Oxidation behavior of αMo–Mo3Si–Mo5SiB2 (T2) three phase system

The cyclic oxidation kinetics and microstructures of the oxide scales have been investigated from 600 to 1400 °C on compositions within the three phase field αMo–Mo3Si–Mo5SiB2. From 600 to 750°C, the oxidation behavior is controlled by increasing volatilization of MoO3 with increasing temperature and, consequently there is no oxidation protection. From 800 to 900 °C, the kinetics show a rapid transient weight loss due to MoO3 volatilization and, a steady state weight loss associated with the formation of a porous outer borosilicate scale and continuous escape of MoO3. At and above 1000 °C, the oxide scale consists of relatively solid and well adherent outer SiO2 scale and an inner reaction zone consisting of αMo and SiO2 phases. In the temperature regime 1000–1300 °C, there is a high degree of oxidation protection characterized by low transient- and steady-state weight losses. The overall oxidation behavior is governed by a competition between volatilization of Mo and the passivation provided by formation of borosilicate glass scale.