High-temperature-resistant passive strain gauge for gas turbine blade monitoring and preparation method and application thereof

Abstract

The invention discloses a high-temperature-resistant passive strain gauge for gas turbine blade monitoring and a preparation method and application thereof, and belongs to the technical field of gas turbine health monitoring. The high-temperature-resistant passive strain gauge comprises a strain gauge substrate, an insulating layer, a snakelike sensitive grid, a fiber bragg grating (FBG) and a yttria-stabilized zirconia (YSZ) protective layer. The strain gauge has the beneficial effects that aiming at the limitation of a traditional sensor in a high-temperature (greater than or equal to 1200 DEG C), high-frequency vibration and corrosion environment, the strain gauge adopts the high-temperature-resistant platinum-tungsten alloy snakelike sensitive grid, the single crystal aluminum oxide ceramic substrate and the sapphire fiber bragg grating to transmit a strain signal through wavelength shift, and an external power supply is not needed; and the Ir-Re alloy is brazed and fixed to the microgroove in the surface of the blade, the shearing strength is high, and the service life is long. The method overcomes the technical bottleneck of strain measurement in a high-temperature environment, is suitable for scenes of aero-engines, gas turbine blades and the like, and remarkably reduces the maintenance cost and improves the monitoring reliability.

Description

Technical Field

[0001] This invention belongs to the field of gas turbine monitoring technology, specifically relating to a high-temperature resistant passive strain gauge for monitoring gas turbine blades, its preparation method, and its application. Background Technology

[0002] Gas turbines, as core power units in aviation, power, and shipbuilding, subject their turbine blades to multiple extreme environments, including high temperatures (above 1200℃), high pressure, high-frequency mechanical vibration, and gas corrosion. The health of the blades directly determines the safety and economy of the unit, and strain monitoring is a core method for assessing blade life, locating high-strain danger zones and quantifying creep and fatigue damage. However, traditional strain gauges face insufficient temperature resistance limits under high temperatures, dynamic loads, and complex environments: conventional metal foil strain gauges (such as constantan) have a maximum operating temperature of ≤400℃, while high-temperature alloy strain gauges (such as Karma alloy) have an upper limit of approximately 800℃, which cannot meet the requirements of gas turbine blades. At high temperatures, material creep and oxidation lead to sensitivity drift and severe signal distortion. Furthermore, traditional strain gauges require lead wires to transmit signals, but high-temperature wires (such as platinum-rhodium alloys) are prone to oxidation and breakage. Moreover, strain gauges require built-in power supplies (such as batteries or thermocouples), which have short lifespans and are difficult to maintain at high temperatures, resulting in wire dependence and power supply limitations.

[0003] Chinese patent application CN103968773A discloses a flexible high-temperature fiber Bragg grating strain gauge capable of two-dimensional strain detection on the surface of complex components. It consists of a cross-shaped or T-shaped high-temperature constant-elastic alloy substrate, high-temperature Bragg gratings A, B, and C, and a high-temperature resistant coating layer. The three high-temperature Bragg gratings are fixed to the substrate along the transverse and longitudinal directions with high-temperature adhesive. High-temperature Bragg gratings A and B are fixed at both ends with high-temperature adhesive, measuring transverse and longitudinal strain respectively. High-temperature Bragg grating C is free at one end, sensing only temperature changes to achieve temperature compensation. In application, the strain gauge needs to be welded or bonded to the surface of the component being measured. This patented flexible high-temperature fiber Bragg grating strain gauge is heat-resistant, flexible, resistant to electromagnetic interference, and easy to install, making it suitable for two-dimensional strain detection on the surface of complex components and enabling quasi-distributed multi-point measurement. However, the strain gauge structure is complex and therefore requires further improvement. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to propose a high-temperature resistant passive strain gauge for monitoring gas turbine blades.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] The first aspect of this invention provides a high-temperature resistant passive strain gauge for monitoring gas turbine blades, comprising a strain gauge substrate, an insulating layer, a serpentine sensing grating, a fiber Bragg grating (FBG), and a yttrium-stabilized zirconia (YSZ) protective layer; the back side of the strain gauge substrate is fixedly connected to the gas turbine blade; the front side of the strain gauge substrate is sequentially provided with the insulating layer, the serpentine sensing grating, the fiber Bragg grating (FBG), and the yttrium-stabilized zirconia (YSZ) protective layer; the insulating layer is disposed on the front side of the strain gauge substrate by chemical vapor deposition; the serpentine sensing grating is formed on the insulating layer by magnetron sputtering and femtosecond laser micromachining technology; the fiber Bragg grating and the serpentine sensing grating are bonded together by high-temperature ceramic adhesive; the YSZ protective layer is deposited on the surface of the fiber Bragg grating by plasma spraying.

[0007] Preferably, the surface of the gas turbine blade is provided with a U-shaped microgroove, and the back side of the strain gauge substrate is fixed to the U-shaped microgroove by brazing.

[0008] Preferably, the back side of the strain gauge substrate is etched with serpentine microchannels.

[0009] Preferably, the insulating layer is made of silicon nitride (Si3N4).

[0010] Preferably, the thickness of the insulating layer is 1 to 3 μm.

[0011] Preferably, the serpentine sensing grid is made of platinum-tungsten alloy (Pt-20%W).

[0012] Preferably, the serpentine sensitive grid is in the form of a periodically zigzagging or wave-shaped serpentine grid.

[0013] Preferably, the thickness of the YSZ protective layer is 3–8 μm.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned high-temperature resistant passive strain gauge, comprising the following steps:

[0015] (1) Substrate pretreatment: Single crystal alumina ceramic sheet is used as the substrate. The front side of the substrate is polished with a femtosecond laser, and a serpentine microchannel is etched on the back side of the substrate with an ultraviolet laser.

[0016] (2) Insulating layer deposition: A silicon nitride (Si3N4) insulating layer is formed by using chemical vapor deposition with silane (SiH4) and ammonia (NH4) as reactant gases.

[0017] (3) Sensitive gate fabrication: Pt-W thin film is deposited on the surface of the insulating layer by magnetron sputtering, and a platinum-tungsten alloy serpentine sensitive gate is fabricated on the Pt-W thin film by femtosecond laser micromachining technology;

[0018] (4) Fiber Bragg grating integration: Fiber Bragg gratings are written into sapphire optical fibers by ultraviolet laser and bonded to serpentine sensitive gratings using YSZ-based high-temperature ceramic adhesive;

[0019] (5) Protective layer spraying: Yttrium-stabilized zirconia powder is sprayed onto the fiber Bragg grating using plasma spraying process, and the sprayed layer is laser remelted to form a YSZ protective layer.

[0020] A third aspect of the present invention proposes the application of the above-mentioned high-temperature resistant passive strain gauge in gas turbine monitoring.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. This invention proposes a suitable high-temperature resistant passive strain gauge that meets the requirements of the high-temperature and high-pressure service environment of blades, and can also get rid of dependence on electrical wires and power supply.

[0023] 2. This strain gauge addresses the limitations of traditional sensors in high-temperature (≥1200℃), high-frequency vibration, and corrosive environments by employing a high-temperature resistant platinum-tungsten alloy serpentine sensing grating, a single-crystal alumina ceramic substrate (with thermal expansion coefficient matching the blade material), and a sapphire fiber optic grating. It transmits strain signals through wavelength shift, eliminating the need for an external power supply. It is fixed to the microgroove on the blade surface by Ir-Re alloy brazing, exhibiting high shear strength and a long lifespan.

[0024] 3. This invention overcomes the technical bottleneck of strain measurement under high temperature conditions, and is applicable to scenarios such as aero-engines and gas turbine blades, significantly reducing maintenance costs and improving monitoring reliability. Attached Figure Description

[0025] Figure 1 This is a cross-sectional schematic diagram of a high-temperature resistant passive strain gauge for monitoring gas turbine blades according to the present invention.

[0026] Figure 2 This is a schematic diagram of the serpentine sensitive grid of the present invention.

[0027] In the figure, 1-gas turbine blade, 2-U-shaped microgroove, 3-insulation layer, 4-strain gauge substrate, 5-serpentine sensitive grid, 6-fiber Bragg grating, 7-YSZ protective layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art.

[0029] Unless otherwise specified, the test materials and reagents used in the following examples are commercially available or prepared by known methods.

[0030] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0031] Example 1:

[0032] A high-temperature resistant passive strain gauge for monitoring gas turbine blades includes a strain gauge substrate, an insulating layer, a serpentine sensing grating, a fiber Bragg grating (FBG), and a yttrium-stabilized zirconia (YSZ) protective layer. The back side of the strain gauge substrate is fixedly connected to the gas turbine blade. A U-shaped microgroove is formed on the surface of the gas turbine blade, and the back side of the strain gauge substrate is fixed to the U-shaped microgroove by brazing. A serpentine microchannel is etched on the back side of the strain gauge substrate, which can dissipate heat through the circulating cooling airflow inside the blade.

[0033] The front side of the strain gauge substrate is sequentially provided with an insulating layer, a serpentine sensing grating, a fiber Bragg grating (FBG), and a yttrium oxide-stabilized zirconia (YSZ) protective layer; the insulating layer is deposited on the front side of the strain gauge substrate by chemical vapor deposition; the insulating layer is made of silicon nitride (Si3N4) and has a thickness of 2μm;

[0034] The serpentine sensitive grid is formed on the insulating layer using magnetron sputtering and femtosecond laser micromachining techniques; the material of the serpentine sensitive grid is platinum-tungsten alloy (Pt-20%W); the serpentine sensitive grid has a periodically folding serpentine shape (zigzag or wave-shaped), and the strain sensitivity is improved by increasing the effective length.

[0035] The fiber Bragg grating and the serpentine sensitive grating are bonded together by high-temperature ceramic adhesive, and the strain is reflected by the wavelength shift of the grating; the YSZ protective layer is deposited on the surface of the fiber Bragg grating by plasma spraying process; the thickness of the YSZ protective layer is 5μm.

[0036] The above-mentioned method for preparing high-temperature resistant passive strain gauges includes the following steps:

[0037] (1) Substrate pretreatment: A single-crystal alumina ceramic sheet (purity ≥99.9%, thickness 50μm) was used as the substrate, and the surface was laser polished to a roughness Ra<0.1μm. A silicon nitride (Si3N4) insulating layer with a thickness of 2μm and a breakdown voltage >500V was deposited on the substrate surface by chemical vapor deposition (CVD) to ensure high-temperature insulation performance. A serpentine microchannel was laser-etched on the back of the substrate: the channel width was 50μm, the depth was 30μm, and the aspect ratio was 0.6. The inner wall of the channel was coated with an aluminum chromium nitride (AlCrN) anti-oxidation coating (thickness 1μm) to improve corrosion resistance.

[0038] (2) Insulating layer deposition: Chemical vapor deposition was used to form a 2μm thick silicon nitride (Si3N4) insulating layer using silane (SiH4) and ammonia (NH4) as reaction gases.

[0039] (3) Sensitive gate fabrication: A PtW thin film (3μm thick) is deposited on the surface of the insulating layer by magnetron sputtering. A platinum-tungsten alloy (Pt-20%W) serpentine sensitive gate is fabricated on the surface of the insulating layer by femtosecond laser micromachining technology: line width 10μm, spacing 20μm, and grid coverage area 3mm×1mm.

[0040] (4) Fiber Bragg grating integration: Sapphire fiber (diameter 80μm, temperature resistance >1500℃) is selected, fiber Bragg grating (FBG) grating area length 5mm, center wavelength 1550nm; the Bragg grating (FBG) is aligned with the serpentine sensitive grating area and bonded and fixed with high temperature ceramic adhesive (YSZ base) to ensure grating strain transfer efficiency ≥95%;

[0041] (5) Protective layer spraying: A yttrium-stabilized zirconia (YSZ) protective layer is deposited on the FBG surface using plasma spraying process: the thickness is 5μm, the porosity is ≤3%, and the spraying temperature is controlled at 800℃ to avoid thermal deformation of the substrate; the coating surface is laser remelted to form a YSZ protective layer, which improves the density and anti-peeling ability, and thus the coating is obtained.

[0042] Specifically applied to gas turbine blade monitoring:

[0043] Install high-temperature resistant passive strain gauges on gas turbine blades:

[0044] U-shaped microgrooves (for embedding strain gauge bodies) were machined on the surface of the gas turbine blades using femtosecond lasers: groove depth 100 μm, width 150 μm; a 20 μm thick yttrium-stabilized zirconia (YSZ) transition layer was sprayed onto the bottom of the grooves to reduce thermal mismatch stress. Ir-20%Re brazing alloy powder (melting point 2300℃) was pre-placed in the microgrooves with a filling rate ≥90%; vacuum brazing was employed (vacuum degree ≤10). -4 The strain gauge substrate is brazed at 1400℃ for 1 hour to form a metallurgical bond with the gas turbine blade. After brazing, the interface is subjected to permeation testing (FPI) to ensure that there are no crack defects.

[0045] Working principle: High-precision strain measurement is achieved under high-temperature environments by changing the physical signal (light or electromagnetic wave) caused by the deformation of a serpentine sensitive grating. The specific process is as follows: When a gas turbine blade is subjected to stress and deformation, the strain is transferred to a platinum-tungsten alloy (Pt-W) serpentine sensitive grating through a brazing layer, causing a change in the grating geometry (ΔL / L). The deformation of the sensitive grating is transferred through the substrate to a sapphire fiber Bragg grating (FBG) integrated within a protective layer. The grating period (Λ) changes with strain, and the reflected light wavelength (λ) changes accordingly. B Offset:

[0046] Δλ B =λ B (1-p e )ε

[0047] In the formula p e Let Δλ be the photoelastic coefficient of the material. B This represents the wavelength offset.

[0048] An external demodulator emits broadband light and receives the reflected signal, calculating the strain value using the wavelength offset. A fiber optic grating (FBG) is physically connected to the demodulator via an optical fiber to transmit the optical signal for strain measurement.

[0049] Example 2:

[0050] The difference between this embodiment and Embodiment 1 is that the thickness of the insulating layer is 1 μm and the thickness of the YSZ protective layer is 8 μm, while the rest is the same as in Embodiment 1.

[0051] Example 3:

[0052] The difference between this embodiment and Embodiment 1 is that the thickness of the insulating layer is 3μm and the thickness of the YSZ protective layer is 3μm, while the rest is the same as in Embodiment 1.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-temperature resistant passive strain gauge for monitoring gas turbine blades, characterized in that, The device comprises a strain gauge substrate, an insulating layer, a serpentine sensing grating, a fiber Bragg grating, and a YSZ protective layer. The back side of the strain gauge substrate is fixedly connected to a gas turbine blade. The front side of the strain gauge substrate is sequentially provided with the insulating layer, the serpentine sensing grating, the fiber Bragg grating, and the YSZ protective layer. The insulating layer is deposited on the front side of the strain gauge substrate by chemical vapor deposition. The serpentine sensing grating is formed on the insulating layer by magnetron sputtering and femtosecond laser micromachining. The fiber Bragg grating and the serpentine sensing grating are bonded together by high-temperature ceramic adhesive. The YSZ protective layer is deposited on the surface of the fiber Bragg grating by plasma spraying.

2. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The surface of the gas turbine blade is provided with a U-shaped microgroove, and the back side of the strain gauge substrate is fixed to the U-shaped microgroove by brazing.

3. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The back side of the strain gauge substrate is etched with serpentine microchannels.

4. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The insulating layer is made of silicon nitride (Si3N4).

5. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The thickness of the insulating layer is 1–3 μm.

6. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The serpentine sensing grid is made of platinum-tungsten alloy (Pt-20%W).

7. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The serpentine sensitive grid is in the shape of a serpentine loop that periodically folds back.

8. The high-temperature resistant passive strain gauge according to claim 1, characterized in that, The thickness of the YSZ protective layer is 3–8 μm.

9. A method for preparing a high-temperature resistant passive strain gauge according to any one of claims 1 to 8, comprising the following steps: (1) Substrate pretreatment: Single crystal alumina ceramic sheet is used as the substrate. The front side of the substrate is polished with a femtosecond laser, and a serpentine microchannel is etched on the back side of the substrate with an ultraviolet laser. (2) Insulating layer deposition: A silicon nitride (Si3N4) insulating layer is formed by using chemical vapor deposition with silane (SiH4) and ammonia (NH4) as reactant gases. (3) Sensitive gate fabrication: Pt-W thin film is deposited on the surface of the insulating layer by magnetron sputtering, and a platinum-tungsten alloy serpentine sensitive gate is fabricated on the Pt-W thin film by femtosecond laser micromachining technology; (4) Fiber Bragg grating integration: Fiber Bragg gratings are written into sapphire optical fibers by ultraviolet laser and bonded to serpentine sensitive gratings using YSZ-based high-temperature ceramic adhesive; (5) Protective layer spraying: Yttrium-stabilized zirconia powder is sprayed onto the fiber Bragg grating using plasma spraying process, and the sprayed layer is laser remelted to form a YSZ protective layer.

10. The application of the high-temperature resistant passive strain gauge according to any one of claims 1 to 8 in gas turbine monitoring.

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