PHASE-COMPOSITION AND CHEMICAL ORDER IN THE SINGLE-CRYSTAL NICKEL-BASE SUPERALLOY MC2

The time evolution of phase composition at 1050-degrees-C in a new single crystal nickel base superalloy (MC2) recently developed, is studied by means of atom-probe techniques. The results indicate that the composition of both gamma and gamma' phases evolves drastically during ageing. The composition of the mu phase was estimated for 100 h at 1050-degrees-C. Atom-probe data demonstrate that mu is a Ta, W, Mo enriched-phase. No impoverishment effect of the gamma solid solution related to the mu phase precipitation was detected. The spatial distribution of mu-forming elements in the gamma phase was investigated in order to find out whether clustering occurs. Ordering phenomena related to chromium were observed in gamma. The long range order in the gamma' phase was also studied. The microanalysis of the material on a (001) superstructure plane allowed the preferential sites of various species to be determined.