On Catastrophic Oxdation of Ti-Zr Alloys

The present authors studied oxidation behaviors of Ti-Zr alloys (ca.5∼90 wt%), using the thermo-balance, X-ray diffraction, electron microscope and optical microscopic methods. The catastrophic oxidation was observed in alloys containing ca. 50∼90 wt%Zr oxidized in air at 700° or 900°C for 30 min or 2 hr. It was verified experimentally that β-phases (cubic type crystals) remaining in substrata were more preferentially oxidized than α-phases (hexagonal close-packed crystals) in the earliest stage of oxidation (500°C, 5 min) of the alloys showing the catastrophic oxidation at 700° or 900°C, and moreover, that these alloys showed breakaway phenomena of the surface oxide scales. The present studies also clarified by X-ray diffraction and optical microscopic observations that the surfaces were mainly covered with porous TiO2ZrO2 or TiO2ZrO2 and ZrO2 layers in the alloy showing the catastrophic oxidation.