AP-FIM analysis of ordered Cu 3Au-(4 at% Pt) alloy

Abstract

The atom probe was used to investigate the effects on the microstructure of adding a ternary element, platinum, to the ordered intermetallic alloy Cu 3Au (L1 2 superstructure). Our aim was to investigate the effect of Pt on the hardening of the material, in particular if any segregation to or precipitation at grain boundaries occurs. The lower field evaporation field of Cu compared to that of Au and Pt made it difficult to avoid preferential field evaporation during APFIM analysis (at 28 K and 15–20% pulse fraction) i.e. evaporation of Cu at the DC field. The effect was largest at a grain boundary, where more Au than Cu was recorded. Under the assumption that Cu is the only atomic species that evaporates preferentially, it was possible to determine the Pt content in the material. It was about 4 at% both in the bulk and close to and at a grain boundary. Essentially all Pt therefore exists in solid solution in the superlattice, providing solid solution hardening of the ordered alloy. EDX analyses performed in both SEM and TEM show a constant platinum content across grain boundaries, thus supporting the atom probe results.