Steam oxidation behavior of Ni-base superalloys 690, 725 and X-750 at 600 and 650 °C

Abstract

Abstract The 1-bar steam oxidation behavior of Ni-base superalloys 690, 725, and X-750 was evaluated at 600 and 650\u202f°C for up to 5000\u202fh. In addition to monitoring mass changes, microstructures of the 5000-h-exposed samples were characterized using scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy. Together with thermodynamic calculations, the scale constitution and possible exfoliation was discussed. Alloy X-750 exhibited the best resistance to steam oxidation with the least metal thickness loss at 600\u202f°C while alloy 690 at 650\u202f°C. Alloy 725 exhibited more than two times metal thickness loss than the other two alloys at 650\u202f°C.