A new mechanism of surface phase formation on precipitation-hardening alloy under ion irradiation

Abstract

Understanding surface modification of materials by Ga-ion milling has attracted growing research interests. This research reports that ion beam milling can induce rapid formation of θ-phase on the surface of a precipitation-hardening Al-Cu alloy. Atom probe tomography analysis reveals that an Al-Cu alloy tip develops a surface Cu-rich layer after electro-polishing. Cu-rich solute clusters in the 1-week naturally aged alloy sample are effective to assist the nucleation for rapid formation of surface θ-phase under the ion milling. The growth of the surface θ-phase is via a combination reaction of the surface Cu-rich layer with the Al matrix, rather than a simple decomposition of the Al-Cu alloy under the Ga ion irradiation. Partition and segregation behaviours of Ga with respect to the surface θ-phase are addressed by this investigation.