Co-cr-ni-ti-w based high-entropy alloy powder, preparation and cobalt-based high-temperature alloy repairing method

Abstract

The application discloses a Co-Cr-Ni-Ti-W system high-entropy alloy powder, a preparation method and a cobalt-based high-temperature alloy repairing method, relates to the alloy repairing field, and the high-entropy alloy powder is composed of Co, Cr, Ni, Ti, W, Al, Ta, Mo, Zr and Sc elements. The application realizes the inhibiting effect on the alloy melting point by adjusting the content of the five elements Co, Cr, Ni, Ti and W, replaces the design idea of using the traditional high-concentration B and Si as the melting-reducing element, avoids the formation of the harmful B-rich and Si-rich phases in the shape and property remodeling area, and obtains the shape and property remodeling area with a compact structure, good interface connection, high gamma volume fraction, excellent morphology and good stability.

Description

Technical Field

[0001] This invention relates to the field of alloy repair, and in particular to a Co-Cr-Ni-Ti-W system high-entropy alloy powder, its preparation, and a method for repairing cobalt-based high-temperature alloys. Background Technology

[0002] Cobalt-based superalloys exhibit superior resistance to thermal fatigue, hot corrosion, and oxidation compared to nickel-based superalloys. However, traditional cobalt-based superalloys are primarily strengthened by carbide precipitation, resulting in significantly lower high-temperature strength compared to nickel-based superalloys strengthened by the γ' phase, thus limiting their application range.

[0003] In 2006, Japanese scholars Sato et al. designed and developed a new type of cobalt-based superalloy strengthened by the precipitation of γ'-Co3(Al,W) phase. Its polycrystalline alloy has creep performance comparable to that of nickel-based polycrystalline alloy IN100 at 900℃, and at the same time has excellent hot working performance, bringing new ideas to the development of γ' phase strengthened cobalt-based superalloys with L12 crystal structure.

[0004] In recent years, researchers have conducted extensive research on cobalt-based superalloys. By adding alloying elements, they have continuously improved the dissolution temperature, volume fraction, and phase stability of the γ' phase, and developed a variety of high-performance γ' phase-strengthened cobalt-based superalloys, such as those reported in patents CN108315600B, CN108385010B, CN109576534B, CN102443721B, CN106435282B, CN109321786B, CN115161517B, and CN113699414B. These alloys can be used to manufacture next-generation heavy-duty gas turbine blades with higher temperature resistance.

[0005] Similar to nickel-based superalloy turbine blades, cobalt-based superalloy hot components operate under extreme conditions such as high temperature, high pressure, high stress, and hot corrosion for extended periods. Inevitably, the substrate surface of these components suffers damage, such as cracks and material reduction. In the field of reshaping high-temperature hot components for heavy-duty gas turbines, powder metallurgy is a commonly used substrate repair method. It enables batch repair of complex, irregularly shaped high-temperature components, offering advantages such as high efficiency and low cost. Existing powder metallurgy repair materials for cobalt-based superalloys primarily involve adding high concentrations of melting point-inhibiting elements B and Si, such as commercial materials AMDRY788 and AMS4783, and the patent CN109909641B. This leads to the formation of large amounts of low-melting-point brittle phases containing boron and silicon in the repair zone, resulting in deterioration of the joint's high-temperature performance. Therefore, it is necessary to develop new cobalt-based superalloy repair materials with better high-temperature performance to address the repair challenges of cobalt-based superalloys strengthened by γ'-Co3(Al,W) phase precipitation. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by providing a Co-Cr-Ni-Ti-W system high-entropy alloy powder, its preparation, and a method for repairing cobalt-based high-temperature alloys. By adjusting the content of five elements—Co, Cr, Ni, Ti, and W—the melting point of the alloy is suppressed, replacing the traditional design approach of using high concentrations of B and Si as melting point reducing elements. This avoids the formation of harmful B- and Si-rich phases in the shape-remodeling zone, resulting in a dense structure, good interface connectivity, high γ' volume fraction, excellent morphology, and good stability in the shape-remodeling zone.

[0007] The technical solution adopted in this invention is as follows: a high-entropy alloy powder based on the Co-Cr-Ni-Ti-W system, characterized in that it comprises the following elements in a mass percentage ratio:

[0008] Cr (14.2%-20.3%), Ni (15.5%-22.5%), Ti (12.3%-18.7%), W (6.2%-8.3%), Al (1.1%-1.9%), Ta (2.2%-3.8%), Mo (0.5%-1.5%), Zr (0.01%-0.5%), Sc (0.01-0.05%), with the remainder being Co and / or unavoidable impurity elements.

[0009] in:

[0010] Cr dissolves in the γ matrix phase, providing solid solution strengthening, and is also a forming element of the Cr2O3 oxide film. Appropriate addition can effectively improve the oxidation resistance and hot corrosion resistance of the remodeling zone. Simultaneously, it can combine with C to form M... 23 C6, M3C2 and M7C3 carbides play a precipitation strengthening role in the substrate, but adding too much Cr promotes the precipitation of harmful TCP phase. Therefore, the present invention limits the Cr content to the range of 14.2wt% to 20.3wt%.

[0011] Ni is infinitely miscible with Co-based solid solutions, which can increase the width of the γ / γ' two-phase region. In this invention, the content of Ni is limited to the range of 15.5wt% to 25.5wt% in order to improve the stability of the γ matrix face-centered hexagonal structure.

[0012] Al is a γ' phase-forming element in cobalt-based superalloys, and its addition directly affects the precipitation amount of the γ' precipitation strengthening phase. A high volume ratio of γ' phase precipitated in the γ matrix significantly improves the high-temperature creep resistance of the reshaped zone. Additionally, Al is a dense oxide layer forming element (Al₂O₃), and appropriate addition can effectively improve the oxidation resistance of the reshaped zone; however, excessive addition leads to a sharp increase in the alloy's melting point. Therefore, this invention limits the Al content to the range of 1.1 wt% to 1.9 wt%. However, this does not mean that the final Al content in the reshaped zone will be lower than that in the substrate. It is important to emphasize that the activator in this invention is used in conjunction with a curing agent in practical applications, and any missing Al can be supplemented by the curing agent used in conjunction with it.

[0013] W is the element that forms the γ' phase in cobalt-based superalloys. In this invention, the content of W is limited to the range of 6.2wt% to 8.3wt%, which can increase the volume fraction of the γ' phase while increasing the dissolution temperature of the γ' phase, suppressing the coarsening of the γ' phase, and the large atomic radius has a significant effect on the solid solution strengthening of the γ phase.

[0014] Ti is a γ' phase strengthening element and also a major melting point suppressing element in this invention. Therefore, the Ti content is limited to the range of 12.3 wt% to 18.7 wt%.

[0015] Ta is a strengthening element for the γ' phase. Limiting the Ta content to the range of 2.2 wt% to 3.8 wt% can improve the stability of the γ' phase.

[0016] Mo is a solid solution strengthening element of the γ phase. When dissolved in the matrix, it causes significant lattice expansion, increases the long-range elastic stress field, thereby hindering dislocation movement and reducing the elastic stress field. In this invention, the content of Mo is limited to the range of 0.5wt% to 1.5wt%, which can significantly improve the various mechanical properties of the shape-remodeling zone and also avoid the fact that the addition of Mo will promote the precipitation of harmful secondary phases.

[0017] Zr and Sc are grain boundary strengthening elements, and their addition in trace amounts can purify grain boundaries. Furthermore, limiting the Zr content to 0.01 wt% to 0.5 wt% and the Sc content to 0.01 wt% to 0.05 wt% in the alloy composition of this invention can improve the fluidity of the liquid phase generated after powder melting, improve the wettability of the liquid phase on the surface of the curing agent powder, increase the density of the shape-remodeling zone, and ensure the processability of the alloy powder of this invention.

[0018] Furthermore, the particle size of the high-entropy alloy powder is 30μm-56μm. The powder sizes in this target particle size range are close, which can achieve near-isothermal melting during the heat preservation stage. This is beneficial for the liquid phase to fill the gaps between the curing agent powder and the substrate interface and between the curing agent powders in a volume-maximized manner, thereby improving the microstructure density of the shape reshaping zone.

[0019] Furthermore, the melting temperature range of this high-entropy alloy powder is 1185℃-1220℃, ensuring that it can be completely melted into a liquid state as a brazing filler during the metallurgical heat preservation process in the shape repair of cobalt-based high-temperature alloys. This liquid state fills the gaps between the curing agent and the substrate through capillary action, and the liquid phase diffuses with the interdiffusion of elements between the curing agent and the liquid phase.

[0020] A preparation method for the aforementioned Co-Cr-Ni-Ti-W system high-entropy alloy powder includes the following steps:

[0021] S1: Material preparation; Prepare elemental metals or intermediate alloys containing relevant elements according to the element ratio;

[0022] S2: Melting; The materials prepared in step S1 are placed in a vacuum environment and / or an Ar protective atmosphere for alloy melting;

[0023] S3: Powder preparation; The alloy produced after melting in step S2 is prepared into alloy powder;

[0024] S4: Screening; Alloy powder with a particle size range of 30μm-56μm is screened out to complete the preparation.

[0025] A method for repairing cobalt-based superalloys, utilizing the aforementioned Co-Cr-Ni-Ti-W system high-entropy alloy powder, includes the following steps:

[0026] S1: Preparation of high-entropy alloy powder; the Co-Cr-Ni-Ti-W system high-entropy alloy powder is prepared using the preparation method described above;

[0027] S2: Preparation of shaping paste; mix high-entropy alloy powder, curing agent powder and binder in proportion to make a paste-like shaping paste;

[0028] S3: Polishing and cleaning; Polishing and cleaning defects on cobalt-based superalloys;

[0029] S4: Defect shape reshaping; The shaping paste prepared in step S2 is filled into the cobalt-based high-temperature alloy that has been polished and cleaned in step S3, and then placed in a vacuum for metallurgical heat preservation. After the heat preservation is completed, it is cooled with the furnace and then heat-treated to complete the defect shape reshaping.

[0030] Further, in step S2, the plastic paste is prepared by mixing 3 parts high-entropy alloy powder, 6 parts curing agent powder and 1 part binder powder according to the mass ratio.

[0031] Further, in step S2, the nominal chemical composition of the curing agent powder is: Cr (6.0 wt%), W (13.0 wt%), Al (7.0 wt%), Ta (3.0 wt%), C (0.2 wt%), with the remainder being Co and / or unavoidable impurity elements; the binder is NICROBRAZ S-BINDR type commercial adhesive.

[0032] Furthermore, in step S3, the device should be ultrasonically cleaned in an alcohol or acetone solution for a sufficient time during cleaning.

[0033] Furthermore, in step S4, the vacuum degree of the vacuum environment for metallurgical insulation is better than 1×10-3 Pa.

[0034] Furthermore, in step S4, the metallurgical insulation temperature is 1230℃-1250℃, and the insulation time is 60min-120min.

[0035] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0036] 1. This invention achieves the inhibition of the melting point of the high-entropy alloy powder by adjusting the content of five main components of high-temperature alloys: Co, Cr, Ni, Ti, and W. This effect is similar to that of traditional melting point reducing elements B and Si, avoiding the formation of large blocks of harmful brittle phases such as B-rich and Si-rich phases in the shape reshaping zone, and effectively improving the high-temperature tensile properties of the repair joint.

[0037] 2. The high-entropy alloy powder of this invention is designed based on the high-entropy alloying theory. It contains a high concentration of Cr, Ni, Ti, and W elements and a low content of Al elements. However, when combined with the curing agent powder provided by this invention, the element concentration of the entire shape reshaping zone can reach the design requirements. Through the metallurgical heat preservation stage and subsequent heat treatment, element interdiffusion promotes the uniform precipitation of the γ' strengthening phase in the obtained shape reshaping zone, which can significantly improve the high-temperature creep performance of the repair joint. Attached Figure Description

[0038] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0039] Figure 1 The microstructure of the DFB-C1 alloy powder disclosed in this invention is shown.

[0040] Figure 2 The macroscopic microstructure of the shape-remodeling zone of the DF-ZNB alloy substrate;

[0041] Figure 3 This is the microstructure of the shape-remodeling zone of the DF-ZNB alloy substrate. Detailed Implementation

[0042] All features disclosed in this specification, or steps in all methods or processes disclosed herein, may be combined in any way, except for mutually exclusive features and / or steps.

[0043] Any feature disclosed in this specification, unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is merely one example of a series of equivalent or similar features.

[0044] Example 1

[0045] like Figure 1 As shown, a high-entropy alloy powder based on the Co-Cr-Ni-Ti-W system, formulated by mass percentage, includes the following elements:

[0046] Cr (14.2%-20.3%), Ni (15.5%-22.5%), Ti (12.3%-18.7%), W (6.2%-8.3%), Al (1.1%-1.9%), Ta (2.2%-3.8%), Mo (0.5%-1.5%), Zr (0.01%-0.5%), Sc (0.01-0.05%), with the remainder being Co and / or unavoidable impurity elements.

[0047] Furthermore, the particle size of the high-entropy alloy powder is 30μm-56μm.

[0048] Furthermore, the melting temperature range of this high-entropy alloy powder is 1185℃-1220℃.

[0049] To further illustrate and explain the technical solution of the present invention, the following non-limiting embodiments are provided. Table 1 shows the embodiments and comparative examples of this embodiment. Comparative example 1 is a commercially available repair material with the grade AMDRY788, comparative example 2 is a commercially available repair material with the grade AMS4783, and comparative example 3 is the alloy composition reported in patent CN109909641B. All element content data below are mass percentage data.

[0050] Table 1. Implementation methods and comparative examples of this embodiment

[0051]

[0052] Compared with Comparative Examples 1-3, Embodiments 1-3 in this example have the following advantages:

[0053] Comparative Examples 1-3 used high concentrations of highly diffusible elements B and Si as melting point inhibitors. The shape-remodeling regions obtained with such materials inevitably generated brittle phases such as borides, silicides, and low-melting-point eutectic phases, significantly deteriorating the mechanical properties of the joint. In contrast to Comparative Examples 1-3, Embodiments 1-3 of this example do not use B and Si as melting point inhibitors, fundamentally avoiding the formation of harmful B- and Si-rich phases.

[0054] like Figure 1 The microstructure of the high-entropy alloy powder prepared with the composition of Embodiment 1 in Table 1 is shown in this embodiment. For the convenience of the following description, the high-entropy alloy powder prepared with the composition of Embodiment 1 in Table 1 is designated as DFB-C1 alloy powder.

[0055] Example 2

[0056] A preparation method for preparing the Co-Cr-Ni-Ti-W system high-entropy alloy powder described in Example 1 includes the following steps:

[0057] S1: Material preparation; Prepare elemental metals or intermediate alloys containing Co, Cr, Ni, Ti, W, Al, Ta, Zr and Sc according to the elemental ratio; in this embodiment, high-purity elemental metals are preferred to avoid introducing too many impurities.

[0058] S2: Melting; The elemental metal prepared in step S1 is placed in a vacuum environment and / or an Ar protective atmosphere for alloy melting; In this embodiment, the vacuum environment is provided by a vacuum arc melting furnace, and the elemental metal is melted in a high-purity Ar protective atmosphere to prevent the elemental metal from being oxidized or reacting with other gases during the melting process; After all the metals are fully liquefied, the power is turned off, the liquid phase solidifies, and the above actions are repeated 8 times to ensure a high degree of melting and mixing, and to obtain a high-entropy alloy ingot with uniform composition (i.e., a cobalt-based high-temperature alloy ingot).

[0059] S3: Powder making; The high-entropy alloy ingot generated after melting in step S2 is made into alloy powder; Specifically, the cobalt-based high-temperature alloy ingot generated in step S2 is a consumable electrode. Its end face is heated by an electric arc and melted into a liquid phase. Through the centrifugal force of the high-speed rotation of the electrode, the liquid is thrown out and crushed into fine droplets, which are then condensed to obtain high-entropy alloy powder (cobalt-based high-temperature alloy powder) with good sphericity and low hollowness.

[0060] S4: Screening; The high-entropy alloy powder obtained in step S3 is screened to separate alloy powder with a particle size range of 30μm-56μm to complete the preparation; The powder size in this target particle size range is close, which can achieve near-isothermal melting in the heat preservation stage, which is conducive to the liquid phase filling the gaps between the curing agent powder and the substrate interface and between the curing agent powders in a volume-maximized form, thereby improving the microstructure density of the shape reshaping zone.

[0061] Example 3

[0062] A method for repairing cobalt-based superalloys, taking the additive repair of defects in DF-ZNB alloy using the DFB-C1 alloy powder described in Example 1 as an example, wherein the DF-ZNB alloy is a γ'-Co3(Al,W) precipitation-strengthened cobalt-based superalloy used in heavy-duty gas turbine blades, with Al ≥ 5wt% and Al + W ≥ 17wt%; includes the following steps:

[0063] S1: Preparation of high-entropy alloy powder; DFB-C1 alloy powder was prepared using the preparation method described in Example 2;

[0064] S2: Preparation of shaping paste; Mix 3 parts DFB-C1 alloy powder, 6 parts curing agent powder and 1 part binder to make a paste-like shaping paste. The paste-like shaping paste has poor fluidity and does not flow easily after filling defects on the cobalt-based superalloy, ensuring stable filling; Moreover, the poor fluidity of the paste-like shaping paste does not mean that it will not flow. Its fluidity properties are sufficient to fill defects on the cobalt-based superalloy and meet the requirements for filling irregularly shaped defects.

[0065] Further, in step S2, the curing agent powder is prepared by ultra-high speed plasma rotating electrode method, with a particle size of 75μm-150μm and a nominal chemical composition of: Cr (6.0wt%), W (13.0wt%), Al (7.0wt%), Ta (3.0wt%), C (0.2wt%), and the remainder being Co and / or unavoidable impurity elements; the binder selected is NICROBRAZ S-BINDR type commercial adhesive.

[0066] S3: Grinding and cleaning; Use a carbide steel drill bit to grind out defects with a length, width and height of 30mm, 2mm and 5mm respectively on the surface of the DF-ZNB alloy (cobalt-based high-temperature alloy) substrate, and place it in an alcohol solution or acetone solution for ultrasonic cleaning for 60 minutes, then take it out and dry it for later use.

[0067] It should be noted that alcohol or acetone solutions can completely dissolve organic matter adhering to the DF-ZNB alloy (cobalt-based high-temperature alloy) substrate, and are easily volatile, leaving no residue. This effectively prevents the repaired area from being affected by organic matter or other impurities, thus ensuring the repair quality. Ultrasonic cleaning achieves cleaning through ultrasonic frequency vibration, resulting in excellent cleaning performance.

[0068] S4: Defect Shape Reshaping; The shaping paste prepared in step S2 is filled into the defects of the DF-ZNB alloy substrate that has been polished and cleaned in step S3, and then placed in a vacuum for metallurgical heat preservation. The vacuum environment can be provided by a vacuum furnace, and the vacuum degree of the provided vacuum environment is better than 1×10 -3Pa; The furnace is kept at 1250℃ for 120 minutes. After the holding period, the furnace is cooled and then heat-treated to complete the reshaping of the defect shape.

[0069] In step S4, heat treatment can restore the performance of the repaired area.

[0070] Furthermore, in step S4, as the temperature of the vacuum furnace gradually increases, the adhesive will completely evaporate before the DFB-C1 alloy powder melts, and the fluidity of the DFB-C1 alloy powder and the curing agent powder gradually increases. Thus, the DFB-C1 alloy powder and the curing powder can completely fill the defects in the DF-ZNB alloy substrate. The complete evaporation of the adhesive can avoid the introduction of adhesive components into the repair area, ensuring the quality of the repair area.

[0071] Furthermore, in step S4, the high-entropy alloy powder is used as a brazing filler metal. It melts during the metallurgical heat preservation stage. The generated liquid phase fills the gap between the curing agent and the substrate through capillary action. As the elements between the liquid phase and the curing agent diffuse into each other, the liquid phase composition changes, the melting point increases, and isothermal solidification occurs.

[0072] After examining the shape-remodeling zone of the DF-ZNB alloy substrate, such as... Figure 2 As shown, the remodeling zone exhibits dense tissue and well-connected interfaces; Figure 3 As shown, the γ' strengthening phase in the shape-remodeling region has excellent morphology and a high volume fraction.

[0073] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A high-entropy alloy powder based on the Co-Cr-Ni-Ti-W system, characterized in that: Formulated by weight percentage, including the following elements: Cr (14.2%-20.3%), Ni (15.5%-22.5%), Ti (12.3%-18.7%), W (6.2%-8.3%), Al (1.1%-1.9%), Ta (2.2%-3.8%), Mo (0.5%-1.5%), Zr (0.01%-0.5%), Sc (0.01-0.05%), with the remainder being Co and unavoidable impurity elements.

2. The high-entropy alloy powder according to claim 1, characterized in that: The particle size of this high-entropy alloy powder is 30μm-56μm.

3. The high-entropy alloy powder according to claim 1, characterized in that: The melting temperature range of this high-entropy alloy powder is 1185℃-1220℃.

4. A preparation method for preparing the Co-Cr-Ni-Ti-W system high-entropy alloy powder according to any one of claims 1-3, characterized in that: Includes the following steps: S1: Material preparation; Prepare elemental metals or intermediate alloys containing relevant elements according to the element ratio; S2: Melting; The materials prepared in step S1 are placed in a vacuum environment and / or an Ar protective atmosphere for alloy melting; S3: Powder preparation; The alloy produced after melting in step S2 is prepared into alloy powder; S4: Screening; Alloy powder with a particle size range of 30μm-56μm is screened out to complete the preparation.

5. A method for repairing cobalt-based superalloys, using the high-entropy alloy powder of the Co-Cr-Ni-Ti-W system as described in any one of claims 1-3, characterized in that: Includes the following steps: S1: Prepare high-entropy alloy powder; Prepare the Co-Cr-Ni-Ti-W system high-entropy alloy powder using the preparation method described in claim 4; S2: Preparation of shaping paste; mix high-entropy alloy powder, curing agent powder and binder in proportion to make a paste-like shaping paste; S3: Polishing and cleaning; Polishing and cleaning defects on cobalt-based superalloys; S4: Defect shape reshaping; The shaping paste prepared in step S2 is filled into the cobalt-based high-temperature alloy that has been polished and cleaned in step S3, and then placed in a vacuum for metallurgical heat preservation. After the heat preservation is completed, it is cooled with the furnace and then heat-treated to complete the defect shape reshaping.

6. The method for repairing cobalt-based superalloys according to claim 5, characterized in that: In step S2, the plastic paste is prepared by mixing 3 parts high-entropy alloy powder, 6 parts curing agent powder and 1 part binder powder according to the mass ratio.

7. The method for repairing cobalt-based superalloys according to claim 5 or 6, characterized in that: In step S2, the nominal chemical composition of the curing agent powder is: Cr (6.0 wt%), W (13.0 wt%), Al (7.0 wt%), Ta (3.0 wt%), C (0.2 wt%), with the remainder being Co and unavoidable impurity elements; the binder is NICROBRAZ S-BINDR type commercial adhesive.

8. The method for repairing cobalt-based superalloys according to claim 5, characterized in that: In step S3, the device should be ultrasonically cleaned in an alcohol or acetone solution for a sufficient time.

9. The method for repairing cobalt-based superalloys according to claim 5, characterized in that: In step S4, the vacuum level of the vacuum environment for metallurgical insulation is better than 1×10-3 Pa.

10. The method for repairing cobalt-based superalloys according to claim 5, characterized in that: In step S4, the metallurgical insulation temperature is 1230℃-1250℃, and the insulation time is 60min-120min.

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