Oxygen Distribution in Titanium Single Crystal Fabricated by Optical Floating-Zone Method under Extremely Low Oxygen Partial Pressure

This study examines the properties of a titanium single crystal fabricated by the floating-zone-melting process in Ar gas flow atmosphere where the partial pressure of oxygen was maintained extremely low at PO2 ¼� 10 � 23 atm by the newly developed oxygen pump system. The distribution of solute oxygen atoms in the obtained single crystal exhibited a peculiar gradient. In the early stage of the titanium single crystal growth, the oxygen content in the single crystal (approximately 1600 ppm) was higher than that in the mother ingot (980 ppm). However, as the crystal growth progressed, the oxygen content gradually decreases and then reduced to 660 ppm in the final stage of crystal growth. Such a gradient of oxygen composition was not detected in titanium single crystals fabricated under conventional, commercial Ar gas flow atmosphere. Owing to the unique gradient of oxygen content formed under extremely low oxygen partial pressure, the Vickers hardness of the single crystal decreased gradually along the crystal growth direction. [doi:10.2320/matertrans.MA200903]