Tungsten-rhenium Thin Film Thermocouples Research Articles

Utilizing screen printing technology to fabricate tungsten-rhenium thick film thermocouples with a maximum temperature limit of 1600 °C

Tungsten-rhenium thick film thermocouples (TFTCs) show excellent potential for in-situ high-temperature monitoring due to their high-temperature resistance. However, the only reported method for preparing tungsten-rhenium thin film thermocouples is magnetron sputtering. The upper limit of temperature resistance of thetungsten-rhenium thin film thermocouples prepared by this method is low because the thickness is reduced by continuous thermal ablation at high temperatures. In this work, screen printing technology is used to prepare tungsten-rhenium TFTCs. The tungsten-rhenium TFTCs’ temperature accuracy is better than ±1.5 %, repeatability is better than 0.9 %, and drift is only 0.26 %/h at 1600 °C. Finally, the tungsten-rhenium TFTC temperature ring array is installed in a tubular furnace for high-temperature monitoring, and the tungsten-rhenium TFTC is heated in the air using a high-temperature flame gun at approximately 1000 °C for up to 30 s. This method to fabricate tungsten-rhenium TFTCs has the potential for temperature measurement in extremely harsh environments.

Horizontal Oxidation Diffusion Behavior of MEMS-Based Tungsten-Rhenium Thin Film Thermocouples.

Tungsten-rhenium thin film thermocouples (TFTCs) are well suited for the surface temperature monitoring of hot components due to their small size, rapid response and low cost. In this study, a tungsten-rhenium TFTC with SiC protective film on all parts except the pads was fabricated by a microelectromechanical system (MEMS) process. During the low to medium temperature (−40 °C to 500 °C) repeatability test phase, the thermal voltage from the TFTC agreed well with that of the standard tungsten-rhenium thermocouple. However, during the high temperature test phase, the TFTC lost electronic response at around 620 °C. Failure analysis of the TFTC tested at 620 °C was performed by microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscope (LSCM) and statistics. The results showed that the pads were oxidized without the protective layer, the number of oxidized protrusions distributed in this TFTC from the pad to the node decreases more and more slowly and the size of the oxidized protrusions also becomes smaller and smaller. This demonstrates the presence of horizontal oxidation diffusion in TFTCs, further illustrating the importance of pad protection and provides a direction for the subsequent structural optimization and the extension of the service life of TFTCs and other sensors.

Simulation, fabrication, and characteristics of high-temperature, quick-response tungsten–rhenium thin-film thermocouples probe sensor

In this study, a tungsten–rhenium thin-film thermocouples (TFTCs) is fabricated via magnetron sputtering on silicon carbide ceramics. Cuboid TFTCs probe is sealed with stainless steel shell to make the TFTCs probe sensor. This sensor has an average Seebeck coefficient of 27.2 µV °C−1 at 1167 °C (temperature difference). The thermal volatilization characteristics, electromotive force behavior, and response time of this tungsten–rhenium TFTC sensor are investigated. The real engine experimental results show that the TFTCs probe sensor can work normally under the high temperature and high-speed air flow environment of 4 Mach and 900 °C. In addition, the correlation between the response speed, substrate thickness, and film thickness is discussed based on simulations of the response to carbon dioxide laser pulses. As indicated by the dynamic experiment results, the laser response time is from 0.49 to 1.51 ms, which is much shorter than that of traditional armored C-type thermocouples (for tungsten–rhenium thermocouples, the response time is around 1 s). Tungsten–rhenium TFTCs probe sensor is a suitable alternative to conventional thermocouples to meet the requirements of measuring high temperatures with a quick response.

Effect of film deposition rate on the thermoelectric output of tungsten-rhenium thin film thermocouples by DC magnetron sputtering

In micro–nano manufacturing, the deposition rate is one of the most basic parameters for the preparation of the film. In this paper, we use the tungsten–rhenium (W-5Re and W-26Re) alloy thin films as the research object and choose direct current (DC) magnetron sputtering to fabricate films on the alumina substrate. With the help of three factors and three levels of an orthogonal table, nine orthogonal experiments are designed to study the influences of argon flow rate, sputtering power and vacuum degree on the deposition rate. Thickness and composition are measured by scanning electron microscopy and x-ray diffraction respectively. In order to maintain the integrity of the film, the deposition thickness of the film is controlled by simulation so that the thermal stress is within the required range. In addition, the thermoelectric output is improved by comparing tungsten-rhenium thin film thermocouples (TFTCs) with different deposition rates. Experimental results show that sputtering power has a greater effect than other factors. The deposition rate of the W-5Re and W-26Re film can reach 24.911 nm min−1 and 25.756 nm min−1 at 600 W. The output of the TFTCs prepared at 600 W is about 10% higher than that at 200 W. TFTCs made with the fastest deposition rate parameters have excellent characteristics which could continuously work at 1273 K and the maximum EMF is 39.7 mV and the average Seebeck coefficient at 1273 K is 31.2 μV K−1.

Effect of heat treatment on thermoelectric properties of tungsten-rhenium thin-film thermocouples by RF magnetron sputtering

Tungsten-rhenium thin-film thermocouples (TFTCs) are designed by finite element analysis (FEA) and fabricated based on radio frequency (RF) magnetron sputtering technology to meet the requirement of high temperature measurement in narrow space. The changes with thickness and thermoelectric property (including Seebeck coefficient, repeatability error) of TFTCs are investigated under different heat treatment time and temperature by the result of morphology observation and heat recycling experiment analysis to optimize heat treatment process parameters. The repeatability error of tungsten-rhenium TFTCs with heat treatment at 300 °C for 6 hours can reach to ±1.028%. The electromotive force behavior (EMF) experiments shows the average Seebeck coefficient of heat treated tungsten-rhenium TFTCs reach to 18.92 µV/°C when the temperature difference is 1165 °C (hot junction temperature is 1327 °C) in inert gases protection environment. The thermoelectric service properties of tungsten-rhenium TFTCs sensor have been improved to be a viable replacement candidate for high temperature measurement in narrow space through this technology.

Effect of magnetron sputtering parameters on adhesion properties of tungsten-rhenium thin film thermocouples

Tungsten-Rhenium (W-Re) thin films were grown on alumina ceramic substrate using the magnetron sputtering technique. The feasibility and reliability of the tungsten-rhenium thin film thermocouples application are largely dependent on the adhesion properties between the W-Re film and substrate. In order to get the good adhesion, we researched the effect of magnetron sputtering parameters on adhesion properties of tungsten-rhenium thin film thermocouples. With the help of three factors and three levels orthogonal table, nine orthogonal experiments were designed to study the influences of argon flow rate, sputtering power and vacuum degree on the performance of adhesion. The result showed that the effect of vacuum degree on adhesion properties was the largest, then come sputtering power, while the effect of the argon flow rate was the least and the optimal parameters combination was: argon flow rate 30 Sccm, sputtering power 400 W and vacuum degree 0.7 × 10−6 Torr.

Range Analysis of Thermal Stress and Optimal Design for Tungsten-Rhenium Thin Film Thermocouples Based on Ceramic Substrates.

A thermal stress range analysis of tungsten-rhenium thin film thermocouples based on ceramic substrates is presented to analyze the falling off and breakage problems caused by the mismatch of the thermal stresses in thin film thermocouples (TFTCs) and substrate, and nano-indentation experiments are done to measure and calculate the film stress to compare with the simulation results. Optimal design and fabrication of tungsten-rhenium TFTCs based on ceramic substrates is reported. Static high temperature tests are carried out, which show the optimization design can effectively reduce the damage caused by the thermal stress mismatch.

Tungsten-rhenium thin film thermocouples for SiC-based ceramic matrix composites.

A tungsten-rhenium thin film thermocouple is designed and fabricated, depending on the principle of thermal-electric effect caused by the high temperature. The characteristics of thin film thermocouples in different temperatures are investigated via numerical analysis and analog simulation. The working mechanism and thermo-electric features of the thermocouples are analyzed depending on the simulation results. Then the thin film thermocouples are fabricated and calibrated. The calibration results show that the thin film thermocouples based on the tungsten-rhenium material achieve ideal static characteristics and work well in the practical applications.