CN114411035A - Precipitation strengthening type medium-entropy alloy suitable for laser additive manufacturing and preparation method thereof - Google Patents

Abstract

The invention provides a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing and a preparation method thereof. The precipitation-strengthened medium-entropy alloy is Ni _a Co _b Cr _c Al _{d Me} , wherein M is Ti, Ta, Nb and one or more elements in Mo, a, b, c, d and e represent the mole percentages of the corresponding elements respectively, b=20%-40%, c=20%-25%, d>1%, e>0, d+e<7%, a+b+c+d+e=100%. The precipitation-strengthened medium-entropy alloy of the present invention is prepared by using the laser selective melting forming technology or the laser three-dimensional forming technology, and realizes the preparation of a novel precipitation-strengthening medium-entropy alloy with high density, no cracks and excellent comprehensive mechanical properties.

Description

Precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing and preparation method thereof

technical field

The invention relates to the technical field of laser additive manufacturing of metal materials, in particular to a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing and a preparation method thereof.

Background technique

High/medium-entropy alloys exhibit an excellent combination of strength, ductility, and fracture toughness, with a wide range of structuring and functionalization based on a brand-new alloy design strategy that employs several main elements of equal or near equal concentration as alloying elements application prospects. High/medium-entropy alloys with FCC structure show good toughness, but their strength is generally low, which is difficult to meet the application requirements of structural materials. Effective method of toughening.

The traditional preparation method of high/medium entropy alloys is mainly arc melting, which has defects such as single shape and size, easy component segregation, shrinkage porosity, shrinkage cavities, etc. This limits the further application and development of high/medium entropy alloys.

Laser additive manufacturing technology is based on the principle of point-by-point, line-by-line, and layer-by-layer accumulation of materials. Through the rapid interaction of high-energy laser beams and metal powders, the near-net shape of complex structures or customized parts is realized with extremely high manufacturing flexibility. This technology has the advantages of high material utilization, high flexibility in the manufacturing process, short cycle, uniform and small microstructure, etc., and provides great potential for the preparation of high/medium entropy alloy components with excellent comprehensive properties, high precision, full density and complex shapes. However, the high temperature gradient and large cooling rate during additive manufacturing usually lead to high thermal residual stress, which is prone to metallurgical defects such as cracks. Especially for precipitation-strengthened high/medium entropy alloys, defects such as liquefaction cracking and strain aging cracking are very likely to occur during the printing process, which affect the structural integrity and comprehensive performance of the components. Therefore, designing a precipitation-strengthened high/medium entropy alloy suitable for laser additive manufacturing is a key problem that needs to be solved urgently in this field.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings of traditional high/medium-entropy alloy preparation methods, provide a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing and a preparation method thereof, and realize a new type of precipitation with high density, no cracks and excellent comprehensive mechanical properties. Preparation of strengthened medium-entropy alloys.

The present invention is achieved through the following technical solutions:

A precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing, wherein the precipitation-strengthened medium-entropy alloy is Ni _a Co _b Cr _c Al _{d Me} , wherein M is one of Ti, Ta, Nb and Mo or Multiple elements, a, b, c, d and e represent the mole percentage of each element respectively, b=20%-40%, c=20%-25%, d>1%, e>0, d+e <7%, a+b+c+d+e=100%.

Preferably, it is prepared by using laser selective melting forming technology.

Further, including:

Step 1, preparation and pretreatment of medium entropy alloy powder

According to the molar percentage of claim 1, get the metal raw material corresponding to each element, adopt the vacuum air atomization method to prepare the medium-entropy alloy pre-alloy spherical powder, sieve, and dry to obtain the medium-entropy alloy powder;

Step 2, laser selective melting to form Ni _a Co _b Cr _c Al _{d Me} precipitation-strengthened medium-entropy alloy

According to the geometric shape of the medium-entropy alloy component to be prepared, a 3D solid model is established and converted into a file in STL format, and imported into the construction software of the laser selective melting forming equipment for layering processing; high-purity argon gas is introduced to make the forming chamber The oxygen content is lower than 300ppm. According to the set process parameters and scanning strategy of laser selective melting and forming, the medium-entropy alloy powder is melted and formed layer by layer to prepare a medium-entropy alloy component.

Further, the process parameters of laser selective melting and forming are as follows: the laser power P is 160-360W, the scanning rate v is 600-1000mm/s, the scanning distance h is 60-80μm, the powder layer thickness t is 30-50μm, and the spot diameter is 30-50μm. is 80 μm, and the volume energy density VED range is 140 J/mm ³ <VED<240 J/mm ³ , where VED=P/vht.

Further, the scanning strategy is 67° rotation scanning, reciprocating scanning, reciprocating interleaving scanning or 45° rotation partition scanning.

Further, it also includes a heat treatment step: heating the medium-entropy alloy component to 600°C to 800°C for 12h≤t≤480h, and water-cooling after the heat preservation to obtain a heat-treated medium-entropy alloy.

Preferably, it is prepared by using a laser three-dimensional forming technology.

Further, including:

Step 1, preparation and pretreatment of medium entropy alloy powder

According to the molar percentage of claim 1, get the metal raw material corresponding to each element, adopt the vacuum air atomization method to prepare the medium-entropy alloy pre-alloy spherical powder, sieve, and dry to obtain the medium-entropy alloy powder;

Step 2 Laser three-dimensional forming Ni _a Co _b Cr _c Al _{d Me} precipitation strengthening type medium entropy alloy

According to the geometric shape of the medium-entropy alloy component to be prepared, a three-dimensional solid model is established and converted into STL format and sent to the laser stereoforming equipment, the printing process parameters and laser scanning path are set, and the medium-entropy alloy powder is sent to the high-energy laser in the laser stereoforming equipment. In the molten pool formed by the beam, by depositing raw materials point by point, line by line and layer by layer on the substrate, the intermediate entropy alloy component is obtained by printing.

Further, the printing process parameters are as follows: the laser power is 2KW-3.5KW, the scanning rate is 300-800mm/min, the powder feeding speed is 5-8g/min, the Z-axis lift is 0.4-1.0mm, and the overlap ratio is 50 %, the spot diameter is 3mm, and the scanning path is a reciprocating interweaving scanning path.

Further, it also includes a heat treatment step: heating the medium-entropy alloy component to 600°C to 800°C for 3h≤t≤480h, and cooling with water after the heat preservation to obtain a heat-treated medium-entropy alloy.

Compared with the prior art, the present invention has the following beneficial effects:

The invention designs a precipitation-strengthening medium-entropy alloy suitable for laser additive manufacturing. In the Ni _a Co _b Cr _c matrix, in the form of multi-principalization, Al and Ti, Ta, Nb or Mo elements are added to promote γ' phase is generated and significantly enhances the strengthening effect of the γ' precipitation phase. It is stipulated that the sum of the above-mentioned Al, Ti, Ta, Nb, and Mo is less than 7%. High susceptibility to liquefaction cracking and strain aging cracking in material manufacturing; on the other hand, γ' precipitates with excellent strengthening effect can be obtained. According to the above formula, the present invention adopts the laser selective melting forming technology and the laser three-dimensional forming technology to realize the preparation of a new type of precipitation-strengthened medium-entropy alloy with high density, no cracks and excellent comprehensive mechanical properties.

Further, the generation of γ' precipitation phase is promoted by heat treatment of the laser additive manufacturing sample, and at the same time, a non-uniform structure with partial recrystallization is obtained, which greatly improves the comprehensive mechanical properties of the precipitation-strengthened medium-entropy alloy designed in the present invention. , further strengthening and toughening of entropy alloys in laser additive manufacturing.

Description of drawings

Fig. 1 is the powder morphology of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy powder formed by laser selective melting in Example 1 of the present invention.

FIG. 2 is a Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy bulk sample prepared by laser selective melting technology in Example 1 of the present invention.

FIG. 3 is the variation law of the density of the entropy alloy in the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ prepared by the laser selective melting technology in Example 1 of the present invention with the bulk energy density.

Fig. 4 is the scanning electron microscope picture of the entropy alloy of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ prepared by casting and laser selective melting technology respectively in Example 1 of the present invention, wherein (a) is the as-cast state, (b) is the deposition state.

FIG. 5 is the room temperature tensile stress-strain curve of the entropy alloy formed in the as-cast state and by laser selective melting of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 1 of the invention.

6 is a scanning electron microscope image (a) and a transmission electron microscope selected area electron diffraction pattern (b) of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy formed by laser selective melting in Example 1 of the present invention after heat treatment at 600° C./12h.

7 is a room temperature tensile stress-strain curve of the entropy alloy formed by laser selective melting and forming of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 1 of the present invention after different heat treatment temperatures and times.

FIG. 8 is the powder morphology of the entropy alloy in the laser three-dimensional forming of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 2 of the present invention.

FIG. 9 is a bulk sample of entropy alloy in Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy formed by laser three-dimensional forming in Example 2 of the present invention.

10 is the room temperature tensile stress-strain curve of the entropy alloy of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ prepared by using different laser powers in Example 2 of the present invention.

FIG. 11 shows the microstructure characteristics of the entropy alloy in the laser three-dimensional forming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 2 of the present invention.

FIG. 12 is the room temperature tensile stress-strain curve of the entropy alloy of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ prepared by using the optimal laser three-dimensional forming process parameters in Example 2 of the present invention.

FIG. 13 is a scanning electron microscope picture of the entropy alloy of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy after heat treatment in Example 2 of the present invention.

14 is the microhardness of the entropy alloy after heat treatment in the laser three-dimensional forming of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 2 of the present invention.

15 is the room temperature tensile stress-strain curve of the laser three-dimensionally formed Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy after heat treatment at 700° C./3h (LSF-HT).

Detailed ways

In order to further understand the present invention, the present invention will be described below in conjunction with the embodiments. These descriptions are only used to further explain the features and advantages of the present invention, and are not intended to limit the claims of the present invention.

The precipitation-strengthened medium-entropy alloy with excellent strong plasticity suitable for laser additive manufacturing according to the present invention, the alloy composition of the precipitation-strengthened medium-entropy alloy is Ni _a Co _b Cr _c Al _{d Me} , wherein a, b, c, d, and e represent the mole percentage of each element respectively, a is the remainder, b=20-40at.%, c=20-25at.%, d>1at.%, e>0, d+e <7 at.%, a+b+c+d+e=100 at.%, the trace element M includes one or more components of Ti, Ta, Nb, and Mo. The selected medium-entropy alloy is pre-alloyed spherical powder prepared by vacuum air atomization or plasma rotating electrode method, and the purity is more than 99.9%.

The present invention provides a preparation method of the above-mentioned precipitation-enhanced medium-entropy alloy laser selective melting forming technology, which comprises the following steps:

1. Preparation and pretreatment of medium entropy alloy powder

According to the molar percentage of each element in the nominal chemical composition of the medium-entropy alloy, the medium-entropy alloy pre-alloyed spherical powder is prepared by vacuum air atomization, and the pre-alloyed spherical powder is sieved, and the powder particle size is 15- 53 μm. The oxygen content and nitrogen content are less than 300 ppm, the preferred oxygen content is 131 ppm, and the nitrogen content is 53 ppm. Before laser selective melting, the pre-alloyed spherical powder was dried at 80°C for 4 h to remove the moisture in the powder, and then placed in the powder feeding cylinder of the laser selective melting equipment.

2. Substrate surface treatment

Select a stainless steel or carbon steel substrate, grind the surface to be deposited, and wash with acetone and alcohol in sequence to remove surface oil stains, then blow dry, install the substrate on a forming platform and level it. Before printing, the substrate is preheated to 100°C-200°C, and the preferred substrate preheating temperature is 200°C.

3. Laser selective melting forming Ni _a Co _b Cr _c Al _{d Me} precipitation-strengthened medium-entropy alloy

The three-dimensional solid model is established on the computer and converted into a file in STL format, and then imported into the construction software of the laser selective melting forming equipment for layered processing. The process parameters of laser selective melting and forming are as follows: laser power P is 160-360W, scanning rate v is 600-1000mm/s, scanning distance h is 60-80μm, powder layer thickness t is 30-50μm, spot diameter is 80μm, Scanning strategies can select 67° rotary scan, reciprocating scan, reciprocating interleaved scan and 45° rotary partition scan path. Before printing, high-purity argon gas with a purity of 99.99 wt. % was introduced to make the oxygen content in the forming chamber less than 300 ppm. According to the set process parameters and scanning path of laser selective melting forming, Ni _a Co _b Cr _c Al _{d Me} medium entropy alloy pre-alloyed spherical powder is melted and formed layer by layer to prepare a bulk sample. The present invention adopts the method of laser selective melting and forming to prepare Ni _a Co _b Cr _c Al _d Me precipitation strengthening type medium entropy alloy, and selects optimized laser selective melting and forming process parameters, that is, high volume energy density _VED (140 J/mm ^{3 )} <VED<240J/mm ³ , VED=P/vht), which can greatly improve the density of the printed alloy, thereby improving its comprehensive mechanical properties, and realizing the complex structure of precipitation-strengthened medium-entropy alloys with high density, no cracks and excellent performance. Integrated precision forming of parts.

The present invention also provides a method for preparing the above-mentioned precipitation-enhanced medium-entropy alloy laser three-dimensional forming technology, comprising the following steps:

1. Preparation and pretreatment of medium entropy alloy powder

According to the molar percentage of each element in the nominal chemical composition of the medium-entropy alloy, the medium-entropy alloy pre-alloyed spherical powder is prepared by vacuum air atomization, and the pre-alloyed spherical powder is sieved, and the powder particle size is 45- 150μm. The oxygen content and nitrogen content are less than 300 ppm, the preferred oxygen content is 131 ppm, and the nitrogen content is 53 ppm. Before the laser three-dimensional forming experiment, the powder was dried to avoid the influence of moisture adsorbed in the powder on the material forming, and then the powder was placed in the powder feeder of the laser three-dimensional forming equipment.

2. Substrate surface treatment

A stainless steel or carbon steel substrate is selected, the surface to be deposited is polished, and then washed with acetone and alcohol in turn to remove oil stains on the surface, and then air-dried to fix the substrate on the forming platform.

3. Laser three-dimensional forming Ni _a Co _b Cr _c Al _{d Me} precipitation strengthened medium entropy alloy

According to the geometric shape of the medium-entropy alloy component, a three-dimensional solid model is established on the computer, converted into STL format and sent to the laser forming equipment, and the printing process parameters and laser scanning path are set. Under the control of the numerical control system, the medium-entropy alloy spherical powder is coaxially transmitted The powder feeding nozzle is sent to the molten pool formed by the high-energy laser beam. By depositing raw materials point by point, line by line and layer by layer on the substrate, the formation of complex components with specific shapes and sizes is realized. The process parameters of the above-mentioned three-dimensional laser forming are as follows: the laser power is 2KW-3.5KW, the scanning rate is 300-800mm/min, the powder feeding speed is 5-8g/min, the Z-axis lift is 0.4-1.0mm, and the lap rate is 0.4-1.0mm. 50%, the spot diameter is 3mm, and the scanning strategy selects reciprocating interleaving scanning, that is, in the same deposition layer, the scanning path is S-shaped, and the scanning direction is rotated 90° for adjacent deposition layers. The above-mentioned laser three-dimensional forming process uses high-purity argon gas as the protective gas and powder carrier gas, and the oxygen content during the printing process is less than 2000ppm. According to the above set process parameters and scanning path of laser three-dimensional forming, Ni _a Co _b Cr _c Al _{d Me} medium entropy alloy powder is melted and formed layer by layer to prepare a bulk sample. By optimizing the laser power, scanning speed, powder feeding speed and Z-axis lift, the quality of the printed alloy can be improved, the microstructure can be optimized, and its comprehensive mechanical properties can be further improved to achieve a fully dense, defect-free, and comprehensive performance. Integrated precision forming of complex structural parts of entropy alloys.

The present invention also provides a heat treatment method for preparing the Ni _a Co _b Cr _c Al _{d Me} precipitation-strengthened medium-entropy alloy by the above-mentioned laser additive manufacturing technology, comprising the following steps:

In the present invention, in order to promote the generation of a high volume fraction of the precipitation phase, the laser additive manufacturing Ni _a Co _b Cr _c Al _{d Me} type precipitation-strengthened medium-entropy alloy is heat-treated. The heat treatment method preferably includes: heating the Ni _a Co _b Cr _c Al _d Me precipitation-strengthened medium-entropy alloy prepared by laser additive manufacturing to 600 ℃ ~ 800 ℃ for heat preservation, and the selected time is _{12h≤t≤480h} (laser). Selective melting and forming) or 3h≤t≤480h (laser three-dimensional forming), water cooling after heat preservation to obtain a medium-entropy alloy after heat treatment. Heat treatment of the above-mentioned laser additive manufacturing Ni _a Co _b Cr _c Al _{d Me} medium entropy alloy can effectively promote the precipitation of a high volume fraction of the precipitation phase, and at the same time obtain an incompletely recrystallized structure, further optimizing the laser additive manufacturing. The comprehensive mechanical properties of Ni _a Co _b Cr _c Al _{d Me} medium-entropy alloys realize the preparation of high-strength and high-toughness medium-entropy alloys.

Example 1

A precipitation-strengthening medium-entropy alloy suitable for laser additive manufacturing, the chemical formula of the medium-entropy alloy is Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ , wherein the ratio of each element is a mole percentage. The selected medium-entropy alloy is gas atomized pre-alloyed spherical powder with a purity greater than 99.9%.

The present embodiment 1 adopts the laser selective melting technology to prepare the entropy alloy forming process as follows:

1. Preparation and pretreatment of medium entropy alloy powder

According to the molar ratio of each element in the above-mentioned nominal chemical composition of the medium-entropy alloy, the pre-alloyed spherical powder of the medium-entropy alloy is prepared by the vacuum air atomization method, and the pre-alloyed powder is sieved, and the particle size of the selected powder is 15- 53 μm, and its typical morphology is shown in Figure 1. The oxygen content was 131 ppm and the nitrogen content was 53 ppm. Before laser selective melting, the powder was dried at 80°C for 4 hours to remove the moisture in the powder. It is then placed in the powder feeding cylinder of the laser selective melting equipment.

2. Substrate surface treatment

A 316L stainless steel substrate was selected, the surface to be deposited was polished, and then washed with acetone and alcohol in turn to remove the surface oil stains, and then blown dry, and the substrate was mounted on a forming platform and leveled. Before printing, the substrates were preheated to 200°C.

3. Laser selective melting forming of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ precipitation-strengthened medium-entropy alloy

A three-dimensional solid model is established on the computer and converted into a file in STL format, which is imported into the construction software of the selective laser melting forming equipment for layered processing. The process parameters of laser selective melting and forming are as follows: the laser power is 160-360W, the scanning rate is 600-1000mm/s, the scanning distance is 60-80μm, the powder layer thickness is 30-50μm, the spot diameter is 80μm, and the scanning strategy is 67 μm. °Rotate scan. Before printing, high-purity argon gas with a purity of 99.99 wt. % was introduced to make the oxygen content in the forming chamber less than 300 ppm.

According to the parameters shown in Table 1, adjust the laser power, scanning rate, and scanning spacing, and fix the powder layer thickness to 30 μm to carry out the laser selective melting forming experiment, and obtain the laser selective melting forming sample as shown in Figure 2. The density of the samples was tested, and the results are shown in Figure 3.

Table 1 Experimental parameters

The optimal process parameters are determined by the experiments shown in Table 1: the laser power is 320W, the scanning speed is 1000mm/s, the scanning spacing is 70μm, and the thickness of the powder layer is 30μm.

4. Microstructure characterization and performance test of laser selective melting forming samples

Scanning electron microscope (SEM) was used to observe the microstructure of the samples formed by the optimal laser melting parameters. As shown in Fig. 4(b), the forming quality of the alloy was good, and no defects such as cracks were observed. The density is greater than 99.6%. Compared with the as-cast microstructure (prepared by vacuum arc melting), the microstructure of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ precipitation-strengthened medium-entropy alloy prepared by laser selective melting deposition is more fine and uniform. Example 1 Selected laser selective melting Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy (SLM) formed by the optimal process parameters has a room temperature yield strength of 671 MPa, a tensile strength of 913 MPa, an elongation of 36%, and a hardness of 671 MPa. is 310HV. Its strength is much higher than that of the as-cast state, and the tensile plasticity is comparable to that of the as-cast state, as shown in Figure 5, where the yield strength of the entropy alloy as-cast (Cast) in Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ is 342MPa, and the tensile strength is 648MPa, and the elongation is 38%.

5. Laser selective melting forming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy heat treatment

Through aging treatment, the formation of entropy alloy precipitates in Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ by laser selective melting is promoted to achieve further strengthening and toughening. In the present invention, the heat treatment method includes heating the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy formed by the optimal laser selective melting parameters to 600℃～800℃ for heat preservation, and the selected time is 12h≤ t≤480h, water cooling after heat preservation to obtain a medium entropy alloy after heat treatment.

Specifically, three sets of experiments were carried out. In one set of experiments, heat treatment was performed at 600 °C for 12 h, in another set of experiments, heat treatment at 700 °C for 12 h, and in another set of experiments, heat treatment at 700 °C for 480 h.

Figure 6 shows the SEM image (a) and TEM image (b) of the SEM image (a) and TEM image (b) of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy formed by laser selective melting and heat treatment at 600 °C for 12 h. From Figure 6 (a) ), partial recrystallization of the deposited structure can be observed, and diffraction spots of the FCC phase and the γ' precipitation phase can be observed simultaneously in Fig. 6(b). The tensile properties of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy heat-treated samples formed by laser selective melting were tested at room temperature. The results are shown in Figure 7. The results show that the strength is greatly improved after heat treatment. After 480h heat treatment, the yield strength can reach 1098MPa, the tensile strength is 1466MPa, and the elongation is 25%.

Example 2

A precipitation-strengthening medium-entropy alloy suitable for laser additive manufacturing, the chemical formula of the medium-entropy alloy is Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ , wherein the ratio of each element is a mole percentage. The selected medium-entropy alloy is gas atomized pre-alloyed spherical powder with a purity greater than 99.9%.

The present embodiment 2 adopts the laser three-dimensional forming technology to prepare the entropy alloy forming process as follows:

1. Preparation and pretreatment of medium entropy alloy powder

According to the molar ratio of each element in the nominal chemical composition of the medium-entropy alloy, the medium-entropy alloy pre-alloy spherical powder is prepared by the vacuum air atomization method, and the pre-alloy spherical powder is sieved, and the powder particle size is 45. -150 μm, and its typical morphology is shown in Figure 8. The oxygen content was 131 ppm and the nitrogen content was 53 ppm. Before the laser three-dimensional forming experiment, the powder was dried to avoid the influence of moisture adsorbed in the powder on the material forming, and then the powder was placed in the powder feeder of the laser three-dimensional forming equipment.

2. Substrate surface treatment

A 316L stainless steel substrate was selected, the surface to be deposited was polished, and washed with acetone and alcohol in turn to remove the surface oil, and then dried, and the substrate was fixed and clamped on the forming platform.

3. Laser three-dimensional forming of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ precipitation-strengthened medium-entropy alloys

According to the geometric shape of the medium-entropy alloy component, a three-dimensional solid model is established on the computer, converted into STL format and sent to the laser forming equipment, and the printing process parameters and laser scanning path are set. The powder nozzle is sent to the molten pool formed by the high-energy laser beam, and the formation of complex components with specific shapes and sizes is realized by depositing raw materials point by point, line by line and layer by layer on the substrate. The process parameters of the above-mentioned three-dimensional laser forming are as follows: the laser power is 2KW-3.5KW, the scanning rate is 300-800mm/min, the powder feeding speed is 5-8g/min, the Z-axis lift is 0.4-1.0mm, and the lap rate is 0.4-1.0mm. 50%, the spot diameter is 3mm, and the scanning strategy selects reciprocating interleaving scanning, that is, in the same deposition layer, the scanning path is S-shaped, and the scanning direction is rotated 90° for adjacent deposition layers. The above-mentioned laser three-dimensional forming process uses high-purity argon gas as the protective gas and powder carrier gas, and the oxygen content during the printing process is less than 2000ppm.

Adjust the laser power, scanning rate, powder feeding speed, and Z-axis lifting amount to explore the optimal process, and print block samples with different linear energy densities. The specific process parameters used are shown in Table 2.

The concrete experimental parameters of table 2 embodiment 2

The Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy bulk sample was prepared using the above laser stereoforming process parameters, and its typical macroscopic morphology is shown in Figure 9. The room temperature tensile properties were tested for the three samples respectively, and the results are shown in Figure 10. Through the test results of mechanical properties, the optimal process parameters are determined: the laser power is 2800W, the scanning speed is 300mm/min, the powder feeding speed is 5g/min, the Z-axis lift is 0.5mm, and the overlap ratio is 50%.

4. Microstructure characterization and performance test of laser three-dimensional forming samples

Electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) were used to observe the microstructure of the formed samples under the optimal parameters. As shown in Figure 11, the alloy forming quality was good, and no defects such as cracks, pores, and poor fusion were observed. . And there is a small amount of γ' nano-scale precipitates in the entropy alloy structure of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ prepared by laser stereoforming technology, as shown in Figure 11(b). The room temperature mechanical properties of the laser three-dimensionally formed Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ entropy alloy prepared with the preferred process parameters are shown in Figure 12. The yield strength along the construction direction (longitudinal direction) is 723 MPa, and the tensile strength is 1078 MPa. The elongation is 39%, the hardness is 355HV; the yield strength along the scanning direction (transverse direction) is 566MPa, the tensile strength is 1011MPa, the elongation is 47%, and the hardness is 284HV. Compared with traditional casting, the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ meso-entropy alloy samples prepared by laser stereoforming have high strong-plastic bonding.

5. Laser three-dimensional forming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ entropy alloy heat treatment.

Further strengthening and toughening can be achieved by further promoting the generation of entropy alloy precipitates in the laser three-dimensional forming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ by aging treatment. In the present invention, the heat treatment method includes: heating the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy formed by laser three-dimensional under optimal process parameters to 700°C for heat preservation, the selected time is 3h, and after the heat preservation is completed Water-cooled to obtain a medium-entropy alloy after heat treatment.

Figure 13 shows the high-magnification scanning electron microscope image of the laser three-dimensionally formed Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy after heat treatment at 700℃/3h. It can be seen that, compared with the original as-deposited structure, the volume fraction of the precipitated phase A significant increase. Figure 14 shows the microhardness variation of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloys prepared with different laser powers after heat treatment. After heat treatment, due to the formation of high volume fraction of precipitates, it can be seen that the hardness is significantly improved. The hardness of the sample with a laser power of 2.8KW after heat treatment at 700℃/3h is about 415HV. Figure 15 shows the tensile properties of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloys with a laser power of 2.8KW after heat treatment at 700°C/3h, the yield strength is 808MPa, the tensile strength is 1168MPa, and the elongation is 32%, compared with the as-deposited samples, the strength is significantly improved due to the generation of precipitates.

Claims (10)

1. A precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing, wherein the precipitation-strengthened medium-entropy alloy is Ni _a Co _b Cr _c Al _{d Me} , wherein M is Ti, Ta, Nb and One or more elements in Mo, a, b, c, d and e represent the mole percentage of each element respectively, b=20%-40%, c=20%-25%, d>1%, e >0, d+e<7%, a+b+c+d+e=100%. 2. The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 1, characterized in that the preparation is performed by using a laser selective melting and forming technology. 3. The preparation method of a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 2, characterized in that, comprising: Step 1, preparation and pretreatment of medium entropy alloy powder According to the molar percentage of claim 1, get the metal raw material corresponding to each element, adopt the vacuum air atomization method to prepare the medium-entropy alloy pre-alloy spherical powder, sieve, and dry to obtain the medium-entropy alloy powder; Step 2, laser selective melting to form Ni _a Co _b Cr _c Al _{d Me} precipitation-strengthened medium-entropy alloy According to the geometric shape of the medium-entropy alloy component to be prepared, a 3D solid model is established and converted into a file in STL format, and imported into the construction software of the laser selective melting forming equipment for layering processing; high-purity argon gas is introduced to make the forming chamber The oxygen content is lower than 300ppm. According to the set process parameters and scanning strategy of laser selective melting and forming, the medium-entropy alloy powder is melted and formed layer by layer to prepare a medium-entropy alloy component. 4. The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 3, wherein the process parameters of laser selective melting and forming are as follows: the laser power P is 160-360 W, the scanning rate v is 600～1000mm/s, the scanning distance h is 60-80μm, the thickness of the powder layer t is 30-50μm, the spot diameter is 80μm, and the volume energy density VED range is 140J/mm ³ <VED<240J/mm ³ , where VED =P/vht. 5. The preparation method of a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 3, wherein the scanning strategy is 67° rotation scanning, reciprocating scanning, reciprocating interweaving scanning or 45° rotation zone scanning . 6 . The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 3 , further comprising a heat treatment step: heating the medium-entropy alloy component to 600℃～800℃ for 12h≤ t≤480h, water cooling after the heat preservation, to obtain the medium entropy alloy after heat treatment. 7 . The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 1 , wherein the preparation is carried out by using a laser three-dimensional forming technology. 8 . 8. The preparation method of a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 7, characterized in that, comprising: Step 1, preparation and pretreatment of medium entropy alloy powder According to the molar percentage of claim 1, get the metal raw material corresponding to each element, adopt the vacuum air atomization method to prepare the medium-entropy alloy pre-alloy spherical powder, sieve, and dry to obtain the medium-entropy alloy powder; Step 2 Laser three-dimensional forming Ni _a Co _b Cr _c Al _{d Me} precipitation strengthening type medium entropy alloy According to the geometric shape of the medium-entropy alloy component to be prepared, a three-dimensional solid model is established and converted into STL format and sent to the laser stereoforming equipment, the printing process parameters and laser scanning path are set, and the medium-entropy alloy powder is sent to the high-energy laser in the laser stereoforming equipment. In the molten pool formed by the beam, by depositing raw materials point by point, line by line and layer by layer on the substrate, the intermediate entropy alloy component is obtained by printing. 9 . The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 8 , wherein the printing process parameters are as follows: the laser power is 2KW～3.5KW, and the scanning rate is 300～800mm/ min, the powder feeding speed is 5-8g/min, the Z-axis lift is 0.4-1.0mm, the overlap ratio is 50%, the spot diameter is 3mm, and the scanning path is a reciprocating interweaving scanning path. 10 . The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 8 , further comprising a heat treatment step: heating the medium-entropy alloy component to 600° C. to 800° C. for 3h≤ t≤480h, water cooling after the heat preservation, to obtain the medium entropy alloy after heat treatment.

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