A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method

Abstract

This invention relates to the field of additive manufacturing metal materials technology, specifically disclosing a low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method. This alloy optimizes the composition of traditional expansion alloys. Its key technology lies in the synergistic addition of trace amounts of rare earth elements lanthanum (La) and boron (B), while strictly limiting the content of copper (Cu), to suppress the formation of low-melting-point phases and reduce grain boundary oxide segregation, thereby significantly improving the alloy's resistance to thermal cracking during high-rate, high-energy-beam additive manufacturing. Compared with existing technologies, the alloy powder provided by this invention enables the additive manufacturing of high-density, low-defect, high-performance expansion alloy components.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing metal materials technology, and specifically discloses a low cracking tendency and low expansion coefficient iron-nickel-cobalt based alloy powder and its preparation method. Background Technology

[0002] Expansion alloys, especially iron-nickel-cobalt alloys represented by 4J32, are widely used in high-end manufacturing fields such as aerospace and precision instruments because they can achieve excellent thermal expansion matching with hard glass and ceramics within a specific temperature range. For example, in microwave components of spacecraft, packaging shells of lasers, and structural components of high-precision sensors, these alloys are key materials for achieving hermetically sealed connections and ensuring the long-term reliability of devices.

[0003] Traditionally, such components have relied primarily on casting and forging followed by complex machining, resulting in low material utilization, long production cycles, and difficulty in manufacturing lightweight parts with complex internal cavities, fine flow channels, or optimized topology. Additive manufacturing technology, especially direct energy deposition (DED), has provided a revolutionary approach for the rapid prototyping of large, complex, integrated expanded alloy components. However, applying expanded alloys to large-scale DED additive manufacturing presents significant challenges. The inherent high energy input, rapid melting and solidification, and cyclic thermal cycling characteristics of the DED process lead to extremely high residual stress within the formed part. Simultaneously, trace amounts of low-melting-point elements (such as Cu, S, and P) in the alloy tend to segregate at grain boundaries during rapid solidification, forming liquid films; and the interaction between the alloy and oxygen and nitrogen in the environment at high temperatures easily generates brittle oxides and nitrides at grain boundaries. These three factors combined significantly weaken grain boundary bonding, making the component highly susceptible to macroscopic thermal cracking under thermal stress, severely impairing its density, mechanical properties, and ultimately, its airtightness.

[0004] While existing technologies include research on optimizing alloy composition to improve hot working performance for traditional processes, there is a lack of expansion alloy composition design specifically for the high heat input and rapid solidification characteristics of DED (Deep Erosion Printing) processes. Conventional expansion alloy powders commonly exhibit high susceptibility to hot cracking, numerous defects in formed parts, and large performance fluctuations during the DED process, hindering the reliable application of this technology in critical aerospace and precision components. Therefore, there is an urgent need to develop a novel alloy powder that combines low expansion characteristics with excellent resistance to hot cracking in DED printing to meet the pressing demands of high-end manufacturing for integrated, high-performance forming of complex precision components. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention aims to solve the following technical problems: providing an iron-nickel-cobalt based expansion alloy powder specifically for additive manufacturing. By specifically designing its composition, it effectively suppresses the tendency of hot cracking caused by the segregation of low-melting-point elements and the formation of brittle phases at grain boundaries, thereby achieving the direct forming of high-density, low-defect, high-performance expansion alloy components, meeting the urgent needs of aerospace, precision instruments and other fields for integrated and highly reliable manufacturing of complex structural components.

[0006] The specific solution of the present invention is as follows:

[0007] This invention provides a low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method, mainly comprising the following steps:

[0008] 1. Alloy powder composition (by mass percentage)

[0009] Ni: 32.0%~33.0%; Co: 4.0%~4.5%; C: 0.02%~0.04%; Cu: ≤0.20%; La: 0.01%~0.015%; B: ≤0.003%; Mn: 0.2%~0.3%; S: ≤0.005%; P: ≤0.005%; O: ≤0.008%; N: ≤0.004%; balance is Fe and unavoidable impurities.

[0010] 2. Preparation method

[0011] The preparation of the alloy powder includes the following steps:

[0012] (1) Pre-alloying smelting: Smelting is carried out according to the above composition ratio. In order to ensure the accurate addition of trace elements La and B and reduce burn-off, they should be added 5 minutes before tapping out of the furnace in the later stage of smelting;

[0013] (2) Powder preparation process: Spherical alloy powder is prepared by inert gas atomization or rotating electrode atomization. If inert gas atomization is used, the atomizing medium is high-purity argon, the main nozzle pressure is 3-5 MPa, and the auxiliary pressure is 1-2 MPa; if rotating electrode atomization is used, the atomizing gas is high-purity argon and helium, the Ar / He ratio is 1:1, and the electrode rotation linear velocity is controlled within the range of 18000-25000 RPM.

[0014] (3) Additive manufacturing process: Laser direct energy deposition is used for additive manufacturing, with inert gas protection, power of 5000-7000 W, powder feeding of 2-2.5 kg / h, and scanning speed of 900-1100 mm / min.

[0015] The technical principles of this invention will now be introduced:

[0016] The core of this invention lies in improving the crack resistance and forming quality of iron-nickel-cobalt-based expansion alloys during high-rate, high-energy beam direct energy deposition processes through the synergistic design of specific components, fundamentally improving the metallurgical basis. Its technical principle is mainly reflected in the synergistic effects at the following three levels:

[0017] 1. Grain boundary purification and suppression of brittle phases

[0018] The addition of the rare earth element lanthanum (La) is one of the key technical means. La has extremely strong chemical reactivity, preferentially combining with harmful impurities such as oxygen (O) and sulfur (S) in the melt to form high-melting-point, stable spherical compounds such as La2O3 and La2O2S. This process achieves dual benefits: on the one hand, it significantly reduces the content of free oxygen and sulfur in the matrix, preventing them from segregating at grain boundaries to form low-melting-point eutectic films; on the other hand, the fine rare earth compounds generated can act as heterogeneous nucleation cores during solidification, refining grains and effectively pinning grain boundaries, inhibiting abnormal grain growth, thereby reducing the tendency for grain boundary weakening and hot crack initiation caused by impurity segregation from the source.

[0019] 2. Grain boundary strengthening and microstructure regulation

[0020] The introduction of trace amounts of boron (B) primarily strengthens grain boundaries. B atoms tend to accumulate in grain boundary regions during solidification and subsequent cooling. This segregation effectively fills grain boundary vacancies, lowers grain boundary energy, and thus significantly enhances grain boundary bonding strength and improves the grain boundaries' resistance to crack propagation. Simultaneously, the interaction between B and elements such as C optimizes carbide precipitation behavior, further strengthening the matrix. The synergy between La and B achieves a dual modification of grain boundaries—both "purifying" and "strengthening"—jointly improving the material's thermoplasticity under rapid thermal cycling in a DED environment.

[0021] 3. Control of low-melting-point elements and improvement of thermal stability

[0022] This invention strictly controls the copper (Cu) content to a low level of ≤0.20% to avoid the formation of a low-melting-point Cu-rich phase at grain boundaries due to excessive Cu. Under the rapid solidification conditions of the DED process, such liquid phase films are a major factor inducing solidification cracks. Reducing the Cu content, combined with the aforementioned La purification of impurities, ensures that grain boundaries maintain sufficient solid-phase strength at high temperatures, even under high heat input, significantly reducing hot cracking susceptibility. Furthermore, precisely controlled Co and Ni contents guarantee that the alloy has a stable and low coefficient of thermal expansion over a wide temperature range, meeting the ultimate functional requirements for packaging matching.

[0023] In summary, this invention constructs an alloy system with high crack resistance and high densification capability through a synergistic composition design of "La purifying grain boundaries, B strengthening grain boundaries, and low Cu avoiding grain boundary embrittlement". This fundamentally solves the technical bottleneck of traditional expansion alloys being prone to cracking due to high energy input in the manufacturing of large DEDs.

[0024] The beneficial effects of this invention are as follows:

[0025] In terms of process performance, this invention significantly improves the crack resistance and forming quality of the alloy during additive manufacturing.

[0026] At the material properties level, this invention achieves synergistic optimization of low expansion characteristics and excellent mechanical properties.

[0027] In terms of application and manufacturing, this invention expands the design freedom and manufacturing efficiency of high-performance expansion alloy components. Detailed Implementation

[0028] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] Example 1

[0030] A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method are characterized by comprising the following steps:

[0031] 1. The pre-alloyed smelting composition is (by mass percentage): Ni: 33.0%; Co: 4.5%; C: 0.03%; Cu: 0.10%; La: 0.015%; B: 0.003%; Mn: 0.2%; S: ≤0.005%; P: ≤0.005%; O: 0.008%; N: ≤0.004%; the balance being Fe and unavoidable impurities.

[0032] 2. Inert gas atomization is adopted, the atomizing gas is high-purity argon, the main spray pressure is 4MPa, the auxiliary pressure is 1MPa, the oxygen content of the expansion alloy powder is increased to 0.012%, the powder sphericity is 95%, a small amount of satellite powder exists, and the flowability is 18.5 s / 50g;

[0033] 3. DED additive manufacturing was employed, with inert gas protection, a power of 7000 W, a powder feed rate of 2.5 kg / h, and a scanning speed of 1000 mm / min. The printed sample achieved a density of 99.8%, and metallographic observation revealed virtually no cracks, although a small amount of porosity was observed, primarily caused by gas-atomized hollow powder and molten pool disturbance. The average coefficient of linear expansion (20–100℃) was 0.761 × 10⁻⁶. -6 / ℃.

[0034] Example 2

[0035] A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method are characterized by comprising the following steps:

[0036] 1. The pre-alloyed smelting composition is (by mass percentage): Ni: 33.0%; Co: 4.5%; C: 0.03%; Cu: 0.10%; La: 0.015%; B: 0.003%; Mn: 0.2%; S: ≤0.005%; P: ≤0.005%; O: 0.008%; N: ≤0.004%; the balance being Fe and unavoidable impurities.

[0037] 2. Atomization is performed using a rotating electrode with high-purity argon and helium as the atomizing gases. The Ar / He ratio is 1:1, the electrode rotation speed is 21000 RPM, the oxygen content of the expanded alloy powder is increased to 0.010%, the powder sphericity is 99%, a very small amount of satellite powder is present, and the flowability is 15.3 s / 50g.

[0038] 3. DED additive manufacturing was employed, with inert gas protection, a power of 6500 W, a powder feed rate of 2 kg / h, and a scanning speed of 900 mm / min. The printed sample had a density of 99.9%, and metallographic observation revealed virtually no cracks, with only a very small amount of porosity, mainly caused by molten pool disturbance. The average coefficient of linear expansion (20–100℃) was 0.676 × 10⁻⁶. -6 / ℃.

[0039] Comparative Example 1

[0040] A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method are characterized by comprising the following steps:

[0041] 1. The pre-alloyed smelting composition is (by mass percentage): Ni: 33.0%; Co: 4.5%; C: 0.03%; Cu: 0.45%; Mn: 0.2%; S: ≤0.005%; P: ≤0.005%; O: 0.008%; N: ≤0.004%; the balance being Fe and unavoidable impurities.

[0042] 2. Inert gas atomization is adopted, and the atomizing gas is high-purity argon. The main spray pressure is 4 MPa and the auxiliary pressure is 1 MPa. The oxygen content of the expansion alloy powder is increased to 0.014%, the powder sphericity is 95%, a small amount of satellite powder exists, and the flowability is 18.5 s / 50g.

[0043] 3. DED additive manufacturing was employed, with inert gas protection, a power of 7000 W, a powder feed rate of 2.5 kg / h, and a scanning speed of 1000 mm / min. The density of the printed sample was 99.4%. Metallographic observation revealed a crack approximately 1 μm wide and 150 μm long. The area near the crack was rich in Cu, and a small amount of Fe-rich oxide was present at the overlap. A small number of pores were also observed, mainly caused by gas atomization of hollow powder and molten pool disturbance. The average coefficient of linear expansion (20–100℃) was 0.760 × 10⁻⁶. -6 / ℃.

[0044] Comparative Example 2

[0045] A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method are characterized by comprising the following steps:

[0046] 1. The pre-alloyed smelting composition is (by mass percentage): Ni: 33.0%; Co: 4.5%; C: 0.03%; Cu: 0.25%; La: 0.015%; B: 0.003%; Mn: 0.2%; S: ≤ 0.005%; P: ≤ 0.005%; O: 0.008%; N: ≤ 0.004%; the balance being Fe and unavoidable impurities.

[0047] 2. Inert gas atomization is adopted, with high-purity argon as the atomizing gas. The main spray pressure is 4 MPa and the auxiliary pressure is 1 MPa. The oxygen content of the expansion alloy powder is increased to 0.012%, the powder sphericity is 95%, a small amount of satellite powder exists, and the flowability is 18.5 s / 50g.

[0048] 3. DED additive manufacturing was employed, with inert gas protection, a power of 7000 W, a powder feed rate of 2.5 kg / h, and a scanning speed of 1000 mm / min. The printed sample density was 99.7%. Metallographic observation revealed a crack approximately 0.5 μm wide and 40 μm long, along with a small amount of porosity, primarily caused by gas-atomized hollow powder and molten pool disturbance. The average coefficient of linear expansion (20–100℃) was 0.718 × 10⁻⁶. -6 / ℃.

[0049] Comparative Example 3

[0050] A low-cracking-prone, low-expansion-cobalt-based iron-nickel-cobalt alloy powder and its preparation method are characterized by comprising the following steps:

[0051] 1. The pre-alloyed smelting composition is (by mass percentage): Ni: 33.0%; Co: 4.5%; C: 0.03%; Cu: 0.12%; La: 0.04%; B: 0.013%; Mn: 0.2%; S: ≤0.005%; P: ≤0.005%; O: 0.008%; N: ≤0.004%; the balance being Fe and unavoidable impurities.

[0052] 2. Inert gas atomization is adopted, with high-purity argon as the atomizing gas. The main spray pressure is 4 MPa and the auxiliary pressure is 1 MPa. The oxygen content of the expansion alloy powder is increased to 0.012%, the powder sphericity is 95%, a small amount of satellite powder exists, and the flowability is 18.5 s / 50g.

[0053] 3. DED additive manufacturing was employed, with inert gas protection, a power of 7000 W, a powder feed rate of 2.5 kg / h, and a scanning speed of 1000 mm / min. The printed sample density was 99.7%. Metallographic observation revealed a crack approximately 1 μm wide and 100 μm long, with a small number of pores near the crack, mainly caused by gas-atomized hollow powder and molten pool disturbance. The average coefficient of linear expansion (20–100℃) was 0.772 × 10⁻⁶. -6 / ℃.

[0054] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-cracking-prone iron-nickel-cobalt based alloy powder for additive manufacturing, characterized in that, Its composition, by mass percentage, includes: Ni: 32.0%–33.0%; Co: 4.0%–4.5%; C: 0.02%–0.04%; Cu: ≤0.20%; La: 0.01%–0.015%; B: ≤0.003%; Mn: 0.2%–0.3%; S: ≤0.005%; P: ≤0.005%; O: ≤0.008%; N: ≤0.004%; the balance being Fe and unavoidable impurities.

2. A method for preparing the iron-nickel-cobalt based alloy powder as described in claim 1, characterized in that, Includes the following steps: (1) Pre-alloying smelting: Smelting is carried out according to the composition ratio described in claim 1, wherein La and B are added in the later stage of smelting and 5 minutes before tapping out of the furnace; (2) Powdering: The alloy melt obtained in step (1) is prepared into spherical powder by inert gas atomization or rotating electrode atomization.

3. The preparation method according to claim 2, characterized in that, In step (2), an inert gas atomization method is used, with high-purity argon as the atomization medium, a main nozzle pressure of 3-5 MPa, and an auxiliary pressure of 1-2 MPa.

4. The preparation method according to claim 2, characterized in that, In step (2), a rotating electrode atomization method is used. The atomizing gas is a mixture of high-purity argon and helium, with a volume ratio of Ar to He of 1:

1. The electrode rotation linear velocity is 18000 to 25000 RPM.

5. An additive manufacturing method for preparing iron-nickel-cobalt based alloy components with low cracking tendency, characterized in that, The alloy powder described in claim 1 is used to form the alloy using a laser direct energy deposition process. The parameters of the laser direct energy deposition process are: laser power 5000-7000 W, powder feed rate 2-2.5 kg / h, scanning speed 900-1100 mm / min, and the process is carried out under inert gas protection.

6. A component manufactured from the alloy powder of claim 1 by an additive manufacturing process, characterized in that, The component has a density of not less than 99.8% in the printed state, and no hot cracks are observed during metallographic examination.