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 iron, which is reported to be immiscible in the equilibrium phase diagram, leads to a metastable Cu50Fe50 alloy, which reverts to its constituents on isothermal annealing at 300 degrees C. We have studied the mechanism of alloy decomposition by in-situ annealing using neutron diffraction and, for the first time for this system, neutron small-angle scattering. 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 fluctuations in scattering length density with a length scale of 200-300 Angstrom in the early stages of annealing the Cu50Fe50 alloy.