A cobalt-based brazing filler metal, a preparation method and application thereof

Abstract

The present application relates to the technical field of welding, in particular to a cobalt-based filler metal, a preparation method and application thereof, the chemical composition of the cobalt-based filler metal comprises Co: 50-70%, Cr: 5-15%, Ni: 6-15%, W: 3-4%, and Zr: 10-30% by mass percentage; the preparation steps comprise weighing the corresponding metal elements according to the above chemical composition, inductive smelting at a temperature of 1500-1600 DEG C, and powdering. The cobalt-based filler metal or the cobalt-based filler metal prepared by the above preparation method has excellent fluidity and wettability and low brittle phase formation tendency, has extremely strong versatility, and the use of the filler metal can obtain uniform welds and perfect filling, the high-temperature performance can meet the use requirements of active parts, and can be applied to repairing surface damage of cobalt-based material workpieces.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to a cobalt-based brazing filler metal, its preparation method, and its application. Background Technology

[0002] Power machinery, especially those used in high-temperature environments or requiring high output power, will inevitably suffer surface damage to its parts under the influence of high-temperature airflow or other harsh conditions, such as surface cracking and ablation damage. This seriously affects the performance and service life of the power machinery.

[0003] Direct replacement of parts with surface damage incurs high costs, so researchers have been exploring repair methods to extend their service life. Currently, the most commonly used welding repair methods are fusion welding and brazing. However, for large-area damage, fusion welding has low repair efficiency and is prone to deformation. In confined spaces, surfacing welding is impractical due to accessibility issues. In contrast, brazing, with its uniform heating, is considered the preferred method for repairing surface damage. It avoids uneven deformation caused by localized heating and significantly improves repair efficiency.

[0004] However, when using brazing for repair in existing technologies, the brazing filler metals often use elements such as B and Si as low-melting-point elements. During the brazing process, brittle intermetallic compound phases are easily formed, which are difficult to remove even through diffusion treatment. These brittle intermetallic compound phases will seriously reduce the mechanical properties of the weldment, and may even render it unusable. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect that when brazing is used to repair surface damage of parts in the prior art, brittle intermetallic compound phases are easily formed, thereby reducing the mechanical properties of the welded parts or even making them unusable. The present invention provides a cobalt-based brazing filler metal, its preparation method and application.

[0006] Therefore, the present invention provides the following technical solution:

[0007] This invention provides a cobalt-based brazing filler metal, the chemical composition of which, by mass percentage, includes: Co: 50%–70%, Cr: 5%–15%, Ni: 6%–15%, W: 3%–4%, Zr: 10%–30%; the preparation steps include mixing the metal elements in proportion, induction melting, and powdering; the melting temperature during induction melting is 1500–1600℃.

[0008] Preferably, the cobalt-based solder has a particle size of 50–150 μm.

[0009] Preferably, the mass ratio of Co to Zr is 5:3 to 7:1.

[0010] This invention provides a method for preparing the above-mentioned cobalt-based solder, comprising the following steps:

[0011] S1: Weigh the metallic elements Co, Cr, Ni, W, and Zr according to the chemical composition, and mix them to obtain a mixed powder;

[0012] S2: Set the vacuum degree to ≤1Pa, heat up to the melting temperature, induction melt the mixed powder, the melting time is t1, cool down to T1, and cast to form an alloy ingot;

[0013] S3: Powdering.

[0014] Preferably, in step S2, t1 is 5 to 20 minutes.

[0015] Preferably, in step S2, T1 is 1350–1450°C.

[0016] Optionally, in step S3, the powder preparation method includes any one of mechanical pulverization, vapor phase deposition synthesis, and vacuum gas atomization.

[0017] Preferably, when using the vacuum gas atomization method for powder preparation, the alloy superheat is 100-200°C, the vacuum degree at the start of melting is ≤0.1Pa, after melting to the alloy superheat, inert gas is introduced to atmospheric pressure, the tail exhaust is turned on for atomization powder spraying, and the cobalt-based brazing filler metal of the specified particle size is obtained by sieving.

[0018] Preferably, the purity of the elemental metals Co, Cr, Ni, W, and Zr used is >99.99%.

[0019] The present invention also provides the above-mentioned cobalt-based brazing filler metal, or the cobalt-based brazing filler metal prepared by the above preparation method, for repairing surface damage of cobalt-based material workpieces.

[0020] Preferably, the material of the cobalt-based workpiece includes cast cobalt-based alloy material, which has a yield strength of 150-200 MPa at its service temperature of 800-900°C. It is often used to manufacture high-temperature stationary components for gas turbines and aero engines, such as X40, X45, FSX414, Steilite, K644, K44, etc.

[0021] The technical solution of the present invention has the following advantages:

[0022] The cobalt-based brazing filler metal provided by this invention comprises, by mass percentage: Co: 50%–70%, Cr: 5%–15%, Ni: 6%–15%, W: 3%–4%, Zr: 10%–30%. Its preparation steps include mixing the elemental metals in proportion, induction melting, and powdering. The induction melting temperature is 1500–1600℃. This cobalt-based brazing filler metal exhibits excellent fluidity and wettability, as well as a low tendency for brittle phase formation. It possesses strong versatility, producing uniform welds with well-filled welds. The defects, brittle phases, and high-temperature performance meet the requirements of existing parts, even those used in E-class, F-class, and even H-class gas turbine turbine turbine blades. Its preparation method is simple, employing pure elemental metal weighing and mixing, and induction melting. The method is reliable, highly applicable, and versatile. Furthermore, the preparation steps remain essentially the same after adjusting the chemical composition of the brazing filler metal, facilitating streamlined operation. In cobalt-based brazing filler metals, elemental Zr and Co form a low-melting-point eutectic phase. Adding Ni and W strengthens this phase, forming a solid solution strengthening phase, thus improving the mechanical properties of the brazed joint. Cr enhances the metal's oxidation resistance. This cobalt-based filler metal effectively addresses the brittle phase defects that often occur when brazing conventional filler metals containing B and Si, thereby reducing prominent mechanical property issues in the weldment. During induction melting, the temperature should not exceed 1600℃, otherwise elemental loss may occur.

[0023] This invention also provides the application of the aforementioned cobalt-based brazing filler metal for repairing surface damage on cobalt-based workpieces. The repaired workpiece can continue to serve until the next maintenance cycle, thereby reducing component scrap rates and bringing significant economic benefits, demonstrating broad application prospects. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the steps in the cobalt-based solder preparation method of the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the eutectic melting principle of the solder in this invention.

[0027] Figure 3 The image shows the weld microstructure obtained by welding using the brazing filler metal in Example 1 of this invention, with a magnification of 500X.

[0028] Figure 4The image shows the weld microstructure obtained by welding using the brazing filler metal in Example 2 of this invention, magnified by 200X.

[0029] Figure 5 The image shows the weld microstructure obtained by welding with the brazing filler metal in Comparative Example 1 of this invention, magnified by 200X.

[0030] Figure 6 The image shows the weld microstructure obtained by welding with the brazing filler metal in Comparative Example 2 of this invention, magnified by 200X.

[0031] Figure 7 The image shows the weld microstructure obtained by welding using the brazing filler metal in Comparative Example 3 of this invention, with a magnification of 1000X.

[0032] Figure 8 The image shows the weld microstructure obtained by welding using the brazing filler metal in Comparative Example 4 of this invention, with a magnification of 1000X.

[0033] Figure 9 The image shows the weld microstructure obtained by welding with the brazing filler metal in Comparative Example 5 of this invention, magnified by 1000X.

[0034] Figure 10 The image shows the weld microstructure obtained by welding using the brazing filler metal in Comparative Example 6 of this invention, magnified by 1000X.

[0035] Figure 11 The image shows the weld microstructure obtained by welding with the brazing filler metal in Comparative Example 7 of this invention, magnified by 1000X.

[0036] Figure 12 The graph shows the creep performance of weld joints obtained by welding with the cobalt-based brazing filler metals obtained in the embodiments and comparative examples of the present invention at 800°C and 170MPa. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a cobalt-based solder and its preparation method. The chemical composition of the cobalt-based solder is Co-9Cr-8Ni-3.5W-15Zr. A schematic diagram of its preparation method is shown below. Figure 1 As shown, it includes the following steps:

[0040] (1) The purity of the Co, Cr, Ni, W and Zr used is all >99.99%. According to the composition ratio of Co-9Cr-8Ni-3.5W-15Zr, that is, the mass percentage of Co 64.5%, Cr 9%, Ni 8%, W 3.5% and Zr 15%, a certain amount of each metal element is taken and mixed evenly to obtain a mixture.

[0041] (2) Using a vacuum induction furnace, set the vacuum degree to 0.5Pa and the temperature to 1550℃, refine the mixture in (1) for 5 minutes, and then cool it down to 1400℃ and cast it to form an alloy rod with a diameter of φ20.

[0042] (3) Use a vacuum atomizing furnace for atomization powder preparation. When the vacuum degree is reduced to 0.05Pa, start the melting process. When the alloy rod in (2) is melted to 1500℃, that is, the alloy superheat is 150℃, argon gas is introduced to atmospheric pressure, and the tail exhaust is turned on for atomization powder spraying. After sieving, cobalt-based brazing filler powder with a particle size of 50-150μm is obtained.

[0043] The principle of this cobalt-based solder is as follows: Figure 2 As shown, a eutectic phase formed by Zr and Co is used as the low-melting-point phase of the brazing filler metal, replacing elements such as B and Si in conventional brazing fillers. The Zr content (at%) at the eutectic point is 12% and 46%, respectively. Elemental Zr and Co are mixed and heated to form a low-melting-point eutectic phase. Adding appropriate amounts of Ni and W forms a solid solution strengthening phase, which improves the mechanical properties of the brazed joint. The addition of Cr is used to improve oxidation resistance.

[0044] Example 2

[0045] This embodiment provides a cobalt-based solder and its preparation method. The only difference between this embodiment and Embodiment 1 is that the chemical composition of the cobalt-based solder is Co-6Cr-6.5Ni-3.8W-20Zr.

[0046] Comparative Example 1

[0047] This comparative example provides a cobalt-based solder and its preparation method. The only difference between this example and Example 1 is that the chemical composition of the cobalt-based solder is Co-6Cr-6.5Ni-3.8W-3Si-3.5B, and the low-melting-point elements used are Si and B.

[0048] Comparative Example 2

[0049] This comparative example provides a cobalt-based solder and its preparation method. The only difference between this example and Example 1 is that the chemical composition of the cobalt-based solder is Co-9Cr-8Ni-3.5W-8Zr, and the Zr content is not within the range of 10% to 30% specified in this invention.

[0050] Comparative Example 3

[0051] This comparative example provides a cobalt-based solder and its preparation method. The only difference between this example and Example 1 is that the chemical composition of the cobalt-based solder is Co-4Cr-8Ni-3.5W-15Zr, and the Cr content is not within the range of 5% to 15% specified in this invention.

[0052] Comparative Example 4

[0053] This comparative example provides a cobalt-based solder and its preparation method. The only difference between this example and Example 1 is that the chemical composition of the cobalt-based solder is Co-9Cr-5Ni-3.5W-15Zr, and the Ni content is not within the range of 6% to 15% specified in this invention.

[0054] Comparative Example 5

[0055] This comparative example provides a cobalt-based solder, which differs from Example 1 only in that the chemical composition of the cobalt-based solder is Co-9Cr-8Ni-5W-15Zr, and the W content is not within the range of 3% to 4% specified in this invention.

[0056] Comparative Example 6

[0057] This comparative example provides a cobalt-based brazing filler metal and its preparation method. The only difference between this example and Example 1 is that the temperature of the vacuum induction furnace in step (2) is set to 1400°C, which is outside the range of 1500-1600°C specified in this invention.

[0058] Comparative Example 7

[0059] This comparative example provides a cobalt-based brazing filler metal and its preparation method. The only difference between this example and Example 1 is that the alloy rod in step (3) is melted to 1400°C in step (2). That is, the alloy superheat is 50°C, which is outside the 100-200°C range specified in this invention.

[0060] Test Example 1

[0061] The cobalt-based brazing filler metals obtained in the embodiments and comparative examples of this invention were used to repair the ablation zones of gas turbine turbine blades. The chemical composition of the gas turbine turbine blades was Co-29Cr-10Ni-7.5W-0.25C. The ablation zones were 20mm × 20mm in size and approximately circular in shape. The brazing process included the following steps:

[0062] (1) Grinding the ablation zone: The ablation zone of the transparent blade is machined into a concave shape by mechanical means to ensure a smooth transition zone.

[0063] (2) Filling with mixed powder: Take cobalt-based alloy powder filler (composition: Co-29Cr-10Ni-7.5W-0.25C) with a mass ratio of 6:2:2, cobalt-based brazing filler obtained in this invention, and binder (Nicrobraz), mix them evenly and fill them into the area to be soldered.

[0064] (3) Vacuum brazing: The blades to be brazed are placed in a vacuum brazing furnace with a vacuum degree of 4.0 × 10⁻⁶. -3 Pa, overall heating, raise the temperature to the set temperature of 1000℃, hold for 20 minutes, then slowly raise the furnace temperature to 1200℃, hold for 70 minutes, and then furnace cool after welding.

[0065] The microstructure of the brazed weld was examined according to GB / T 13298-2015 "Methods for Examination of Microstructure of Metals". The microstructure images obtained are as follows: Figures 3-11 As shown.

[0066] From the diagram, we can see that... Figure 3 , 4 The welds obtained by brazing using the cobalt-based brazing filler metals from Examples 1 and 2 respectively showed no obvious defects or brittle phases. The brazing filler metal structure was uniform and well-filled. This is attributed to the excellent fluidity and wettability of the cobalt-based brazing filler metal provided by the present invention, as well as its low tendency to form brittle phases. Figures 5-11 The welds obtained by brazing using cobalt-based brazing filler metals from Comparative Examples 1 to 7 all exhibited defects such as porosity and brittle phases, and the brazing filler metal microstructure was not uniform.

[0067] Test Example 2

[0068] The high-temperature creep life of the weld joint obtained after welding in Test Example 1 was tested. The test conditions were 800℃ and 170MPa. The standard used was GB / T2039-2008. The specific method was as follows: a standard creep thin plate specimen was taken perpendicular to the weld direction, ensuring that the weld was in the middle of the specimen. The specimen was heated to 800℃ using a high-temperature creep testing machine, and a constant tensile force (170MPa) was applied along the specimen axis until the specimen broke. Its creep life was then determined.

[0069] The statistical charts of creep performance of each weld joint are as follows: Figure 12 As shown in the figure, the brazed joints obtained by brazing using the cobalt-based brazing filler metals in Examples 1 and 2 have excellent creep performance under high temperature and high pressure, with a value of more than 90% of the base material. However, the brazed joints obtained by brazing using the cobalt-based brazing filler metals in Comparative Examples 1 to 7 have very poor creep performance under high temperature and high pressure, with a value of only 58% to 76% of the base material. This is precisely because of the influence of defects such as porosity and brittle phase in the weld.

[0070] In summary, the weld obtained by brazing using the cobalt-based brazing filler metal provided by this invention has no obvious defects or brittle phases. The filler metal has a uniform structure and is well-filled, exhibiting excellent durability under high temperature and high pressure. It can be widely used for welding repair of surface cracks and ablation damage on the turbine blades of in-service heavy-duty gas turbines, reducing the scrap rate of components and bringing huge economic benefits, and has broad application prospects.

[0071] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A cobalt-based solder, characterized in that, The chemical composition by mass percentage is: Co: 50%~70%, Cr: 5%~15%, Ni: 6%~15%, W: 3%~4%, Zr: 10%~30%; it does not contain B or Si. Its preparation steps include mixing elemental metals in proportion, induction melting, and powdering; The melting temperature during induction melting is 1500~1600℃; The cobalt-based brazing filler metal is used to repair surface damage on cobalt-based material workpieces.

2. The cobalt-based solder according to claim 1, characterized in that, The cobalt-based solder has a particle size of 50~150μm.

3. The cobalt-based solder according to claim 1, characterized in that, The mass ratio of Co to Zr is 5:3 to 7:

1.

4. A method for preparing a cobalt-based solder according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Weigh the metallic elements Co, Cr, Ni, W, and Zr according to the chemical composition, and mix them to obtain a mixed powder; S2: Set the vacuum degree to ≤1Pa, heat up to the melting temperature, induction melt the mixed powder, the melting time is t1, cool down to T1, and cast to form an alloy ingot; S3: Powdering.

5. The method for preparing cobalt-based solder according to claim 4, characterized in that, In step S2, t1 is 5~20 min; And / or, in step S2, T1 is 1350~1450℃.

6. The method for preparing cobalt-based solder according to claim 4, characterized in that, In step S3, the powder preparation method includes any one of mechanical pulverization, vapor phase deposition synthesis, and vacuum gas atomization.

7. The method for preparing cobalt-based solder according to claim 6, characterized in that, When using the vacuum gas atomization method for powder production, the alloy superheat is 100~200℃, the vacuum degree at the start of melting is ≤0.1Pa, after melting to the alloy superheat, inert gas is introduced to atmospheric pressure, the tail exhaust is turned on for atomization powder spraying, and cobalt-based brazing filler metal is obtained by sieving.

8. The method for preparing cobalt-based solder according to any one of claims 4 to 7, characterized in that, The purity of the elemental metals Co, Cr, Ni, W, and Zr used is >99.99%.

9. The application of a cobalt-based brazing filler metal according to any one of claims 1 to 3 or a cobalt-based brazing filler metal prepared by any one of claims 4 to 8 for repairing surface damage of cobalt-based material workpieces.

10. The application according to claim 9, characterized in that, The material of the cobalt-based workpiece includes cast cobalt-based alloy material, wherein the yield strength of the cast cobalt-based alloy material at 800~900℃ is 150~200MPa.

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