Structural aspect of decomposition of metastable γ-Mn-Cu alloys

The analysis of neutron diffraction experiments on a special ‘null-matrix’ γ-Mn-Cu alloy, together with improved data on the variation of cell dimensions of γ-Mn-Cu alloys with composition, has provided information on the decomposition of the metastable γ-Mn-Cu phase. The decomposition behaviour of these alloys has been explained recently in terms of a metastable miscibility gap. The present findings are in accordance with this suggestion, although it is apparent that α-phase precipitation can occur at lower temperatures and after shorter anneal times than was previously thought. The initial phase separation occurs in such a way that the manganese-deficient and manganese-rich components have the same cell dimensions, and in the manganese-rich component the cubic to tetragonal cell distortion appears to be suppressed in the initial stages of the segregation.w