A nickel-chromium-aluminum-yttrium transition layer having a gradient variation in aluminum composition on a nickel-based alloy

Abstract

The application discloses a nickel-chromium-aluminum-yttrium transition layer with gradient change of aluminum component on a nickel-based alloy, and belongs to the technical field of thin film sensor design and production. The transition layer comprises a NiCrAlY film and a thermally grown alpha-Al2O3 layer. The Al content in the NiCrAlY film gradually increases from bottom to top, and the NiCrAlY film is obtained by double-target sputtering of two NiCrAlY targets with different Al contents. The thermally grown alpha-Al2O3 layer is obtained by vacuum aluminum deposition and thermal oxidation. The NiCrAlY layer has sufficient Al elements on the surface, and sufficient Al can be enriched on the surface of the NiCrAlY layer by using shorter annealing time and lower annealing temperature, so that the damage of the substrate caused by long heat treatment time and high temperature is reduced; the generation of flat, dense and sufficient-thickness alpha-Al2O3 in the subsequent oxidation process is facilitated, and the subsequent growth of an oxide insulating layer with good performance is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of thin film sensor design and manufacturing technology, specifically relating to a NiCrAlY precursor thin film with Al composition gradient variation and a thermally grown alumina transition layer for preparing high-temperature thin film sensors on nickel-based superalloys. Background Technology

[0002] In turbine manufacturing technology based on nickel-based superalloys, turbine blades operate in high-temperature environments for extended periods, enduring substantial thermal loads. The uneven temperature distribution on the blade surface, coupled with complex strain loads during rapid temperature increases, ultimately leads to blade ablation and fracture. Therefore, obtaining accurate information on the surface temperature field distribution and strain of turbine blades is crucial for aero-engine fault diagnosis and the development of novel blade cooling technologies. Thin-film sensors, employing thin-film deposition technology and surface patterning processes, directly deposit traditional thermoelectric strain-sensitive films onto the surface of the measured component. They offer numerous advantages, including small size, light weight, accurate measurement, rapid response, minimal interference with the testing environment, no damage to the structure of the measured component, real-time dynamic temperature measurement output, easy arraying of measurement points, and resistance to environmental interference. Therefore, developing stable thin-film temperature / strain sensors is of great significance for aero-engine research.

[0003] Nickel-based superalloys have good electrical conductivity (e.g., Inconel 718 alloy has a room temperature conductivity of 8.4 × 10⁻⁶). 5 For the thin-film temperature sensor to maintain stable performance (S / m), good electrical isolation is required between the sensitive thin film and the nickel-based superalloy substrate. The best-performing insulating layers at high temperatures are a series of oxide insulating layers primarily composed of alumina. These insulating layers have a low coefficient of thermal expansion (the coefficient of thermal expansion of alumina is 8 × 10⁻⁶). -6 The coefficient of thermal expansion of nickel-based superalloys (e.g., Inconel 718 alloy has a coefficient of thermal expansion of 1.1–2.2 × 10⁻⁶) is similar to that of nickel-based superalloys. -5 The difference between the thermal expansion coefficients is significant. When the insulating layer sputtered on the alloy substrate is subjected to high temperature and drastic temperature changes, cracking and detachment may occur due to the difference in thermal expansion coefficients. Therefore, it is necessary to study a transition layer with a gradually changing thermal expansion coefficient to improve the adhesion strength between the substrate and the insulating layer and enhance the working ability of thin film sensors in complex high-temperature environments.

[0004] NiCrAlY is widely used as an intermediate metal transition between nickel-based superalloys and insulating layers. NiCrAlY alloys exhibit good adhesion to various nickel-based superalloys. Furthermore, insulating layers such as α-Al₂O₃ and Al₂O₃ thermally grown on the NiCrAlY surface through an aluminization oxidation process show good interfacial bonding and similar coefficients of thermal expansion. In the thermal growth process, aluminum initially participates in thermal oxidation to form alumina. However, when Al is insufficient, oxides of Cr and Ni are formed. Therefore, to generate a smooth and uniform thermal oxide layer, sufficient Al is required on the NiCrAlY surface. Thus, vacuum annealing is necessary before thermal oxidation to segregate Al onto the NiCrAlY surface. However, experimental results show that excessively long heat treatment times lead to numerous grain coarsening and recrystallization-induced pores on the transition layer surface, which is detrimental to the subsequent oxidation process and the formation of a smooth and dense thermal oxide layer. Furthermore, SEM and EDS characterization of the cross-section of the NiCrAlY layer after aluminization showed that during vacuum annealing, Al elements inside the NiCrAlY layer segregated to the film surface. The reduction of Al elements at the bottom of the NiCrAlY layer caused a depletion layer to appear in the transition layer, impairing the structural strength of the NiCrAlY layer and leading to fracture and detachment. Therefore, in order to improve the smoothness and mechanical strength of the transition layer, it is necessary to increase the Al content of the surface NiCrAlY layer while controlling the Al element ratio at the bottom of the NiCrAlY layer. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by proposing a nickel-chromium-aluminum-yttrium transition layer with a gradient variation in aluminum composition on a nickel-based alloy.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A nickel-chromium-aluminum-yttrium transition layer with a gradient aluminum composition on a nickel-based alloy, the transition layer comprising a NiCrAlY thin film and a thermally grown α-Al2O3 layer; the Al content in the NiCrAlY thin film gradually increases from bottom to top, and is obtained by dual-target sputtering using two NiCrAlY targets with different aluminum contents, the thickness of the NiCrAlY thin film being 10–20 μm; the thermally grown α-Al2O3 layer being obtained by vacuum aluminum deposition and thermal oxidation, the thickness being 1–2 μm.

[0008] Furthermore, by adjusting the power of two NiCrAlY targets with different aluminum contents, the sputtering rate of the two targets can be controlled, thereby obtaining a NiCrAlY thin film with the Al content gradually increasing from bottom to top.

[0009] A method for preparing a nickel-chromium-aluminum-yttrium transition layer with a gradient aluminum composition on a nickel-based alloy includes the following steps:

[0010] Step 1: Surface treatment of nickel-based alloys;

[0011] The surface of the nickel-based alloy was mechanically polished, then ultrasonically cleaned in acetone, ethanol and deionized water in sequence. After completion, the alloy surface was dried and activated in an ion surface treatment furnace.

[0012] Step 2: Deposit NiCrAlY thin films with varying Al content on nickel-based alloys by dual-target magnetron sputtering;

[0013] The nickel-based alloy processed in step 1 was placed into a multi-target co-sputtering vacuum coating equipment. A NiCrAlY target with an aluminum content of 0.5%–10% (wt.%) was used as the first target, and a NiCrAlY target with an aluminum content of 10%–20% (wt.%) was used as the second target. The equipment was evacuated to a vacuum of 8 × 10⁻⁶. -4 Below Pa, the nickel-based alloy substrate is heated to 300–600 °C; the first target is pre-sputtered at a power of 100–500 W and the second target at a power of 10–50 W for 10–30 min; then, sputtering is performed for 6–10 hours at a power of 100–500 W for the first target and 10–50 W for the second target. During sputtering, the sputtering power of the first target is reduced every 1–2 hours while the sputtering power of the second target is increased, until the sputtering power of the first target drops to 0; the first target is turned off, and sputtering of the second target continues for 1–2 hours to obtain a NiCrAlY thin film with a thickness of 10–20 μm and a gradient Al content.

[0014] Step 3: Vacuum aluminum deposition and thermal oxidation of NiCrAlY thin films;

[0015] The nickel-based alloy with NiCrAlY film deposited in step 2 was placed in an annealing furnace, and the quartz tube was evacuated to a vacuum level of 8 × 10⁻⁶. -4 After the temperature drops below Pa, the temperature is raised to 900–1000℃ and held for 2–6 hours. Vacuum aluminum deposition enriches the surface of the NiCrAlY film with Al elements. Then, oxygen is introduced into the quartz tube, and the oxygen partial pressure is controlled at about 100 Pa. Oxidation treatment is carried out for 6–12 hours to obtain a thermally grown α-Al2O3 layer with a thickness of 1–2 μm.

[0016] Furthermore, in step 2, during the sputtering process, the total sputtering power of the first target and the second target (the sum of the sputtering power of the first target and the second target) remains unchanged.

[0017] In traditional NiCrAlY transition layers, the upper layer contains relatively little Al, requiring high annealing temperatures and durations for vacuum annealing. This allows Al from the bottom layer to segregate to the surface, ensuring sufficient Al for the subsequent thermal oxidation process. However, the bottom NiCrAlY layer develops a depletion layer due to Al segregation, leading to fracture.

[0018] The NiCrAlY transition layer with a gradient Al composition provided by this invention has a lower Al content at the bottom, which prevents cavities from forming at the bottom of the NiCrAlY film due to Al segregation to the surface, ensuring good adhesion between the transition layer and the nickel-based superalloy. The upper layer of the film has sufficient Al, allowing for ample Al enrichment on the NiCrAlY surface with shorter annealing times and lower annealing temperatures. This reduces heat treatment time and temperature, avoiding substrate loss at high temperatures and vias formed on the transition layer surface due to recrystallization. Simultaneously, the relatively abundant Al content on the surface reduces the need for Al segregation at the bottom, minimizing structural damage caused by Al segregation and improving the strength of the transition layer. The resulting transition layer has a bottom of γ-NiCrAl and a surface of α-Al₂O₃, with no obvious interfaces or pores, effectively improving the sensor's thermal shock resistance and high-temperature stability.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The nickel-chromium-aluminum-yttrium transition layer with gradient aluminum composition of the present invention serves as an intermediate adhesive layer between the nickel-based superalloy and the insulating layer. NiCrAlY generates α-Al2O3 on the surface through aluminum oxidation. This composite transition layer can achieve matching of the thermal expansion coefficients of the insulating layer and the nickel-based superalloy.

[0021] 2. This invention utilizes two NiCrAlY targets with different Al contents and employs a dual-target sputtering process to obtain a NiCrAlY film with a gradually increasing Al content from bottom to top. This gradual transition in composition results in good adhesion within the film. The NiCrAlY layer surface has sufficient Al, allowing for more efficient Al enrichment with shorter annealing times and lower annealing temperatures. This reduces damage to the substrate caused by excessively long heat treatment times and temperatures; avoids problems such as grain coarsening and via-hole formation after recrystallization on the NiCrAlY film surface; and facilitates the formation of a smooth, dense, and sufficiently thick α-Al₂O₃ layer during subsequent oxidation, which is beneficial for the subsequent growth of a high-performance oxide insulating layer.

[0022] 3. The surface of the NiCrAlY film with gradient aluminum composition of the present invention already has a relatively rich Al content, which can reduce the need for Al element segregation inside. Therefore, a low Al content is maintained at the bottom of the transition layer, which can prevent the NiCrAlY film from breaking due to the segregation of Al elements to the surface and the formation of a depletion layer at the bottom of the NiCrAlY film. This ensures good adhesion between the composite transition layer and the nickel-based superalloy.

[0023] 4. This invention utilizes a dual-target sputtering process, adjusting the power of two NiCrAlY targets during the sputtering process to control the sputtering rate of the two targets, thereby achieving a gradual change in the thin film composition, avoiding interface problems between the two thin films, and forming a uniform and continuous NiCrAlY thin film with a gradient change in Al composition on a nickel-based alloy. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a high-temperature thin-film sensor based on the transition layer of the present invention, provided as an example. Detailed Implementation

[0025] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example

[0027] like Figure 1 The diagram shown is a schematic of the structure of a high-temperature thin-film sensor based on the transition layer of the present invention provided in an embodiment. It includes a nickel-based alloy substrate, a NiCrAlY thin film with a gradient change in Al content, a thermally grown Al2O3, a magnetron sputtered Al2O3 insulating layer, and a Pt thin-film thermal resistor arranged sequentially from bottom to top.

[0028] The method for fabricating a high-temperature thin-film sensor based on the transition layer of the present invention, as provided in the embodiments, specifically includes the following steps:

[0029] Step 1: Mechanically polish the nickel-based alloy substrate until the Ra value is below 0.04;

[0030] Step 2: Place the nickel-based alloy substrate in acetone, ethanol and deionized water in sequence for ultrasonic cleaning for 10 minutes each to remove organic contaminants and dust particles from the substrate surface, and then dry it with a dry argon gas flow.

[0031] Step 3: The nickel-based alloy substrate is placed in an ion surface treatment furnace for surface activation treatment to remove adsorbed oxygen on the surface of the alloy substrate and improve the adhesion between the nickel-based alloy substrate and the subsequent film layer.

[0032] Step 4: Fix the surface-treated nickel-based alloy substrate using a coating fixture and place it into a multi-target co-sputtering vacuum coating equipment. Use a NiCrAlY target with an aluminum content of 5% (wt.%) as the first target and a NiCrAlY target with an aluminum content of 15% (wt.%) as the second target. Evacuate the equipment to 8×10⁻⁶. -4 Below Pa, the nickel-based alloy substrate is heated to 450℃; the first target is pre-sputtered at a power of 180W and the second target at a power of 20W for 20min; then, sputtering is performed for 8 hours under the conditions of the first target power of 180W and the second target power of 20W. During the sputtering process, the sputtering power of the first target is reduced by 5W every 2 hours while the sputtering power of the second target is increased by 5W, until the sputtering power of the first target drops to 0; the first target is turned off and the second target is sputtered at a power of 200W for 2h to obtain a NiCrAlY film with a thickness of 15μm and a gradient change in Al content;

[0033] Step 5: Place the nickel-based alloy with NiCrAlY thin film deposited in Step 4 into an annealing furnace, and evacuate the quartz tube to a vacuum level of 8 × 10⁻⁶. -4 After the temperature drops below Pa, the temperature is raised to 950℃ and held for 3 hours. After vacuum aluminum precipitation to enrich the surface of the NiCrAlY film with Al elements, oxygen is introduced into the quartz tube and the oxygen partial pressure is controlled at 100 Pa. Oxidation treatment is carried out for 12 hours to obtain a thermally grown α-Al2O3 layer with a thickness of 2 μm.

[0034] Step 6: Fix the composite substrate with transition layer obtained in Step 5 using a coating fixture, place it in a magnetron sputtering apparatus, and evacuate the apparatus cavity to a vacuum level of 8 × 10⁻⁶. -4 Below Pa, oxygen and argon are introduced, with an oxygen flow rate of 6 sccm and an argon flow rate of 48 sccm. The temperature is raised to 200℃ and the gas pressure is controlled at 0.2 Pa. Reactive sputtering is performed using an Al target to generate an aluminum oxide insulating layer with a thickness of 2 μm.

[0035] Step 7: Anneal the composite substrate obtained in Step 6 at 800°C for 2 hours under atmospheric conditions;

[0036] Step 8: Fix the composite substrate and the thermal resistance mask obtained in Step 7 using a coating fixture, place them in a magnetron sputtering apparatus, and evacuate the apparatus cavity to a vacuum level of 8 × 10⁻⁶. -4 Below Pa, argon gas is introduced at a flow rate of 35 sccm, the temperature is raised to 450℃, and the gas pressure is controlled at 0.4 Pa. A Pt target is used for reactive sputtering to generate a Pt thermal resistor with a thickness of 0.5 μm.

[0037] After undergoing five thermal shock tests using the natural cooling method at 1000℃, the composite transition layer on the nickel-based alloy obtained in step 5 was subjected to an adhesion test using the cross-cut adhesion method. The results showed that no grids peeled off from the composite transition layer, and the adhesion test result was graded as 0, proving that the transition layer has good thermal shock resistance and adhesion.

[0038] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method of producing a nickel-chromium-aluminum-yttrium transition layer with a gradient change in the aluminum composition on a nickel-based alloy, characterized in that The method comprises the following steps: Step 1, surface treatment of the nickel-based alloy; Mechanical polishing is performed on the surface of the nickel-based alloy, and then the surface is ultrasonically cleaned in acetone, ethanol and deionized water in sequence; after the completion, the surface of the alloy is dried, and an activation treatment is performed by using an ion surface treatment furnace; Step 2, depositing a NiCrAlY film with gradient change of Al content on the nickel-based alloy by double-target magnetron sputtering; The nickel-based alloy treated in step 1 is placed into a multi-target co-sputtering vacuum coating device, a NiCrAlY target with an aluminum content of 0.5% to 10% is used as the first target, and a NiCrAlY target with an aluminum content of 10% to 20% is used as the second target, the device is vacuumed to 8×10 -4 The nickel-based alloy substrate is heated to 300 to 600℃, the first target is pre-sputtered at a power of 100 to 500W, and the second target is pre-sputtered at a power of 10 to 50W; then, the first target is sputtered at a power of 100 to 500W, and the second target is sputtered at a power of 10 to 50W for 6 to 10 hours, during the sputtering process, the sputtering power of the first target is reduced and the sputtering power of the second target is increased every 1 to 2 hours until the sputtering power of the first target is reduced to 0; the first target is turned off, and the second target continues to be sputtered for 1 to 2 hours to obtain a NiCrAlY film with a thickness of 10 to 20μm and a gradient change in Al content; Step 3, vacuum aluminum deposition and thermal oxidation of the NiCrAlY film; The nickel-based alloy on which the NiCrAlY thin film was deposited in Step 2 was put into an annealing furnace, and a quartz tube was vacuumed to 8 x 10 -4 After the pressure was reduced to 100 Pa or less, the temperature was raised to 900 to 1000°C, and the NiCrAlY thin film was enriched with Al by vacuuming aluminum, oxygen was introduced into the quartz tube, the partial pressure of oxygen was controlled at 100 Pa, and oxidation treatment was performed for 6 to 12 hours to obtain a thermally grown α-Al2O3 layer having a thickness of 1 to 2 μm.

2. The method of claim 1, wherein the method is characterized by: During the sputtering process in step 2, the total sputtering power of the first target and the second target remains unchanged.

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