Powder metallurgy high-temperature-resistant nanophase reinforced high-entropy alloy and preparation method thereof

Abstract

The invention discloses a powder metallurgy high-temperature-resistant nanophase reinforced high-entropy alloy and a preparation method thereof, and belongs to the technical field of metal materials. The high-temperature-resistant nanophase reinforced high-entropy alloy for powder metallurgy comprises Ni and the following raw materials in percentage by mass: 22.0 to 25.9 percent of Co, 8.0 to 9.7 percent of Cr, 7.0 to 8.7 percent of Fe, 3.3 to 4.5 percent of Ti, 3.5 to 4.9 percent of Al, 3.0 to 3.5 percent of Ta, 0.6 to 1.2 percent of Nb, 1.3 to 2.0 percent of W, 0.6 to 1.1 percent of Mo, 0.1 to 0.3 percent of Hf, 0.01 to 0.05 percent of Zr, 0.05 to 0.3 percent of B and inevitable impurities. The powder metallurgy high-temperature-resistant nanophase reinforced high-entropy alloy is of an FCC and L12 double-phase structure and has excellent room / high-temperature mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly relates to a powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy and a preparation method thereof. Background Art

[0002] With the development of aero-engine technology, high-temperature load-bearing structures such as aero-engine blades and combustion chamber casings have strict requirements for the high-temperature strength and toughness, creep properties, oxidation resistance, etc. of materials. At present, the research and development of high-temperature resistant (700 - 900 °C) and high specific strength materials for combustion chamber casings is in a bottleneck stage. For example, nickel-based superalloys have good strength, tissue stability, and oxidation resistance during long-term service below 750 °C, but their specific strength (tensile strength / density) is relatively low, and there is a problem of medium-temperature grain boundary brittleness (such as the ductility of the U720Li superalloy drops suddenly from more than 15% to 3% at 750 °C), which will affect the performance reliability of aero-engines; although the second-generation TiAl alloy that has been applied abroad has a low density and high specific strength, it has large room-temperature brittleness, and it is still difficult to break through the use temperature of 750 °C; the third-generation TiAl alloy for use above 800 °C is still in the research and development stage, and its room-temperature brittleness and high-temperature tissue stability problems have not been solved. Based on the above situation, it is particularly urgent to develop new high-performance high-temperature structural materials with high thermal stability, high strength, and toughness.

[0003] Compared with traditional nickel-based / cobalt-based superalloys, high-entropy alloys have excellent room / high-temperature mechanical properties and functional characteristics due to the strong high-entropy effect, lattice distortion effect, diffusion retardation effect, and interaction between multiple principal elements, and have great application potential in complex high-temperature resistant structural parts such as military aero-engines. At present, the widely studied single-phase FCC-structured FeCoCrNi-based high-entropy alloys usually exhibit good ductility, but their strength is relatively low, and it is difficult to meet the performance requirements of advanced high-temperature structural materials.

[0004] Introducing ductile nano-particles and strengthening by second-phase dispersion is an important means to improve the strength of materials (especially high-temperature strength). The L12-type nano-phase strengthened high-entropy alloy combines the advantages of a high-entropy matrix and nano-phase strengthening, can overcome the problem of the imbalance between the strength and plasticity of a single solid-solution high-entropy alloy, and enable the alloy to achieve a better match of room / high-temperature strength and toughness. However, from the perspective of composition design, the equiatomic ratio or near-equiatomic ratio composition of this type of high-entropy alloy is not conducive to obtaining the best composition combination for L12 nano-phase strengthening, so that the material cannot maintain a high specific strength during high-temperature service. Therefore, developing alloy materials with low density and excellent room / high-temperature properties is an important goal for promoting the application and development in the high-temperature engineering field. Summary of the Invention

[0005] The object of the present invention is to provide a powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy and its preparation method to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: A powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, by mass percentage, includes Ni and the following raw materials: Co 22.0 - 25.9%, Cr 8.0 - 9.7%, Fe 7.0 - 8.7%, Ti 3.3 - 4.5%, Al 3.5 - 4.9%, Ta 3.0 - 3.5%, Nb 0.6 - 1.2%, W 1.3 - 2.0%, Mo 0.6 - 1.1%, Hf 0.1 - 0.3%, Zr 0.01 - 0.05%, B 0.05 - 0.3% and inevitable impurities.

[0008] Another technical solution of the present invention: A preparation method of the above-mentioned powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, including the following steps:

[0009] Weigh the raw materials (such as master alloy FeW and TiTa) according to mass percentage, mix them, melt and powder them to obtain alloy powder;

[0010] Press the alloy powder to obtain a bulk material;

[0011] Perform heat treatment on the bulk material to obtain the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy.

[0012] Further, the powdering method includes gas atomization powdering; the gas atomization powdering is carried out under a protective atmosphere.

[0013] Further, the pressing method includes hot isostatic pressing;

[0014] The hot isostatic pressing specifically includes: in an environment with a vacuum degree ≤ 0.4 Pa, first heat at a heating rate of 8 - 15 °C / min to 700 - 900 °C, then heat at a heating rate of 4 - 8 °C / min to 1100 - 1300 °C and hold for 60 - 300 min, and apply a pressure of 100 - 200 MPa during the hot isostatic pressing process.

[0015] Further, the heat treatment includes: first performing solution treatment, and then performing intermediate heat treatment.

[0016] Further, the solution treatment temperature is 1150 - 1250 °C, and the holding time is 12 - 25 h.

[0017] Further, the intermediate heat treatment temperature is 780 - 920 °C, and the holding time is 25 - 50 h.

[0018] The third technical solution of the present invention: An application of the above-mentioned powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy in the preparation of aero-engines or gas turbines.

[0019] For the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy of the present invention, by controlling the mass percentage of Ni to be 39.8 - 46.0%, the mass percentage of Co to be 22.0 - 25.9%, and the mass percentage of Fe to be 7.0 - 8.7%, a face-centered cubic matrix can be stabilized. Meanwhile, by adding Al with a mass percentage of 3.5 - 4.9% and Ti with a mass percentage of 3.3 - 4.5%, high-density L12 precipitates can be obtained. After precipitation hardening (i.e., heat treatment below the dissolution temperature of the L12 phase to precipitate a high volume fraction of the L12 phase), the alloy can have a stable L12 phase (which plays a precipitation strengthening role) at room temperature and high temperature, and a relatively high Al content is prone to form an alumina film to improve oxidation resistance; by doping a quantitative amount of Cr element (8.0 - 9.7%) to form a dense chromium oxide film, the high-temperature hot corrosion and oxidation resistance of the alloy are further improved; and by adding elements of W (1.3 - 2.0%), Mo (0.6 - 1.1%) and Hf (0.1 - 0.3%), solid solution strengthening of the matrix and slow coarsening kinetics of the precipitate are achieved. At the same time, the addition of these large-sized refractory micro-elements can increase the degree of lattice distortion of the alloy, which is beneficial to the improvement of the high-temperature strength of the alloy (having high strength and phase stability at high temperature to ensure the creep properties of the alloy); then a small amount of B (0.05 - 0.3%) and Zr (0.01 - 0.05%) are micro-alloyed for grain boundary strengthening, thereby significantly improving the high-temperature strength and creep properties of the alloy.

[0020] Elements of Ta and Nb are added to the alloy of the present invention. Ta and Nb elements can not only enhance the strength of the alloy as solid solution strengthening atoms, but also, as L12 phase forming elements, increase the content of the L12 phase, which is beneficial to the improvement of the high-temperature strength of the alloy. However, an excessive amount of the L12 phase is prone to cause deterioration of the overall processing performance of the alloy, and the addition of excessive Ta and Nb elements is prone to react with elements such as Co and Cr to form Laves phases such as Co2Ta and Cr2Nb, which is not conducive to the plastic deformation behavior of the alloy. Therefore, the present invention controls the mass percentage of Ta to be 3.0 - 3.5% and the mass percentage of Nb to be 0.6 - 1.2%.

[0021] Meanwhile, the addition of Nb can also reduce the hot cracking sensitivity of the alloy during the preparation process (such as during heat treatment with a high degree of supercooling).

[0022] The alloy composed of the above components of the present invention has a wide hot working window (370 - 420 °C. When processed within this region, the alloy will not become unstable and fail), and excellent plasticity. During the forming process, obvious pores and cracks will not occur, and the forming rate is high. By adding and controlling the contents of Ti, Al, Nb, and Ta elements, not only can the characteristics of age hardening be fully utilized, but also the good workability of the alloy can be ensured to achieve a uniform and dispersed distribution of the L12 phase.

[0023] The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy of the present invention combines the plasticity of the FeCoCrNi matrix and the strength of the Ni3(Ti,Al)-type L12 phase nanoparticles. Through the solution strengthening, grain boundary strengthening, etc. of elements such as Mo, Nb, Ta, Hf, W, Zr, and B, it has a yield strength of 926 - 940 MPa at 800 °C, and the density ≤ 8.24 g / cm 3 , meeting the design and usage requirements of advanced aero-engines and gas turbines.

[0024] The present invention discloses the following technical effects:

[0025] (1) The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy of the present invention has an FCC and L12 dual-phase structure, has excellent room / high-temperature mechanical properties, and is suitable for complex working conditions such as high temperature and high pressure.

[0026] (2) The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy of the present invention can reach a tensile strength of 940 MPa at 800 °C, an elongation after fracture of 8.6%, and at the same time the density can be reduced to 8.10 g / cm 3 , meeting the design and usage requirements of advanced aerospace structural materials.

[0027] (3) The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared by the present invention has a lower alloy density, excellent high-temperature tensile properties, plasticity, and creep properties. There are no micro-cracks and pores during the forming process, meeting the design and usage requirements of advanced aero-engines and gas turbines, and can be applied to the hot-end components of advanced aero-engines and gas turbines. This alloy not only has excellent high-temperature strength, but also has good plasticity at room temperature and high temperature. There are no micro-cracks and pores during the forming process, has good workability, the forming process is simple, and is suitable for industrial production and popularization. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 XRD pattern and particle size distribution diagram of the alloy powder prepared in Example 1 of the present invention, wherein (a) is the XRD pattern and (b) is the particle size distribution diagram;

[0030] Figure 2 XRD pattern and scanning electron microscope micrograph of the powder metallurgy high-temperature resistant nano-phase reinforced high-entropy alloy prepared in Example 1 of the present invention, wherein (a) is the XRD pattern and (b) is the scanning electron microscope micrograph;

[0031] Figure 3 Mechanical property comparison diagram of the powder metallurgy high-temperature resistant nano-phase reinforced high-entropy alloy prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention;

[0032] Figure 4 Oxidation property diagram of the powder metallurgy high-temperature resistant nano-phase reinforced high-entropy alloy prepared in Example 1 of the present invention. Detailed implementation manners

[0033] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0036] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0037] As used herein, "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0038] Example 1

[0039] A preparation method of a powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy:

[0040] (1) For the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, by mass percentage, the components are as follows: Co 24.5%, Cr 9.5%, Fe 8.0%, Ti 4.2%, Al 4.0%, Ta 3.2%, Nb 1.0%, W 2.0%, Mo 0.7%, Hf 0.1%, Zr 0.01%, B 0.1%, and the balance is Ni and inevitable impurities;

[0041] Weigh the raw materials according to the above mass percentages, mix and heat them, and perform gas atomization powder making after full melting to obtain alloy powder (the particle size distribution is mainly between 10 and 100 μm);

[0042] (2) In an environment with a vacuum degree ≤ 0.4 Pa, perform hot isostatic pressing on the stainless steel sheath containing the alloy powder (first heat it at a heating rate of 10 °C / min to 800 °C, and then heat it at a heating rate of 8 °C / min to 1200 °C, and hold for 3 h), and apply a pressure of 200 MPa during the whole hot isostatic pressing process to obtain a bulk material with a stainless steel sheath.

[0043] (3) Perform cutting, trimming and deburring on the bulk material with a stainless steel sheath to obtain alloy bars.

[0044] (4) Subject the alloy bars to solution treatment at 1200 °C for 24 h to remove the original powder boundaries of the alloy and obtain alloy bars.

[0045] (5) Subject the alloy bars obtained after the treatment in step (4) to aging treatment at 800 °C for 50 h to obtain a powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy.

[0046] The XRD pattern of the alloy powder prepared in this example is shown in Figure 1 Figure (a), and the particle size distribution diagram is shown in Figure 1 Figure (b).

[0047] It can be seen from Figure 1 that the alloy powder prepared in this example has a single-phase FCC structure, the particle size distribution is mainly between 10 and 100 μm, and the average particle size is 47.6 μm.

[0048] The XRD pattern of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this example is shown in Figure 2Figure (a) of Figure 2 Figure (b) of

[0049] It can be seen from Figure 2 that the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this embodiment has a dual-phase FCC / L12 structure, and a high density of L12 phases are uniformly distributed in the FCC matrix.

[0050] The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in step (5) is processed into a dog-bone tensile specimen with a gauge length of 8 mm, a width of 3 mm, and a thickness of 2 mm, and a tensile experiment is carried out on a universal mechanical testing machine at a rate of 1 mm / min; the tensile strength at 800 °C is measured to be 940 MPa, and the elongation after fracture is 8.6%.

[0051] Example 2

[0052] Same as Example 1, the difference is only that step (2) is specifically: in an environment with a vacuum degree ≤ 0.4 Pa, hot isostatic pressing is carried out on the stainless steel cladding containing alloy powder (first heating to 800 °C at a heating rate of 10 °C / min, and then heating to 1100 °C at a heating rate of 8 °C / min, and holding for 3 h), and a pressure of 200 MPa is applied during the whole hot isostatic pressing process to obtain a bulk material with a stainless steel cladding.

[0053] The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this embodiment has a tensile strength of 926 MPa at 800 °C and an elongation after fracture of 8.2%.

[0054] Comparative Example 1

[0055] Same as Example 1, the difference is only that the alloy raw materials do not contain Ti and Al elements. The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, by mass percentage, has the following components: Co 24.5%, Cr 9.5%, Fe 8.0%, Ta 3.2%, Nb 1.0%, W 2.0%, Mo 0.7%, Hf 0.1%, Zr 0.01%, B 0.1%, and the balance is Ni and unavoidable impurities.

[0056] The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this comparative example has a tensile strength of 161 MPa at 800 °C and an elongation after fracture of 62.9%.

[0057] Comparative Example 2

[0058] Same as Example 1, with the only difference being that the alloy raw materials do not contain the elements of W, Mo, and Hf. The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, by mass percentage, has the following components: Co 24.5%, Cr 9.5%, Fe 8.0%, Ti 4.2%, Al 4.0%, Ta 3.2%, Nb 1.0%, Zr 0.01%, B 0.1%, and the balance is Ni and inevitable impurities.

[0059] The tensile strength of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this comparative example at 800 °C is 725 MPa, and the elongation after fracture is 3.1%.

[0060] Comparative Example 3

[0061] Same as Example 1, with the only difference being that the amounts of Ti and Al elements are changed. The powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, by mass percentage, has the following components: Co 24.5%, Cr 9.5%, Fe 8.0%, Ti 7.0%, Al 7.0%, Ta 3.2%, Nb 1.0%, W 2.0%, Mo 0.7%, Hf 0.1%, Zr 0.01%, B 0.1%, and the balance is Ni and inevitable impurities.

[0062] The tensile strength of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy prepared in this comparative example at 800 °C is 870 MPa, and the elongation after fracture is 3.6%.

[0063] The high-temperature tensile properties and densities of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloys prepared in the examples and comparative examples are shown in Table 1 and Figure 3 。

[0064] Table 1 High-temperature tensile properties and densities of high-entropy alloys

[0065]

[0066] From Figure 4 it can be seen that after the high-entropy alloy prepared in Example 1 undergoes high-temperature oxidation at 700 °C or 800 °C in air for 108 h, the mass increment (i.e., mass gain) is small, indicating excellent oxidation resistance and meeting the usage requirements of the alloy in high-temperature extreme environments.

[0067] The above-described examples are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy, characterized in that, By mass percentage, it includes Ni and the following raw materials: Co 22.0 - 25.9%, Cr 8.0 - 9.7%, Fe 7.0 - 8.7%, Ti 3.3 - 4.5%, Al 3.5 - 4.9%, Ta 3.0 - 3.5%, Nb 0.6 - 1.2%, W 1.3 - 2.0%, Mo 0.6 - 1.1%, Hf 0.1 - 0.3%, Zr 0.01 - 0.05%, B 0.05 - 0.3% and inevitable impurities.

2. The preparation method of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy according to claim 1, characterized in that, It includes the following steps: Weigh the raw materials according to the mass percentage, mix them and then melt and powder them to obtain alloy powder; Press the alloy powder to obtain a bulk material; Perform heat treatment on the bulk material to obtain the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy.

3. The preparation method according to claim 2, wherein The method of powder making includes gas atomization powder making.

4. The preparation method according to claim 2, characterized in that, The method of pressing includes hot isostatic pressing; The specific process of hot isostatic pressing includes: under the condition that the vacuum degree ≤ 0.4 Pa, first heat it at a heating rate of 8 - 15 °C / min to 700 - 900 °C, then heat it at a heating rate of 4 - 8 °C / min to 1100 - 1300 °C and keep it warm for 60 - 300 min, and apply a pressure of 100 - 200 MPa during the hot isostatic pressing process.

5. The preparation method according to claim 2, characterized in that, The heat treatment includes: first performing solution treatment, and then performing intermediate heat treatment.

6. The preparation method according to claim 5, characterized in that, The solution treatment temperature is 1150 - 1250 °C, and the holding time is 12 - 25 h.

7. The preparation method according to claim 5, characterized in that, The intermediate heat treatment temperature is 780 - 920 °C, and the holding time is 25 - 50 h.

8. Application of the powder metallurgy high-temperature resistant nano-phase strengthened high-entropy alloy according to claim 1 in the preparation of an aeroengine or a gas turbine.

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