MECHANICAL ALLOYING AND THERMAL-DECOMPOSITION OF FERROMAGNETIC NANOCRYSTALLINE FCC-CU50FE50

The mechanical alloying of usually immiscible Fe and Cu is monitored by magnetic and structural measurements. The Fe component of a mixture of global composition Fe50Cu50 is found to dissolve into the Cu-f.c.c. matrix after nanofragmentation following a previously developed thermodynamic model. The resulting nanocrystalline f.c.c. FeCu supersaturated solid solution with a Curie temperature of about 480 K is found to phase-separate above 500 K through a spinodal decomposition mechanism that occurs independently in each nanograin with little grain growth. The evolution of magnetization and of the diffraction patterns during decomposition indicate that more than 50% of the emerging Fe-rich zones remain f.c.c. after the exothemic heat release corresponding to chemical phase-separation. The decomposition of supersaturated f.c.c. FeCu thus generates Fe-rich f.c.c. zones that have not been obtained by mechanical alloying or vapor-deposition techniques and provides interesting information on the magnetic properties of gamma-Fe(Cu) which is found to be ferromagnetic as compared to pure gamma-Fe which is antiferromagnetic.