A [gamma] apos; crack-free laser powder bed additive manufacturing method for strengthened nickel-based alloy

Abstract

The invention discloses a crack-free laser powder bed additive manufacturing method for gamma'reinforced nickel-based alloy, which comprises the following steps: firstly, preparing raw material alloy powder, and detecting the total content of Al and Ti elements in the alloy powder; then the powder is loaded into a forming bin, a layer of powder is quantitatively laid every time, a powder bed is scanned through laser, laser energy input and the scanning speed are controlled, the powder bed is rapidly melted and solidified, a layer of solid is formed, the layer height of the solid is 0.02-0.05 mm, and the higher the total content of Al and Ti elements in the alloy powder is, the smaller the layer height is; and after a layer of entity is formed, the forming substrate is controlled to descend by the height of a construction layer, a layer of powder is laid again, laser scanning is conducted again, and the steps are repeated till construction is completed. According to the method, a cooperative control strategy of thin-layer thermal control is adopted, nucleation and expansion of cracks are restrained by controlling the descending height of a formed substrate and controlling laser parameters, and the crack-free laser additive meeting the requirements is manufactured.

Description

Technical Field

[0001] The present invention belongs to the fields of nickel-based superalloys and additive manufacturing, and particularly relates to a crack-free laser powder bed additive manufacturing method for γ'-strengthened nickel-based alloys. Background Art

[0002] With the development of demands in the aviation and energy fields, components with high temperature resistance, corrosion resistance, and complex structures are widely needed. To meet these requirements, γ'-high temperature nickel-based alloys characterized by high Al and Ti contents, which can withstand temperatures above 900 °C and are suitable for additive manufacturing technology (3D printing), have become indispensable materials for components such as engines and gas turbines. Among them, nickel-based alloys with a high γ'-phase content can be applied to higher working temperatures. However, such high-temperature nickel-based alloys are extremely prone to cracking during additive manufacturing (3D printing). Because the additive manufacturing process brings a high cooling rate of up to 10 5 K / s or more and a large temperature gradient, which is the fundamental reason for the cracking of such high-temperature nickel-based alloys. When the crack density reaches 10 mm / mm 2 or more, it usually causes the strength, ductility, fatigue performance, and creep performance of the component to decrease by more than 90%, making it difficult to meet the load-bearing requirements.

[0003] To address this problem, there have been several improvements in the industry for crack-free additive manufacturing of nickel-based superalloys, but none of them are perfect: Method 1: Adjust the elemental composition of the high-temperature nickel-based alloy, improve the microscopic tissue characteristics through alloying, and enhance the strength and plasticity of the component to achieve the purpose of reducing cracking sensitivity. However, regulating existing elements usually sacrifices the strength of the alloy to improve toughness to avoid cracking, which has a negative impact on the alloy properties. The method of adding rare earth elements brings high costs. Taking the Re (rhenium) element as an example, calculated according to the addition amount of 1.0 wt.%, the price of the Re element accounts for about 27% of the powder cost.

[0004] Method 2: By adding high-melting-point ceramic particles to the nickel-based high-temperature alloy powder used as the additive manufacturing raw material, nucleation sites are introduced to promote grain refinement, increase the toughness of the alloy, and reduce cracking sensitivity. In fact, grain refinement increases the grain boundaries, which will significantly reduce the high-temperature mechanical properties of the alloy, reduce the creep life, and affect the application of nickel-based high-temperature alloys in hot-end components. Reducing the strengthening phase will also cause the same consequences.

[0005] Method 3: Eliminate the microcracks generated during the manufacturing process through post-treatment, which can achieve the purpose of manufacturing crack-free nickel-based high-temperature alloy components. However, the healing of internal defects will lead to a reduction in the contour accuracy of the component, increase the component tolerance, limit its application in high-precision scenarios, and the additional post-treatment means will also increase the process complexity and cost.

[0006] Method 4: Additive manufacturing of crack-prone high-temperature nickel-based alloys is achieved by alternately depositing difficult-to-weld and easy-to-weld high-temperature nickel-based alloys in the additive manufacturing process. Essentially, it still achieves additive manufacturing of crack-free high-temperature nickel-based alloys by regulating the composition of high-temperature nickel-based alloys. Moreover, it is difficult to accurately calculate the alloy element composition of the final component. And the process of alternately depositing two materials results in a composition gradient inside the component, which has a negative impact on the isotropy of alloy properties. Summary of the Invention

[0007] To solve the above problems, the present invention discloses a crack-free laser powder bed additive manufacturing method for γ'-strengthened nickel-based alloys, which does not adjust the alloy composition, does not add auxiliary materials, and does not attach additional post-treatment processes. It uses a process method of synergistically controlling thin-layer deposition and heat input to achieve laser additive manufacturing of γ'-phase strengthened nickel-based alloys. The process is scientific and simple, eliminates cracks from the source, has low cost, high repeatability, and wide applicability.

[0008] To achieve the above object, the technical solution of the present invention is as follows: A crack-free laser powder bed additive manufacturing method for γ'-strengthened nickel-based alloys, comprising the following steps: S1. Prepare the raw alloy powder and detect the total content of Al and Ti elements in the alloy powder in mass percentage; S2. Load the powder into the forming chamber, seal the forming chamber, and use high-purity argon to reduce the oxygen content in the forming chamber to below 1000 ppm; S3. Use a powder spreading device to spread a fixed amount of a layer of powder onto the forming substrate below the forming chamber to form a powder bed; S4. Use a laser to scan the powder bed, control the laser energy input and scanning speed, so that the powder bed quickly melts and solidifies to form a layer of solid. The layer height of this layer of solid is between 0.02 - 0.05 mm, and the higher the total content of Al and Ti elements in the alloy powder, the smaller the layer height; S5. Control the forming substrate to descend by a building layer height (layer height); S6. Repeat the above steps S3 - S5 until the building is completed.

[0009] Further, the alloy powder described in step S1 is spherical powder with a particle size less than 53 μm.

[0010] Further, the laser power described in step S1 is 140 - 240 W.

[0011] Further, the laser scanning speed described in step S1 is 700 - 1400 mm / s.

[0012] The working principle of the present invention is: Laser additive manufacturing of γ'-phase strengthened nickel-based alloys is achieved by synergistically controlling thin-layer deposition and heat input: The thin-layer process realizes the coordinated regulation of the molten pool morphology and thermodynamic behavior by controlling the dynamic matching of the quality of the single-layer deposited material and the thermal input parameters. In terms of controlling the molten pool morphology, by reducing the single-layer deposition thickness and matching the reduced laser energy input, a shallow and wide molten pool is formed, improving the stability of melt convection, promoting the escape of bubbles in the molten pool and uniform fusion, and effectively reducing the generation of stress concentration sources such as unfused defects and pores.

[0013] In terms of thermal input regulation, thin-layer deposition combined with controlling the laser energy input and scanning speed significantly reduces the depth of the heat-affected zone and the interlayer temperature gradient, thereby effectively suppressing the interlayer accumulation of residual stress and avoiding the vertical direction stress concentration phenomenon caused by the thick-layer process, achieving a more uniform stress distribution.

[0014] In terms of the evolution of the microstructure, the thin-layer process effectively suppresses the continuous growth of coarse columnar grains and promotes the formation of equiaxed fine grains by reducing the volume of the single-layer molten pool and increasing the cooling rate. The increased grain boundary density not only hinders the crack propagation path but also reduces grain boundary segregation and the local enrichment of low-melting-point eutectic phases.

[0015] Through the synergistic effect of the above three aspects, this process method jointly suppresses the nucleation and propagation of cracks, realizing crack-free additive manufacturing of γ'-high-temperature nickel-based alloys.

[0016] The beneficial effects of the present invention are as follows: (1) The present invention adopts a synergistic control strategy of thin-layer thermal control. By controlling the lowering height of the forming substrate in step 5 and the corresponding laser parameters in step 4, the nucleation and propagation of cracks are suppressed, and crack-free laser additives that meet the requirements are manufactured.

[0017] (2) The present invention does not require adding extra expensive elements or auxiliary materials to the alloy, reducing the cost of crack-free manufacturing while not changing the alloy composition.

[0018] (3) The present invention does not require an additional post-treatment process, eliminates cracks from the material source, and shortens the process flow. Description of the Drawings

[0019] Figure 1 It is a process flow chart of the process method described in the present invention. Figure 2 It is a cracked alloy structure obtained from the parameters of 0.06 mm thick-layer powder during the processing of Inconel 939 alloy in the embodiment of the present invention.

[0020] Figure 3 It is a crack-free alloy structure obtained from the parameters of 0.03 mm thin-layer powder during the processing of Inconel 939 alloy in the embodiment of the present invention. Detailed Embodiments

[0021] The present invention will be further illustrated below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0022] As shown in the figure, a crack-free laser powder bed additive manufacturing method for a γ'-strengthened nickel-based alloy according to the present invention first prepares raw alloy powder and detects the total content of Al and Ti elements in the alloy powder in mass percentage; then loads the powder into the forming chamber and lays a thin layer of powder quantitatively each time. The thickness of the powder layer is between 0.02 - 0.05 mm, specifically determined by the total content of Al and Ti elements. The higher the total content of Al and Ti elements, the smaller the layer thickness. Use a laser to scan the powder bed, control the laser energy input and scanning speed according to the powder layer thickness, so that the powder bed quickly melts and solidifies to form a solid layer. After one solid layer is formed, control the forming substrate to descend by the height of one build layer, then lay another layer of powder, and re-scan with the laser. Repeat the above steps until the construction is completed. The process method of the present invention has two key points, namely selecting the thickness of the thin layer powder according to the total content of Al and Ti elements, and the corresponding relationship between the building laser parameters and the thickness of the thin layer powder.

[0023] The descending height of each layer of the substrate needs to be determined according to the total content of Al and Ti elements in the raw material alloy. The preferred descending height of the thin layer substrate for alloys with different Al and Ti element contents is shown in Table 1.

[0024] Table 1 Preferred descending height of the thin layer substrate corresponding to different Al and Ti element contents

[0025] According to the selected descending height of the thin layer substrate, the corresponding laser parameter range is shown in Table 2.

[0026] Table 2 Laser parameter system corresponding to different descending heights of the thin layer substrate

[0027] Select the thin layer thickness and the corresponding parameter system according to the above strategy and apply them to steps 4 and 5, then the crack-free laser powder bed additive manufacturing of the γ'-high temperature nickel-based alloy can be realized.

[0028] Taking the crack-free laser powder bed additive manufacturing of Inconel 939 alloy (the composition is shown in Table 3, which is a typical γ'-strengthened nickel-based alloy with a total content of Al and Ti elements of 5.6 wt.%) as an example, Table 3 Standard composition of Inconel939

[0029] When the layer thickness is 0.06-0.08mm, the laser power is 200-240W, the scanning speed is 700-1000mm / s, and the scanning interval is 0.03-0.09mm, there are many cracks in the formed component. When the more preferred substrate drop height is 0.03mm, and the laser power and scanning speed are adjusted to 160-200W and 1100-1200mm / s, the crack density is significantly reduced. The metallographic photos before and after the layer thickness optimization are as follows: Figure 2 and 3 .

Claims

1. A crack-free laser powder bed additive manufacturing method for γ'-strengthened nickel-based alloys, characterized in that: It includes the following steps: S1. Prepare raw material alloy powder and detect the total content of Al and Ti elements in the alloy powder; S2. Load the powder into the forming chamber, seal the forming chamber, and use high-purity argon to reduce the oxygen content in the forming chamber to below 1000 ppm; S3. Use a powder spreading device to spread a fixed amount of a layer of powder onto the forming substrate below the forming chamber to form a powder bed; S4. Use a laser to scan the powder bed, control the laser energy input and scanning speed, so that the powder bed quickly melts and solidifies to form a layer of solid. The layer height of this layer of solid is between 0.02 - 0.05 mm. The higher the total content of Al and Ti elements in the alloy powder, the smaller the layer height; S5. Control the forming substrate to descend by the height of one build layer; S6. Repeat the above steps S3 - S5 until the construction is completed.

2. The crack-free laser powder bed additive manufacturing method of a high proportion γ'-phase high-temperature nickel-based alloy according to claim 1, characterized in that: The alloy powder described in step S1 is spherical powder with a particle size less than 53 μm.

3. A crack-free laser powder bed additive manufacturing method for a high proportion γ'-phase high-temperature nickel-based alloy according to claim 1, characterized in that: The laser power described in step S1 is 140 - 240 W.

4. The crack-free laser powder bed additive manufacturing method for a high proportion γ'-phase superalloy according to claim 1, characterized in that: The laser scanning speed described in step S1 is 700 - 1400 mm / s.

5. A crack-free laser powder bed additive manufacturing method for a high proportion γ'-phase superalloy according to claim 1, characterized in that: Its working principle is: Adopt the collaborative control of thin-layer deposition and heat input to realize the laser additive manufacturing of γ'-phase strengthened nickel-based alloy: The thin-layer process realizes the collaborative regulation of the melt pool morphology and thermodynamic behavior by controlling the dynamic matching of the mass of the single-layer deposited material and the heat input parameters. In terms of the control of the melt pool morphology, by reducing the single-layer deposition thickness and matching the reduced laser energy input, a shallow and wide melt pool is formed, improving the stability of melt convection, promoting the escape of bubbles in the melt pool and uniform fusion, and effectively reducing the generation of stress concentration sources such as unfused defects and pores; In terms of heat input regulation, the thin-layer deposition combines the control of laser energy input and scanning speed, resulting in a significant reduction in the depth of the heat-affected zone and a decrease in the interlayer temperature gradient, thereby effectively suppressing the interlayer accumulation of residual stress and avoiding the vertical direction stress concentration phenomenon caused by the thick-layer process, and realizing a more uniform stress distribution; In terms of the evolution of the microstructure, the thin-layer process effectively suppresses the continuous growth of coarse columnar grains and promotes the formation of equiaxed fine grains by reducing the volume of the single-layer melt pool and increasing the cooling rate. The increased grain boundary density not only hinders the crack propagation path but also reduces the grain boundary segregation and the local enrichment of the eutectic phase with a low melting point; Through the synergistic effect of the above three aspects, this process method jointly suppresses the nucleation and propagation of cracks and realizes the crack-free additive manufacturing of γ'-phase high-temperature nickel-based alloy.

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