A laser drilling method for heterogeneous composite materials based on zoning parameter regulation

Abstract

The application belongs to the technical field of laser precision machining, and particularly relates to a laser drilling method for heterogeneous composite materials based on partition parameter regulation. f In view of the problems that a multilayer heterogeneous structure such as a SiC / SiC composite material is prone to hole wall cracking, interface delamination and re-solidification blockage in through-hole machining, the workpiece is divided into a coating area and a matrix area, the scanning speed, the focal point increment and the scanning number matching the material characteristics are selected respectively, and linear variable pitch spiral scanning combined with workpiece self-rotation is adopted to realize the relative uniform distribution of the energy density in the hole. On the premise of ensuring the integrity of the coating / matrix interface, the method can effectively reduce the hole taper and obtain a high-quality through-hole with smooth hole wall and significantly reduced defects.

Description

Technical Field

[0001] This invention belongs to the field of laser precision machining technology, and particularly relates to a method for coating SiC. f Laser hole fabrication method for heterogeneous multilayer structures such as SiC composite materials. Background Technology

[0002] Silicon carbide fiber reinforced silicon carbide (SiC) f SiC composites, with their superior high-temperature mechanical properties, excellent oxidation resistance, and outstanding thermal shock stability, have become important candidate materials for hot-end structural components of aero-engines (such as gas turbine blades, combustion chamber liners, and turbine casing liners). Environment and temperature are generally considered to be factors affecting SiC... f The main factors affecting the mechanical properties of SiC composites are water vapor. However, water vapor environments above 1200 °C lead to a significant degradation in their fatigue properties and a decrease in fatigue limit stress. To address this issue, in SiC... f Spraying functional ceramic coatings onto the surface of SiC composite materials is the most effective solution to improve their performance in extreme environments. Among them, thermal barrier coatings can significantly reduce the peak temperature of the substrate surface, while environmental barrier coatings can effectively inhibit water vapor corrosion. The superposition of thermal barrier and environmental barrier coatings can not only establish a steep temperature gradient, but also block the penetration of complex atmospheres, thereby maintaining the mechanical properties of the components under harsh thermal shock and thermal corrosion environments.

[0003] Currently, machining film cooling holes on the surface of hot-end components of aero-engines has become an important method for achieving efficient cooling. Cooling gas flows along the hole wall in the form of a thin film, which not only effectively isolates high heat flux and reduces wall temperature, but also inhibits the initiation and propagation of thermal fatigue cracks. However, in coated SiC... f Traditional processes for micropore fabrication in SiC composites have significant limitations. Laser processing, with its high precision, non-contact nature, and localized high energy density, is considered one of the most effective methods for processing ceramic matrix composites. In particular, most non-metallic materials exhibit good absorption characteristics for short-wavelength lasers, which can effectively suppress the expansion of the heat-affected zone while improving ablation efficiency. However, functional coatings and substrates typically have significant differences in thermophysical properties, making laser processing prone to problems such as pore wall cracking and interface delamination.

[0004] The laser scanning trajectory affects the surface spatial energy distribution during the drilling process. Typically, laser spiral scanning and concentric circle scanning are the two most common methods for micro-hole machining. It should be noted that, under a fixed scanning speed and pulse frequency, when using equidistant spiral or concentric circle scanning, as the radius decreases, the laser's single-turn scanning time shortens rapidly. The revisit interval of adjacent scanning trajectories on the same local area becomes shorter, and the material is re-energized before it has fully cooled. This results in significantly higher heat accumulation in the central region compared to the edges, causing non-uniform ablation rates. This accumulation continues during the multi-layer, multi-turn stacking process, leading to problems such as under-burning at the hole edge and excessive taper. Summary of the Invention

[0005] To address the aforementioned challenges, the present invention aims to propose a laser-based hole-making method for heterogeneous composite materials based on partition parameter control.

[0006] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0007] A laser-based hole-forming method for heterogeneous composite materials based on partition parameter control:

[0008] During laser scanning, segmented parameter control is applied to different functional areas. The workpiece is divided into a coating area and a substrate area, and corresponding parameters are applied to these two areas respectively.

[0009] The laser scanning trajectory using a linear variable-pitch spiral ensures a uniform energy density across the scanned single layer.

[0010] By employing functional segmented parameter control and a linear variable pitch spiral laser scanning trajectory, the two work synergistically to reduce the overall taper of the through-hole, avoiding defects such as carbon deposition, coating microcracks, and re-solidification blockage, resulting in a smooth hole wall surface, complete fiber texture, and simultaneous improvement in morphological quality.

[0011] Includes the following steps:

[0012] (1) Determine the parameters of the laser scanning trajectory of the linear variable pitch helix according to the required aperture diameter, wherein the parameters do not include the outer diameter of the linear variable pitch helix;

[0013] (2) Determine the inner diameter of the spiral line based on the bottom morphology of the hole in the pre-hole exploration experiment. The bottom morphology includes whether there is a protrusion or a depression at the bottom of the hole. If there is a protrusion, reduce the inner diameter of the spiral line; if there is a depression, increase the inner diameter of the spiral line until the bottom of the hole is flat. At this time, the inner diameter of the spiral line remains unchanged, and the spiral trajectory parameters are completely determined and remain unchanged.

[0014] (3) Determine the corresponding parameters in different functional areas: Each functional area corresponds to a set of scanning parameters, including: laser scanning speed, focal increment, and corresponding number of scans.

[0015] (4) Hole making is performed according to the parameters determined above.

[0016] As a preferred method, the scanning parameters of the linear variable pitch helix in step (1) include: the outer diameter of the helix, the minimum pitch, and the pitch increment.

[0017] The smaller the diameter of the hole to be drilled, the smaller the outer diameter of the helix, while the minimum pitch and pitch increment remain unchanged.

[0018] As a preferred embodiment, the protrusion in step (2) is the residue of the central material at the bottom of the hole, and the depression is caused by over-ablation of the bottom of the hole.

[0019] As a preferred method, the rule for determining the laser scanning speed in step (3) is: to ensure that a flat hole bottom morphology is obtained when processing under a determined scanning trajectory.

[0020] The rule for determining the focus increment is: the actual material depth removed in each scan is equal to the material thickness to be removed;

[0021] The rule for determining the number of scans is: the product of the focal spot increment and the number of scans equals the actual depth of material removal;

[0022] As a preferred approach, the coating region and the substrate region are different heterogeneous material layers.

[0023] As a preferred method, the rule for determining the minimum pitch in step (1) is: 30%–50% of the spot diameter.

[0024] The rule for determining the pitch increment in step (1) is: 10%-20% of the minimum pitch.

[0025] As a preferred method, when drilling the hole in step (4):

[0026] The laser scanning trajectory of the linear variable pitch helix is ​​coordinated with the rotation of the workpiece. As the helix radius decreases, the pitch increases linearly, automatically compensating for changes in angular velocity, improving energy distribution, avoiding depressions caused by concentrated energy at the center, and ensuring uniform heat input to the coating / substrate composite material in space and time, thereby improving the quality and stability of through-hole processing.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) It reduces the laser revisit frequency and heat accumulation in the central region during hole making and alleviates the problem of center-edge removal imbalance.

[0029] (2) A set of optimized zone drilling parameters were determined—v1 of 500 mm / s and Δf1 of 3.9 μm were used in the coating area, and v2 of 300 mm / s and Δf2 of 11.5 μm were used in the substrate area. These parameters ensure complete material removal and suppress significant central protrusions and edge depressions.

[0030] (3) The regional parameter control strategy can effectively suppress the generation of cracks in the coating and the coating-substrate interface area, thereby achieving stable ablation removal while maintaining high pore wall quality.

[0031] (4) A through-hole with a taper angle of 1.16° was obtained by adopting a regional parameter control strategy, achieving good hole shape accuracy. Overall, this invention is a SiC with ceramic coating. f This provides an effective approach for high-quality through-hole drilling of SiC composite materials. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of an ultraviolet nanosecond laser processing system.

[0033] Figure 2 A schematic diagram of the linear variable pitch spiral scanning and functional segmentation parameter control process: (a) scanning trajectory; (b) segmentation parameter settings.

[0034] Figure 3 Comparison of different laser scanning trajectories: (a) linear variable pitch spiral; (b) equidistant spiral; (c) X and Y direction profiles of the two trajectories obtained by laser confocal microscopy.

[0035] Figure 4 The results represent the morphological response of the coating area under different combinations of process parameters.

[0036] (a) v = 100 mm / s, Δf = 28 μm; (b) v = 100 mm / s, Δf = 33 μm; (c) v = 100 mm / s, Δf = 38 μm; (d) Comparison of profile lines when v = 100 mm / s;

[0037] (e) v = 500 mm / s, Δf = 3.4 μm; (f) v = 500 mm / s, Δf = 3.9 μm; (g) v = 500 mm / s, Δf = 4.4 μm; (h) Comparison of profile lines at v = 500 mm / s;

[0038] (i) v = 1000 mm / s, Δf = 1.4 μm; (j) v = 1000 mm / s, Δf = 1.9 μm; (k) v = 1000 mm / s, Δf = 2.4 μm; (l) Comparison of profile lines when v = 1000 mm / s.

[0039] Figure 5 The results represent the morphological response of the coating area under different combinations of process parameters.

[0040] (a) v = 100 mm / s, Δf = 45 μm; (b) v = 100 mm / s, Δf = 50 μm; (c) v = 100 mm / s, Δf = 55 μm; (d) Comparison of profile lines at v = 100 mm / s;

[0041] (e) v = 300 mm / s, Δf = 11 μm; (f) v = 300 mm / s, Δf = 11.5 μm; (g) v = 300 mm / s, Δf = 12 μm; (h) Comparison of profile lines at v = 300 mm / s;

[0042] (i) v = 900 mm / s, Δf = 3.8 μm; (j) v = 900 mm / s, Δf = 4.3 μm; (k) v = 900 mm / s, Δf = 4.8 μm; (l) Comparison of profile lines when v = 900 mm / s.

[0043] Figure 6 (a) Results of the flatness of the hole bottom in the coating area investigation experiment; (b) Results of the flatness of the hole bottom in the substrate area investigation experiment.

[0044] Figure 7 SEM and EDS results of through-holes for functional segment parameter adjustment control: (a) SEM image of through-hole, Mag=200X; (b,e,h,k) SEM image of hole wall magnification, Mag=800X; (c,f,i,l) SEM image of hole wall magnification, Mag=3000X; (d,g,j,m) corresponding EDS point scanning results.

[0045] Figure 8 SEM and EDS results of through holes were generated for the full coating parameter strategy. (a) SEM image of through hole, Mag=200X; (b,e,h,k) SEM image of hole wall magnification, Mag=800X; (c,f,i,l) SEM image of hole wall magnification, Mag=3000X; (d,g,j,m) corresponding EDS point scan results.

[0046] Figure 9 SEM and EDS results of through holes were generated for the full matrix parameter strategy. (a) SEM image of through hole, Mag=200X; (b,e,h,k) SEM image of hole wall magnification, Mag=800X; (c,f,i,l) SEM image of hole wall magnification, Mag=3000X; (d,g,j,m) corresponding EDS point scanning results.

[0047] Figure 10 Optical microscope measurements of the inlet and outlet under different hole-making strategies: (a), (b) Inlet and outlet of functional segment parameter control strategy; (c), (d) Inlet and outlet of full coating parameter strategy; (e), (f) Inlet and outlet of full substrate parameter strategy. Detailed Implementation

[0048] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] Example 1

[0050] A laser hole-making method for heterogeneous composite materials based on partitioned parameter control is proposed. During laser scanning, segmented parameter control is applied to different functional areas, including coating area and substrate area, and corresponding parameters are applied to these two areas respectively.

[0051] The laser scanning trajectory using a linear variable-pitch spiral ensures a uniform energy density across the scanned single layer.

[0052] By employing functional segmented parameter control and a linear variable pitch spiral laser scanning trajectory, the two work synergistically to reduce the overall taper of the through-hole, avoiding defects such as carbon deposition, coating microcracks, and re-solidification blockage, resulting in a smooth hole wall surface, complete fiber texture, and simultaneous improvement in morphological quality.

[0053] Specifically, a laser-based hole-forming method for heterogeneous composite materials based on partition parameter control includes the following steps:

[0054] (1) Determine the parameters of the laser scanning trajectory of the linear variable pitch helix according to the required aperture diameter, wherein the parameters do not include the outer diameter of the linear variable pitch helix;

[0055] (2) Determine the inner diameter of the spiral line based on the bottom morphology of the hole in the pre-hole exploration experiment. The bottom morphology includes whether there is a protrusion or a depression at the bottom of the hole. If there is a protrusion, reduce the inner diameter of the spiral line; if there is a depression, increase the inner diameter of the spiral line until the bottom of the hole is flat. At this time, the inner diameter of the spiral line remains unchanged, and the spiral trajectory parameters are completely determined and remain unchanged.

[0056] (3) Determine the corresponding parameters in different functional areas: Each functional area corresponds to a set of scanning parameters, including: laser scanning speed, focal increment, and corresponding number of scans.

[0057] (4) Drill holes according to the parameters determined above.

[0058] Preferably, the scanning parameters of the linear variable-pitch helix in step (1) include: the outer diameter of the helix, the minimum pitch, and the pitch increment.

[0059] The smaller the diameter of the hole to be drilled, the smaller the outer diameter of the helix, while the minimum pitch and pitch increment remain unchanged.

[0060] Preferably, the protrusion in step (2) is the residue of the central material at the bottom of the hole, and the depression is caused by over-ablation of the bottom of the hole.

[0061] Preferably, the rule for determining the laser scanning speed in step (3) is: to ensure that a flat hole bottom morphology is obtained when processing under a determined scanning trajectory.

[0062] The rule for determining the focus increment is: the actual material depth removed in each scan is equal to the material thickness to be removed;

[0063] The rule for determining the number of scans is: the product of the focal spot increment and the number of scans equals the actual depth of material removal;

[0064] Preferably, the coating area and the substrate area are different heterogeneous material layers.

[0065] Preferably, the rule for determining the minimum pitch in step (1) is 30%–50% of the spot diameter.

[0066] The rule for determining the pitch increment in step (1) is: 10%-20% of the minimum pitch.

[0067] Preferably, in step (4) when making the hole:

[0068] The laser scanning trajectory of the linear variable pitch screw is coordinated with the rotation of the workpiece. As the scanning radius decreases, the pitch is synchronously amplified, automatically compensating for changes in angular velocity, improving energy distribution, avoiding depressions caused by energy concentration at the center, and ensuring uniform heat input distribution of the laser to the coating / substrate composite material in space and time, thereby improving the quality and stability of through-hole processing.

[0069] Example 2

[0070] 2.1 Experimental Setup

[0071] Figure 1 A schematic diagram of the working principle of the ultraviolet nanosecond laser processing system (6-axis motion platform + 2-axis galvanometer) is shown. The entire machine uses a marble bed and is equipped with an air-bearing module to improve structural stability and vibration reduction performance. The motion control mainly includes: XY-axis long-stroke linear motor displacement platform, Z-axis electric lifting table, high-speed and high-precision servo rotary table, etc. The laser scanning system consists of an ultraviolet nanosecond laser with a wavelength of 355nm and a maximum output power of 30W, and a two-dimensional galvanometer with a maximum scanning speed of 6000 mm / s.

[0072] 2.2 Experimental Materials

[0073] The sample used in this invention is 2.5D SiC with a T / EBC coating. f SiC composite material plates, supplied by Suzhou Sailifei Ceramic Fiber Co., Ltd., China. Measurements show that SiC... f The SiC matrix thickness is 4.9 ± 0.2 mm. The reinforcement consists of SiC fibers with a volume fraction of approximately 40%, a linear density of 280 tex, and a single filament tensile strength exceeding 2.3 GPa. The T / EBC coating is prepared by atmospheric plasma spraying (APS) and has a total thickness of 1.10 ± 0.11 mm. It consists of a three-layer structure: an outer YSZ thermal barrier coating (TBC) with a thickness of approximately 0.70 ± 0.07 mm; a middle rare earth silicate environmental barrier coating (EBC) with a thickness of approximately 0.30 ± 0.03 mm; and an inner Si bonding layer with a thickness of approximately 0.10 ± 0.01 mm.

[0074] 2.3 Experimental Design

[0075] The linear variable pitch spiral scanning process used in this invention is as follows: Figure 2 As shown in (a). During the spiral scan, the spacing between adjacent trajectories decreases from the center outwards: the spacing at the edge is set to p. min The interval increases linearly by Δp per lap, and the interval of the nth lap is p. min +nΔp. This strategy effectively reduces the peak energy density at the center of the hole, alleviating the problem of uneven ablation caused by excessive energy concentration. Furthermore, during multi-layer scanning, the laser needs to be switched on and off at the hole edge, inevitably resulting in transition zones with identical positions. If the workpiece remains stationary, these zones will overlap, leading to localized over-ablation and under-ablation in adjacent areas, causing hole wall degradation and other problems. Therefore, this invention addresses this issue by introducing a slow spin (10 rpm) of the workpiece.

[0076] When the single-layer removal depth is matched with the laser focus step increment, the laser focus can remain near the surface as the processing evolves, thereby achieving layer-by-layer controllable removal, improving ablation efficiency, and suppressing thermal damage. Therefore, based on a pre-determined linear variable-pitch spiral scanning trajectory, this invention achieves deterministic and controllable removal of deep micropores in multilayer heterogeneous composite materials by rationally selecting the scanning speed v and focus increment Δf. As shown in Figure 2(b), in the surface coating region (YSZ / rare earth silicate / binder phase), since the absorption rate and thermal diffusivity of each component to 355 nm wavelength laser are similar, a uniform focus increment Δf1 is used to complete stable removal; while in the matrix region (SiC... f / SiC), considering its higher hardness and thermal diffusion characteristics, the focal increment Δf2 is set to meet the principle of matching its removal depth.

[0077] In this invention, the linear pitch increment Δp is a constant. The laser scanning speed v is used to change the spatial overlap rate of adjacent pulses on the scanning path to optimize the surface energy density distribution, thereby adjusting the monolayer ablation depth. The number of scans N is the number of helical scans at each focal position, such that N×Δf equals the actual removal depth. Based on the principle of matching the monolayer removal depth with the focal increment, this invention studies the blind hole forming characteristics of the coating region and the substrate region under different scanning speeds and focal increments. Based on the previous experimental results, experiments were designed, as shown in Tables 1 and 2. It should be noted that the hole forming in the substrate region first achieves complete coating removal using the optimal processing parameters for the coating region, and then a blind hole of approximately 1 mm depth is processed under the same trajectory and workpiece rotation conditions.

[0078] After optimizing the parameters of the coating and substrate regions, a comparative experiment was designed to further evaluate the influence of different scanning trajectories on the ablation morphology and energy distribution using two scanning methods: equidistant spiral and linear variable-pitch spiral.

[0079] Based on the optimization of process parameters and the determination of the scanning trajectory, to verify the effectiveness of the "functional segmented parameter control-linear variable pitch spiral" strategy in machining through holes, a through-hole experimental study was conducted, with each experiment being independently repeated three times. As shown in Table 3, the current experiments included three scanning strategies: functional segmented parameter control strategy, full-process coating parameter strategy, and full-process substrate parameter strategy. As mentioned earlier, the current research focuses on hole wall integrity, hole taper, and machining efficiency.

[0080] Table 1 Laser hole drilling parameters in the coated area

[0081]

[0082] Table 2 Laser hole drilling parameters in the substrate region

[0083]

[0084] Table 3 Experimental parameters for through-hole drilling

[0085]

[0086] 3 Results and Discussion

[0087] 3.1 Study on material ablation behavior under different scanning trajectories

[0088] The ablation morphology of the coating area under two scanning trajectories, namely equidistant spiral and linear variable-pitch spiral, is as follows: Figure 3 As shown. As expected, under equidistant spiral conditions, the excessive overlap of the light spot in the central region leads to excessive energy concentration, resulting in excessive ablation at the center of the hole, while the energy density near the hole wall is relatively low, and material removal is insufficient. Its three-dimensional morphology is characterized by increased taper accompanied by step-like undulations at the edges, such as... Figure 3 As shown in (a) and (c). In contrast, the linear variable-pitch screw achieves radial energy input balance by simultaneously increasing the pitch when the ablation radius decreases, thus offsetting the energy enrichment caused by the increase in the inner ring angular velocity. The resulting three-dimensional morphology is a regular "bowl bottom" shape, without a central depression or edge steps, as shown in (a) and (c). Figure 3 As shown in (b). Further profile results indicate that sidewall under-etching is effectively suppressed. In summary, linear variable-pitch spiral scanning can significantly homogenize the radial energy distribution, thereby reducing taper and improving borehole wall quality.

[0089] 3.2 Influence of Laser Ablation Process Parameters on Hole Geometric Accuracy

[0090] Figure 4 The three-dimensional structural features and cross-sectional measurement results of blind holes in the coating region under different laser ablation conditions are presented. When the scanning speed is 100 mm / s, the removal depth changes significantly as the focal spot increment increases from 28 μm to 38 μm, such as... Figure 4 As shown in (a)-(d), when the focal increment is 33 μm, the removal depth is close to the preset 1.1 mm, but it is difficult to achieve uniform layer-by-layer removal at the current scanning speed. When the focal increment is too large, the accumulated defocus between layers causes the focal point to gradually move away from the surface to be processed, resulting in insufficient energy density and a decrease in ablation depth. Smaller focal increments are accompanied by more laser scans, which can achieve complete removal of the coating area, but the total depth exceeds the target value. Due to SiC f / SiC has a lower ablation threshold than the coating structure, and under the same scanning conditions, the substrate area is more likely to form obvious depressions.

[0091] When the laser scanning speed increased to 500 mm / s, the uniformity of material layer removal was significantly improved. Similarly, the relatively large focal increment (4.4 μm) led to incomplete coating removal, such as... Figure 4As shown in (g). However, a smaller focal increment (3.4 μm) will induce over-ablation, as... Figure 4 As shown in (e). Specifically, when the focal increment is 3.9 μm, the bottom of the hole is flat, the coating material is completely removed, and no ablation occurs. Furthermore, at a laser scanning speed of 1000 mm / s, as... Figure 4 In (i)–(l), due to the uneven distribution of ablation energy, different degrees of protrusions exist at the bottom of the hole under different focal increment conditions.

[0092] Figure 5 The effects of different combinations of process parameters on substrate removal behavior and pore bottom morphology were demonstrated. As mentioned earlier, each experiment first removed a 1.1 mm coating structure from the surface using a laser scanning speed of 500 mm / s and a focal increment of 3.9 μm, and then continued with laser removal of the substrate material. When the scanning speed was 100 mm / s, such as... Figure 5 In (a)-(d), the 45 μm focal increment results in a removal depth much greater than 1 mm, leading to over-ablation. It should be noted that, although... Figure 5 (a) and (d) exhibit a flat bottom feature, but during drilling of thick samples, the continuous accumulation of defocusing leads to severe taper and a significant decrease in processing efficiency in the later stages, making through-hole machining impossible. When the focal increment is 55 μm, the bottom morphology of the hole is uneven because the single-layer removal depth is less than the focal increment, and the focal position is lower than the surface to be processed, resulting in incomplete ablation. Although the X and Y section depths are close to the expectation when the focal increment is 50 μm, uneven ablation still exists. When the laser scanning speed is 300 mm / s, such as Figure 5 Similar phenomena were observed in (e)-(h). Compared to Figure 5 (a)-(d) show further improved bottom flatness, significantly reduced X / Y profile fluctuations, and higher linear overlap, indicating more consistent layer-by-layer removal at this speed. This is because pulse overlap and heat accumulation are in a better balance range, reducing microscopic fluctuations caused by dynamic defocusing and uneven radial energy distribution. In contrast, when the laser scanning speed increases to 900 mm / s, pulse overlap decreases significantly, heat accumulation weakens, and the laser ablation process becomes more sensitive to focal increment. Smaller focal increments result in poor profile linear overlap, as shown in (i)-(l) of Figure 5. When the focal increments are 4.3 μm and 4.8 μm, although the total removal is close to 2100 μm, a geometric depression exists at the center of the bottom of the hole due to non-uniform ablation.

[0093] Figure 6Figures (a) and (b) illustrate the variation of hole bottom flatness in the coated and substrate regions under different combinations of process parameters. The hole bottom flatness index is quantified by the standard deviation of all depth points within the hole bottom region along the X and Y axial profiles; a smaller value indicates that the hole bottom is closer to a horizontal plane. The average value is then calculated for the X and Y directions. Figure 6 (a) It can be seen that the flatness of the coating area is highly sensitive to the scanning speed v and the focal increment Δf. The hole flatness produced under the A5 parameter combination (v=500 mm / s, Δf=3.9 μm) is the best, with a value of only 13.32, indicating that this set of parameters achieves the best match between the single-layer removal amount and the focal increment. Figure 6 (b) shows the flatness results of the substrate area, exhibiting a similar pattern to the coated area. The best hole flatness (25.82) was achieved with the B5 parameter combination (v=300 mm / s, Δf=11.5 μm), indicating that this combination achieved a uniform energy distribution. In general, the scanning speed and focus increment must be matched to ensure an appropriate removal depth, and only with a suitable scanning speed can a flat hole bottom be obtained.

[0094] On the other hand, the high thermal diffusivity of the substrate region means that the heat generated by laser heating diffuses more quickly along the material. With the same circuit and pulse energy, high thermal diffusivity leads to a decrease in energy absorbed per unit area, resulting in reduced removal efficiency. Therefore, to achieve sufficient single-turn removal depth in the high thermal diffusivity substrate region, the scanning speed needs to be reduced to prolong the interaction time between the laser and the material and increase energy deposition. Conversely, in the low thermal diffusivity coating region, the scanning speed can be appropriately increased to avoid excessive heat accumulation. This segmented speed adjustment based on functional zones balances the removal efficiency of both the coating and substrate regions with the hole wall quality. Therefore, under the same laser scanning trajectory, different parameters are selected based on functional zones. The laser scanning speed for processing the coating region is relatively higher at 500 mm / s, while the laser scanning speed for processing the substrate region is relatively lower at 300 mm / s. Ultimately, A5 (coating region) and B5 (substrate region) were determined as the optimal parameter combinations, laying the foundation for subsequent experiments on functional zone segmented parameter control strategies.

[0095] 3.3 Influence of different through-hole drilling strategies on hole wall quality

[0096] Building upon the aforementioned research, this invention further explores the pore wall morphology characteristics under different pore-forming strategies. To facilitate SEM observation, the samples were ground with 400-grit sandpaper after the through-holes were prepared to expose the internal structure. Microstructural characteristics of typical regions in the coating, coating / substrate interface, substrate, and pore bottom were captured sequentially from the pore top downwards according to depth, and characteristic points (EDS1, EDS2, EDS3) were then selected for energy dispersive spectroscopy (EDS) analysis. In the bar chart, besides C, O, and Si, "Others" represents the total atomic percentage of coating elements such as Y, Zr, and Yb.

[0097] Figure 7 The results of through-hole machining based on functional segmentation parameter control are shown. Overall SEM image is shown below. Figure 7 (a) The pore wall profile is clear and continuous with good penetration, and no local collapse or pore blockage is observed. The results indicate that there are no obvious cracks in the coated area, but significant oxide particle accumulation is present, as shown in Figures 7(b)-(d). In the coating / substrate transition zone, the pore walls are locally covered with oxides, but no interface delamination or interface cracking is observed. Similarly, obvious oxide layer coverage is observed in the upper half of the substrate area, such as... Figure 7 As shown in (e)-(g). This is because SiC f The SiC composite contains pores with a specific volume fraction. Residual oxygen reacts chemically with SiC fibers and the matrix at high temperatures, and the resulting oxides such as silica are sprayed back along the pore channels and deposited on the upstream of the pore walls under the action of the backflow plume.

[0098] In the bottom area of ​​the hole, such as Figure 7 (k)-(l), the SEM images of the pore walls show a longitudinally and transversely distributed SiC fiber texture, accompanied by a small amount of remelted particles and oxide traces, but the overall structure is uniform and dense. Oxide deposition is effectively suppressed, further confirming the conclusion that the oxides originate from the pores within the matrix. Therefore, it can be inferred that further reducing the SiC... f The internal pores of the SiC composite effectively suppress oxide adhesion. Overall, the functional segmentation parameter control strategy, combined with optimal parameters for each region, ensured complete removal of the coating area and clear exposure of the substrate area. Simultaneously, no large-scale peeling or cracking occurred at the coating / substrate interface, and the overall pore walls remained continuous and smooth. This result highlights the significant advantages of this process in through-hole processing of heterogeneous layered materials, ensuring both precise selective material removal and maintaining pore wall quality and structural integrity.

[0099] Figure 8Experimental results were presented for through-hole machining using a single coating parameter. In the coated area, the hole wall was clearly visible with no obvious oxide deposition, but a small amount of re-solidified particles were observed locally, and numerous cracks were visible on the hole wall. The root cause is that directly applying the "focal increment of the coating area" to the substrate machining inevitably increases the number of ablation layers and residence time. The combined effect of long-term backflow plume and periodic thermal shock induces microscopic cracking of the hole wall. Figure 8 (b)-(c). Furthermore, under current conditions, the matrix ablation is in negative defocusing, and the plume intensity is relatively low, thus... Figure 7 Compared to (b)-(c), oxide adhesion on the pore walls of the coated area is significantly reduced. Meanwhile, compared to... Figure 7 (a), Figure 8 (a) has fewer internal pores, leading to active oxidation of silicon carbide with low oxygen content. The backflow plume typically contains less SiO, CO gas, and PyC interface layer debris. Some debris adheres to the upper pore walls, resulting in a significant increase in C content in the coating area. Furthermore, the relatively low oxidation reaction rate results in a smaller oxide coverage area than... Figure 7 (a) Thus, significant oxide accumulation exists only in the substrate region adjacent to the pores and in the coating / substrate interface region. It should be noted that although the laser irradiation process remains defocused in the substrate region, the bottom fibers still maintain good integrity, and the SiC fiber clusters and SiC particles are clearly visible.

[0100] Figure 9 Experimental results are presented using a through-hole fabrication strategy employing only matrix parameters. From Figure 9 (a) It is evident that although the pores are interconnected, the pore walls in the substrate area are rough, accompanied by obvious cracks and pore opening defects, resulting in poor overall forming quality. In the coating area, for example... Figure 9 (b)–(c), because the focal increment is much greater than the actual removal depth per turn, the focal point deviates from the surface to be processed layer by layer, resulting in insufficient local energy density, uneven thermal stress distribution, and the formation of microcracks and oxide layer accumulation. In the coating / substrate transition zone, such as... Figure 9 (e)–(f) show significant delamination cracks propagating along the interface, accompanied by spalling of the pore wall material. This is mainly due to insufficient cross-boundary removal energy and the accumulation of thermal gradients, leading to stress concentration under the influence of the difference in thermophysical properties between the two materials, inducing interfacial delamination. In the matrix region, such as... Figure 9In (h)–(i), localized hole walls collapse and are covered with a thick layer of oxidized slag; while in the bottom region of the hole, as shown in Figures 9(k)–(l), the hole opening is extremely narrow and the edge slag accumulates severely, exhibiting typical "incomplete penetration" characteristics. The fundamental reason is that the focus deviation causes energy to decay exponentially along the depth direction, with most of the energy dissipated in the upstream and hole wall scattering and oxidation processes, making it difficult to form an effective removal flux at the bottom of the hole. Overall, processing using only substrate parameters will lead to defects such as insufficient coating removal, interface delamination, and incomplete penetration at the bottom of the hole.

[0101] In summary, the SEM / EDS results systematically verified the effectiveness of the proposed "functional segmentation parameter control strategy" laser hole-making process. This process achieved stable and controlled layered removal in the coating region. A smooth transition was achieved at the coating / substrate interface, without macro-peeling or interface instability; oxide residues were only present in the substrate region adjacent to the pores. At the bottom of the pores, the fiber texture of the pore walls was clear, the matrix composition remained intact, and no thermal damage propagation or material degradation was observed. Furthermore, common defects such as coating blockage, interface peeling, and re-solidification accumulation were not observed during the processing, and the pore walls remained continuous and intact. Further analysis shows that, for multilayer heterogeneous material structures, matching the focal increment (Δf) with the actual removal depth per loop is the core condition for ensuring processing quality. When Δf is set too large, the focal point lags behind the material surface layer by layer, resulting in insufficient energy deposition and an out-of-focus accumulation effect, which in turn leads to defects such as incomplete removal and excessively large hole wall taper. Conversely, when Δf is too small, the laser dwell effect is significantly enhanced, and heat cannot dissipate in time, causing heat accumulation and energy redundancy, leading to hole wall ablation and deterioration and severely reducing processing efficiency. Therefore, only by segmenting and adjusting parameters according to functional regions to achieve dynamic adaptation between Δf and material removal behavior can the controllable removal of both coating and substrate be achieved, thus realizing the synergistic optimization of hole wall quality, structural integrity, and processing efficiency.

[0102] 3.4 Influence of different hole-making strategies on through-hole taper

[0103] Figure 10 Optical microscopy measurements of the inlet and outlet morphology and the taper of the through-holes under different drilling strategies are presented. The results show significant differences in roundness between different strategies: the inlet roundness under the functional segmentation parameter control strategy is as follows... Figure 10 (a) Φ1114.27 μm, outlet as Figure 10 (b) Φ870.97 μm, vertical diameter difference ≈243 μm, and rounded outlet profile; under the full coating parameter strategy, the inlet is as follows: Figure 10 (c) Φ1125.35 μm, outlet as Figure 10 (d) Φ887.45 μm, upper and lower diameter difference ≈238 μm, outlet roundness is still good; under the full matrix parameter strategy, the inlet is as follows Figure 10(e) Φ1107.26 μm, while the outlet is as follows Figure 10 (f) With a diameter of only 469.32 μm and a top-to-bottom diameter difference of ≈638 μm, it exhibits the largest taper and a noticeably irregular notch at the exit, resulting in extremely poor roundness and insufficient permeability. In summary, all three processing strategies can produce through-holes close to 1.1 mm at the inlet side. However, at the outlet side, the full-process substrate parameter strategy suffers from insufficient energy due to excessive focus compensation. While it can penetrate the coating area, the energy is severely attenuated in the substrate area, rendering it almost ineffective as a through-hole.

[0104] The functional segmented parameter control strategy resulted in a film bore with a taper of approximately 1.16°, achieving a balance between efficiency and bore quality. By optimizing parameters for different regions, extreme results from a single parameter setting can be avoided, ensuring both fast processing speed and controlling the taper angle within a reasonable range. Experience in laser borehole fabrication shows that if the focal increment is too small, the focal point will remain close to the surface being processed, generally still achieving penetration, but resulting in significantly reduced processing efficiency. Conversely, if the focal increment is too large, the focal point quickly falls behind the material surface, and laser energy cannot be effectively deposited on the next layer of the interface to be processed, leading to either impassable boreholes or extremely large borehole tapers.

[0105] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A laser-based hole-forming method for heterogeneous composite materials based on partitioned parameter control, characterized in that: During laser scanning, segmented parameter control is applied to different functional areas. The workpiece is divided into a coating area and a substrate area, and corresponding parameters are applied to these two areas respectively. The laser scanning trajectory of the linear variable pitch spiral ensures the uniformity of energy density in the scanned single layer; Includes the following steps: (1) Determine the parameters of the laser scanning trajectory of the linear variable pitch helix according to the required hole diameter. The parameters do not include the inner diameter of the linear variable pitch helix. The scanning parameters of the linear variable pitch helix in step (1) include: the outer diameter of the helix, the minimum pitch, and the pitch increment. The smaller the required hole diameter, the smaller the outer diameter of the helix, while the minimum pitch and pitch increment remain unchanged. (2) Determine the inner diameter of the spiral line based on the bottom morphology of the hole in the pre-hole exploration experiment. The bottom morphology includes whether there is a protrusion or a depression at the bottom of the hole. If there is a protrusion, reduce the inner diameter of the spiral line; if there is a depression, increase the inner diameter of the spiral line until the bottom of the hole is flat. At this time, the inner diameter of the spiral line remains unchanged, and the spiral trajectory parameters are completely determined and remain unchanged. (3) Determine the corresponding parameters in different functional areas: Each functional area corresponds to a set of scanning parameters, including: laser scanning speed, focal increment, and corresponding number of scans; The final determined scanning parameters for through-hole fabrication are as follows: Coating region: scanning speed v1 = 500 mm / s; focal increment Δf1 = 3.9 μm; number of scans N1 = 283; Substrate region: scanning speed v2 = 300 mm / s; focal increment Δf2 = 11.5 μm; number of scans N2 = 427; (4) Drill holes according to the parameters determined above; during step (4) drilling: the laser scanning trajectory of the linear variable pitch screw is coordinated with the rotation of the workpiece. As the screw radius decreases, the pitch increases linearly, automatically compensating for the change in angular velocity; The samples used were 2.5D SiC with a T / EBC coating. f / SiC composite board, the T / EBC coating consists of a three-layer structure: the outer layer is YSZ thermal barrier coating TBC, the middle layer is rare earth silicate environmental barrier coating EBC, and the inner layer is Si bonding layer; The linear variable-pitch spiral scanning process is employed, where the spacing between adjacent trajectories decreases from the center outwards during the spiral scanning process. The spacing at the edges is set to... p min Δ increases linearly with each revolution p , No. n The spacing between the rings is p min +n Δ p .

2. The laser drilling method for heterogeneous composite materials based on partition parameter control according to claim 1, characterized in that: The protrusion in step (2) is the residual material in the center of the hole bottom, and the depression is caused by over-ablation of the hole bottom.

3. The laser drilling method for heterogeneous composite materials based on partition parameter control according to claim 1, characterized in that: The rule for determining the laser scanning speed in step (3) is: to ensure a flat hole bottom morphology during processing under a defined scanning trajectory. The rule for determining the focus increment is: the actual material depth removed in each scan is equal to the material thickness to be removed; The rule for determining the number of scans is: the product of the focal increment and the number of scans equals the actual depth of material removal.

4. The laser drilling method for heterogeneous composite materials based on partition parameter control according to claim 1, characterized in that: The coating area and the substrate area are different heterogeneous material layers.

5. The method for laser drilling of heterogeneous composite materials based on partition parameter control according to claim 1, characterized in that: The rule for determining the minimum pitch in step (1) is: 30%–50% of the spot diameter; The rule for determining the pitch increment in step (1) is: 10%-20% of the minimum pitch.

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