CN114411035B - Precipitation strengthening type medium-entropy alloy suitable for laser additive manufacturing and preparation method thereof - Google Patents

Abstract

The present invention provides a precipitation-enhanced medium-entropy alloy suitable for laser additive manufacturing and a preparation method thereof, wherein the precipitation-enhanced 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 respectively represent the molar percentages of the corresponding elements, b=20%-40%, c=20%-25%, d>1%, e>0, d+e<7%, a+b+c+d+e=100%. The precipitation-enhanced medium-entropy alloy of the present invention is prepared by laser selective melting forming technology or laser three-dimensional forming technology, and realizes the preparation of a new type of precipitation-enhanced medium-entropy alloy with high density, no cracks and excellent comprehensive mechanical properties.

Description

Precipitation-enhanced 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-enhanced medium-entropy alloy suitable for laser additive manufacturing and a preparation method thereof.

Background technique

High/medium-entropy alloys use a new alloy design strategy, using several iso-concentration or near-iso-concentration main elements as alloying elements, exhibiting an excellent combination of strength, ductility and fracture toughness, with a wide range of structuring and functionalization Application prospects. High/medium entropy alloys with FCC structure exhibit 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 based on arc melting, which has defects such as single shape and size, prone to component segregation, shrinkage porosity, and shrinkage cavities. The further application and development of high/medium entropy alloys are limited.

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 action of high-energy laser beams and metal powders, with high manufacturing flexibility, the near-net shape of complex structures or customized parts is realized. This technology has the advantages of high material utilization, high flexibility in the manufacturing process, short cycle time, uniform and fine microstructure, etc., and provides great potential for the preparation of high-/medium-entropy alloy components with excellent comprehensive performance, high-precision full-density and complex shapes. However, the high temperature gradient and large cooling rate in the additive manufacturing process 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 prone to occur during the printing process, which affects the structural integrity and comprehensive performance of the component. Therefore, designing precipitation-strengthened high/medium entropy alloys suitable for laser additive manufacturing is a key problem that needs to be solved urgently in this field.

Contents 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 its preparation method, 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 realized through the following technical solutions:

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

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

Further, including:

Step 1, preparation and pretreatment of medium entropy alloy powder

According to the mole percentage described in claim 1, the metal raw materials corresponding to each element are taken, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by vacuum atomization, sieved, and dried to obtain the medium-entropy alloy powder;

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

Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared and convert it into a file in STL format, import it into the construction software of the laser selective melting forming equipment, and perform layered processing; inject high-purity argon gas 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, and the medium-entropy alloy component is prepared.

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

Further, the scanning strategy is 67° rotating scanning, reciprocating scanning, reciprocating interlaced scanning or 45° rotating partition scanning.

Further, a heat treatment step is also included: raising the temperature of the medium-entropy alloy component to 600° C. to 800° C. for 12 hours ≤ t ≤ 480 hours, and water cooling after the heat preservation is completed to obtain the heat-treated medium-entropy alloy.

Preferably, it is prepared by laser stereoforming technology.

Further, including:

Step 1, preparation and pretreatment of medium entropy alloy powder

According to the mole percentage described in claim 1, the metal raw materials corresponding to each element are taken, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by vacuum atomization, sieved, and dried to obtain the medium-entropy alloy powder;

Step 2 Laser Stereo Forming Ni _a Co _b Cr _c Al _d M _e Precipitation Strengthened Medium Entropy Alloy

Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared, convert it into STL format and send it to the laser three-dimensional forming equipment, set the printing process parameters and laser scanning path, and send the medium-entropy alloy powder to the high-energy laser in the laser three-dimensional forming equipment In the molten pool formed by the beam, the medium-entropy alloy components are printed by depositing raw materials point by point, line by line, and layer by layer on the substrate.

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

Further, a heat treatment step is also included: raising the temperature of the medium-entropy alloy member to 600° C. to 800° C. for 3 hours ≤ t ≤ 480 hours, and water cooling after the heat preservation is completed to obtain the heat-treated medium-entropy alloy.

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

The present invention designs a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing. In the form of multi-principalization in the Ni _a Co _b Cr _c matrix, Al and Ti, Ta, Nb or Mo elements are added to promote γ' phase produced and significantly enhanced the strengthening effect of the γ' precipitated phase. The sum of the above-mentioned Al, Ti, Ta, Nb, and Mo is stipulated to be less than 7%. The reason is that on the one hand, the problem of poor formability in the additive manufacturing process caused by the high volume fraction of the γ' phase is overcome, that is, the alloy is reduced in the laser amplified phase. High susceptibility to liquefaction cracking and strain aging cracking in material manufacturing; on the other hand, it can obtain γ' precipitated phase with excellent strengthening effect. According to the above formula, the present invention respectively 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, by heat-treating the laser additive manufacturing samples to promote the generation of γ' precipitates, and at the same time obtain a heterogeneous structure with partial recrystallization, which greatly improves the comprehensive mechanical properties of the precipitation-strengthened medium-entropy alloy designed in the present invention , to achieve further strengthening and toughening of entropy alloys in laser additive manufacturing.

Description of drawings

Fig. 1 is the morphology of the medium-entropy alloy powder of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ 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 shows the change law of the compactness of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy with the bulk energy density prepared by laser selective melting technology in Example 1 of the present invention.

Figure 4 is a scanning electron microscope image of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy prepared by casting and laser selective melting techniques in Example 1 of the present invention, where (a) is cast and (b) is deposited state.

Fig. 5 is the tensile stress-strain curve at room temperature of the as-cast and laser selective melting formed Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloys in Example 1 of the present invention.

Fig. 6 is a scanning electron microscope picture (a) and a transmission electron microscope selective area electron diffraction picture (b) of a Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy heat-treated at 600°C/12h in Example 1 of the present invention.

Fig. 7 is the tensile stress-strain curve at room temperature 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 different heat treatment temperatures and times.

Fig. 8 is the morphology of the medium entropy alloy powder of the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 2 of the present invention.

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

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

Fig. 11 is the microstructure characteristics of the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy in Example 2 of the present invention.

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

Fig. 13 is a scanning electron micrograph of the heat-treated medium-entropy alloy of the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ in Example 2 of the present invention.

Fig. 14 shows the microhardness of the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy in Example 2 of the present invention after heat treatment.

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

detailed description

In order to further understand the present invention, the present invention will be described below in conjunction with the examples. These descriptions are only 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 described in 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, e respectively represent the mole percentage of each element, a is the balance, 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 of Ti, Ta, Nb, Mo. The selected medium entropy alloy is pre-alloyed spherical powder prepared by vacuum atomization or plasma rotating electrode method, and the purity is greater than 99.9%.

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

1. Preparation and pretreatment of medium entropy alloy powder

Proportioning is carried out according to the mole percentage of each element in the nominal chemical composition of the medium-entropy alloy, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by the vacuum atomization method, and the pre-alloyed spherical powder is sieved, and the particle size of the selected powder is 15- 53 μm. The oxygen content and nitrogen content are less than 300ppm, the preferred oxygen content is 131ppm, and the nitrogen content is 53ppm. Before laser selective melting, the pre-alloyed spherical powder is dried at 80°C for 4 hours 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, polish the surface to be deposited, and clean it with acetone and alcohol in order to remove surface oil, then dry it, install the substrate on the 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. Ni _a Co _b Cr _c Al _{d Me} precipitation-strengthened medium-entropy alloy formed by laser selective melting

Create a three-dimensional solid model on the computer and convert it into a file in STL format, and import it into the construction software of the laser selection melting forming equipment for layering processing. The process parameters of laser selective melting and forming are as follows: laser power P is 160-360W, scanning speed v is 600-1000mm/s, scanning distance h is 60-80μm, powder layer thickness t is 30-50μm, spot diameter is 80μm, The scanning strategy can choose 67° rotating scanning, reciprocating scanning, reciprocating interleaving scanning and 45° rotating partition scanning path. Before printing, high-purity argon gas with a purity of 99.99wt.% is injected to keep the oxygen content in the forming chamber below 300ppm. According to the set process parameters and scanning path of laser selective melting forming, Ni _a Co _b Cr _c Al _d Me _mesophilic alloy pre-alloyed spherical powder was melted layer by layer to prepare block samples. In the present invention, Ni _a Co _b Cr _c Al _d Me precipitation-enhanced medium-entropy alloy is prepared by laser selective melting and forming, and by selecting optimized laser selective melting and forming process parameters, that is, high volume energy density VED ( _140J /mm ³ <VED<240J/mm ³ , VED=P/vht), which can greatly increase the density of the printed alloy, thereby improving its comprehensive mechanical properties, and realizing a high-density, crack-free, and excellent-performance precipitation-strengthened medium-entropy alloy complex structure Integrated precision forming of parts.

The present invention also provides a preparation method of the above-mentioned precipitation-strengthened medium-entropy alloy by laser three-dimensional forming technology, comprising the following steps:

1. Preparation and pretreatment of medium entropy alloy powder

Proportioning is carried out according to the mole percentage of each element in the nominal chemical composition of the medium-entropy alloy, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by the vacuum atomization method, and the pre-alloyed spherical powder is sieved, and the particle size of the selected powder is 45- 150 μm. The oxygen content and nitrogen content are less than 300ppm, the preferred oxygen content is 131ppm, and the nitrogen content is 53ppm. Before the laser three-dimensional forming experiment, the powder was dried to avoid the influence of the moisture absorbed 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

Select a stainless steel or carbon steel substrate, polish the surface to be deposited, and clean it with acetone and alcohol in order to remove surface oil, then dry it, and fix the substrate on the forming platform.

3. 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, a three-dimensional solid model is established on the computer and converted into STL format and sent to the laser forming equipment. 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 The powder feeding nozzle is sent to the molten pool formed by the high-energy laser beam, and the formation of complex components of 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 laser three-dimensional forming are as follows: laser power is 2KW ~ 3.5KW, scanning speed is 300 ~ 800mm/min, powder feeding speed is 5-8g/min, Z-axis lift is 0.4-1.0mm, lap rate 50%, the diameter of the spot is 3mm, and the scanning strategy is reciprocating and interlaced 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 as the protective gas and powder-carrying gas, and the oxygen content in the printing process is lower than 2000ppm. According to the process parameters and scanning path of the laser stereoforming set above, the Ni _a Co _b Cr _c Al _d Me _mestropic alloy powder was melted layer by layer to prepare a block sample. By optimizing the laser power, scanning speed, powder feeding speed and Z-axis lift, the quality of the printed alloy can be improved and the microstructure can be optimized to further improve its comprehensive mechanical properties and achieve a precipitation-strengthened medium with full density, no defects and excellent comprehensive performance. Integrated precision forming of complex structural parts of entropy alloys.

The present invention also provides a heat treatment method for preparing Ni _a Co _b Cr _c Al _{d Me} precipitation-enhanced 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 precipitates with a high volume fraction, heat treatment is performed on the Ni _a Co _b Cr _c Al _{d Me} type precipitation-strengthened medium-entropy alloy produced by laser additive manufacturing. 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°C-800°C and keeping it warm for a selected time of _{12h≤t≤480h} (laser Selective melting and forming) or 3h≤t≤480h (laser three-dimensional forming), water cooling after heat preservation, to obtain a heat-treated medium-entropy alloy. 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 precipitated phases with a high volume fraction, and at the same time obtain an incompletely recrystallized structure, further optimizing laser additive manufacturing The comprehensive mechanical properties of Ni _a Co _b Cr _c Al _d Me _e medium entropy alloy, to achieve the preparation of high strength and high toughness medium entropy alloy.

Example 1

A precipitation-strengthened 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 a gas-atomized pre-alloyed spherical powder with a purity greater than 99.9%.

In Example 1, the forming process of the medium entropy alloy prepared by laser selective melting technology is 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 above-mentioned medium-entropy alloy, the medium-entropy alloy pre-alloyed spherical powder is prepared by vacuum atomization method, and the pre-alloyed powder is sieved, and the particle size of the selected powder is 15- 53 μm, and its typical shape is shown in Figure 1. The oxygen content was 131 ppm and the nitrogen content was 53 ppm. Before laser selective melting, the powder is dried at 80°C for 4 hours to remove the moisture in the powder. Then it is placed in the powder feeding cylinder of the laser selective melting equipment.

2. Substrate surface treatment

Select a 316L stainless steel substrate, polish the surface to be deposited, and clean it with acetone and alcohol in order to remove surface oil, then dry it, install the substrate on the forming platform and level it. Before printing, the substrate was preheated to 200 °C.

3. Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ precipitation-strengthened medium-entropy alloy formed by laser selective melting

Create a three-dimensional solid model on the computer and convert it into a file in STL format, and import it into the construction software of the laser melting forming equipment for layering. The process parameters of laser selective melting and forming are as follows: laser power is 160-360W, scanning speed is 600-1000mm/s, scanning distance is 60-80μm, powder layer thickness is 30-50μm, spot diameter is 80μm, scanning strategy is 67 ° Rotate scan. Before printing, high-purity argon gas with a purity of 99.99wt.% is injected to keep the oxygen content in the forming chamber below 300ppm.

According to the parameters shown in Table 1, the laser power, scanning rate, and scanning distance were adjusted, and the thickness of the powder layer was fixed at 30 μm to carry out the laser selective melting forming experiment. The laser selective melting forming sample was obtained 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 through the experiments shown in Table 1: the laser power is 320W, the scanning speed is 1000mm/s, the scanning distance is 70μm, and the powder layer thickness is 30μm.

4. Structural characterization and performance testing of laser selective melting forming samples

A scanning electron microscope (SEM) was used to observe the microstructure of the sample formed with the optimal laser selective melting parameters. As shown in Figure 4(b), the alloy forming quality was good, and no defects such as cracks were observed. Density greater than 99.6%. Compared with the as-cast (prepared by vacuum arc melting method), 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 finer and more uniform. Example 1 The room temperature yield strength of the laser selective melting Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy (SLM) formed by selecting the optimal process parameters is 671MPa, the tensile strength is 913MPa, the elongation is 36%, and the hardness It is 310HV. Its strength is much higher than that of the as _- cast state, and its _{tensile plasticity} is _equivalent to that of the as _- cast state. It is 648MPa and the elongation is 38%.

5. Heat treatment of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy formed by laser selective melting

The aging treatment promotes the formation of entropy alloy precipitates in Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ formed by laser selective melting to achieve further strengthening and toughening. In the present invention, the heat treatment method includes raising the temperature of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy formed with optimal laser selective melting parameters to 600°C-800°C and keeping it warm for a selected time of 12h≤ t ≤ 480h, water cooling after heat preservation, to obtain a heat-treated medium entropy alloy.

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

Figure 6 is the scanning electron microscope image (a) and the 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 and heat treatment at 600 °C/12h, from Figure 6 (a ), it can be observed that the deposited structure has partially recrystallized, and the diffraction spots of the FCC phase and the γ' precipitated phase can be observed simultaneously in Figure 6(b). The room temperature tensile property test was carried out on the heat-treated samples of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloys formed by laser selective melting. After 480h heat treatment, the yield strength can reach 1098MPa, the tensile strength is 1466MPa, and the elongation is 25%.

Example 2

A precipitation-strengthened 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 a gas-atomized pre-alloyed spherical powder with a purity greater than 99.9%.

Present embodiment 2 adopts laser three-dimensional forming technology to prepare medium 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-alloyed spherical powder is prepared by vacuum atomization method, and the pre-alloyed spherical powder is sieved, and the particle size of the powder is 45 -150μm, 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 the moisture absorbed 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

Select a 316L stainless steel substrate, polish the surface to be deposited, and clean it with acetone and alcohol in order to remove surface oil, then dry it, and fix the substrate on the forming platform.

3. Laser three-dimensional forming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ 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 and converted into STL format and sent to the laser forming equipment. The printing process parameters and laser scanning path are set. Under the control of the numerical control system, the medium-entropy alloy powder is sent coaxially. The powder nozzle is sent to the molten pool formed by the high-energy laser beam, and the complex components of specific shapes and sizes are formed by depositing raw materials point by point, line by line, and layer by layer on the substrate. The process parameters of the above laser three-dimensional forming are as follows: laser power is 2KW ~ 3.5KW, scanning speed is 300 ~ 800mm/min, powder feeding speed is 5-8g/min, Z-axis lift is 0.4-1.0mm, lap rate 50%, the diameter of the spot is 3mm, and the scanning strategy is reciprocating and interlaced 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 as the protective gas and powder-carrying gas, and the oxygen content in the printing process is lower than 2000ppm.

Adjust the laser power, scanning rate, powder feeding speed, and Z-axis lift 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 parameter 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. Three samples were tested for tensile properties at room temperature, and the results are shown in Figure 10. Through the mechanical performance test results, the optimal process parameters are determined: laser power is 2800W, scanning speed is 300mm/min, powder feeding speed is 5g/min, Z-axis lift is 0.5mm, and the overlap rate is 50%.

4. Structural 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 sample under optimal parameters. As shown in Figure 11, the alloy forming quality is good, and no cracks, pores, poor fusion and other defects are observed. . And there is a small amount of γ' nano-scale precipitates in the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ entropy alloy microstructure prepared by laser stereoforming technology, as shown in Figure 11(b). The room temperature mechanical properties of the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy prepared with optimal process parameters are shown in Figure 12. The yield strength along the construction direction (longitudinal direction) is 723MPa, and the tensile strength is 1078MPa. 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 medium entropy alloy sample prepared by laser stereoforming method has high strong plastic bonding.

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

Furthermore, the aging treatment is used to promote the generation of entropy alloy precipitates in the laser stereoforming Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ to achieve further strengthening and toughening. In the present invention, the heat treatment method includes raising the temperature of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium-entropy alloy formed by laser stereoforming under the optimal process parameters to 700°C for a selected time of 3 hours. Water cooling to obtain a heat-treated medium entropy alloy.

Figure 13 shows the high-magnification scanning electron microscope pictures of the laser stereoforming 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 deposited state structure, the volume fraction of the precipitated phase A significant increase. Fig. 14 shows the variation law of microhardness after heat treatment of Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloys prepared with different laser powers. After heat treatment, due to the 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 is about 415HV after heat treatment at 700℃/3h. Figure 15 shows the tensile properties of the Ni ₃₅ Co ₃₅ Cr ₂₅ Ti ₃ Al ₂ medium entropy alloy 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 sample, its strength has been significantly improved due to the generation of precipitated phases.

Claims (6)

1. The precipitation strengthening type medium entropy alloy suitable for laser additive manufacturing is characterized in that, the precipitation strengthening type 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 respectively represent the mole percentage of each element, 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 is prepared by laser selective melting forming technology; including: Step 1, preparation and pretreatment of medium entropy alloy powder According to the above molar percentages, the metal raw materials corresponding to each element are taken, and a medium-entropy alloy pre-alloyed spherical powder is prepared by a vacuum atomization method, sieved, and dried to obtain a medium-entropy alloy powder; Step 2, laser selective melting forming Ni _a Co _b Cr _c Al _{d Me} precipitation strengthened medium entropy alloy Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared and convert it into a file in STL format, import it into the construction software of the laser selective melting forming equipment, and perform layered processing; inject high-purity argon gas 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 layer by layer to prepare the medium entropy alloy components; The process parameters of laser selective melting and forming are as follows: laser power P is 160-360W, scanning speed v is 600-1000mm/s, scanning distance h is 60-80μm, powder layer thickness t is 30-50μm, and spot diameter is 80μm. The range of volume energy density VED is 140J/mm ³ < VED < 240J/mm ³ , where VED=P/vht; Alternatively, the precipitation-strengthened medium-entropy alloy is prepared by laser stereoforming technology; including: Step 1, preparation and pretreatment of medium entropy alloy powder According to the above molar percentages, the metal raw materials corresponding to each element are taken, and a medium-entropy alloy pre-alloyed spherical powder is prepared by a vacuum atomization method, sieved, and dried to obtain a medium-entropy alloy powder; Step 2 Laser Stereo Forming Ni _a Co _b Cr _c Al _d M _e Precipitation Strengthened Medium Entropy Alloy Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared, convert it into STL format and send it to the laser three-dimensional forming equipment, set the printing process parameters and laser scanning path, and send the medium-entropy alloy powder to the high-energy laser in the laser three-dimensional forming equipment In the molten pool formed by the beam, the medium-entropy alloy components are printed by depositing raw materials point by point, line by line, and layer by layer on the substrate; The printing process parameters are as follows: laser power is 2kW~3.5kW, scanning speed is 300~800mm/min, powder feeding speed is 5~8g/min, Z-axis lift is 0.4~1.0mm, overlapping rate is 50%, spot The diameter is 3mm, and the scanning path is a reciprocating interweaving scanning path. 2. The preparation method of the precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 1, characterized in that, it is prepared by laser selective melting forming technology; comprising: Step 1, preparation and pretreatment of medium entropy alloy powder According to the mole percentage described in claim 1, the metal raw materials corresponding to each element are taken, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by vacuum atomization, sieved, and dried to obtain the medium-entropy alloy powder; Step 2, laser selective melting forming Ni _a Co _b Cr _c Al _{d Me} precipitation strengthened medium entropy alloy Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared and convert it into a file in STL format, import it into the construction software of the laser selective melting forming equipment, and perform layered processing; inject high-purity argon gas 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 layer by layer to prepare the medium entropy alloy components; The process parameters of laser selective melting and forming are as follows: laser power P is 160-360W, scanning speed v is 600-1000mm/s, scanning distance h is 60-80μm, powder layer thickness t is 30-50μm, and spot diameter is 80μm. The range of volume energy density VED is 140J/mm ³ < VED < 240J/mm ³ , where VED=P/vht. 3. The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 2, wherein the scanning strategy is 67°rotational scanning, reciprocating scanning, reciprocating interweaving scanning or 45°rotating partition scanning. 4. The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 2, further comprising a heat treatment step: raising the temperature of the medium-entropy alloy component to 600ºC-800ºC for 12h ≤ t ≤ 480h, water cooling after heat preservation, to obtain a heat-treated medium entropy alloy. 5. The preparation method of the precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 1, characterized in that, it is prepared by laser three-dimensional forming technology; comprising: Step 1, preparation and pretreatment of medium entropy alloy powder According to the mole percentage described in claim 1, the metal raw materials corresponding to each element are taken, and the pre-alloyed spherical powder of the medium-entropy alloy is prepared by vacuum atomization, sieved, and dried to obtain the medium-entropy alloy powder; Step 2 Laser Stereo Forming Ni _a Co _b Cr _c Al _d M _e Precipitation Strengthened Medium Entropy Alloy Establish a three-dimensional solid model according to the geometric shape of the medium-entropy alloy component to be prepared, convert it into STL format and send it to the laser three-dimensional forming equipment, set the printing process parameters and laser scanning path, and send the medium-entropy alloy powder to the high-energy laser in the laser three-dimensional forming equipment In the molten pool formed by the beam, the medium-entropy alloy components are printed by depositing raw materials point by point, line by line, and layer by layer on the substrate; The printing process parameters are as follows: laser power is 2kW~3.5kW, scanning speed is 300~800mm/min, powder feeding speed is 5~8g/min, Z-axis lift is 0.4~1.0mm, overlapping rate is 50%, spot The diameter is 3mm, and the scanning path is a reciprocating interweaving scanning path. 6. The method for preparing a precipitation-strengthened medium-entropy alloy suitable for laser additive manufacturing according to claim 5, further comprising a heat treatment step: raising the temperature of the medium-entropy alloy component to 600ºC-800ºC for 3h ≤ t ≤ 480h, water cooling after heat preservation, to obtain a heat-treated medium entropy alloy.

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