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 (γ phase) and precipitate (γ′ phase), was studied. The high spatial resolution of the atom probe allows to analyse the γ−γ′ interface. The transition from matrix to γ′ phase takes place within one atomic layer. The boundary is enriched with titanium. Layer-by-layer analysis of (001) planes of the L12 ordered γ′ phase reveals alternating Ni- and Al-rich planes. The probability of site occupation by different elements could be evaluated. An approximate formula of the γ′ phase is given by (Ni81 Ti3 Ta2 Cr5 Co7 W2)3 (Ni20 Al70 Ta6 Co2 W2). Rhenium is found mainly in the matrix and has a tendency to build clusters.