On a metastable miscibility gap in γ-Mn-Cu alloys and the origin of their high damping capacity

A metastable miscibility gap has been found which explains the decomposition behaviour of γ-Mn-Cu alloys. Hardness measurements as well as results of other authors were used to outline the boundaries of the two-phase region. Electron microscopy provided direct evidence for the phase separation prior to α-Mn precipitation. A tweed structure was observed which coarsened upon annealing. The existence of the miscibility gap gives rise to the observed increase of the Neel temperature upon annealing as well as to the microstructural changes affecting the variations in specific damping capacity upon ageing, i.e. an initial increase and subsequent decrease of the damping capacity with ageing time.