GTBL042-10 GTBL042-Callister-v2 August 13, 2007 18:16
Summary • 393Binary Isomorphous Systems
Development of Microstructure in Isomorphous Alloys
Mechanical Properties of Isomorphous Alloys
Several different kinds of phase diagram were discussed for metallic systems. Isomor-
phous diagrams are those for which there is complete solubility in the solid phase;
the copper–nickel system displays this behavior. Also discussed for alloys belonging
to isomorphous systems were the development of microstructure for both cases of
equilibrium and nonequilibrium cooling, and the dependence of mechanical charac-
teristics on composition.Binary Eutectic Systems
Development of Microstructure in Eutectic Alloys
In a eutectic reaction, as found in some alloy systems, a liquid phase transforms
isothermally to two different solid phases upon cooling. Such a reaction is noted on
the copper–silver and lead–tin phase diagrams. Complete solid solubility for all com-
positions does not exist; instead, solid solutions are terminal—there is only a limited
solubility of each component in the other. Four different kinds of microstructures
that may develop for the equilibrium cooling of alloys belonging to eutectic systems
were discussed.Equilibrium Diagrams Having Intermediate Phases or Compounds
Eutectoid and Peritectic Reactions
Congruent Phase Transformations
Other equilibrium phase diagrams are more complex, having intermediate com-
pounds and/or phases, possibly more than a single eutectic, and other reactions in-
cluding eutectoid, peritectic, and congruent phase transformations. These are found
for copper–zinc and magnesium–lead systems.Ceramic Phase Diagrams
Phase diagrams for the Al 2 O 3 –Cr 2 O 3 , MgO–Al 2 O 3 , ZrO 2 –CaO, and SiO 2 –Al 2 O 3
systems were discussed. These diagrams are especially useful in assessing the high-
temperature performance of ceramic materials.The Gibbs Phase Rule
The Gibbs phase rule was introduced; it is a simple equation that relates the number
of phases present in a system at equilibrium with the number of degrees of freedom,
the number of components, and the number of noncompositional variables.The Iron–Iron Carbide (Fe–Fe 3 C) Phase Diagram
Development of Microstructure in Iron–Carbon Alloys
Considerable attention was given to the iron–carbon system, and specifically, the
iron–iron carbide phase diagram, which technologically is one of the most important.
The development of microstructure in many iron–carbon alloys and steels depends
on the eutectoid reaction in which the FCC austenite phase of composition 0.76
wt% C transforms isothermally to the BCCαferrite phase (0.022 wt% C) and the
intermetallic compound, cementite (Fe 3 C). The microstructural product of an iron–
carbon alloy of eutectoid composition is pearlite, a microconstituent consisting of
alternating layers of ferrite and cementite. The microstructures of alloys having car-
bon contents less than the eutectoid (hypoeutectoid) are comprised of a proeutectoid