Brittle fracture resistant high-temperature alloy and preparation method and application thereof

Abstract

The invention relates to the technical field of metal materials, in particular to an anti-brittle fracture high-temperature alloy and a preparation method and application thereof. The embrittlement-resistant high-temperature alloy comprises a heterogeneous grain structure, the heterogeneous grain structure comprises a plurality of equiaxed grain areas and a plurality of columnar grain areas, each equiaxed grain area is formed by gathering equiaxed grains, each columnar grain area is formed by gathering columnar grains, and the average size of the columnar grains is larger than that of the equiaxed grains; the columnar grain areas and the equiaxed grain areas are distributed at intervals, and the total number of low-angle grain boundaries and coincident position lattice grain boundaries in formed grain boundaries is larger than that of high-angle grain boundaries. According to the high-temperature alloy, the equiaxed grain form in an existing high-temperature alloy is changed, starting from the angle of grain and grain boundary dual improvement or further from the angle of phase distribution, the brittleness of the high-temperature alloy is greatly reduced, and the cracking risk is reduced. The material can serve for a long time in a high-temperature environment and can be used for aero-engines, power units, oil and gas exploitation equipment, gas turbines and the like.

Description

Technical Field

[0001] The present application relates to the technical field of metal materials, and in particular to a high-temperature alloy resistant to brittle cracking and a preparation method and application thereof. Background Art

[0002] Due to their excellent high-temperature strength and oxidation resistance, high-temperature alloys play a vital role in a variety of fields such as aerospace, energy, automobiles, chemicals, metallurgy, and high-temperature electronics, making them the preferred materials for today's extreme high-temperature environments. Although these high-temperature alloys exhibit excellent mechanical properties over a wide temperature range from low to high temperatures, they suffer from brittle cracking, which means poor toughness and ductility. This is especially serious at medium temperatures such as 800°C, which greatly limits the safe use of high-temperature alloys in this temperature range. Summary of the Invention

[0003] The purpose of this application is to provide a high-temperature alloy that is resistant to brittle cracking, and a preparation method and application thereof, in order to solve the problem that high-temperature alloys in the prior art are prone to brittle cracking, especially the more serious problem in the medium temperature range.

[0004] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0005] In a first aspect, the present application provides a brittle cracking resistant high-temperature alloy, comprising a heterogeneous grain structure, the heterogeneous grain structure comprising a plurality of equiaxed grain regions and a plurality of columnar grain regions, wherein a single equiaxed grain region is formed by an aggregation of equiaxed grains, and a single columnar grain region is formed by an aggregation of columnar grains, wherein the average size of the columnar grains is greater than the average size of the equiaxed grains;

[0006] The columnar grain regions and the equiaxed grain regions are spaced apart from each other, and among the grain boundaries formed, the total number of low-angle grain boundaries and coincident position lattice grain boundaries is greater than that of high-angle grain boundaries.

[0007] The brittle crack-resistant high-temperature alloy of the present application changes the equiaxed grain morphology in existing high-temperature alloys, and forms a heterogeneous grain structure with regions formed by the aggregation of columnar grains and equiaxed grains. In addition, a large number of low-angle grain boundaries and overlapping position lattice grain boundaries are introduced into the grain boundaries between the two regions. The total number is greater than that of high-angle grain boundaries. This improves the phenomenon of a large number of high-angle grain boundaries being continuously connected in existing high-temperature alloys, which is beneficial to inhibiting the formation and propagation of cracks, alleviating intergranular embrittlement and fracture, and promoting intergranular toughening, while producing a significant ductility effect. Therefore, it is beneficial to reduce brittleness and cracking risk on a macro scale. In addition, the growth orientation of equiaxed grains is random and isotropic, while columnar grains are preferentially grown and anisotropic. Columnar grains are beneficial to reducing the connectivity of high-angle grain boundaries. At the same time, columnar grains with a relatively large average size can store high-density dislocations and undissipated distortion energy, thereby improving the thermal stability of the grains. On the one hand, the brittle cracking-resistant high-temperature alloy after the introduction of columnar grains to form a heterogeneous grain structure can maintain high-temperature strength and meet the basic requirements of high-temperature alloys; on the other hand, it makes it difficult for large-sized columnar grains to transform into equiaxed grains; on the other hand, it cooperates with equiaxed grains to enhance toughness and reduce brittleness. In summary, the brittle cracking-resistant high-temperature alloy of the present application has good mechanical strength at high temperatures from the perspective of dual improvement of grains and grain boundaries, meeting the basic requirements of high-temperature alloys, while greatly reducing brittleness and cracking risks, especially improving the brittle cracking phenomenon when used at intermediate temperatures.

[0008] In a second aspect, the present application provides a method for preparing a brittle crack resistant high temperature alloy, comprising the following steps:

[0009] The raw materials of the alloy are mixed and smelted according to a stoichiometric ratio and then subjected to a homogenization heat treatment to obtain a homogeneous alloy;

[0010] The homogeneous alloy is cold-rolled and then annealed to obtain a heterogeneous alloy;

[0011] The heterogeneous alloy is kept at different temperatures and subjected to a two-phase aging treatment to obtain a brittle crack resistant high temperature alloy.

[0012] The preparation method of the present application first melts and then performs a homogenization heat treatment, which is beneficial to the uniform distribution of components and the strengthening of the precipitate phase. Then, a large number of columnar grains are formed through cold rolling and annealing heat treatment, thereby forming an uneven heterogeneous grain structure, and suppressing the recrystallization of the columnar grains to reduce their conversion into equiaxed grains, thereby obtaining a non-homogeneous alloy. Finally, a two-phase aging treatment is performed to precipitate the precipitate phase from the matrix phase. A large number of low-angle grain boundaries and overlapping position lattice grain boundaries are introduced into the grains between the columnar grain region and the equiaxed grain region, reducing the connectivity of the high-angle grain boundaries, so that the high-temperature alloy meets the thermal stability requirements while reducing intergranular embrittlement and cracking, and improving toughness. The preparation method is process-controllable and suitable for the needs of large-scale industrial production.

[0013] On the third aspect, the present application provides the application of brittle crack resistant high-temperature alloys, which will include the brittle crack resistant high-temperature alloys of the above application or the brittle crack resistant high-temperature alloys prepared by the preparation method of the above application and applied to at least one of aircraft engines, power units, oil and gas production equipment, and gas turbines.

[0014] Since the above-mentioned brittle cracking-resistant high-temperature alloy has good high-temperature strength, it also reduces brittleness, alleviates cracking, and improves toughness, especially has excellent medium-temperature brittle cracking resistance at intermediate temperatures. Therefore, it can serve for a long time in a high-temperature environment and can be used in aerospace, power generation and other fields, especially in at least one of aircraft engines, power units, oil and gas production equipment, and gas turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 This is a schematic diagram of the main steps in the method for preparing a brittle crack resistant high-temperature alloy in Example 1 of the present application;

[0017] Figure 2 1 is a stress-strain curve diagram of the high-temperature alloy of Example 1 and Comparative Example 1 of the present application at 800° C.;

[0018] Figure 3 This is a SEM characterization image of the brittle cracking resistant high-temperature alloy of Example 1 of the present application;

[0019] Figure 4 This is an SEM characterization image of different grain regions of the embrittlement-resistant high-temperature alloy in Example 1 of the present application;

[0020] Figure 5 This is the EBSD characterization image of the brittle cracking resistant high-temperature alloy in Example 1 of the present application;

[0021] Figure 6 This is the SEM characterization image of the high-temperature alloy of Comparative Example 1. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0023] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items.

[0025] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0026] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0027] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0028] Description of terms in this application:

[0029] High-temperature alloys are a class of metal materials based on iron, nickel, or cobalt that can withstand long-term operation at temperatures above 600°C and under certain stresses, exhibiting excellent high-temperature strength. Of course, temperatures above 600°C can be further divided into different grades. For example, temperatures around 800°C are generally referred to as intermediate temperatures, or simply "medium temperature."

[0030] Low-angle grain boundary (LAGB) and high-angle grain boundary (HAGB): In materials science, the orientation angle θ = 15° is generally used as the boundary. Angles below this angle are called low-angle grain boundaries, and angles above this angle are called high-angle grain boundaries.

[0031] Therefore, terms such as high-temperature alloy, low-angle grain boundary, and high-angle grain boundary in this application are clear and accurate.

[0032] Coincident Site Lattice Grain Boundary (CSLGB): After the periodic extension of the two crystal lattices, some lattice points overlap to form a three-dimensional lattice, which is the coincident site lattice (CSL). The grain boundary of the close-packed plane or low-index plane is the coincident site lattice grain boundary (CSLGB).

[0033] Geometrically required dislocation (GND): A type of dislocation that must exist in order to maintain the continuity and lattice integrity of the crystal during plastic deformation or in the presence of grain boundaries or interfaces. It is generally a type of dislocation caused by lattice rotation and local strain gradients during the process.

[0034] While existing high-temperature alloys exhibit good strength even at high temperatures, they are often highly brittle, or have low toughness and ductility, making them prone to cracking. This is especially true when used at intermediate temperatures, where brittleness is more pronounced and cracking is more likely than at low or high temperatures. On the one hand, most high-temperature alloys are equiaxed high-entropy alloys. At intermediate temperatures, their grain boundaries often form a large amount of brittle Heusler phases, which are the preferred sites for crack initiation and propagation during plastic deformation. Especially at temperatures around 800°C, fracture along grain boundaries is highly likely to occur, leading to severe embrittlement and cracking. On the other hand, the grain boundaries formed by the equiaxed grains of high-temperature alloys are often HAGBs, and existing high-temperature alloys rarely consider the impact of grain boundary characteristics on the toughness of polycrystalline high-temperature alloys.

[0035] To solve the above technical problems, the first aspect of the embodiments of the present application provides a brittle cracking resistant high-temperature alloy, comprising a heterogeneous grain structure, wherein the heterogeneous grain structure includes a plurality of equiaxed grain regions and a plurality of columnar grain regions, wherein a single equiaxed grain region is formed by an aggregation of equiaxed grains; a single columnar grain region is formed by an aggregation of columnar grains, and the average size of the columnar grains is larger than the average size of the equiaxed grains;

[0036] The columnar grain regions and the equiaxed grain regions are spaced apart from each other, and in the grain boundaries formed between the columnar grain regions and the equiaxed grain regions, the total number of low-angle grain boundaries and coincident position lattice grain boundaries is greater than that of high-angle grain boundaries.

[0037] The brittle crack-resistant high-temperature alloy of the present application embodiment changes the equiaxed grain morphology of existing high-temperature alloys. Instead, it forms a heterogeneous grain structure with regions formed by the aggregation of columnar grains and equiaxed grains. In addition, a large number of low-angle grain boundaries and overlapping lattice grain boundaries are introduced into the grain boundaries between the two regions. The total number is greater than that of high-angle grain boundaries. This improves the phenomenon of a large number of high-angle grain boundaries being continuously connected in existing high-temperature alloys, helps to inhibit the formation and propagation of cracks, alleviates intergranular embrittlement and fracture, promotes intergranular toughening, and produces a significant ductility effect. Therefore, it is beneficial to reduce brittleness and cracking risk on a macro scale. In addition, the growth orientation of equiaxed grains is random and isotropic, while columnar grains are preferentially grown and anisotropic. Columnar grains are beneficial to reducing the connectivity of high-angle grain boundaries. At the same time, columnar grains with a relatively large average size can store a high density of dislocations and undissipated distortion energy, thereby improving the thermal stability of the grains. On the one hand, the brittle cracking-resistant high-temperature alloy after the introduction of columnar grains to form a heterogeneous grain structure can maintain high-temperature strength and meet the basic requirements of high-temperature alloys; on the other hand, it makes it difficult for large-sized columnar grains to transform into equiaxed grains; on the other hand, it cooperates with equiaxed grains to enhance toughness and reduce brittleness. In summary, the brittle cracking-resistant high-temperature alloy of the embodiment of the present application has good mechanical strength at high temperatures from the perspective of dual improvement of grains and grain boundaries, meeting the basic requirements of high-temperature alloys, while greatly reducing brittleness and cracking risks, especially improving the brittle cracking phenomenon when used at intermediate temperatures.

[0038] You can refer to Figure 3 、 Figure 4 As shown, the interspaced distribution of columnar grain regions and equiaxed grain regions facilitates the formation of a large number of grain boundaries between the columnar and equiaxed grain regions. This, combined with the high number of low-angle grain boundaries and overlapping lattice grain boundaries, further reduces intergranular embrittlement and fracture, improving the alloy's resistance to brittle cracking. In some embodiments, the total volume of the columnar grain regions is greater than that of the equiaxed grain regions. The introduction of columnar grain regions larger than the equiaxed grain regions further reduces the connectivity of high-angle grain boundaries, preventing the formation and propagation of cracks. Compared to prior art equiaxed grain high-temperature alloys, this further reduces brittleness and cracking risk while also maintaining high-temperature strength.

[0039] In some embodiments, the distribution density of geometrically required dislocations in the columnar grain region is higher than the distribution density of geometrically required dislocations in the equiaxed grain region. These high-density geometrically required dislocations in the columnar grain region are beneficial to improving thermal stability, improving the high-temperature strength of the alloy, and reducing the transformation of columnar grains into equiaxed grains, so that the columnar grain region and the equiaxed grain region can play the above-mentioned synergistic role. If the columnar grains are transformed into equiaxed grains in large quantities through recrystallization, the total number of low-angle grain boundaries and overlapping position lattice grain boundaries will continue to decrease, so that the high-angle grain boundaries will be restored to connectivity, which will greatly weaken the intergranular toughening effect. Once a crack occurs, it is very easy to propagate rapidly along the high-angle grain boundary network. In the embodiment, the distribution density of geometrically required dislocations in the columnar grain region can be 3 to 5×10 14 m 2 , optional 4×10 14 m 2 In the embodiment, the distribution density of geometrically required dislocations in the equiaxed grain region may be 3 to 5×10 13 m 2 , optional 4×10 13 m 2 , which is about one order of magnitude lower than the distribution density in the columnar grain region. These distribution densities are further beneficial to improving the thermal stability of the columnar grains.

[0040] On the basis of solving technical problems by improving both grain morphology and grain boundary characteristics, the performance can be further improved by combining the physical characteristics of the high-temperature alloy. In the embodiment, the brittle cracking resistant high-temperature alloy may include a matrix phase (parent phase, γ phase) and a precipitation phase (precipitation phase, γ' phase). The formation of a precipitation phase after saturation of the solid solution is beneficial to consuming distortion energy, reducing the driving force of recrystallization, and improving the stability of columnar grains. In the embodiment, the mass proportion of the precipitation phase in the brittle cracking resistant high-temperature alloy can be 36.4% to 40.7%, and can be optionally 38.3%. Such a high content and high distribution density of the precipitation phase is also beneficial to hindering the recombination of dislocations, producing a pinning effect on the grain boundaries, and further reducing intergranular brittleness and intergranular cracking.

[0041] In an embodiment, the matrix phase of the brittle crack resistant high-temperature alloy includes a face-centered cubic phase (FCC phase), the precipitate phase includes an L12 phase, and the precipitate phase includes an ordered precipitate phase and a discontinuous precipitate phase; wherein the ordered precipitate phase is distributed in the columnar grain region and the equiaxed grain region, and the discontinuous precipitate phase is distributed between the columnar grain region and the equiaxed grain region. Optionally, the molar percentage of the ordered precipitate phase in the columnar grain region is 36.4% to 38.8%; the molar percentage of the ordered precipitate phase in the equiaxed grain region is 36.9% to 40.7%. The distribution of the precipitate phase is conducive to further consuming distortion energy, reducing the driving force of recrystallization, and improving the thermal stability of the columnar grains; it also further hinders the recombination of dislocations, produces a pinning effect on the grain boundaries, and further reduces intergranular brittleness and intergranular cracking.

[0042] In summary, under the dual optimization of grain morphology and grain boundary characteristics, or further coordinated with the phase distribution, the brittleness of high-temperature alloys can be significantly reduced, cracking can be reduced, and toughness and tensile ductility can be improved. This solution can be applied to various types of high-temperature alloys, such as forged nickel-based high-temperature alloys, precipitation-hardened aluminum alloys, and the like. In some embodiments, the brittle cracking-resistant high-temperature alloy includes a Ni-Co-Fe-Cr-MB alloy, wherein M includes at least one of Al, Ti, Ta, and Nb. This type of alloy belongs to a high-entropy alloy system, can achieve good interface bonding of the alloy phase, and has good high-temperature strength. The introduction of the B element is beneficial to further reduce cracking. In the exemplary embodiment, M may include but is not limited to Al, Ti and Ta, Al and Ti, Al and Ta, and the like.

[0043] In some embodiments, in the Ni-Co-Fe-Cr-MB alloy, the molar ratio of Ni:Co:Fe:Cr:M:B can be (20-40):(0-30):(0-20):(0-20):(3-18):(0-3), which has good high temperature strength and belongs to a high temperature alloy. In a further embodiment, the molar ratio can be (20-40):(20-30):(10-20):(3-18):(0-3), and most alloys of these systems have good high temperature strength. In a further embodiment, M includes Al and also includes Ti and / or Ta. The general chemical formula of the alloy can be Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti x Ta 6-x B 0.1 , wherein x is 0 to 6. In the embodiment, the chemical composition can be Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti4Ta2B 0.1 .

[0044] A second aspect of the present invention provides a method for preparing a high-temperature alloy resistant to brittle cracking, comprising the following steps:

[0045] S10: mixing and melting the raw materials of the alloy according to a stoichiometric ratio and then performing a homogenization heat treatment to obtain a homogeneous alloy;

[0046] S20: cold-rolling the homogeneous alloy and then performing annealing heat treatment to obtain a heterogeneous alloy;

[0047] S30: The heterogeneous alloy is kept at different temperatures for dual-phase aging treatment to obtain a brittle crack resistant high-temperature alloy.

[0048] The preparation method of the embodiment of the present application is first smelted and then subjected to homogenization heat treatment, which is conducive to uniform distribution of components and strengthening of precipitation phase. Then, a large number of columnar grains are formed through cold rolling and annealing heat treatment, thereby forming an uneven heterogeneous grain structure, and suppressing the recrystallization of columnar grains to reduce their conversion into equiaxed grains, thereby obtaining a non-homogeneous alloy. Finally, a two-phase aging treatment is performed to precipitate the precipitation phase from the matrix phase. A large number of low-angle grain boundaries and overlapping position lattice grain boundaries are introduced into the grains between the columnar grain region and the equiaxed grain region, reducing the connectivity of high-angle grain boundaries, so that the high-temperature alloy meets the thermal stability while reducing intergranular embrittlement and cracking, and improving toughness. The preparation method is process-controllable and suitable for the needs of large-scale industrial production.

[0049] Step S10 is the step of preparing a homogeneous alloy from the raw materials. The raw materials for the alloy can refer to the element types in the above-mentioned brittle crack-resistant high-temperature alloy. In the embodiment, when the alloy is a Ni-Co-Fe-Cr-MB alloy, the raw materials for the alloy can include raw materials containing Ni, Co, Fe, Cr, M, and B, with M including at least one of Al, Ti, Ta, and Nb. The raw materials can be high-purity metal ingots or alloy ingots of each metal element, or boron. Adding boron helps provide a certain degree of plasticity during the subsequent cold rolling process at room temperature, otherwise it is prone to cracking. The raw materials are proportioned according to the stoichiometric ratio and then mixed and melted. The melting method can include, but is not limited to, arc melting. Arc melting can be used to melt the raw materials under the protection of high-purity argon. When melting the high-temperature alloy, the melting should be repeated as many times as possible to ensure that the components are melted and mixed evenly. Melting can be performed 3 to 5 times.

[0050] After smelting, it can be cast into a copper mold to form it and then subjected to homogenization heat treatment. In the embodiment, the temperature of the homogenization heat treatment can be 1100-1150°C, and the homogenization heat treatment can be optionally performed at 1150°C for 2 hours. The homogenization heat treatment keeps the components evenly distributed and is conducive to subsequent precipitation strengthening.

[0051] Step S20 involves cold rolling and annealing. The homogeneous alloy can be cooled to room temperature and then cold rolled at room temperature. In some embodiments, the cold rolling reduces the thickness of the homogeneous alloy by 65% ​​to 70%, or approximately 67%. The cold rolling process causes the grains to deform and gradually form columnar grains, accumulating distortion energy for the subsequent recrystallization process. Annealing after cold rolling can further inhibit recrystallization, reduce the transformation of columnar grains into equiaxed grains, and configure the columnar and equiaxed grains into a non-uniform, heterogeneous grain structure. In some embodiments, the annealing temperature can be 1150°C for 20 to 25 seconds. In one embodiment, the annealing can be performed at 1150°C for 20 seconds. The annealing process involves rapidly placing the cold-rolled alloy ingot into a high-temperature environment for rapid annealing. This annealing temperature is beneficial for inhibiting recrystallization. However, if the temperature is too low or too high, a large amount of recrystallization will still occur, forming equiaxed grains, reducing the toughening effect. Furthermore, the annealing duration is crucial. If the high-temperature annealing time is too long, the columnar grains will recrystallize into equiaxed grains, destroying the heterogeneous structure and resulting in a homogeneous high-temperature alloy, which is not within the technical solution of this application. Furthermore, the grain boundaries will once again become connected at high angles, significantly reducing the toughening effect.

[0052] Step S30 is a dual-phase aging treatment step, which allows the precipitation phase to precipitate in large quantities from the matrix phase, combining the aforementioned grain morphology and grain boundary characteristics to reduce intergranular brittleness. Taking the alloy raw materials as an example, including raw materials containing Ni, Co, Fe, Cr, M, and B, where M includes at least one of Al, Ti, Ta, and Nb, the dual-phase aging treatment sequentially includes a first aging treatment and a second aging treatment; wherein the first aging treatment temperature is 1000°C and the holding time is 4 hours. In some embodiments, the second aging treatment temperature is 800°C and the holding time is 12-16 hours. These parameters facilitate the large-scale precipitation of the precipitate phase from the matrix phase, particularly in the equiaxed grain region and columnar grain region, forming an ordered precipitation phase, while a large number of discontinuous precipitation phases form in the grain boundary region. The high-density nano-precipitates formed during the dual-phase aging treatment effectively hinder dislocation rearrangement and produce a pinning effect on the grain boundaries, inhibiting the subsequent recrystallization process and promoting the thermal stability of the columnar grain structure. In a demonstration, an alloy ingot can be held at 1000°C for 4 hours and 800°C for 16 hours. Dual-phase aging with these parameters effectively reduces the precipitation of brittle impurities such as the Heusler phase at grain boundaries, resulting in a higher content of the L12 phase. Further improvements in phase distribution are achieved by combining precipitation strengthening with grain morphology and grain boundary structure strengthening. The resulting high-temperature alloy exhibits excellent high-temperature strength, reduced brittleness, and mitigated cracking, particularly within the intermediate temperature range, demonstrating excellent resistance to medium-temperature embrittlement cracking.

[0053] The third aspect of the embodiments of the present application provides the application of brittle cracking resistant high-temperature alloys, which include the brittle cracking resistant high-temperature alloys of the above embodiments of the present application or the brittle cracking resistant high-temperature alloys prepared by the preparation methods of the above embodiments of the present application in at least one of aircraft engines, power units, oil and gas production equipment, and gas turbines.

[0054] Since the above-mentioned brittle cracking-resistant high-temperature alloy has good high-temperature strength, it also reduces brittleness, alleviates cracking, and improves toughness, especially has excellent medium-temperature brittle cracking resistance at intermediate temperatures. Therefore, it can serve for a long time in a high-temperature environment and can be used in aerospace, power generation and other fields, especially in at least one of aircraft engines, power units, oil and gas production equipment, and gas turbines.

[0055] In the embodiment, the brittle fracture resistant high temperature alloy can be used to manufacture jet engines, turbine blades, gas turbine blades, fuel pipes and other components and devices serving in high temperature extreme environments.

[0056] The following describes the details in conjunction with specific embodiments.

[0057] Example 1

[0058] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The chemical formula of the alloy is Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti4Ta2B 0.1 , where the numbers are the molar ratios of the elements, containing equiaxed grain regions and columnar grain regions, forming a non-uniform heterogeneous grain structure as a whole.

[0059] like Figure 1 As shown, the preparation method of the brittle crack resistant high temperature alloy includes the following steps S1 to S7:

[0060] S1: Prepare pure metal ingots of Ni, Co, Fe, Cr, Al, Ti, and Ta with a purity of 99.99 wt.% and elemental B, and mix them according to the above molar ratio;

[0061] S2: A high entropy alloy ingot is obtained by arc melting under high-purity argon protection;

[0062] S3: Casting the high entropy alloy ingot into a copper mold to form it;

[0063] S4: The alloy was homogenized at 1150° C. for 2 hours.

[0064] S5: cold rolling using a cold rolling mill to reduce its thickness by approximately 67%;

[0065] S6: The alloy is subjected to rapid annealing at 1150°C for about 20 seconds.

[0066] S7: The alloy is subjected to a dual-phase aging treatment of holding at 1000°C for 4 hours and holding at 800°C for 16 hours.

[0067] Example 2

[0068] This embodiment provides a brittle crack resistant high-temperature alloy and a preparation method thereof. The only difference from Example 1 is that the annealing time in step S6 is changed to 25 seconds, and the other steps are the same.

[0069] Example 3

[0070] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The only difference from the embodiment 1 is that the alloy is changed to the following chemical formula according to the molar ratio of elements: Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti2Ta4B 0.1 , the raw materials in step S1 are also adjusted accordingly, and the other steps are the same.

[0071] Example 4

[0072] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The only difference from the embodiment 1 is that no boron is added, and the alloy is changed to the following chemical formula according to the molar ratio of elements: Ni 30 Co 30 Fe 13 Cr 15 Al6Ti2Ta4, the raw materials in step S1 are also adjusted accordingly, and the other steps are the same.

[0073] Example 5

[0074] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The only difference from the embodiment 1 is that the alloy is changed to the following chemical formula according to the molar ratio of elements: Ni 29.9 Co 30 Fe 13 Cr 15 Al 12 B 0.1 , the raw materials in step S1 are also adjusted accordingly, and the other steps are the same.

[0075] Example 6

[0076] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The only difference from the embodiment 1 is that the alloy is changed to the following chemical formula according to the molar ratio of elements: Ni 29.9 Co 30 Fe 13 Cr 15 Ti 12 B0.1 , the raw materials in step S1 are also adjusted accordingly, and the other steps are the same.

[0077] Example 7

[0078] This embodiment provides a high-temperature alloy resistant to brittle cracking and a preparation method thereof. The only difference from the embodiment 1 is that the alloy is changed to the following chemical formula according to the molar ratio of elements: Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti6B 0.1 , the raw materials in step S1 are also adjusted accordingly, and the other steps are the same.

[0079] Comparative Example 1

[0080] This comparative example provides a high-temperature alloy and a preparation method thereof. The chemical formula of the alloy is: Ni 29.9 Co 30 Fe 13 Cr 15 Al6Ti4Ta2B 0.1 , where the numbers are the molar ratios of the elements, containing equiaxed grains and uniform distribution overall.

[0081] like Figure 1 As shown, the preparation method of the brittle crack resistant high temperature alloy includes the following steps S1 to S7

[0082] S1: Prepare pure metal ingots of Ni, Co, Fe, Cr, Al, Ti, and Ta with a purity of 99.99 wt.% and elemental B, and mix them according to the above molar ratio;

[0083] S2: A high entropy alloy ingot is obtained by arc melting under high-purity argon protection;

[0084] S3: Casting the high entropy alloy ingot into a copper mold to form it;

[0085] S4: The alloy was homogenized at 1150° C. for 2 hours.

[0086] S5: cold rolling using a cold rolling mill to reduce its thickness by approximately 67%;

[0087] S6: The alloy is subjected to a long-term annealing at 1150°C for about 150 seconds to form a homogeneous system of equiaxed grains.

[0088] S7: The alloy is subjected to a dual-phase aging treatment of holding at 1000°C for 4 hours and holding at 800°C for 16 hours.

[0089] Comparative Example 2

[0090] This comparative example provides a high-temperature alloy and a preparation method thereof. The only difference from Example 1 is that in step S6, the annealing temperature is changed to 1300° C., and the other steps are the same. It is found that a homogeneous system of equiaxed grains is also formed.

[0091] Comparative Example 3

[0092] This comparative example provides a high-temperature alloy and a preparation method thereof. The only difference from Example 1 is that in step S6, the annealing temperature is changed to 900° C., and the other steps are the same. It is found that a homogeneous system of equiaxed grains is also formed.

[0093] Related performance tests and result analysis

[0094] The high temperature alloys of Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to tensile tests at 800°C to obtain stress-strain diagrams. Figure 2 It can be seen that the high-temperature alloy of the heterogeneous structure of Example 1 has a tensile elongation of about 20%, high toughness, and is not easy to crack. Similarly, Examples 2 to 6 also have similar tensile elongation and are not easy to crack. Figure 2 The high-temperature alloy with a homogeneous structure in Comparative Example 1 has almost no tensile elongation, is very brittle, and is easily cracked after stretching. The results of Comparative Examples 2 and 3 are similar.

[0095] The high temperature alloys of Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to scanning electron microscopy and electron backscatter diffraction tests to obtain SEM and EBSD images. The SEM image of Example 1 is shown in FIG. Figure 3 As shown, the SEM schematic diagram of the different crystal regions and the formed grain boundaries of the heterogeneous grain structure of Example 1 is shown in FIG. Figure 4 As shown in the figure, it can be seen that the anti-brittle cracking high-temperature alloy of Example 1 forms a columnar grain region and an equiaxed grain region, forming a heterogeneous structure. Figure 5 Further analysis, such as by EBSD, shows that the grain boundaries of Example 1 contain a large number of low-angle grain boundaries and overlapping lattice grain boundaries. The test results of Examples 2 to 6 are similar. The SEM image of Comparative Example 1, shown in Figure 6, shows a homogeneous structure of equiaxed grains containing a large number of interconnected high-angle grain boundaries. The test results of Comparative Examples 2 and 3 are similar.

[0096] In addition to the above-mentioned tests on the prepared alloys, the following conclusions can be drawn by further combining relevant tests during the preparation method and means such as atomic probe tomography (APT). In the cold rolling treatment of step S5 of the preparation method of Example 1, various crystal defects such as dislocations and stacking defects accumulate a large amount of distortion energy. Subsequent recrystallization occurs preferentially at locations with a higher dislocation density, such as grain boundaries, while areas with relatively low defect density still do not undergo recrystallization during the transient annealing at 1150°C in step S6. The areas where no recrystallization occurs promote ordered precipitation in the subsequent dual-phase aging treatment in step S7. On the one hand, the stored distortion energy reduces the activation energy barrier of the disordered phase transition and provides additional nucleation sites; on the other hand, dislocations act as conduit diffusion channels, accelerating the diffusion of elements for particle growth.

[0097] In this way, the ordered phase precipitates rapidly in step S7, thereby reducing the distortion energy stored in the non-recrystallized region, thereby reducing the driving force and increasing the critical nucleus size for recrystallization. In addition to reducing the driving force for recrystallization, the ordered precipitated phase exerts a pinning force on grain boundary migration, which also inhibits recrystallization. The pinning effect from the columnar grains increases the critical size for nucleation, resulting in delayed recrystallization. The dual-phase aging treatment in step S7 further increases the density of the precipitated phase and the associated pinning effect. The high-density precipitated phase effectively hinders dislocation rearrangement and has a pinning effect on the grain boundaries, which creates an additional barrier to grain boundary migration and recrystallization, further reducing intergranular embrittlement, reducing intergranular cracking, and improving toughness.

[0098] Therefore, the stored distortion energy is dissipated by thermally activated dislocations and rearrangements at 800°C in the dual-phase aging treatment of step S7, and even up to 70% of the total distortion energy can be consumed. Distortion energy is the driving force for recrystallization, and such consumption helps to reduce recrystallization and stabilize the heterogeneous columnar grain structure. Therefore, the high-density ordered precipitates effectively inhibit the recrystallization process at 800°C, and these retained heterogeneous columnar grain structures significantly alleviate the intergranular brittleness at medium temperature. In step S7, it was also observed that Ni, Al, and Ti elements are concentrated in the ordered precipitates to form the L12 phase, while the contents of Co, Fe, and Cr are relatively low in the ordered precipitates. It was also observed that the distribution density of geometrically required dislocations in the columnar grain region is approximately 4×10 14 m 2 , which is significantly higher than the distribution density in the equiaxed grain region of about 4×10 13 m 2 , about 1 order of magnitude higher.

[0099] Through detailed EBSD and other analyses, it was found that in comparative example 1, due to the long annealing heat treatment time in step S6, a nearly completely recrystallized microstructure was observed during the subsequent annealing at 800°C for only 30 minutes in step S7, forming a homogeneous structure with a large number of high-angle grain boundary interconnected networks at the grain boundaries, which was particularly fragile when cracks were generated and propagated.

[0100] In contrast, further testing showed that in Example 1, due to the very short annealing heat treatment time in step S6, the columnar crystal regions in the heterogeneous structure did not recrystallize even after annealing at 800°C for 120 hours in step S7. Subsequently, even under long-term medium-temperature heat exposure, the retained heterogeneous columnar grain structure showed excellent resistance to intermediate-temperature embrittlement, and the test results of the high-temperature alloys of Examples 2 to 6 were similar. This illustrates the feasibility of improving resistance to intermediate-temperature embrittlement by regulating grain boundary characteristics and distribution. By introducing large-sized columnar grain regions and introducing a large number of low-angle grain boundaries and overlapping position lattice grain boundaries into the grain boundaries between the equiaxed grain regions, the interconnected network of high-angle grain boundaries is destroyed, resulting in good resistance to crack generation and expansion, providing intergranular toughening effects, and thus obtaining excellent tensile ductility at medium temperatures.

[0101] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A brittle crack resistant high temperature alloy, characterized in that: The heterogeneous grain structure includes a plurality of equiaxed grain regions and a plurality of columnar grain regions, wherein a single equiaxed grain region is formed by an aggregation of equiaxed grains, a single columnar grain region is formed by an aggregation of columnar grains, and an average size of the columnar grains is larger than an average size of the equiaxed grains; The columnar grain regions and the equiaxed grain regions are spaced apart from each other, and in the formed grain boundaries, the total number of low-angle grain boundaries and overlapping position lattice grain boundaries is greater than that of high-angle grain boundaries.

2. The embrittlement-resistant high-temperature alloy according to claim 1, characterized in that: The total volume of the columnar grain region is greater than the total volume of the equiaxed grain region; And / or, the distribution density of geometrically required dislocations in the columnar grain region is higher than the distribution density of geometrically required dislocations in the equiaxed grain region.

3. The embrittlement-resistant high-temperature alloy according to claim 1 or 2, characterized in that: The distribution density of geometrically necessary dislocations in the columnar grain region is 3 to 5×10 14 m 2 ; And / or, the distribution density of geometrically required dislocations in the equiaxed grain region is 3 to 5×10 13 m 2 .

4. The embrittlement-resistant high-temperature alloy according to claim 1 or 2, characterized in that: The matrix phase of the brittle crack resistant high-temperature alloy includes a face-centered cubic phase, the precipitation phase includes an L12 phase, and the precipitation phase includes an ordered precipitation phase and a discontinuous precipitation phase; wherein the ordered precipitation phase is distributed in the columnar grain region and the equiaxed grain region, and the discontinuous precipitation phase is distributed between the columnar grain region and the equiaxed grain region.

5. The embrittlement-resistant high-temperature alloy according to claim 4, characterized in that: The molar percentage of the ordered precipitated phase in the columnar grain region is 36.4% to 38.8%; The molar percentage of the ordered precipitated phase in the equiaxed grain region is 36.9% to 40.7%.

6. The embrittlement-resistant high-temperature alloy according to any one of claims 1, 2, and 5, characterized in that: It includes a Ni-Co-Fe-Cr-MB alloy, wherein M includes at least one of Al, Ti, Ta, and Nb, and the molar ratio of Ni:Co:Fe:Cr:M:B is (20-40):(0-30):(0-20):(0-20):(3-18):(0-3).

7. A method for preparing a brittle crack resistant high temperature alloy, characterized in that: The steps include: The raw materials of the alloy are mixed and smelted according to a stoichiometric ratio and then subjected to a homogenization heat treatment to obtain a homogeneous alloy; cold-rolling the homogeneous alloy and then performing annealing heat treatment to obtain a heterogeneous alloy; The heterogeneous alloy is kept at different temperatures and subjected to a dual-phase aging treatment to obtain a brittle crack resistant high-temperature alloy.

8. The method for preparing the embrittlement-resistant high-temperature alloy according to claim 7, characterized in that: The raw materials of the alloy include raw materials containing Ni, Co, Fe, Cr, M, and B, M includes at least one of Al, Ti, Ta, and Nb, and the dual-phase aging treatment includes a first aging treatment and a second aging treatment in sequence; The temperature of the first aging treatment is 1000°C and the holding time is 4 hours; And / or, the temperature of the second aging treatment is 800° C., and the holding time is 12 to 16 hours.

9. The method for preparing the embrittlement-resistant high-temperature alloy according to claim 7 or 8, characterized in that: The temperature of the homogenization heat treatment is 1100-1150°C; and / or, the cold rolling treatment reduces the thickness of the homogeneous alloy by 65% ​​to 70%; And / or, the annealing heat treatment is performed at a temperature of 1150° C. for a duration of 20 to 25 seconds.

10. Application of brittle crack resistant high temperature alloy, characterized by: The brittle crack resistant high-temperature alloy according to any one of claims 1 to 6 or the brittle crack resistant high-temperature alloy prepared by the preparation method according to any one of claims 7 to 9 is applied to at least one of an aircraft engine, a power unit, oil and gas production equipment, and a gas turbine.

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