Chapter 9 Phase diagrams Introduction Solubility limit Phases Phase equilibria Binary isomorphous systems Definitions and basic concepts Component: pure metals and/or compounds of which an alloy is composed System: a specific body of material under consideration A phase: a homogeneous portion of a system that has uniform physical and chemical characteristics Equilibrium: a system is at equilibrium if its free energy is at a minimum under some specified combination of temperature, pressure, and composition. Phase equilibrium: minimum energy for a system with multiple phases Phase diagram: Information about phases as function of T, composition, and pressure 1 Solubility limit Examples: phase diagram- water-sugar system 10 0 Solubility 80 Limit L (liquid) 60 L + 40 (liquid solution S i.e., syrup) (solid 20 sugar) Temperature (°C) 0 20 40 6065 80 10 0 Co=Composition (wt% sugar) Pure Water Pure Sugar 2 Examples B(100,70) D(100,90) 1 phase 2 phases 10 0 80 L • water- (liquid) sugar + system 60 L S (liquid solution 40 (solid i.e., syrup) sugar) 20 A(70, 20) Temperature (°C) 2 phases 0 0 20 40 60 70 80 10 0 Co=Composition (wt% sugar) Binary isomorphous systems Complete liquid and solid solubility of the two components Cu-Ni solid solution liquidus line solidus line melting temperatures phase composition phase relative amount: tie line and lever rule 3 Binary isomorphous systems (continue) Determine phase composition: lever rule • Liquid amount • Solid amount Determination of the number and types of phases present • Rule 1: If we know T and Co, then we know: --the # and types of phases present. T(°C) 160 0 150 0 L (liquid) s du ui iq 140 0 l us lid so α 130 0 + α B(1250,35) L (FCC solid 120 0 solution) 110 0 A(1100,60) 100 0 0 20 40 60 80 10 0 wt% Ni 4 The composition of each phase • Rule 2: If we know T and Co, then we know: --the composition of each phase. T(°C) A T tie line A dus qui 130 0 L (liquid) li α + L s B lidu TB so α α + 120 0 L D (solid) TD 20 3032 35 4043 50 CLCo Cα wt% Ni The amount of each phase • Rule 3: If we know T and Co, then we know: --the amount of each phase (given in wt%). • Examples: T(°C) A T tie line A dus qui 130 0 L (liquid) li α L + B us olid TB R S s α + α 120 0 L D TD (solid) 20 3032 35 4043 50 CLCo Cα wt% Ni 5 Development of microstructure Cu-Ag binary eutectic systems 6 Cu-Ag Binary eutectic systems Pb-Sn Binary eutectic systems Low melting temp, solder Example: Known 40% Sn+60%Pt, T=1500C Find phases, phase composition, and relative amount 7 Binary eutectic systems (Example) Explain how spreading salt on ice that is at a temperature below 00C can cause the ice to melt. Binary eutectic systems (example) Relative amount Liquid Primary α α 8.