Refractory multi-principal element alloy with intermediate-temperature phase stability, method for preparing same, and use thereof

Abstract

The application provides a refractory multi-principal element alloy with medium-temperature phase stability, a preparation method and application thereof. a Hf b Nb c Ta d , wherein 28%<=a<=38%, 18%<=b<=26%, 25%<=c<=35%, 8%<=d<=18%, and a+b+c+d=100%, a, b, c and d respectively correspond to the mole percentage of elements. The application further discloses a preparation method of the refractory multi-principal element alloy with medium-temperature phase stability. The refractory multi-principal element alloy with medium-temperature phase stability is still single-phase BCC structure under the condition of 500-700 DEG C and 150-250h holding, and has excellent room-temperature mechanical properties, the yield strength is 730-830 MPa, and the elongation after breaking is more than 20%.

Description

Technical Field

[0001] The present invention relates to alloy technology, and in particular to a refractory multi-principal-component alloy with medium-temperature phase stability, a preparation method thereof, and uses thereof. Background Art

[0002] Over the past two decades, high-entropy alloys (HEAs) have garnered widespread attention due to their unique design concepts. Refractory HEAs have also experienced rapid development due to their excellent high-temperature mechanical properties. However, while currently developed refractory HEAs exhibit high strength, they generally suffer from low ductility. Only the HfNbTaTiZr refractory HEAs and their ternary and quaternary alloys exhibit some tensile ductility, suggesting that the HfNbTaTiZr system, as the most promising refractory HEAs, is expected to be used as high-temperature structural components in aerospace applications. After annealing at temperatures above ~1000°C, the as-cast HfNbTaTiZr refractory HEAs remain stable as body-centered cubic (BCC) solid solutions due to the significant contribution of configurational entropy to the Gibbs free energy expression. However, studies have shown that TiZrHfNbTa exhibits poor phase stability at intermediate temperatures (600-1000°C), typically precipitating secondary BCC or HCP phases along grain boundaries. Even varying the elemental content cannot maintain a single-phase BCC structure at intermediate temperatures. As a promising candidate to replace traditional high-temperature alloys, maintaining an unchanging phase structure at operating temperatures is essential. Otherwise, this phase decomposition would undoubtedly increase the risk of brittleness in harsh thermal environments. Therefore, designing refractory high-entropy alloys with intermediate-temperature phase stability remains a significant challenge. Summary of the Invention

[0003] The present invention aims to address the problem of poor intermediate-temperature phase stability of current refractory high-entropy alloys and propose a refractory multi-principal element alloy with intermediate-temperature phase stability. The alloy retains a single-phase BCC structure when heated at 500-700°C for 150-250 hours and has good tensile properties.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: a refractory multi-principal alloy with medium temperature phase stability, the general formula of which is Ti a Hf b Nb c Ta d , where 28%≤a≤38%, 18%≤b≤26%, 25%≤c≤35%, 8%≤d≤18%, and a+b+c+d=100%, where a, b, c and d correspond to the molar percentages of the elements respectively.

[0005] Furthermore, the general formula Ti a Hf b Nb cTa d Medium: 29.5%≤a≤35.5%, 23.5%≤b≤25.2%, 28.5%≤c≤30.5% and 8.5%≤d≤16.5%.

[0006] Furthermore, the refractory multi-principal component alloy with intermediate temperature phase stability still maintains a single-phase BCC structure when kept at 500-700°C for 150-250 hours. The refractory multi-principal component alloy with intermediate temperature phase stability still maintains a single-phase BCC structure when kept at 600°C for 200 hours.

[0007] Another object of the present invention is to disclose a method for preparing a refractory multi-principal component alloy having medium-temperature phase stability, comprising the following steps:

[0008] Step 1: Remove the oxide scale and impurities on the surface of the metal raw materials Ti, Hf, Nb and Ta, then perform ultrasonic cleaning and place them in a drying oven for drying;

[0009] Step 2: Weigh the metal element raw materials according to the molar percentage in the above general formula;

[0010] Step 3: Place the metal raw materials Ti, Hf, Nb and Ta into a vacuum arc melting furnace and pump the vacuum degree of the arc furnace to 3×10 -3 ~5×10 -3 Pa, and then filled with argon to -0.05 ~ -0.04MPa, the alloy was melted in an inert gas atmosphere, and electromagnetic stirring was used to prepare a refractory multi-principal alloy.

[0011] Furthermore, the purity of the metal element raw materials Ti, Hf, Nb, and Ta is above 99.9 wt%.

[0012] Furthermore, in step 1, the metal element raw materials Ti, Hf, Nb and Ta are polished with SiC sandpaper to remove surface oxide scale and impurities.

[0013] Furthermore, during the ultrasonic cleaning in step 1, the metal element raw material is cleaned 3 to 5 times, with each cleaning time being 5 to 8 minutes.

[0014] Furthermore, in step three, when placing the metal element raw materials, Ti with a low melting point and Ta with intrinsic plasticity are placed at the bottom of the crucible, and Hf and Nb with a high melting point are placed at the top.

[0015] Furthermore, before the alloy is smelted in step 3, the Ti ingot is first smelted 2 to 5 times, with each smelting time being 60 to 90 seconds, so as to remove excess oxygen in the vacuum arc melting furnace chamber as much as possible.

[0016] Further, the current is controlled at 400-500 A when the alloy of step three is smelted, and the smelting is repeated for 6-8 times, and the arc should be continued for 2-3 min each time to ensure that the alloy is fully melted.

[0017] Further, the alloy of step three is smelted with the aid of electromagnetic stirring, and the current frequency is 5-7 Hz.

[0018] Further, the refractory multi-principal element alloy button ingot prepared in step three is subjected to heat treatment, and better yield strength can be obtained.

[0019] Further, the heat treatment is a solid solution and annealing double process.

[0020] Further, the solid solution and annealing double process comprises the following steps: the solid solution temperature is 1150-1250 DEG C, the holding time is 2-3 h, the annealing temperature is 500-700 DEG C, the annealing time is 150-250 h, and then water quenching.

[0021] Further, the selected heat treatment adopts a box-type heat treatment furnace.

[0022] Another object of the present application also discloses the use of the refractory multi-principal element alloy with medium-temperature phase stability in the field of engineering structures.

[0023] Further, the use of the refractory multi-principal element alloy with medium-temperature phase stability in the field of aerospace high-temperature structural parts.

[0024] The refractory multi-principal element alloy with medium-temperature phase stability, the preparation method and the use of the present application have the following advantages compared with the prior art:

[0025] 1), the present application selects the BCC stable elements Nb and Ta with high melting point, combines the intrinsic brittle element Hf and the low-density high-melting point element Ti as the principal element, and obtains a series of refractory multi-principal element alloys with medium-temperature phase stability by adjusting the content of each element;

[0026] 2), the refractory multi-principal element alloy with medium-temperature phase stability not only has good phase stability in the medium-temperature temperature range (600-1000 DEG C), but also exhibits excellent mechanical properties, and the yield strength of the alloy is improved from 730-830 MPa to 840-950 MPa after heat treatment, and the fracture elongation still maintains a high level of about 10%, so that the alloy has potential application prospect in the field of engineering structures;

[0027] 3) The present invention has a refractory multi-principal alloy with medium-temperature phase stability. It not only has excellent room temperature mechanical properties (yield strength of 730-830 MPa, elongation after fracture exceeding 20%), but also the high melting point elements Ti, Nb, Hf and Ta can make the alloy have good high-temperature mechanical properties, and can be used as a candidate material for high-temperature structural parts.

[0028] In summary, the refractory multi-principal component alloy described in the present invention has good phase stability. Its crystal structure remains unchanged after being kept at 600°C for 200 hours, and it still maintains a single-phase BCC structure. The refractory multi-principal component alloy described in the present invention also exhibits excellent mechanical properties. After heat treatment, the yield strength of the alloy is increased from 830MPa to 950MPa, while the elongation at break remains at a high level of ~10%, which is expected to realize the engineering application of refractory high-entropy alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Ti of Example 1 30 Hf 25 Nb 30 Ta 15 Microstructure images of refractory multi-principal alloy in cast state;

[0030] Figure 2 Ti of Example 1 30 Hf 25 Nb 30 Ta 15 Microstructure images of refractory multi-principal alloy in annealed state;

[0031] Figure 3 Ti of Example 1 30 Hf 25 Nb 30 Ta 15 XRD patterns of refractory multi-principal alloys in cast and annealed states;

[0032] Figure 4 Ti of Example 1 30 Hf 25 Nb 30 Ta 15 Tensile engineering stress-engineering strain curves of refractory multi-principal alloys in cast and annealed states;

[0033] Figure 5 Ti of Example 2 35 Hf 25 Nb 30 Ta 10 Microstructure images of refractory multi-principal alloy in cast state;

[0034] Figure 6 Ti of Example 2 35 Hf 25Nb 30 Ta 10 Microstructure images of refractory multi-principal alloy in annealed state;

[0035] Figure 7 Ti of Example 2 35 Hf 25 Nb 30 Ta 10 XRD patterns of refractory multi-principal alloys in cast and annealed states;

[0036] Figure 8 Ti of Example 2 35 Hf 25 Nb 30 Ta 10 Tensile engineering stress-engineering strain curves of refractory multi-principal component alloys in cast and annealed states. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the embodiments:

[0038] Example 1

[0039] This embodiment provides a refractory multi-principal alloy with medium temperature phase stability, the chemical formula of which is Ti 30 Hf 25 Nb 30 Ta 15 , the specific preparation method is as follows:

[0040] Step 1: Select high-melting-point BCC stabilizing elements Nb and Ta, combined with the intrinsic brittle element Hf and the low-density, high-melting-point element Ti as the main elements; the selected raw materials have a purity of more than 99.9wt.%; the surfaces of the selected metal elements Ti, Hf, Nb and Ta are polished with different types of SiC sandpaper to remove oxide scale and stains on the surface of the raw materials, then placed in different containers, ultrasonically cleaned with alcohol, and then placed in a drying oven for 5 hours for drying.

[0041] Step 2: Convert the designed alloy composition from molar ratio to mass ratio. Based on the total mass of the raw materials being 50 g, the weighed masses of the metal raw materials Ti, Hf, Nb and Ta are 6.300 g, 19.571 g, 12.225 g and 11.904 g, respectively. Then, use an electronic balance to weigh them and place them in sample bags.

[0042] Step 3: Place the prepared raw materials in step 2 into the copper crucible of the vacuum arc furnace, place the low melting point Ti and intrinsic plasticity Ta at the bottom of the crucible, and place the high melting point Hf and Nb at the top; close the door and evacuate to 4.5×10 -3Pa, stop vacuuming, open the inflation valve, and fill with argon to -0.05MPa; before alloy melting, first melt the Ti ingot 4 times, each melting for 60s, then melt the alloy ingot, and repeat the melting 8 times. The melting current is controlled at 450A, and each melting arc should last for 3min and be supplemented by electromagnetic stirring technology. The current frequency is 5Hz to ensure that the refractory multi-principal alloy is fully mixed.

[0043] Step 4: The refractory multi-principal alloy obtained in step 3 is solutionized at 1200°C for 3 hours, and then kept at 600°C for 200 hours. After the heat treatment, the sample is taken out and water quenched. A box-type heat treatment furnace is used for the entire heat treatment process.

[0044] The crystal structure, microstructure and mechanical properties of the refractory multi-principal alloy with medium-temperature phase stability prepared in Example 1 were characterized; Electron probe microscopy (EPMA) analysis was performed on Example 1. Figure 1 and Figure 2 Example 1Ti 30 Hf 25 Nb 30 Ta 15 Microscopic morphology images of refractory multi-principal alloys in the as-cast and annealed states. As can be seen from the figures, Example 1 has a typical dendritic morphology in the as-cast state, and an equiaxed crystal morphology in the annealed state, with no second phase precipitation. Figure 3 Example 1Ti 30 Hf 25 Nb 30 Ta 15 The XRD patterns of the refractory multi-principal alloy in the cast and annealed states show that Example 1 has a single-phase BCC crystal structure in both the cast and annealed states, indicating that Example 1 has good medium-temperature phase stability. Figure 4 Example 1Ti 30 Hf 25 Nb 30 Ta 15 The tensile engineering stress-engineering strain curves of the refractory multi-principal component alloy in the cast and annealed states show that compared with the cast alloy, the yield strength of the refractory multi-principal component alloy increases from 830MPa to 950MPa after annealing, while the elongation at break remains at a high level of ~10%.

[0045] Example 2

[0046] This embodiment provides a refractory multi-principal alloy with medium temperature phase stability, the chemical formula of which is Ti 35 Hf 25 Nb 30 Ta 10 The preparation method of the alloy is the same as that of Example 1.

[0047] Figure 5With Figure 6 Example 2 Ti 35 Hf 25 Nb 30 Ta 10 Micro-morphology pictures of the as-cast and annealed refractory multi-principal element alloy, similar to example 1, example 2 is a typical dendritic morphology in the as-cast state, and is an equiaxed crystal morphology in the annealed state, and no second phase is precipitated; Figure 7 Example 2 Ti 35 Hf 25 Nb 30 Ta 10 XRD patterns of the as-cast and annealed refractory multi-principal element alloy, from the spectrum, example 7 is a single-phase BCC crystal structure in the as-cast and annealed states, which indicates that example 2 has good medium-temperature phase stability; Figure 8 Example 2 Ti 35 Hf 25 Nb 30 Ta 10 Tensile engineering stress-engineering strain curves of the as-cast and annealed refractory multi-principal element alloy, similar to example 1, after annealing, the yield strength of the refractory multi-principal element alloy is increased from 740 MPa to 840 MPa, and the elongation at break is slightly reduced, but still maintains a good level, so it has great application prospects in the engineering application field.

[0048] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A refractory multi-principal alloy with medium-temperature phase stability, characterized in that: Its general formula is Ti a Hf b Nb c Ta d , where 29.5%≤ a ≤35.5%, 23.5%≤ b ≤25.2%, 28.5%≤ c ≤30.5% and 8.5%≤ d ≤16.5%, and a+b+c+d=100%, where a, b, c and d correspond to the molar percentages of the elements respectively; Refractory multi-principal alloys with medium-temperature phase stability maintain a single-phase BCC structure when heated at 500-700°C for 150-250 hours. Refractory multi-principal alloy with medium-temperature phase stability has a room temperature yield strength of 730-830 MPa and an elongation after fracture exceeding 20%; The method for preparing the refractory multi-principal component alloy with medium-temperature phase stability comprises the following steps: Step 1: Remove the oxide scale and impurities on the surface of the metal raw materials Ti, Hf, Nb and Ta, then perform ultrasonic cleaning and place them in a drying oven for drying; Step 2: Weigh the metal element raw materials according to the molar percentage in the above general formula; Step 3: Place the metal raw materials Ti, Hf, Nb and Ta into a vacuum arc melting furnace and pump the vacuum degree of the arc furnace to 3×10 -3 ~5×10 -3 Pa, and then filled with argon to -0.05~-0.04MPa, and the alloy was melted in an inert gas atmosphere, assisted by electromagnetic stirring, to prepare a refractory multi-principal element alloy.

2. The refractory multi-principal alloy with medium-temperature phase stability according to claim 1, characterized in that: Step 3: When placing the metal element raw materials, place the low-melting-point Ti and intrinsically plastic Ta at the bottom of the crucible, and the high-melting-point Hf and Nb at the top.

3. The refractory multi-principal alloy with medium-temperature phase stability according to claim 1, characterized in that: Step 3 Before alloy melting, melt the Ti ingot 2 to 5 times, each melting for 60 to 90 seconds, to remove as much excess oxygen as possible in the vacuum arc melting furnace chamber.

4. The refractory multi-principal component alloy with medium-temperature phase stability according to claim 1, characterized in that: During step 3 alloy melting, the current is controlled at 400~500A, and the melting is repeated 6~8 times. Each melting arc should last for 2~3 minutes.

5. The refractory multi-principal component alloy with medium-temperature phase stability according to claim 1, characterized in that: During the alloy melting in step 3, electromagnetic stirring is used with a current frequency of 5-7 Hz.

6. The refractory multi-principal component alloy with medium-temperature phase stability according to claim 1, characterized in that: Heat treatment of the refractory multi-principal alloy button ingot prepared in step three can obtain better yield strength.

7. The refractory multi-principal component alloy with medium-temperature phase stability according to claim 6, characterized in that: The heat treatment is a dual process of solution treatment and annealing.

8. Use of the refractory multi-principal component alloy with medium-temperature phase stability as claimed in claim 1 in the field of engineering structures.

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