Chemical composition measurements of a nickel-base superalloy by atom probe field ion microscopy

Single crystals of the rhenium-containing nickel-base superalloy CMSX-4 were investigated using a time of flight atom probe. The distribution of the alloying elements in the two phases, matrix (gamma phase) and precipitate (gamma' phase), was studied. The high spatial resolution of the atom probe allows to analyse the gamma-gamma' interface. The transition from matrix to gamma' phase takes place within one atomic layer. The boundary is enriched with titanium. Layer-by-layer analysis of (001) planes of the L1(2) ordered gamma' phase reveals alternating Ni- and Al-rich planes. The probability of site occupation by different elements could be evaluated. An approximate formula of the gamma' phase is given by (Ni-81 Ti-3 Ta-2 Cr-5 Co-7 W-2)(3) (Ni-20 Al-70 Ta-6 Co-2 W-2). Rhenium is found mainly in the matrix and has a tendency to build clusters.