Method for optimizing components of single crystal alloy for additive manufacturing

Abstract

The invention discloses an optimal design method for components of a single-crystal high-temperature alloy for additive manufacturing, and belongs to the field of additive manufacturing. The invention particularly relates to a method for optimizing components of a single crystal alloy for additive manufacturing. The design method comprises the following specific steps: (1) designing a model alloy; (2) preparing a single-crystal high-temperature alloy substrate in a directional solidification furnace; (3) according to the model alloy, a computer is adopted to carry out proportion calculation on alloy components; (4) argon atomization is conducted on materials with different alloy components, and powder with different components is put into a powder feeding tank; (5) additive manufacturing is conducted, and the powder feeding amount of different powder feeding tanks is adjusted in the additive manufacturing process; and (6) analyzing the relationship between mixed crystals and alloy components by adopting a metallographic analysis method. The influence of the components of the alloy on the formation tendency of the defects such as mixed crystals in the additive manufacturing process is shown. The method is simple and feasible in technology, and is particularly suitable for material selection and process optimization in the additive manufacturing repair process of high-temperature parts in the fields of spaceflight, aviation, ships, petrochemical engineering and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and specifically to a method for optimizing the composition of single-crystal alloys for additive manufacturing. This method is simple and convenient to operate, can quickly and preliminarily screen the high-temperature alloy compositions suitable for additive manufacturing, and is particularly suitable for the additive manufacturing and repair of single-crystal high-temperature alloy components in the fields of aerospace, aviation, shipbuilding, petrochemical industry, etc. Background Art:

[0002] Single-crystal high-temperature alloys are key structural materials that are indispensable for aviation, aerospace, energy, nuclear industry, petrochemical industry, national defense weaponry, and national economic construction. Due to the improvement of the dynamic fuel efficiency of aeroengines, the structure of single-crystal components has become very complex, increasing the difficulty of traditional precision casting. Although additive manufacturing has unique advantages in the preparation of complex components, since existing high-temperature alloy materials are developed based on traditional preparation processes such as casting and forging, as an emerging method for preparing components, additive manufacturing urgently needs to develop high-temperature alloy materials suitable for the additive manufacturing process.

[0003] Currently, the design of materials for the additive manufacturing of high-temperature alloys mainly focuses on the control of solidification cracks. However, with the improvement of aeroengine efficiency, high-temperature structural components have changed from equiaxed crystals to single crystals. Therefore, it is necessary to conduct research and development on the composition of single-crystal high-temperature alloys for additive manufacturing to provide for the preparation of complex high-temperature components. In addition, after the property service of single-crystal components is damaged, the use of additive methods for repair and remanufacturing can effectively reduce the service cost of the engine. Although the industry tends to use alloys with the same composition as the original during the repair process, these alloys have a narrow process parameter range during the additive manufacturing process, are prone to defects such as polycrystals, and reduce the high-temperature mechanical properties of the alloy, becoming a major hidden danger during the service process of the components. Controlling the polycrystals of additive manufacturing single-crystal high-temperature alloys has become the key to the repair of single-crystal components, and the tendency of additive manufacturing single-crystal polycrystals has become a very important link in the optimization of process parameters during the laser repair process. Therefore, during the additive manufacturing repair process of single-crystal high-temperature alloy components, it is necessary to evaluate the tendency of polycrystal formation in additive manufacturing single-crystal high-temperature alloys, which is beneficial to improving the yield rate and reducing production costs. Summary of the Invention:

[0004] The purpose of the present invention is to provide a method for optimizing the composition of single-crystal alloys for additive manufacturing, to solve the problems of long design cycle and high cost of the composition design of special high-temperature alloys for additive manufacturing. Through the design of base alloy powder and post-added powder, the composition of additive manufacturing alloys can be effectively selected, and it can guide the repair and remanufacturing of single-crystal high-temperature alloy components, reducing the manufacturing and maintenance costs of single-crystal components.

[0005] The technical solution of the present invention is:

[0006] A method for optimizing the composition of single-crystal alloys for additive manufacturing, characterized in that, due to the high temperature of the molten pool during the laser additive manufacturing process, the alloy powders with different added components can achieve uniform composition in a short time. According to the classical theory of directional solidification, alloys with different compositions exhibit different solidification characteristics. When the alloy composition changes, the local supercooling degree may change, resulting in the formation of polycrystals and other defects. The formation of such defects can significantly damage the integrity of the additively manufactured single crystal, thereby affecting the mechanical properties of the single-crystal superalloy. On the model single-crystal alloy, by adjusting the content of different components and the laser process parameters, different compositions and microstructures are formed in the additive manufacturing area. Through optical on-line detection, signal acquisition and analysis are carried out on the additive manufacturing area. When cracks are detected, it indicates that polycrystals have been formed during the additive manufacturing process, and then the additive manufacturing experiment is stopped. Metallographic analysis is performed on the samples without cracks to analyze the location where the polycrystals are formed, so as to analyze the influence law of the component content on the volume fraction of polycrystal formation. When the polycrystal ratio is greater than or equal to 1%, it is considered that polycrystals have been formed, and thus the influence law of the components on the polycrystals is analyzed.

[0007] First, design the composition of the model alloy, with the composition being Co 29 - 23%, Ni 70 - 75%, Al 1 - 2%. After vacuum induction melting, a single-crystal substrate is prepared on a directional solidification furnace.

[0008] Secondly, prepare alloys with different compositions: Cr 8 - 12%, W 2 - 6%, Mo 0.5 - 3%, Ta 4 - 6%, Al 3 - 5%, Hf 0 - 1.3%, the balance being Ni, with a particle size of 50 - 80 microns, an oxygen content of 100 - 150 ppm, and a nitrogen content of 80 - 100 ppm, to reduce the influence of impurity elements on the forming quality.

[0009] Finally, during the additive manufacturing process, different component powders are added. The preferred addition sequence is Cr change, W change, Mo change, Ta change, Hf change, Al change, so as to achieve the change of composition. For the laser forming process parameters, the laser power is 1000 - 1200 W, the total powder feeding amount is 3 - 4 g / min, and the scanning speed is 200 - 500 mm / min.

[0010] The design concept of the present invention is:

[0011] The method of the present invention is based on the fact that changes in material composition and process during alloy solidification can lead to changes in the degree of supercooling during alloy solidification, resulting in the easy formation of polycrystalline defects during the additive manufacturing process. By changing the alloy composition or process during the additive manufacturing process, the present invention realizes the change of the temperature field caused by the composition change, realizes the optimization of the composition, and at the same time couples the change of the laser process parameters to realize the optimization based on the latest composition and process parameters. It can also analyze the ability of polycrystalline high-temperature alloys with different compositions and additive manufacturing processes to form polycrystalline defects. Therefore, the biggest feature of the present invention is that it can quickly evaluate the processability of additive manufacturing high-temperature alloys, and realize the rapid optimization of the composition of single-crystal alloys for additive manufacturing and the optimization of the preparation process.

[0012] The advantages and beneficial effects of the present invention are as follows:

[0013] 1. According to the composition characteristics of single-crystal high-temperature alloys, the present invention evaluates the laws of the composition, process and their relationship with polycrystalline defects of single-crystal high-temperature alloys for additive manufacturing by changing the alloy composition and process during the additive manufacturing process. The evaluation results of this method can be used as the basis for the selection of alloys and additive manufacturing processes.

[0014] 2. The present invention can provide a basis for the selection of materials and processes for repairing single-crystal high-temperature alloy components by additive manufacturing, which is beneficial to guiding the repair and remanufacturing of single-crystal components.

[0015] 3. The present invention is simple to operate, reasonably designed, highly operable, can significantly reduce the production and maintenance costs of additive manufacturing single-crystal high-temperature alloy components, and the method has low cost. It can not only be applied to single-crystal high-temperature alloys, but also be used for the selection of other high-temperature alloys, wear-resistant steels and other materials, which is beneficial to popularization and application. Description of the Drawings:

[0016] Figure 1 Morphology of polycrystalline defects in additive manufacturing single-crystal alloys (change of tungsten element). Detailed Embodiments:

[0017] Based on the high temperature of the molten pool during the laser additive manufacturing process, the alloy powders with different added components can achieve uniform composition in a short time. According to the classical theory of directional solidification, for alloys with different compositions, their solidification characteristics show different features. When the alloy composition changes, the local supercooling degree may change, resulting in the formation of heterocrystals and other defects. The formation of these defects can significantly damage the integrity of the single crystal in additive manufacturing, thus affecting the mechanical properties of single crystal superalloys. On a nickel-based model single crystal alloy, by adjusting the different components and contents of the nickel-based alloy, different compositions and microstructures are formed in the additive manufacturing area. Signal acquisition and analysis of the additive manufacturing area are carried out through optical on-line detection (thermal imaging and digital image). When cracks are detected, it indicates that heterocrystals have been formed during the additive manufacturing process. Then, the additive manufacturing experiment is stopped, and metallographic analysis is performed on the samples without cracks to analyze the location where the heterocrystals are formed, so as to analyze the influence law of composition on heterocrystals and obtain the optimized composition of the nickel-based alloy.

[0018] In the specific implementation process, the method of the present invention is based on the fact that changes in material composition and process during the alloy solidification process will cause changes in the supercooling degree during the alloy solidification process, resulting in the easy formation of heterocrystal defects during the additive manufacturing process. The present invention realizes the change of the temperature field caused by the change of composition through the change of alloy composition or process during the additive manufacturing process, realizes the optimization of composition, and at the same time couples the change of laser process parameters to realize the optimization based on the latest composition and process parameters. It can also analyze the formation ability of heterocrystals in single crystal superalloys with different compositions and additive manufacturing processes. Therefore, the biggest feature of the present invention is that it can quickly evaluate the processability of additive manufacturing superalloys, and realize the rapid optimization of the composition of single crystal alloys for additive manufacturing and the optimization of the preparation process.

[0019] The method for optimizing the composition of single crystal alloys for additive manufacturing of the present invention is specifically as follows:

[0020] Step 1: The composition of the model alloy is Co 29 - 23%, Ni 70 - 75%, Al 1 - 2%. After vacuum induction melting, a single crystal substrate and atomized powder are prepared on a directional solidification furnace.

[0021] Step 2: Prepare alloys with different compositions: Cr 8 - 12%, W 2 - 6%, Mo 0.5 - 3%, Ta 4 - 6%, Al 3 - 5%, Hf 0 - 1.3%, the balance is Ni, the particle size is 50 - 80 microns, the oxygen content is 100 - 150 ppm, and the nitrogen content is 80 - 100 ppm to reduce the influence of impurity elements on the forming quality.

[0022] Step 3: Additive manufacturing process. Add powders with different compositions, and the preferred addition order is W variation, Cr variation, Mo variation, Ta variation, Hf variation, Al variation, so as to achieve composition variation. Laser forming process parameters: laser power is 1000 - 1200 W, total powder feeding amount is 3 - 4 g / min, and scanning speed is 200 - 500 mm / min.

[0023] Next, the present invention will be further elaborated in detail through examples and drawings.

[0024] Example

[0025] In this example, according to the composition of the alloy in the preliminary design model of the alloy to be studied, by mass, the composition is Co 27%, Ni 71%, Al 2%. After vacuum induction melting, a single crystal substrate is prepared on a directional solidification furnace. Argon atomization is used to prepare alloys with different compositions: Cr 8 - 12%, W 2 - 6%, Mo 0.5 - 3%, Ta 4 - 6%, Al 3 - 5%, Hf 0 - 1.3%, and the balance is Ni; the particle size of each metal powder raw material is 50 - 80 microns, the oxygen content is 100 - 150 ppm, and the nitrogen content is 80 - 100 ppm to reduce the influence of impurity elements on the forming quality. Put the metal powders to be studied into their respective powder barrels. In the additive manufacturing process, add powders with different compositions, and the preferred addition order is Cr variation, W variation, Mo variation, Ta variation, Hf variation, Al variation, so as to achieve composition variation. Laser forming process parameters: laser power is 1200 W, total powder feeding amount is 4 g / min, and scanning speed is 500 mm / min.

[0026] The process of adjusting the different compositions and contents of the nickel-based alloy is as follows:

[0027] During the laser additive manufacturing process, starting from nickel being 100%, add each other metal component in the alloy except nickel to it in turn; as the additive manufacturing progresses, gradually increase the addition of each other metal component from low to high, so that the addition amount of each other metal component in the manufactured additive gradually increases from low to high according to the set range;

[0028] Relative to nickel, the addition amount of each other metal component starts from the lowest amount required for the alloy to be prepared (the first stage) until cracks appear in the additive or the highest amount, and the increasing range is 20% of the value obtained by subtracting the lowest amount from the highest amount of this metal;

[0029] Select the addition amount of the other metal component when cracks appear in the additive (the Nth stage, N is an integer greater than or equal to 1), or the addition amount of the other metal component at the previous increasing range before cracks appear in the additive (the N - 1th stage) as the content of this metal component in the optimized nickel-based alloy (the Nth stage or the N - 1th stage);

[0030] When the addition amount of the metal component reaches the highest amount required for the alloy to be prepared, no cracks appear in the additive, and the highest amount is taken as the content of this metal component in the optimized nickel-based alloy.

[0031] With the progress of additive manufacturing, each time other metal components are added, the height of the prepared additive is equal to 1 mm.

[0032] Finally, the composition of the nickel-based alloy is determined as follows by mass: Cr 12%, W 3%, Mo 2%, Ta 6%, Al 4.5%, Hf 1.1%, and the balance is Ni; an additive with a diameter of 10 mm and a height of 20 - 30 mm is prepared using the optimized nickel-based alloy composition, and the product has no abnormal grains and good quality.

[0033] Such as Figure 1 As shown, through the analysis of the macro-corrosion morphology of fixed height and the EBSD crystal orientation analysis, it can be seen that under the same additive manufacturing process conditions, the change of alloy composition has a greater impact on the formation of abnormal grains.

[0034] The working process and results of the present invention are as follows:

[0035] In the present invention, by designing the basic alloy composition, the basic alloy is prepared into a substrate by a directional solidification furnace as the substrate for laser additive manufacturing single crystals, and at the same time, the basic alloy is prepared into powder by argon gas atomization; metal powders are also prepared for other alloy components to be studied, and the above powders are placed in different powder tanks. During the additive manufacturing process, by adjusting the powder feeding rate of the powders in different powder tanks, continuous preparation of powders with different compositions is realized. At the same time, when the powder compositions are the same, the laser forming process can be adjusted. During the additive process, on-line optical detection is adopted. Once a crack formation signal appears, it indicates that abnormal grains have been formed in the sample and cracking has occurred under the action of stress, and the experiment can be terminated immediately and analyzed. By using this method, the influence of different composition materials and processes on the formation law of abnormal grains can be quickly realized, so as to quickly optimize the alloy composition, providing a basis for designing single crystal superalloys with weak tendency to form abnormal grains.

[0036] The results of the examples show that the present invention has the characteristics of simple preparation process and low cost, can solve the problems of large powder requirements and high single experiment cost in the research and development process of the composition of additive manufacturing special single crystal superalloys, can quickly screen the composition of single crystal superalloys with a large tendency to form abnormal grains, and is thus beneficial to the research and development of additive manufacturing single crystal superalloy materials.

Claims

1. A method for optimizing the composition of single-crystal alloys for additive manufacturing, characterized in that, due to the high temperature of the molten pool during the laser additive manufacturing process, alloy powders with different added components can achieve composition uniformity in a short time; according to the classical theory of directional solidification, alloys with different components have different solidification characteristics. When the alloy composition changes, the local undercooling degree may change, resulting in the formation of heterocrystals and other defects. The formation of such defects can significantly damage the integrity of the single crystal in additive manufacturing, thereby affecting the mechanical properties of single-crystal superalloys; on a nickel-based model single-crystal alloy, by adjusting the different components and contents of the nickel-based alloy, different components and microstructures are formed in the additive manufacturing area. Through optical on-line detection, signal acquisition and analysis are carried out on the additive manufacturing area. When cracks are detected, it indicates that heterocrystals have been formed during the additive manufacturing process, and the additive manufacturing experiment is stopped.

2. The method for optimizing the composition of single-crystal alloys for additive manufacturing according to claim 1, characterized in that, the process of adjusting the different components and contents of the nickel-based alloy is as follows: During the laser additive manufacturing process, starting with nickel at 100%, each other metal component in the alloy except nickel is sequentially added to it; as the additive manufacturing progresses, the addition of each other metal component is gradually increased from low to high, so that the addition amount of each other metal component in the manufactured additive increases gradually from low to high according to a set range; Relative to nickel, the addition amount of each other metal component starts from the lowest amount required for the alloy to be prepared (the first stage) until cracks appear in the additive or the highest amount, and the increase range is 5% to 50% of the value obtained by subtracting the lowest amount from the highest amount of this metal, preferably 10 - 30%; Select the addition amount of the other metal component when cracks appear in the additive (the Nth stage, N is an integer greater than or equal to 1), or the addition amount of the other metal component at the previous increase range before cracks appear in the additive (the N - 1th stage) as the content of this metal component in the optimized nickel-based alloy (the Nth stage or the N - 1th stage); When the addition amount of the metal component reaches the highest amount required for the alloy to be prepared and no cracks have appeared in the additive, use its highest amount as the content of this metal component in the optimized nickel-based alloy.

3. The method for optimizing the composition of single-crystal alloys for additive manufacturing according to claim 2, characterized in that, With each additional addition of another metal component during the additive manufacturing process, the height of the prepared additive is greater than or equal to 1 mm.

4. The method for optimizing the composition of single-crystal alloys for additive manufacturing according to claim 1, characterized in that, The composition of the model alloy is Co 29 - 23%, Ni 70 - 75%, Al 1 - 2%. After vacuum induction melting, a single-crystal substrate is prepared on a directional solidification furnace.

5. The method for optimizing the composition of single-crystal alloys for additive manufacturing according to claim 1 or 2 or 3, characterized in that, The composition requirements for the alloy to be prepared are Cr 8 - 12%, W 2 - 6%, Mo 0.5 - 3%, Ta 4 - 6%, Al 3 - 5%, Hf 0 - 1.3%, and the balance is Ni.

6. The method for optimizing the composition of single-crystal alloys for additive manufacturing according to claim 1 or 2 or 3, It is characterized in that the nickel-based alloy to be prepared is an aluminum-containing nickel-based alloy, and aluminum is the last metal component optimized except nickel.

7. The method for optimizing the composition of a single-crystal alloy for additive manufacturing according to claim 5, It is characterized in that in the additive manufacturing process, powders with different compositions are added. The preferred addition sequence is Cr change, W change, Mo change, Ta change, Hf change, Al change, so as to achieve the change of composition.

8. The method for optimizing the composition of a single-crystal alloy for additive manufacturing according to any one of claims 1-7, It is characterized in that alloy powders with different compositions are prepared. The particle size of the metal raw material is 50-80 microns, the oxygen content is 100-150 ppm, and the nitrogen content is 80-100 ppm, so as to reduce the influence of impurity elements on the forming quality or defects.

9. The method for optimizing the composition of a single-crystal alloy for additive manufacturing according to any one of claims 1-7, It is characterized in that for the laser forming process parameters, the laser power is 1000-1200 W, the total powder feeding amount is 3-4 g / min, and the scanning speed is 200-500 mm / min.

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