CN114959331B - Method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing - Google Patents

Abstract

The invention discloses a method for preparing a nickel-based single crystal superalloy based on coaxial powder-feeding laser additive manufacturing, which specifically includes: performing coaxial powder-feeding laser additive manufacturing on a forged or cast nickel-based superalloy substrate and Add an auxiliary infrared light source to heat and form a sample with a certain size; use the side of the additive part with the characteristics of directional solidification as the substrate for the second laser additive manufacturing to obtain an additively formed sample with basically the same crystal orientation, and repeat the first step. Two steps until the single crystal structure is obtained; the part except the last additive forming is cut off, and the remaining part is a single crystal superalloy with completely consistent crystal orientation. The beneficial effects of the present invention are: the single crystal preparation method provided utilizes the characteristics of directional heat dissipation and directional growth of laser additive manufacturing to realize the transition of crystal orientation from random to directional and then to single crystal, which is more efficient than techniques such as crystal selection method and seed crystal method. high feature.

Description

Method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing

technical field

The invention relates to the field of laser additive manufacturing, in particular to a method for preparing a nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing.

Background technique

As a method for producing a single crystal, a crystal selection method, a seed crystal method, a seed crystal plus selection method, and the like are known to the public. However, there is currently no method for multiple crystal selection based on the laser additive manufacturing technology using the epitaxial growth characteristics of nickel-based superalloys.

Single crystal superalloys are mainly used in the manufacture of aero-engines and gas turbine hot-end turbine blades. They have good high-temperature strength, oxidation resistance and corrosion resistance, fatigue resistance and creep resistance, fracture performance and structural stability. And its temperature bearing capacity is a key technical index to improve engine performance, efficiency and reliability.

In some developed countries in Europe and the United States, the research and development of single crystal superalloys was carried out early and the technology maturity is high, but the research and development of single crystal superalloys and the development of single crystal blades have always been attached great importance. Although the performance of single crystal engine blades is relatively excellent, the material and manufacturing costs of single crystal blades are as high as tens of thousands of dollars, and their service life is limited by defects such as thermal fatigue cracks, blade tip corrosion, surface wear and thermal corrosion. The replacement of single crystal blades greatly affects the operating costs of modern aero-engines and gas turbines.

At present, the advanced aero-engine blades mostly use directionally solidified cast nickel-based single-crystal superalloys with excellent high-temperature mechanical properties. The appearance of miscellaneous grain boundaries will affect the integrity of dendrite crystals, reduce the mechanical properties of single crystal alloys, and lead to a decrease in the pass rate of single crystal blades. The mechanical properties of nickel-based single crystal superalloys have significant anisotropy, which has the advantage of ensuring the best performance in the stress direction, but the deviation of crystal orientation will seriously affect the high temperature mechanical properties of single crystal blades.

The key to the manufacture of single crystal blades is how to avoid the generation of miscellaneous crystal defects and ensure the integrity of the single crystal structure. The crystal selection process will have an important impact on the single crystal orientation and the formation of single crystal defects, which will ultimately affect the mechanical properties of the alloy. Some scholars have found that in the process of laser additive manufacturing, as the distance from the surface of the forged substrate increases, the equiaxed crystal structure gradually transforms into an oriented structure, and when it reaches a certain height, the equiaxed crystal structure completely transforms into a oriented structure. It is feasible to directly prepare single crystal superalloys by laser additive manufacturing technology.

Contents of the invention

Aiming at the problem that miscellaneous crystals are likely to exist in the process of preparing nickel-based single crystal superalloys in the current laser additive manufacturing process, the present invention discloses a method for preparing nickel-based single crystal superalloys based on coaxial powder feeding laser additive manufacturing. The crystal selection method is simple to operate, can effectively improve the qualified rate of preparing single crystals, and reduce the production cost of manufacturing nickel-based single crystal superalloys.

The present invention adopts the following technical scheme: a method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing, which is characterized in that it includes four steps:

The first step is to use coaxial powder feeding laser additive manufacturing of nickel-based superalloy on the forged or cast alloy substrate; the proportion of uniformly oriented dendrites in the directionally solidified structure is 70%;

The second step is crystal selection. After stress-relief annealing the additive part sample in the first step, the side of the additive part is milled until the surface is flat, and the same coaxial powder-feeding laser amplification as in the first step is used as the substrate. The material manufacturing process parameters are used to carry out the second-step laser material addition process; the proportion of dendrites with consistent orientation in the directional solidification structure is 95%;

The third step is to repeat the crystal selection, using the sample of the additive part obtained after the second step of crystal selection as the substrate, and repeat the second step of the crystal selection process; after the third step of crystal selection, the obtained additive area The proportion of dendrites with consistent orientation in the structure is 100%, and a single crystal structure with completely consistent crystal orientation is obtained;

In the fourth step, the wire cutting part of the substrate is removed, and the same stress relief annealing treatment as in the second step is performed again, and the remaining part is the required single crystal superalloy sample.

Further, the first step is to use coaxial powder feeding laser additive manufacturing of nickel-based superalloy on the forged or cast alloy substrate, specifically:

(1) On the forged or cast alloy substrate, a sample of a certain size is formed by laser additive material multi-layer multi-channel unidirectional linear deposition;

(2) During the laser heat input process, there is a high temperature gradient and a high solidification rate, and the structure of the additive area is a dendrite structure of directional solidification;

(3) Limit the heat dissipation conditions during the coaxial powder feeding process, use the auxiliary infrared light source to heat the surface around the additive part sample, reduce the heat dissipation in the horizontal direction of the molten pool, and only dissipate heat through the substrate downward, so that the heat dissipation direction is In the vertical direction, dendrites grow preferentially along the direction of heat dissipation;

(4) The proportion of dendrites with uniform orientation is increased to 70%.

Further, for the forged or cast alloy substrate in the first step, the average grain size of the equiaxed grains is 10-30 μm, and the grain width of the columnar grain structure obtained by the coaxial powder feeding laser additive manufacturing is 200 μm. ~500μm; in the second and third steps, the columnar grain width gradually increases, and finally a single crystal structure is obtained.

Furthermore, in the first and second steps, during the coaxial powder feeding process, the auxiliary infrared light source is used to heat the surface around the additive part sample, so as to reduce the heat dissipation in the horizontal direction of the molten pool, and obtain branches with a more consistent growth direction. The crystal structure is heated by optical radiation without contact, and the metallurgical characteristics of the small molten pool of additive manufacturing are brought into play. The working temperature range of the auxiliary infrared light source is 800-1000 ° C, the heating power is 20-30KW, and the heating range can reach the molten pool 5 to 10 times the size, the heating depth can reach 0.4 to 1mm, ensuring that there is no temperature gradient in the molten pool in the horizontal direction, and the heat only diffuses downward through the substrate.

Further, the process of coaxial powder-feeding laser additive manufacturing, the specific process parameters include: the laser scanning strategy adopts the multi-layer multi-channel unidirectional linear deposition method, adopts the strategy of small energy input, large spot size and large scanning speed, laser Power 800～1200W, scanning speed 10～20mm/s, spot diameter 3～5mm, overlap rate 20～30%, single layer height 0.05～0.1mm, powder feeding rate 3～8g/min, powder-carrying gas flow 5～ 10L/min, using argon for overall protection.

Further, in the multi-layer multi-channel unidirectional linear deposition method, each layer in each layer adopts a unidirectional and linear scanning method during the additive manufacturing process. Compared with other currently known laser scanning strategies, It is easier to obtain a directional solidification structure with more consistent dendrite orientation by using multi-layer multi-channel unidirectional linear deposition.

Further, the coaxial powder feeding additive manufacturing alloy sample obtained in the second step is subjected to stress relief annealing, and the side of the additive part is used as the substrate to perform the second step; preferably, the stress relief annealing process is heating to 300-500°C, more preferably 500°C; keep warm for 4-8 hours, more preferably 4 hours.

Further, the stress relief annealing process uses a muffle furnace or a vacuum heat treatment furnace with a temperature control accuracy of ±1°C and can work continuously for a long time; the temperature is raised to 500°C at a heating rate of less than 100°C per minute, kept for 4 hours, and then Furnace cooling or cooling to room temperature at a cooling rate of less than 100°C per minute.

The beneficial effects of the present invention are: the single crystal preparation method provided utilizes the characteristics of directional heat dissipation and directional growth of laser additive manufacturing to realize the transition of crystal orientation from random to directional and then to single crystal, which is more efficient than techniques such as crystal selection method and seed crystal method. high feature. Using coaxial powder-feeding laser additive manufacturing technology can realize moldless, fast, fully dense and near-net shape of high-performance complex structure metal parts, and adopt the method of infrared-assisted multiple vertical crystal selection announced by the present invention to be faster Formed parts with directional growth and uniform dendrite structure can be obtained more efficiently.

Description of drawings

Below in conjunction with accompanying drawing, the present invention is further described:

Fig. 1 is the flow chart of the crystal selection method adopted in the present invention.

Fig. 2 is an equiaxed grain microstructure diagram of the forged GH4169 alloy substrate of the present invention.

Fig. 3 is a microstructure diagram of the first step of dendrite growth direction on the forged GH4169 alloy substrate of the present invention.

Fig. 4 is a microstructure diagram of the second step dendrite growth direction perpendicular to the dendrite growth direction obtained in the first step according to the present invention.

Detailed ways

The core idea of the present invention is to provide a method for obtaining a nickel-based single crystal superalloy based on coaxial powder-feeding laser additive manufacturing, which can obtain a directional solidified structure with less miscellaneous crystals and improve the pass rate of preparing single crystals.

The formed part after laser material addition has relatively large internal stress, and the present invention preferably further includes performing stress relief annealing on the nickel-based single crystal superalloy formed part and cooling it to room temperature. In the present invention, the cooling is preferably furnace cooling or air cooling.

The present invention adopts the following technical scheme: a method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing, which is characterized in that it includes four steps:

The first step is to use coaxial powder feeding laser additive manufacturing of nickel-based superalloy on the forged or cast alloy substrate; the proportion of uniformly oriented dendrites in the directionally solidified structure is 70%;

The second step is crystal selection. Firstly, the additive part sample in the first step is stress-relieved and annealed, and then the side of the additive part is milled until the surface is flat. The same coaxial powder-feeding laser as the first step is used as the substrate. Additive manufacturing process parameters for the second step of laser additive process; the proportion of uniformly oriented dendrites in the directional solidification structure is 95%;

The third step is to repeat the crystal selection, using the sample of the additive part obtained after the second step of crystal selection as the substrate, and repeat the second step of the crystal selection process; after the third step of crystal selection, the obtained additive area The proportion of dendrites with consistent orientation in the structure is 100%, and a single crystal structure with completely consistent crystal orientation is obtained;

In the fourth step, the wire cutting part of the substrate is removed, and the same stress relief annealing treatment as in the second step is performed again, and the remaining part is the required single crystal superalloy sample.

In the first step, the specific process is to use multi-layer multi-channel unidirectional linear deposition method laser additive forming of a certain size of the sample on the forged or cast alloy substrate, due to the high temperature gradient and high solidification speed in the process of laser heat input And other characteristics, the structure of the additive zone is a dendrite structure of directional solidification. At the same time, limit the heat dissipation conditions during the coaxial powder feeding process, use the auxiliary infrared light source to heat the surface around the additive part sample, reduce the heat dissipation in the horizontal direction of the molten pool, and only dissipate heat through the substrate downward, so that heat dissipation can also be guaranteed In the vertical direction, dendrites will preferentially grow along the direction of heat dissipation. In the process of coaxial powder feeding without adding auxiliary infrared light source to control the heat dissipation direction, the proportion of dendrites with uniform orientation is only 50% to 60%. After adding auxiliary infrared light source to control the heat dissipation direction, the proportion of dendrites with uniform orientation The ratio increased by around 10% to 70%. Although dendrites with certain directional solidification characteristics have been obtained in the first step, since the forged or cast alloy substrate is equiaxed, the crystal orientations between equiaxed crystals are different, resulting in dendrites in the additive area. The orientation difference between crystals becomes larger when these equiaxed crystals are used as the substrate for directional solidification and growth, so there are still a large number of miscellaneous crystals in the structure, and the proportion of dendrites with uniform orientation is only 70%. The obtained directional solidified structure is far from the standard of single crystal structure.

In the first step, at present, research on the preparation of nickel-based superalloys by coaxial powder-feeding laser additive manufacturing is only aimed at the forming content in the first step of the present invention. There is a case of heating to control the growth direction of dendrites, and there is no case of further crystal selection of the obtained dendrite structure with directional solidification characteristics to obtain a single crystal alloy. Compared with the directionally solidified structure with uniformly oriented dendrites accounting for only 70%, the proportion of uniformly oriented dendrites in the single crystal structure reaches 100%. The single crystal structure eliminates the transverse grain boundary, and the consistency of grain orientation makes the alloy have better mechanical properties in a specific direction at high temperature. However, the technical efficiency of the traditional crystal selection method and seed crystal method is too low. Therefore, the present invention obtains a single crystal alloy by selecting crystals for the coaxial powder feeding laser additive manufacturing of nickel-based superalloys, which is low in cost and high in efficiency. Compared with the traditional method, the single crystal structure has the same effect.

In the first step, there are dendrite orientations with inconsistent orientation in the structure of coaxial powder-feeding laser additive manufacturing. Due to the complexity of microscopic growth conditions, the deviation behavior of dendrite orientation is random and uncontrollable. The closer the distance to the substrate, the more chaotic the direction of dendrite growth; in order to obtain a single crystal structure with a more consistent orientation, it is necessary to control the heat dissipation direction of the molten pool. Adding an auxiliary infrared light source around the sample to heat, the proportion of uniformly oriented dendrites in the obtained structure increased by 10%, but it did not reach the standard for producing single crystal alloys. Therefore, the present invention sets the crystal selection process of the second step and the third step.

In the second step, since the proportion of uniformly oriented dendrites in the substrate structure at this time can reach 70%, compared with direct laser additive manufacturing on forged or cast equiaxed crystal alloy substrates, dendrites in When the dendrites are used as the base to grow, the orientation difference between them is very small, that is, the number of dendrites that compete for growth is small. At the same time, due to the addition of an auxiliary infrared light source to control the heat dissipation direction of the molten pool, the obtained dendrites have consistent orientations. The proportion of dendrites reaches 95%.

In the third step, repeat the process of the second step to repeat crystal selection. Finally, the present invention obtains a single crystal structure with completely consistent dendrite orientation by repeating the crystal selection process. The qualified rate of single crystals obtained by traditional techniques such as crystal selection method and seed crystal method is 90%, but in the present invention, the qualified rate of single crystals obtained by repeated crystal selection in the third step is 100%, and the time used is reduced to 1 of the traditional method. /10, which not only improves efficiency, but also saves costs.

The method for obtaining a nickel-based single crystal superalloy based on coaxial powder-feeding laser additive manufacturing provided by the present invention will be described in detail below in conjunction with examples, but they should not be construed as limiting the protection scope of the present invention.

Example 1

Obtain GH4169 single crystal superalloy based on coaxial powder feeding laser additive manufacturing

Grind and remove scale on the wrought nickel-based superalloy substrate with alloy grade GH4169 to remove the scale, and clean the surface with alcohol or acetone; fix the nickel-based superalloy substrate in a tooling with cooling function on the fixture. The single crystal structure with completely consistent crystal orientation is obtained by coaxial powder feeding laser additive multiple times of crystal selection.

As shown in Figure 1, a single crystal preparation method based on coaxial powder-feeding laser additive manufacturing according to the present invention, through a four-step crystal selection process, finally obtains a dendrite with a uniform orientation accounting for 100%. single crystal structure. Among them, the first step: Coaxial powder feeding laser additive manufacturing of GH4169 alloy on the polished and cleaned forged GH4169 alloy substrate, using multi-layer multi-channel unidirectional linear deposition method, due to the equiaxed crystal in the area close to the substrate The grain orientation is inconsistent, and the growth direction of the columnar dendrites growing along the equiaxed grain boundaries is also different. There is an instability zone within a certain area, and the average orientation difference between grains in the instability zone is larger, which frequently occurs Defects such as monotectic crystals, miscellaneous crystals, freckles, and small-angle grain boundaries. The appearance of grain boundaries splits the integrity of the crystal and significantly reduces the mechanical properties of the single crystal alloy. At this time, although the additive part has directional structure characteristics, the dendrites grow The direction is not consistent, the dispersion is very large, and the proportion of dendrites with uniform orientation is only 70%. In the process of directional solidification, the competitive growth of grains controlled by heat flow is the main reason for grain elimination selection, therefore, the dendrites with uniform orientation eliminate the dendrites with other orientation during the competitive growth process. The second step: the laser additively manufactured GH4169 alloy sample with the preliminary directional solidification structure obtained in the first step is subjected to stress relief annealing, and then it is cut from the forged superalloy substrate, and the first step is added. The side of the sample is milled until the surface is flat, and the added part is used as the substrate for the second step of laser additive forming. At this time, the proportion of uniformly oriented dendrites in the structure is 95%. The third step: Repeat the crystal selection, using the additive part sample obtained after the second step of crystal selection as the substrate, repeat the second step of the crystal selection process; after the third step of crystal selection, the obtained additive area The proportion of dendrites with uniform orientation in the structure is 100%, and a single crystal structure with all crystal orientations is obtained; the fourth step is to cut off part of the substrate by wire cutting, and perform the same stress relief annealing treatment as the second step, and the remaining part That is, the required single crystal superalloy sample.

Fig. 2 is a microstructure diagram of equiaxed grains of a forged GH4169 alloy substrate. The average grain size of equiaxed grains in the forged alloy substrate is 10-30 μm.

Figure 3 shows the first step of crystal selection process on the forged GH4169 alloy substrate. The substrate in the lower region is an equiaxed crystal structure with different grain orientations, and the upper region is the first step of dendrite growth direction in the additive area. Although it has Directional structure characteristics, but the dendrite growth direction is not consistent, the dispersion is very large, and the proportion of uniformly oriented dendrites is only 70%; the columnar crystal structure obtained by the coaxial powder feeding laser additive manufacturing has a grain width of 460 μm . In the second and third steps, the width of the columnar grains increases gradually, and finally a single crystal structure is obtained.

Figure 4 shows the direction of dendrite growth in the second step, which is the second step of crystal selection process in the direction of dendrite growth in the first step, and the laser additive manufacturing GH4169 alloy sample with a preliminary directional solidification structure obtained in the first step It was cut from the forged GH4169 alloy substrate, and the side of the first-step additive forming sample was milled until the surface was flat, and the second-step laser additive forming was performed on this additive part as the substrate. At this time, the proportion of uniformly oriented dendrites in the structure is 95%. After repeated crystal selection in the third step, the proportion of dendrites with consistent orientation in the structure is 100%, and it can be considered that a single crystal structure with completely consistent dendrite orientation can be obtained.

Example 2

Obtain GH3625 single crystal superalloy based on coaxial powder feeding laser additive manufacturing

Grind and remove scale on the wrought nickel-based superalloy substrate with an alloy grade of GH3625 that needs to be added, and clean the surface with alcohol or acetone; fix and clamp the nickel-based superalloy substrate on a tooling with cooling function on the fixture. The single crystal structure with completely consistent crystal orientation is obtained by coaxial powder feeding laser additive multiple times of crystal selection.

The bottom of the deposition area is equiaxed grains with a width of about 8 μm, and the directionally solidified columnar grains are tightly arranged epitaxially along the deposition height direction, usually containing multiple grains with different orientations that are constantly competing for growth.

The laser additively manufactured GH3625 alloy sample obtained in the first step of forming with a preliminary directional solidification structure was cut from the forged superalloy substrate by wire cutting for the second step of laser additive forming. After the crystal selection process in the second and third steps, the proportion of dendrites with consistent orientation in the structure is 100%, and it can be considered that a single crystal structure with completely consistent crystal orientation is obtained.

Metallographic structure observation and scanning electron microscope observation were carried out on the GH3625 single crystal superalloy sample obtained based on coaxial powder feeding laser additive manufacturing described in Example 2, and the results were similar to those shown in Figures 2 to 4, indicating that the crystal selection process described in the present invention The method can obtain single crystal samples with completely consistent dendrite orientation.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (4)

1. The method for preparing the nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing is characterized by comprising the following four steps:

firstly, manufacturing nickel-based superalloy on a forged or cast alloy substrate by adopting coaxial powder feeding laser additive; the proportion of dendrites with consistent orientation in the directional solidification structure is 70 percent;

secondly, selecting crystals, carrying out stress relief annealing on the material-increasing piece sample in the first step, milling the side surface of the material-increasing part until the surface is flat, and carrying out a second-step laser material-increasing process by taking the material-increasing part sample as a substrate and adopting the same coaxial powder-feeding laser material-increasing manufacturing process parameters as the first step; the proportion of dendrites with consistent orientation in the directional solidification structure is 95 percent;

thirdly, repeating the crystal selection, and repeating the crystal selection process of the second step by taking the material-increasing piece sample obtained after the crystal selection of the second step as a substrate; after the third step of crystal selection, the proportion of dendrites with consistent orientation in the obtained material-increasing region tissue is 100%, and all the monocrystal tissues with consistent crystal orientation are obtained;

fourthly, cutting and cutting off part of the substrate linearly, and carrying out the same stress relief annealing treatment in the second step again, wherein the rest part is the required monocrystal superalloy sample;

in the first step, the average grain size of the equiaxed crystal is 10-30 mu m, and the grain width of columnar crystal structures obtained by coaxial powder feeding laser additive manufacturing is 200-500 mu m; in the second step and the third step, the widths of columnar crystal grains are gradually increased, and a single crystal structure is finally obtained;

in the first step and the second step, the peripheral surface of the additive part sample is heated by an auxiliary infrared light source in the coaxial powder feeding process, the heat dissipation of a molten pool in the horizontal direction is reduced, then a dendrite structure with more consistent growth direction is obtained, the optical radiation is adopted for non-contact heating, the metallurgical characteristics of a micro molten pool for additive manufacturing are brought into play, the working temperature range of the auxiliary infrared light source is 800-1000 ℃, the heating power is 20-30 KW, the heating range can reach 5-10 times of the size of the molten pool, the heating depth can reach 0.4-1 mm, the fact that the molten pool has no temperature gradient in the horizontal direction is ensured, and the heat only diffuses downwards through a substrate.

2. The method for preparing the nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:

the first step adopts coaxial powder feeding laser material adding to manufacture nickel-based superalloy on a forging state or casting state alloy baseplate specifically comprises the following steps:

(1) Forming a sample with a certain size on a forged or cast alloy substrate by adopting a multilayer multi-channel unidirectional linear deposition mode laser material increase;

(2) The laser heat input process is high temperature gradient and high solidification speed, and the tissue of the material adding area is a dendritic crystal tissue which is directionally solidified;

(3) The heat dissipation conditions in the coaxial powder feeding process are limited, the peripheral surfaces of the additive piece samples are heated by using auxiliary infrared light sources, the heat dissipation in the horizontal direction of a molten pool is reduced, only the substrate is used for dissipating heat downwards, so that the heat dissipation direction is vertical, and dendrites preferentially grow along the heat dissipation direction;

(4) The proportion of dendrites with consistent orientation is increased to 70%.

3. The method for preparing the nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:

the coaxial powder feeding laser additive manufacturing process comprises the following specific process parameters: the laser scanning strategy adopts a multilayer multichannel unidirectional straight line deposition mode, adopts a strategy with small energy input, large light spot size and large scanning speed, has the laser power of 800-1200W, the scanning speed of 10-20 mm/s, the light spot diameter of 3-5 mm, the lap joint rate of 20-30%, the single layer height of 0.05-0.1 mm, the powder feeding speed of 3-8 g/min and the powder carrying gas flow of 5-10L/min, and adopts argon gas for integral protection.

4. The method for preparing the nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing according to claim 2, wherein the method comprises the following steps:

in the multilayer multichannel unidirectional linear deposition mode, each layer in the additive manufacturing process adopts a unidirectional and linear scanning mode, and compared with other known laser scanning strategies, the multilayer multichannel unidirectional linear deposition mode is adopted to more easily obtain a directional solidification structure with more consistent dendrite orientation.

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