Oxidation behavior of AlMgB14-TiB2 composite at elevated temperature

The isothermal oxidation behavior of AlMgB14-TiB2 composite was investigated at the temperature range from 600 degrees C to 1000 degrees C in air for 10 h. The results showed that the oxidation kinetics of this composite obeyed the parabolic law with an activation energy of 176 +/- 20 kJ mol(-1) from 700 degrees C to 1000 degrees C, the corresponding parabolic rate constant increased from 0.0069 x 10(-8) kg(2) m(-4) s(-1) to 138.75 x 10(-8) kg(2) m(-4) s(-1). The SEM micrograph of the oxidized surface at 700 degrees C for 10 h indicated that only the TiB2 phase was changed. The AlMgB14 phase changed at 800 degrees C in air, and the oxide scale consisting of TiO2 and borate glass dissolved with MgO and Al2O3. Meanwhile, a number of pores also existed in the oxide scales. The oxide scales at 1000 degrees C were divided into three layers: an outer glassy B2O3 layer, a middle oxide layer with small size pores, and a reaction layer with large size pores formed as the oxidation of the A1MgB14 phase. The formation mechanism of the oxidized layers was analyzed. (C) 2015 Elsevier B.V. All rights reserved.