A method for improving the strength and toughness of refractory high entropy alloys by doping rare earth Ce

Abstract

The present invention discloses a method for doping rare earth Ce to improve the strength and toughness of refractory high entropy alloys, comprising the following steps: S1, batching, weighing Nb, Ti, Zr, V pure metal raw materials and Ce pure rare earth raw materials according to the composition ratio; the Ce content is 0 to 0.01 at% according to the atomic percentage; S2, smelting, placing the weighed raw materials into a smelting furnace for smelting to obtain a refractory high entropy alloy ingot with uniform composition. The present invention adopts the above-mentioned method of doping rare earth Ce to improve the strength and toughness of refractory high entropy alloys. Rare earth Ce has a significant grain refinement effect and precipitates a second phase at the grain boundary that is conducive to plastic deformation, which can solve the problem of Nb 0.5 TZV 0.5 The problem of poor room temperature plasticity of refractory high entropy alloys is solved, and a good match between room temperature tensile yield strength and plasticity is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, in particular to a method for improving the strength and toughness of a refractory high entropy alloy by doping with rare earth Ce. Background Art

[0002] Refractory high-entropy alloys (RHEAs) are composed of four or more refractory metal elements from groups IV to VI (V, Cr, Ti, Mo, Nb, Ta, W, Zr, Hf, etc.) in equimolar or unequal molar ratios. To achieve more comprehensive performance, many non-refractory metals such as Al, Si, Co, and Ni are also added to RHEA systems. However, most RHEA systems have disadvantages such as high density, poor room-temperature plasticity, and high-temperature oxidation resistance, which seriously limit their practical application in high-temperature fields. Therefore, achieving lightweight RHEAs, improving their deformability at room temperature, improving their high-temperature oxidation resistance, and effectively reducing their cost are the basic research directions for achieving the widespread application of RHEAs.

[0003] Nb-Ti-Zr-V refractory high entropy alloys composed of low-density elements can effectively reduce the density of the alloy and have a high melting point and high high-temperature yield strength. They are expected to become ideal candidates for new structural materials or high-temperature thermal protection systems. It has been reported that the room temperature plasticity of refractory high entropy alloys can be improved by reducing the valence electron concentration VEC (<4.4). Nb with a VEC of 4.33 0.5 TZV 0.5 Refractory high entropy alloys have lower density (6.1g / cm 3 ) and better room temperature plasticity (ε~4.44%).

[0004] In addition, the method of improving room temperature plasticity by microalloying with Ce elements has been successfully applied in Mg alloys, Fe-Mn-C steels, Al alloys and Co-Al-W high-temperature alloys, but there is a lack of research on the application of Ce elements in high-entropy alloys.

[0005] Therefore, the rare earth element Ce is used to treat Nb 0.5 TZV 0.5 Microalloying refractory high-entropy alloys and improving the room-temperature plasticity of refractory high-entropy alloys by refining grains and precipitating second phases at grain boundaries are technical issues that urgently need to be addressed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for doping rare earth Ce to improve the toughness of refractory high entropy alloys, by refining the grains and changing the type of grain boundary precipitation phase to increase the Nb 0.5 TZV 0.5 The room temperature tensile plasticity of refractory high entropy alloys and the good matching of room temperature tensile yield strength and plasticity are achieved.

[0007] To achieve the above object, the present invention provides a method for doping rare earth Ce to improve the toughness of a refractory high entropy alloy, comprising the following steps:

[0008] S1. Ingredients: weigh pure metal raw materials of Nb, Ti, Zr, and V and pure rare earth raw materials of Ce according to the composition ratio; the Ce content is 0 to 0.01 at% according to atomic percentage;

[0009] S2. Melting: placing the weighed raw materials into a melting furnace for melting to obtain a refractory high-entropy alloy ingot with uniform composition.

[0010] Preferably, the atomic percentage ratio of Nb, Ti, Zr, V, and Ce in step S1 is (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 .

[0011] Preferably, before weighing the raw materials in step S1, the block and flaky raw materials are mechanically polished and ultrasonically cleaned in acetone or anhydrous ethanol to remove oxide films and other sediment impurities.

[0012] Preferably, in step S2, the weighed raw materials Ce, Ti, V, Zr and Nb are sequentially placed into the Nb foil in order of melting point from low to high, and then coated together and placed at the bottom of the copper crucible.

[0013] Preferably, in step S2, the vacuum is drawn to 4-5×10 -3 Pa, and filled with high-purity argon gas to 1.0×10 5 Pa was used for protection, and the raw materials were repeatedly melted 5-6 times under argon protection, and magnetic stirring was turned on during the melting process.

[0014] Therefore, the present invention adopts the above-mentioned method of doping rare earth Ce to improve the strength and toughness of refractory high entropy alloys, which has the following technical effects:

[0015] (1) Nb containing 0.005 at.% rare earth element Ce 0.5 TZV 0.5 The average grain size of the refractory high entropy alloy is 248.6 μm, and the same composition of Nb without rare earth element doping 0.5 TZV 0.5 The average grain size of the refractory high entropy alloy is 338.3 μm, and the rare earth element Ce is doped in Nb 0.5 TZV 0.5 The average grain size can be significantly reduced in refractory high entropy alloys;

[0016] (2)(Nb 0.5TZV 0.5 ) 99.995 Ce 0.005 The precipitation of V-Ce-rich and Zr-poor bands with BCC crystal structure at the grain boundaries in refractory high entropy alloys is more conducive to the deformation of dislocations crossing grain boundaries, promoting the formation of dimple fractures, and thus increasing Nb 0.5 TZV 0.5 Room temperature tensile plasticity of refractory high entropy alloys.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0019] Figure 1 XRD patterns of as-cast samples of Examples 1 to 3 of a method for doping rare earth Ce to improve the toughness of refractory high entropy alloys according to the present invention;

[0020] Figure 2 Metallographic microstructures (OM) of as-cast samples of Examples 1 to 3 of a method for doping rare earth Ce to improve the toughness of a refractory high-entropy alloy according to the present invention;

[0021] Figure 3 EBSD orientation mapping (IPF) images of as-cast samples of embodiments 1 to 3 of the method for doping rare earth Ce to improve the toughness of refractory high entropy alloys according to the present invention;

[0022] Figure 4 The present invention is a method for doping rare earth Ce to improve the toughness of refractory high entropy alloys. The as-cast samples are characterized by grain boundary microstructure (TEM) and element distribution (TEM-EDS) according to Examples 2 and 3.

[0023] Figure 5 These are scanning electron microscope (SEM) images of the fracture surfaces of as-cast and tensile samples of Examples 1 to 3 of a method for doping rare earth Ce to improve the strength and toughness of a refractory high-entropy alloy according to the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0025] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0026] Example 1

[0027] A method for increasing the toughness of a refractory high entropy alloy by doping with rare earth Ce comprises the following steps:

[0028] S1, ingredients, according to the atomic percentage ratio (Nb 0.5 TZV 0.5 ) 100 Ce0 is made of pure metal raw materials of 99.99% purity Nb, 99.995% purity Ti, 99.95% purity Zr, 99.95% purity V and 99.99% purity Ce pure rare earth raw material.

[0029] Before weighing, the block and flake raw materials were mechanically polished and ultrasonically cleaned in acetone to remove the oxide film and other sediment impurities to ensure the accuracy of sample preparation.

[0030] S2. Melting: The weighed raw materials are placed in the order of melting point from low to high (Ce, Ti, V, Zr, Nb) in the Nb foil, wrapped together and placed at the bottom of the copper crucible. When melting the sample, vacuum is drawn to 4×10 -3 Pa, and filled with high-purity Ar gas to 1.0×10 5 Pa was used for protection. The raw materials were repeatedly melted 5 times under argon protection. During the melting process, magnetic stirring was turned on to ensure uniform composition and reduce segregation. Finally, a mass of about 200g and uniform composition (Nb 0.5 TZV 0.5 ) 100 Ce0 refractory high entropy alloy.

[0031] S3. Sample preparation: Cut the melted ingot according to the size of the tensile testing equipment mold to obtain a tensile specimen.

[0032] Example 2

[0033] A method for doping rare earth Ce to improve the toughness of refractory high entropy alloys, the specific steps are the same as those in Example 1, except that: the atomic percentage ratio is (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 .

[0034] Example 3

[0035] A method for doping rare earth Ce to improve the toughness of refractory high entropy alloys, the specific steps are the same as those in Example 1, except that: the atomic percentage ratio is (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01.

[0036] Effect Examples

[0037] The tensile test specimens obtained in Examples 1 to 3 were subjected to room temperature tensile mechanical property tests.

[0038] The room temperature tensile mechanical properties test was carried out on a 10 kN MTS universal testing machine at a tensile strain rate of 10 -3 s -1 Before use, the specimens were polished with 200#, 400#, 600#, 800#, and 1000# sandpaper to remove any wire cutting marks on the sample surface. After the specimens went through the plastic deformation stage, the test was stopped when the stress-strain curve passed the maximum stress and began to decline. To ensure data reproducibility, the experiment was repeated three times for each alloy composition.

[0039] After the specimens completed the room temperature tensile properties test, the test results of yield strength, tensile strength and elongation are shown in Table 1.

[0040] Table 1 Room temperature tensile properties of three refractory high entropy alloys

[0041]

[0042] Effect Example 2

[0043] (1) The cast (Nb) obtained in Examples 1 to 3 was analyzed using a D / MAX-2500 multifunctional X-ray diffractometer (XRD) from Rigaku Corporation of Japan. 0.5 TZV 0.5 ) 100 Ce0、(Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01 Phase composition analysis of the block.

[0044] All three samples were polished flat using 2000 grit sandpaper for measurement. XRD measurements were performed using a Cu Kα target with a λ of 0.15405 nm, an operating voltage of 40 kV, a current of 200 mA, a scan speed of 5° / min, and a scanning range of 20-90°. After the tests, the diffraction peaks were calibrated and analyzed using Jade 6 software.

[0045] The XRD patterns of the cast samples obtained in Examples 1 to 3 are as follows: Figure 1 As shown, Figure 1 1, 2, and 3 correspond to the first, second, and third embodiments respectively. It can be concluded that (Nb0.5 TZV 0.5 ) 100 Ce0、(Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01 The three cast refractory high entropy alloys are composed of single-phase BCC solid solution, indicating that the doping of trace Ce elements does not cause the degradation of Nb 0.5 TZV 0.5 Changes in the phase structure of refractory high-entropy alloys.

[0046] (2) The cast (Nb 0.5 TZV 0.5 ) 100 Ce0、(Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01 The three refractory high-entropy alloy ingots were sequentially polished with 400-3000 grit abrasive paper and then mechanically polished with SiO2 polishing slurry. The dendritic morphology of the three as-cast samples was characterized using a Leica LEICADM 4000 metallographic microscope. Grain size information was obtained by scanning the as-cast samples of the three refractory high-entropy alloys using an Electron Backscattered Diffraction (EBSD) probe mounted on an Apreo S LoVac field-emission scanning electron microscope. The backscattered electrons were collected at an accelerating voltage of 20 kV and a scanning step size of 1-3 μm.

[0047] The metallographic microstructures of the as-cast samples obtained in Examples 1 to 3 are shown in FIG. Figure 2 As shown, Figure 2 (a)1 corresponds to the as-cast sample in Example 1, Figure 2 (b)2 corresponds to the as-cast sample in Example 2, Figure 2 (c)3 corresponds to the as-cast sample in Example 3. 0.5 TZV 0.5 ) 100 Ce0、(Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV0.5 ) 99.99 Ce 0.01 All three cast refractory high entropy alloys have obvious dendritic structure.

[0048] The EBSD orientation imaging (IPF) of the cast samples obtained in Examples 1 to 3 is as follows: Figure 3 shown. Figure 3 (a)1 and (a')1 correspond to the as-cast samples in Example 1. Figure 3 (b)1 and (b')1 correspond to the as-cast samples in Example 2. Figure 3 (c)1 and (c')1 correspond to the as-cast samples in Example 3.

[0049] From the figure, we can see that (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 The average grain size of the as-cast sample is the smallest, which is 248.6 μm; (Nb 0.5 TZV 0.5 ) 100 The average grain size of the Ce0 as-cast sample is the largest, which is 338.3 μm, indicating that the doping of an appropriate amount of Ce element can significantly refine the grains.

[0050] The smallest grain size (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 The room temperature tensile elongation of the as-cast sample is the highest, reaching 6.95±0.47%; at the same time, the yield strength can still be maintained at 960.14±33.89MPa, which is comparable to (Nb 0.5 TZV 0.5 ) 100 The yield strength of Ce0 is 987.77±26.17MPa, which is not much different (as shown in Table 1).

[0051] Therefore, the doping of 0.005 at.% Ce element can effectively achieve a good match between room temperature tensile yield strength and plasticity.

[0052] (3) Using GL-696 ion thinning instrument, the (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01As-cast samples of two refractory high-entropy alloys were thinned to observe the micromorphology, grain boundary structure, and element distribution of the precipitated phase at the grain boundaries near the thinning location. Observations were performed using a JEM-2100F transmission electron microscope (TEM) operating at 200 kV and 20 mA filament current.

[0053] The grain boundary microstructure characteristics (TEM) and element distribution (TEM-EDS) of the cast samples of Example 2 and Example 3 are as follows: Figure 4 shown.

[0054] Figure 4 (a) Example 2 grain boundary (GB) morphology, Figure 4 (b) is a partial enlarged view of box b in (a). Figure 4 (c) is the element distribution curve of straight line AB in (b).

[0055] It can be concluded that there are banded precipitates with rich V-Ce and poor Zr and BCC crystal structure at the grain boundaries of Example 2. This is more conducive to the deformation of dislocations crossing grain boundaries, promoting the formation of dimple fractures, and thus improving (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 Room temperature tensile plasticity of refractory high entropy alloys (as shown in Table 1).

[0056] Figure 4 (d) is the grain boundary (GB) morphology of Example 3, Figure 4 (e) is a partial enlarged view of box e in (d). Figure 4 (f) is the element distribution curve of straight line CD in (e).

[0057] It can be concluded that the ω phase with rich V-Ce and poor Ti and HCP crystal structure precipitates at the grain boundary of Example 3. The brittle ω phase will hinder the dislocation movement and is not conducive to plastic deformation, making (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01 The room temperature tensile plasticity of refractory high entropy alloys is significantly reduced (as shown in Table 1).

[0058] (4) The room temperature tensile fracture morphologies of three refractory high entropy alloys were characterized using an Apreo S LoVac field emission scanning electron microscope (SEM).

[0059] The SEM images of the fracture surfaces of the tensile samples obtained in Examples 1 to 3 are as follows: Figure 5 shown.

[0060] (Nb 0.5 TZV 0.5 ) 100 Ce0、(Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 and (Nb 0.5 TZV 0.5 ) 99.99 Ce 0.01 The fracture morphologies of the three refractory high entropy alloys all have mixed fracture characteristics, including ductile and brittle fracture modes. Figure 5 (a) Figure 5 (b) Figure 5 In (c), boxes 1 and 2 are dimple and brittle fracture features, respectively. (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 The ductile fracture characteristics with the highest proportion (61.7%) indicate that it has the best room temperature plasticity, as shown in Table 1.

[0061] Therefore, the present invention adopts the above-mentioned method of doping rare earth Ce to improve the strength and toughness of refractory high entropy alloys, which can solve the problem of poor room temperature plasticity of existing refractory high entropy alloys and achieve a good match between room temperature tensile yield strength and plasticity.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for doping rare earth Ce to improve the toughness of refractory high entropy alloys, characterized in that: The steps include: S1. Ingredients: weigh pure metal raw materials of Nb, Ti, Zr, V and pure rare earth raw materials of Ce according to the composition ratio; the atomic percentage ratio of Nb, Ti, Zr, V and Ce is (Nb 0.5 TZV 0.5 ) 99.995 Ce 0.005 ; S2. Melting: placing the weighed raw materials into a melting furnace for melting to obtain a refractory high-entropy alloy ingot with uniform composition.

2. The method of increasing the toughness of a refractory high entropy alloy by doping with rare earth Ce according to claim 1, characterized in that: Before weighing the raw materials in step S1, the block and flaky raw materials are mechanically polished and placed in acetone or anhydrous ethanol for ultrasonic cleaning to remove the oxide film and other sediment impurities.

3. The method of increasing the toughness of a refractory high entropy alloy by doping with rare earth Ce according to claim 1, characterized in that: In step S2, the weighed raw materials Ce, Ti, V, Zr, and Nb are sequentially placed into the Nb foil in order of melting point from low to high, and then coated together and placed at the bottom of the copper crucible.

4. The method of increasing the toughness of a refractory high entropy alloy by doping with rare earth Ce according to claim 1, characterized in that: In the step S2, the vacuum is drawn to 4-5×10 -3 Pa, and filled with high-purity argon gas to 1.0×10 5 Pa was used for protection, and the raw materials were repeatedly melted 5-6 times under argon protection, and magnetic stirring was turned on during the melting process.

5. A rare earth element Ce in increasing Nb 0.5 TZV 0.5 The application of refractory high entropy alloy in room temperature plasticity is characterized by: The rare earth element Ce is added to Nb according to the atomic percentage ratio in claim 1 0.5 TZV 0.5 Refractory high entropy alloys.

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