Determination of phase diagrams to understand the equilibria among phases in metallic and ceramic systems has been of paramount interest in many areas of materials research. Traditionally, phase diagrams have been determined by (i) selecting several experimental compositions to map the region in the system of interest, (ii) exposing the alloys to temperature to achieve equilibrium, and (iii) characterizing one or more of the physical properties of the bulk material such as the crystal structure(s), magnetic property, metallography, etc., to determine the number and type of phases present in each alloy. Phase boundaries are then determined by delineating the regions of alloy compositions with respect to the number and types of phases present. The traditional methods suffer from several drawbacks, the major ones being (i) the need for numerous samples, (ii) difficulties in accurately determining multi-phase regions, (iii) assumption that the bulk samples are macroscopically and microscopically homogeneous, and (iv) difficulties in establishing the attainment of equilibrium. The limitations of these traditional methods mainly stem from their inherent inability to characterize the crystal structure and composition of the individual phasesCI). More recently, methods have been developed to determine phase boundaries by x-ray microprobe analysis of bulk diffusion couples (2). Though this approach offers some advantages over the conventional methods, it is still limited by the poor spatial resolution of x-ray microprobe analysis.