Surface segregation of Ni-Cu binary alloys studied by an atom- probe.

A newly developed focusing-type time-of-flight atom-probe (field ion microscope) was applied for the detailed investigation of surface segregation in Ni-Cu binary alloys over the entire composition range. Strong enrichment of copper was observed in the Ni-rich alloys, in agreement with previous reports. The surface enrichment factor and heat of Cu segregation were determined experimentally and were found to agree with various theoretical results. Cu segregation was limited to the topmost surface layer in almost all of the cases. The adjacent subsurface region exhibited small oscillations in the composition.