Multilayers provide an ideal tool to study thermodynamics of heterogeneous systems far from equilibrium. In this study, synthesis, characterization, thermal stability and phase equilibrium of multilayers are investigated based on Au-Pt system. Au-50%Pt multilayers were first formed by repeated rolling and folding. The microstructure was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These methods revealed that the process reduced layer thicknesses to below 30nm. However, delaminating and non-uniform spacings were also observed in some regions. To get well- welded and regular multilayers, the experiment was redesigned. The improved approach, involving repeated cutting, stacking, annealing and cold rolling, has yielded uniform multilayers with interlamellar spacings as low as 6nm. XRD demonstrated the formation of a homogeneous solid solution during cold rolling at room temperature. TEM suggested that the multilayers were discontinuously homogenized via steady state motion of boundaries. The reason for the solid solution formation is that the stored interface energy is higher than the energy barrier for solid solution formation. The solid solution is unstable. It decomposes into Au and Pt after heating to 500°C at 50°C/min by differential scanning calorimetry (DSC). The phase diagram is strongly modified in the nanometer range when we take into account of interface energy. The grain size dependent phase diagram model of Au-Pt system shows that the melting points of Au and Pt can be lowered more than 300K if the average grain size is reduced to 10nm. The melting temperature of Au/Pt multilayers has been studied with theoretical and experimental approaches. High speed laser heating was used to minimize any modification of the multilayer structure prior to melting. The qualitative experimental results are shown to be in agreement with expectations. / Thesis / Master of Applied Science (MASc)