In Situ Laser Fabrication of Polymer-Derived Ceramic Composite Thin-Film Sensors for Harsh Environments

Rapid laser fabrication of indium tin oxide and polymer-derived ceramic composite thin films for high-temperature sensors

Thin-film sensors are essential for real-time monitoring of components in high-temperature environments. Traditional fabrication methods often involve complicated fabrication steps or require prolonged high-temperature annealing, limiting their practical applicability. Here, we present an approach using direct ink writing and laser scanning (DIW-LS) to fabricate high-temperature functional thin films. An indium tin oxide (ITO)/preceramic polymer (PP) ink suitable for DIW was developed. Under LS, the ITO/PP thin film shrank in volume. Meanwhile, the rapid pyrolysis of PP into amorphous precursor-derived ceramic (PDC) facilitated the faster sintering of ITO nanoparticles and improved the densification of the thin film. This process realized the formation of a conductive network of interconnected ITO nanoparticles. The results show that the ITO/PDC thin film exhibits excellent stability, with a drift rate of 4.7 % at 1000 °C for 25 h, and withstands temperatures up to 1250 °C in the ambient atmosphere. It is also sensitive to strain, with a maximum gauge factor of -6.0. As a proof of concept, we have used DIW-LS technology to fabricate a thin-film heat flux sensor on the surface of the turbine blade, capable of measuring heat flux densities over 1 MW/m2. This DIW-LS process provides a viable approach for the integrated, rapid, and flexible fabrication of thin film sensors for harsh environments.

La(Ca)CrO3-Filled SiCN Precursor Thin Film Temperature Sensor Capable to Measure up to 1100 °C High Temperature

Thin-film sensors are regarded as advanced technologies for in situ condition monitoring of components operating in harsh environments, such as aerospace engines. Nevertheless, these sensors encounter challenges due to the high-temperature oxidation of materials and intricate manufacturing processes. This paper presents a simple method to fabricate high temperature-resistant oxidized SiCN precursor and La(Ca)CrO3 composite thin film temperature sensors by screen printing and air annealing. The developed sensor demonstrates a broad temperature response ranging from 200 °C to 1100 °C with negative temperature coefficients (NTC). It exhibits exceptional resistance to high-temperature oxidation and maintains performance stability. Notably, the sensor's resistance changes by 3% after exposure to an 1100 °C air environment for 1 h. This oxidation resistance improvement surpasses the currently reported SiCN precursor thin-film sensors. Additionally, the sensor's temperature coefficient of resistance (TCR) can reach up to -7900 ppm/°C at 200 °C. This strategy is expected to be used for other high-temperature thin-film sensors such as strain gauges, heat flux sensors, and thermocouples. There is great potential for applications in high-temperature field monitoring.

Rapid Printing of High-Temperature Polymer-Derived Ceramic Composite Thin-Film Thermistor with Laser Pyrolysis

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.

Thin-Film Platinum Resistance Temperature Detector with a SiCN/Yttria-Stabilized Zirconia Protective Layer by Direct Ink Writing for High-Temperature Applications

In situ temperature monitoring of curved high-temperature components in extreme environments is challenging for a variety of applications in fields such as aero engines and gas turbines. Recently, extrusion-based direct ink writing (DIW) has been utilized to fabricate platinum (Pt) resistance temperature detectors (RTDs). However, the current Pt RTD prepared by DIW technology suffers from a limited temperature range and poor high-temperature stability. Here, DIW technology and yttria-stabilized zirconia (YSZ)-modified precursor ceramic film packaging have been used to build a Pt RTD with high-temperature resistance, small disturbance, and high stability. The results indicate that the protective layer formed by the liquid phase anchors the Pt particles and reduces the agglomeration and volatilization of the Pt sensitive layer at high temperature. Attributed to the SiCN/YSZ protective layer, the temperature resistance curve of the Pt RTD in the range of 50-800 °C has little deviation from the fitting curve, and the fitting correlation coefficient is above 0.9999. Interestingly, the Pt RTD also has high repeatability and stability. The high temperature resistance drift rate is only 0.05%/h after 100 h of long-term testing at 800 °C and can withstand butane flame up to ∼1300 °C without damage. Moreover, the Pt RTD can be conformally deposited on the outer ring of aerospace bearings by DIW technology and then realize on-site, nondestructive, and real-time monitoring of bearing temperature. The fabricated Pt RTD shows great potential for high-temperature applications, and the novel technology proposed provides a feasible pathway for temperature monitoring of aeroengine internal curved hot-end components.