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 were 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 observed in a confocal laser scanning microscope. Metallographic analyses were performed on the samples by optical and scanning electron microscopy. The rapidly solidified samples melted far below the equilibrium melting point. The melted and resolidified samples mostly consisted of structures similar to those seen in alloys with a miscible gap. It is proposed that this type of behaviour is a result of lattice defects formed 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 equilibrium melting point. This could explain the observed phase structure and the melting of the alloy below the equilibrium melting point.