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 sin gle crystal nickel base superalloy (MC2) recently developed, is studie d by means of atom-probe techniques. The results indicate that the com position of both gamma and gamma' phases evolves drastically during ag eing. 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 t o the mu phase precipitation was detected. The spatial distribution of mu-forming elements in the gamma phase was investigated in order to f ind out whether clustering occurs. Ordering phenomena related to chrom ium were observed in gamma. The long range order in the gamma' phase w as also studied. The microanalysis of the material on a (001) superstr ucture plane allowed the preferential sites of various species to be d etermined.