High Temperature Oxidation Resistant Coatings Of W-Re Alloy Thermocouple

Tungsten-Rhenium （W-Re） alloy thermocouple is one of most commonly used hightemperature sensors whose measuring upper limit could achieve to2800.℃However, W-Realloy is very easy oxidized at high temperature. It should used in reducing, inert and vacuumatmosphere. While it used in oxidization or air atmosphere, anti-oxidization protectionshould be applied. The purpose of this research is to fabricate oxidation resistant coatings（ORCs） and develop a proper coating process of ORCs. ORCs should improve the upperlimit of measuring temperature and working time in oxidization atmosphere on the basis ofno extended of reponse time of thermocouple.First, thermal stress and thermal strain of candidate materials of ORCs were simulatedby finite element method. Then roughness model of interface between ORC and W-Re alloywas developed and showed that roughness affected thermal strain distinctly. Based onsimulation results, ZrB₂and HfO₂were choosen as candidate of ORC materials.ZrB₂and HfO₂mixed sol was prepared by Sol-Gel method. ORCs were made bypulling method around10layers. Then coatings heated in vacuum atmosphere and airatmosphere and accomplished with high uniformity and condensation.Chemical changes of ORCs were analyzed by Differential Thermal Analysis （DTA） andThermogravimetric Analysis （TG）. Phases of ORCs were analyzed by X-ray Diffraction（XRD）. The results showed that materials of coatings mainly formed ZrO₂and HfO₂.However, ZrB₂phase would form in vacuum atmosphere at higher temperature. The surfacesof coatings were analyzed by three dimension （3D） microscope. Results indicated thatdifferent materials and coating processes influenced uniformity and condensation of ORCssignificantly.W-Re thermocouples were tested by oxyacetylene torch at2300℃and results showedthat thermocouples could bear more than300s at this condition without slough of ORCs.