Method for laser additive manufacturing of high strength refractory high-entropy alloys and products thereof

Abstract

The application discloses a kind of laser additive manufacturing high strength tough refractory high-entropy alloy method and its product, belong to additive manufacturing technical field.The laser additive manufacturing high strength tough refractory high-entropy alloy method disclosed in the application directly uses large-size Nb, Ta, Ti, Hf and Zr2.5Nb mixed element powder, based on laser deposition technology, realizes good metallurgical combination between high melting point refractory elements by laser smelting.The refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 prepared by the method of the application is completely body-centered cubic structure, has higher hardness, strength and good ductility.The preparation process of the application is simple, the production cost is low, the powder utilization rate is high, and the alloy product has excellent performance, can meet the high performance requirements of strength and toughness materials in modern industry.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of additive manufacturing, and particularly relates to a method for laser additive manufacturing of high-strength and high-toughness refractory high-entropy alloy and a product thereof. BACKGROUND

[0002] High-entropy alloy (HEA) is also known as multi-principal element alloy, which usually contains five or more principal elements, and has excellent mechanical properties, friction and wear properties, corrosion resistance and high-temperature resistance. On the basis of high-entropy alloy, Senkov et al. [1] In 2010, the concept of refractory high-entropy alloy was first proposed, which has attracted widespread attention from scholars and has become one of the research hotspots in the field of high-entropy alloy in recent years, and has broad application prospects in important industrial fields such as aerospace, shipbuilding and automobile.

[0003] Although the refractory high-entropy alloy has broad prospects, the extremely high melting point and the significant difference in density between the elements make the preparation process difficult. Arc melting is the most commonly used preparation method, and is usually assisted by a heat treatment process to improve the microstructure and performance. In the arc melting process, the ingot is often melted repeatedly to obtain uniform composition, and the difference in density between the elements still causes serious segregation. The heat treatment process needs to heat the metal to a high temperature and keep it for a long time, so as to improve the performance, eliminate residual stress and improve uniformity, but the long time of keeping warm is easy to form coarse grain structure, and the equipment investment is large, the production cycle is long, and the energy consumption is high. Therefore, how to quickly and low-costly prepare the refractory high-entropy alloy with excellent performance is the research hotspot in the field at present.

[0004] Additive manufacturing (AM) technology is a technology that uses a layer-by-layer accumulation method to manufacture solid parts, which can effectively reduce material loss and reduce production cycle. And the additive manufacturing process has a faster heating and cooling rate, and is more likely to obtain fine grain structure, which can play the performance advantages of high-entropy alloy while meeting the industrialization needs. Moreover, the additive manufacturing technology can use pre-alloyed powder prepared by gas atomization, water atomization or mechanical alloying for preparation, or use element powder for printing finished products through in-situ alloying, thereby avoiding the long development process.

[0005] In the additive manufacturing process, the inherent short thermal cycle time limits the flow of molten elements and the formation of microstructure, and it is difficult to ensure the complete melting of high-melting-point refractory elements such as W, Ta and Nb. Higher temperature gradient will produce larger residual stress, which may cause deformation and cracking of the part. The refractory high-entropy alloys prepared by additive manufacturing reported at present are usually brittle at room temperature, will fail due to cracking under low compression strain, and have limited formability. The NbMoTaW prepared by additive manufacturing of the United States Sandia National Laboratory shows obvious cracks and porosity throughout the sample height [2] . The NbMoTa alloy prepared by additive manufacturing of Xi'an Jiaotong University only shows a compression strain of 5.8% at room temperature due to metallurgical defects such as porosity and intergranular cracks [3] .

[0006] Laser remelting technology can melt the un-melted powder particles through multiple scanning of metal powder, ensure better metallurgical bonding between high-melting-point refractory elements, and eliminate defects on the surface and inside of the part. Moreover, remelting allows the gas trapped in the molten pool to have enough time to overflow the surface, eliminating the porosity inside the part. Some researchers have tried to combine laser remelting technology with additive manufacturing of refractory high-entropy alloys, and found its application potential. The University of Bochum Ruhr in Germany first obtained TiZrNbHfTa high-entropy alloy by laser deposition combined with laser remelting technology, directly alloying the mixture of refractory element powders in situ [4] .

[0007] In view of the above problems, the present application provides a Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy prepared by laser smelting technology, which has high compression strength and toughness. Moreover, the preparation process is simple, the production cycle is short, and the production cost is low.

[0008] The relevant disclosure documents of the present application include:

[0009] [1]O.N,Senkov,and,et al.Refractory high-entropy alloys[J].Intermetallics,2010,18(9):1758-1765.DOI:10.1016 / j.intermet.2010.05.014.

[0010] [2] M. A. Melia, S. R. Whetten, R. Puckett, M. Jones, M. J. Heiden, N. Argibay, A. B. Kustas, High-throughput additive manufacturing and characterization of refractory high entropy alloys, Applied Materials Today 19 (2020).

[0011] [3] Q. Li, H. Zhang, D. Li, Z. Chen, F. Wang, M. Wu, Comparative study of the microstructures and mechanical properties of laser metal deposited and vacuum arc melted refractory NbMoTa medium-entropy alloy, International Journal of Refractory Metals & Hard Materials 88 (2020).

[0012] [4] H. Dobbelstein, E. L. Gurevich, E. P. George, A. Ostendorf, G. Laplanche, Laser metal deposition of a refractory TiZrNbHfTa high-entropy alloy, Additive Manufacturing 24 (2018) 386-390. SUMMARY

[0013] To solve the problem of additive manufacturing of refractory high-entropy alloys at present, the application provides a method for laser additive manufacturing of high-toughness refractory high-entropy alloys and a product thereof. The method is based on laser directional energy deposition technology, and better metallurgical bonding between high-melting-point refractory elements is achieved through laser remelting technology, and defects on the surface and inside of the part are eliminated, the forming quality is ensured, and the method has the advantages of simple preparation process, short production cycle, low production cost and the like.

[0014] According to another aspect of the application, a method for preparing a refractory high-entropy alloy by laser additive manufacturing is provided, comprising the following steps:

[0015] Step one: Put the Nb, Ta, Ti, Hf and Zr2.5Nb powders in a closed glass container in a certain proportion, and shake manually for 1 min to mix uniformly.

[0016] Step two: Put the uniformly mixed powders in a 120℃ drying oven for 2 hours.

[0017] Step three: Before laser deposition, protect the deposition chamber with 99.99% pure argon gas throughout the process.

[0018] Step four: Turn on the laser to preheat the pure Ti substrate for 2 seconds before powder feeding.

[0019] Step five: Turn on the coaxial powder feeding and use the laser to deposit on the Ti substrate.

[0020] Step six: After 4 seconds of continuous powder feeding, turn off the coaxial powder feeding and use the laser to continuously melt the deposited body for 15 seconds.

[0021] Step seven: Turn off the laser, and after lifting the deposition head by 4 mm, repeat the above steps to deposit the second layer.

[0022] Step eight: Repeat the above deposition steps until the desired height is reached, and the deposition is complete.

[0023] The particle size of the Nb, Ta, Ti, Hf and Zr2.5Nb powders is 45-150 μm.

[0024] The Nb, Ta, Ti, Hf and Zr2.5Nb powders are combined in a molar ratio of 8:5:3:3:1.

[0025] The substrate is a 12 mm thick pure Ti plate.

[0026] The specific conditions of the laser deposition are as follows:

[0027] The laser power is 4000 W throughout the process.

[0028] The deposition device has a spot diameter of 3 mm.

[0029] The distance between the deposition head and the Ti substrate is 12.5 mm, and the deposition head is lifted by 4 mm after each layer of deposition.

[0030] During the deposition process, 99.99% pure argon gas is introduced into the closed deposition chamber for protection throughout the process, with a gas flow rate of 20 L / min.

[0031] The powder feeding rate is 0.8 r / min, and the powder feeding gas is also 99.99% pure argon gas with a pressure of 0.2-0.3 MPa.

[0032] According to another aspect of the present application, there is provided a high-ductile refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 prepared by the above method.

[0033] The additive manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy is entirely composed of a body-centered cubic phase.

[0034] The additive manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy has a microhardness of about 270 HV0.2.

[0035] The additive manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy has a density of about 11.02 g / cm 3 .

[0036] The additive manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy has a compressive yield strength of about 1021 MPa without fracture at 35% engineering strain.

[0037] Advantages and beneficial effects of the present application:

[0038] The preparation method provided by the present application directly uses large-size mixed element powder, and realizes good metallurgical combination between high-melting-point refractory elements based on laser deposition technology through laser remelting. The preparation process is simple, the production cost is low, and the powder utilization rate is high.

[0039] The additive manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy provided by the present application is entirely a body-centered cubic structure, has high hardness, strength and toughness, and can meet higher performance requirements for ductile materials in modern industry. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The figure is a flowchart of the preparation method of the present application;

[0041] Figure 2 The figure is a two-layer (left) and three-layer (right) structure diagram of the Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy prepared by the present application, and the minimum scale value of the ruler in the figure is 1 mm;

[0042] Figure 3 The figure is an SEM diagram of the Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy prepared by the present application;

[0043] Figure 4 The figure is an XRD diagram of the Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy prepared by the present application;

[0044] Figure 5A compression stress-strain curve of the Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy prepared in the application at room temperature is shown in the figure. DETAILED DESCRIPTION

[0045] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific examples.

[0046] The element powders used in the following examples are commercially available spherical powders purchased from Xi'an Sailong Additive Technology Co., Ltd., including titanium (Ti, purity 99.95%), niobium-zirconium powder (Zr2.5Nb, purity 99.5%), hafnium (Hf, purity 99.95%), niobium (Nb, purity 99.95%), and tantalum (Ta, purity 99.95%), with a size of 53 μm-150 μm.

[0047] Example 1

[0048] A method for laser additive manufacturing of high-strength and high-toughness refractory high-entropy alloy, which utilizes a laser melting and deposition device for laser additive manufacturing, with a laser power of 4000 W and a spot diameter of 3 mm, and the main process is as shown in Figure 1 The steps include the following:

[0049] Step one: Put the Nb, Ta, Ti, Hf and Zr2.5Nb powders in a certain proportion into a sealed glass container, and shake manually for 1 min to mix uniformly.

[0050] Step two: Put the uniformly mixed powders into a 120℃ drying oven and dry for 2 hours.

[0051] Step three: Before laser deposition, pass 99.99% pure argon through the deposition closed chamber for whole-process protection.

[0052] Step four: Turn on the laser to preheat the pure Ti substrate for 2 seconds before feeding the powder.

[0053] Step five: Turn on the coaxial powder feeding and use the laser to deposit on the Ti substrate.

[0054] Step six: After continuously feeding the powder for 4 seconds, turn off the coaxial powder feeding and use the laser to continuously melt and deposit the body for 15 seconds.

[0055] Step seven: Turn off the laser, lift the deposition head by 4 mm, and then repeat the above steps to deposit the second layer.

[0056] Step eight: Repeat the above deposition steps until the desired height is reached, and the deposition is completed to obtain the refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5, as shown in Figure 2

[0057] ​The refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 was analyzed and tested, and the specific methods and results are as follows:

[0058] (1) The SEM analysis was performed by using APREO S LOVAC high-resolution scanning electron microscope. The results, as shown in Figure 3 , the laser deposited high-entropy alloy showed dendritic structure, which was composed of bright dendritic regions and relatively dark interdendritic regions.

[0059] (2) The XRD analysis was performed by using TTR-III X-ray diffractometer on the cross section of the deposited sample, using Cu-Kα radiation , the scanning speed was 4° / min, and the collection 2θ range was 20-110°. The results, as shown in 4, the XRD chart showed that the refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 was completely body-centered cubic structure.

[0060] (3) The static compression experiment was tested by using 5-ton electronic universal testing machine. At least 3 samples were measured at 0.001 / s strain rate, and the results, as shown in Figure 5 , finally obtained the yield strength of the refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 was 1021 MPa, and there was no fracture at 35% engineering strain.

[0061] (4) According to the Archimedes drainage method, the density of the refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 was 11.02 g / cm 3 .

[0062] (5) The microhardness of the refractory high-entropy alloy Nb40Ta25Ti15Hf15Zr5 was measured by using Vickers microhardness tester, and the microhardness was about 270 HV0.2.

Claims

1. A method of laser additive manufacturing of high strength and toughness refractory high entropy alloys, characterized in that, The Nb, Ta, Ti, Hf and Zr2.5Nb powders after drying treatment are mixed in a certain proportion, and are melted layer by layer by using a laser deposition device under the protection of inert gas to realize in-situ alloying among high-melting-point refractory elements, and are deposited on a substrate to prepare a high-strength and high-toughness refractory high-entropy alloy. S1: introducing inert gas into a deposition closed chamber; S2: opening coaxial powder feeding, and melting and depositing on the substrate by using laser; S3: closing the coaxial powder feeding after continuously feeding powder for 4 seconds, and continuously melting and depositing the body by using laser for 15 seconds; S4: closing the laser, and lifting the deposition head by 4 mm; The above steps S2-S4 are repeated to deposit a new layer until the deposition reaches the required height, and the deposition is ended.

2. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The Nb, Ta, Ti, Hf and Zr2.5Nb powders are uniformly mixed in a molar ratio of 8:5:3:3:

1.

3. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 2, wherein, The specific method of uniform mixing is that the Nb, Ta, Ti, Hf and Zr2.5Nb powders are placed in a closed glass container in a certain proportion and are shaken to be uniformly mixed.

4. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The particle size of the Nb, Ta, Ti, Hf and Zr2.5Nb powders is 45-150 μm.

5. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The drying treatment condition is specifically that the drying is performed in a 120℃ drying oven for 2 hours.

6. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The substrate is a 12mm-thick pure Ti plate, the distance between the deposition head and the Ti substrate is 12.5mm, and the laser is turned on to preheat the substrate for 2 seconds before powder feeding.

7. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The laser power of the laser deposition is 4000W, and the spot diameter is 3mm.

8. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The powder feeding speed is 0.8r / min, and the powder feeding gas is 99.99% pure argon.

9. The method of laser additive manufacturing of high strength refractory high entropy alloys of claim 1, wherein, The inert gas is 99.99% pure argon with a gas flow rate of 20L / min.

10. The product prepared by the laser additive manufacturing method of the high-strength and high-toughness refractory high-entropy alloy according to any one of claims 1-9.

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