This chapter provides a brief overview of monotectic alloy systems and reactions. It begins by presenting a monotectic phase diagram and identifying important points, lines, and regions. It then describes the monotectic reactions that occur in copper-lead systems and the associated solidification structures. It also discusses the morphology of the microstructure produced during directional solidification and the classification criteria of low- and high-dome alloys.

Phase diagrams are graphical representations that show the phases present in the material at various compositions, temperatures, and pressures. This chapter begins with a section describing the construction of phase diagrams for the simple binary isomorphous system. A binary phase diagram can be used to determine three important types of information: the phases that are present, the composition of the phases, and the percentages or fractions of the phases. The chapter then describes the construction of one common type of binary phase diagram i.e., the eutectic alloy system. The major eutectic systems include the aluminum-silicon eutectic system and the lead-tin eutectic system. The chapter discusses the construction of eutectic phase diagrams from free energy curves. It also provides information on peritectic, monotectic, and solid-state reactions in alloy systems. The presence of intermediate phases is also described. Finally, a brief section provides some information on ternary phase diagrams.