MELTING TEMPERATURE, TRANSFORMATION AND METASTABLE PHASE-DIAGRAM OF RAPIDLY SOLIDIFIED AG-CU ALLOYS

Cu-Ag samples produced during rapid solidification experiments using a Planar Flow Melt Spinning Process or a levitation casting technique w ere rapidly heated in a mirror furnace to a variety of temperatures at rates between 100 and 1.6 K/s. The surface of each sample was observe d in a confocal laser scanning microscope. Metallographic analyses wer e performed on the samples by optical and scanning electron microscopy . The rapidly solidified samples melted far below the equilibrium melt ing point. The melted and resolidified samples mostly consisted of str uctures similar to those seen in alloys with a miscible gap. It is pro posed that this type of behaviour is a result of lattice defects forme d during the rapid solidification process. The effect of these defects on the thermodynamic properties was investigated. A metastable phase diagram with a miscibility gap can be constructed below the equilibriu m melting point. This could explain the observed phase structure and t he melting of the alloy below the equilibrium melting point.