589g, pure manganese is 18.286g, and pure nickel is 19.536g, totaling 100g. The purity of each selected alloy raw material reaches 99.9wt%. The raw materials are ultrasonically cleaned in alcohol for 8 minutes to remove impurities adsorbed on the surface. The cleaned raw materials are weighed according to the calculated mass and marked.

[0035] The prepared alloy raw materials are placed in the copper crucible in the order of density from low to high and from bottom to top (Al, Cr, Mn, Fe, Ni). After the furnace is loaded, the furnace is closed and vacuumed. When the vacuum degree reaches 4×10 -3 Pa, fill with 0.05MPa high-purity argon gas for protection, and then strike the arc. After the arc is struck, gradually increase the current to 300A~400A for melting. Melt for one minute, turn the alloy ingot over and then melt for at least one minute, then turn it over again, and repeat the melting for more than six times to ensure the uniformity of the melting of the alloy sample. Finally, cool it in the furnace to obtain the cast alloy sample.

[0036] The multi-scale high entropy alloy of this embodiment is composed of BCC phase and B2 phase. Figure 1 As shown, the B2 phase has a dual size distribution: a lath-shaped p-B2 phase (about 5 μm long and 500 nm wide) and a spherical s-B2 phase (about 500 nm in diameter). Figure 3 (a) shows. The alloy density is 6.992g / cm 3 The compressive yield strength at room temperature, 400℃, 600℃, 800℃ and 1000℃ are 1200MPa, 1040MPa, 660MPa, 235MPa and 75MPa, respectively, and the specific yield strength is 172MPa / (g / cm 3 )、149MPa / (g / cm 3 )、94MPa / (g / cm 3 )、34MPa / (g / cm 3 )、11MPa / (g / cm 3 ),like Figure 3 (b) as shown.

[0037] Example 3

[0038] This embodiment discloses a Cr-Mn-Fe-Ni-Al-M series high specific strength high entropy alloy, the general formula of the alloy is Cr a Mn b Fe c Ni d Al e , designed according to atomic percentage, e = 11.1%, a + b + c + d = 88.9%, and a = b = c = d, that is, the alloy composition is Al 11.1 (CrFeMnNi) 88.9 , and its preparation method is:

[0039] Before mixing, the atomic percentage of Al 11.1 (CrFeMnNi) 88.9 The high entropy alloy is converted into mass percentage, and the required cast alloy is determined to be 100g. The required pure aluminum is 4.588g, pure chromium is 17.705g, pure iron is 19.016g, pure manganese is 18.706g, and pure nickel is 19.985g, totaling 100g. The purity of each selected alloy raw material reaches 99.9wt%. The raw materials are ultrasonically cleaned in alcohol for 10 minutes to remove impurities adsorbed on the surface. The cleaned raw materials are weighed according to the calculated mass and marked.

[0040] The prepared alloy raw materials are placed in the copper crucible in the order of density from low to high and from bottom to top (Al, Cr, Mn, Fe, Ni). After the furnace is loaded, the furnace is closed and vacuumed. When the vacuum degree reaches 5×10 -3 Pa, fill with 0.05MPa high-purity argon gas for protection, and then strike the arc. After the arc is struck, gradually increase the current to 300A~400A for melting. Melt for one minute, turn the alloy ingot over and then melt for at least one minute, then turn it over again, and repeat the melting for more than six times to ensure the uniformity of the melting of the alloy sample. Finally, cool it in the furnace to obtain the cast alloy sample.

[0041] The multi-scale high entropy alloy of this embodiment is composed of BCC phase and B2 phase. Figure 1 As shown, the B2 phase has a dual size distribution: a lath-shaped p-B2 phase (about 2 μm long and 600 nm wide) and a spherical s-B2 phase (about 550 nm in diameter). Figure 4 (a) shows. The alloy density is 7.089g / cm 3The compressive yield strength at room temperature, 400℃, 600℃, 800℃ and 1000℃ are 1150MPa, 950MPa, 600MPa, 220MPa and 70MPa, respectively, and the specific yield strength is 162MPa / (g / cm 3 )、134MPa / (g / cm 3 )、85MPa / (g / cm 3 )、31MPa / (g / cm 3 )、10MPa / (g / cm 3 ),like Figure 4 (b) as shown.

[0042] The present invention abandons the expensive and high-density Co element, and through Examples 1-3 and Figure 1-4 It can be seen that the proportions of Mn, Cr, Fe, and Ni are all controlled above 20%. The addition of Al and Cr improves the high-temperature oxidation resistance of the alloy. The higher the Al content, the higher the high-temperature strength and specific strength. When e = 16.7%, a + b + c + d = 83.3%, and a = b = c = d = 20.8%, the high-entropy alloy of this system has excellent room temperature and high-temperature mechanical properties. Its specific yield strength at room temperature, 400 ° C and 600 ° C is as high as 178 MPa / (g / cm 3 )、156MPa / (g / cm 3 )、96MPa / (g / cm 3 ), which is superior to traditional Inconel 718 nickel-based alloy.

[0043] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A Cr-Fe-Mn-Ni-Al series high specific strength multi-scale structure high entropy alloy, characterized in that: The general formula of the alloy is Cr a Mn b Fe c Ni d Al e , where a, b, c, d and e are molar ratios, e=16.7%, a+b+c+d=83.3%, and a=b=c=d; The preparation method thereof comprises the following specific steps: (1) Select granular alloy raw materials of chromium, manganese, iron, nickel and aluminum, and perform ultrasonic cleaning on each raw material for 5-10 minutes to remove impurities adsorbed on the surface. Before mixing, convert the molar ratio of the alloy components in the designed general formula into mass percentage and weigh them according to mass percentage; (2) the raw materials processed in step (1) are distributed in the order of density from low to high and from bottom to top, so as to ensure that the low-density alloy floats up and the high-density alloy sinks during the smelting process. The density difference thus formed can make the alloy melt more uniform to a certain extent; (3) Close the furnace and evacuate the vacuum. When the vacuum degree reaches 3×10 -3 Pa~ 5×10 -3 Pa, 0.05 MPa of high-purity argon gas was filled in for protection, and the current was gradually increased for melting. The alloy ingot was turned over and melted repeatedly for more than 6 times to ensure the uniformity of the melting of the alloy sample. Finally, the cast alloy sample was obtained by cooling with the furnace.

2. A Cr-Fe-Mn-Ni-Al system high specific strength multi-scale structure high entropy alloy as claimed in claim 1, characterized in that: In the step (1), each of the selected alloy raw materials is an industrial grade pure raw material with a purity of 99.9wt%.

3. A Cr-Fe-Mn-Ni-Al system high specific strength multi-scale structure high entropy alloy as claimed in claim 1, characterized in that: In the step (3), add a current of 300-400A for melting, hold for one minute, then turn over and melt again, hold for at least one minute each time, and repeat the melting five to six times.

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