Oxide-scale evolution and dynamic oxidation mechanism of ZrB2-SiC in high-enthalpy plasma wind tunnel

In this work, a 1 MW Plasma wind tunnel was employed to study the dynamic oxidation mechanisms of ZrB2-SiC at heat flux ranging 0.5-5.0 MW/m(2) in reduced pressure. The results show a transition in the uppermost oxide layer from SiO2-rich glass to SiO2 when increasing heat flux from approximate to 0.55 and approximate to 1.70 MW/m(2) (approximate to 1100 degrees C and approximate to 1340 degrees C) to approximate to 2.50 MW/m(2) (approximate to 1550 degrees C). A temperature fluctuation was highlighted at approximate to 2.50 MW/m(2). At higher heat flux (>= 3.5 MW/m(2)), a 'thermal instability' occurred at approximate to 1650 degrees C. In addition, the ZrO2 grain structure was temperature dependent, particularly at approximate to 1.70 MW/m(2) where the ZrO2 grain evolved from tiny grain, to equiaxed grain and to columnar grain. At higher heat flux (>= 2.50 MW/m(2)), columnar grains were observed prior to the `thermal instability'. Finally, as oxidation of ZrB2-SiC was a diffusion-control process, the oxidation rate was dependent not only on temperature, but on grain structure of ZrO2.