SURFACE SEGREGATION OF Ti IN Fe-Ti ALLOYS.

The behavior of Ti in Fe-0. 29, 0. 64 and 1. 48 wt% Ti alloys has been investigated using a time-of-flight atom-probe. Ti segregates to the surface when Fe-Ti samples are heated at and above 600 degree C in vacuum. Attempts were made to study chemisorption induced surface segregation using H//2, D//2 and CO. However no significant effects have been observed so far. When heated in O//2 gas, two distinctly different types of oxidation were observed depending upon O//2 partial pressure. At the lower O//2 pressure (10** minus **9 Torr), Ti oxide scale was formed on the surface, which markedly slows further oxidation of the alloy substrate, while at the higher O//2 pressure (10** minus **5 Torr) subsurface oxidation occurred, forming Fe oxides and Ti-rich clusters within the alloy matrix.