High-hardness corrosion-resistant light refractory high-entropy alloy and preparation method thereof

Abstract

The invention relates to the technical field of light refractory high-entropy alloys, in particular to a high-hardness corrosion-resistant light refractory high-entropy alloy and a preparation method thereof. The alloy is prepared by the method. The method comprises the following steps: sequentially putting the raw material components with required mass percentages into a crucible according to a sequence from low melting points to high melting points; the crucible is put into a smelting furnace in which air is exhausted to be smelted, and inert gas is introduced during smelting; after smelting, cooling to obtain a cast ingot; and after the cast ingot is turned over, the cast ingot is repeatedly smelted for 4-7 times, and the alloy is obtained. The alloy prepared by the invention has high hardness, corrosion resistance and light weight.

Description

Technical Field

[0001] The present invention relates to the technical field of lightweight refractory high-entropy alloys, and specifically relates to a high-hardness, corrosion-resistant lightweight refractory high-entropy alloy and a preparation method thereof. Background Art

[0002] Refractory high-entropy alloys are a class of high-density alloys formed by four or more main refractory elements, and their relatively high density (generally higher than 9.9 g / cm 3 ) severely restricts the application scope of the alloys. Lightweight refractory high-entropy alloys, on the basis of traditional refractory high-entropy alloys, use light elements such as Al, Ti, and Zr to replace high-density elements such as Ta, W, and Re, and have the characteristics of low density, high hardness, corrosion resistance, and high temperature resistance, and have important application values in aerospace turbine engines and marine navigation gas turbines, etc.

[0003] However, there is a significant restrictive relationship between the hardness and corrosion resistance of lightweight refractory high-entropy alloys. By adding a large amount of Al and Ti, the density of the alloy can be significantly reduced, and there is an extremely low mixing enthalpy (-44 KJ / mol and -30 KJ / mol) between Al and Zr, and between Al and Ti. Compounds such as Zr5Al3 and AlTi are easily formed in lightweight refractory high-entropy alloys. These compound phases are usually hard and brittle phases, which are effective ways to improve the strength and hardness of lightweight refractory high-entropy alloys. However, in corrosive solutions, the main corrosion failure mode of multiphase alloys is pitting corrosion at the phase interface, and the presence of intermediate compound phases (such as Zr5Al3 and AlTi) will induce serious pitting corrosion phenomena, thereby reducing the corrosion resistance of lightweight refractory high-entropy alloys.

[0004] Therefore, in order to better meet the corrosion resistance requirements of marine gas turbines in a marine corrosion environment, it is necessary to develop a high-hardness, corrosion-resistant lightweight refractory high-entropy alloy and a preparation method thereof to solve the problem that the corrosion resistance of lightweight refractory high-entropy alloys in the prior art decreases due to the presence of intermediate compound phases (such as Zr5Al3 and AlTi), and at the same time have relatively high hardness. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-hardness, corrosion-resistant lightweight refractory high-entropy alloy and a preparation method thereof. The specific technical solutions are as follows: In the first aspect, the present invention provides a high-hardness, corrosion-resistant lightweight refractory high-entropy alloy, which is composed of the following raw material components in mass percentages: Al 3% - 9%, Nb 32% - 43%, Ti 15% - 26%, V 1% - 4%, Cr 15% - 18%, and Mo 12% - 19%.

[0006] Optionally, the alloy is composed of the following raw material components by mass percentage: Al 3% - 4%, Nb 32% - 33%, Ti 25% - 26%, V 3% - 4%, Cr 16% - 17%, and Mo 18% - 19%.

[0007] Optionally, each of the raw material components is a metal single - crystal particle with a purity higher than 99.95%.

[0008] Optionally, the alloy is an amorphous body - centered cubic solid - solution single - phase structure.

[0009] Optionally, the hardness of the alloy is above 500 HV.

[0010] Optionally, the pitting corrosion resistance voltage of the alloy in a 3.5% NaCl solution by mass percentage is higher than 2.0 V.

[0011] In a second aspect, the present invention provides a method for preparing the high - hardness, corrosion - resistant, lightweight, refractory high - entropy alloy as described above, which includes: Step S1: Place each of the required raw material components in a crucible in ascending order of melting point from bottom to top. Step S2: Place the crucible in a melting furnace from which air has been exhausted, and introduce an inert gas during melting. Step S3: After melting, obtain an ingot through cooling; after turning the ingot over, repeat Step S2 to melt the ingot 4 - 7 times to obtain the alloy; wherein, the ingot needs to be turned over before each repeated melting.

[0012] Optionally, in Step S2, a vacuum pump is used to exhaust the air in the melting furnace, and the vacuum is controlled to be 4×10 -3 ~6×10 -3 Pa.

[0013] Optionally, the inert gas includes argon; the purity of the argon is 99.99%; the pressure of the inert gas in the melting furnace is 0.04 - 0.06 MPa.

[0014] Optionally, the melting furnace includes a vacuum arc melting furnace; during melting, the melting temperature is 2300 - 2800 °C, and the melting time is 5 - 10 min.

[0015] Applying the technical solution of the present invention has at least the following beneficial effects: (1) A high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy provided by the present invention has high-hardness, corrosion-resistant, and lightweight properties. Specifically, the present invention uses three elements with corrosion-resistant properties, namely Al, Nb, and Ti, and by adjusting the mass percentage contents of Al, Nb, and Ti, the mixing enthalpy of the alloy is controlled between -13.7 KJ / mol and -8.3 KJ / mol. A higher mixing enthalpy value can inhibit the formation of intermetallic compound phases, enabling the alloy to maintain a single disordered body-centered cubic solid solution single-phase structure, that is, the BCC_A2 structure, thereby avoiding pitting corrosion at the phase interfaces between different phases and effectively improving the corrosion resistance of the alloy. In addition, the atomic radii of Nb elements differ significantly from those of Al and Ti elements. By increasing the content of Al elements, the proportion of Al elements with smaller atomic radii in the lattice points of the alloy is increased, significantly intensifying lattice distortion, thereby enhancing the solid solution strengthening effect and improving the hardness of the alloy. In addition, a large amount of low-density Al and Ti elements are used in the alloy, making the density of the alloy between 6.42 and 6.53 g / cm 3 , much lower than that of traditional refractory high-entropy alloys (density ≥ 9.9 g / cm 3 ), breaking through the application limitations of lightweight refractory high-entropy alloys.

[0016] (2) A preparation method of a high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy provided by the present invention uses step S1 to sequentially place each raw material component from bottom to top into the crucible in ascending order of melting point, which is used to ensure that after the crucible is placed in the melting furnace, with the heat source in the melting furnace above the crucible as the reference point, each raw material component approaches the heat source in descending order of melting point, which helps each raw material component to be fully melted; step S2 is used to evacuate the air in the melting furnace and introduce an inert gas during melting, which is used to prevent the alloy from being oxidized during melting and resulting in impurity compound phases, thereby reducing the corrosion resistance of the alloy; step S3 is used to repeat melting to ensure sufficient melting and obtain an alloy with the BCC_A2 structure.

[0017] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings to further elaborate on the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 is the X-ray diffraction pattern of the alloy obtained in Examples 1 to 3; Figure 2 is the microscopic structure diagram of the alloy obtained in Example 1; Figure 3It is the microstructure diagram of the alloy obtained in Example 2; Figure 4 It is the microstructure diagram of the alloy obtained in Example 3; Figure 5 It is the electrochemical polarization curve of the alloys obtained in Examples 1 - 3 in a 3.5% NaCl solution by mass percentage. Specific Embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0020] Example 1: A high - hardness, corrosion - resistant, lightweight and refractory high - entropy alloy, and its preparation method is as follows: Step S1: Weigh each of the raw material components with the required mass percentages, and place them in the crucible from bottom to top in ascending order of melting point to ensure that after the crucible is placed in the melting furnace, with the heat source in the melting furnace above the crucible as the reference point, each raw material component approaches the heat source in descending order of melting point, which helps the raw material components to be fully melted; among them, the mass percentages of each raw material component are: Al 8.8%, Nb 42.6%, Ti 15.7%, V 3.3%, Cr 17% and Mo 12.6%; each raw material component is a metal single - element particle with a purity higher than 99.95%; when weighing, the mass error of each raw material component is within ±0.1 g; Step S2: Place the crucible in a melting furnace with air exhausted, and introduce an inert gas during melting; Step S3: After melting, cool it with a water - cooled copper mold to obtain a button - shaped ingot; after turning the ingot over, repeat Step S2 to melt the ingot 5 times to obtain the alloy; among them, the ingot needs to be turned over before each repeated melting.

[0021] In Step S2, a vacuum pump is used to exhaust the air in the melting furnace, and the vacuum is controlled to 5×10 -3 Pa.

[0022] The inert gas is argon; the purity of the argon is 99.99%; the pressure of the inert gas in the melting furnace is 0.05 MPa.

[0023] The melting furnace is a vacuum arc melting furnace; during melting, the melting temperature used is 2450 ± 50 °C, and the melting time is 6 min.

[0024] Example 2: Differing from Example 1, the mass percentages of the respective raw material components are as follows: Al 6.1%, Nb 33.2%, Ti 23.3%, V 1.7%, Cr 16.9%, and Mo 18.8%.

[0025] Example 3: Differing from Example 1, the mass percentages of the respective raw material components are as follows: Al 3.4%, Nb 32.5%, Ti 25.9%, V 3.2%, Cr 16.6%, and Mo 18.4%.

[0026] Comparative Example 1: Differing from Example 1, the mass percentages of the respective raw material components are as follows: Al 1.7%, Nb 29.6%, Ti 30.5%, V 3.2%, Cr 16.6%, and Mo 18.4%.

[0027] Comparative Example 2: Differing from Example 1, the mass percentages of the respective raw material components are as follows: Nb 26.3%, Ti 13.5%, V 14.4%, Cr 9.2%, Mo 20.4%, and Zr 16.2%.

[0028] Comparative Example 3: Differing from Example 1, the air in the melting furnace was not evacuated using a vacuum pump, and no inert gas was introduced.

[0029] Comparative Example 4: Differing from Example 1, the melting was repeated 3 times.

[0030] The phase analysis of the alloys obtained in Examples 1 to 3 was carried out using an Advance D8 X-ray diffractometer, with a Cu Kα radiation source, an accelerating voltage of 0 KV, a current of 40 mA, a diffraction angle range of 20° to 100°, and a scanning speed of minutes. The results are as Figure 1 shown.

[0031] It can be Figure 1 seen that the characteristic diffraction peaks corresponding to the (110) crystal plane, (200) crystal plane, (211) crystal plane, and (220) crystal plane of the alloys obtained in Examples 1 to 3 indicate that the alloys obtained in Examples 1 to 3 are all disordered BCC_A2 single-phase structures.

[0032] Furthermore, a JXA-8530F electron probe microanalyzer was used to analyze the microstructures of the alloys obtained in Examples 1 to 3. From Figures 2 to 4It can be seen that the alloys obtained in Examples 1 to 3 formed an obvious dendritic structure, but no precipitation phase appeared. This indicates that the alloys obtained in Examples 1 to 3 are single-phase structures. Combining with Figure 1 it is known that this single-phase structure is a disordered BCC_A2 single-phase structure.

[0033] Furthermore, the alloys obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were sampled respectively for density, hardness and corrosion resistance tests. The test results are shown in Table 1. Among them, the density test method is as follows: The density was measured by the Archimedes method at 25 °C with water as the immersion medium. The hardness test method is as follows: The hardness of the alloy was measured on the polished surface using a Vickers hardness tester with a load of 500 g and a holding time of 15 s. Five points were tested for each specimen to calculate the average hardness. The corrosion resistance test method is as follows: The electrochemical characteristics of the alloy were measured using a Princeton Versa STAT 4 electrochemical workstation. The auxiliary electrode was a platinum plate, and the reference electrode was a saturated calomel electrode (SCE); A high-hardness, corrosion-resistant, lightweight and refractory high-entropy alloy specimen with a size of 10×10×3 mm was cut as the working electrode, and the surface of the specimen was polished with sandpaper. The polarization voltage and current density of the specimen were measured in a 3.5% mass percentage NaCl solution, the scanning rate was set at 1 mV / s, starting from the initial potential of -1.0 V until the current density reached 0.01 A / cm 2 ends. Figure 5 is the electrochemical polarization curve of the alloy specimens obtained in Examples 1 to 3.

[0034] Table 1 Test results of density, hardness and corrosion resistance

[0035] From the data in Table 1, it can be seen that the alloys obtained in Examples 1 to 3 of the present invention have relatively high hardness and pitting voltage on the premise of having a relatively low density, showing lightweight, high-hardness and corrosion-resistant properties.

[0036] By comparing Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, the amount of Al was reduced and the amount of Ti was increased, resulting in a decrease in the hardness and pitting voltage of the alloy, while the density changed little. This is because reducing the amount of Al decreases the proportion of the Al element with a relatively small atomic radius in the lattice points, reduces the lattice distortion, thereby weakening the solid solution strengthening effect and reducing the hardness of the alloy; while a high amount of Ti is likely to form a second phase with Nb, Cr and Mo, and pitting occurs at the phase interface, resulting in a decrease in the pitting voltage. As for the little change in density, it is because both the Al element and the Ti element are lightweight elements, so the density of the alloy changes little when the amount of Al is reduced and the amount of Ti is increased.

[0037] By comparing Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, Al was not used, while Zr was increased, resulting in an increase in the alloy density and a decrease in the pitting potential, but having little effect on the hardness. This is because Al was not used and Zr was increased, resulting in the formation of the brittle second phase Cr2Zr in the alloy, reducing the corrosion resistance and causing the pitting potential to decrease, but having little effect on the hardness. The increase in density is because the density of Zr is greater than that of Al, resulting in an increase in the alloy density.

[0038] By comparing Example 1 and Comparative Example 3, it can be seen that in Comparative Example 3, the air in the melting furnace was not exhausted by a vacuum pump and no inert gas was introduced, resulting in a decrease in the pitting potential. This is because there are discontinuous oxides in the alloy, reducing the corrosion resistance and causing the pitting potential to decrease.

[0039] By comparing Example 1 and Comparative Example 4, it can be seen that too few melting times in Comparative Example 4 would lead to uneven melting of the raw material components and serious element segregation, resulting in a significant decrease in the alloy hardness and pitting potential.

[0040] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-hardness, corrosion-resistant, lightweight and refractory high-entropy alloy, characterized in that, It is composed of the following raw material components by mass percentage: Al 3% - 9%, Nb 32% - 43%, Ti 15% - 26%, V 1% - 4%, Cr 15% - 18% and Mo 12% - 19%.

2. The high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy according to claim 1, characterized in that, It is composed of the following raw material components by mass percentage: Al 3% - 4%, Nb 32% - 33%, Ti 25% - 26%, V 3% - 4%, Cr 16% - 17% and Mo 18% - 19%.

3. The high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy according to claim 1, wherein Each of the said raw material components is a metallic single - crystal particle with a purity higher than 99.95%.

4. The high-hardness, corrosion-resistant, lightweight and refractory high-entropy alloy according to claim 1, characterized in that, The said alloy is a disordered body - centered cubic solid - solution single - phase structure.

5. The high-hardness, corrosion-resistant, lightweight and refractory high-entropy alloy according to claim 1, wherein, The hardness of the said alloy is above 500HV.

6. The high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy according to claim 1, characterized in that, The pitting corrosion resistance voltage of the said alloy in a 3.5% NaCl solution by mass percentage is higher than 2.0V.

7. A method for preparing a high-hardness, corrosion-resistant, lightweight refractory high-entropy alloy according to any one of claims 1 to 6, characterized in that, It includes: Step S1: Put each of the said raw material components with the required mass percentage into a crucible in ascending order of melting point from bottom to top. Step S2: Put the crucible into a melting furnace with exhausted air for melting, and introduce an inert gas during melting. Step S3: After melting, obtain an ingot through cooling; after turning the ingot over, repeat Step S2 to melt the ingot 4 - 7 times to obtain the said alloy; among them, the ingot needs to be turned over before each repeated melting.

8. The preparation method according to claim 7, characterized in that, In the step S2, a vacuum pump is used to exhaust the air in the melting furnace, and the vacuum is controlled to be 4×10 -3 ~6×10 -3 Pa.

9. The preparation method according to claim 7, characterized in that The said inert gas includes argon; the purity of the argon is 99.99%; the pressure of the inert gas in the melting furnace is 0.04 - 0.06MPa.

10. The preparation method according to claim 7, characterized in that, The said melting furnace includes a vacuum arc melting furnace; during melting, the melting temperature adopted is 2300 - 2800°C, and the melting time is 5 - 10min.

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