A low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance and a preparation method thereof

Abstract

The application belongs to the field of metal material high-temperature alloy, and discloses a low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance and a preparation method. The cobalt-based high-temperature alloy comprises Co, Ni, Al, Ti, Ta, Cr, B, Zr and inevitable impurity elements; the atomic percentage of each element is as follows: 20-40% of Ni, 5-15% of Al, 1-15% of Ta, 0-2% of Ti, 5-12% of Cr, 0-1% of B, 0-1% of Zr, and the rest is Co and inevitable impurity elements. The application significantly improves the plasticity and oxidation resistance of the alloy by adding micro-alloying elements and corrosion-resistant Cr elements, and reduces the density of the alloy by removing the W element in the gamma'-Co3(Al, W) phase.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloys of metallic materials, and more specifically, relates to a low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance, and its preparation method. Background Technology

[0002] Compared to nickel-based superalloys, cobalt-based superalloys exhibit superior resistance to hot corrosion, thermal fatigue, and weldability, making them a key material for hot-end components in advanced propulsion systems used in aerospace, energy, and nuclear industries. Traditional strengthening methods for cobalt-based superalloys primarily involve solid solution strengthening and carbide strengthening. However, their high-temperature strength and heat resistance are significantly lower than those of nickel-based superalloys strengthened by the γ' phase (Ni3Al), thus limiting their widespread application under high-temperature and high-load conditions.

[0003] In 2006, J. Sato et al. discovered a coherent γ′-Co3(Al,W) phase in Co-Al-W alloys. Subsequent studies, through alloying, increased the dissolution temperature of the γ′ phase to above 1100℃, achieving a long-term stable γ / γ′ two-phase microstructure at high temperatures. Furthermore, the high-temperature mechanical properties of the alloy could be improved through coherent strengthening and precipitation strengthening (achieving excellent high-temperature properties similar to nickel-based superalloys). The high-temperature strength of this type of γ′-phase strengthened cobalt-based superalloy is significantly higher than that of traditional cobalt-based superalloys, even surpassing nickel-based superalloys at certain temperatures (≥1000℃). This type of γ′-phase strengthened cobalt-based superalloy also inherits the excellent environmental resistance and wear resistance of traditional cobalt-based superalloys. In addition, recent research reports that the creep properties of Co-Al-W-Ta-Ti pentagonal single-crystal alloys are approaching those of second-generation nickel-based single-crystal superalloys, indicating that this type of alloy has broad application prospects.

[0004] Although existing research has yielded a series of important advances, the shortcomings of this type of γ' phase-strengthened cobalt-based superalloy remain quite obvious, mainly in three aspects. First, compared with nickel-based superalloys, they have poor plasticity and low elongation; second, the alloys have weak resistance to high-temperature oxidation, limiting their service temperature; and third, the alloys have high density, which limits their application range.

[0005] Therefore, the development of low-density cobalt-based superalloys with high elongation and high oxidation resistance, and their preparation methods, is of great significance for promoting the engineering application of cobalt-based superalloys. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-density cobalt-based superalloy with high elongation and high oxidation resistance, along with its preparation method. This invention employs the addition of microalloying elements and corrosion-resistant Cr elements to significantly improve the alloy's plasticity and oxidation resistance, and reduces the alloy's density by removing W elements from the γ′-Co3(Al,W) phase.

[0007] To achieve the above objectives, the present invention provides a low-density cobalt-based superalloy with high elongation and high oxidation resistance (having a high-temperature stable γ / γ′ dual-phase structure), wherein the cobalt-based superalloy includes Co, Ni, Al, Ti, Ta, Cr, B, Zr and unavoidable impurity elements;

[0008] The atomic percentages of each element are: 20-40% Ni, 5-15% Al, 1-15% Ta, 0-2% Ti, 5-12% Cr, 0-1% B, 0-1% Zr, with the remainder being Co and unavoidable impurity elements.

[0009] According to the present invention, preferably, the atomic percentage of each element is: 25-35% Ni, 8-12% Al, 1-10% Ta, 0.05-1.5% Ti, 8-12% Cr, 0.01-0.3% B, 0.01-0.5% Zr, with the remainder being Co and unavoidable impurity elements.

[0010] The design concept for determining the alloy composition in this invention is:

[0011] (1) Ni: Adding Ni can improve the stability of the γ / γ′ phase, increase the dissolution temperature of the γ′ phase, and reduce the lattice mismatch between the γ / γ′ phases.

[0012] (2) Al: By adding Al as a constituent element of the γ′ phase, the oxidation resistance of the alloy is improved and the diffusion of O into the alloy is hindered.

[0013] (3)Ti: Adding Ti increases the volume fraction and stability of the γ′ phase, thereby promoting the precipitation of the γ′ phase.

[0014] (4)Ta: Adding Ta can improve the stability and volume fraction of the γ′ phase and increase the stacking fault energy.

[0015] (5) Cr: Adding Cr element improves the oxidation resistance of the alloy and prevents O element from continuing to diffuse into the alloy.

[0016] (6)B: Adding B element can improve the bonding force of single crystal subgrain boundaries and enhance the plasticity of the alloy.

[0017] (7) Zr: Adding Zr can improve the bonding force of single-crystal subgrain boundaries and enhance the plasticity of the alloy.

[0018] According to the present invention, preferably, the total atomic percentage of Al, Ti and Ta is less than 16%.

[0019] According to the present invention, preferably, the content of the unavoidable impurity elements is less than 0.1 wt% based on the total weight of the cobalt-based superalloy.

[0020] According to the present invention, preferably, the density of the high elongation and high oxidation resistance low-density cobalt-based superalloy is ≤8.38 g / cm³. 3 Under conditions of 750-850℃, the yield strength is ≥550MPa, the tensile strength is ≥700MPa, and the elongation after fracture is ≥50%.

[0021] According to the present invention, preferably, the high elongation and high oxidation resistance low-density cobalt-based superalloy exhibits an oxidation weight gain of less than 1 mg / cm³ under conditions of 800℃-1000℃. 2 .

[0022] Another aspect of the present invention provides a method for preparing the high elongation and high oxidation resistance low-density cobalt-based superalloy, comprising: sequentially mixing pure Co, pure Al, pure Ni, pure Ta, pure Cr, pure Ti, pure Zr and Ni-B master alloys through vacuum induction melting, spiral crystal selection and solution aging treatment to obtain the high elongation and high oxidation resistance low-density cobalt-based superalloy (with a high-temperature stable γ / γ′ dual-phase structure).

[0023] According to the present invention, preferably, the Co content in the pure Co is ≥99.90 wt.%; the Al content in the pure Al is ≥99.90 wt.%; the Ni content in the pure Ni is ≥99.90 wt.%; the Ta content in the pure Ta is ≥99.90 wt.%; the Cr content in the pure Cr is ≥99.90 wt.%; the Ti content in the pure Ti is ≥99.90 wt.%; the Zr content in the pure Zr is ≥99.90 wt.%; and the Ni-B master alloy is Ni-8 to 12 wt.% B.

[0024] According to the present invention, preferably, the preparation method includes:

[0025] S1: Use low power (3-8kw) preheating to remove moisture and impurities from the pure Co, pure Al, pure Ni, pure Ta, pure Cr, pure Ti, pure Zr and Ni-B master alloy; mix and melt pure Ni, pure Ta and pure Cr to obtain a first melt; mix and melt the first melt, pure Al, pure Ti and pure Zr to obtain a second melt, and cast it to obtain a low-density cobalt-based high-temperature alloy master alloy ingot;

[0026] S2: A portion of the ingot is cut from the low-density cobalt-based high-temperature alloy master alloy ingot using wire cutting. This portion of the ingot is then polished and sandblasted to obtain a deoxidized ingot, which is then sent to a single-crystal directional solidification device. The single-crystal directional solidification device is then evacuated, and the deoxidized ingot is heated inside the device to obtain a third melt. This melt is then cooled and poured into a single-crystal investment mold for single-crystal directional solidification to obtain a single-crystal alloy test bar.

[0027] S3: The single-crystal alloy test bar is subjected to solution aging treatment to obtain the low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance.

[0028] According to the present invention, preferably, the equipment for step S1 includes a vacuum electromagnetic induction melting furnace;

[0029] The operating conditions for obtaining the first melt include: the power of the vacuum electromagnetic induction melting furnace is 15-30kw, the temperature is first raised to 1500℃-1600℃, then cooled to 1450℃-1500℃ and held for 10-20min.

[0030] The operating conditions for obtaining the second melt include: the power of the vacuum electromagnetic induction melting furnace is 15-30kw, the temperature is first raised to 1500℃-1600℃ and held for 3-6 minutes, then cooled to 1400℃-1450℃ and poured.

[0031] In this invention, in step S1, a vacuum electromagnetic induction melting furnace is used to melt the raw materials of the high elongation and high oxidation resistance low density cobalt-based high-temperature alloy of this invention. Moreover, the induction power supply of the vacuum electromagnetic induction melting furnace of this invention generates an electromagnetic stirring effect while induction heating the cobalt-based alloy melt, which makes the alloy elements in the melt more uniformly distributed and reduces the occurrence of macro segregation.

[0032] According to the present invention, preferably, in step S2:

[0033] The deoxidized ingot is heated to 1550-1600℃ and held at that temperature for 20-30℃ in the single-crystal directional solidification apparatus to obtain a third melt, which is then cooled to 1545-1555℃ and poured into a single-crystal investment mold. Single-crystal directional solidification is then carried out at a pulling rate of 50-200μm / s.

[0034] The temperature of the single crystal melting mold is 1520-1540℃, and the bottom of the single crystal melting mold is equipped with a spiral crystal selector.

[0035] According to the present invention, preferably, in step S3:

[0036] The solution treatment temperature is 1200-1320℃, and the treatment time is 20-50h.

[0037] The aging treatment temperature is 800-1000℃, and the treatment time is 20-100h.

[0038] The beneficial effects of the technical solution of the present invention are as follows:

[0039] (1) By removing the W element from the existing γ′-Co3(Al,W) phase, the present invention reduces the density of the alloy, while increasing the Ni element content, expanding the γ / γ′ phase two-phase region of the alloy and stabilizing the γ′ phase, and also increasing the dissolution temperature of the γ′ phase.

[0040] (2) Trace amounts of B and Zr elements were added to the cobalt-based high-temperature alloy of the present invention, which improved the bonding force of the single crystal subgrain boundaries and enhanced the plasticity of the alloy.

[0041] (3) The density of the cobalt-based superalloy of the present invention is ≤8.38 g / cm³. 3 It exhibits excellent high-temperature mechanical properties at 800℃, with a yield strength of 564.5MPa, a tensile strength of 731.0MPa, and an elongation after fracture of up to 53.3%.

[0042] (4) The cobalt-based superalloy of the present invention has excellent oxidation resistance, and the oxidation weight gain is less than 1 mg / cm³ in the temperature range of 800℃-1000℃. 2 It is lower than most reported cobalt-based alloys, and also lower than conventional MAR-M 509 cobalt-based superalloy and Udimet 720 nickel-based superalloy.

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0044] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0045] Figure 1 The microstructure of the single-crystal alloy test rod prepared in Example 1 of the present invention is shown.

[0046] Figure 2 The image shows a microstructure of a low-density cobalt-based superalloy with high elongation and high oxidation resistance prepared in Example 1 of the present invention.

[0047] Figure 3 The engineering stress-strain curve of the low-density cobalt-based superalloy with high elongation and high oxidation resistance prepared in Example 1 of the present invention is shown at 800°C (where “Engineering stress” is stress and “Engineering strain” is strain). Detailed Implementation

[0048] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0049] Example 1

[0050] This embodiment provides a low-density cobalt-based superalloy with high elongation and high oxidation resistance. The cobalt-based superalloy includes Co, Ni, Al, Ti, Ta, Cr, B, Zr, and unavoidable impurity elements.

[0051] The atomic percentages (at.%) of each element are: 29.4% Ni, 10.4% Al, 4.0% Ta, 1.5% Ti, 11.2% Cr, 0.05% B, 0.05% Zr, with the remainder being Co and unavoidable impurity elements. The content of the unavoidable impurity elements, based on the total weight of the cobalt-based superalloy, is less than 0.06 wt%.

[0052] The preparation methods of the above-mentioned low-density cobalt-based superalloys with high elongation and high oxidation resistance include:

[0053] S1: In a vacuum electromagnetic induction melting furnace, preheating with low power (6 kW) removes moisture and impurities from the 99.90 wt.% pure Co, 99.95 wt.% pure Al, 99.9 wt.% pure Ni, 99.99 wt.% pure Ta, 99.9 wt.% pure Cr, 99.9 wt.% pure Ti, 99.9 wt.% pure Zr and Ni-10 wt.% B master alloy. Then, pure Ni, pure Ta and pure Cr are mixed and melted. The specific operation includes: adjusting to high power (25 kW), rapidly heating to 1550℃, then lowering the temperature to 1460℃ and holding for 10-20 minutes to obtain the first melt. The first melt, pure Al, pure Ti and pure Zr are mixed and melted. The specific operation includes: rapidly heating to 1550℃, holding for 3-6 minutes, then lowering the temperature to 1450℃ to obtain the second melt, which is then poured to obtain a low-density cobalt-based high-temperature alloy master alloy ingot.

[0054] S2: A portion of the ingot of suitable size is cut from the low-density cobalt-based high-temperature alloy master alloy ingot using wire cutting. The ingot is then ground and sandblasted to remove the oxide scale from its surface, resulting in a de-oxidized ingot, which is then placed in the crucible of a single-crystal directional solidification device. The single-crystal directional solidification device is then evacuated, and the de-oxidized ingot is heated to 1580°C and held at 25°C within the device to completely melt the ingot. Once the melt has cooled to 1550°C, it is poured into a single-crystal casting mold with a spiral crystal selector at the bottom. Single-crystal directional solidification is then performed at a pulling rate of 70 μm / s to obtain a single-crystal alloy test bar.

[0055] S3: The single-crystal alloy specimen was subjected to solution treatment and aging treatment at 1290℃ for 24 hours, followed by aging treatment at 900℃ for 30 hours, resulting in a low-density cobalt-based superalloy with high elongation and high oxidation resistance, having a density of 8.24 g / cm³. 3 .

[0056] The microstructure image of the cobalt-based superalloy prepared in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that after directional solidification, it exhibits a typical dendritic structure; after solution treatment and aging... Figure 2 The microstructure of the cobalt-based superalloy prepared in this embodiment is a typical γ / γ′ two-phase microstructure.

[0057] like Figure 3 The figure shows the engineering stress-strain curve of the cobalt-based superalloy prepared in this embodiment at 800°C. Figure 3 It can be seen that the cobalt-based superalloy prepared in this embodiment has a yield strength of 564.5 MPa, a tensile strength of 731.0 MPa, and an elongation after fracture of 53.3% at 800℃.

[0058] The cobalt-based superalloy prepared in this embodiment gained 0.3 mg / cm³ in weight after oxidation at 1000℃ for 100 hours. 2 .

[0059] Example 2

[0060] This embodiment provides a low-density cobalt-based superalloy with high elongation and high oxidation resistance. The cobalt-based superalloy includes Co, Ni, Al, Ti, Ta, Cr, B, Zr, and unavoidable impurity elements. The only difference from Example 1 is that the Cr content (atomic percentage, at.%) in the alloy is reduced from 11.2% to 9.4%.

[0061] The low-density cobalt-based superalloy prepared in this embodiment has a density of 8.24 g / cm³. 3 Increased to 8.35 g / cm³ 3The yield strength at 800℃ is 586.3 MPa, the tensile strength is 781.2 MPa, the elongation after fracture is 51.1%, and the weight gain after 100h oxidation at 1000℃ is 0.8 mg / cm³. 2 Therefore, a high Cr content is a guarantee of excellent antioxidant properties.

[0062] Example 3

[0063] This embodiment provides a low-density cobalt-based superalloy with high elongation and high oxidation resistance. This cobalt-based superalloy includes Co, Ni, Al, Ti, Ta, Cr, B, Zr, and unavoidable impurity elements. The alloy composition is the same as in Example 1, but the preparation method is different, as detailed below:

[0064] S1: Same as in Example 1, a low-density cobalt-based high-temperature alloy master alloy ingot is obtained;

[0065] The only difference between S2 and Example 1 is that the single crystal preparation pulling speed is increased from 70 μm / s in Example 1 to 140 μm / s, resulting in a single crystal alloy test rod;

[0066] S3: The single crystal alloy test bar is subjected to solution aging treatment at a temperature of 1300℃ for 16 hours, and aging treatment at a temperature of 900℃ for 30 hours to obtain a low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance.

[0067] The dendrite spacing of the cobalt-based superalloy prepared in this embodiment is reduced by 20% compared to the alloy in Example 1. Its yield strength at 800℃ is 592.5 MPa, tensile strength is 792.1 MPa, elongation after fracture is 59.2%, and its weight gain after oxidation at 1000℃ for 100 hours is 0.3 mg / cm³. 2 Therefore, it can be seen that the optimized preparation process in Example 3 can improve the high-temperature mechanical properties of the alloy.

[0068] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A low-density cobalt-based superalloy with high elongation and high oxidation resistance, characterized in that, This cobalt-based superalloy includes Co, Ni, Al, Ti, Ta, Cr, B, Zr, and unavoidable impurity elements; The atomic percentages of each element are: 25-35% Ni, 8-12% Al, 1-10% Ta, 0.05-1.5% Ti, 8-12% Cr, 0.05-0.3% B, 0.01-0.5% Zr, with the remainder being Co and unavoidable impurity elements; The preparation method of the high elongation and high oxidation resistance low density cobalt-based superalloy includes: sequentially mixing pure Co, pure Al, pure Ni, pure Ta, pure Cr, pure Ti, pure Zr and Ni-B master alloy, performing vacuum induction melting, spiral crystal selection and solid solution aging treatment to obtain the high elongation and high oxidation resistance low density cobalt-based superalloy. In a single-crystal directional solidification apparatus, the deoxidized ingot is heated to 1550-1600℃ and held for 20-30℃ to obtain a third melt. The melt is then cooled to 1545-1555℃ and poured into a single-crystal investment mold. Single-crystal directional solidification is then carried out at a pulling rate of 50-200μm / s. The temperature of the single crystal melting mold is 1520-1540℃, and the bottom of the single crystal melting mold is equipped with a spiral crystal selector; The solution treatment temperature is 1200-1320℃, and the treatment time is 20-50h. The aging treatment temperature is 800-1000℃, and the treatment time is 20-100h.

2. The low-density cobalt-based superalloy with high elongation and high oxidation resistance according to claim 1, wherein, The total atomic percentage of Al, Ti, and Ta is less than 16%; Based on the total weight of the cobalt-based superalloy, the content of the unavoidable impurity elements is less than 0.1 wt%.

3. The low-density cobalt-based superalloy with high elongation and high oxidation resistance according to claim 1 or 2, wherein, The high elongation and high oxidation resistance low-density cobalt-based superalloy has a density ≤8.38 g / cm³. 3 Under conditions of 750-850℃, the yield strength is ≥550MPa, the tensile strength is ≥700MPa, and the elongation after fracture is ≥50%. The high elongation and high oxidation resistance low-density cobalt-based superalloy exhibits an oxidation weight gain of less than 1 mg / cm³ at 800℃-1000℃. 2 .

4. The low-density cobalt-based superalloy with high elongation and high oxidation resistance according to claim 1, wherein, The pure Co has a Co content of ≥99.90 wt.%; the pure Al has an Al content of ≥99.90 wt.%; the pure Ni has a Ni content of ≥99.90 wt.%; the pure Ta has a Ta content of ≥99.90 wt.%; the pure Cr has a Cr content of ≥99.90 wt.%; the pure Ti has a Ti content of ≥99.90 wt.%; the pure Zr has a Zr content of ≥99.90 wt.%; and the Ni-B master alloy is Ni-8~12 wt.%B.

5. The low-density cobalt-based superalloy with high elongation and high oxidation resistance according to claim 1, wherein, The preparation method includes: S1: Preheating removes moisture and impurities from the pure Co, pure Al, pure Ni, pure Ta, pure Cr, pure Ti, pure Zr and Ni-B master alloy; pure Ni, pure Ta and pure Cr are mixed and melted to obtain a first melt; the first melt, pure Al, pure Ti and pure Zr are mixed and melted to obtain a second melt, which is then cast to obtain a low-density cobalt-based high-temperature alloy master alloy ingot; S2: A portion of the ingot is cut from the low-density cobalt-based high-temperature alloy master alloy ingot using wire cutting. This portion of the ingot is then polished and sandblasted to obtain a deoxidized ingot, which is then sent to a single-crystal directional solidification device. The single-crystal directional solidification device is then evacuated, and the deoxidized ingot is heated inside the device to obtain a third melt. This melt is then cooled and poured into a single-crystal investment mold for single-crystal directional solidification to obtain a single-crystal alloy test bar. S3: The single-crystal alloy test bar is subjected to solution aging treatment to obtain the low-density cobalt-based high-temperature alloy with high elongation and high oxidation resistance.

6. The low-density cobalt-based superalloy with high elongation and high oxidation resistance according to claim 5, wherein, The equipment for step S1 includes a vacuum electromagnetic induction melting furnace; The operating conditions for obtaining the first melt include: the power of the vacuum electromagnetic induction melting furnace is 15-30kw, the temperature is first raised to 1500℃-1600℃, then cooled to 1450℃-1500℃ and held for 10-20min. The operating conditions for obtaining the second melt include: the power of the vacuum electromagnetic induction melting furnace is 15-30kw, the temperature is first raised to 1500℃-1600℃ and held for 3-6 minutes, then cooled to 1400℃-1450℃ and poured.

7. The method for preparing the high elongation and high oxidation resistance low-density cobalt-based superalloy according to any one of claims 1-6, characterized in that, The preparation method includes: sequentially mixing pure Co, pure Al, pure Ni, pure Ta, pure Cr, pure Ti, pure Zr and Ni-B master alloys through vacuum induction melting, spiral crystal selection and solution aging treatment to obtain the high elongation and high oxidation resistance low density cobalt-based high-temperature alloy.

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