High-temperature oxidation behavior of Co-doped WB2 ceramics in air

Abstract

With the high melting point, excellent mechanical properties and good thermal stability, WB2 is a candidate of the promising high-temperature structural materials. WB2 ceramics were hot pressed at low temperatures (~1500°C) with a small amount of Co as sintering aids, achieving high relative density and mechanical properties. In this paper, Co-doped WB2 ceramics were selected as test materials to carry out the oxidation experiments systematically. The oxidation resistance of the samples was evaluated at temperatures of 800°C, 1200°C, and 1600°C in static air. At 1200°C and below, Co-doped WB2 ceramics still possessed good oxidation resistance. The oxidation behaviors of the Co-doped WB2 ceramics were studied and the oxidation mechanism was discussed in detail. Besides, the oxidation kinetics of the Co-doped WB2 ceramics at 1200°C were studied. The result showed the oxidation rate of WB2 ceramics basically obeyed a parabolic law at 1200°C. The existence of Co aids was not good for the oxidation resistance of WB2 ceramics, mainly due to the increasing oxygen vacancy concentration of the oxide scale. The phase compositions, the microstructure of the surface and cross section of the oxidized samples were characterized using X-ray diffraction and scan electron microscopy along with energy dispersive spectrometry. Beneath the surface, the oxide scale of Co-doped WB2 ceramics consisted of mainly WO3 skeleton layer and glassy B2O3 layer, which contributed to the good oxidation resistance at 1200°C.