SOFTENING EFFECT IN NANOCRYSTALLINE FE-CU SUPERSATURATED SOLID-SOLUTIONS

Nanocrystalline supersaturated solid solutions (SSS) of Fe-Cu with b.c .c. lattice structure have been prepared by high energy mechanical mil ling. The Vickers hardness, lattice parameter, average grain size and atomic level strains of the specimen were measured as a function of co mposition by micro- and nanoindentation methods as well as X-ray diffr action analysis. With increasing Cu-content softening has been observe d in Fe-Cu SSS with respect to nanocrystallineFe. In comparison, Fe-Cr alloys characterized by a negative enthalpy of mixing exhibit mechani cal strengthening. It is suggested that the different strengthening te ndencies for nanocrystalline solid solutions relate to structural as w ell as chemical aspects of the internal interfaces.