Tungsten-rhenium thermocouple sensor for in-situ ultra-high temperature measurement of hypersonic aircraft surface

The tungsten-rhenium thermocouple sensor is widely used in the ultra-high temperature measurement in the metallurgy, aerospace, aviation, nuclear power industries due to its advantages of high sensitivity, high melting point, fast response and low cost. However, the tungsten-rhenium thermocouples are susceptible to the rapid oxidation condition at high temperature. To extend the applicability of the tungsten-rhenium thermocouple into the super oxidizing environment, it is crucial to design an oxidation-resistant layer for providing the tungsten-rhenium thermocouple the protection from the oxidation. Besides considering the good antioxidant characteristics, the oxidation-resistant layer should be fabricated with strong surface adhesion to the tungsten-rhenium substrate, so as to normally operate without any failure under the hypersonic airflow. Moreover, the thermal compatibility between the materials of the oxidation-resistant layer and the tungsten-rhenium alloy is also an important factor to improve the thermal shock resistance, as well as the high thermal conductance to keep the fast thermal response. In this research, compound coating layer consisting of ZrO
2
, HfO
2
, ZrB
2
and SiC was chosen for protecting tungsten-rhenium alloys from oxidation. The oxidation-resistant coating layer was grown by sol-gel method on the surface of tungsten-rhenium thermocouple sensor and the coating process was investigated. After annealing treatment in vacuum environment the dense and smooth oxidation-resistant coating layer was successfully prepared. The surface morphology was analyzed by 3D microscope. It was found that the different fabrication process has a significant impact on the quality of the oxidation-resistant coating layer. Finally the tungsten-rhenium thermocouple was tested by 2500 °C oxyacetylene flame at oxidation atmosphere and it was found that the thermocouples can stay working for more than 1800 seconds.