Method for improving strength and reducing anisotropy of 4D printing high-entropy shape memory alloy

Abstract

The invention discloses a method for improving strength and reducing anisotropy of a 4D printed high-entropy shape memory alloy, which comprises the following steps: mixing the high-entropy shape memory alloy with a certain amount of nano TiN particles to obtain mixed powder; and then the obtained mixed alloy powder is subjected to laser powder bed melting LPBF printing, then the TiN / high-entropy shape memory alloy composite material obtained through printing is subjected to heat treatment, and the high-strength and low-anisotropy compact TiN / high-entropy shape memory alloy composite material is obtained. According to the method, nano-particles TiN are added, 4D printing shape memory alloy grains are refined, the yield strength of the 4D printing shape memory alloy grains is improved, the number of grain boundaries perpendicular to the printing direction and parallel to the printing direction of a microstructure in a sample is close, then heat treatment is conducted on the printed alloy, and the shape memory performance of the alloy is improved through the synergistic effect of the nano-particles TiN and the grain boundaries. The highest vertical recoverable strain is improved to 5.0-6.1%, and the anisotropy of the shape memory performance is reduced from 55.9% of direct printing to 3.1-9.0%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy preparation, and in particular to a method for improving the strength and reducing anisotropy of 4D printing high-entropy shape memory alloy. BACKGROUND

[0002] Currently, 4D printing is a 3D printing with an added time dimension, and the printed parts can change their shape under external stimuli (heat, light, electricity, etc.), so it is a revolutionary intelligent manufacturing method. The key to metal 4D printing is shape memory alloy, and the shape memory of the shape memory alloy is realized through reversible martensitic phase change. The specific process is as follows: stress-induced martensitic phase change occurs during loading, and the shape changes from austenite to martensite along the loading direction to bear the shape change; subsequently, when heated to above the austenite transformation temperature, the martensite reversibly transforms into austenite, and the shape returns to the pre-deformation state. Traditionally, NiTi shape memory alloy is used for 4D printing, but the Ni loss is large during laser printing, resulting in poor printing performance, and due to the epitaxial growth of columnar crystal structure, there is strong anisotropy. In addition, the traditional FeMnSi series shape memory alloy also has obvious columnar crystal structure, which makes its shape memory performance have obvious anisotropy, and the shape memory performance is lower than that of NiTi, and the strength also has room for improvement. The above problems seriously restrict the application and popularization of shape memory alloy 4D printing technology.

[0003] Therefore, it is of great engineering application value to develop 4D printing shape memory alloy powder with high strength and high isotropy and process. SUMMARY

[0004] The present application discloses a method for improving the strength and reducing the anisotropy of 4D printing high-entropy shape memory alloy to solve any of the existing and other potential problems.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a method for improving the strength and reducing the anisotropy of 4D printing high-entropy shape memory alloy, which specifically comprises the following steps: S1) First, mix the high-entropy shape memory alloy with a certain amount of nano-particle TiN to obtain a mixed powder; S2) Laser powder bed fusion (LPBF) printing is performed on the mixed alloy powder obtained in S1) to obtain a TiN / high-entropy shape memory alloy composite material; S3) Heat treatment is performed on the TiN / high-entropy shape memory alloy composite material obtained in S2) to obtain a high-strength and low-anisotropy dense TiN / high-entropy shape memory alloy composite material.

[0006] Further, the mass percentage of nano-particle TiN in the mixed powder in S1) is 0.5%-2.0%. The powder mixing mode is mechanical powder mixing.

[0007] Further, the specific process parameters of the laser powder bed fusion LPBF printing in S2) are: laser power: 180-250 W, scanning speed: 600-1400 mm / s, scanning interval: 50-80 mu m, layer thickness: 30 mu m.

[0008] Further, the heat treatment temperature in S3) is 650-900 DEG C, and the time is 10-20 minutes.

[0009] Further, the vertical maximum recoverable strain of the high-density TiN / high-entropy shape memory alloy composite material is increased to 5.9%, and the anisotropy of the shape memory performance is reduced from 56% of direct printing to 3%, the yield strength can reach 812.8 MPa, and the tensile strength can reach 1111.5 MPa.

[0010] Further, the TiN / high-entropy shape memory alloy composite material is prepared by the above method.

[0011] The mechanism of the application is: the method mixes nano titanium nitride powder and high-entropy shape memory alloy powder by mechanical powder mixing, and the three-dimensional powder mixer fully mixes the nano titanium nitride powder to be evenly distributed on the surface of the micron high-entropy shape memory alloy powder. Laser powder bed fusion LPBF printing is performed to obtain a dense TiN / high-entropy shape memory alloy composite material sample. Due to grain refinement and dispersion strengthening, the yield strength of the high-entropy shape memory alloy is increased by more than 200 MPa. Due to the conversion of columnar crystals to equiaxed crystals, the crystal boundary distribution is changed, and the equiaxed grains are obtained, so that the number of horizontal and vertical grain boundaries is equal, thereby reducing the anisotropy of the high-entropy shape memory performance. At the same time, due to the heat treatment, the residual stress is reduced, thereby reducing the number of twin crystals and layer lattices caused by the printing thermal history, so that the stress-induced reversible martensitic phase change has more space, and the loss of shape memory performance caused by grain refinement is compensated. In summary, the nano particle mixed printing combined with the heat treatment after printing obtains the high-strength low-anisotropy 4D printing effect.

[0012] The beneficial effects of the application are: due to the above technical scheme, the strength of the high-entropy shape memory alloy obtained by the method of the application is increased by 37%; after heat treatment, the shape memory performance is maintained at about 6.1%; and the anisotropy of the 4D printing in the horizontal and vertical directions is greatly reduced, the memory performance is reduced from 55.9% to 3.1-9,0%, and the mechanical performance is reduced from 40% to 24%. In summary, the addition of nano particles improves the comprehensive performance of the 4D printed high-entropy shape memory alloy. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1A flow chart of a method for improving the strength and reducing anisotropy of a 4D printed high-entropy shape memory alloy according to the present application. Figure 2 A schematic diagram of a nano-TiN particle, a high-entropy shape memory alloy powder, and a mixed powder in the method according to the present application.

[0014] Figure 3 A schematic diagram of a mechanical property curve of a shape memory alloy prepared by the method according to the present application.

[0015] Figure 4 A comparative schematic diagram of the influence of mixing nano-particles and subsequent heat treatment on the shape memory performance of a 4D printed shape memory alloy in the method according to the present application; (a) influence of nano-TiN addition on the deformation recovery ratio of a 4D printed high-entropy shape memory alloy, (b) influence of nano-TiN addition on the recoverable strain of a 4D printed high-entropy shape memory alloy, (c) influence of heat treatment on the deformation recovery ratio of a 4D printed TiN / HESMA, and (d) influence of heat treatment on the deformation recoverable strain of a 4D printed TiN / HESMA.

[0016] Figure 5 A comparative schematic diagram of the influence of mixing nano-particles and subsequent heat treatment on the shape memory performance of a 4D printed shape memory alloy in the method according to the present application; (a) influence of nano-TiN addition on the deformation recovery ratio of a 4D printed high-entropy shape memory alloy, (b) influence of nano-TiN addition on the recoverable strain of a 4D printed high-entropy shape memory alloy, (c) influence of heat treatment on the deformation recovery ratio of a 4D printed TiN / HESMA. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments will be described below clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0018] As shown in the drawings, the method for improving the strength and reducing anisotropy of a 4D printed high-entropy shape memory alloy according to the present application specifically comprises the following steps: Figure 1 S1) first mix a high-entropy shape memory alloy with a certain amount of nano-TiN particles to obtain a mixed powder; S2) perform laser powder bed fusion (LPBF) printing on the mixed alloy powder obtained in S1) to obtain a dense TiN / high-entropy shape memory alloy composite material; S3) perform heat treatment on the TiN / high-entropy shape memory alloy composite material obtained in S2) to obtain a high-strength and low-anisotropy dense TiN / high-entropy shape memory alloy composite material; S3) perform heat treatment on the TiN / high-entropy shape memory alloy composite material obtained in S2) to obtain a high-strength and low-anisotropy dense TiN / high-entropy shape memory alloy composite material; The vertical maximum recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is increased to 5.0%-6.1%, and the anisotropy ratio of shape memory performance is reduced from 56% of direct printing to 3.1-9.0%, the yield strength value is 650.0-900.0 MPa, and the tensile strength is 900.0-1350.0 MPa.

[0019] Example 1 S1) First, mix the high-entropy shape memory alloy with 0.5% of nano-TiN particles by weight to obtain a mixed powder; S2) The mixed alloy powder obtained in S1) is subjected to laser powder bed fusion LPBF printing to obtain a dense TiN / high-entropy shape memory alloy composite material; S3) The TiN / high-entropy shape memory alloy composite material obtained in S2) is subjected to heat treatment to obtain a high-strength low-anisotropy dense TiN / high-entropy shape memory alloy composite material; The vertical maximum recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is 6.1%, and the anisotropy ratio of shape memory performance is reduced from 56% of direct printing to 17%, the yield strength is 672.4 MPa, and the tensile strength is 1321.3 MPa.

[0020] Example 2 S1) First, mix the high-entropy shape memory alloy with 1.0% of nano-TiN particles to obtain a mixed powder; S2) The mixed alloy powder obtained in S1) is subjected to laser powder bed fusion LPBF printing to obtain a dense TiN / high-entropy shape memory alloy composite material; The specific process parameters of laser powder bed fusion LPBF printing are: laser power: 180 W, scanning speed: 1400 mm / s, scanning interval: 50 μm, layer thickness: 30 μm.

[0021] S3) The TiN / high-entropy shape memory alloy composite material obtained in S2) is subjected to heat treatment, the heating temperature is 800℃, and the holding time is 15 minutes, to obtain a high-strength low-anisotropy dense TiN / high-entropy shape memory alloy composite material; The vertical maximum recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is increased to 5.9%, and the anisotropy ratio of shape memory performance is reduced from 56% of direct printing to 3%, the yield strength is 812.8 MPa, and the tensile strength is 1111.5 MPa.

[0022] Example 3 S1) First, mix the high-entropy shape memory alloy with 1.5% of nano-TiN particles to obtain a mixed powder; S2) the mixed alloy powder obtained in S1) is subjected to laser powder bed fusion (LPBF) printing to obtain a dense TiN / high-entropy shape memory alloy composite material; The specific process parameters of the laser powder bed fusion (LPBF) printing are as follows: laser power: 250 W, scanning speed: 600 mm / s, scanning interval: 50 µm, and layer thickness: 30 µm. S3) the TiN / high-entropy shape memory alloy composite material obtained in S2) is subjected to heat treatment at a heating temperature of 700 ℃ for 12 minutes to obtain a high-strength low-anisotropy dense TiN / high-entropy shape memory alloy composite material. The vertical maximum recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is increased to 5.9%, and the anisotropy ratio of the shape memory performance is reduced from 56% of the direct printing to 10%, the yield strength is 712.8 MPa, and the tensile strength is 1012.7 MPa.

[0023] Example 4 S1) high-entropy shape memory alloy is first mixed with 2.0% nano-particle TiN to obtain a mixed powder; S2) the mixed alloy powder obtained in S1) is subjected to laser powder bed fusion (LPBF) printing to obtain a dense TiN / high-entropy shape memory alloy composite material; The specific process parameters of the laser powder bed fusion (LPBF) printing are as follows: laser power: 220 W, scanning speed: 1200 mm / s, scanning interval: 75 µm, and layer thickness: 30 µm.

[0024] S3) the TiN / high-entropy shape memory alloy composite material obtained in S2) is subjected to heat treatment at a heating temperature of 650 ℃ for 20 minutes to obtain a high-strength low-anisotropy dense TiN / high-entropy shape memory alloy composite material. The vertical maximum recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is increased to 5.2%, and the anisotropy ratio of the shape memory performance is reduced from 56% of the direct printing to 7%, the yield strength is 867.1 MPa, and the tensile strength is 907.6 MPa.

[0025] The influence of the mixing of nano-particles and the subsequent heat treatment on the shape memory performance of the 4D-printed shape memory alloy in the method of the present application is shown in the comparison schematic diagram as shown in Figure 4 (a) the influence of the addition of nano-TiN on the deformation recovery ratio of the 4D-printed high-entropy shape memory alloy, (b) the influence of the addition of nano-TiN on the recoverable strain of the 4D-printed high-entropy shape memory alloy, (c) the influence of the heat treatment on the deformation recovery ratio of the 4D-printed TiN / HESMA, and (d) the influence of the heat treatment on the deformation recoverable strain of the 4D-printed TiN / HESMA.

[0026] Effects of mixed nanoparticles and subsequent heat treatment on shape memory performance of 4D printed shape memory alloy as shown in Figure 5 (a) is the effect of nano TiN addition on the deformation recovery ratio of 4D printed high-entropy shape memory alloy, (b) is the effect of nano TiN addition on the recoverable strain of 4D printed high-entropy shape memory alloy, (c) is the effect of heat treatment on the deformation recovery ratio of 4D printed TiN / HESMA, and (d) is the effect of heat treatment on the recoverable strain of 4D printed TiN / HESMA.

[0027] Table 1 is the effect of adding nanoparticles on the mechanical properties and functional characteristics of 4D printed high-entropy shape memory alloy: Note: HESMA is high-entropy shape memory alloy, H is horizontal sample, and V is vertical sample.

[0028] The above has carried out the detailed explanation to the present application, but the present application is not limited to the above-mentioned embodiment, still can make various changes or substitution within the knowledge range possessed by the person skilled in the art without departing from the purpose of the present application, makes many other changes without departing from the concept and range of the present application. It should be understood that the present application is not limited to a specific embodiment, and the scope of the present application is defined by the claims.

Claims

1. A method for improving strength and reducing anisotropy of 4D-printed high-entropy shape memory alloys, characterized in that, The method specifically includes the following steps: S1) First, mix the high-entropy shape memory alloy with a certain amount of TiN nanoparticles to obtain a mixed powder; S2) The mixed alloy powder obtained in S1) is subjected to laser powder bed melting LPBF printing to obtain TiN / high entropy shape memory alloy composite material; S3) Heat-treat the TiN / high-entropy shape memory alloy composite material obtained in S2) to obtain a high-strength, low-anisotropy, dense TiN / high-entropy shape memory alloy composite material.

2. The method according to claim 1, characterized in that, The mass percentage of nano-TiN particles in the mixed powder in S1) is 0.5%-2.0%; The powder is mixed mechanically.

3. The method according to claim 1, characterized in that, The specific process parameters for laser powder bed fusion LPBF printing in S2) are as follows: laser power: 180-250W, scanning speed: 600-1400mm / s, scanning spacing: 50-80μm, and layer thickness: 30μm.

4. The method according to claim 1, characterized in that, The heat treatment temperature in S3) is 650-900℃, and the time is 10-20 minutes.

5. The method according to claim 1, characterized in that, The vertical recoverable strain of the dense TiN / high-entropy shape memory alloy composite material is increased to 5.0%-6.1%, and the anisotropy ratio of the shape memory performance is reduced from 56% in direct printing to 3.1-9.0%. The yield strength is 650.0-900.0 MPa, and the tensile strength is 900.0-1350.0 MPa.

6. A TiN / high-entropy shape memory alloy composite material, characterized in that, The TiN / high-entropy shape memory alloy composite material is prepared by the method described in any one of claims 1-5.

Images