High-equiaxed-grain-ratio nickel-based high-temperature alloy for additive manufacturing

Abstract

The present invention provides a high-equiaxed-grain-ratio nickel-based high-temperature alloy for additive manufacturing. In view of the problem of cracking in a nickel-based high-temperature alloy for additive manufacturing, microalloying appropriate amounts of rare earths Hf and Y is proposed for the first time to regulate the microstructure of a printed alloy, thereby eliminating strong texture along a construction direction, inhibiting the growth of columnar grains, and directly obtaining a high-equiaxed-grain-ratio alloy, reducing the cracking sensitivity, eliminating cracks during additive manufacturing, and solving the problem of cracking during heat treatment. According to the present invention, a nickel-based high-temperature alloy having a high equiaxed grain ratio and no cracks can be prepared within a relatively wide printing parameter range. In addition, the high equiaxed grain ratio in the alloy prepared in the present invention has never been observed in nickel-based high-temperature alloys for additive manufacturing. The present invention has a rational composition design and a simple preparation process, the obtained product has excellent performance, and the additive manufacturing process has a large range of parameters, facilitating large-scale industrial production and practical application.

Description

A nickel-based high-temperature alloy with high equiaxed crystal ratio for additive manufacturing Technical Field

[0001] The present invention relates to a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing, belonging to the field of high-temperature alloys and additive manufacturing. Background Art

[0002] Nickel-based high-temperature alloys have excellent strength, damage tolerance and durability, and are the preferred structural materials for hot-end components in aerospace. However, this type of alloy is very prone to cracking during the additive manufacturing process. A lot of research has been carried out to address the cracking problem of nickel-based high-temperature alloys in additive manufacturing. Dang reduced the crack density of the additively manufactured IN738 alloy by increasing the substrate preheating temperature and reducing the temperature gradient, thereby improving the mechanical properties. However, the prepared IN738 alloy has a columnar crystal structure and cannot completely eliminate cracking. Cheng reduced the size of the cellular structure and grains by in-situ forming a second phase, effectively inhibiting the initiation and expansion of cracks.

[0003] Xu et al. investigated the effects of scanning strategies with 0°, 90°, and 67° interlayer rotation angles on microstructure and cracking behavior. Using a 67° interlayer rotation angle, they produced nearly crack-free, locally equiaxed Inconel 738 alloy samples. Wei et al. optimized process parameters such as laser power and scanning speed for SLM-fabricated René 104 nickel-based superalloy, improving the relative strength and mechanical properties of the formed parts. However, the alloy's microstructure was columnar, and crack defects could not be eliminated. Yang fabricated René 104 nickel-based superalloy using direct laser fabrication (DLF), which exhibited a columnar structure and formed pores and cracks. Hot isostatic pressing (HIP) eliminated cracks in the additively manufactured René 104 nickel-based superalloy. Chinese patent CN202010891059.X discloses a method for eliminating crack defects in SLM-formed nickel-based superalloys. By adding a ceramic second phase to the nickel-based superalloy, a dense, crack-free additively manufactured nickel-based superalloy can be obtained. This patent does not mention equiaxed crystals. Chinese patent CN202010891107.5 discloses a method for preventing cracking in selective laser-melted nickel-based superalloys. By reducing the low-melting-point phase-forming elements Zr and B in the nickel-based superalloy and adjusting the total Al and Ti content in the alloy to ≤4.5wt%, a component with high relative density, no crack defects, and excellent mechanical properties was produced. This patent also does not mention equiaxed crystals. Yu et al. suppressed solidification cracking of IN738LC alloy during the SLM process by adjusting the Hf content, refining the grain size, and increasing the proportion of equiaxed crystals. Chinese patent CN202010891045.8 discloses a method for eliminating cracks in 3D-printed nickel-based superalloys. Addressing the problem of cracking in 3D-printed γ′-precipitation-strengthened nickel-based superalloys, the method proposes using rare earth microalloying to reduce the crack sensitivity of 3D-printed γ′-precipitation-strengthened nickel-based superalloys, broaden the 3D printing process window, inhibit the occurrence of 3D-printed cracks, significantly improve the strength and ductility of formed parts, and effectively prevent cracking during subsequent processing, such as storage cracking between process steps and subsequent heat treatment cracking. The resulting γ′-precipitation-strengthened nickel-based superalloy, René 104, exhibits no cracking, a relative density exceeding 99.4%, a yield strength and tensile strength of 935 MPa and 1256 MPa, respectively, and an elongation exceeding 14.0%. The patent also does not address equiaxed grains. Technical issues

[0004] The above studies have not considered the important influence of grain morphology on the mechanical properties of additively manufactured alloys, especially cracking sensitivity, and cannot fundamentally solve the problem of cracking in additively manufactured nickel-based high-temperature alloys.

[0005] Therefore, the present invention proposes for the first time the idea of ​​designing the composition of nickel-based high-temperature alloys modified with trace Hf and Y elements. By modifying and regulating the alloy microstructure with trace Hf and Y elements, the additive manufacturing forming performance of the alloy is improved. For the first time, a nickel-based high-temperature alloy with a very high proportion of equiaxed crystal structure is obtained in the additive manufacturing process, which solves the problem of printing cracking, greatly broadens the forming process window, and designs a nickel-based high-temperature alloy with a high proportion of equiaxed crystals that is completely suitable for additive manufacturing. Technical Solutions

[0006] To address these issues, the present invention builds upon the inventors' team's previous research (Chinese Patent CN202010891045.8). This invention proposes, for the first time, a compositional design strategy for a nickel-based superalloy for additive manufacturing that directly achieves a high equiaxed crystal fraction. By microalloying with an appropriate amount of rare earth Y in combination with Hf, the as-printed alloy microstructure is manipulated, eliminating strong texture along the build direction and suppressing columnar crystal growth. This results in an alloy with a high equiaxed crystal fraction, reducing crack susceptibility and eliminating additive manufacturing cracking. This invention enables the production of crack-free nickel-based superalloys with a high equiaxed crystal fraction over a wide range of printing parameters. Furthermore, the high equiaxed crystal fraction observed in the alloys produced by this invention has never been observed in previously reported additive manufacturing nickel-based superalloys.

[0007] The present invention discloses a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The nickel-based high-temperature alloy is a printed product obtained by additive manufacturing using rare earth micro-alloyed nickel-based high-temperature alloy powder as raw material. The alloy has a high equiaxed crystal ratio and is free of additive manufacturing cracks.

[0008] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The nickel-based high-temperature alloy powder comprises the following components in percentage by mass:

[0009] Co: 14-23%; Cr: 11-15%; Al: 2-5%; Ti: 3-6%; Mo: 2.7-5%; W: 0.5-3%; Ta: 0.5-4%; Nb: 0.25-3%; Zr: 0.02-0.06%; B: 0.01-0.05%; C: 0.0015-0.1%;

[0010] Rare earth RE: 0.05-0.50%, preferably 0.05-0.18%, more preferably 0.05-0.13%; the balance is Ni;

[0011] Alternatively, other nickel-based high-temperature alloys are used as the matrix, and 0.05-0.50 wt. %, preferably 0.05-0.18 wt. %, and more preferably 0.05-0.13 wt. % of RE is added to the matrix;

[0012] The RE includes Hf and Y.

[0013] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The other base nickel-based high-temperature alloy is selected from the nickel-based high-temperature alloys currently reported for additive manufacturing, especially nickel-based high-temperature alloys that are sensitive to cracking during additive manufacturing, preferably one of Inconel 625, Inconel 718, Inconel 939, Haynes 188, GH3230, GH3536, GH4169, René 104, IN738LC, CM247LC, CMSX-4, and Hastelloy X, preferably René 104, in which RE is used to replace part of the Ni.

[0014] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing, wherein the rare earth RE is composed of Hf and Y; or the rare earth RE is composed of at least one selected from Sc, La, and Ce and Hf and Y, preferably consisting of Hf and Y in a mass ratio of 1:1;

[0015] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The nickel-based high-temperature alloy powder is prepared by a gas atomization method. The gas should be helium, argon, or a mixture of argon and helium, wherein the oxygen content is less than 0.0001 wt.%.

[0016] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The particle size range of the nickel-based high-temperature alloy powder is controlled to be 10-70 μm, preferably 10-53 μm.

[0017] The present invention discloses a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The additive manufacturing technology is selected from one of laser powder bed melting, electron beam melting or coaxial powder feeding laser forming technology, and laser powder bed melting is preferred.

[0018] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The nickel-based high-temperature alloy has an equiaxed crystal ratio of more than 90%, an average grain size of less than 50 μm, an average grain aspect ratio of less than 2.2, and no additive manufacturing cracks.

[0019] The present invention discloses a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The nickel-based high-temperature alloy has a yield strength of 820-1019 MPa, a tensile strength of 1121-1235 MPa, and an elongation of 20.3-29.6%.

[0020] The present invention provides a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing, wherein the powder used for printing comprises the following components by mass percentage:

[0021] Co 20.6%; Cr 13%; Al 3.4%; Ti 3.9%; Mo 3.8%; W 2.1%; Ta 2.4%; Nb 0.9%; Zr 0.05%; B 0.03%; C 0.05%; RE 0.13wt.%, rare earth elements consisting of Hf and Y in a mass ratio of 1:1; the balance is Ni; the particle size of the powder used for printing is 15-53 μm;

[0022] Use the following printing parameters:

[0023] Laser power: 230-330 W, scanning rate: 500-1000 mm / s, overlap spacing: 90 μm, powder layer thickness: 40 μm, interlayer angle: 67°; none of the obtained series of products experienced additive manufacturing cracking.

[0024] The René104HfY alloy, obtained at a laser input power of 320 W and a scanning speed of 800 mm / s, achieved a relative density of 99.7%, room-temperature yield strength and tensile strength of 823 MPa and 1158 MPa, respectively, with an elongation of 24.6%. The alloy contained over 90% equiaxed grains, with an average grain size of 40-46 μm and an average grain aspect ratio of 1.4-1.6.

[0025] After optimization, the as-printed René104HfY alloy was kept at 1170°C for 2 hours and air-cooled to room temperature to obtain the high-temperature treated René104HfY nickel-based high-temperature alloy. No heat treatment cracking occurred, and its room-temperature yield strength and tensile strength were 1089 MPa and 1398 MPa, respectively, with an elongation of 12.4%.

[0026] After optimization, the as-printed René104HfY alloy was kept at 815°C for 8 hours and air-cooled to room temperature to obtain the high-temperature treated René104HfY nickel-based high-temperature alloy. No heat treatment cracking occurred, and its room-temperature yield strength and tensile strength were 1221 MPa and 1374 MPa, respectively, with an elongation of 4.9%. Beneficial effects

[0027] This invention proposes for the first time a design concept for a nickel-based high-temperature alloy composition for additive manufacturing that can directly obtain a near-equiaxed crystal structure. Rare earth microalloying hinders the growth of grains in the alloy matrix along the outer edge of the construction direction, further refines the grains, and inhibits the formation of columnar crystals, thereby obtaining a near-equiaxed crystal structure, greatly reducing cracking sensitivity, and inhibiting cracking during the additive manufacturing process, thereby achieving a significant increase in alloy strength and plasticity. Using the nickel-based high-temperature alloy composition proposed in this invention as a printing raw material, formed parts without additive manufacturing cracks can be obtained within a large parameter range, and no cracking will occur after long-term storage and direct high-temperature solution treatment.

[0028] (1) This invention proposes for the first time a design concept for the composition of a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. A nickel-based high-temperature alloy with an equiaxed crystal ratio of more than 90%, an average grain size of less than 50 μm, and an average grain aspect ratio of less than 2.2 is prepared using additive manufacturing technology, completely eliminating additive manufacturing cracks.

[0029] (2) This invention proposes for the first time a design concept for the composition of nickel-based high-temperature alloys with a high equiaxed crystal ratio for additive manufacturing. By using rare earth microalloying, the growth of grains in the alloy matrix along the outer edge of the construction direction is hindered, the grains are further refined, and the formation of columnar crystals is suppressed, thereby obtaining a near-equiaxed crystal structure, optimizing the printing formability, reducing internal stress concentration, and significantly reducing the additive manufacturing cracking sensitivity of the alloy.

[0030] (3) The present invention proposes for the first time a design concept for the composition of nickel-based high-temperature alloys with a high equiaxed crystal ratio for additive manufacturing. It can be used in multiple alloy systems and adopt multiple additive manufacturing technologies to obtain crack-free nickel-based high-temperature alloys with a high equiaxed crystal ratio within a large parameter range.

[0031] (4) The present invention proposes for the first time a design concept for the composition of a nickel-based high-temperature alloy with a high equiaxed crystal ratio for additive manufacturing. The prepared alloy has stable properties and does not crack after long-term storage. It can also be directly subjected to high-temperature heat treatment without the need for low-temperature annealing for stress relief.

[0032] In summary, the present invention proposes for the first time a design concept for the composition of nickel-based high-temperature alloys for additive manufacturing that can directly obtain near-equiaxed crystal structures. Rare earth microalloying hinders the growth of the outer edges of the grains in the alloy matrix along the direction of construction, further refines the grains, and inhibits the formation of columnar crystals, thereby obtaining an alloy with a high equiaxed crystal ratio, inhibiting additive manufacturing cracking, completely eliminating additive manufacturing cracks, and solving the problem of heat treatment cracking. Using the nickel-based high-temperature alloy composition proposed in the present invention as a printing raw material, in multiple alloy systems, using a variety of additive manufacturing technologies, crack-free formed parts with a high equiaxed crystal ratio can be obtained within a large parameter range, and have excellent strength and plasticity. The prepared alloy has stable properties and does not crack after long-term storage. It can also be directly subjected to high-temperature heat treatment without the need for low-temperature annealing stress relief treatment. The present invention provides a new composition design concept for the development of high-performance crack-free nickel-based high-temperature alloys for additive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a metallographic image of René 104HfY alloy prepared by laser powder bed fusion in Example 1.

[0034] FIG2 is the EBSD result of René104HfY alloy prepared with the optimal process parameters in Example 1, (a) XY plane and (b) XZ plane.

[0035] FIG3 is a metallographic image of the solution heat treated René104HfY alloy of Example 2.

[0036] FIG4 is a metallographic image of the René104HfY alloy subjected to aging heat treatment in Example 3.

[0037] FIG5 is a metallographic image of the René104HfY alloy subjected to solution treatment and aging heat treatment in Example 4.

[0038] FIG6 is a metallographic image of René104HfY alloy prepared using non-optimal process parameters in Comparative Example 1.

[0039] FIG7 is a metallographic image of the René104HfY alloy subjected to solution heat treatment in comparative example 2.

[0040] FIG8 is a metallographic image of the comparative example three-aging heat treatment René104HfY alloy. Modes for Carrying Out the Invention

[0041] Example 1:

[0042] René 104 nickel-based high-temperature alloy was selected as the alloy matrix, and Hf and Y microalloyed René 104HfY alloy powder was prepared by argon atomization method. The specific composition is as follows (wt.%):

[0043] Co 20.6%; Cr 13%; Al 3.4%; Ti 3.9%; Mo 3.8%; W 2.1%; Ta 2.4%; Nb 0.9%; Zr 0.05%; B 0.03%; C 0.05%; RE 0.13wt.% (rare earth elements are Hf and Y in a mass ratio of 1:1); the balance is Ni. The alloy powder obtained by vibration screening for laser powder bed fusion forming has a particle size of 15-53 μm.

[0044] First, René 104HfY alloy powder was dried in a vacuum oven at 100°C for 4 hours. The dried powder was then loaded into a powder supply cylinder for spreading. The printing substrate was preheated to 170°C, and nitrogen was introduced into the working chamber until the oxygen content was below 0.0001 wt%. Printing parameters were then set within the following ranges: laser power: 230-330 W, scan rate: 500-1000 mm / s, overlap spacing: 90 μm, powder layer thickness: 40 μm, and interlayer rotation angle: 67°. Metallographic images of a batch of as-printed René 104HfY alloy are shown in Figure 1. The results in Figure 1 demonstrate that cracking of the René 104HfY alloy was avoided over a wide range of parameters when formed using laser powder bed fusion.

[0045] The René 104HfY alloy, obtained at a laser input power of 320 W and a scanning speed of 800 mm / s, exhibited minimal defects and a maximum relative density of 99.7%. Its room-temperature yield strength and tensile strength were 823 MPa and 1158 MPa, respectively, and its elongation was 24.6%. Further EBSD analysis of the XZ and XY planes is shown in Figure 2. The results indicate that the alloy contains over 90% equiaxed grains, with an average grain size of 45.3 μm and an average grain aspect ratio of 1.5. This finding is new to this research and has not been observed in other reported nickel-based superalloys produced by additive manufacturing.

[0046] Example 2:

[0047] The optimal printed René 104HfY alloy sample obtained in Example 1 was solution-heat treated. The printed product was held at 1170°C for 2 hours and then air-cooled to room temperature. This resulted in a high-temperature solution-treated René 104HfY nickel-based superalloy, which exhibited no heat-treatment cracking. Its room-temperature yield strength and tensile strength were 1089 MPa and 1398 MPa, respectively, and its elongation was 12.4%. The metallographic image of the high-temperature solution-treated René 104HfY alloy, shown in Figure 3, shows no cracks.

[0048] Example 3:

[0049] The optimal printed René 104HfY alloy sample obtained in Example 1 was subjected to aging heat treatment. The as-printed product was held at 815°C for 8 hours and then air-cooled to room temperature. The resulting high-temperature-treated René 104HfY nickel-based superalloy exhibited no heat-treatment cracking. Its room-temperature yield strength and tensile strength were 1221 MPa and 1374 MPa, respectively. The metallographic image of the heat-treated René 104HfY alloy shows no cracks, as shown in Figure 4.

[0050] Example 4:

[0051] The optimal printed sample, René 104HfY alloy, obtained in Example 1, was subjected to solution and aging heat treatment. The printed product was held at 1200°C for 2 hours, air-cooled to room temperature, then held at 815°C for 8 hours, and air-cooled to room temperature. The resulting heat-treated René 104HfY nickel-based superalloy showed no heat-treatment cracking. Its room-temperature yield strength and tensile strength were 1230 MPa and 1470 MPa, respectively, and its elongation was 10.8%. The metallographic image of the René 104HfY alloy after heat treatment is shown in Figure 5, showing no cracks.

[0052] Comparative Example 1:

[0053] Using René 104HfY alloy powder as the raw material, printing was performed according to the protocol described in Example 1. The printing parameters were: laser power: 350 W, scan rate: 500 mm / s, overlap spacing: 90 μm, powder layer thickness: 40 μm, and interlayer rotation angle: 67°. The resulting René 104HfY alloy exhibited the highest number of porosity defects and the lowest relative density, at 97%. Its room-temperature yield strength and tensile strength were 785 MPa and 1095 MPa, respectively, and its elongation was 18.6%. The metallographic image, shown in Figure 6, shows that the pores are primarily located at the bottom of the molten pool.

[0054] Comparative Example 2:

[0055] The printed René104HfY alloy sample obtained in Comparative Example 1 was solution heat treated. The printed product was held at 1170°C for 2 hours and then air-cooled to room temperature to produce a high-temperature solution-treated René104HfY nickel-based superalloy. Heat-treatment cracking occurred in the sample. Its room-temperature yield strength and tensile strength were 989 MPa and 1175 MPa, respectively, and its elongation was 6.4%. The metallographic image of the high-temperature solution-treated René104HfY alloy, showing heat-treatment cracking, is shown in Figure 7.

[0056] Comparative Example 3:

[0057] The printed René104HfY alloy sample obtained in Comparative Example 1 was subjected to aging heat treatment. The printed product was held at 815°C for 8 hours and then air-cooled to room temperature. This high-temperature treated René104HfY nickel-based superalloy exhibited heat treatment cracking, with room-temperature yield strength and tensile strength of 1186 MPa and 1314 MPa, respectively. The metallographic image of the René104HfY alloy after heat treatment is shown in Figure 8, showing the presence of heat treatment cracks.

Claims

1. A nickel-based superalloy with a high proportion of columnar grains for additive manufacturing, characterized in that: The nickel-based superalloy is a as-built product obtained by additive manufacturing using nickel-based superalloy powder as raw material. The alloy has a high equiaxed crystal proportion and no additive manufacturing cracks. The nickel-based superalloy powder, by mass percentage, comprises the following components: Co: 14-23%; Cr: 11-15%; Al: 2-5%; Ti: 3-6%; Mo: 2.7-5%; W：0.5-3%； Ta: 0.5-4%; Nb ：0.25-3%； Zr：0.02-0.06%； B：0.01-0.05%； C：0.0015-0.1%； Rare earth RE: 0.05-0.50 %; the balance is Ni; Or taking other nickel-based superalloys as the matrix, especially nickel-based superalloys sensitive to additive manufacturing cracking, adding 0.05-0.5 wt. % of RE to the matrix; The RE comprises Hf and Y.

2. The high columnar crystal proportion nickel-based superalloy for additive manufacturing according to claim 1, characterized in that: The other matrix nickel-based superalloys are selected from one of Inconel 625, Inconel 718, Inconel 939, Haynes 188, GH3230, GH3536, GH4169, René 104, IN738LC, CM247LC, CMSX-4, Hastelloy X, preferably René 104, and using RE to replace part of the Ni therein.

3. The high columnar crystal proportion nickel-based superalloy for additive manufacturing according to claim 1, wherein: RE is composed of Hf and Y; or rare earth RE is composed of at least one of Sc, La, Ce and Hf and Y, preferably composed of Hf and Y in a mass ratio of 1:

1.

4. The high columnar crystal proportion nickel-based superalloy for additive manufacturing according to claim 1, wherein: The nickel-based superalloy powder is prepared by gas atomization method. The gas should be helium, argon, or a mixed gas of argon and helium, and the oxygen content is less than 0.0001 wt. %.

5. An equiaxed crystal-dominated nickel-based superalloy for additive manufacturing according to claim 1, characterized in that: The particle size range of the nickel-based superalloy powder is controlled at 10-70 μm, preferably 10-53 μm.

6. The high columnar crystal proportion nickel-based superalloy for additive manufacturing according to claim 1, wherein: The additive manufacturing technology is selected from one of laser powder bed fusion, electron beam melting or coaxial powder feeding laser forming technology, preferably laser powder bed fusion.

7. The high columnar crystal proportion nickel-based superalloy for additive manufacturing according to claim 1, characterized in that: In the nickel-based superalloy, the proportion of equiaxed crystals in the grains exceeds 90%, the average grain size is less than 50 μm, the average grain aspect ratio is 1.4-2.2, and the nickel-based superalloy has no additive manufacturing cracks.

8. An equiaxed crystal-dominated nickel-based superalloy for additive manufacturing according to claim 1, characterized in that: The yield strength of the nickel-based superalloy is 820-1019 MPa, the tensile strength is 1121-1235 MPa, and the elongation is 20.3-29.6%.

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