A repair paste of cobalt-based superalloy and a preparation method and a repair method thereof

Abstract

The application discloses a kind of cobalt-based superalloy repair paste and its preparation method, repair method, it is related to cobalt-based superalloy repair field, according to mass percentage ratio, the repair paste is mechanically mixed by 30-40% activating agent, 5-10% stabilizer, 50-60% solidifying agent and 5-10% bonding agent, wherein the composition elements of activating agent have Cr, N i, W, Ta, Re, B, Y, the rest is Co and inevitable impurity element;The composition elements of stabilizer have Cr, W, N i, Mo, and the rest is Co and inevitable impurity element;Repair method includes coating repair paste, metallurgical heat preservation and performance recovery heat treatment, repair shape.The application can be used for the shape of cobalt-based superalloy hot part and nature remodeling, the obtained repair area is not generated brittle harmful phase such as large boride and boron-rich eutectic phase, joint high-temperature strength is high, effectively solve the problem of cobalt-based superalloy hot part additive repair.

Description

Technical Field

[0001] This invention relates to the field of cobalt-based superalloy repair, and in particular to a repair paste for cobalt-based superalloys and its repair method. Background Technology

[0002] Cobalt-based superalloys are a class of alloys with cobalt as the main component, containing significant amounts of nickel, chromium, and tungsten, and small amounts of molybdenum, niobium, tantalum, titanium, and carbon. At high temperatures, they exhibit superior resistance to hot corrosion, high strength, and excellent thermal fatigue resistance compared to nickel-based superalloys, making them highly suitable for manufacturing high-temperature components such as turbine blades and burner nozzles for aero-engines, industrial gas turbines, and marine gas turbines. Due to their long-term operation in ultra-high temperature environments and under extremely complex stress conditions, these high-temperature components are highly susceptible to structural integrity failures such as ablation, material reduction, and cracking. Repairing damaged areas using appropriate and effective methods can significantly extend the service life of components and reduce the unit's operation and maintenance costs.

[0003] For cobalt-based superalloy thermal components with complex shapes and multiple thin-walled structures (such as turbine blades), the flexible powder metallurgy repair technology can effectively repair damage defects. Traditional repair materials consist of a combination of a low-melting-point alloy powder and a high-melting-point alloy powder. At high temperatures, the low-melting-point alloy powder melts to form a liquid phase, which wets and fills the gap between the substrate and the high-melting-point alloy powder, and undergoes isothermal solidification to form a metallurgical bonding joint.

[0004] Low-melting-point alloy powders typically contain high concentrations of active elements Si and B, such as commercial grades AMDRY788 (Co-21Ni-22Cr-14W-2Si-2B) and AMS4783 (Co-17Ni-19Cr-4W-8Si-0.8B), to suppress the melting point of the alloy. However, due to the introduction of high concentrations of Si and B, the repaired joint contains a large amount of bulk borides, silicides, and brittle phases such as low-melting-point B- and Si-rich eutectic compounds, resulting in poor high-temperature mechanical properties and limited application scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a repair paste and repair method for cobalt-based superalloys, which can be used for the shape and structural reshaping of cobalt-based superalloy hot parts. The repaired area is free from the formation of brittle and harmful phases such as large borides and boron-rich eutectic phases, and the joint has high high-temperature strength, effectively solving the problem of additive repair of cobalt-based superalloy hot parts.

[0006] The technical solution adopted in this invention is as follows: A repair paste for cobalt-based high-temperature alloys, wherein, by mass percentage, the repair paste is composed of an activator (30-40%), a stabilizer (5-10%), a curing agent (50-60%), and an adhesive (5-10%); wherein:

[0007] The activator contains, by weight percentage, Cr (7.3%–11.8%), Ni (9.1%–14.7%), W (0.7%–3.9%), Ta (0.7%–5.9%), Re (0%–3.9%), B (1.8%–3.60%), and Y (0.01%–0.05%), with the remainder being Co and unavoidable impurity elements;

[0008] The stabilizer contains, by weight percentage, Cr (19.3%–25.8%), W (21.1%–28.7%), Ni (7.1%–12.9%), and Mo (0.7%–3.9%), with the remainder being Co and unavoidable impurity elements.

[0009] Specifically, the activator melts during the metallurgical heat preservation stage, and the resulting liquid phase fills the gaps between the stabilizer, curing agent and substrate through capillary action. As the concentration of melting point inhibiting element B in the liquid phase decreases, isothermal solidification occurs. The roles of the elements used are as follows.

[0010] Cr (7.3wt%~11.8wt%) is an indispensable alloying element in cobalt-based superalloys. Most of it can dissolve in the γ phase, and a small amount forms carbides, resulting in a relatively small solid solution strengthening effect. However, 7.3wt%~11.8wt% of Cr can significantly improve the high-temperature oxidation resistance and hot corrosion resistance of the shape-remodeling zone.

[0011] Ni (9.1wt%~14.7wt%), on the one hand, can improve the stability of face-centered cubic cobalt-based austenite under high temperature conditions by inhibiting its transformation to a close-packed hexagonal crystal structure at lower temperatures; on the other hand, it can also maintain the durability of the repair zone (the area after the damage is repaired) and avoid excessive addition leading to a decrease in durability.

[0012] W (0.7wt%–3.9wt%) is an important solid solution strengthening element in cobalt-based superalloys. It has a large atomic size and can significantly cause lattice expansion, forming a large long-range stress field, which hinders dislocation movement and significantly improves the tensile and creep properties of the alloy. The W content in cobalt-based superalloys is generally as high as 10wt% or more. However, W is a boride-forming element, and 0.7wt%–3.9wt% W can prevent the formation of large-sized borides after the activator melts.

[0013] Ta (0.7wt%–5.9wt%) and Re (0wt%–3.9wt%) have large atomic sizes, similar to W. When dissolved in the matrix, they can significantly cause lattice expansion, resulting in a significant solid solution strengthening effect. Ta does not readily combine with boron and can be effectively retained in the matrix phase. Re can effectively improve the wettability of the liquid phase formed after the activator melts. However, both of these elements are rare and expensive. 0.7wt%–5.9wt% Ta and 0wt%–3.9wt% Re can maintain their effects while minimizing costs.

[0014] B (1.8wt%–3.6wt%), as a melting point inhibitor.

[0015] Y (0.01wt%~0.05wt%), where Y is a rare earth element, can purify grain boundaries when added in trace amounts.

[0016] Stabilizers are used to absorb element B in the liquid phase and promote isothermal solidification of the liquid phase. The functions of the elements used are as follows.

[0017] Cr (19.3wt%–25.8wt%) is used to form Cr-rich borides of the types CrB2, CrB, and Cr5B3.

[0018] W (21.1wt%–28.7wt%) is used to form W-rich borates such as W2B.

[0019] Ni (7.1wt% to 12.9wt%) is used to stabilize face-centered cubic matrices.

[0020] Mo (0.7wt%–3.9wt%) is used to form Mo-rich borides such as MoB2, while avoiding excessive addition that could lead to the precipitation of the μ phase.

[0021] Furthermore, the melting temperature range of the activator is controlled between 1090℃ and 1160℃ to ensure that the activator can completely melt during the metallurgical heat preservation process when the repair paste repairs the damaged area.

[0022] Furthermore, the curing agent is a commercially available alloy powder such as FSX414, K640, G-65, Mar-M509, HS-25, etc., preferably a commercially available alloy powder of the same material as the part being repaired, used to fill large gaps in the damaged area, with a particle size of 78μm to 150μm.

[0023] Furthermore, the adhesive is a commercial adhesive of the NICROBRAZ S-BINDR type, which is used to formulate the activator, stabilizer and curing agent into a paste.

[0024] Furthermore, the adhesive can completely evaporate below 100°C, preventing adhesive residue from remaining in the material of the repair area.

[0025] Furthermore, the repair paste is in paste form, which reduces its fluidity and makes it stable when applied to the remodeling area, preventing it from detaching before it is heated and melted. The viscous consistency also makes it easier to fill the remodeling area. Specifically, the viscous texture provides a certain degree of fluidity, allowing the repair agent to change shape according to the size of the area being filled, thus satisfying the filling of irregular remodeling areas. Its fluidity also allows for complete filling, reducing defects and gaps in the remodeling area.

[0026] Furthermore, this repair paste can be used, but is not limited to, repairing cobalt-based high-temperature alloy thermal components with substrates such as FSX414, K640, G-65, Mar-M509, and HS-25.

[0027] A preparation method for preparing the repair paste of the cobalt-based superalloy includes the following steps:

[0028] A1: Preparation of activators and stabilizers;

[0029] A2: The activator, stabilizer, curing agent and adhesive are fully mixed by ball milling according to the corresponding mass percentages to complete the preparation of the repair paste for cobalt-based high-temperature alloys.

[0030] Furthermore, in step A2, a planetary ball mill is used for ball milling. The jar and grinding balls used in the ball mill are both made of tungsten carbide. The ball-to-material ratio is (6-8):1. The ball milling time is 15-60 minutes and the rotation speed is 300-500 r / min to ensure thorough mixing.

[0031] It should be noted that high-purity argon gas needs to be introduced into the tank during ball milling so that the activator, stabilizer, curing agent and binder can mix in the argon atmosphere, achieving a protective effect and preventing oxidation.

[0032] Furthermore, the activator is prepared using an ultra-high speed plasma rotating electrode method, and the particle size of the prepared activator is 30μm to 53μm. This ensures that the activator can be fully melted during metallurgical heat preservation when repairing the damaged area, and prevents the activator particle size from being too large and affecting the melting effect.

[0033] Furthermore, the stabilizer was prepared using other atomization methods, and the particle size of the prepared stabilizer was 0–20 μm.

[0034] A method for repairing cobalt-based superalloys, utilizing the aforementioned repair paste for cobalt-based superalloys, includes the following steps:

[0035] S1: Apply the repair paste to the damaged area of ​​the cobalt-based superalloy component;

[0036] S2: Place the cobalt-based high-temperature alloy parts coated with repair paste in a vacuum environment for metallurgical heat preservation, and then cool them with the furnace after heat preservation.

[0037] S3: Perform performance recovery heat treatment on cobalt-based high-temperature alloy parts, and complete the shape and property reshaping of the damaged area after reshaping.

[0038] Furthermore, before step S1, the damaged area needs to be polished and cleaned; the polishing is done by mechanical polishing to remove the surface oxide layer; the cleaning is done by wiping with high-purity alcohol or high-purity acetone to remove surface oil and metal shavings.

[0039] Furthermore, in step S2, the temperature of the metallurgical heat preservation is controlled at 1170℃~1200℃, and the heat preservation time is controlled at 20min~40min.

[0040] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0041] 1. The activator disclosed in this invention introduces elements nickel, chromium, tungsten, tantalum and rhenium as solid solution strengthening elements, and introduces element boron as a melting point inhibiting element; the disclosed stabilizer can induce boron to form fine borides with little harm to the performance of the repair joint during metallurgical heat preservation, thereby significantly improving the mechanical properties of the repair joint.

[0042] 2. By introducing a stabilizer, this invention enables the rapid absorption of boron, a melting point suppressing element in the liquid phase during the metallurgical insulation stage, by the small-sized stabilizer, forming fine-sized particulate borides that are dispersed in the repair area. This effectively suppresses the formation of brittle phases such as large borides and low-melting-point boron-rich eutectic phases, effectively inhibits the diffusion of boron into the substrate and prevents damage to the substrate, and effectively suppresses the significant loss of solid solution strengthening elements chromium, tungsten, and molybdenum in the curing agent, thus significantly improving the high-temperature mechanical properties of the repair joint. Attached Figure Description

[0043] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0044] Figure 1 This describes the microstructure of the activator of this invention;

[0045] Figure 2 This describes the microstructure of the curing agent of this invention;

[0046] Figure 3 This invention describes the microstructure of the repaired FSX414 alloy blade.

[0047] Figure 4 This is a flowchart of the repair method for cobalt-based superalloys disclosed in this invention. Detailed Implementation

[0048] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0049] 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.

[0050] Example 1

[0051] A repair paste for cobalt-based high-temperature alloys, comprising, by weight percentage, an activator (30-40%), a stabilizer (5-10%), a curing agent (50-60%), and an adhesive (5-10%); wherein:

[0052] The activator contains, by weight percentage, Cr (7.3%–11.8%), Ni (9.1%–14.7%), W (0.7%–3.9%), Ta (0.7%–5.9%), Re (0%–3.9%), B (1.8%–3.60%), and Y (0.01%–0.05%), with the remainder being Co and unavoidable impurity elements;

[0053] The stabilizer contains, by weight percentage, Cr (19.3%–25.8%), W (21.1%–28.7%), Ni (7.1%–12.9%), and Mo (0.7%–3.9%), with the remainder being Co and unavoidable impurity elements.

[0054] To further illustrate and explain the technical solution of the present invention, the following non-limiting embodiments are provided. Table 1 shows the embodiments of the activator and stabilizer in this example.

[0055] Table 1: Implementation methods of activators and stabilizers in this embodiment

[0056]

[0057] The curing agent is commercial alloy powder of grades such as FSX414, K640, G-65, Mar-M509, and HS-25, with a particle size of 78μm to 150μm; the binder is NICROBRAZ S-BINDR type commercial adhesive.

[0058] To further illustrate the effects of the present invention, in this embodiment, three repair materials for repairing damaged areas of cobalt-based superalloys are listed as Comparative Example 1, Comparative Example 2 and Comparative Example 3, and their chemical compositions are detailed in Table 2.

[0059] Table 2: Chemical composition of the repair materials used in Comparative Examples 1-3

[0060] Co Bal. Bal. Bal. Cr 22.0 19.0 16.0 Ni 21.0 17.0 21.0 Al / / 2.0 W 14.0 4.0 12.0 Ti / / 0.5 Mo / / 0.5 Nb / / 0.5 La 0.03 / / Si 2.0 8.0 1.2 B 2.0 0.8 2.0 Melting point 1166℃ 1121℃ /

[0061] Comparative Examples 1-3 achieved melting point suppression by introducing high concentrations of Si and / or B. However, the difference from the present invention is that the repair materials provided in Comparative Examples 1-3 contain high concentrations of borides, silicide-forming elements Cr and W. This leads to the in-situ precipitation of large-sized brittle phases such as borides and silicides in the liquid phase during the metallurgical heat preservation stage. Furthermore, the residual B will continue to generate low-melting-point brittle B-rich eutectic phases, resulting in a severe decrease in the mechanical properties of the repaired area.

[0062] In comparison with the comparative examples, the technical advantages of the present invention are as follows: the activator of the present invention does not contain Si, thus avoiding the formation of a Si-rich phase in the repair zone; it contains low concentrations of Cr and W, the elements that generate borides, thus suppressing the precipitation of large borides; by introducing an appropriate amount of small-sized stabilizer, B is induced to precipitate in the form of small-sized borides, which are dispersed in the shape reshaping zone, suppressing the precipitation of low-melting-point boron-containing eutectic phase, and significantly improving the high-temperature mechanical properties of the repair joint.

[0063] Example 2

[0064] A preparation method for preparing a repair paste for a cobalt-based superalloy with grade DFG-FSX414 includes the following steps:

[0065] A1: Preparation of activator and stabilizer; wherein: the DFB-C1 activator disclosed in Example 1 was prepared using the ultra-high speed plasma rotating electrode method. Figure 1 The morphology of the prepared activator is shown; the DFB-W1 stabilizer disclosed in Example 1 was prepared using other atomization methods; the curing agent was FSX414 alloy powder, and the microstructure of the curing agent is shown in the figure. Figure 2 As shown; the adhesive is NICROBRAZS-BINDR commercial adhesive.

[0066] A2: Mix DFB-C1 activator, DFB-W1 stabilizer, FSX414 alloy powder and binder in a mass percentage of 30:10:55:5. After mixing, place the mixture in a tungsten carbide ball mill jar, add tungsten carbide grinding balls at a ball-to-material ratio of 6:1, introduce high-purity argon gas into the jar, seal it, and then mechanically ball mill it for 15 minutes at a speed of 300 r / min on a planetary ball mill. After ball milling, separate the grinding balls with a sieve to obtain DFG-FSX414 repair paste.

[0067] Example 3

[0068] A preparation method for preparing a repair paste for a cobalt-based superalloy with grade DFG-K640 includes the following steps:

[0069] A1: Preparation of activator and stabilizer; wherein: the DFB-C2 activator disclosed in Example 1 was prepared by ultra-high speed plasma rotating electrode method; the DFB-W2 stabilizer disclosed in Example 1 was prepared by other atomization methods; the curing agent was K640 alloy powder, and the binder was NICROBRAZ S-BINDR type commercial adhesive.

[0070] A2: Mix DFB-C2 activator, DFB-W2 stabilizer, K640 alloy powder and binder in a mass percentage of 30:8:54:8. After mixing, place the mixture in a tungsten carbide ball mill jar, add tungsten carbide grinding balls at a ball-to-material ratio of 7:1, introduce high-purity argon gas into the jar, seal it, and then mechanically ball mill it for 15 minutes at a speed of 500 r / min on a planetary ball mill. After ball milling, separate the grinding balls with a sieve to obtain DFG-K640 repair paste.

[0071] Example 4

[0072] A method for repairing cobalt-based superalloys, using the DFG-FSX414 repair paste prepared in Example 2 to repair shape-damaged cobalt-based superalloy blades made of FSX414 alloy, wherein the nominal chemical composition of FSX414 alloy is Co-29wt%, Cr-10wt%, Ni-7.5wt%, W-1wt%, Fe-0.25wt%, C-0.01wt%, and B, includes the following steps:

[0073] S1: Apply DFG-FSX414 repair paste to the damaged area of ​​the cobalt-based high-temperature alloy blade that has been polished and cleaned, and then shape it.

[0074] S2: The cobalt-based high-temperature alloy blade coated with repair paste is placed in a vacuum environment with a vacuum degree better than 1×10-3 Pa for metallurgical heat preservation. The heat preservation temperature is 1180℃ and the heat preservation time is 20min. After heat preservation, it is cooled with the furnace. The vacuum environment is provided by a vacuum furnace.

[0075] S3: According to the heat treatment standards for blades, the cobalt-based high-temperature alloy blades are subjected to performance recovery heat treatment, and the shape and properties of the damaged area are reshaped after modification.

[0076] Before step S1, the oxide layer on the defective surface of the FSX414 alloy blade is removed by mechanical grinding with a carbide steel drill bit. The defect size is less than 20mm×20mm×3mm. After grinding, the ground surface is wiped with high-purity alcohol.

[0077] like Figure 3As shown, the repaired area has dense tissue and good interface connectivity, and no heterogeneous weakened phases were found.

[0078] In this embodiment, the repair joint (including the repair area) was made into a tensile test specimen. The room temperature yield strength was 476 MPa, the room temperature tensile strength was 584 MPa, and the room temperature tensile strength reached 78.6% of the base material. The 650℃ high temperature yield strength was 275 MPa, the 650℃ high temperature tensile strength was 389 MPa, and the 650℃ high temperature tensile strength reached 63.4% of the base material.

[0079] 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 repair paste for cobalt-based high-temperature alloys, characterized in that: By weight percentage, this repair paste is composed of an activator (30-40%), a stabilizer (5-10%), a hardener (50-60%), and a binder (5-10%); wherein: The activator contains, by weight percentage: Cr: 7.3%–11.8%, Ni: 9.1%–14.7%, W: 0.7%–3.9%, Ta: 0.7%–5.9%, Re: 0%–3.9%, B: 1.8%–3.60%, Y: 0.01%–0.05%, with the remainder being Co and unavoidable impurity elements; The stabilizer contains, by weight percentage, Cr: 19.3%–25.8%, W: 21.1%–28.7%, Ni: 7.1%–12.9%, Mo: 0.7%–3.9%, with the remainder being Co and unavoidable impurity elements.

2. The repair ointment according to claim 1, characterized in that: The melting temperature range of the activator is controlled between 1090℃ and 1160℃.

3. The repair ointment according to claim 1, characterized in that: The adhesive is capable of completely evaporating at temperatures below 100°C.

4. The repair ointment according to any one of claims 1-3, characterized in that: The repair ointment is in paste form.

5. A preparation method for preparing a repair paste of the cobalt-based superalloy as described in any one of claims 1-4, characterized in that: Includes the following steps: A1: Preparation of activators and stabilizers; A2: The activator, stabilizer, curing agent and binder are fully mixed by ball milling according to the corresponding mass percentages to complete the preparation of the repair paste for cobalt-based high-temperature alloys.

6. The preparation method according to claim 5, characterized in that: The activator was prepared using an ultra-high speed plasma rotating electrode method, and the particle size of the prepared activator was 30 μm to 53 μm.

7. A method for repairing cobalt-based superalloys, using the repair paste for cobalt-based superalloys according to any one of claims 1-4, characterized in that: Includes the following steps: S1: Apply the repair paste to the damaged area of ​​the cobalt-based superalloy component; S2: The cobalt-based high-temperature alloy parts coated with repair paste are placed in a vacuum environment for metallurgical heat preservation, and then cooled with the furnace after heat preservation. S3: Perform performance recovery heat treatment on cobalt-based high-temperature alloy parts, and complete the shape and property reshaping of the damaged area after reshaping.

8. The repair method according to claim 7, characterized in that: Before step S1, the damaged area needs to be polished and cleaned.

9. The repair method according to claim 7, characterized in that: In step S2, the temperature of metallurgical heat preservation is controlled at 1170℃~1200℃, and the heat preservation time is controlled at 20min~40min.

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