A STUDY OF PHASE-SEPARATION IN METASTABLE CU50FE50 ALLOYS BY NEUTRON-DIFFRACTION AND NEUTRON SMALL-ANGLE SCATTERING

The mechanical alloying (MA) of an equiatomic mixture of copper and ir on, which is reported to be immiscible in the equilibrium phase diagra m, leads to a metastable Cu50Fe50 alloy, which reverts to its constitu ents on isothermal annealing at 300 degrees C. We have studied the mec hanism of alloy decomposition by in-situ annealing using neutron diffr action and, for the first time for this system, neutron small-angle sc attering. Evidence has been found of spinodal decomposition, which was predicted in this system on the basis of thermodynamic arguments. The neutron small-angle scattering data point to the existence of fluctua tions in scattering length density with a length scale of 200-300 Angs trom in the early stages of annealing the Cu50Fe50 alloy.