A method for laser drilling of high-temperature alloys with thermal barrier coatings

Abstract

This application provides a laser drilling method for high-temperature alloys with thermal barrier coatings, belonging to the technical field of laser precision for hot-end components of aero-engines. Specifically, it includes spraying a sacrificial protective slurry onto the surface of the thermal barrier coating and the metal substrate of the workpiece to be processed, and after drying, forming a sacrificial protective layer on the surface of the workpiece to be processed, covering the area to be processed; using a millisecond laser to process a bottom hole with a diameter of d0 from the surface of the thermal barrier coating or the metal substrate of the workpiece; using a millisecond laser to sequentially perform n turns of rotary cutting to enlarge the bottom hole from the surface of the thermal barrier coating or the metal substrate until it is enlarged to the target hole diameter df, with the theoretical value of the annular cross-sectional area corresponding to the area removed in each turn being equal; removing the sacrificial protective layer and cleaning the hole wall. This processing method improves the drilling quality.

Description

Technical Field

[0001] This application relates to the field of laser precision machining of hot-end components of aero-engines, and in particular to a method for laser drilling of high-temperature alloys with thermal barrier coatings. Background Technology

[0002] The operating temperature at the turbine inlet of an aero-engine far exceeds the tolerance limit of nickel-based superalloys. Components commonly employ a structure combining a superalloy substrate with a thermal barrier coating, and numerous film cooling holes are machined to achieve cooling. The thermal barrier coating consists of a ceramic insulating surface layer and a metal bonding layer. The thermophysical properties of the ceramic, bonding layer, and superalloy substrate differ significantly. During millisecond laser hole drilling, molten material is prone to spattering. This spatter adheres to the hole surface, not only reducing film cooling efficiency but also easily causing coating cracking, delamination, or even peeling, jeopardizing the component's service safety.

[0003] Traditional incremental rotary reaming and enlarging processes with constant diameter exhibit significant differences in material removal rates across different rings. This leads to severe heat accumulation in the inner rings and excessive material removal in the outer rings, resulting in intense spattering. High spatter rates at the hole opening cause localized separation of the thermal barrier coating, and an excessively thick remelted layer on the hole wall. Some improved processes require the use of various lasers, such as nanosecond and femtosecond lasers, to create the holes. These processes necessitate station relocation, introducing alignment errors. Furthermore, the high equipment investment and long processing cycles make it difficult to meet the requirements of mass production.

[0004] Existing anti-spatter sacrificial coating solutions either lack high-temperature resistance or fail to match the optimal coating thickness for laser drilling of thermal barrier coatings, and are not combined with rotary cutting and hole enlargement processes, thus failing to simultaneously improve processing quality from both the perspectives of reducing spatter generation and preventing spatter adhesion. Summary of the Invention

[0005] In view of this, this application provides a laser drilling method for high-temperature alloys with thermal barrier coatings, which solves the problems in the prior art and improves the drilling quality.

[0006] This application provides a laser drilling method for high-temperature alloys with thermal barrier coatings, employing the following technical solution: A method for laser drilling of high-temperature alloys with thermal barrier coatings includes: Step 1: Spray sacrificial protective slurry onto the thermal barrier coating and metal substrate surface of the workpiece to be processed area and dry it to form a sacrificial protective layer on the surface of the workpiece to be processed area, the sacrificial protective layer covering the processing area. Step 2: Use a millisecond laser to machine a bottom hole with a diameter of d0 from the surface of the thermal barrier coating on the workpiece or the surface of the metal substrate in the area to be processed; Step 3: Use a millisecond laser to perform n turns of rotary cutting and enlarging on the bottom hole from the surface of the thermal barrier coating of the workpiece or the surface of the metal substrate until the hole is enlarged to the target hole diameter df. The theoretical value of the annular cross-sectional area corresponding to the area removed in each turn is equal. The deviation between the actual value and the theoretical value of the annular cross-sectional area corresponding to the area removed in any turn is controlled within ±10%, and n is greater than or equal to 2. Step 4: Remove the sacrificial protective layer and clean the borehole walls.

[0007] Optionally, in step 3, the instantaneous aperture dk after the kth rotary cut satisfies: ; In this case, k takes values ​​from 1 to n.

[0008] Optionally, the thickness of the sacrificial protective layer in step 1 is 0.08-0.12 mm.

[0009] Optionally, in step 1, the method for preparing the sacrificial protective layer includes: Hexagonal boron nitride powder and deionized water were mixed in a mass ratio of 1:(2-3) to form a solution; Add 0.5-1% of a dispersant to the mixed solution and ultrasonically disperse for 25-35 minutes to form a uniform sacrificial protective slurry; In step 1, the workpiece coated with the sacrificial protective slurry is dried at 80-120°C to obtain the sacrificial protective layer.

[0010] Optionally, the dispersant may be sodium polyacrylate, sodium hexametaphosphate, or polyvinylpyrrolidone.

[0011] Optionally, steps 2 and 3 are performed using the same millisecond laser, with a pulse width of 0.1-10 ms and a wavelength of 1064 nm.

[0012] Optionally, in step 2, the bottom hole is processed using a pulse train with progressively decreasing peak power, and the power attenuation coefficient is 0.7-0.9.

[0013] Optionally, the millisecond laser power in step 3 is 60-80% of the peak power of the first millisecond laser pulse in step 2.

[0014] Optionally, in steps 2 and 3, an auxiliary gas is used to purge the processing area during the processing. The auxiliary gas is oxygen, nitrogen, compressed air or argon, and the pressure of the auxiliary gas is 0.3-1.5 MPa.

[0015] Optionally, in step 4, the sacrificial protective layer is removed by ultrasonic cleaning, and the cleaning solution is deionized water.

[0016] In summary, this application includes the following beneficial technical effects: This application organically combines equal volume removal path planning, two-step laser drilling with bottom hole plus rotary cutting and enlargement, and a sacrificial protective layer to construct an inseparable technical whole. Through the unexpected synergistic effect among the three, it achieves a comprehensive improvement in the quality and efficiency of laser drilling of high-temperature alloys with thermal barrier coatings.

[0017] The method described in this application significantly reduces the thickness of the remelted layer to 42-55µm, which is about 25%-45% thinner than the 60-80µm of the prior art. This is beneficial for improving the cooling performance and service life of the film cooling holes. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a laser drilling method for high-temperature alloys with thermal barrier coatings. Detailed Implementation

[0020] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0021] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0023] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0025] This application provides a method for laser drilling of high-temperature alloys with thermal barrier coatings.

[0026] A method for laser drilling of high-temperature alloys with thermal barrier coatings includes: Step 1: Spray sacrificial protective slurry onto the thermal barrier coating surface and the metal substrate surface of the workpiece to be processed area and dry it to form a sacrificial protective layer on the surface of the workpiece to be processed area, which covers the processing area.

[0027] Step 2: Use a millisecond laser to machine a bottom hole with a diameter of d0 from the surface of the thermal barrier coating on the workpiece or the surface of the metal substrate in the area to be processed.

[0028] Step 3: Use a millisecond laser to perform n turns of rotary cutting to enlarge the hole from the surface of the thermal barrier coating or the metal substrate until the target hole diameter df is reached. Based on the theoretical value that the annular cross-sectional area corresponding to the area removed in each turn is equal, determine the hole diameter after each turn of rotary cutting and the path of the millisecond laser during each turn of rotary cutting. The deviation between the actual value and the theoretical value of the annular cross-sectional area corresponding to the area removed in any turn is controlled within ±10%, and n is greater than or equal to 2.

[0029] Step 4: Remove the sacrificial protective layer and clean the borehole walls.

[0030] The equal-volume removal principle proposed in this application refers to ensuring that the annular cross-sectional area removed in each turn is strictly equal or controlled within a preset threshold range during the rotary cutting and reaming process, with a deviation within ±10%. Compared with the existing equal-diameter incremental method, the equal-volume method fundamentally eliminates the problems of heat accumulation caused by an excessively small inner ring cross-sectional area and severe spattering caused by an excessively large outer ring cross-sectional area. Specifically, the core physical significance of the equal-volume method lies in the fact that the laser energy input in each turn is proportional to the amount of material removed, avoiding localized overheating or spattering bursts caused by a mismatch between energy input and removal amount. Experiments show that the equal-volume method can reduce the spattering area from 13.2% under the equal-diameter method to 4.0%, a reduction of approximately 70%, achieving a source reduction effect.

[0031] In step 3, the instantaneous aperture dk after the kth rotary cut satisfies: ; In this case, k takes values ​​from 1 to n.

[0032] The formula for calculating the instantaneous aperture dk after the kth rotary cutting is derived as follows: During the k-th rotation, the laser beam moves along a circle with radius rk = dk / 2, removing an annular region with inner radius rk-1 and outer radius rk. The cross-sectional area Ak removed in the k-th rotation is: ; According to the principle of equal volume removal, the cross-sectional area removed in each ring is strictly equal: A1=A2=……=An=A Total removed cross-sectional area for: ; Therefore, the cross-sectional area is removed by a single loop. for: ; The cumulative cross-sectional area removed in the kth cycle is: (1); Meanwhile, the cumulative cross-sectional area can also be expressed as: (2); By combining the above formulas (1) and (2) and simplifying them, we can obtain the formula for calculating the instantaneous aperture dk after the kth turn of rotary cutting.

[0033] The thickness of the sacrificial protective layer in step 1 is 0.08-0.12 mm. The preparation method of the sacrificial protective layer in step 1 includes: mixing hexagonal boron nitride powder with deionized water at a mass ratio of 1:(2-3); adding a dispersant accounting for 0.5-1% of the total mass of the mixture to the solution, and ultrasonically dispersing for 25-35 minutes to form a uniform sacrificial protective slurry; drying the workpiece coated with the sacrificial protective slurry at 80-120°C to obtain the sacrificial protective layer. The dispersant is sodium polyacrylate, sodium hexametaphosphate, or polyvinylpyrrolidone. The hexagonal boron nitride powder has a purity ≥99% and an average particle size of 1-10 µm; the ultrasonic power for ultrasonic dispersion is 200-400 W. The sacrificial protective slurry is uniformly coated onto the surface of the workpiece to be processed using a spray gun or brush, and the coating area should extend at least 5 mm beyond the edge of the target aperture.

[0034] This application involves spraying a boron nitride sacrificial protective layer onto the workpiece surface in the area to be processed. Utilizing the low surface energy, high-temperature stability, and layered structure of hexagonal boron nitride, it prevents spatter generated during laser processing from adhering to the workpiece surface. This prevents chemical reactions with the molten metal and allows the spatter to peel off along with the workpiece after processing, leaving no residue. This achieves a surface protection strategy that blocks spatter adhesion from the end. A key innovation of this boron nitride sacrificial protective layer lies in the fact that, through systematic experimental optimization, the optimal thickness range of 0.08-0.12 mm for laser drilling of high-temperature alloys with thermal barrier coatings was determined.

[0035] A thickness of less than 0.08 mm may not be able to form a complete and continuous covering film, and there may be local exposed areas. Splashes can directly contact the workpiece surface through the exposed areas, and the anti-splash adhesion effect is significantly reduced.

[0036] The optimal thickness range is 0.08-0.12 mm. Within this range, the boron nitride sacrificial protective layer can form a complete and uniform covering film, fully covering the workpiece surface. Simultaneously, the moderate thickness of the boron nitride sacrificial protective layer results in a short laser penetration time and minimal impact on processing efficiency. Experimental data shows that within this range, the spatter area is controlled at 1.5-2.0%, and the coating separation distance is less than 0.6 mm, meeting the processing quality requirements for film cooling holes in aero-engines.

[0037] For thicknesses greater than 0.12 mm, the laser requires a longer time to penetrate the boron nitride sacrificial protective layer to reach the workpiece surface, resulting in a 10-15% increase in processing time. Furthermore, excessively thick boron nitride sacrificial protective layers are prone to cracking and peeling under laser thermal shock, thus reducing their protective effect. In addition, excessively thick coatings increase the workload of spraying and removal processes.

[0038] In one embodiment, the thickness of the boron nitride protective layer is 0.10 mm. This strikes the optimal balance between protective effect and processing efficiency, resulting in a splatter area of ​​1.7% and a relatively small coating separation distance.

[0039] Steps 2 and 3 are performed using the same millisecond laser. The pulse width of the millisecond laser is 0.1-10 ms, the wavelength is 1064 nm, and the laser beam is parallel to the axial direction of the hole.

[0040] This application uses the same millisecond laser to sequentially complete the two processes of bottom hole processing in step 2 and rotary cutting and reaming in step 3, without changing the laser or transferring the workpiece. In step 2, a small-diameter bottom hole is machined on the workpiece using a millisecond laser, with a diameter ranging from 0.2 to 0.3 mm, penetrating the thermal barrier coating and the metal substrate. In step 3, at the same station, using the same millisecond laser, the bottom hole is gradually enlarged to the target diameter (0.6-0.8 mm) according to a rotary cutting path planned based on the principle of equal volume removal. The core advantages of this millisecond laser hole-making method are: eliminating the equipment switching and alignment errors between nanosecond and millisecond lasers in the three-step method; avoiding the low efficiency and high cost problems of femtosecond lasers in the millisecond-femtosecond two-step method; and simplifying the process flow, with a single hole processing time of only 7.5-12 seconds, representing a 37-60% increase in efficiency compared to the three-step method. Moreover, the equipment investment is low, requiring only a millisecond laser, without the need for nanosecond or femtosecond lasers. Compared to the three-step method, the equipment investment is reduced by more than 50%, and the maintenance cost is also reduced accordingly. In step 2, the bottom hole is machined using a pulse train with progressively decreasing peak power, with a power attenuation coefficient of 0.7-0.9. The peak power is selected within the range of 1-5kW depending on the workpiece material and the type of thermal barrier coating.

[0041] The millisecond laser power in step 3 is 60-80% of the peak power of the first pulse of the millisecond laser in step 2, and the pulse frequency is 20-100Hz.

[0042] In steps 2 and 3, an auxiliary gas is used to purge the processing area during the processing. The auxiliary gas is oxygen, nitrogen, compressed air or argon, and the pressure of the auxiliary gas is 0.3-1.5 MPa; this can promptly remove molten material and splashes.

[0043] In step 4, the sacrificial protective layer is removed by ultrasonic cleaning, using deionized water as the cleaning solution. Ultrasonic cleaning conditions: frequency 40kHz, temperature 40-60°C, time 5-10 minutes.

[0044] After cleaning, the hole shape is inspected, including hole diameter measurement, hole wall roughness inspection, remelted layer thickness measurement, inlet / outlet roundness evaluation, and thermal barrier coating separation distance measurement. This application provides a specific embodiment 1 of a laser drilling method for high-temperature alloys with thermal barrier coatings: The workpiece in this embodiment is a GH4169 nickel-based superalloy substrate with a thickness of 2 mm. A PS-PVD thermal barrier coating is prepared on the surface, consisting of 8 wt% Y₂O₃-stabilized ZrO₂ with a thickness of 350 µm, and a NiCoCrAlY binder layer with a thickness of 100 µm. The processing requirements are: to machine 25° inclined film cooling holes with a target hole diameter df = 0.8 mm, measured perpendicular to the workpiece surface, and a hole depth of approximately 4.7 mm.

[0045] like Figure 1 As shown, a method for laser drilling of high-temperature alloys with thermal barrier coatings includes: Step 1, Spraying the sacrificial protective layer: Mix hexagonal boron nitride powder and deionized water at a mass ratio of 1:2.5, add 0.8% sodium polyacrylate dispersant, and ultrasonically disperse for 30 minutes at an ultrasonic power of 300W to form a uniform slurry. Use a spray gun to spray the slurry onto the thermal barrier coating surface and the metal substrate surface of the area to be processed on the workpiece. The coating area diameter is 15mm, extending >5mm beyond the edge of the target hole. Dry at 100°C for 30 minutes, resulting in a sacrificial protective layer coating thickness of 0.10mm.

[0046] Step 2, Millisecond laser bottom hole processing: Laser parameters: wavelength 1064nm, pulse width 2ms, peak power of the first pulse 3.5kW, power attenuation coefficient 0.85, pulse train length 15 pulses, auxiliary gas is compressed air, pressure 0.8MPa; a bottom hole with a diameter d0=0.3mm is processed from one side of the thermal barrier coating surface of the workpiece in the area to be processed.

[0047] Step 3, equal-volume rotary reaming: Using a millisecond laser, the bottom hole is successively reamed n times from the thermal barrier surface of the workpiece until it is enlarged to the target hole diameter df. Let the number of rotary reaming turns n=3. Calculate the intermediate hole diameter: mm; mm; Laser rotary cutting parameters: laser power 2.5kW, pulse width 1.5ms, pulse frequency 50Hz, auxiliary gas compressed air pressure 0.6MPa, scanning speed matched according to pulse frequency and aperture. Two rotary cuts are completed sequentially to d1=0.523mm and d2=0.676mm, and the last rotary cut enlarges the hole to df=0.8mm.

[0048] Step 4, Remove the protective layer and clean: Blow away most of the sacrificial protective layer and splashes with compressed air, then ultrasonically clean with the following parameters: frequency 40kHz, 50°C, 8 minutes.

[0049] Test results: Spatter area 1.7%, thermal barrier coating separation distance 0mm, no visible coating separation, remelted layer thickness 48µm, hole wall roughness Ra3.8µm, inlet roundness 0.96, outlet roundness 0.92, processing time 7.5s.

[0050] When this application combines the equal volume method with a sacrificial protective layer, the splash area is reduced from 13.2% to 1.5-2.0%, a reduction of 87%. This effect far exceeds the theoretical value of simply adding the two together. The equal volume method reduces splash area to 4.0%, while the sacrificial protective layer alone reduces splash adhesion by approximately 62%. The simple combination of the two reduces splash adhesion by 4.0% × (1-62%), resulting in a reduction of 1.5-1.6%, with the actual value of 1.7% approaching the theoretical limit. This indicates a significant synergistic enhancement effect when combining the equal volume method with the sacrificial protective layer in this application. The mechanism is that the equal volume method not only reduces the total amount of splash but also makes the splash particle size distribution more uniform and the particles smaller, while the sacrificial protective layer has a better anti-adhesion effect on small-sized splash particles, forming a virtuous cycle of producing less and easier protection.

[0051] The method of this application has good versatility and can be adapted to three thermal barrier coating types, namely APS, EB-PVD and PS-PVD, and various nickel-based high-temperature alloy substrates such as GH4169, GH3536, GH3230, DZ125 and M951, by adjusting the laser parameters.

[0052] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for laser drilling of high-temperature alloys with thermal barrier coatings, characterized in that, include: Step 1: Spray sacrificial protective slurry onto the thermal barrier coating surface and the metal substrate surface of the workpiece to be processed area and dry it to form a sacrificial protective layer on the surface of the workpiece to be processed area, and the sacrificial protective layer covers the processing area. Step 2: Use a millisecond laser to machine a bottom hole with a diameter of d0 from the surface of the thermal barrier coating on the workpiece or the surface of the metal substrate in the area to be processed; Step 3: Use a millisecond laser to perform n turns of rotary cutting and enlarging on the bottom hole from the surface of the thermal barrier coating of the workpiece or the surface of the metal substrate until the hole is enlarged to the target hole diameter df. The theoretical value of the annular cross-sectional area corresponding to the area removed in each turn is equal. The deviation between the actual value and the theoretical value of the annular cross-sectional area corresponding to the area removed in any turn is controlled within ±10%, and n is greater than or equal to 2. Step 4: Remove the sacrificial protective layer and clean the borehole walls.

2. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, In step 3, the instantaneous aperture dk after the kth rotary cut satisfies: ； In this case, k takes values ​​from 1 to n.

3. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, The thickness of the sacrificial protective layer in step 1 is 0.08-0.12 mm.

4. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, In step 1, the method for preparing the sacrificial protective layer includes: Hexagonal boron nitride powder and deionized water were mixed in a mass ratio of 1:(2-3) to form a solution; Add 0.5-1% of a dispersant to the mixed solution and ultrasonically disperse for 25-35 minutes to form a uniform sacrificial protective slurry; In step 1, the workpiece coated with the sacrificial protective slurry is dried at 80-120°C to obtain the sacrificial protective layer.

5. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 4, characterized in that, The dispersant is sodium polyacrylate, sodium hexametaphosphate, or polyvinylpyrrolidone.

6. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, Steps 2 and 3 are performed using the same millisecond laser, with a pulse width of 0.1-10 ms and a wavelength of 1064 nm.

7. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, In step 2, the bottom hole is processed using a pulse train with progressively decreasing peak power, and the power attenuation coefficient is 0.7-0.

9.

8. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, The millisecond laser power in step 3 is 60-80% of the peak power of the first millisecond laser pulse in step 2.

9. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, In steps 2 and 3, the processing area is purged with an auxiliary gas during the processing. The auxiliary gas is oxygen, nitrogen, compressed air or argon, and the pressure of the auxiliary gas is 0.3-1.5 MPa.

10. The laser drilling method for high-temperature alloys with thermal barrier coatings according to claim 1, characterized in that, In step 4, the sacrificial protective layer is removed by ultrasonic cleaning, and the cleaning solution is deionized water.

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