A high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy and its preparation method

Abstract

The present invention relates to the technical field of lightweight, refractory, high-entropy alloys, and more specifically, to a highly hard, corrosion-resistant, lightweight, refractory high-entropy alloy and a method for preparing the same. The alloy is produced by this method. The method comprises placing the required mass percentages of the raw material components into a crucible in ascending order of melting point; placing the crucible into a fully air-exhausted smelting furnace for smelting while introducing an inert gas; cooling the smelting process to obtain an ingot; flipping the ingot over, and then repeating the smelting process 4 to 7 times to obtain the alloy. The alloy produced by the present invention exhibits high hardness, corrosion resistance, and lightweight properties.

Description

Technical Field

[0001] The present invention relates to the technical field of lightweight refractory high-entropy alloys, and in particular 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 type of high-density alloys formed by four or more main refractory elements. Their high density (generally higher than 9.9 g / cm 3 ) severely limits the alloy's application range. Lightweight refractory high-entropy alloys, based on traditional refractory high-entropy alloys, use lightweight elements such as Al, Ti, and Zr to replace high-density elements such as Ta, W, and Re. These alloys offer low density, high hardness, corrosion resistance, and high-temperature resistance, and have important applications in aerospace turbine engines and marine gas turbines.

[0003] However, there is a significant constraint between the hardness and corrosion resistance of lightweight refractory high-entropy alloys. The addition of large amounts of Al and Ti can significantly reduce the alloy's density. Furthermore, the extremely low mixing enthalpies between Al and Zr, and Al and Ti (-44 kJ / mol and -30 kJ / mol), facilitate the formation of compound phases such as Zr5Al3 and AlTi in lightweight refractory high-entropy alloys. These compound phases are typically hard and brittle, offering an effective approach to improving the strength and hardness of lightweight refractory high-entropy alloys. However, in corrosive solutions, the primary corrosion failure mode of multiphase alloys is pitting at the phase interface, and the presence of intermediate compound phases (such as Zr5Al3 and AlTi) can induce severe pitting, thereby reducing the corrosion resistance of lightweight refractory high-entropy alloys.

[0004] Therefore, in order to better meet the corrosion resistance requirements of ship gas turbines in marine corrosive environments, it is necessary to develop a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy and its preparation method to solve the problem of reduced corrosion resistance of lightweight refractory high-entropy alloys in the existing technology due to the presence of intermediate compound phases (such as Zr5Al3 and AlTi), while also having higher hardness. Summary of the Invention

[0005] The present invention aims to provide a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy and a preparation method thereof. The specific technical scheme is as follows:

[0006] In a first aspect, the present invention provides a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy composed of the following raw material components in the following mass percentages: Al 3%~9%, Nb 32%~43%, Ti 15%~26%, V 1%~4%, Cr 15%~18% and Mo 12%~19%.

[0007] Optionally, the alloy is composed of the following raw material components in the following mass percentages: Al 3%-4%, Nb 32%-33%, Ti 25%-26%, V 3%-4%, Cr 16%-17% and Mo 18%-19%.

[0008] Optionally, each of the raw material components is a metal element particle with a purity higher than 99.95%.

[0009] Optionally, the alloy has a disordered body-centered cubic solid solution single-phase structure.

[0010] Optionally, the hardness of the alloy is above 500 HV.

[0011] Optionally, the alloy has an anti-pitting corrosion voltage higher than 2.0 V in a 3.5% by mass NaCl solution.

[0012] In a second aspect, the present invention provides a method for preparing the high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy, comprising:

[0013] Step S1, placing the raw material components of the required mass percentage into a crucible from bottom to top in the order of melting point from low to high;

[0014] Step S2, placing the crucible into a melting furnace from which all air has been exhausted for melting, and introducing an inert gas during the melting;

[0015] Step S3: After smelting, cool the ingot to obtain an ingot; turn the ingot over, and repeat step S2 to smelt the ingot 4 to 7 times to obtain the alloy; wherein the ingot needs to be turned over before each repeated smelting.

[0016] Optionally, in step S2, a vacuum pump is used to exhaust the air in the smelting furnace, and the vacuum is controlled to 4×10 -3 ~6×10 -3 Pa.

[0017] Optionally, the inert gas includes argon; the purity of the argon is 99.99%; and the pressure of the inert gas in the smelting furnace is 0.04~0.06MPa.

[0018] Optionally, the smelting furnace includes a vacuum arc melting furnace; during smelting, the smelting temperature adopted is 2300~2800℃, and the smelting time is 5~10min.

[0019] The application of the technical solution of the present invention has at least the following beneficial effects:

[0020] (1) The present invention provides a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy with high hardness, corrosion-resistant and lightweight properties. Specifically, the present invention uses three elements with corrosion resistance, namely Al, Nb and Ti, and by regulating the mass percentage of Al, Nb and Ti, the mixing enthalpy of the alloy is controlled between -13.7 KJ / mol and -8.3 KJ / mol. The higher mixing enthalpy value can inhibit the formation of intermetallic compound phases, so that the alloy maintains a single disordered body-centered cubic solid solution single-phase structure, namely BCC_A2 structure, thereby avoiding pitting corrosion at the phase interface between different phases and effectively improving the corrosion resistance of the alloy. In addition, the atomic radius of the Nb element is quite different from that of the Al and Ti elements. By increasing the content of the Al element, the proportion of the Al element with a smaller atomic radius in the lattice lattice in the alloy is increased, which significantly aggravates the lattice distortion, thereby enhancing the solid solution strengthening effect and improving the hardness of the alloy. In addition, the present invention uses a large amount of low-density Al and Ti elements in the alloy, so that the density of the alloy is between 6.42 and 6.53 g / cm 3 , which is much lower than traditional refractory high entropy alloys (density ≥9.9 g / cm 3 ), breaking through the application limitations of lightweight refractory high-entropy alloys.

[0021] (2) The present invention provides a method for preparing a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy, which comprises placing the raw material components into a crucible from bottom to top in the order of melting point from low to high in step S1, so as to ensure that after the crucible is placed in a smelting furnace, the raw material components are positioned close to the heat source in the smelting furnace above the crucible as a base point in the order of melting point from high to low, which helps to fully melt the raw material components; exhausting the air from the smelting furnace in step S2, and introducing an inert gas during smelting, so as to avoid oxidation of the alloy during smelting and the formation of a mixed compound phase, thereby reducing the corrosion resistance of the alloy; and repeating the smelting in step S3 to ensure sufficient smelting to obtain a BCC_A2 structural alloy.

[0022] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 is the X-ray diffraction pattern of the alloy obtained in Examples 1 to 3;

[0025] Figure 2 is a microstructure diagram of the alloy obtained in Example 1;

[0026] Figure 3 is a microstructure diagram of the alloy obtained in Example 2;

[0027] Figure 4 is a microstructure diagram of the alloy obtained in Example 3;

[0028] Figure 5 1 is the electrochemical polarization curve of the alloy obtained in Examples 1 to 3 in a 3.5% by mass NaCl solution. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy, the preparation method of which is as follows:

[0032] Step S1: Weighing the required mass percentages of the raw material components and placing them into a crucible from bottom to top in descending order of melting point, to ensure that after the crucible is placed in a smelting furnace, the raw material components are positioned close to the heat source in the smelting furnace above the crucible, with the heat source located above the crucible as the base point, thereby facilitating sufficient melting of the raw material components. The mass percentages of the raw material components are: Al 8.8%, Nb 42.6%, Ti 15.7%, V 3.3%, Cr 17%, and Mo 12.6%. The raw material components are all metal elemental particles with a purity greater than 99.95%. When weighing, the mass error of each raw material component is within ±0.1g.

[0033] Step S2, placing the crucible into a melting furnace from which all air has been exhausted for melting, and introducing an inert gas during the melting;

[0034] Step S3: After smelting, the ingot is cooled in a water-cooled copper mold to obtain a button-shaped ingot; after turning the ingot over, repeating step S2 to smelt the ingot 5 times to obtain the alloy; wherein the ingot needs to be turned over before each repeated smelting.

[0035] In step S2, a vacuum pump is used to exhaust the air in the smelting furnace, and the vacuum is controlled to 5×10 -3 Pa.

[0036] The inert gas is argon; the purity of the argon is 99.99%; the pressure of the inert gas in the smelting furnace is 0.05 MPa.

[0037] The melting furnace is a vacuum arc melting furnace; during melting, the melting temperature adopted is 2450±50°C and the melting time is 6 minutes.

[0038] Example 2:

[0039] Different from Example 1, the mass percentages of the raw material components are: Al 6.1%, Nb 33.2%, Ti 23.3%, V 1.7%, Cr 16.9% and Mo 18.8%.

[0040] Example 3:

[0041] Different from Example 1, the mass percentages of the raw material components are: Al 3.4%, Nb 32.5%, Ti 25.9%, V 3.2%, Cr 16.6% and Mo 18.4%.

[0042] Comparative Example 1:

[0043] Different from Example 1, the mass percentages of the raw material components are: Al 1.7%, Nb 29.6%, Ti 30.5%, V 3.2%, Cr 16.6% and Mo 18.4%.

[0044] Comparative Example 2:

[0045] Different from Example 1, the mass percentages of the raw material components are: Nb 26.3%, Ti 13.5%, V 14.4%, Cr 9.2%, Mo 20.4% and Zr 16.2%.

[0046] Comparative Example 3:

[0047] Different from Example 1, no vacuum pump was used to exhaust the air in the smelting furnace, and no inert gas was introduced.

[0048] Comparative Example 4:

[0049] The difference from Example 1 is that the smelting is repeated 3 times.

[0050] The phase analysis of the alloys obtained in Examples 1 to 3 was performed using an Advance D8 X-ray diffractometer using 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 result is Figure 1 shown.

[0051] Depend on Figure 1It is known that the alloys obtained in Examples 1 to 3 have characteristic diffraction peaks corresponding to the (110) crystal plane, the (200) crystal plane, the (211) crystal plane and the (220) crystal plane, which indicates that the alloys obtained in Examples 1 to 3 are all disordered BCC_A2 single-phase structures.

[0052] Furthermore, the microstructure of the alloys obtained in Examples 1 to 3 was analyzed using a JXA-8530F electron probe microanalyzer. Figures 2 to 4 It can be seen that the alloys obtained in Examples 1 to 3 formed a clear dendrite structure, but no precipitation phase appeared. This shows that the alloys obtained in Examples 1 to 3 are single-phase structures. Figure 1 It is known that the single-phase structure is a disordered BCC_A2 single-phase structure.

[0053] Furthermore, samples of the alloys obtained in Examples 1-3 and Comparative Examples 1-4 were taken for density, hardness, and corrosion resistance testing. The test results are shown in Table 1. Density was measured using the Archimedean method at 25°C with water as the immersion medium. Hardness was measured using a Vickers hardness tester on the polished surface, with a load of 500 g and a hold time of 15 seconds. Five points on each sample were tested to calculate the average hardness. Corrosion resistance was measured using a Princeton Versa STAT 4 electrochemical workstation, using a platinum plate as the auxiliary electrode and a saturated calomel electrode (SCE) as the reference electrode. 10 × 10 × 3 mm specimens of the high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy were cut and used as the working electrode. The specimen surface was sanded and polished. The polarization voltage and current density of the specimens were measured in a 3.5% (mass) NaCl solution at a scan rate of 1 mV / s, starting from an initial potential of -1.0 V until the current density reached 0.01 A / cm2. 2 Finish. Figure 5 1 is the electrochemical polarization curve of the alloy samples obtained in Examples 1 to 3.

[0054] Table 1 Density, hardness and corrosion resistance test results

[0055]

[0056] From the data in Table 1, it can be seen that the alloys obtained in Examples 1 to 3 of the present invention have higher hardness and higher pitting voltage while having lower density, showing light weight, high hardness and corrosion resistance.

[0057] By comparing Example 1 and Comparative Example 1, it can be seen that reducing the Al content and increasing the Ti content in Comparative Example 1 reduces the alloy hardness and pitting voltage, while the density does not change much. This is because reducing the Al content reduces the proportion of Al, an element with a smaller atomic radius, in the lattice, reducing lattice distortion, thereby weakening the solid solution strengthening effect and reducing the alloy hardness. High Ti content, on the other hand, easily forms a second phase with Nb, Cr, and Mo, causing pitting at the phase interface, which reduces the pitting voltage. As for the small change in density, this is because both Al and Ti are lightweight elements, and reducing the Al content and increasing the Ti content results in little change in the alloy density.

[0058] Comparing Example 1 and Comparative Example 2 reveals that the addition of Zr, while omitting Al, increases the alloy density and decreases the pitting voltage, but has little effect on hardness. This is because the addition of Zr, while omitting Al, forms a brittle second phase of Cr2Zr in the alloy, reducing corrosion resistance and lowering the pitting voltage, but having little effect on hardness. The increased density is due to the Zr density being greater than that of Al, which increases the alloy density.

[0059] Comparison of Example 1 and Comparative Example 3 reveals that in Comparative Example 3, no vacuum pump was used to evacuate the air from the furnace, and no inert gas was introduced, resulting in a decrease in the pitting voltage. This is because the presence of discontinuous oxides in the alloy reduces corrosion resistance, leading to a decrease in the pitting voltage.

[0060] By comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, too few smelting times will lead to uneven smelting of raw material components and severe element segregation, resulting in a significant decrease in alloy hardness and pitting voltage.

[0061] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy, characterized in that: It is composed of the following raw material components in the following mass percentages: Al 3%~9%, Nb 32%~43%, Ti 15%~26%, V 1%~4%, Cr 15%~18% and Mo 12%~19%; The alloy has a disordered body-centered cubic solid solution single-phase structure; The preparation method of the high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy comprises: Step S1, placing the raw material components of the required mass percentage into a crucible from bottom to top in the order of melting point from low to high; Step S2: Place the crucible in a melting furnace that has been completely evacuated of air and introduce inert gas during smelting; exhaust the air in the melting furnace using a vacuum pump and control the vacuum to 4×10 -3 ~6×10 -3 Pa; Step S3: After smelting, cool the ingot to obtain an ingot; turn the ingot over, and repeat step S2 to smelt the ingot 4 to 7 times to obtain the alloy; wherein the ingot needs to be turned over before each repeated smelting.

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 in the following mass percentages: 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, characterized in that: Each of the raw material components is a metal element particle with a purity higher than 99.95%.

4. The high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy according to claim 1, characterized in that: The hardness of the alloy is above 500 HV.

5. The high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy according to claim 1, characterized in that: The alloy has an anti-pitting corrosion voltage higher than 2.0 V in a 3.5% by mass NaCl solution.

6. A method for preparing a high-hardness, corrosion-resistant, lightweight, refractory high-entropy alloy according to any one of claims 1 to 5, characterized in that: include: Step S1, placing the raw material components of the required mass percentage into a crucible from bottom to top in the order of melting point from low to high; Step S2: Place the crucible in a melting furnace that has been completely evacuated of air and introduce inert gas during smelting; exhaust the air in the melting furnace using a vacuum pump and control the vacuum to 4×10 -3 ~6×10 -3 Pa; Step S3: After smelting, cool the ingot to obtain an ingot; turn the ingot over, and repeat step S2 to smelt the ingot 4 to 7 times to obtain the alloy; wherein the ingot needs to be turned over before each repeated smelting.

7. The preparation method according to claim 6, characterized in that The inert gas includes argon; the purity of the argon is 99.99%; the pressure of the inert gas in the smelting furnace is 0.04~0.06MPa.

8. The preparation method according to claim 6, characterized in that The smelting furnace includes a vacuum arc melting furnace; during smelting, the smelting temperature adopted is 2300-2800°C, and the smelting time is 5-10 minutes.

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