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

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