Brass phase diagram

The copper-zinc system (which includes brasses) has one eutectoid reaction. Mark the eutectoid point on the phase diagram (Fig. A 1.38). 

Figure 20. Cu-Zn (brass) Subramanian, P.R., Chakrabarti, D.J., and Laughlin, D.E., Eds., Phase Diagrams of Binary Copper Alloys, p. 487, ASM International, Materials Park, OH, 1994. Reprinted with permission.

Khandpur KA, Forster SJ, Bates SF, Hamley WI, Ryan JA, Brass W, Alrndal K, Mortensen K (1995) Polyisoprene-polystyrene diblock copolymer phase diagram near the order-disorder transition. Macromolecules 28 8796-8806... 

It is necessary to establish a foundation of definitions and basic concepts relating to alloys, phases, and equilibrium before delving into the interpretation and utilization of phase diagrams. The term component is frequently used in this discussion components are pure metals and/or compounds of which an alloy is composed. For example, in a copper-zinc brass, the components are Cu and Zn. Solute and solvent,... 

The most common copper alloys are the brasses, for whieh zine, as a snbstitntional impurity, is the predominant alloying element. As may be observed for the eopper-zinc phase diagram (Figure 9.19), the a phase is stable for eoneentrations up to approximately 35 wt% Zn. This phase has an FCC crystal structure, and a-brasses are relatively soft, ductile, and easily cold worked. Brass alloys having a higher zinc content contain both a and p phases at room temperature. The P phase has an ordered BCC crystal structure and is harder and stronger than the a phase consequently, a + p alloys are generally hot worked. 

The Cu-Zn system (see Figure 2.7) displays a number of intermediate solid solutions that arise due to limited solubility between the two elements. For example, at low wt% Zn, which incidently is the composition of alloys known as brass, the relatively pure copper a phase is able to accommodate small amounts of Zn as an impurity in the crystal structure. This is known as a terminal solid phase, and the solubility limit where intermediate solid solutions (such as a + /S) begin to occur is called the solvus line. Some of the three-phase transformations that are found in this diagram include a peritectic (5 - - L -> e) and a eutectoid (5 -> y - - e). Remember that these three-phase transformations are defined for equilibrium coohng processes, not heating or nonequihbrium conditions. 

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