ch10-Phase_Diagrams - Phase Diagrams Chapter 10 Chapter 10(part 1 Introduction Solubility Limits Phases Phase Equilibrium Interpretation of Phase

ch10-Phase_Diagrams - Phase Diagrams Chapter 10 Chapter...

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Phase Diagrams Chapter 10
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Chapter 10 (part 1) Introduction Solubility Limits Phases Phase Equilibrium Interpretation of Phase Diagrams Binary Isomorphous Systems (Cu-Ni) Development of Microstructure Mechanical Properties Binary Eutectic Systems Development of Eutectic Alloy Microstructure
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3 Components : The elements or compounds that are mixed initially (Al and Cu). Phases : A phase is a homogenous, physically distinct and mechanically separable portion of the material with a given chemical composition and structure ( and ). (darker phase) (lighter phase) Components and Phases Aluminum- Copper Alloy
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Phase Equilibria: Solubility Limit Solution – solid, liquid, or gas solutions, single phase Mixture – more than one phase Question: What is the solubility limit for sugar in water at 20°C? Answer: 65 wt% sugar . At 20°C, if C < 65 wt% sugar: syrup At 20°C, if C > 65 wt% sugar: syrup + sugar 65 Solubility Limit : Maximum concentration for which only a single phase solution exists. Sugar/Water Phase Diagram Sugar Temperature (°C) 0 20 40 60 80 100 C = Composition (wt% sugar) L (liquid solution i.e., syrup) Solubility Limit L (liquid) + S (solid sugar) 20 40 60 80 100 Water
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5 Equilibrium A system is at equilibrium if its free energy is at a minimum, given a specified combination of temperature , pressure and composition. The (macroscopic) characteristics of the system do not change with time — the system is stable. A change in T, P or C for the system will result in an increase in the free energy and possible changes to another state whereby the free energy is lowered.
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One Component Phase Diagram 6
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7 Phase Diagrams Indicate phases as a function of Temp, Comp and Pressure. Focus on: - binary systems: 2 components . - independent variables: T and C ( P = 1 atm is almost always used). Cu-Ni system • 2 phases: L (liquid) (FCC solid solution) • 3 different phase fields: L L + wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T(°C) L (liquid) (FCC solid solution) L + liquidus so lidus
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8 Changing T can change # of phases: path A to B . Changing C o can change # of phases: path B to D . Effect of Temperature & Composition (C o ) wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T(°C) L (liquid) (FCC solid solution) L + liquidus so lidus A B D Cu Cu-Ni system
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9 Rule 1: If we know T and C o , then we know: --how many phases and which phases are present. Examples: wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T(°C) L (liquid) (FCC solid solution) A(1100,60) B (1250,35) Cu-Ni phase diagram A(1100, 60): 1 phase: B(1250, 35): 2 phases: L + Determination of phase(s) present Melting points: Cu = 1085°C, Ni = 1453 °C Solidus - Temperature where alloy is completely solid . Above this line, liquefaction begins. Liquidus - Temperature where alloy is completely liquid . Below this line, solidification begins.
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10 Rule 2: If we know T and C o , then we know: --the composition of each phase.
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