CN114959331A - Method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing - Google Patents
Method for preparing nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0433—Nickel- or cobalt-based alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
- B22F10/60—Treatment of workpieces or articles after build-up
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
- B33Y40/20—Post-treatment, e.g. curing, coating or polishing
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C19/03—Alloys based on nickel or cobalt based on nickel
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- B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
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- B22F10/64—Treatment of workpieces or articles after build-up by thermal means
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Abstract
The invention discloses a method for preparing a nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing, which specifically comprises the following steps: carrying out coaxial powder feeding laser additive manufacturing on a forged or cast nickel-based high-temperature alloy substrate, adding an auxiliary infrared light source for heating, and forming a sample with a certain size; performing secondary laser additive manufacturing by taking the side surface of the additive part with the characteristic of the directional solidification structure as a substrate to obtain an additive forming sample with basically consistent crystal orientation, and repeating the second step until a single crystal structure is obtained; and cutting off the part except the last additive forming, wherein the rest part is the single crystal superalloy with completely consistent crystal orientation. The invention has the beneficial effects that: the provided single crystal preparation method utilizes the characteristics of directional heat dissipation and directional growth of laser additive manufacturing to realize the transition from random to directional crystal orientation to single crystal, and has the characteristic of high efficiency compared with the technologies such as a crystal selection method, a seed crystal method and the like.
Description
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
As a method for producing a single crystal, a seed crystal method, a seed crystal plus seed crystal method, and the like are known. But at present, a method for selecting crystals for multiple times by utilizing the epitaxial growth characteristic of the nickel-based superalloy based on a laser additive manufacturing technology does not exist.
The single crystal high temperature alloy is mainly used for manufacturing turbine blades at the hot end of aeroengines and gas turbines, and has good high temperature strength, oxidation resistance, corrosion resistance, fatigue resistance, creep resistance, fracture performance and structural stability. The temperature bearing capacity is a key technical index for improving the performance, efficiency and reliability of the engine.
In developed countries in Europe and America, research and development of single crystal high temperature alloy are carried out early and the technical maturity is high, but the research and development of single crystal high temperature alloy and the research and development of single crystal blades are always very important. Although the performance of a single crystal engine blade is excellent, the material and manufacturing cost of the single crystal blade is up to ten thousand dollars, and the service life of the single crystal engine blade is limited by defects such as thermal fatigue cracks, blade tip corrosion, surface abrasion and thermal corrosion. The replacement of single crystal blades greatly affects the operating costs of modern aircraft engines and gas turbines.
At present, the advanced aeroengine blade material is mainly prepared from directionally solidified cast nickel-based single crystal superalloy with excellent high-temperature mechanical property, but due to the fact that the directionally solidified and single crystal blade is complex in appearance and has a complex hollow air-cooled structure inside, defects such as monotectic crystal, mixed crystal, small-angle crystal boundary and the like frequently occur in the manufacturing process, the integrity of dendritic crystal is affected by the mixed crystal boundary, the mechanical property of the single crystal alloy is reduced, and the qualification rate of the single crystal blade is reduced. The mechanical properties of the nickel-based single crystal superalloy have remarkable anisotropy, the advantage of the nickel-based single crystal superalloy is that the best performance in the stress direction can be ensured, but the deviation of the crystal orientation can seriously affect the high-temperature mechanical properties of the single crystal blade.
The key to the manufacture of single crystal blades is how to avoid the generation of mixed crystal defects and ensure the integrity of the single crystal structure. The crystal selection process can have important influence on the orientation of the single crystal and the formation of single crystal defects, and finally the mechanical property of the alloy is acted. The researchers found that in the laser additive manufacturing process, the equiaxial crystal structure gradually changes to the oriented structure along with the increase of the distance from the surface of the forged substrate, and when the equiaxial crystal structure reaches a certain height, the equiaxial crystal structure completely changes to the oriented structure, which indicates that the direct preparation of the single crystal superalloy by using the laser additive manufacturing technology is feasible.
Disclosure of Invention
Aiming at the problem that mixed crystals are easy to exist in the process of preparing the nickel-based single crystal superalloy by the conventional laser additive manufacturing, the invention discloses a method for preparing the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing.
The invention adopts the following technical scheme: a method for preparing a nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing is characterized by comprising the following four steps:
firstly, manufacturing a nickel-based high-temperature alloy on a forged or cast alloy substrate by adopting coaxial powder feeding laser additive manufacturing; the dendritic crystal with consistent orientation accounts for 70% in the directional solidification structure;
secondly, selecting crystals, namely milling the side surface of the material adding part to be smooth after stress relief annealing is carried out on the material adding part sample in the first step, and carrying out a second-step laser material adding process on the substrate by adopting the same coaxial powder feeding laser material adding manufacturing process parameters as those in the first step; the proportion of dendrites with consistent orientation in the directional solidification structure is 95 percent;
thirdly, crystal selection is repeated, the material increase piece sample obtained after the crystal selection in the second step is used as a substrate, and the crystal selection process in the second step is repeated; after crystal selection in the third step, the dendritic crystal with consistent orientation accounts for 100% in the obtained material increase zone structure, and a single crystal structure with all crystal orientations completely consistent is obtained;
and fourthly, cutting off the substrate part by lines, and performing the stress relief annealing treatment in the second step again to obtain the residual part which is the required single crystal high temperature alloy sample.
Further, the first step of manufacturing the nickel-based superalloy on the forged or cast alloy substrate by adopting coaxial powder feeding laser additive manufacturing specifically comprises the following steps:
(1) adopting a multilayer multi-channel unidirectional linear deposition mode to perform laser material increase on a forged or cast alloy substrate to form a sample with a certain size;
(2) the laser heat input process is high temperature gradient and high solidification speed, and the material increase area structure is a directionally solidified dendritic crystal structure;
(3) limiting the heat dissipation conditions in the coaxial powder feeding process, heating the peripheral surface of the material piece sample by using an auxiliary infrared light source, reducing the heat dissipation of a molten pool in the horizontal direction, and only downwards dissipating heat through a substrate to ensure that the heat dissipation direction is the vertical direction and dendritic crystals preferentially grow in the heat dissipation direction;
(4) the proportion of dendrites with consistent orientation is increased to 70%.
Furthermore, in the forged or cast alloy substrate in the first step, the average isometric crystal grain size is 10-30 μm, and the width of the columnar crystal structure crystal grain obtained by the coaxial powder feeding laser additive manufacturing is 200-500 μm; in the second and third steps, the width of the columnar crystal grains is gradually increased, and a single crystal structure is finally obtained.
Furthermore, in the first step and the second step, auxiliary infrared light sources are utilized to heat the peripheral surface of a material increase piece sample in the coaxial powder feeding process, the heat dissipation of the horizontal direction of a molten pool is reduced, dendritic crystal tissues with more consistent growth directions are obtained, the metallurgical characteristics of a small molten pool in material increase manufacturing are exerted by adopting optical radiation non-contact heating, the working temperature range of the auxiliary infrared light sources 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 molten pool is guaranteed not to have a temperature gradient in the horizontal direction, and heat is only diffused downwards through a substrate.
Further, the specific process parameters of the coaxial powder feeding laser additive manufacturing process include: the laser scanning strategy adopts a multilayer multi-channel one-way linear deposition mode, adopts the strategies of small energy input, large spot size and large scanning speed, has the laser power of 800-1200W, the scanning speed of 10-20 mm/s, the 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 rate of 3-8 g/min and the powder carrying gas flow of 5-10L/min, and adopts argon gas for integral protection.
Furthermore, in the multi-layer multi-channel unidirectional linear deposition mode, in the additive manufacturing process, each channel in each layer adopts a unidirectional and linear scanning mode, and compared with other laser scanning strategies known at present, the multi-layer multi-channel unidirectional linear deposition mode is easier to obtain a directional solidification structure with more consistent dendritic crystal orientation.
Further, the coaxial powder feeding additive manufacturing alloy sample obtained in the second step is subjected to stress relief annealing, and the side face of the additive part is used as a substrate to perform the second step; preferably, the stress relief annealing process is carried out by heating to 300-500 ℃, and more preferably to 500 ℃; and keeping the temperature for 4-8 hours, and preferably for 4 hours.
Furthermore, the stress relief annealing process uses a muffle furnace or a vacuum heat treatment furnace which has the temperature control accuracy of +/-1 ℃ and can continuously work for a long time; heating to 500 deg.C at a rate of less than 100 deg.C per minute, holding for 4 hr, and cooling to room temperature at furnace cooling rate or at a rate of less than 100 deg.C per minute.
The invention has the beneficial effects that: the provided single crystal preparation method utilizes the characteristics of directional heat dissipation and directional growth of laser additive manufacturing to realize the transition from random to directional crystal orientation to single crystal, and has the characteristic of high efficiency compared with the techniques such as a crystal selection method, a seed crystal method and the like. By adopting the coaxial powder feeding laser additive manufacturing technology, the die-free, rapid and fully-compact near-net forming of the high-performance metal part with the complex structure can be realized, and the formed part with the directionally-grown uniform dendritic crystal structure can be prepared more rapidly and efficiently by adopting the infrared-assisted multiple vertical crystal selection method disclosed by the invention.
Drawings
The invention is further described below with reference to the accompanying drawings:
FIG. 1 is a flow chart of a crystal selection method adopted by the present invention.
FIG. 2 is an isometric crystal microstructure of a forged GH4169 alloy substrate according to the invention.
FIG. 3 is a first step dendrite growth direction microstructure on a wrought GH4169 alloy substrate according to the present invention.
FIG. 4 is a second step dendrite growth direction microstructure perpendicular to the dendrite growth direction obtained in the first step of the present invention.
Detailed Description
The core idea of the invention is to provide the method for obtaining the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing, which can obtain a directional solidification structure with less mixed crystals and improve the qualification rate of preparing single crystals.
The formed piece has large internal stress after laser material addition, and the invention preferably also comprises the steps of performing stress relief annealing on the nickel-based single crystal superalloy formed piece and cooling the formed piece to room temperature. In the present invention, the cooling is preferably furnace cooling or air cooling.
The invention adopts the following technical scheme: a method for preparing a nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing is characterized by comprising the following four steps:
firstly, manufacturing a nickel-based high-temperature alloy on a forged or cast alloy substrate by adopting coaxial powder feeding laser additive manufacturing; the dendritic crystal with consistent orientation accounts for 70% in the directional solidification structure;
secondly, selecting crystals, namely firstly performing stress relief annealing on the sample of the material added part in the first step, and then milling the side surface of the material added part until the surface is flat, and performing a second-step laser material adding process on the substrate by using the side surface as the same coaxial powder feeding laser material adding manufacturing process parameters as those in the first step; the proportion of dendrites with consistent orientation in the directional solidification structure is 95 percent;
thirdly, crystal selection is repeated, the material increase piece sample obtained after the crystal selection in the second step is used as a substrate, and the crystal selection process in the second step is repeated; after crystal selection in the third step, the dendritic crystal with consistent orientation accounts for 100% in the obtained material increase zone structure, and a single crystal structure with all crystal orientations completely consistent is obtained;
and fourthly, cutting off the substrate part by lines, and performing the stress relief annealing treatment in the second step again to obtain the residual part which is the required single crystal high temperature alloy sample.
In the first step, the concrete process is that a sample with a certain size is formed by adopting a multi-layer multi-channel unidirectional linear deposition mode on a forged or cast alloy substrate through laser material increase, and because the laser material increase has the characteristics of high temperature gradient, high solidification speed and the like in the laser heat input process, the material increase area structure is a directionally solidified dendritic crystal structure. Meanwhile, the heat dissipation condition in the coaxial powder feeding process is limited, the auxiliary infrared light source is utilized to heat the peripheral surface of the sample of the material piece, the heat dissipation in the horizontal direction of a molten pool is reduced, the heat dissipation is downward only through the substrate, and thus the heat dissipation can also ensure that dendritic crystals preferentially grow in the vertical direction along the heat dissipation direction. Under the condition that an auxiliary infrared light source is not added to control the heat dissipation direction in the coaxial powder feeding process, the proportion of the dendritic crystals with consistent orientation is only 50% -60%, and after the auxiliary infrared light source is added to control the heat dissipation direction, the proportion of the dendritic crystals with consistent orientation is increased by about 10%, and reaches 70%. Although dendrites with certain directional solidification structure characteristics are obtained in the first step, as the forged or cast alloy substrate structure is isometric crystals, the crystal orientations of the isometric crystals are different, so that the orientation difference among the dendrites in an additive area is large when the dendrites grow in a directional solidification mode by taking the isometric crystals as a base, the number of mixed crystals with a large proportion exists in the structure, the proportion of the dendrites with consistent orientations is only 70%, and the obtained directional solidification structure is far from the standard of a single crystal structure.
In the first step, at present, research on the preparation of the nickel-based superalloy by the coaxial powder feeding laser additive manufacturing only aims at the forming content in the first step of the invention, and there is no case of controlling the growth direction of dendrites by heating the peripheral surface of an additive sample by using an auxiliary infrared light source, and there is no case of obtaining a single crystal alloy by further crystal selection of the obtained dendrite structure with directional solidification characteristics. Compared with the directional solidification structure with the dendritic crystal with the same orientation, the directional solidification structure has the advantage that the dendritic crystal with the same orientation in the single crystal structure accounts for 100 percent. Transverse grain boundaries are eliminated by the single crystal structure, and the consistency of the grain orientation enables the alloy to have better mechanical properties in a specific direction at high temperature. The traditional crystal selection method, the seed crystal method and the like have low technical efficiency, so the single crystal alloy is obtained by carrying out crystal selection on the nickel-based superalloy manufactured by the coaxial powder feeding laser additive manufacturing method, the cost is low, the efficiency is high, and the obtained single crystal structure has the same effect compared with the traditional method.
In the first step, dendritic crystal directions with inconsistent orientations exist in the structure manufactured by the coaxial powder feeding laser additive manufacturing, and the deviation behavior of the dendritic crystal directions is random and uncontrollable due to the complexity of microscopic growth conditions. The closer the distance to the substrate, the more disorderly the direction of dendrite growth; in order to obtain a single crystal structure with more consistent orientation, the heat dissipation direction of a molten pool needs to be controlled, in the coaxial powder feeding process, an auxiliary infrared light source is added around a material adding piece sample for heating, and the proportion of dendrites with consistent orientation in the obtained structure is increased by 10 percent, but the dendrites do not reach the standard of producing single crystal alloy. Therefore, the invention is provided with the crystal selection processes of the second step and the third step.
In the second step, because the proportion of the dendrites with the same orientation in the substrate structure can reach 70%, compared with the situation that laser additive manufacturing is directly carried out on an axial-crystal alloy substrate in a forging state or a casting state, the orientation difference of the dendrites is very small when the dendrites are grown by taking the dendrites as a substrate, namely the number of the dendrites which have competitive growth is small, and meanwhile, because an auxiliary infrared light source is added to control the heat dissipation direction of a molten pool, the proportion of the dendrites with the same orientation in the obtained dendrite structure reaches 95%.
In the third step, the process of the second step is repeated to perform repeated crystallization. Finally, the invention obtains a single crystal structure with completely consistent dendritic crystal orientation through repeated crystallization process. The traditional method for obtaining the single crystal through the technologies of the crystal selection method, the seed crystal method and the like has the qualification rate of 90 percent, the invention has the qualification rate of 100 percent through the repeated crystal selection in the third step, the used time is reduced to 1/10 percent of the traditional method, the efficiency is improved, and the cost is saved.
The method for obtaining the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing provided by the invention is described in detail with reference to the following examples, but the method cannot be construed as limiting the scope of the invention.
Example 1
GH4169 single-crystal high-temperature alloy obtained based on coaxial powder feeding laser additive manufacturing
Polishing the material-added part of a forged nickel-based high-temperature alloy substrate with an alloy mark GH4169 to remove oxide skin, and cleaning the surface by using alcohol or acetone; and fixedly clamping the nickel-based high-temperature alloy substrate on a tool clamp with a cooling function. And (3) obtaining a single crystal structure with completely consistent crystal orientation by adopting coaxial powder feeding laser additive crystal selection for multiple times.
As shown in figure 1, the single crystal preparation method based on coaxial powder feeding laser additive manufacturing of the invention finally obtains a single crystal structure with dendritic crystals of consistent orientation accounting for 100% through a four-step crystal selection process. Wherein, the first step is as follows: the GH4169 alloy is manufactured by coaxially feeding powder and laser additive on a forged GH4169 alloy substrate which is polished and cleaned, a multilayer multi-channel unidirectional linear deposition mode is adopted, isometric crystal grains in a region close to the substrate are not consistent in orientation, the growth directions of columnar dendritic crystals growing along isometric crystal boundaries are different, a destabilization region in a certain region range exists, the average orientation difference among the crystal grains in the destabilization region is larger, defects such as partial crystals, mixed crystals, freckles, small-angle crystal boundaries and the like frequently occur in the manufacturing process, the crystal boundaries fracture the integrity of the crystals, the mechanical property of the single crystal alloy is obviously reduced, at the moment, the additive part has directional tissue characteristics, but the growth directions of the dendritic crystals are inconsistent, the dispersity is high, and the proportion of the dendritic crystals with the same orientation is only 70%. The competitive growth of the heat flux controlled grains during directional solidification is the primary cause of grain elimination selection, and therefore, dendrites with consistent orientation eliminate dendrites with other orientations during competitive growth. The second step is that: and performing stress relief annealing on the laser additive manufacturing GH4169 alloy sample with the primary directional solidification structure obtained by the first-step forming, cutting the sample from a forged high-temperature alloy substrate, milling the side surface of the sample subjected to the first-step additive forming until the surface is flat, and performing the second-step laser additive forming on the substrate by using the additive part. At this time, the proportion of dendrites having uniform orientation in the structure was 95%. The third step: repeating the crystal selection, and repeating the crystal selection process of the second step by taking the material increase piece sample obtained after the crystal selection of the second step as a substrate; after crystal selection in the third step, the dendritic crystal with consistent orientation accounts for 100% in the obtained material increase zone structure, and a single crystal structure with all crystal orientations completely consistent is obtained; and fourthly, cutting off the substrate part by lines, and performing the stress relief annealing treatment in the second step again to obtain the residual part which is the required single crystal high temperature alloy sample.
FIG. 2 is an isometric crystal microstructure of a forged GH4169 alloy substrate, wherein the average crystal grain size of the isometric crystals in the forged alloy substrate is 10-30 μm.
FIG. 3 is a first step of crystal selection process on a forged GH4169 alloy substrate, wherein the substrate in a lower region is an equiaxed crystal structure with different crystal grain orientations, and the substrate in an upper region is a dendritic crystal growth direction in the first step of an additive region, although the dendritic crystal growth direction is not consistent and has a directional structure characteristic, the dispersity is high, and the proportion of dendritic crystals with consistent orientations is only 70%; the width of the columnar crystal structure crystal grain obtained by the coaxial powder feeding laser additive manufacturing is 460 microns. In the second and third steps, the width of the columnar crystal grains is gradually increased, and a single crystal structure is finally obtained.
And FIG. 4 shows a second dendrite growth direction, which is to perform a second crystal selection process in the first dendrite growth direction, cut the laser additive manufacturing GH4169 alloy sample with the primary directional solidification structure obtained by the first step forming from a forged GH4169 alloy substrate, mill the side surface of the first step additive manufacturing sample until the surface is flat, and perform the second step laser additive manufacturing on the substrate by using the additive part. At this time, the proportion of dendrites having uniform orientation in the structure was 95%. After the repeated crystal selection process of the third step, the proportion of the dendrites with consistent orientation in the structure is 100%, and the single crystal structure with the completely consistent dendrite orientation can be obtained.
Example 2
GH3625 single crystal high-temperature alloy obtained based on coaxial powder feeding laser additive manufacturing
Polishing the material-added part of a forged nickel-based high-temperature alloy substrate with an alloy mark GH3625 to remove oxide skin, and cleaning the surface by using alcohol or acetone; and fixedly clamping the nickel-based high-temperature alloy substrate on a tool clamp with a cooling function. And (3) obtaining a single crystal structure with completely consistent crystal orientation by adopting coaxial powder feeding laser material increase and multiple crystal selection.
The bottom of the deposition area is an equiaxial crystal with the width of about 8 mu m, a directionally solidified columnar crystal structure which is in close arrangement along the direction of the deposition height in an epitaxial growth mode, and generally contains a plurality of crystal grains with different orientations which continuously compete for growth.
And cutting off the laser additive manufacturing GH3625 alloy sample with the primary directional solidification structure obtained by the first-step forming from the forged high-temperature alloy substrate by adopting linear cutting to perform second-step laser additive forming. Through the crystal selection process of the second step and the third step, the proportion of dendrites with consistent orientation in the structure is 100 percent, and the single crystal structure with completely consistent crystal orientation can be obtained.
Metallographic structure observation and scanning electron microscope observation are carried out on the GH3625 single-crystal high-temperature alloy sample obtained based on the coaxial powder feeding laser additive manufacturing in the embodiment 2, and the results are similar to those in the figures 2-4, which shows that the single-crystal sample with completely consistent dendritic crystal orientation can be obtained by the crystal selection method.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to 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 (6)
1. A method for preparing a nickel-based single crystal superalloy based on coaxial powder feeding laser additive manufacturing is characterized by comprising the following four steps:
firstly, manufacturing a nickel-based high-temperature alloy on a forged or cast alloy substrate by adopting coaxial powder feeding laser additive manufacturing; the dendritic crystal with consistent orientation accounts for 70% of the directional solidification structure;
secondly, selecting crystals, namely milling the side surface of the material adding part to be smooth after stress relief annealing is carried out on the material adding part sample in the first step, and carrying out a second-step laser material adding process on the substrate by adopting the same coaxial powder feeding laser material adding manufacturing process parameters as those in the first step; the proportion of dendrites with consistent orientation in the directional solidification structure is 95 percent;
thirdly, crystal selection is repeated, the material increase piece sample obtained after the crystal selection in the second step is used as a substrate, and the crystal selection process in the second step is repeated; after crystal selection in the third step, the dendritic crystal with consistent orientation accounts for 100% in the obtained material increase zone structure, and a single crystal structure with all crystal orientations completely consistent is obtained;
and fourthly, cutting off the substrate part by lines, and performing the stress relief annealing treatment in the second step again to obtain the residual part which is the required single crystal high temperature alloy sample.
2. The method for preparing the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:
the first step of manufacturing the nickel-based high-temperature alloy on the forged or cast alloy substrate by adopting coaxial powder feeding laser additive manufacturing specifically comprises the following steps:
(1) adopting a multilayer multi-channel unidirectional linear deposition mode to perform laser material increase on a forged or cast alloy substrate to form a sample with a certain size;
(2) the laser heat input process is high temperature gradient and high solidification speed, and the material increase area structure is a directionally solidified dendritic crystal structure;
(3) limiting the heat dissipation condition in the coaxial powder feeding process, heating the peripheral surface of the material piece sample by using an auxiliary infrared light source, reducing the heat dissipation of a molten pool in the horizontal direction, and only radiating downwards through a substrate to ensure that the heat dissipation direction is the vertical direction and dendritic crystals preferentially grow in 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 the coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:
in the forged or cast alloy substrate in the first step, the average crystal grain size of equiaxial crystals is 10-30 μm, and the width of columnar crystal structure crystal grains obtained by the coaxial powder feeding laser additive manufacturing is 200-500 μm; in the second and third steps, the width of the columnar crystal grains is gradually increased, and a single crystal structure is finally obtained.
4. The method for preparing the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:
in the first step and the second step, utilize supplementary infrared light source to heat the surface all around of increase material spare sample at coaxial powder feeding in-process, reduce the heat dissipation of molten bath horizontal direction, and then obtain the more unanimous dendritic crystal tissue of growing direction, adopt optical radiation contactless heating, give play to the metallurgical characteristics of the small molten bath of vibration material disk, supplementary infrared light source operating temperature range be 800 ~ 1000 ℃, heating power is 20 ~ 30KW, the scope of heating can reach 5 ~ 10 times of molten bath size, the depth of heating can reach 0.4 ~ 1mm, guarantees that the molten bath does not have temperature gradient in the horizontal direction, and the heat only diffuses downwards through the base plate.
5. The method for preparing the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:
the process for the coaxial powder feeding laser additive manufacturing comprises the following specific process parameters: the laser scanning strategy adopts a multilayer multi-channel unidirectional linear deposition mode, adopts the strategies of small energy input, large light spot size and large scanning speed, adopts 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 rate of 3-8 g/min and the powder carrying gas flow of 5-10L/min, and adopts argon gas for integral protection.
6. The method for preparing the nickel-based single crystal superalloy based on the coaxial powder feeding laser additive manufacturing according to claim 1, wherein the method comprises the following steps:
in the multi-layer multi-channel unidirectional linear deposition mode, each channel in each layer in the additive manufacturing process adopts a unidirectional and linear scanning mode, and compared with other laser scanning strategies known at present, the multi-layer multi-channel unidirectional linear deposition mode is adopted to obtain a directional solidification structure with more consistent dendritic crystal orientation more easily.
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