Fe-Ti合金におけるTiの表面偏析

概要

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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°C in vacuum. Enrichment of Ti (includes titanium oxide formation) at the outermost surface layer is 90% at the (110) and (111) planes, 50% at the (211) plane and 70% at the (100) plane. At the (100) plane Ti enrichment extends to the first 4-5 layers while it is limited to only two layers at the other planes. Attempts were made to study chemisorption induced surface segregation using H2, D2 and CO. However no significant effects have been observed so far. When heated in O2 gas, two distinctly different types of oxidation were observed depending upon O2 partial pressure. At the lower O2 pressure (10-9 Torr), Ti oxide scale was formed on the surface, which markedly slows further oxidation of the alloy substrate, while at the higher O2 pressure (10-5 Torr) subsurface oxidation occurred, forming Fe oxides and Ti-rich clusters within the alloy matrix.
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