A low crack sensitivity additively applicable nickel-based high-temperature alloy and preparation method

Abstract

The present invention provides a low-crack-sensitivity nickel-based high-temperature alloy suitable for additive manufacturing and a preparation method, belonging to the technical field of nickel-based high-temperature alloys for additive manufacturing. The solution of the present invention is as follows: the chemical composition of the nickel-based high-temperature alloy for additive manufacturing is as follows, in weight percentage: Al 6.0-6.5wt%, Co 14.4-14.8wt%, Cr 5.6-6.0wt%, Mo 0.01-0.05wt%, Ta 0.8-1.5wt%, Ti 0.01-0.05wt%, W 2.1-2.5wt%, C 0.1-0.3wt%, B 0.01-0.1wt%, Nb 2.0-2.5wt%, and the balance is Ni. The present invention provides a nickel-based high-temperature alloy for additive manufacturing that does not exhibit microcracks under additive processing conditions, has low void defects, and has high-temperature performance and good structural stability.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of nickel-based high-temperature alloys, and in particular to an additively manufactured nickel-based high-temperature alloy with low crack sensitivity and a preparation method thereof. Background Art

[0002] Nickel-based high-temperature alloys have become the preferred material for key components of aircraft gas turbines due to their excellent high-temperature stability and mechanical properties. Due to the extremely complex operating environment of nickel-based high-temperature alloys, the geometric morphology of components made of nickel-based alloys is also more complex. Although investment casting, as a traditional processing method, can perform precision casting, the processing technology is relatively complicated and the processing efficiency is relatively low. Additive manufacturing technology can process complex geometric shapes, can achieve fewer processing processes, has higher processing freedom and more efficient material utilization. However, there is a problem of high crack sensitivity in the additive manufacturing of nickel-based alloys. The process optimization methods currently used for existing commercial nickel-based alloys cannot completely eliminate cracks. Optimizing the composition of nickel-based alloys according to additive metallurgical conditions can effectively solve the defect problem.

[0003] Research has shown that cracks in additive manufacturing can be broadly categorized as thermal cracks and aging cracks. Thermal cracks primarily form at the end of the alloy's solidification phase. Grain-boundary strengthening elements such as C and B segregate at grain boundaries, forming low-melting-point phases. During layered printing, the upper ion beam remelts the lower low-melting-point phases, causing liquefaction cracks. Aging cracks, on the other hand, originate in the pure solid phase. As the alloy cools, the matrix toughness decreases and a secondary phase rapidly precipitates, triggering severe stress concentration and resulting in a high susceptibility to solid-state aging cracking.

[0004] The existing technology for developing nickel-based high-temperature alloys suitable for additive manufacturing with low crack sensitivity cannot ensure sufficient γ' phase content to obtain excellent high-temperature mechanical properties and good high-temperature structural stability. It is difficult to control the contents of Al, Ta, and Ti elements within appropriate ranges and regulate the segregation behavior of trace elements such as C and B. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a low crack-sensitive additively applicable nickel-based high-temperature alloy and a preparation method. The purpose is to provide a method for preparing an additively manufactured nickel-based high-temperature alloy that does not exhibit microcrack defects under a wide range of additive processing conditions, has low hole defects, and at the same time has excellent high-temperature performance and good structural stability.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] The low crack sensitivity additive-suitable nickel-based high-temperature alloy of the present invention comprises the following components and mass percentages: Al 6.0-6.5wt%, Co 14.4-14.8wt%, Cr 5.6-6.0wt%, Mo 0.01-0.05wt%, Ta 0.8-1.5wt%, Ti 0.01-0.05wt%, W 2.1-2.5wt%, C 0.1-0.3wt%, B 0.01-0.1wt%, Nb 2.0-2.5wt%, and the balance is Ni.

[0008] The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%;

[0009] The carbide area fraction of the nickel-based high-temperature alloy suitable for the additive manufacturing is 4%-7%;

[0010] The instantaneous tensile properties of the nickel-based high-temperature alloy suitable for the additive are as follows: At room temperature, the tensile strength σ of the nickel-based high-temperature alloy suitable for the additive is b ≥1200MPa, elongation A≥20%; at a temperature not higher than 800℃, the tensile strength σ of the nickel-based high-temperature alloy used in the additive is b ≥930MPa, elongation A≥9%; at a temperature of 800-900℃, the tensile strength σ of the nickel-based high-temperature alloy used in the additive is b ≥480MPa, elongation A≥18%;

[0011] The present invention proposes a method for preparing the above-mentioned additively applied nickel-based high-temperature alloy, comprising the following steps:

[0012] Step (1): vacuum induction melting and casting, followed by grinding and sand blowing to obtain a master alloy;

[0013] Step (2): preparing alloy powder by argon atomization method using the master alloy in step (1);

[0014] Step (3): Printing the alloy powder in step (2) into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process;

[0015] The vacuum induction melting temperature in step (1) is 1550-1600°C for 5-8 minutes; the casting temperature is 1450-1500°C; the master alloy has an impurity element content of less than 5 ppm;

[0016] In the argon atomization process in step (2), the powder spraying pressure is 7-9 MPa and the temperature is 1540-1560°C;

[0017] The external morphology of the alloy powder in step (2) is nearly spherical, containing a small amount of satellite particles, and the particle size D50 of the alloy powder is 90-100 μm;

[0018] The laser metal deposition process parameters in step (3) are: power of 900-1600 W, scanning speed of 240-840 mm / min, filling spacing of 1.2-2.0 mm, layer thickness of 60-70 μm, and powder feeding speed of 6.8 g / min.

[0019] Compared with the prior art, the additively manufactured nickel-based high-temperature alloy and the preparation method thereof of the present invention have at least the following beneficial effects:

[0020] 1. The present invention provides an additively manufactured nickel-based superalloy. By utilizing a high Al content and appropriate Ta and Ti contents to control the volume fraction of the γ' phase (30%-50%), the alloy maintains high-temperature performance while strengthening the γ and γ' phases and effectively suppressing the formation of a low-melting-point eutectic of the γ / γ' phase. Furthermore, solid-solution strengthening elements such as high concentrations of Co and Cr, appropriate amounts of W, and a small amount of Mo are added to enhance the matrix's intrinsic strength, while trace amounts of the grain boundary elements C and B strengthen the grain boundaries. Furthermore, an appropriate amount of Nb is added to generate a carbide content that inhibits the segregation of B at grain boundaries, thereby preventing the formation of liquefaction and solidification cracks caused by B segregation. By manipulating the composition, the precipitation behavior of the γ' phase is modified to prevent the formation of solid-state aging cracks. Specifically, during the alloy cooling process, the precipitation of the γ' phase is minimized while maintaining a high γ' phase content at 900°C. At the same time, the effects of alloy element precipitation strengthening, solid solution strengthening, and grain boundary strengthening are brought into play to improve the medium and high temperature mechanical properties of the alloy, maintain high temperature structural stability, and enable the alloy to reach the level of high-performance additive manufacturing high-temperature alloys.

[0021] 2. The alloy of the present invention, on the one hand, contains only one precious metal, Ta, and its content is relatively low, resulting in low overall cost. On the other hand, by increasing the Al / Ta ratio and adding a small amount of Ti, the present invention ensures the formation efficiency of the γ' phase, reduces the precipitation rate of the γ' phase, and avoids solid-state aging cracking of the alloy, while ensuring a high γ' phase content (30%-50%), guaranteeing high-temperature performance. Second, the addition of B increases the alloy's hot crack sensitivity, while its absence deteriorates its high-temperature performance. The introduction of NbC carbides effectively suppresses the segregation of B at grain boundaries, thereby avoiding liquefaction cracking and solidification cracking caused by B segregation. The high Al / Ta ratio and the introduction of NbC carbides designed in this application can prevent the generation of cracks while maintaining good high-temperature performance.

[0022] 3. The microstructure of the additively manufactured nickel-based superalloy of this invention exhibits columnar crystals growing along the build direction; carbides are dispersed between dendrite trunks and dendrites, with an area fraction of approximately 4%-6%; and no cracks form. The nickel-based superalloy of this invention exhibits excellent mechanical properties in the laser metal deposition-printed state without the need for subsequent heat treatment.

[0023] 4. The additive manufacturing method for preparing nickel-based superalloys of this invention improves laser density during the specific process, overcoming the defects caused by the refractory elements W, Mo, and Ta, allowing them to leverage their respective advantages. This method eliminates crack formation while reducing the formation of voids.

[0024] 5. The nickel-based superalloy composition and preparation method provided by this invention enable additively manufactured nickel-based superalloys to be free of microcrack defects across a wide range of additive processing conditions, exhibiting excellent formability, strong process adaptability, and good structural stability. Compared to existing alloys, the additively manufactured nickel-based superalloy of this invention exhibits superior strength and ductility at room temperature, intermediate temperature, and high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The defect area fraction distribution and metallographic structure images of the cubic prism sample under different process parameters according to the embodiment of the present invention are shown;

[0026] Figure 2 Scanning microstructure diagrams of the longitudinal and cross sections of rectangular prism samples according to an embodiment of the present invention;

[0027] Figure 3 This is a diagram showing the element distribution results of the rectangular prism sample according to an embodiment of the present invention based on ToF-SIMS characterization;

[0028] Figure 4 The carbide characterization results of the rectangular prism sample according to the embodiment of the present invention based on transmission electron microscopy;

[0029] Figure 5 The carbide area fraction distribution and scanning microstructure diagram of the cubic prism sample of the embodiment of the present invention under different process parameters. Implementation Method

[0030] In order to further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose of the invention, the specific implementation methods, structural features and effects of the present invention application are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0031] The primary objective of this invention is to provide and produce a nickel-based superalloy suitable for additive manufacturing that combines excellent high-temperature performance with good structural stability, no crack defects, and low levels of porosity. Specifically, the alloy is produced under additive metallurgical conditions without cracks, while also containing low levels of defects such as porosity. This enables the additively manufactured nickel-based superalloy to exhibit excellent tensile strength and plasticity at room temperature, intermediate temperature, and high temperature. This addresses the technical issues of existing additively manufactured superalloys, such as poor formability and difficulty controlling defects.

[0032] The technical solutions of the present invention are as follows:

[0033] The present invention provides an additively manufactured nickel-based high-temperature alloy, wherein the chemical composition of the additively manufactured nickel-based high-temperature alloy is as follows, in weight percentage: Al 6.0-6.5wt%; Co 14.4-14.8wt%; Cr 5.6-6.0wt%; Mo 0.01-0.05wt%; Ta 0.8-1.5wt%; Ti 0.01-0.05wt%; W 2.1-2.5wt%; C 0.1-0.3wt%; B 0.01-0.1wt%; Nb 2.0-2.5wt%; and the balance is Ni.

[0034] The design of the chemical composition of the above-mentioned additively manufactured nickel-based high-temperature alloy is explained as follows:

[0035] (1) In the existing technology, the content of γ' phase in additively manufactured nickel-based high-temperature alloys is relatively low. The reason is that during the cooling process of the alloy, the toughness of the matrix decreases, and the rapid precipitation of high-content γ' phase leads to severe stress concentration, resulting in the alloy having high aging crack sensitivity.

[0036] (2) In the existing technology, in order to maintain the high-temperature mechanical properties of nickel-based high-temperature alloys manufactured by additive manufacturing, it is always inevitable to add grain boundary strengthening elements such as C and B to the alloy. However, the segregation of low-melting-point borides along the grain boundaries often causes liquid cracking and solidification cracking during the additive manufacturing process, making the alloy highly sensitive to thermal cracking.

[0037] The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%;

[0038] The carbide area fraction of the nickel-based high-temperature alloy suitable for the additive manufacturing is 4%-7%;

[0039] The instantaneous tensile properties of the nickel-based high-temperature alloy suitable for the additive are as follows: At room temperature, the tensile strength σ of the nickel-based high-temperature alloy suitable for the additive is b ≥1200MPa, elongation A≥20%; at a temperature not higher than 800℃, the tensile strength σ of the nickel-based high-temperature alloy used in the additive is b≥930MPa, elongation A≥9%; at a temperature of 800-900℃, the tensile strength σ of the nickel-based high-temperature alloy used in the additive is b ≥480MPa, elongation A≥18%;

[0040] A method for preparing a nickel-based high-temperature alloy by additive manufacturing comprises the following steps:

[0041] Step 1: Prepare nickel-based high-temperature alloy powder based on vacuum induction melting and argon atomization method.

[0042] Step 2: Using a laser metal deposition process, the alloy powder was printed into an additively manufactured nickel-based high-temperature alloy (i.e., laser metal deposition printed state). The laser metal deposition process parameters were: power of 900-1600 W, scan speed of 240-840 mm / min, fill spacing of 1.2-2.0 mm, layer thickness of 60-70 μm, and powder feed rate of 6.8 g / min. Cubic prism samples with a length, width, and height of 10 mm × 10 mm × 10 mm and rectangular prism samples with a length, width, and height of 16 mm × 16 mm × 60 mm were printed.

[0043] It should be noted that in the above process, since the chemical composition of the alloy of the present invention contains refractory elements such as W, Ta, and Mo, an alloy with fewer defects and better performance can be obtained when the laser energy density (power, scanning speed, powder feeding speed, and laser diameter) of the laser metal deposition process is set higher.

[0044] Here, the obtained additively manufactured nickel-based high-temperature alloy has a high volume fraction of γ' strengthening phase, and does not form cracks during the layered printing process and has structural characteristics such as low level of void defects.

[0045] The present invention is further described below by means of specific embodiments: Example

[0046] In this embodiment, a crack-free additive manufacturing nickel-based high-temperature alloy is prepared. The chemical composition thereof is shown in Table 1:

[0047] Table 1

[0048]

[0049] The specific preparation steps are as follows:

[0050] Nickel-based high-temperature alloy powder was prepared by vacuum induction melting and argon atomization. The external morphology of the powder was nearly spherical with only a small number of satellite particles. The D10, D50 and D90 of the powder were distributed around 48μm, 97μm and 173μm, respectively.

[0051] The alloy powder was printed into an additively manufactured nickel-based superalloy using a laser metal deposition process (i.e., laser metal deposition printed state). The laser metal deposition process parameters were: power of 900-1600 W, scan speed of 480-840 mm / min, fill spacing of 1.2-2.0 mm, layer thickness of 60 μm, and powder feed rate of 6.8 g / min. Thirty-two cubic samples measuring 10 mm x 10 mm x 10 mm were printed.

[0052] The alloy powder was then printed into a nickel-based superalloy for additive manufacturing (i.e., laser metal deposition printing) using a laser metal deposition process. The laser metal deposition process parameters were: power of 1500W, scan speed of 480mm / min, fill spacing of 1.55mm, layer thickness of 70μm, and powder feed rate of 6.8g / min. A rectangular prism sample measuring 16mm x 16mm x 60mm in length, width, and height was printed.

[0053] Here, the defect area fraction distribution and metallographic structure pictures of the cube samples prepared in this example under different process parameters are shown in the figure. Figure 1 As shown. Figure 1 It can be seen from the figure that the cube samples prepared in this example have the following characteristics: no cracks were detected under different laser powers and scanning speeds, only a small amount of holes existed, and the total hole area fraction was much lower than 0.2%, which shows a very wide laser processing window. Figure 1 It can be seen that even the sample with the highest defect has a defect area fraction of only 0.17%, while when the printing parameters are 1500W, 600mm / min (laser volume energy density is 161J / mm 3 ), nearly defect-free bulk samples can be obtained (the defect area fraction is kept at 0.03%, which is much better than IN718 and comparable to IN625), with excellent printability.

[0054] On the one hand, the SEM characterization results of the longitudinal and cross sections of the rectangular prism samples prepared in this example are as follows Figure 2 As shown. Figure 2 It can be seen that the rectangular prism sample prepared in this example has the following structural characteristics:

[0055] Microstructural features in both cross-sections and longitudinal sections reveal that the interdendritic regions of the rectangular prism sample prepared in this example contain a high density of uniformly distributed MC carbides, with only a small number of pores present in the interdendritic regions near the carbides. Furthermore, the area fraction of MC carbides is approximately 5.5%, indicating the presence of a large number of MC / γ phase boundaries.

[0056] On the one hand, the ToF-SIMS characterization results of the rectangular prism sample prepared in this example are as follows Figure 3As shown. Figure 3 As can be seen from the figure, the elemental distribution of the rectangular prism sample prepared in this example exhibits the following characteristics: B is uniformly distributed throughout the alloy, with no localized enrichment. Furthermore, the high concentrations of C and Nb overlap, indicating the formation of NbC carbides, which effectively suppresses the segregation of B between dendrites.

[0057] On the one hand, the transmission electron microscopy characterization results of the interdendritic NbC carbides of the rectangular prism sample prepared in this example are as follows Figure 4 As shown. Figure 3 As can be seen from the figure, the NbC carbides between the dendrites of the rectangular prism sample prepared in this example have the following characteristics: a clear B peak can be observed at the NbC / γ interface, confirming the design strategy of enriching the B element at the carbide / γ phase interface. The presence of the NbC / γ interface makes the B atoms more uniform in space, thus avoiding the uncontrollable segregation of the B element at the grain boundary. Figure 4 (c) shows a high-resolution image centered on the phase boundary, showing a nearly coherent interface (100) with the face-centered cubic FCC matrix, where the electron diffraction pattern again confirms that the precipitated phase is NbC carbide.

[0058] On the one hand, the carbide area fraction distribution and SEM characterization results of the cube samples prepared in this example under different process parameters are as follows Figure 5 As shown. Figure 5 It can be seen from the figure that the cubic samples prepared in this example have the following characteristics: within the entire range of process parameters, the content of NbC carbides remains quite stable, almost at a constant level of about 5.4%. Figure 4 As can be seen in the figure, varying volumetric energy density leads to variations in dendrite arm spacing but has little effect on the proportion of NbC carbides. This independence of carbide content from process parameters ensures that the NbC / γ phase boundary remains extensive regardless of process parameter variations, resulting in high process robustness for the additively manufactured nickel-based superalloy prepared by this invention.

[0059] The instantaneous tensile properties of the additively manufactured nickel-based high-temperature alloy rectangular prism sample prepared in this example (laser metal deposition printed state, not heat treated) at different temperatures are shown in Table 2.

[0060] Table 2

[0061]

[0062] Table 2 shows that the additively manufactured nickel-based superalloy prepared in this example exhibits high tensile strength and good ductility at room temperature. At 800°C, the alloy's tensile strength and elongation both decrease slightly but remain at a high level, primarily due to the crack-free matrix. At 900°C, the strength decreases rapidly, but the tensile strength still reaches 485 MPa, demonstrating the alloy's excellent medium- and high-temperature strength and ductility.

Claims

1. A low crack sensitivity additively applicable nickel-based high-temperature alloy, characterized in that: The components and mass percentages are as follows: Al 6.0-6.5wt%, Co 14.4-14.8wt%, Cr 5.6-6.0wt%, Mo 0.01-0.05wt%, Ta 0.8-1.5wt%, Ti 0.01-0.05wt%, W 2.1-2.5wt%, C 0.1-0.3wt%, B 0.01-0.1wt%, Nb 2.0-2.5wt%, and the balance is Ni; The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%; The carbide area fraction of the nickel-based high-temperature alloy suitable for the additive manufacturing process is 4%-7%.

2. A method for preparing the additive-suitable nickel-based high-temperature alloy with low crack sensitivity according to claim 1, characterized in that: The steps include: Step (1): vacuum induction melting and casting, followed by grinding and sand blowing to obtain a master alloy; Step (2): preparing alloy powder by argon atomization method using the master alloy in step (1); Step (3): Printing the alloy powder in step (2) into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process.

3. The method for preparing a low crack sensitivity additively applicable nickel-based high-temperature alloy according to claim 2, characterized in that: The temperature of the vacuum induction melting in step (1) is 1550-1600°C, and the time is 5-8 minutes; the temperature of the casting is 1450-1500°C.

4. The method for preparing a low crack sensitivity additively applicable nickel-based high-temperature alloy according to claim 2, characterized in that: The master alloy is a master alloy with an impurity element content of less than 5 ppm.

5. The method for preparing a low crack sensitivity additively applicable nickel-based high-temperature alloy according to claim 2, characterized in that: In the argon atomization method in step (2), the powder spraying pressure is 7-9 MPa and the temperature is 1540-1560°C.

6. The method for preparing a low crack sensitivity additively applicable nickel-based high-temperature alloy according to claim 2, characterized in that: The external morphology of the alloy powder in step (2) is nearly spherical, containing a small amount of satellite particles, and the particle size D50 of the alloy powder is 90-100 μm.

7. The method for preparing a low crack sensitivity additively applicable nickel-based high-temperature alloy according to claim 2, characterized in that: The laser metal deposition process parameters in step (3) are: power of 900-1600 W, scanning speed of 240-840 mm / min, filling spacing of 1.2-2.0 mm, layer thickness of 60-70 μm, and powder feeding speed of 6.8 g / min.

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