A pulsed laser repair method for aero-engine casting K438 bearing bracket

Abstract

This invention discloses a pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine. The method first repairs most defects through solution treatment, making the repaired area less prone to cracking and reducing risk. Then, laser cladding is performed using a welding alloy containing a high proportion of W and Mo. The addition of W and Mo reduces the tendency of carbides M3B2 and MC to form a continuous network at grain boundaries, improving crack resistance and enhancing the crack resistance of the welding wire. This method ensures similar performance to the repaired substrate while increasing the plasticity of the weld, thus reducing weld cracks and other defects. Simultaneously, it improves tempering stability, thereby more effectively reducing residual stress and improving the wear resistance and corrosion resistance of the weld. This method solves the problems of high repair difficulty and the inability of laser powder melting technology to guarantee the stability of the repair process in existing K438 bearing housing bracket repair methods.

Description

Technical Field

[0001] This invention relates to the field of laser repair technology for the surface of aero-engine parts, and more specifically, to a pulsed laser repair method for a cast K438 bearing housing bracket of an aero-engine. Background Technology

[0002] Hot-section components of aero-engines are high-temperature alloy castings, which are subsequently machined to achieve the required dimensions and structure. Because castings are highly susceptible to metallurgical defects such as shrinkage porosity and inclusions during production, these defects are difficult to detect in the raw state but become apparent during machining. This can lead to parts failing to meet design requirements, such as the K438 bearing housing bracket, which exhibits dimensional deviations after machining. To address such issues, welding / electroplating processes are typically used to repair the dimensional discrepancies.

[0003] (1) Manual arc welding / tungsten inert gas welding / electron beam welding technology. This technology involves cleaning and drying the surface of the part, and then using welding rods made of specific materials to repair the pits on the surface of the part. After repair, the part is free of surface pit defects. However, the disadvantages are high welding heat input, large heat-affected zone, large part deformation, easy burn-through of the part, and difficulty in guaranteeing the size of the repaired part.

[0004] (2) Electroplating / spraying technology. Applying a coating or spraying to the pits on the surface of the part can effectively repair the pits. However, this method is only suitable for repairing micron-sized pits. It is not efficient for repairing millimeter-sized pits. Furthermore, the coating does not form a metallurgical bond with the substrate, which will significantly reduce the load-bearing capacity of the part.

[0005] Both of the above methods are insufficient to meet the performance requirements after processing, especially when welding or repairing K438 high-temperature alloys. The presence of reinforcing phase-forming elements such as Al, Ti, and Nb in the alloy deteriorates its weldability. Specifically, Nb, Al, and Ti form γ and γ' (Ni3Al, Ni3Ti) eutectic phases. The presence of Nb easily leads to Nb-rich Laves and NbC eutectic phases. Furthermore, B in the alloy readily forms low-melting-point eutectic compounds such as M3B2 and MC with Nb and other alloying elements. Under the welding thermal cycle, these low-melting-point phases liquefy at the grain boundaries to form liquid films, which are highly susceptible to hot cracking during welding. CN202111321608.0 discloses a K438 high-temperature alloy welding method that determines process parameters by adjusting laser power, welding speed, defocusing amount, and beam output program, and concentrates the laser at the weld seam for continuous welding. This effectively suppresses hot cracking tendency and improves product forming quality and weld pass rate. This patent utilizes the advantages of laser welding, such as small laser spot diameter, concentrated energy density, low heat input, high operational flexibility, and uniform and fine microstructure after repair. It has the advantages of a small heat-affected zone and minimal impact on overall performance, and can suppress the formation of hot cracks in K438 high-temperature alloys to a certain extent. However, when repairing defects in parts, it is necessary not only to reduce the presence of a large number of low-melting-point eutectic phases at the grain boundaries that cause cracks, but also to select suitable welding wire materials to maintain good strength with the substrate, and to reduce welding heat input through appropriate welding processes, thereby reducing repair defects. Existing technologies that only control the process parameters of laser processing to improve welding quality are often insufficient, resulting in low wear resistance and plasticity of the weld, making it difficult to guarantee the stability of the repair process. Summary of the Invention

[0006] The main technical problem to be solved by this invention is that the existing technology for laser welding of K438 bearing housing brackets has shortcomings such as low wear resistance and plasticity of the weld and poor stability of the repair process. This invention provides a pulsed laser repair method for casting K438 bearing housing brackets for aero-engines.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine, comprising the following steps:

[0009] S1. Perform solution treatment on the parts, and then clean and polish the defects and the surrounding surfaces of the parts.

[0010] S2. Use alloy welding wire to perform pulsed laser welding on the defective parts;

[0011] The alloy welding wire comprises Cr 14.5–16.5 wt.%, W 3.0–4.5 wt.%, Mo 15–17 wt.%, Fe 4–7 wt.%, with the remainder being Ni;

[0012] The pulse width of the pulsed laser welding is 9-15ms, the pulse peak is 2.3-2.9kW, the defocusing amount is -6-6mm, and the laser energy acting on the part is 26-33J.

[0013] S3. After grinding the welded parts flat, perform aging treatment, then sandblasting and tempering to remove residual stress, and finally complete the repair of the aero-engine cast bearing housing bracket.

[0014] Further, the solution treatment includes heating to 1150–1170°C, holding at that temperature for 2–3 hours, and then cooling to room temperature. Because the K438 alloy contains a large number of low-melting-point eutectic phases at the grain boundaries, welds are prone to cracking. This invention performs a solution treatment first, repairing most defects in the solution-treated state in advance, reducing the likelihood of cracking and improving the yield rate of parts. Preferably, the solution treatment includes heating to 1160°C, holding at that temperature for 2.5 hours, and then cooling to room temperature.

[0015] Furthermore, the cooling includes:

[0016] First stage: The furnace temperature is cooled to 860-880°C at a rate of 10-15°C / min; preferably, it is cooled to 870°C at a rate of 12°C / min.

[0017] Second stage: The furnace temperature is cooled to room temperature at a rate of 5-10℃ / min; preferably, it is cooled to room temperature at a rate of 8℃ / min.

[0018] Furthermore, the alloy welding wire comprises 15.3 wt.% Cr, 3.3 wt.% W, 16.1 wt.% Mo, 5.2 wt.% Fe, with the remainder being Ni.

[0019] Furthermore, the pulsed laser welding parameters are preferably:

[0020] The pulsed laser welding pulse width is 9ms, the peak pulse is 2.3kW, the defocusing distance is -6mm, and the laser energy applied to the part is 26.90J; or

[0021] The pulsed laser welding pulse width is 13ms, the peak pulse power is 2.3kW, the defocusing distance is 3mm, and the laser energy applied to the part is 27.58J; or

[0022] The pulsed laser welding pulse width is 13ms, the peak pulse is 2.5kW, the defocusing distance is 6mm, and the laser energy applied to the part is 29.66J; or

[0023] The pulsed laser welding has a pulse width of 15ms, a pulse peak of 2.3kW, a defocusing amount of 6mm, and a laser energy of 27.96J applied to the part.

[0024] Furthermore, the pulsed laser welding also includes a spot spacing of 0.20–0.50 mm, a focal length of 200 mm, and an argon flow rate of 5.5–7.5 L / min.

[0025] Furthermore, the aging treatment involves heating to 840–850°C at a rate of 10–15°C / min, holding at that temperature for 23–24 hours, and then cooling to room temperature at a rate of 5–10°C / min. During the aging treatment, the combined effect of strain caused by welding residual stress and restraint stress, along with the reduction in plasticity during the aging process, leads to strain-aging crack sensitivity, resulting in cracks propagating along grain boundaries near the fusion line. Post-weld shot peening of the weld heat-affected zone, changing the welding tensile stress to compressive stress, can effectively prevent cracks generated during post-weld aging treatment.

[0026] Preferably, the aging treatment involves heating to 840°C at a rate of 12°C / min, holding at that temperature for 24 hours, and then cooling to room temperature at a rate of 8°C / min.

[0027] Furthermore, the method also includes examining defects using a stereomicroscope, fluorescence, and X-rays.

[0028] Furthermore, if there are defects in the welding, laser repair welding is performed after tempering, followed by aging treatment, sandblasting, and tempering to remove residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

[0029] Compared with existing technologies, the beneficial effects are:

[0030] This invention first repairs most defects in advance through solution treatment, making the repaired area of ​​the K438 bearing housing bracket less prone to cracking and reducing risk. Then, laser cladding is performed using a welding alloy containing a high proportion of W and Mo. The addition of W and Mo reduces the tendency of carbides M3B2 and MC to form a continuous network at grain boundaries, improving crack resistance and thus enhancing the crack resistance of the welding wire. This ensures performance similar to the base material while increasing the weld's plasticity, which is beneficial for reducing weld cracks and other defects. Simultaneously, it improves tempering stability, thereby more effectively reducing residual stress, and also improves the weld's wear resistance and corrosion resistance. This invention reduces the Al and Ti content, ensuring fewer subsequent aging precipitates (γ' phase), improving plasticity while reducing strength, and mitigating welding stress through plastic deformation.

[0031] This invention strictly controls the laser repair parameters. Under the parameter settings of laser energy and defocusing amount, a repair area with good bonding between each weld, no microcracks, lack of fusion, inclusions and other defects, and uniform structure in the molten pool is obtained, which improves the service life of the K438 bearing seat bracket for aero-engine casting. Attached Figure Description

[0032] Figure 1 This is a macroscopic image of a single weld seam under a 45x microscope;

[0033] Figure 2 It is a metallographic image of a single weld.

[0034] Figure 3 This is a laser-repaired image;

[0035] (a) is an appearance image of the laser weld surface; (b) is an image of the molten pool surface morphology; (c) is an image of the weld surface fluorescence detection; and (d) is an image of the metallographic cross-section of the repaired area.

[0036] Figure 4 These are surface morphology images of the weld pools of different alloy welding wires ①, ②, and ③.

[0037] Figure 5 It is ① a metallographic cross-sectional view of the area repaired by the alloy welding wire. Detailed Implementation

[0038] The following examples further explain and clarify the invention, but the specific examples do not limit the invention in any way.

[0039] The main components (wt.%) of the K438 bearing housing bracket for aero-engine casting used in this invention include:

[0040]

[0041] Example 1

[0042] This embodiment provides a pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine, the steps of which include:

[0043] S1. Heat the part to 1160℃ and hold for 2.5 hours. First, cool it to 870℃ at a rate of 12℃ / min, and then cool it to room temperature at a rate of 8℃ / min to complete the solution treatment. Use fluorescence and X-ray to inspect the part for internal porosity and inclusion defects. Then clean and polish the defects and the surrounding surfaces of the part.

[0044] S2. Use alloy welding wire to perform pulsed laser welding on the defective parts.

[0045] The alloy welding wire comprises: Cr 15.3 wt.%, W 3.3 wt.%, Mo 16.1 wt.%, Fe 5.2 wt.%, with the remainder being Ni.

[0046] The pulsed laser welding has a pulse width of 9–15 ms, a pulse peak of 2.3–2.9 kW, a defocusing amount of -6–6 mm, a laser energy of 26–33 J applied to the part, a focal length of 200 mm, and an argon flow rate of 6.5 L / min.

[0047] S3. After grinding the welded parts smooth, inspect them with X-ray. If no obvious defects are found, perform aging treatment by heating to 840℃ at 12℃ / min and holding for 24 hours, then cooling to room temperature at a rate of 8℃ / min. Next, perform sandblasting and tempering to eliminate residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

[0048] The specific parameter settings for pulsed laser welding are shown in the table below. Single-pass tests should be conducted according to these parameters.

[0049]

[0050]

[0051] The macroscopic morphology of a single weld was observed using a 45x microscope, such as... Figure 1 As shown, no cracks or lack of fusion were observed on the surface of the molten pool of specimens 1-16#. The molten pools were elliptical and aesthetically pleasing. After lapping, the welds of each molten pool exhibited a fish-scale pattern, indicating that the welds were well bonded together.

[0052] Depend on Figure 2 The metallographic observation images of the single-pass welds shown indicate that the molten pool morphology varies under different process parameters. This variation is mainly reflected in the differences in the size of pores, the depth of the molten pool, the width of the molten pool, and the height of the weld. Large pores, ranging from 0.2mm to 0.5mm in diameter, are observed in the molten pools of specimens #3, #4, #8, #11, and #16. Small pores, less than 0.1mm in size, are present in the molten pools of specimens #6 and #12. Significant overheating is observed in the molten pools of specimens #10, #12, and #15, while a distinct "key" effect is present in the molten pools of specimens #2, #5, and #7. Compared to other parameters, specimens #1, #9, #13, and #14 show a higher advantage in repair due to the different process parameters, with no obvious pore formation.

[0053] like Figure 3The laser repair images shown are examined under a 45x microscope. (a) The weld surface is intact, with no missing material or weld beads. (b) The weld pools show good overlap, with no cracks or lack of fusion. (c) Fluorescence imaging of the weld joint after grinding reveals no obvious defects on the repaired surface, and subsequent X-ray examination did not reveal any internal defects in the weld pool, indicating no significant defects in the laser-repaired sample. (d) The metallographic cross-section of the repaired area shows a small number of pores, but no microcracks, lack of fusion, inclusions, or other defects. The microstructure within the weld pool is uniform, and there is good metallurgical bonding with the K438 substrate.

[0054] Example 2

[0055] This embodiment is based on the method described in Embodiment 1, and uses alloy welding electrodes of different materials for repair. The composition of the welding wire is as follows:

[0056] ① The composition of the alloy welding wire includes: Cr 20.5~23.0wt.%, W 0.2~1.0wt.%, Mo 8.0~10.0wt.%, Fe 17~20wt.%, and the remainder is Ni.

[0057] ② The composition of the alloy welding wire includes: Cr 14.0~16.0wt.%, W 1.7~2.2wt.%, Mo 1.7~2.2wt.%, Al 2.4-2.8wt.%, Ti 2.1~2.5wt.%, Ni 33.0~36.0wt.%, with the remainder being Fe.

[0058] ③ The composition of the alloy welding wire includes: Cr 23.5~26.5wt.%, W 13.0~16.0wt.%, Al 0.1-0.5wt.%, Ti 0.3~0.7wt.%, Fe 2~4wt.%, and the remainder is Ni.

[0059] The pulsed laser welding has a pulse width of 13ms, a pulse peak of 2.9kW, a defocusing amount of +3mm, a focal length of 200mm, and a laser energy of 27.58J applied to the part.

[0060] S3. After grinding the welded parts flat, X-ray inspection is performed, followed by aging treatment, sandblasting, and tempering to eliminate residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

[0061] Figure 4The images show the surface morphology of the molten pools of different alloy welding wires. (a) shows the surface morphology of the molten pool of alloy ①, where no cracks or lack of fusion are observed on the surface of the molten pool, and the molten pool is elliptical and has a beautiful shape. (b) shows the surface morphology of the molten pool of alloy ②, where the molten pool collapses and the surface of the molten pool is wrinkled, making it unsuitable for repair welding of K438 material. (c) shows the surface morphology of the molten pool of alloy ③, where the molten pool is flat and there are obvious signs of lack of fusion, making it unsuitable for pulsed laser repair of K438 material.

[0062] Figure 5 The image shows a metallographic photograph of the area repaired by alloy welding wire ①. Multiple pores and cracks are visible in the image, indicating that alloy welding wire ① is prone to producing pores and cracks under multi-pass welds. Therefore, alloy welding wire ① is not suitable for pulsed laser repair of K438 material.

[0063] Example 3

[0064] This embodiment provides a pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine, the steps of which include:

[0065] S1. Heat the part to 1150℃ and hold for 3 hours. First, cool it to 880℃ at a rate of 10℃ / min, then cool it to room temperature at a rate of 5℃ / min to complete the solution treatment. Use fluorescence and X-ray to inspect the part for internal porosity and inclusion defects. Then clean and polish the defects and the surrounding surfaces of the part.

[0066] S2. Use alloy welding wire to perform pulsed laser welding on the defective parts.

[0067] The alloy welding wire comprises 14.5 wt.% Cr, 3.0 wt.% W, 15 wt.% Mo, 4 wt.% Fe, with the remainder being Ni;

[0068] The pulsed laser welding has a pulse width of 13ms, a pulse peak of 2.9kW, a defocusing amount of +3mm, a focal length of 200mm, and a laser energy of 27.58J applied to the part.

[0069] S3. After grinding the repaired parts smooth, inspect them with X-ray. If no obvious defects are found, perform aging treatment by heating to 840℃ at 10℃ / min and holding for 24 hours, then cooling to room temperature at a rate of 5℃ / min. Next, perform sandblasting and tempering to eliminate residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

[0070] If obvious defects are found, laser welding is performed after removing the defects until no defects are found. Then, aging treatment is carried out, followed by sandblasting and tempering to relieve residual stress and complete the repair of the aero-engine cast bearing housing bracket.

[0071] Example 4

[0072] This embodiment provides a pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine, the steps of which include:

[0073] S1. Heat the part to 1170℃ and hold for 2 hours. First, cool it to 860℃ at a rate of 15℃ / min, then cool it to room temperature at a rate of 10℃ / min to complete the solution treatment. Use fluorescence and X-ray to inspect the part for internal porosity and inclusion defects. Then clean and polish the defects and the surrounding surfaces of the part.

[0074] S2. Use alloy welding wire to perform pulsed laser welding on the defective parts.

[0075] The alloy welding wire comprises 16.5 wt.% Cr, 4.5 wt.% W, 17 wt.% Mo, 7 wt.% Fe, with the remainder being Ni.

[0076] The pulsed laser welding has a pulse width of 13ms, a pulse peak of 2.9kW, a defocusing amount of +3mm, a focal length of 200mm, and a laser energy of 27.58J applied to the part.

[0077] S3. After grinding the repaired parts smooth, inspect them with X-ray. If no obvious defects are found, perform aging treatment by heating to 850℃ at 15℃ / min and holding for 23 hours, then cooling to room temperature at a rate of 10℃ / min. Next, perform sandblasting and tempering to eliminate residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

[0078] If obvious defects are found, laser welding is performed after removing the defects until no defects are found. Then, aging treatment is carried out, followed by sandblasting and tempering to relieve residual stress and complete the repair of the aero-engine cast bearing housing bracket.

[0079] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A pulsed laser repair method for a cast K438 bearing housing bracket of an aero-engine, characterized in that the steps include... include: S1. Perform solution treatment on the parts, and then clean and polish the defects and the surrounding surfaces of the parts. The solution treatment includes heating to 1150~1170℃, holding at that temperature for 2~3 hours, and then cooling to room temperature. The cooling process includes: First stage: Cool to 860-880℃ at a rate of 10~15℃ / min; Second stage: Cool to room temperature at a rate of 5~10℃ / min; S2. Use alloy welding wire to perform pulsed laser welding on the defective parts; The alloy welding wire comprises Cr 14.5–16.5 wt.%, W 3.0–4.5 wt.%, Mo 15–17 wt.%, Fe 4–7 wt.%, with the remainder being Ni; The pulse width of the pulsed laser welding is 9~15ms, the pulse peak is 2.3~2.9kW, the defocusing amount is -6~6mm, and the laser energy acting on the part is 26~33J; S3. After grinding the welded parts flat, perform aging treatment, then sandblasting and tempering to remove residual stress, and finally complete the repair of the aero-engine cast bearing housing bracket.

2. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, The solution treatment includes heating to 1160°C, holding at that temperature for 2.5 hours, and then cooling to room temperature.

3. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, The alloy welding wire comprises 15.3 wt.% Cr, 3.3 wt.% W, 16.1 wt.% Mo, 5.2 wt.% Fe, with the remainder being Ni.

4. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, The pulsed laser welding parameters also include a dot pitch of 0.20~0.50mm, a focal length of 200mm, and an argon flow rate of 5.5~7.5L / min.

5. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, The aging process involves heating to 840-850℃ at a rate of 10-15℃ / min, holding at that temperature for 23-24 hours, and then cooling to room temperature at a rate of 5-10℃ / min.

6. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 5, characterized in that, The aging process involves heating to 840°C at a rate of 12°C / min, holding at that temperature for 24 hours, and then cooling to room temperature at a rate of 8°C / min.

7. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, The method also includes using stereomicroscopy, fluorescence, and X-rays to inspect defects.

8. The pulsed laser repair method for the cast K438 bearing housing bracket of an aero-engine according to claim 1, characterized in that, If there are defects in the welding, after tempering, laser welding and grinding are performed, followed by aging treatment, sandblasting, and tempering to eliminate residual stress, thus completing the repair of the aero-engine cast bearing housing bracket.

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