Nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing and preparation method

Abstract

The invention provides a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing and a preparation method, and belongs to the technical field of nickel-based high-temperature alloys for additive manufacturing, the nickel-based high-temperature alloy for additive manufacturing is prepared from the following chemical components in percentage by weight: 5.5 to 6.0 weight percent of Al, 14.0 to 14.4 weight percent of Co, 7.0 to 7.5 weight percent of Cr, 0.01 to 0.05 weight percent of Mo, 0.4 to 1.0 weight percent of Ta, 0.01 to 0.03 weight percent of Ti, 2.1 to 2.5 weight percent of W, 0.1 to 0.3 weight percent of C, 0.01 to 0.03 weight percent of B, 2.0 to 2.5 weight percent of Nb and the balance of Ni. The nickel-based high-temperature alloy suitable for additive manufacturing, which has excellent high-temperature oxidation resistance, no crack defect and low hole defect, is prepared, that is, the crack-free alloy is prepared under the additive metallurgy condition, and meanwhile, the defects such as low-level holes are contained; and on the basis, the additive manufacturing nickel-based high-temperature alloy has excellent high-temperature oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of nickel-based high-temperature alloys for additive manufacturing, and in particular to a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing 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 use environment of nickel-based high-temperature alloys, the geometric morphology of parts made of nickel-based alloys is also more complex. Additive manufacturing technology provides new ideas for processing components with complex spatial geometries. However, additive manufacturing of nickel-based alloys has the problem of high crack sensitivity, and it is difficult to effectively prepare crack-free samples with existing commercial nickel-based alloys. In addition, with the increase in engine operating temperature, high-temperature oxidation failure has become the most important failure form of nickel-based alloys in the service process. How to improve the high-temperature oxidation resistance of alloys has received widespread attention from scholars. In response to the above problems, the current main solution is to develop new nickel-based alloy compositions to achieve synergistic optimization of high-temperature oxidation resistance and additive printing performance.

[0003] Studies have shown that cracks in the additive manufacturing process can be roughly divided into two types: thermal cracks and aging cracks. Thermal cracks are mainly formed in the final solidification stage or remelting stage of the alloy, and the liquid phase cannot be compensated in time. Aging cracks occur in the pure solid phase stage. During the cooling process of the alloy, the matrix toughness decreases and the second phase precipitates rapidly, which causes severe stress concentration and cracks. For the thermal cracks and aging cracks that occur in the additive manufacturing process, the corresponding indicators are used for optimization. Thermal cracks occur in the solidification or remelting stage. Therefore, the temperature difference between the liquid phase and the solid phase is used to predict the sensitivity to thermal cracks. The larger the temperature difference, the larger the interval in which the liquid phase stays, and the greater the sensitivity to thermal cracks. Aging cracks occur during the cooling process due to the rapid precipitation of the second phase. Therefore, during the cooling process, the equilibrium volume fraction of the second phase is used to describe the speed of the second phase precipitation from the temperature when the second phase is 80% to the temperature of the solid phase. If the value is larger, the second phase precipitation rate is greater, the easier it is to cause stress concentration, and the greater the sensitivity to solid cracks.

[0004] In the existing technology, the development of nickel-based high-temperature alloys suitable for additive manufacturing mainly focuses on their printing performance. Through composition design, thermal crack sensitivity and solid crack sensitivity are synergistically optimized to design nickel-based high-temperature alloys with good printing performance. However, as the working temperature increases, high-temperature oxidation and the accompanying oxidation-assisted cracking and other damages seriously affect the high-temperature performance of nickel-based alloys. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention calculates the Gibbs free energy of aluminum oxide formation at the design temperature while taking into account its oxidation performance while optimizing thermal crack sensitivity and solid crack sensitivity in a coordinated manner. The present invention provides an additively applicable nickel-based high-temperature alloy with excellent high-temperature oxidation resistance and a preparation method, and aims to provide an additively manufactured nickel-based high-temperature alloy and a preparation method that does not have microcrack defects under wide-area additive processing conditions, has good printing performance, and has excellent high-temperature oxidation resistance.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing, comprising the following components and mass percentages: Al: 5.5-6.0wt%, Co: 14.0-14.4wt%, Cr: 7.0-7.5wt%, Mo: 0.01-0.05wt%, Ta: 0.4-1.0wt%, Ti: 0.01-0.03wt%, W: 2.1-2.5wt%, C: 0.1-0.3wt%, B: 0.01-0.03wt%, Nb: 2.0-2.5wt%, and the balance is Ni.

[0007] The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%.

[0008] The instantaneous tensile property of the nickel-based high-temperature alloy suitable for the additive material is, at room temperature, the tensile strength σ of the nickel-based high-temperature alloy suitable for the additive material is b ≥1200MPa, elongation A≥10%.

[0009] The high-temperature oxidation resistance of the nickel-based high-temperature alloy suitable for the additive is that, in an air atmosphere, the holding temperature is 1000°C, the holding time is 24 hours, and the weight gain per unit area is not more than 0.60 mg·cm -2 ; A continuous and complete oxide layer is formed without obvious peeling, and the inner layer is a continuous Al2O3 layer, which has a good protective effect at high temperatures.

[0010] A method for preparing a nickel-based high-temperature alloy suitable for high-temperature oxidation-resistant additive materials comprises the following steps: Step (1): weighing Al, Co, Cr, Mo, Ta, Ti, W, C, B, Nb, and Ni with a purity of 99.9 wt% according to a proportion, performing vacuum induction melting and casting, and then grinding and sand blowing treatment to obtain a master alloy; Step (2): preparing alloy powder by using argon atomization method on the master alloy; Step (3): Printing the alloy powder into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process.

[0011] Furthermore, the vacuum induction melting temperature in step (1) is 1550-1600°C for 5-8 min; the casting temperature is 1450-1500°C; and the master alloy has an impurity element content of less than 5 ppm.

[0012] Furthermore, in the argon atomization method in step (2), the powder spraying pressure is 7-9 MPa and the temperature is 1540-1560°C.

[0013] Furthermore, the external morphology of the alloy powder in step (2) is nearly spherical, contains a small amount of satellite particles, and the particle size D50 of the alloy powder is 85-95 μm.

[0014] Furthermore, the laser metal deposition process parameters in step (3) are: power of 1000-1500 W, scanning speed of 480-840 mm / min, filling spacing of 1.2-2.0 mm, layer thickness of 600-700 μm, and powder feeding speed of 6.8 g / min.

[0015] 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: 1. The present invention provides an additively manufactured nickel-based high-temperature alloy, which controls the volume fraction of the γ' phase (30%-50%) by using a higher Al content and an appropriate Ta content and Ti content to ensure high-temperature performance while strengthening the γ phase and the γ' phase, and effectively inhibiting the formation of the low-melting-point eutectic phase of the γ / γ' phase. In addition, a higher content of Co, Cr, an appropriate content of W, and a small amount of Mo and other solid solution strengthening elements are added to strengthen the intrinsic strength of the matrix and a trace amount of grain boundary elements C and B to strengthen the grain boundaries. On this basis, an appropriate content of Nb is added to generate a certain level of carbide content to inhibit the segregation of B elements at the grain boundaries, thereby avoiding the formation of liquid cracks and solidification cracks caused by the segregation of B elements. The precipitation behavior of the γ' phase is changed by composition regulation to avoid the formation of solid-state aging cracks: that is, during the cooling process of the alloy, the precipitation of the γ' phase is made as slow as possible, while maintaining a high γ' phase content at 900°C. At the same time, the alloy elements have the effects of precipitation strengthening, solid solution strengthening, and grain boundary strengthening, which improves the medium and high temperature mechanical properties of the alloy, maintains the high temperature structure stability, and makes the alloy reach the level of high-performance additive manufacturing high-temperature alloy;

[0016] 2. For the alloy of the present invention, on the one hand, in the alloy design stage, under the premise of synergistically optimizing the thermal crack sensitivity and solid crack sensitivity, in order to improve its oxidation resistance, the Gibbs free energy and effective valence of Al2O3 formation at 900°C are calculated, and the formation of a continuous Al2O3 layer is predicted by optimizing the alloy composition, and finally the optimal composition for forming a continuous Al2O3 layer is determined. On the other hand, Ta element is a precious metal. Replacing part of Ta with Al can save costs, ensure the formation efficiency of the γ' phase, reduce the precipitation rate of the γ' phase, and reduce the solid crack sensitivity; at the same time, it ensures that a continuous and dense Al2O3 protective layer can be stably formed at high temperatures, effectively preventing further intrusion of O and outward diffusion of matrix alloy elements, so that it has good high-temperature oxidation resistance;

[0017] 3. The microstructure of the additively manufactured nickel-based superalloy of the present invention exhibits columnar crystals growing along the construction direction; no cracks are formed. The nickel-based superalloy of the present invention has excellent mechanical properties in the laser metal deposition printing state without subsequent heat treatment;

[0018] 4. The additively manufactured nickel-based high-temperature alloy of the present invention, in an air atmosphere, has a holding temperature of 1000°C, a holding time of 24 hours, and a unit area weight gain of no more than 0.6 mg·cm -2 After oxidation, a dense protective oxide layer is formed on the surface without peeling, which has a good protective effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The defect area fraction distribution and metallographic structure pictures of the cubic column sample of Example 1 of the present invention under different process parameters; Figure 2 Scanning microstructure diagrams of different magnifications of the rectangular column sample of Example 1 of the present invention; Figure 3 The room temperature tensile curve and fracture scanning microstructure diagram of the rectangular column sample of Example 1 of the present invention; Figure 4 Thermogravimetric curve and cross-sectional oxide scale element distribution diagram of the cubic column sample of Example 1 of the present invention in air atmosphere at a holding temperature of 1000° C. for 24 hours; Figure 5 This is a microscopic result of scanning the surface oxide scale of a cubic column sample of Example 1 of the present invention in an air atmosphere at a holding temperature of 1000° C. for 24 hours; Figure 6 This is the result of slight incident XRD and cross-sectional morphology and EDS line scanning result of the surface oxide scale of the cubic column sample of Example 1 of the present invention in an air atmosphere with a holding temperature of 1000° C. and a holding time of 24 hours. DETAILED DESCRIPTION

[0020] In order to further explain 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 are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0021] The main purpose of the present invention is to provide and prepare a nickel-based high-temperature alloy suitable for additive manufacturing that has excellent high-temperature oxidation resistance, no crack defects and low hole defects, that is, to prepare a crack-free alloy under additive metallurgical conditions, while containing low-level defects such as holes, so that the additive-manufactured nickel-based high-temperature alloy has excellent high-temperature oxidation resistance. It solves the technical problems of poor formability, difficult to control defects, and difficulty in taking into account oxidation resistance in existing additive-manufactured high-temperature alloys.

[0022] The technical solution of the present invention is as follows: A nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing, wherein the chemical composition of the nickel-based high-temperature alloy for additive manufacturing is as follows, in weight percentage: Al 5.5-6.0wt%, Co 14.0-14.4wt%, Cr 7.0-7.5wt%, Mo 0.01-0.05wt%, Ta 0.4-1.0wt%, Ti 0.01-0.03wt%, W 2.1-2.5wt%, C 0.1-0.3wt%, B 0.01-0.03wt%, Nb 2.0-2.5wt%, and the balance is Ni.

[0023] The design of the chemical composition of the above-mentioned additively manufactured nickel-based high-temperature alloy is explained as follows: (1) In the prior art, the γ' phase content 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 a high content of γ' phase leads to severe stress concentration, resulting in the alloy having high aging crack sensitivity.

[0024] (2) In the existing technology, the development of nickel-based high-temperature alloys suitable for additive manufacturing mainly focuses on their printing performance, but fails to take into account their high-temperature oxidation resistance. Therefore, this design synergistically optimizes the thermal crack sensitivity and solid crack sensitivity, while ensuring that it has good printing performance; fully considers the high-temperature oxidation behavior of nickel-based high-temperature alloys, calculates the Gibbs free energy of alumina formation at the design temperature through composition design, so that it spontaneously forms a continuous alumina protective layer at high temperature. The continuous alumina protective layer has a high melting point and thermal stability, which improves its high-temperature oxidation resistance.

[0025] The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%; The instantaneous tensile property of the nickel-based high-temperature alloy suitable for the additive material is, at room temperature, the tensile strength σ of the nickel-based high-temperature alloy suitable for the additive material is b ≥1200MPa, elongation A≥10%.

[0026] The high-temperature oxidation resistance of the nickel-based high-temperature alloy suitable for the additive is that, in an air atmosphere, at 1000°C, for 24 hours, the weight gain per unit area is not more than 0.6 mg·cm -2 ; A continuous and complete oxide layer is formed without obvious peeling, and the inner layer is a continuous Al2O3 layer, which has a good protective effect at high temperatures.

[0027] A method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing comprises the following steps: Step 1: Prepare nickel-based high-temperature alloy powder based on vacuum induction melting and argon atomization method.

[0028] Step 2: Print the alloy powder into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process (i.e., laser metal deposition printed state). The laser metal deposition process parameters are: power of 1000-1500 W, scanning speed of 480-840 mm / min, filling spacing of 1.2-2.0 mm, layer thickness of 600-700 μm, powder feeding speed of 6.8 g / min, and print out cubic column samples and rectangular column samples.

[0029] It should be noted here that: in the above process, since the chemical composition of the alloy of the present invention contains refractory elements such as W, Ta, Mo, etc., when the laser energy density (power, scanning speed, powder feeding speed, laser diameter) of the laser metal deposition process is set to a larger value, an alloy with fewer defects and better performance can be obtained.

[0030] 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.

[0031] The present invention is further described below by means of specific examples.

[0032] Example 1

[0033] In this embodiment, a crack-free additively manufactured nickel-based high-temperature alloy is prepared, and its chemical composition is as follows: Al 5.83wt%, Co 14.1wt%, Cr 7.28wt%, Mo 0.03wt%, Ta 0.66wt%, Ti 0.01wt%, W 2.25wt%, C 0.21wt%, B0.02wt%, Nb 2.1wt%, and the balance is Ni.

[0034] The specific preparation steps are as follows: Nickel-based high-temperature alloy powder was prepared based on vacuum induction melting and argon atomization, where the vacuum induction melting temperature was 1580°C, the time was 7 min, the casting temperature was 1480°C, the argon atomization pressure was 9 MPa, and the temperature was 1550°C. The external morphology of the powder is nearly spherical with only a small number of satellite particles, and the D10, D50 and D90 of the powder are distributed around 46μm, 98μm and 171μm, respectively.

[0035] The alloy powder is printed into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process (ie, a laser metal deposition printed state). The laser metal deposition process parameters are as follows: power of 1000-1500W, scanning speed of 480-840mm / min, filling spacing of 1.2-2.0mm, layer thickness of 600μm, powder feeding speed of 6.8g / min, and 24 cube samples with a length, width and height of 10mm×10mm×10mm were printed; among them, the sample with the best printing performance among the 24 samples was selected for 16mm×16mm×60mm large-block printing, and the laser metal deposition process parameters are as follows: power of 1500W, scanning speed of 480mm / min, filling spacing of 1.55mm, layer thickness of 700μm, powder feeding speed of 6.8g / min, and rectangular column samples with a length, width and height of 16mm×16mm×60mm and cubic column samples with a length, width and height of 10mm×10mm×10mm were printed.

[0036] The rectangular column sample prepared in this embodiment has a yield strength of 681 MPa, an ultimate tensile strength of about 1238 MPa, and a total elongation of about 10.4% at room temperature.

[0037] The cubic column sample prepared in this example was subjected to 1000℃-24h-air oxidation, and the weight gain per unit area was: 0.59mg·cm -2 ; from Figure 1 It can be seen that the cube sample prepared in Example 1 has the following characteristics: no cracks are detected under different laser powers and scanning speeds, only a small amount of holes exist, and the total hole area fraction is much lower than 0.25%, which has a fairly wide laser processing window. Figure 1 It can be seen that even for the sample with the highest defect, the defect area fraction is only 0.39%, while when the laser volume energy density is 135 J / mm 3 When the defect area fraction is kept at 0.05%, which is much better than IN718 and comparable to IN625, a nearly defect-free bulk sample can be obtained with excellent printability.

[0038] from Figure 2Scanning microstructures at different magnifications show that the interdendritic region of the rectangular columnar sample prepared in Example 1 contains high-density and uniformly distributed (Nb, Ta) C carbides, and only a small amount of pores exist in the interdendritic region near the carbides.

[0039] from Figure 3 The room temperature tensile curve and the fracture scanning microstructure diagram show that the yield strength is 681Mpa, the ultimate tensile strength is about 1238Mpa, and the total elongation is about 10.4%. The test sample shows a typical ductile fracture morphology, which is characterized by a cone with plastic fracture characteristics. The central fiber area contains many deep pits and agglomerated micropores without any brittle fracture characteristics such as cleavage or intergranular fracture. The shear band shows tearing ridges, indicating necking during the tensile test. Carbides can be consistently observed on the fracture surface and crack path, which means that the crack mainly starts in the ID area along the carbide / matrix interface. The crack then propagates in the sample, leading to failure.

[0040] from Figure 4 After oxidation, the thermogravimetric curve and the distribution diagram of the oxide scale elements of the cubic column sample of Example 1 of the present invention show that after 1000℃-24h-air oxidation, the weight gain per unit area is: 0.59mg·cm -2 ; From the cross section, it can be seen that an oxide layer is formed with an outer layer rich in Cr and Co and an inner layer rich in Al. The inner Al2O3 layer is continuous, providing good high-temperature oxidation resistance.

[0041] from Figure 5 After oxidation of the cubic column sample of Example 1 of the present invention, it can be seen from the scanning microscopic result of the surface oxide scale that the oxide layer is continuous and complete without peeling. It can be seen from the figure that the polygonal grains with clear edges and corners show the typical morphology of aluminum-containing spinel; and the morphology of flocculated particles. In summary, the outer scales are mainly rich in Al, with slight enrichment of Ni, Cr and Co, and there is no significant difference in the chemical composition of the spinel phase and the flocculated phase.

[0042] from Figure 6 After oxidation of the cubic column sample of Example 1 of the present invention, the surface oxide scale slightly incident XRD results and cross-sectional morphology and EDS line scanning results show that the peaks of Al2O3, Cr2O3, CoAl2O4, Co3O4 and NiO are clearly detected; from the cross-sectional line scanning results, it can be seen that Al and Co enriched co-aggregates are detected in the outer layer, which are mainly identified as Co- and Al-rich spinels, the Cr-rich layer is mainly Cr2O3, and the Al-rich layer is mainly Al2O3. The complete and stable Al2O3 layer can effectively prevent oxygen from diffusing into the matrix, ensuring its good high-temperature antioxidant performance.

[0043] In summary, the present invention prepares a nickel-based high-temperature alloy suitable for additive manufacturing that has excellent high-temperature oxidation resistance, no crack defects, and low pore defects; that is, a crack-free alloy is prepared under additive metallurgical conditions, and at the same time contains low levels of defects such as pores, and on this basis, it also has excellent high-temperature oxidation resistance. A new design idea for nickel-based high-temperature alloys suitable for additive manufacturing is provided. On the basis of optimizing crack sensitivity to ensure its printing performance; further considering its oxidation performance, the Gibbs free energy required to form continuous aluminum oxide at the design temperature is calculated, so that a continuous aluminum oxide protective layer is formed at high temperature, thereby improving its high-temperature oxidation resistance. This solves the problem that it is difficult to take into account both good printing performance and excellent high-temperature oxidation resistance when designing nickel-based high-temperature alloys.

Claims

1. A nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing, characterized in that: The components and mass percentages are as follows: Al: 5.5-6.0wt%, Co: 14.0-14.4wt%, Cr: 7.0-7.5wt%, Mo: 0.01-0.05wt%, Ta: 0.4-1.0wt%, Ti: 0.01-0.03wt%, W: 2.1-2.5wt%, C: 0.1-0.3wt%, B: 0.01-0.03wt%, Nb: 2.0-2.5wt%, and the balance is Ni; The high-temperature oxidation resistance of the nickel-based high-temperature alloy suitable for the additive is that, in an air atmosphere, the holding temperature is 1000°C, the holding time is 24 hours, and the weight gain per unit area is not more than 0.60 mg·cm -2 A continuous and complete oxide layer is formed on the surface of the alloy, and the inner layer of the alloy is a continuous Al2O3 layer. The alloy has a good protective effect at high temperatures.

2. The nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 1, characterized in that: The volume fraction of the γ' phase in the nickel-based high-temperature alloy suitable for the additive is 30-40%.

3. The nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 1, characterized in that: The instantaneous tensile property of the nickel-based high-temperature alloy suitable for the additive material is, at room temperature, the tensile strength σ of the nickel-based high-temperature alloy suitable for the additive material is b ≥1200MPa, elongation A≥10%.

4. A method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to any one of claims 1 to 3, characterized in that: The steps include: Step (1): weighing Al, Co, Cr, Mo, Ta, Ti, W, C, B, Nb, and Ni with a purity of 99.9 wt% according to a proportion, performing vacuum induction melting and casting, and then grinding and sand blowing to obtain a master alloy; Step (2): preparing alloy powder by using argon atomization method on the master alloy; Step (3): Printing the alloy powder into an additively manufactured nickel-based high-temperature alloy based on a laser metal deposition process.

5. The method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 4, 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; and the master alloy is a master alloy with an impurity element content of less than 5 ppm.

6. The method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 4, 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.

7. The method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 4, 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 85-95 μm.

8. The method for preparing a nickel-based high-temperature alloy for high-temperature oxidation-resistant additive manufacturing according to claim 4, characterized in that: The laser metal deposition process parameters in step (3) are: power of 1000-1500 W, scanning speed of 480-840 mm / min, filling spacing of 1.2-2.0 mm, layer thickness of 600-700 μm, and powder feeding speed of 6.8 g / min.

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