A method for preparing a turbine rotor blade surface quasi-wall shear stress sensor by magnetron sputtering deposition and application thereof

Abstract

The present application relates to the technical field of vacuum coating deposition and metal material surface treatment, and discloses a method for preparing a quasi-wall shear stress sensor on the surface of a turbine rotor blade by magnetron sputtering deposition and application. The method sprays or deposits an insulating layer on the surface of the turbine rotor blade to achieve an electrical isolation effect, and then sequentially performs cleaning, ion beam bombardment and vacuum drying to activate the deposition interface; a flexible mask is designed and assembled based on the blade surface topography data, and a nickel or platinum thin film is deposited in situ in the mask opening limited area by magnetron sputtering to form a substrate-free thin film quasi-wall shear stress sensitive element; after replacing the wire mask, a copper thin film is sputtered in situ to form a plated wire electrically connected to the sensitive element; finally, the prepared quasi-wall shear stress sensitive element and plated wire are subjected to electrical continuity detection and insulation integrity detection. The present application can eliminate substrate step disturbance, improve film-substrate adhesion and high-temperature service stability, and is suitable for turbine boundary layer shear stress testing.

Description

Technical Field

[0001] This invention belongs to the field of vacuum deposition and metal surface treatment technology, and relates to a metal thin film patterning process for in-situ magnetron sputtering deposition on the surface of turbine rotor blades with the assistance of masking process. In particular, it relates to a method for preparing a quasi-wall shear force sensor on the surface of a turbine rotor blade by magnetron sputtering deposition and its application. Background Technology

[0002] In aerodynamic experiments on aero-engine turbine components, precise measurements of the flow state on the blade surface, such as the spatial distribution of wall shear stress, are essential for verifying designs and analyzing boundary layer transition characteristics. These measurements are used to validate numerical simulations, assess the effectiveness of cooling structures, and verify blade profile designs. Regarding the measurement of quasi-wall shear forces, thin-film sensors and other thin-film sensing elements have become standard testing methods in the industry due to their fast response and ability to perform in-plane micro-area measurements. However, they still face several constraints in the actual service environment of turbine rotor blade surfaces.

[0003] Traditional thermal films are commercial products that fabricate metal sensing structures on a flexible polyimide substrate. In experiments, this single sheet of thermal film with a flexible substrate needs to be adhered to the surface of a turbine rotor blade. However, this type of thermal film with a flexible substrate is unsuitable for actual turbine boundary layer flow measurements: the polyimide substrate itself has a certain thickness (typically 50 μm), and with the adhesive layer used for adhesion, a noticeable raised step is formed on the originally smooth blade surface. For low-pressure turbine rotor blades with chord lengths only on the order of centimeters, this step alters the original flow channel structure and changes the local shape and surface roughness distribution of the blade surface, thus affecting the flow field and causing a shift in the boundary layer development process. This leads to changes in the flow state when the airflow passes the location of the thermal film, resulting in changes in the transition point, separation bubble scale, and reattachment position at the location of the thermal film. Consequently, the measured object is disturbed, and the measurement results are difficult to correlate with the sensorless state. Furthermore, polyimide materials are limited to cold-state testing. At high temperatures, they are prone to deformation and melting, leading to sensor failure or even detachment. This can cause foreign object damage (FOD) in high-speed engines or experimental platforms, affecting test safety. In addition, hot-film leads typically need to cross the blade surface and connect to an external data acquisition system. Improper fixing and insulation of the wiring harness can easily lead to wear-through, short circuits, or increased contact resistance under high-speed flow scouring, thermal cycling, and abrasion, resulting in increased signal noise and decreased repeatability.

[0004] In summary, existing thermal films and related thin-film elements for quasi-wall shear force measurement commonly suffer from problems in turbine rotor blade applications, such as stepped perturbation flow fields, insufficient reliability of curved surface bonding, limited temperature resistance and thermal cycling performance, and limited stability of high-temperature electrical connections. These issues make it difficult to meet the surface flow testing requirements of modern aero-engine turbine components under high-fidelity, high-reliability, and extreme environments. Therefore, how to achieve low-disturbance, high-reliability thin-film sensing element structure forming and long-term reliable service under the complex surface conditions of turbine rotor blades is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] (a) Purpose of the invention To address the issues of flow field interference and poor heat resistance caused by the polyimide substrate in traditional thermal films, this invention aims to provide a magnetron sputtering deposition method and application for preparing a quasi-wall shear force sensor on the surface of a turbine rotor blade. This method achieves electrical isolation by spraying or depositing an insulating coating on the blade surface, and uses mask selection control to achieve in-situ forming and positioning of the sensitive resistor pattern and lead pattern. This reduces the disturbance to near-wall flow caused by the sensor's additional thickness and edge steps. Furthermore, through engineering design of the thin film material system, film thickness, and electrical connection structure, the adhesion stability and electrical consistency of the thin film layer system under high-temperature thermal cycling and vibration loads are improved, enabling stable output and repeatable measurement of the quasi-wall shear force signal. This supports high-precision measurement and experimental applications of the spatial distribution of wall shear stress in turbine components.

[0006] (II) Technical Solution To achieve the objective of this invention and solve its technical problems, the present invention adopts the following technical solution: The first objective of this invention is to provide a magnetron sputtering deposition method for fabricating a quasi-wall shear force sensor on the surface of a turbine rotor blade. This method is used to form a substrate-free thin-film quasi-wall shear force sensing element on the suction and / or pressure surfaces of a turbine rotor blade and to extract signals. The method includes at least the following steps: SS1. Substrate Surface Pretreatment: Select the suction surface and / or pressure surface of the turbine rotor blade as the substrate. Clean the substrate surface, bombard it with ion beam and dry it to remove oil, particles and weak bonding layers and increase the surface energy of the substrate to activate the deposition sites. The surface is activated and meets the roughness and adhesion conditions required for thin film deposition. Then, an insulating coating is sprayed or deposited to form an insulating substrate surface to achieve electrical isolation and meet the insulation conditions. SS2. Sensitive element mask design and assembly: Based on the surface topography data of the insulating substrate and the geometric topology of the sensitive element of the quasi-wall shear sensor, a sensitive element mask with a preset opening pattern feature that matches the substrate contour is designed. The mask is positioned and fixed on the surface of the insulating substrate to define the area to be deposited. SS3. In-situ patterned deposition of sensitive elements: Under vacuum conditions, a magnetron sputtering process is used to in-situ sputter and deposit a thin film of nickel or platinum metal on the surface of an insulating substrate in the area defined by the mask opening pattern of the sensitive element, forming a quasi-wall shear sensitive element with preset pattern features. The thickness uniformity of the metal film and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power. SS4. Conductor Mask Design and Assembly: Based on the electrical connection position of the quasi-wall shear sensitive element, design a conductor mask with a preset opening routing pattern. Remove the sensitive element mask and position and cover the conductor mask on the surface of the insulating substrate, so that the routing opening of the conductor mask is aligned with the electrical connection end and the area to be deposited for coating conductor is defined. SS5. In-situ patterned deposition of coated wires: Under vacuum conditions, a magnetron sputtering process is used to in-situ deposit a copper metal thin film on the surface of an insulating substrate through the wiring opening of the wire mask, forming a coated wire that is electrically connected to the quasi-wall shear-sensitive element. The thickness uniformity of the coated wire and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power. SS6. Mask Removal and Consistency Testing: Remove the conductor mask and clean the deposition area to complete the fabrication of the substrate-free thin-film quasi-wall shear sensor. Perform electrical continuity testing and insulation integrity testing on the quasi-wall shear sensing element and the coated conductor.

[0007] The second objective of this invention is to provide a quasi-wall shear force sensor structure for the surface of a turbine rotor blade, which is prepared using the magnetron sputtering deposition method for the quasi-wall shear force sensor for the surface of a turbine rotor blade described above.

[0008] The third objective of this invention is to provide a turbine rotor blade surface flow field testing system, including the turbine rotor blade surface quasi-wall shear force sensor structure described above.

[0009] (III) Technical Effects Compared with the prior art, the method for preparing and applying the quasi-wall shear force sensor on the surface of the turbine rotor blade by magnetron sputtering of the present invention has the following beneficial and significant technical effects: (1) The present invention pre-sprays or deposits insulating material on the surface of turbine rotor blades to form an insulating substrate surface, and then constructs a substrate-free thin film quasi-wall shear sensor in situ on the surface of the insulating substrate by magnetron sputtering. This avoids the geometric steps and additional roughness formed by the traditional hot-film polyimide substrate and adhesive layer, thereby reducing the disturbance to the boundary layer transition and near-wall flow state, and improving the authenticity and comparability of the spatial distribution measurement of wall shear stress.

[0010] (2) Before deposition, the present invention performs cleaning, in-situ ion beam bombardment and vacuum drying to improve surface energy and activate deposition sites; based on the blade surface morphology data, mask design and bonding assembly are performed to realize in-situ patterned deposition of magnetron sputtering, avoiding the problem of poor compatibility of traditional photolithography on curved surfaces and thermal barrier coating surfaces; and through mask bonding alignment, the patterned integral forming of sensitive elements and coated wires is realized. At the same time, by coordinating the target-substrate distance and sputtering power and combining the workpiece attitude / rotation compensation curved surface shading effect, the uniformity of film thickness and the clarity of pattern edges are improved, ensuring the geometric consistency and resistance consistency of sensitive elements, thereby improving the shear force measurement resolution and batch repeatability.

[0011] (3) The present invention introduces a transition layer and a lead-out thickening layer on the conductor side, and combines low temperature annealing stabilization, four-wire resistance and insulation integrity detection, conductor encapsulation protection and bonding encapsulation, so that the electrical signal of the sensitive element can still be stably led out and reliably transmitted under the coupling effect of high temperature thermal cycling and rotor vibration load, reducing the probability of resistance drift and connection failure, thereby improving the service stability under long-term test conditions. Attached Figure Description

[0012] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood in conjunction with the following description of the embodiments, in which: Figure 1 A flowchart illustrating the implementation of a magnetron sputtering deposition method for fabricating a quasi-wall shear force sensor on the surface of a turbine rotor blade, as provided in this embodiment of the invention. Figure 2 The diagram shows a quasi-wall shear sensor and coated wire structure fabricated on the surface of a low-pressure turbine rotor blade by magnetron sputtering, wherein: (a) is the case where the sensor structure is formed on the surface of the suction surface substrate, and (b) is the case where the sensor structure is formed on the surface of the pressure surface substrate. Figure 3 This is a magnified schematic diagram of a partial structure of a quasi-wall shear force sensor and a coated wire. In the diagram, area A is the sensing core area of ​​the sensitive element, and area B is the coated wire area.

[0013] Explanation of reference numerals in the attached figures: 10 - suction surface substrate surface, 20 - pressure surface substrate surface, 30 - quasi-wall shear force sensor, 31 - quasi-wall shear force sensitive element, 32 - coated wire. Detailed Implementation

[0014] The purpose of this invention is to provide a magnetron sputtering deposition method and application for fabricating a quasi-wall shear force sensor on the surface of a turbine rotor blade. This method forms a substrate-free thin-film quasi-wall shear force sensing element on the insulating surfaces of the suction and pressure surfaces of a turbine rotor blade with an insulating coating, and enables signal extraction. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in more detail below with reference to the accompanying drawings of the embodiments. The described embodiments are some, but not all, of this invention, and are exemplary and intended to explain the invention, not to limit it. It should be noted that "substrate-free thin film" in this text refers to eliminating the traditional flexible substrate such as polyimide, with the sensing and lead film layer directly constructed on the surface of the blade's insulating coating, thereby significantly reducing step height and aerodynamic interference.

[0015] As a specific example, such as Figure 1 As shown, the magnetron sputtering deposition method for fabricating a quasi-wall shear force sensor on the surface of a turbine rotor blade of the present invention eliminates the polyimide organic substrate relied upon by traditional flexible hot-film sensors. It directly integrates the quasi-wall shear force sensing element and signal transmission wires onto the curved surface of the turbine rotor blade with an insulating coating in the form of a substrate-free thin film by magnetron sputtering. This reduces the total film thickness to the micrometer level, eliminating the pain points of sensor failure, peeling, and substrate thermal resistance interference caused by insufficient thermal stability of the polyimide substrate under high-temperature rotor conditions. Simultaneously, it minimizes interference with the boundary layer flow state on the blade surface. The method mainly includes the following steps: SS1. Substrate surface pretreatment: The suction and / or pressure surfaces of turbine rotor blades are selected as substrates. The substrate surfaces are cleaned, bombarded with ion beams, and dried to remove oil, micro- and nano-particles, and weakly bonded layers. By breaking the molecular bonds on the substrate surface, high-density dangling bonds and defect active sites are generated, thereby significantly activating deposition sites and improving surface free energy and wettability. This activates the substrate surface and meets the roughness and adhesion conditions required for thin film deposition. Then, an insulating coating is sprayed or deposited on the substrate surface to form an insulating substrate surface, which meets the insulation performance and achieves its electrical isolation effect.

[0016] Specifically, the substrate surface cleaning includes: ultrasonic cleaning with acetone as a solvent to remove organic contaminants, with an ultrasonic cleaning time of no less than 10 min, an ultrasonic power density of no less than 50 W / L, and a water bath temperature maintained between 40℃ and 60℃; followed by ultrasonic cleaning with ethanol as a solvent to remove residual acetone, with an ethanol ultrasonic cleaning time of no less than 5 min; rinsing with deionized water and then drying with nitrogen gas, using nitrogen gas with a purity of no less than 99.999%, and a nitrogen blowing pressure controlled between 0.2 and 0.4 MPa; after drying, it should be kept in an oven at 60-80℃ for no less than 30 min to thoroughly remove trace amounts of residual moisture from the substrate surface and microporous structure, preventing moisture from degassing in the vacuum chamber and causing degradation of the background vacuum and water vapor inclusion defects in the film; ion beam bombardment is performed in the same vacuum environment before magnetron sputtering deposition, with an ion beam energy of 300-800 Ω·cm. An eV argon ion beam is used to directionally bombard the substrate surface for at least 10 minutes. The incident angle of the argon ion beam relative to the substrate normal is maintained between 30° and 60° to balance etching efficiency and surface damage control. Weak bonding layers, oxides, and residual contaminants on the substrate surface are removed by sputtering etching. After ion beam treatment, vacuum drying is performed to achieve a clean microstructure with active deposition sites and the surface roughness required for thin film deposition. Subsequently, an insulating coating is fabricated on the substrate surface using methods such as spraying or deposition to form an insulating substrate surface to meet electrical isolation performance requirements.

[0017] SS2. Sensitive Element Mask Design and Assembly: Based on the surface morphology data of the insulating substrate and the geometric topology of the sensing element of the quasi-wall shear sensor, a sensing element mask with a preset opening pattern is designed to match the substrate contour. The mask is positioned and fixed on the surface of the insulating substrate to define the area to be deposited for the patterned sensing element.

[0018] Preferably, the surface topography data of the insulating substrate is obtained through three-dimensional scanning or contour measurement. The sensitive element mask is a flexible mask that fits the curved surface of the blade. The mask is provided with a positioning structure for matching the geometric reference of the insulating substrate surface. The positioning structure is preferably a reusable geometric stop, pin hole, boundary reference surface or sputter-resistant positioning mark, and the alignment deviation should not exceed ±30 μm. When the mask is covered and fixed, the mask lifting is suppressed by mechanical clamping, vacuum adsorption or temporary adhesion. The local bonding gap between the mask and the substrate should be uniformly controlled and not exceed 20 μm. The size of the gap directly determines the width of the transition zone of diffraction deposition at the edge of the pattern. In areas with large curvature, vacuum adsorption or mechanical pressure should be used to improve the uniformity of mask bonding and prevent the deposition material from diffraction deposition at the edge of the mask pattern. This ensures that the edge clarity and dimensional accuracy of the formed thin film pattern feature meet the sensing resolution requirements of the quasi-wall shear sensor.

[0019] SS3. In-situ patterned deposition of sensitive elements: Under vacuum conditions, magnetron sputtering is used to in-situ deposit a thin film of nickel or platinum metal on the surface of an insulating substrate within the area defined by the mask opening pattern of the sensing element, forming a quasi-wall shear sensing element with preset pattern characteristics. The uniformity of the metal film thickness and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power. Preferably, the in-situ magnetron sputtering deposition under vacuum conditions includes: S301. Fixture Clamping and Vacuuming: Clamp the turbine rotor blades, after assembling the sensitive element mask, into the magnetron sputtering cavity. The clamping fixture should ensure that the blades have adjustable degrees of freedom in their orientation within the cavity, so as to optimize the uniformity of thin film deposition by changing the relative positional relationship between the blade's deposition area and the target surface. After the blades are installed, ensure that the deposition area corresponding to the opening pattern of the sensitive element mask faces the sputtering source, and that the mask edges are well-fitted without warping. Then, activate the evacuation system to evacuate the cavity to a working vacuum level that meets the deposition conditions. The background vacuum level should not exceed 5 × 10⁻⁶. -4 Pa, and should be kept stable at this background vacuum level for at least 5 minutes before the working gas is introduced, to ensure that the partial pressure of residual gas (especially water vapor and oxygen) in the chamber is low enough to avoid it from mixing into the film during the deposition process and causing oxidation inclusions or interface oxide layers. S302. Sputtering Atmosphere Establishment and Plasma Stabilization: High-purity argon gas is introduced into the magnetron sputtering cavity as the sputtering working gas. The argon gas flow rate is adjusted to stabilize the working gas pressure in the cavity to a preset value within the range of 0.3~1.0 Pa. The gas pressure stability criterion is that the gas pressure fluctuation amplitude does not exceed ±2% of the set value within 2 consecutive minutes. The plasma discharge is ignited and maintained stably. The plasma stability is confirmed by the continuous and stable readings of the target voltage and discharge power, the power fluctuation does not exceed ±5% of the set value, and the stable duration is not less than 2 minutes, so that the sputtering particle flux and energy state remain stable. S303. Target pre-sputtering and surface cleaning: With the surface of the insulating substrate shielded, a pre-sputtering treatment of nickel or platinum target for a duration of not less than 10 minutes shall be performed. The pre-sputtering power density shall be set to 70% to 80% of the formal deposition power density to remove the contamination layer on the target surface and stabilize the sputtering rate. Sputtering particles generated during pre-sputtering shall be intercepted by baffles throughout the process. After pre-sputtering, the target voltage and discharge power readings shall be confirmed to be stable before switching to the formal deposition parameters. S304. Patterned Deposition and Bond Strength Control: Unmasking is performed within the area defined by the mask opening pattern of the sensitive element to form a quasi-wall shear sensitive element with preset pattern characteristics. The DC magnetron sputtering power density for the actual deposition is controlled at 2–8 W / cm².2 Within the specified range, the target-substrate distance is set to 50~300 mm; the incident energy of the sputtered particles should be controlled within a reasonable range to ensure that the film has a moderate atomic filling density and internal stress state. Excessive incident energy will lead to excessive compressive stress in the film and cause failure of the film-substrate interface, while excessive incident energy will result in loose columnar crystal structure, high resistivity and decreased fatigue resistance. During the deposition process, the deposition rate and incident energy are controlled by adjusting the target-substrate distance and sputtering power, and the deposition direction is kept consistent with the local normal of the blade target base by changing the clamping posture or rotating the blade. The blade rotation speed is preferably set between 5~15 r / min to improve the uniformity of film thickness while avoiding fluctuations in plasma discharge state and periodic deviations in deposition direction caused by excessive rotation speed. S305. Thickness Termination Control and Cooling Exit: The deposition time is controlled according to the pre-calibrated deposition rate to maintain the film thickness within the range of 0.2–0.5 μm. The deposition rate calibration should be performed on a substitute sample under the same target-substrate distance, working gas pressure, and power density conditions as the actual deposition, and confirmed by a step gauge. The calibration results should be valid within 48 hours before the actual deposition. If the target material has been replaced, left idle for an extended period, or the cumulative sputtering time exceeds the equipment's specified threshold, recalibration is required. After deposition, discharge is stopped, and the film is cooled in a vacuum environment. During the cooling phase, the vacuum level in the cavity should be maintained at no less than 1 × 10⁻⁶. -3 Pa, the blade outlet temperature should not exceed 50℃ to prevent oxidation and sudden change in thermal stress of the film substrate when exposed to the atmosphere at high temperature, so that the film reaches a thermally stable state before masking, and to perform resistance consistency detection on the quasi-wall shear sensitive element after deposition, so as to control the electrical dispersion caused by thickness fluctuation within the preset limit.

[0020] Furthermore, to improve the long-term bonding reliability of the quasi-wall shear sensing element under the coupled conditions of high-temperature thermal cycling and vibration fatigue loads on turbine rotor blades, a titanium or chromium metal adhesion layer with a thickness of 5-30 nm is first sputtered and deposited within the area defined by the mask opening pattern of the sensing element before sputtering and depositing a nickel or platinum metal thin film. The adhesion layer chemically bonds with the surface of the insulating coating to improve the bonding energy of the film-substrate interface. After the adhesion layer is deposited, a nickel or platinum metal thin film is continuously deposited to form the quasi-wall shear sensing element without breaking the vacuum. Continuous deposition (i.e., directly depositing the functional layer without breaking the vacuum after the adhesion layer is deposited) is a key operational constraint to ensure interface quality: if the adhesion layer is exposed to the atmosphere after deposition, a natural oxide layer will quickly form on its surface, which will severely weaken the interfacial bonding strength between it and the subsequent nickel or platinum functional layer, causing the film system to fail prematurely under thermomechanical loads. This improves the adhesion reliability of the sensing element under the coupled effects of high-temperature thermal cycling and rotor vibration loads without increasing the geometric steps, and reduces the risk of microcrack propagation caused by stress concentration in the edge area of ​​the sensing element.

[0021] Furthermore, the quasi-wall shear force sensing element is formed using a differential bridge or half-bridge resistor topology. At least two resistor arms are simultaneously deposited within the area defined by the same mask opening pattern, ensuring consistent temperature and strain field coupling conditions within the same substrate region. In subsequent steps SS4 and SS5, independent leads are laid for the bridge nodes to achieve Wheatstone bridge or differential measurement connections. This improves the common-mode rejection capability and measurement signal-to-noise ratio of the shear force signal under the background of temperature drift and electromagnetic interference of rotating blades, reduces zero-point drift caused by temperature sensitivity in single-ended measurements, and enhances the engineering usability of dynamic shear force measurement.

[0022] SS4. Wire Mask Design and Assembly: Based on the electrical connection position of the quasi-wall shear force sensitive element, a wire mask with a preset opening routing pattern is designed. The sensitive element mask is removed and the wire mask is positioned, covered and fixed on the surface of the insulating substrate, so that the routing opening of the wire mask is aligned with the electrical connection end and the area to be deposited for the coated wire is defined.

[0023] Preferably, while aligning the wiring openings of the conductor mask with the electrical connection end of the quasi-wall shear-sensitive element, the opening coverage length of the conductor mask within the overlap area of ​​the electrical connection end is not less than 200 μm. This ensures that the surface contact electrical connection area has a stable and sufficiently low contact resistance, limits the length and width of the overlap area between the conductor and the sensitive element, and allows the subsequently deposited coated conductor to form a surface contact electrical connection structure with the sensitive element within the overlap area. Furthermore, the mask pattern constraint prevents the conductor from crossing non-target areas, thereby improving electrical connection reliability and reducing the risk of insulation failure caused by misdeposition. Additionally, the wiring openings of the conductor mask define an external connection area at the end of the coated conductor, preferably with a size of not less than 1 mm × 2 mm. mm, its area is larger than the linewidth projection area of ​​the coated conductor, so as to facilitate subsequent electrical connection with external conductors. The external connection area is set at a position far away from the main aerodynamic measurement area, thereby reducing the impact of the external connection structure on the flow state of the blade surface and improving assembly reliability. After the conductor mask is assembled, the alignment between the mask wiring opening and the electrical connection end of the deposited sensitive element should be checked with the same geometric reference used in step SS2. The alignment deviation should not exceed ±30μm to prevent insufficient contact area of ​​the overlap area or conductor crossing the boundary of the sensitive element pattern due to alignment error.

[0024] SS5. In-situ patterned deposition of coated conductors: Under vacuum conditions, a magnetron sputtering process is used to deposit a copper metal thin film in situ on the surface of an insulating substrate through the wiring opening of a wire mask, forming a coated wire that is electrically connected to a quasi-wall shear-sensitive element. The thickness uniformity of the coated wire and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power.

[0025] Preferably, in step SS5, before sputtering and depositing the copper metal thin film, a titanium or chromium metal transition layer with a thickness of 10-50 nm is first sputtered and deposited within the area defined by the opening of the conductor mask. A gradient modulus transition region is constructed by chemically bonding the atoms of the transition layer with oxygen atoms on the surface of the insulating substrate. This improves the interfacial bonding strength and adhesion reliability between the copper metal-coated conductor and the surface of the insulating substrate and the electrical connection terminals of the quasi-wall shear-sensitive element, preventing interfacial peeling failure of the coated conductor under the coupled effects of thermal cycling loads and rotor rotational vibration loads in a high-temperature gas environment. During the sputtering and deposition of the copper metal thin film, the base vacuum level is not higher than 5.0 × 10⁻⁶. -3 The sputtering working pressure is 0.5~1.2 Pa, and the sputtering power density is 3~8 W / cm³. 2 During the deposition process, the substrate temperature is maintained at 50~150 ℃. A moderate increase in substrate temperature helps to improve the migration rate of copper atoms on the deposition surface, thereby improving the film density, reducing the film resistivity, and enhancing the interfacial bonding force between copper grains and the transition layer. At the same time, the substrate temperature should be prevented from exceeding 150 ℃ to avoid interdiffusion reaction at the copper / transition layer interface, which would cause an increase in contact resistance. The thickness of the copper metal film is controlled at 2~3 μm. By changing the clamping posture or rotating the blade workpiece, the deposition direction is kept consistent with the local normal of the blade to improve the uniformity of the metal film thickness within the preset pattern area and reduce the risk of under-plating and over-plating in the edge area. After the copper metal film sputtering deposition is completed, a metal thickening layer is further deposited in the lead-out area to reduce the lead resistance and improve the mechanical load-bearing capacity of the external connection. The pattern of the metal thickening layer is still defined by the mask opening and electrically connected to the coated wire. At the same time, the lead-out area is subjected to surface encapsulation treatment to improve the connection reliability of the lead-out under vibration, temperature gradient, and humid heat environments while maintaining insulation integrity.

[0026] In addition, in steps SS3 and SS5, after the sputtering deposition of the metal thin film is completed, the deposited thin film is subjected to low-temperature annealing treatment to reduce the residual stress of the metal thin film and stabilize the electrical properties of the thin film. This includes heating the blade to a preset annealing temperature at a preset heating rate and holding it at a preset holding time in an inert atmosphere or vacuum environment. The heating rate is preferably controlled at 5~10. The annealing rate is set at ℃ / min to prevent rapid heating from causing sudden changes in thermal stress within the film. The preset annealing temperature is lower than the upper limit of the thermal stability of the insulating coating and lower than the tempering temperature of the blade substrate, allowing the metal film to release stress and stabilize its structure without damaging the insulating substrate and its interface structure. After the heat preservation is completed, the film is cooled to room temperature in a controlled manner, with the cooling rate controlled to no more than 10℃ / min, in order to effectively reduce the risk of interfacial cracking and local warping caused by thermal shock. During the cooling process, the temperature gradient between the blade and the film layer system is kept under control to reduce the risk of interfacial cracking and local warping caused by thermal shock. After annealing, the resistance and electrical continuity of the shear force sensitive element on the alignment wall and the coated wire are retested, and the insulation integrity is checked. Based on the retest results, it is determined whether the stability of the film's electrical parameters and the consistency of its preparation meet the preset criteria.

[0027] SS6. Mask Removal and Consistency Detection: After removing the conductor mask and cleaning the deposition area, the substrate-free thin-film quasi-wall shear sensor is fabricated. Electrical continuity and insulation integrity tests are then performed on the quasi-wall shear sensing element and the coated conductor. Specifically, after fabrication, an electrical continuity test, including four-wire resistance measurement, is preferably performed on the quasi-wall shear sensing element and coated conductor. The result is compared with the theoretical value calculated based on film thickness, pattern size, and material resistivity; a deviation of no more than ±10% is considered acceptable. An insulation resistance test is then performed between the insulating coating and the metal film to determine the conduction state of the sensing element, the continuity of the conductor, and the insulation integrity. A DC voltage of no less than 100 V is applied between the sensing element and the blade substrate, and the insulation resistance is measured. An insulation resistance value of no less than 10 MΩ is considered acceptable. The insulation resistance test should be performed one by one between the blade substrate and each independent sensing channel. Simultaneously, the mutual insulation resistance between any adjacent conductor channels must be verified, requiring no less than 100 MΩ to prevent crosstalk between channels from affecting the accuracy of multi-channel dynamic measurements.

[0028] After completing step SS6, the process also includes the deposition of a protective encapsulation layer for the coated wire and wire bonding encapsulation steps: A mask is used to shield the sensing area of ​​the quasi-wall shear force sensitive element. An insulating protective film of silicon dioxide or aluminum oxide with a thickness of 100~500 nm is deposited on the surface of the coated wire using magnetron sputtering. This encapsulates and protects the coated wire, preventing oxidation, corrosion, and structural degradation in the high-temperature oxidizing gas environment. Simultaneously, it maintains direct contact between the sensing area of ​​the quasi-wall shear force sensitive element and the fluid to ensure measurement sensitivity. Then, high-temperature conductive silver paste is used to bond a fine metal wire to the end of the coated wire to meet the engineering requirements for reliable blade signal transmission.

[0029] The core of the quasi-wall shear force sensor structure for turbine rotor blades based on magnetron sputtering technology prepared in this invention lies in eliminating the traditional polyimide substrate and directly integrating the sensor element and transmission wires onto the blade surface. For example... Figure 2 As shown, the quasi-wall shear sensor 30 can be arranged on the target flow area of ​​the suction surface substrate 10 or the pressure surface substrate 20, and form an array of measuring points along the flow direction to cover the shear stress changes at key locations such as transition points and separation points.

[0030] like Figure 2 As shown in Figure (a), an array of quasi-wall shear force sensors distributed along the flow direction is arranged in a typical flow region (such as near the estimated transition point or separation point) on the substrate surface 10 of the suction surface of the low-pressure turbine rotor blade. Figure 2 As shown in Figure (b), a sensor array is also integrated on the pressure surface substrate 20 of the low-pressure turbine rotor blade. Due to the removal of the polyimide substrate, the total thickness of the film layer formed by magnetron sputtering alone is only in the micrometer range (2-3 μm). This structure is highly compatible with the blade surface, eliminating the physical steps formed by traditional thermal films on the blade surface, thereby ensuring the original flow state within the boundary layer and effectively avoiding the risks of sensor failure and detachment under high-temperature conditions caused by the polyimide substrate.

[0031] Figure 3 The magnified structure shown is an integrated structure composed of multiple independent sensing channels: Quasi-wall shear force sensor unit: located at Figure 3Region A shown is a thin film filament made of nickel (Ni) or platinum (Pt) material, corresponding to the sensing core region of the wall shear force sensing element 31. This region has the smallest cross-sectional area and the largest resistance, and is the core area of ​​Joule heat concentration, used to sense changes in the intensity of convective heat transfer of the fluid on the wall. The linewidth and thickness of the sensing element together determine its nominal resistance value. In a typical design, the resistance value of a single arm is controlled in the range of 6 to 8 ohms to obtain sufficient output voltage sensitivity when matched with an external constant current or constant temperature excitation circuit, while controlling the self-heating power to a level that does not significantly disturb the measured near-wall flow field.

[0032] Coated lead wire unit: A vertical strip structure directly connected to the sensitive core area. Located in... Figure 3 As shown in region B, corresponding to the coated wire 32 and its overlapping electrical connection area, its width is significantly larger than that of the sensor unit. This size design ensures that when current passes through, most of the heat is generated in the core sensing area, effectively reducing the interference of wire self-heating on the test results, and the signal is extracted through the external connection area and the metal filament lead. The cross-sectional area of ​​the copper-coated wire is designed to make its ohmic dissipation under the measurement operating current much smaller than that of the sensing element. Engineering experience shows that when the current density in the wire area is less than 1 / 10 of that in the sensing element area, the parasitic contribution of wire self-heating to the measurement signal is negligible. The above goal is achieved by appropriately widening the wire width (typically 5 to 10 times or more the width of the sensing element), thus forming a functional zoning design with concentrated electrothermal sensing in region A and low-resistance, high-efficiency conduction in region B.

[0033] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for fabricating a quasi-wall shear force sensor on the surface of a turbine rotor blade by magnetron sputtering deposition, characterized in that, For forming a substrate-free thin-film quasi-wall shear force sensing element on the suction and / or pressure surfaces of turbine rotor blades and achieving signal extraction, the method includes at least the following steps: SS1. Select the suction surface and / or pressure surface of the turbine rotor blade as the substrate, clean the substrate surface, bombard it with ion beam and dry it, and then uniformly deposit an insulating coating to form an insulating substrate surface; SS2. Based on the surface topography data of the insulating substrate and the geometric topology of the sensing element of the quasi-wall shear force sensor, design a sensing element mask that matches the substrate contour and has a preset opening pattern feature. Position the mask and cover and fix it on the surface of the insulating substrate to define the area to be deposited for the sensing element. SS3. Under vacuum conditions, a magnetron sputtering process is used to in-situ deposit a thin film of nickel or platinum metal on the surface of an insulating substrate within the area defined by the mask opening pattern, forming a quasi-wall shear sensing element with preset pattern characteristics. The uniformity of film thickness and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power. The surface morphology data of the insulating substrate is obtained through three-dimensional scanning or contour measurement. The sensing element mask is a flexible mask that fits the curved surface of the blade. The mask is provided with a positioning structure for matching the geometric reference of the insulating substrate surface. When the mask is covered and fixed, mechanical clamping, vacuum adsorption or temporary adhesion is used to suppress mask lifting and prevent the deposited material from diffracting at the edge of the mask pattern. SS4. Based on the electrical connection position of the quasi-wall shear force sensitive element, design a conductor mask with a preset opening routing pattern. Remove the sensitive element mask and position and fix the conductor mask on the surface of the insulating substrate, aligning the routing opening of the conductor mask with the electrical connection end and defining the area to be deposited on the coated conductor. While aligning the routing opening of the conductor mask with the electrical connection end of the quasi-wall shear force sensitive element, the length and width of the overlap area between the conductor and the sensitive element are limited, allowing the subsequently deposited coated conductor to form a surface contact electrical connection structure with the sensitive element within the overlap area. The mask pattern constraint prevents the conductor from crossing non-target areas. The routing opening of the conductor mask defines an external connection area at the end of the coated conductor, the area of ​​which is larger than the linewidth projection area of ​​the coated conductor, and the external connection area is located away from the pneumatic measurement area. SS5. Under vacuum conditions, a magnetron sputtering process is used to deposit a copper metal thin film in situ on the surface of an insulating substrate through the wiring opening of a conductor mask. This forms a coated conductor electrically connected to a quasi-wall shear-sensitive element. The thickness uniformity of the coated conductor and the film-substrate bonding strength are ensured by adjusting the target-substrate distance and sputtering power. After the copper metal thin film is deposited, a metal thickening layer is further deposited in the lead-out region to reduce the resistance of the lead sheet and improve the mechanical load-bearing capacity of the external connection. The pattern of the metal thickening layer is still defined by the mask opening and is electrically connected to the coated conductor. At the same time, surface encapsulation treatment is performed on the lead-out region to improve the connection reliability of the lead-out under vibration, temperature gradient and humid heat environments while maintaining insulation integrity. SS6. Remove the conductor mask and clean the deposition area. Perform electrical continuity testing and insulation integrity testing on the prepared quasi-wall shear sensing element and the coated conductor. After completing step SS6, the sensing area of ​​the quasi-wall shear-sensitive element is blocked by a mask. An insulating protective film composed of silicon dioxide or aluminum oxide with a thickness of 100~500 nm is deposited on the surface of the coated wire using a magnetron sputtering process. Then, at the lead-out end of the coated wire, a metal filament lead is bonded to the end of the coated wire using high-temperature conductive silver paste.

2. The method according to claim 1, characterized in that, In step SS1, the cleaning of the turbine rotor blade substrate surface includes: ultrasonic cleaning of the substrate surface with acetone as solvent to remove organic contaminants, followed by ultrasonic cleaning with ethanol as solvent to remove residual acetone, rinsing with deionized water and drying with nitrogen; the ion beam bombardment is completed in the same vacuum environment before magnetron sputtering deposition, the substrate surface is directionally bombarded with argon ion beam, and vacuum drying is performed after ion beam treatment; finally, an insulating coating is uniformly deposited on the substrate surface to form an insulating substrate surface.

3. The method according to claim 1, characterized in that, Step SS3, when performing in-situ magnetron sputtering deposition under vacuum conditions, includes at least the following sub-steps: S301. Tooling clamping and vacuuming: Clamp the turbine rotor blades after assembling the sensitive element mask into the magnetron sputtering cavity, so that the area to be deposited corresponding to the opening pattern of the sensitive element mask faces the sputtering source, and start the vacuuming system to evacuate the cavity to a working vacuum state that meets the deposition conditions. S302. Sputtering atmosphere establishment and plasma stabilization: High-purity argon gas is introduced into the magnetron sputtering cavity as the sputtering working gas. The argon gas flow rate is adjusted to stabilize the working gas pressure of the cavity to a preset value within the range of 0.3~1.0 Pa. The plasma discharge is ignited and maintained stably to keep the sputtered particle flux and energy state stable. S303. Target pre-sputtering and surface cleaning: Under the condition of shielding the surface of the insulating substrate, perform pre-sputtering treatment on the nickel target or platinum target for a duration of not less than 10 minutes. The pre-sputtering power density is set to 70%~80% of the formal deposition power density to remove the contamination layer on the target surface and stabilize the sputtering rate. S304. Patterned Deposition and Bonding Strength Control: Unmasking and sputtering deposition are carried out within the area defined by the opening pattern of the sensitive element mask to form a quasi-wall shear sensitive element with preset pattern characteristics. During the deposition process, the deposition rate and incident energy are controlled by adjusting the target-base distance and sputtering power. The deposition direction is kept consistent with the local normal of the blade target base by changing the clamping posture or rotating the blade. S305. Thickness Termination Control and Cooling Exit: The deposition time is controlled according to the pre-calibrated deposition rate to keep the film thickness within the range of 0.2~0.5 μm. After deposition is completed, the discharge is stopped and the film is cooled in a vacuum environment so that the film reaches a thermally stable state before mask removal. The resistance consistency of the quasi-wall shear sensitive element after deposition is tested to control the electrical dispersion caused by thickness fluctuations within the preset limit.

4. The method according to claim 1 or 3, characterized in that, In step SS3, before sputtering and depositing a nickel or platinum metal thin film, a titanium or chromium metal adhesion layer with a thickness of 5-30 nm is first sputtered and deposited within the area defined by the mask opening pattern of the sensing element. After the adhesion layer is deposited, a nickel or platinum metal thin film is continuously deposited under vacuum conditions to form a quasi-wall shear sensing element. Furthermore, the quasi-wall shear sensing element formed in step SS3 adopts a differential bridge or half-bridge resistor topology, and at least two resistor arms are simultaneously deposited within the same mask opening pattern area to ensure that they have consistent temperature and strain field coupling conditions in the same substrate area. In subsequent steps SS4 and SS5, independent leads are laid for the bridge nodes to realize Wheatstone bridge or differential measurement connection.

5. The method according to claim 1, characterized in that, In step SS5, before sputtering and depositing the copper metal thin film, a titanium or chromium metal transition layer with a thickness of 10–50 nm is first sputtered and deposited within the area defined by the opening of the wire mask trace; during the sputtering and depositing of the copper metal thin film, the base vacuum level does not exceed 5.0 × 10⁻⁶. -3 The sputtering working pressure is 0.5~1.2 Pa, and the sputtering power density is 3~8 W / cm³. 2 During the deposition process, the substrate temperature is maintained at 50~150 °C, the thickness of the copper metal film is controlled at 2~3 μm, and the deposition direction is kept consistent with the local normal of the blade by changing the clamping posture or rotating the blade. After the copper metal film sputtering deposition is completed, a metal thickening layer is further deposited in the lead-out area. The pattern of the metal thickening layer is still defined by the mask opening and electrically connected to the coating wire. At the same time, the lead-out area is subjected to surface encapsulation treatment.

6. The method according to claim 1, characterized in that, In steps SS3 and SS5, after sputtering deposition, the deposited film undergoes low-temperature annealing to reduce residual stress and stabilize electrical properties, including: In an inert atmosphere or vacuum environment, the blade is heated to a preset annealing temperature at a preset heating rate and held for a preset holding time. The preset annealing temperature is lower than the upper limit of the thermal stability of the insulating coating and lower than the tempering temperature of the blade substrate. After the holding time is completed, the blade is cooled to room temperature in a controlled manner. After annealing, the resistance and electrical continuity of the shear force sensitive element on the wall and the coated wire are retested, and the insulation integrity is checked.

7. The method according to claim 1, characterized in that, In step SS6, after the fabrication of the quasi-wall shear sensor is completed, an electrical continuity test including four-wire resistance measurement is performed between the quasi-wall shear sensing element and the coated wire, and the result is compared with the theoretical value calculated based on the film thickness, pattern size and material resistivity. A deviation of no more than ±10% is considered acceptable. An insulation resistance test is also performed between the insulating coating and the metal film. A DC voltage of no less than 100 V is applied between the quasi-wall shear sensing element and the blade substrate, and the insulation resistance is measured. An insulation resistance value of no less than 10 MΩ is considered acceptable.

8. A structure for a quasi-wall shear force sensor on the surface of a turbine rotor blade, characterized in that, The preparation method is the magnetron sputtering deposition method for preparing quasi-wall shear force sensors on the surface of turbine rotor blades as described in any one of claims 1 to 7.

9. A turbine rotor blade surface flow field testing system, characterized in that, It includes the quasi-wall shear force sensor structure on the surface of the turbine rotor blade as described in claim 8.

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