Atom probe analysis of segregation in Fe--0.15 wt. % Ti

A compositional analysis of a Fe-Ti alloy was carried out using a time-of-flight atom probe. It was found that titanium atoms are segregated to the surface and grain boundaries after heating to 1073 or 1273 K at 10-6 Pa (10-8 Torr). A decreasing titanium concentration profile extends over several atomic distances and even at 20 atomic distances from the surface the Ti concentration is above the nominal bulk value. In the outermost surface layers and in the grain boundaries titanium is present in the form of oxide, mainly TiO and TiO2, whereas in the subsurface atom-layer region it is present as randomly distributed titanium atoms and to a lesser degree as clusters of Ti around impurities, such as C, N, and O