A high entropy alloy with high specific strength and corrosion resistance and preparation method thereof

Abstract

The present invention relates to a high entropy alloy with high specific strength and corrosion resistance and a preparation method thereof. The expression of the high entropy alloy is: Cr a V b Nb c Al d M e ; Wherein M is one or two of Ti, Zr and Mo, and the molar ratios of a, b, c, d and e are in the range of 0≤a≤1.5, 0≤b≤1.5, 0.5≤c≤20, 0≤d≤3, 0≤e≤2 respectively; the preparation method adopts non-consumable vacuum arc melting process. The present invention selects Al with low density, V, Cr, Nb with high melting point, and Mo, Ti and Zr elements with excellent corrosion resistance as raw materials, so that the high entropy alloy obtains high specific strength, excellent corrosion resistance and thermal stability. The selected material elements are relatively rich, non-consumable vacuum arc melting is adopted, the operation is simple, the production cycle is short, and the cost is low. The product has a good application prospect.

Description

Technical Field

[0001] The invention relates to a high entropy alloy with high specific strength and corrosion resistance and a preparation method thereof, and specifically belongs to the technical field of high entropy alloys. Background Art

[0002] High entropy alloys are generally composed of five or more elements as the main elements. Compared with traditional binary or ternary alloys, high entropy alloys can form simple solid solution structures, such as body-centered cubic (BCC), face-centered cubic (FCC) and hexagonal close-packed (HCP) structures, and have high entropy effect, cocktail effect, hysteresis diffusion effect and lattice distortion effect. These unique properties make high entropy alloys have many excellent properties compared to traditional alloys, such as high hardness, balance of strength and ductility, and excellent corrosion resistance, fatigue resistance and wear resistance.

[0003] In recent years, the processes used to prepare high entropy alloys include mechanical alloying, spark plasma sintering, arc furnace melting and laser cladding. Mechanical alloying is often used in conjunction with spark plasma sintering to prepare high entropy alloy blocks. This method can alleviate the problem of uneven chemical composition inside the material, but it is easy to introduce impurities during the ball milling process and has a high oxidation tendency. The materials prepared by the laser cladding method have small shape changes, fine and uniform microstructures, and high matrix solid solubility, but they consume a lot of powder and are costly. The vacuum arc melting process is simple to operate, can melt elements with higher melting points, and has a short production cycle.

[0004] Usually the high entropy alloy WNbMoTa (ρ = 13.75g / cm 3 ) and WNbMoTaV(ρ=12.36g / cm 3 ) has a high density, which easily leads to low specific strength of the alloy. At the same time, in order to adapt to the special working conditions of high entropy alloys, it is also necessary to have good corrosion resistance. In view of the current status of high entropy alloys, it is necessary to reduce the density of high entropy alloys as much as possible and improve the corrosion resistance of high entropy alloys. The present invention proposes to use lightweight elements Al to replace the dense and brittle elements such as Mo and W in the alloy, so as to reduce the density of the high entropy alloy while giving the material high specific strength. In addition, the density of the lightweight high entropy alloy is further reduced by adding titanium, while the specific strength and corrosion resistance can be further improved. Summary of the invention

[0005] In view of the problems of low specific strength and poor corrosion resistance of existing alloys, the purpose of the present invention is to provide a method for preparing a high-entropy alloy with high specific strength and high corrosion resistance. By adjusting the ratio between the elements of the alloy raw materials and adopting a non-consumable vacuum arc furnace for melting, a high-entropy alloy with both high specific strength and excellent corrosion resistance is obtained.

[0006] The expression of a high entropy alloy with high specific strength and corrosion resistance of the present invention is: Cra V b Nb c Al d M e ; wherein M is one or two of Ti, Zr and Mo, and the molar ratios of a, b, c, d and e are in the ranges of 0≤a≤1.5, 0≤b≤1.5, 0.5≤c≤20, 0≤d≤3, 0≤e≤2 respectively.

[0007] The present invention discloses a method for preparing a high-entropy alloy with high specific strength and corrosion resistance, which adopts a non-consumable vacuum arc melting process, and the specific steps are as follows:

[0008] Step 1: The materials M, Cr, V, Nb and Al are respectively polished with sandpaper, and then ultrasonically cleaned and air-dried for later use;

[0009] Step 2: After the above materials are mixed in proportion, Al, Cr, V, Nb, and M are placed in a copper pot in a non-consumable vacuum arc furnace in order of melting point from low to high, and sponge titanium is placed in another copper pot in the non-consumable vacuum arc furnace, which is then evacuated to a vacuum state and filled with argon gas for protection;

[0010] Step 3: First, melt the titanium sponge, repeat twice to absorb the air in the furnace chamber, and then melt the M, Cr, V, Nb and Al materials, repeat the melting five times, and turn the materials over after each melting to make the materials melt evenly to obtain a high entropy alloy.

[0011] The purity of the M, Cr, V, Nb and Al materials is above 99.9%.

[0012] The ultrasonic cleaning time is 15-30 minutes, and the cleaning liquid is acetone or ethanol.

[0013] The vacuum degree of the non-consumable vacuum arc melting is controlled to 1×10 -3 Pa.

[0014] The purity of the argon gas is 99.9%.

[0015] The time for melting the titanium sponge is 2±0.1 min.

[0016] Each melting time of the material is 2±0.1 min.

[0017] The melting current of the material is 250A each time.

[0018] Beneficial effects of the present invention: The present invention designs a high entropy alloy raw material formula, selects Al with low density, V, Cr, Nb with high melting points, and Mo, Ti and Zr elements with excellent corrosion resistance as raw materials, so that the high entropy alloy obtains high specific strength, excellent corrosion resistance and thermal stability. Since the material elements are relatively abundant and low-cost, the product has a good application prospect; the preparation process of the high entropy alloy of the present invention adopts non-consumable vacuum arc melting, which is simple to operate, has a short production cycle and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : XRD pattern of the high entropy alloy of the present invention;

[0020] Figure 2 : Compressive stress-strain curve of the high entropy alloy of the present invention;

[0021] Figure 3 : Polarization curve of the high entropy alloy of the present invention in 3.5% NaCl solution;

[0022] Figure 4 : Polarization curve of the high entropy alloy of the present invention in 1 mol / L HCl solution;

[0023] Figure 5 : DSC curve of the high entropy alloy of the present invention. DETAILED DESCRIPTION

[0024] Example 1

[0025] The preparation method of the high entropy alloy of the present invention is as follows:

[0026] Step 1: Select Ti as the added element, and polish Ti, Cr, V, Nb and Al with a purity of more than 99.9% with sandpaper to remove surface oxides, then put them in acetone for ultrasonic cleaning for 20 minutes, and then blow dry with a hair dryer for later use.

[0027] Step 2: Prepare the ingredients according to the molar ratio, where a=1, b=1, c=0.5, d=0.5, and e=1.

[0028] Step 3: Place the weighed Al, Ti, Cr, V, and Nb in the copper crucible in the non-consumable vacuum arc furnace in the order of melting point from low to high. At the same time, place the titanium sponge in another copper crucible in the non-consumable vacuum arc furnace. Turn on the vacuum pump and draw the vacuum degree in the furnace to 1×10 -3Pa, turn off the vacuum pump, and then fill the furnace with high-purity argon gas with a purity of 99.9%. First, melt sponge titanium for 2 minutes, repeat the melting twice to absorb the air in the furnace chamber, and then melt the high-entropy alloy raw material, repeat the melting 5 times, turn the high-entropy alloy raw material over after each melting, and ensure that the melting time of each time is 2±0.1min, so that the alloy is melted evenly to obtain a high-entropy alloy. The melting current of each time is 250A.

[0029] The high-entropy alloy prepared above was turned over to the third copper crucible in the non-consumable vacuum arc furnace. The high-entropy alloy was first melted with a current of 250A, and then the current was increased to 500A. The high-entropy alloy was quickly punched into a plate-shaped mold for punching. The current switch was turned off, and it was taken out after waiting for 10 minutes to obtain a Φ4mm×70mm rod-shaped high-entropy alloy.

[0030] The rod-shaped high entropy alloy was cut into Φ4mm×8mm cylinders by an electric spark wire cutting machine to make compression specimens. The compression performance of the specimens at room temperature was tested on an electronic universal testing machine. The compression rate was selected to be 0.1mm·min -1 .

[0031] Depend on Figure 1 The X-ray diffraction pattern shows that the structure of the high entropy alloy is a simple BCC solid solution structure; the density of the high entropy alloy measured by the Archimedean drainage method is 5.640 g·cm -3 , which is lower than that of common high entropy alloys (7 g·cm -3 ).

[0032] Depend on Figure 2 From the compressive stress-strain curve, it can be obtained that the strength of the high entropy alloy at fracture is 1267MPa, which is higher than most high entropy alloys (<1200MPa). Since the specific strength of a material is defined as the strength of the material (the force per unit area when it is broken) divided by its apparent density, its specific strength is about 224.6 MPa·cm 3 · g -1 , so it has good comprehensive mechanical properties.

[0033] Example 2

[0034] The preparation method of the high entropy alloy of the present invention is as follows:

[0035] Step 1: Grind Cr, V, Nb and Al with a purity of more than 99.9% with sandpaper to remove surface oxides, then ultrasonically clean them in acetone for 20 minutes, and then blow dry them with a hair dryer for later use.

[0036] Step 2: Prepare the ingredients according to the molar ratio, where a=1, b=1, c=1, d=1, and e=0.

[0037] Step 3: Place the weighed Al, Cr, V, and Nb in the copper crucible in the non-consumable vacuum arc furnace in the order of melting point from low to high. At the same time, place the titanium sponge in another copper crucible in the non-consumable vacuum arc furnace. Turn on the vacuum pump and draw the vacuum degree in the furnace to 1×10 -3 Pa, turn off the vacuum pump, and then fill the melting furnace with high-purity argon with a purity of 99.9%. First, melt the sponge titanium for 2 minutes, and repeat the melting twice to absorb the air in the furnace chamber. Then, melt the alloy raw materials again, repeat the melting 5 times, turn the alloy raw materials over after each melting, and ensure that the time of each melting is 2±0.1min, so that the alloy is melted evenly to obtain a high entropy alloy. The above melting current is 250A each time.

[0038] The prepared high entropy alloy was turned over to the third copper crucible in the non-consumable vacuum arc furnace, and the high entropy alloy was first melted with a current of 250A, and then the current was increased to 500A, and the molten high entropy alloy was quickly punched into a plate-shaped mold for punching, and the current switch was turned off, and it was taken out after waiting for 10 minutes to obtain a 70mm×10mm×2mm plate-shaped high entropy alloy. Then the plate-shaped high entropy alloy was cut into a 10mm×10mm×10mm cube by an electric spark wire cutting machine as a sample for corrosion performance test. The corrosion performance of the high entropy alloy was tested by the PARSTAT 2273 workstation, and 316 stainless steel was selected as a comparison, the auxiliary electrode was a platinum electrode, and the reference electrode was a calomel electrode.

[0039] Depend on Figure 3 It can be seen that the self-corrosion potential of high entropy alloy in 3.5% NaCl solution is -0.6V, the pitting potential is 1.55V, and its passivation zone is about twice that of 316 stainless steel. Figure 4 It can be seen that the self-corrosion potential of high entropy alloy in 1 mol / L HCl solution is -0.3V, the pitting potential is 0.96V, its passivation zone is about twice that of 316 stainless steel, and the BCC single-phase structure (see Figure 1 ) is more corrosion resistant than the multiphase structure of 316 stainless steel, and the wider passivation platform indicates that the high entropy alloy has formed a stable protective passivation film and is less prone to pitting corrosion.

[0040] Example 3

[0041] The preparation method of the high entropy alloy of the present invention is as follows:

[0042] Step 1: Select Ti as the added element, and polish Ti, Cr, V, Nb and Al with a purity of more than 99.9% with sandpaper to remove surface oxides, then put them in acetone for ultrasonic cleaning for 20 minutes, and then blow dry with a hair dryer for later use.

[0043] Step 2: Prepare the ingredients according to the molar ratio, where a=1, b=1, c=1, d=3, and e=2.

[0044] Step 3: Place the weighed Al, Ti, Cr, V, and Nb in the copper crucible of the non-consumable vacuum arc furnace in turn, and place the titanium sponge in another copper crucible. Turn on the vacuum pump and draw the vacuum degree in the furnace to 1×10 -3 Pa, turn off the vacuum pump, and then fill the furnace with high-purity argon gas with a purity of 99.9%. First, melt the sponge titanium for 2 minutes, repeat the melting twice to absorb the oxygen in the furnace chamber, and then melt the alloy raw materials, repeat the melting 5 times, turn the alloy raw materials over after each melting, and ensure that the melting time of each time is 2±0.1min, so that the alloy is melted evenly to obtain a high entropy alloy.

[0045] The prepared high entropy alloy was turned over to the third copper crucible in the non-consumable vacuum arc furnace, and the high entropy alloy was first melted with a current of 250A, and then the current was increased to 500A, and the molten high entropy alloy was quickly punched into a plate-shaped mold for punching, and the current switch was turned off, and it was taken out after waiting for 10 minutes to obtain a rod-shaped high entropy alloy of Φ4mm×70mm. The rod-shaped high entropy alloy was cut into a cylinder of Φ4mm×6mm by an electric spark wire cutting machine, and then it was inlaid on a hot inlay machine, and the hardness of the high entropy alloy was measured by a Vickers hardness tester, and the test force was selected as 300gf, and the loading time was 15s.

[0046] The hardness of the high entropy alloy was measured by Vickers hardness tester to be 658.9HV. The DSC curve of the high entropy alloy was obtained by differential scanning calorimetry, such as Figure 5 As shown, the sample did not melt in the range of 35°C-1300°C, indicating that the high entropy alloy has a high melting point and good thermal stability.

Claims

1. A high entropy alloy with high specific strength and corrosion resistance, characterized in that: The expression of the high entropy alloy is: Cr a V b Nb c Al d ; The molar ratio ranges of a, b, c, and d are: 1≤a≤1.5, 1≤b≤1.5, 0.5≤c≤1.0, 1≤d≤3, respectively.

2. A method for preparing a high entropy alloy with high specific strength and corrosion resistance, characterized in that: The preparation method uses Al, Cr, V, and Nb as raw materials and adopts a non-consumable vacuum arc melting process to prepare a high entropy alloy with a single BCC phase. The specific steps are as follows: Step 1: Grind the Cr, V, Nb and Al materials with sandpaper respectively, and then ultrasonically clean and air-dry them for later use; the purity of the four element materials of Al, Cr, V and Nb is above 99.9%, the ultrasonic cleaning time is 15-30 minutes, and the cleaning fluid is acetone or ethanol; Step 2: After the above materials are mixed in proportion, Al, Cr, V, and Nb are placed in a copper pot in a non-consumable vacuum arc furnace in order of melting point from low to high, and sponge titanium is placed in another copper pot in the non-consumable vacuum arc furnace, which is then evacuated to a vacuum state and filled with argon gas for protection; Step 3: First, the sponge titanium is melted, and the process is repeated twice to absorb the air in the furnace chamber, and then the Cr, V, Nb and Al materials are melted, and the melting is repeated five times. After each melting, the materials are turned over to make the materials melt evenly to obtain a high entropy alloy; the process parameters of the vacuum arc melting are: melting current 250A, sponge titanium melting time and single melting time are 2±0.1min, and the gas pressure in the melting furnace is 1×10 -3 Pa, the purity of argon is above 99.9%.

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