Method for improving room temperature tensile ductility of refractory high-entropy alloys

Abstract

The application is a method for improving the room temperature tensile plasticity of a refractory high-entropy alloy, the refractory high-entropy alloy being a cast AlCrNbMoTaTiHf alloy, the method first preliminarily obtaining a good room temperature plasticity AlCrNbMoTaTiHf refractory high-entropy alloy composition by adjusting the component ratio, and then further improving the room temperature tensile plasticity of the cast refractory high-entropy alloy by a hot isostatic pressing and heat treatment synchronous processing method, the technical scheme of the application provides a new path for improving the room temperature tensile plasticity of the cast refractory high-entropy alloy by reasonable component design and matched hot isostatic pressing and heat treatment synchronous processing, the technical scheme of the application has a short process flow, high production efficiency, and is suitable for high-entropy alloy components directly formed in a cast state.

Description

TECHNICAL FIELD

[0001] The application is a method for improving the room temperature tensile plasticity of a refractory high-entropy alloy, the refractory high-entropy alloy being a cast AlCrNbMoTaTiHf alloy, and belongs to the technical field of metal materials. BACKGROUND

[0002] Refractory high-entropy alloys composed of refractory elements have excellent high-temperature performance and other advantages, and are extremely potential new high-temperature metal materials, but the refractory high-entropy alloys are typically BCC crystal structures, and generally have the problem of insufficient room temperature plasticity. The AlCrNbMoTaTiHf high-entropy alloy is an important high-temperature structural material among the refractory high-entropy alloys, and can be used in aerospace high-temperature parts in the future as a casting, and, similar to other refractory high-entropy alloys, also has the problem of insufficient room temperature plasticity.

[0003] At present, the problem of insufficient room temperature plasticity of refractory high-entropy alloys is mainly solved by alloy composition control. In addition to composition control, plastic deformation and heat treatment are also important ways to improve the room temperature tensile plasticity of refractory high-entropy alloys, but the above measures cannot effectively improve the room temperature tensile plasticity of cast refractory high-entropy alloys. SUMMARY

[0004] The application provides a method for improving the room temperature tensile plasticity of a refractory high-entropy alloy, the refractory high-entropy alloy being a cast AlCrNbMoTaTiHf alloy. The method first preliminarily obtains an AlCrNbMoTaTiHf refractory high-entropy alloy composition with relatively good room temperature plasticity by adjusting the component ratio, and then further improves the room temperature tensile plasticity of the cast refractory high-entropy alloy by a method of synchronous heat isostatic pressing and heat treatment.

[0005] To achieve the above object, the technical scheme of the application is as follows:

[0006] The method for improving the room temperature tensile plasticity of a refractory high-entropy alloy according to the application is aimed at a cast AlCrNbMoTaTiHf alloy, and the molar expression of the AlCrNbMoTaTiHf alloy is Al a Cr b Nb c Mo d Ta e Ti f Hf g , wherein a = 2-8, b = 2-6, c = 18-28, d = 4-9, e = 6-14, f = 30-40, and g >= 15, 8 < a + b + d < 16, and a + b + c + d + e + f + g = 100.

[0007] The technical scheme of the present application firstly obtains an AlCrNbMoTaTiHf refractory high-entropy alloy composition with good room temperature plasticity by adjusting the component ratio, and the determination process of the alloy composition is described as follows:

[0008] The previous study found that when the content of Al element in the AlCrNbMoTaTiHf refractory high-entropy alloy is more than 8at%, the Al element will cause the lattice distortion of the alloy to increase, and is easy to precipitate the brittle phase A2, which will cause the room temperature / high temperature plasticity of the high-entropy alloy to decrease obviously, especially the room temperature tensile plasticity is as low as less than 0.5%, but in order to ensure that the high-entropy alloy has a certain oxidation resistance, the content of Al element is finally determined to be 2-8at%.

[0009] When the content of Cr element in the high-entropy alloy is more than 6at%, the volume fraction of Laves phase in the alloy is more than 25%, and the aggregation into sheet causes the deformation coordination ability of the alloy with the matrix to be poor, the room temperature tensile plasticity of the high-entropy alloy is less than 2%, in order to ensure that the high-entropy alloy has a certain oxidation resistance, the content of Cr element is finally determined to be 2-6at%.

[0010] When the content of Mo element in the high-entropy alloy is more than 9at%, the lattice distortion strengthening effect of Mo element is too large, which causes the room temperature continuous deformation ability of the matrix to decrease sharply, resulting in the room temperature tensile plasticity of the high-entropy alloy being less than 4%; although the decrease of Mo content can improve the room temperature plasticity of the alloy, when the content of Mo is less than 4at%, the lattice distortion strengthening effect of Mo element is not obvious, which causes the room temperature strength of the high-entropy alloy to be lower than 948MPa, so the content of Mo is finally determined to be 4-9at%.

[0011] The previous study also found that if the contents of Al, Cr and Mo are all at the upper limit (the content of Al is 8at%, the content of Cr is 6at%, and the content of Mo is 9at%), the lattice distortion effect caused by the synergistic effect of the three elements is stronger, which causes the room temperature tensile plasticity of the refractory high-entropy alloy to be less than 5%. Further research and verification through multiple experiments found that when the total content of Al, Cr and Mo is not higher than 16at%, the refractory high-entropy alloy can have good room temperature tensile plasticity, and the average value is not less than 10%.

[0012] The effect of Hf element on the room temperature tensile plasticity of AlCrNbMoTaTiHf refractory high-entropy alloy is also very significant. Previous studies have found that when the content of Hf element is less than 15at%, the room temperature tensile plasticity of the high-entropy alloy is significantly reduced, and the elongation is less than 5%. On the contrary, when the content of Hf element is not less than 15at%, a high-melting-point white Hf-rich phase is precipitated in the high-entropy alloy matrix. This precipitated phase can effectively disperse the stress concentration in the BCC matrix during room temperature tensile deformation, enhance the deformation coordination, and thus significantly improve the room temperature tensile plasticity of the high-entropy alloy. Therefore, the content of Hf element in the refractory high-entropy alloy should be not less than 15at%.

[0013] The technical scheme of the present application is directed to the preparation process of the AlCrNbMoTaTiHf alloy, which includes simultaneous hot isostatic pressing and heat treatment. The process steps are as follows:

[0014] Step one: According to the molar expression of the AlCrNbMoTaTiHf alloy, the molar percentage of each component is converted to weight percentage. The elemental metals Al, Cr, Nb, Mo, Ta, Ti and Hf are weighed, and the electromagnetic suspension melting furnace is used to melt the metal raw materials to obtain a high-entropy alloy ingot. Then the alloy ingot is subjected to 3-6 times of turnover melting and slowly cooled to obtain a as-cast AlCrNbMoTaTiHf high-entropy alloy ingot.

[0015] Step two: The as-cast AlCrNbMoTaTiHf high-entropy alloy ingot prepared in step one is placed in a hot isostatic pressing device. First, it is heated to 600-800℃ and held for 2-4h. Then it is heated to 1160-1250℃ with temperature and pressure rising, and hot isostatic pressing is performed at a pressure not less than 100MPa, and held for 1-2h.

[0016] Step three: After that, the heating is stopped under pressure, and the as-cast AlCrNbMoTaTiHf high-entropy alloy ingot is slowly cooled to 1000-1050℃ with the furnace, then the pressure is released and quickly cooled to room temperature.

[0017] Further, the purity of the elemental metals Al, Cr, Nb, Mo, Ta, Ti and Hf in step one is greater than 99.9%.

[0018] Further, the pressure range of the hot isostatic pressing in step two is 120-180MPa.

[0019] Further, the slow cooling rate of the furnace in step three is 60-100℃ / h.

[0020] The AlCrNbMoTaTiHf high-entropy alloy has good material properties of room temperature tensile plasticity after alloy component optimization and experimental verification. However, the as-cast refractory high-entropy alloy ingot has internal casting defects, and the casting defects are easy to be used as crack sources to cause the premature fracture of the sample in the room temperature tensile process. Moreover, the size of the high-entropy alloy ingot for experimental verification is small, and the size of the high-entropy alloy ingot for engineering is large, which inevitably leads to the increase of the number of internal defects of the ingot, the increase of the volume of internal defects in some regions, and the increase of the dispersion degree of the room temperature tensile plasticity data of the large-size ingot. The hot isostatic pressing technology can close the internal defects of the as-cast refractory high-entropy alloy to the maximum extent, prevent the premature fracture of the sample, and reduce the dispersion degree of the tensile plasticity data through the three-way compressive stress under certain temperature, pressure and time.

[0021] In addition to the hot isostatic pressing technology, considering that the AlCrNbMoTaTiHf high-entropy alloy with good room temperature plasticity has the characteristics of low-melting-point phase and high-melting-point phase, it is also necessary to match the corresponding heat treatment, that is, to dissolve the low-melting-point phase at a low temperature + to dissolve the high-melting-point phase at a high temperature which is 10-20 DEG C higher than the high-melting-point phase, and then to precipitate relatively coarse high-melting-point Hf-rich phase through slow cooling after high-temperature heat treatment. Only through the matching hot isostatic pressing + heat treatment process, the maximum potential of the room temperature tensile of the as-cast AlCrNbMoTaTiHf high-entropy alloy material can be realized, and the expected effect of the alloy component design optimization can be achieved.

[0022] The present application synchronously processes the hot isostatic pressing and the heat treatment, which can not only ensure the corresponding heat treatment of the refractory high-entropy alloy, but also effectively close the internal defects of the as-cast high-entropy alloy, and can greatly improve the room temperature tensile plasticity of the as-cast high-entropy alloy. The early experimental results show that the room temperature tensile plasticity of the AlCrNbMoTaTiHf high-entropy alloy after melting and casting is 11.8%, and the room temperature tensile plasticity of the high-entropy alloy of this composition after synchronous processing of the hot isostatic pressing and the heat treatment is 15.9%, which shows that the room temperature tensile plasticity is increased by 34.7% after synchronous processing of the hot isostatic pressing and the heat treatment.

[0023] In addition, the synchronous processing process of the hot isostatic pressing and the heat treatment has a short process flow, high production efficiency and low energy consumption cost, and provides a new path for further improving the room temperature tensile plasticity of the as-cast AlCrNbMoTaTiHf high-entropy alloy.

[0024] The beneficial technical effects of the technical scheme of the present application can be summarized as follows:

[0025] I. The present application controls the content of Cr element to reduce the precipitation amount of harmful phase Laves in the matrix, controls the content of Al and Mo to improve the continuous deformation ability of the matrix at room temperature, and increases the content of Hf element to increase the content of beneficial Hf-rich phase to enhance deformation coordination, thereby improving the room temperature tensile plasticity of the as-cast AlCrNbMoTaTiHf refractory high-entropy alloy.

[0026] II. The present application uses the method of synchronous processing of hot isostatic pressing and heat treatment to maximize the closure of internal defects of the as-cast refractory high-entropy alloy, and also increases the beneficial Hf-rich phase through low-temperature + high-temperature two-stage dissolution and slow cooling heat treatment, thereby improving the room temperature tensile plasticity of the as-cast high-entropy alloy. The process method has a short process flow, high production efficiency, and low energy consumption cost, and provides a new path for further improving the room temperature tensile plasticity of the as-cast AlCrNbMoTaTiHf high-entropy alloy.

[0027] III. The method of the present application is also applicable to improving the room temperature tensile plasticity of other as-cast refractory high-entropy alloy systems, and the synchronous processing method of hot isostatic pressing and heat treatment is also applicable to improving the room temperature tensile plasticity of other laser additive refractory high-entropy alloy systems. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The room temperature tensile curve of the as-cast Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 refractory high-entropy alloy in Example 1.

[0029] Figure 2 The room temperature tensile curve of the as-cast Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21 refractory high-entropy alloy in Example 2.

[0030] Figure 3 The room temperature tensile curve of the as-cast Al4Cr3Nb 24 Mo6Ta8Ti 37 Hf 18 refractory high-entropy alloy in Example 3.

[0031] Figure 4 The room temperature tensile curve of the as-cast Al4Cr2Nb 24 Mo5Ta8Ti 35 Hf 22 refractory high-entropy alloy in Example 4. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be further described below in combination with the drawings and examples:

[0033] Example 1

[0034] The process steps for preparing the as-cast AlCrNbMoTaTiHf refractory high-entropy alloy with high room-temperature tensile plasticity according to the technical scheme of the present application are as follows:

[0035] Step 1: The molar expression of the as-cast refractory high-entropy alloy in this example is Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 According to the molar expression, the weight percentages of each component are: Al 1.4%, Cr 1.1%, Nb 21.7%, Mo 5.8%, Ta 16.6%, Ti 17.1%, and Hf 36.3%. The impurities on the surfaces of the metal elements Al, Cr, Nb, Mo, Ta, Ti, and Hf are removed, and the metal elements are cleaned with acetone by ultrasonic cleaning and then taken out for drying;

[0036] Step 2: The weighed metal elements are placed in an electromagnetic levitation melting furnace, vacuumed to 2.5×10 -3 Pa, and then high-purity argon is filled for melting. After the metal raw materials are melted, a refractory high-entropy alloy ingot is obtained. Then, each alloy ingot is subjected to 4 times of overturning melting and slow cooling, and finally an as-cast Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 refractory high-entropy alloy ingot is obtained.

[0037] Step 3: The as-cast Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 refractory high-entropy alloy ingot is placed in a hot isostatic pressing device, and first heated to 780℃ with the furnace, and then heated and pressurized to 1180℃ and 150MPa for hot isostatic pressing treatment, and then held for 2h.

[0038] Step 4: After that, the heating is stopped under pressure, and the as-cast Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 refractory high-entropy alloy ingot is slowly cooled to 1020℃ at a rate of 100℃ / h with the furnace, and then depressurized and rapidly cooled to room temperature.

[0039] Tensile samples are cut from the as-cast Al5Cr2Nb 23 Mo6Ta9Ti 35 Hf 20 refractory high-entropy alloy ingot prepared in this example, and room-temperature tensile property tests are performed using a universal tensile testing machine, and the results are as follows: Figure 1The as-cast refractory high-entropy alloy has a room temperature tensile elongation of 23.5%, indicating that the alloy has good room temperature tensile plasticity.

[0040] Example 2

[0041] The process steps for preparing the as-cast AlCrNbMoTaTiHf refractory high-entropy alloy with high room temperature tensile plasticity according to the technical scheme of the present application are as follows:

[0042] Step one, the molar expression of the as-cast refractory high-entropy alloy in this embodiment is Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21 According to the molar expression, the weight percentage of each component is: Al 1.7%, Cr 1.1%, Nb 21.0%, Mo 4.9%, Ta 14.9%, Ti 17.8%, and Hf 38.6%. The impurities on the surface of the metal elements Al, Cr, Nb, Mo, Ta, Ti, and Hf raw materials are removed, and the raw materials are cleaned with acetone ultrasonic cleaning and then taken out for drying;

[0043] Step two, the weighed metal elements are placed in an electromagnetic levitation melting furnace, vacuumed to 2.5x10 -3 Pa, and then high-purity argon is filled for melting. After the metal raw materials are melted, a refractory high-entropy alloy ingot is obtained. Then, each alloy ingot is subjected to 3 times of overturning melting and slow cooling, and finally an as-cast Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21 refractory high-entropy alloy ingot is obtained.

[0044] Step three, the as-cast Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21 refractory high-entropy alloy ingot is placed in a hot isostatic pressing device, and first heated to 750℃ with the furnace, and then heated and pressurized to 1205℃ and 140MPa for hot isostatic pressing treatment, and then held for 1.5h.

[0045] Step four, then stop heating under pressure, and slowly cool the as-cast Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21 refractory high-entropy alloy ingot to 1000℃ at a rate of 60℃ / h with the furnace, and then depressurize and quickly cool to room temperature.

[0046] The as-cast Al6Cr2Nb 22 Mo5Ta8Ti 36 Hf 21Tensile samples were cut from the refractory high-entropy alloy ingot, and room temperature tensile property test was carried out by using a universal tensile testing machine, and the results are shown in Table 1. Figure 2 The room temperature tensile elongation of the as-cast refractory high-entropy alloy is 17.7%, indicating that the alloy has good room temperature tensile plasticity.

[0047] Example 3

[0048] The process steps for preparing the as-cast AlCrNbMoTaTiHf refractory high-entropy alloy with high room temperature tensile plasticity according to the technical scheme of the present application are as follows:

[0049] Step 1: The molar expression of the as-cast refractory high-entropy alloy in this embodiment is Al4Cr3Nb 24 Mo6Ta8Ti 37 Hf 18 According to the molar expression, the weight percentage of each component is: Al 1.1%, Cr 1.6%, Nb 23.5%, Mo 6.1%, Ta 15.2%, Ti 18.7%, and Hf 33.8%. The impurities on the surface of the metal elements Al, Cr, Nb, Mo, Ta, Ti, and Hf are removed, and the metal elements are cleaned with acetone by ultrasonic wave and then taken out for drying;

[0050] Step 2: The weighed metal elements are placed in an electromagnetic levitation melting furnace, vacuumized to 2.5x10 -3 Pa, and then high-purity argon is filled for melting. After the metal raw materials are melted, a refractory high-entropy alloy ingot is obtained. Then, each alloy ingot is subjected to 5 times of overturning melting and slow cooling, and finally an as-cast Al4Cr3Nb 24 Mo6Ta8Ti 37 Hf 18 refractory high-entropy alloy ingot is obtained.

[0051] Step 3: The as-cast Al4Cr3Nb 24 Mo6Ta8Ti 37 Hf 18 refractory high-entropy alloy ingot is placed in a hot isostatic pressing device, and first heated to 680℃ with the furnace, and then heated and pressurized to 1190℃ and 160MPa for hot isostatic pressing treatment, and then held for 1.5h.

[0052] Step 4: Then stop heating under pressure, and slowly cool the as-cast Al4Cr3Nb 24 Mo6Ta8Ti 37 Hf 18 refractory high-entropy alloy ingot to 1050℃ at a rate of 90℃ / h with the furnace, and then depressurize and quickly cool to room temperature.

[0053] The as-cast Al4Cr3Nb24 Mo6Ta8Ti 37 Hf 18 The tensile sample was cut from the refractory high-entropy alloy ingot, and the room temperature tensile property test was carried out by using a universal tensile testing machine, and the results are shown in Figure 3 The room temperature tensile elongation of the as-cast refractory high-entropy alloy is 20.4%, indicating that the alloy has good room temperature tensile plasticity.

[0054] Example 4

[0055] The process steps for preparing the as-cast AlCrNbMoTaTiHf refractory high-entropy alloy with high room temperature tensile plasticity according to the technical scheme of the present application are as follows:

[0056] Step one, the molar expression of the as-cast refractory high-entropy alloy in this embodiment is Al4Cr2Nb 24 Mo5Ta8Ti 35 Hf 22 According to the molar expression, the weight percentage of each component is: Al 1.1%, Cr 1.0%, Nb 22.4%, Mo 4.8%, Ta 14.5%, Ti 16.8%, Hf 39.4%; remove the impurities on the surface of the metal elements Al, Cr, Nb, Mo, Ta, Ti and Hf raw materials, and use acetone ultrasonic cleaning, and take out for drying;

[0057] Step two, put the weighed metal elements into the electromagnetic suspension melting furnace, vacuumize to 2.5x10 -3 Pa, then fill high-purity argon for melting, and then get the refractory high-entropy alloy ingot after the metal raw materials are melted, then perform 3 times of overturning melting and slow cooling for each alloy ingot, and finally get the as-cast Al4Cr2Nb 24 Mo5Ta8Ti 35 Hf 22 refractory high-entropy alloy ingot;

[0058] Step three, place the as-cast Al4Cr2Nb 24 Mo5Ta8Ti 35 Hf 22 refractory high-entropy alloy ingot in the hot isostatic pressing equipment, first heat it to 700℃ with the furnace, keep it for 3h, then heat it to 1220℃ and press it to 180MPa with the furnace in the way of heating and pressurizing, and keep it for 1h;

[0059] Step four, then stop heating under the pressure state, cool the as-cast Al4Cr2Nb 24 Mo5Ta8Ti 35 Hf 22 refractory high-entropy alloy ingot to 1010℃ with the furnace at a speed of 80℃ / h, then release the pressure and cool it to room temperature quickly.

[0060] The as-cast Al4Cr2Nb prepared in this embodiment 24 Mo5Ta8Ti 35 Hf 22 Tensile specimens were cut from refractory high-entropy alloy ingots, and their room temperature tensile properties were tested using a universal tensile testing machine. The results are as follows: Figure 4 As shown, the room temperature tensile elongation of this as-cast refractory high-entropy alloy is 24.1%, indicating that the alloy has good room temperature tensile plasticity.

Claims

1. A method for improving the tensile ductility at room temperature of a refractory high-entropy alloy, the refractory high-entropy alloy being a cast AlCrNbMoTaTiHf alloy, characterized in that: The molar expression of the AlCrNbMoTaTiHf alloy is Al a Cr b Nb c Mo d Ta e Ti f Hf g wherein: a = 2-8, b = 2-6, c = 18-28, d = 4-9, e = 6-14, f = 30-40, g ≥ 15, 8 < a + b + d < 16, a + b + c + d + e + f + g = 100. The preparation process of the AlCrNbMoTaTiHf alloy includes hot isostatic pressing and heat treatment simultaneously, and the process steps are as follows: Step one, according to the mole expression of the AlCrNbMoTaTiHf alloy, the mole percentage of each component is converted into the weight percentage, the metal elements Al, Cr, Nb, Mo, Ta, Ti and Hf are weighed, the electromagnetic suspension melting furnace is used to melt the metal raw materials to obtain the high-entropy alloy ingot, then the alloy ingot is subjected to 3-6 times of turnover smelting and slowly cooled to obtain the as-cast AlCrNbMoTaTiHf high-entropy alloy ingot; Step two, the as-cast AlCrNbMoTaTiHf high-entropy alloy ingot prepared in step one is placed in a hot isostatic pressing device, first heated to 600-800 DEG C, and then heated to 1160-1250 DEG C at a temperature and pressure rising mode, and then hot isostatic pressing is carried out at a pressure of not less than 100 MPa, and then heat preservation for 1-2 h; Step three, then stop heating in the pressure maintaining state, slowly cool the as-cast AlCrNbMoTaTiHf high-entropy alloy ingot to 1000-1050 DEG C, then unload the pressure and quickly cool to room temperature.

2. The method of claim 1, wherein the refractory high-entropy alloy has a room temperature tensile ductility of at least 5%. The purity of the metal elements Al, Cr, Nb, Mo, Ta, Ti and Hf in step one is greater than 99.9%.

3. The method of claim 1, wherein the refractory high-entropy alloy has a room temperature tensile ductility of at least 5%. The pressure range of the hot isostatic pressing in step two is 120-180 MPa.

4. The method of claim 1, wherein the refractory high-entropy alloy has a room temperature tensile ductility of at least 10%. The slow cooling rate of the furnace in step three is 60-100 DEG C / h.

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