ABSTRACT
Monitoring high-temperature strain on curved components in harsh environments is a challenge for a wide range of applications, including in aircraft engines, gas turbines, and hypersonic vehicles. Although there are significant improvements in the preparation of high-temperature piezoresistive film on planar surfaces using 3D printing methods, there are still difficulties with poor surface compatibility and high-temperature strain testing on curved surfaces. Herein, a conformal direct ink writing (CDIW) system coupled with an error feedback regulation strategy was used to fabricate high-precision, thick films on curved surfaces. This strategy enabled the maximum amount of error in the distance between the needle and the substrate on a curved surface to be regulated from 155 to 4 µm. A conformal Pt thick-film strain gauge (CPTFSG) with a room-temperature strain coefficient of 1.7 was created on a curved metallic substrate for the first time. The resistance drift rate at 800 °C for 1 h was 1.1%, which demonstrated the excellent stability and oxidation resistance of the CPTFSG. High-temperature dynamic strain tests up to 769 °C revealed that the sensor had excellent high-temperature strain test performance. Furthermore, the CPTFSG was conformally deposited on an aero-engine turbine blade to perform in situ tensile and compressive strain testing at room temperature. High-temperature strain tests were conducted at 100 and 200 °C for 600 and 580 µÎµ, respectively, demonstrating a high steady-state response consistent with the commercial high-temperature strain transducer. In addition, steady-state strain tests at high temperatures up to 496 °C were tested. The CDIW error modulation strategy provides a highly promising approach for the high-precision fabrication of Pt thick films on complex surfaces and driving in situ sensing of high-temperature parameters on curved components toward practical applications.
ABSTRACT
A high-temperature thin/thick-film strain gauge (TFSG) shows development prospects for in situ strain monitoring of hot-end components due to their small perturbations, no damage, and fast response. Direct ink writing (DIW) 3D printing is an emerging and facile approach for the rapid fabrication of TFSG. However, TFSGs prepared based on 3D printing with both high thermal stability and low temperature coefficient of resistance (TCR) over a wide temperature range remain a great challenge. Here, we report a AgPd TFSG with a glass-ceramic protective layer based on DIW. By encapsulating the AgPd sensitive layer and regulating the Pd content, the AgPd TFSG demonstrated a low TCR (191.6 ppm/°C) from 50 to 800 °C and ultrahigh stability (with a resistance drift rate of 0.14%/h at 800 °C). Meanwhile, the achieved specifications for strain detection included a strain sensing range of ±500 µÎµ, fast response time of 153 ms, gauge factor of 0.75 at 800 °C, and high durability of >8000 cyclic loading tests. The AgPd TFSG effectively monitors strain in superalloys and can be directly deposited onto cylindrical surfaces, demonstrating the scalability of the presented approach. This work provides a strategy to develop TFSGs for in situ sensing of complex curved surfaces in harsh environments.
ABSTRACT
Polymer-derived ceramic (PDC) thin-film sensors have a very high potential for extreme environments. However, the erosion caused by high-temperature airflow at the hot-end poses a significant challenge to the stability of PDC thin-film sensors. Here, we fabricate a thin-film coating by PDC/TiB2/B composite ceramic material, which can be used to enhance the oxidation resistance and ablation resistance of the sensors. Due to the formation of a dense oxide layer on the surface of the thin-film coating in a high-temperature air environment, it effectively prevents the ingress of oxygen as a pivotal barrier. The coating exhibits an exceptionally thin oxide layer thickness of merely 8 µm, while its oxidation resistance was rigorously assessed under air exposure at 800 °C, proving its enduring protection for a minimum duration of 10 h. Additionally, during ablation testing using a flame gun that can generate temperatures of up to 1000 °C, the linear ablation rate of thin-film coating is merely 1.04 µm/min. Our analysis reveals that the volatilization of B2O3 occurs while new SiO2 is formed on the thin-film coating surface. This phenomenon leads to the absorption of heat, thereby enhancing the ablative resistance performance of the thin-film sensor. The results indicate that the thin-film sensor exhibits exceptional resistance to oxidation and ablation when protected by the coating, which has great potential for aerospace applications.
ABSTRACT
Polymer-derived ceramic (PDC)-based high-temperature thin-film sensors (HTTFSs) exhibit promising applications in the condition monitoring of critical components in aerospace. However, fabricating PDC-based HTTFS integrated with high-efficiency, high-temperature anti-oxidation, and customized patterns remains challenging. In this work, we introduce a rapid and flexible selecting laser pyrolysis combined with a direct ink writing process to print double-layer high-temperature antioxidant PDC composite thin-film thermistors under ambient conditions. The sensitive layer (SL) was directly written on an insulating substrate with excellent conductivity by laser-induced graphitization. Then, the antioxidant layer (AOL) was written on the surface of the SL to realize the integrated manufacturing of double-functional layers. Through characterization analysis, it was shown that B2O3 and SiO2 glass phases generated by the PDC composite AOL could effectively prevent oxygen intrusion. Therefore, the fabricated PDC composite thermistors exhibited a negative temperature coefficient in the temperature range from 100 to 1100 °C and high repeatability below 800 °C. Meanwhile, it has excellent high-temperature stability at 800 °C with a resistance change of only 2.4% in 2 h. Furthermore, the high-temperature electrical behavior of the thermistor was analyzed. The temperature dependence of the conductivity for this thermistor has shown an agreement with the Mott's variable range hopping mechanism. Additionally, the thermistor was fabricated on the surface of an aero-engine blade to verify its feasibility below 800 °C, showing the great potential of this work for state sensing on the surface of high-temperature components, especially for customized requirements.
