Lecture 12 - Phase Diagrams Phase Diagrams ISSUES TO...

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1 Phase Diagrams Phase Diagrams ISSUES TO ADDRESS. .. • When we combine two elements. .. what equilibrium state do we get? • In particular, if we specify. .. --a composition (e.g., wt% Cu - wt% Ni), and --a temperature ( T ) then. .. How many phases do we get? What is the composition of each phase? How much of each phase do we get? Phase Diagrams Phase Diagrams Phase B Phase A Nickel atom Copper atom
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2 Phase Phase Equilibria Equilibria : Solubility Limit : Solubility Limit Introduction – Solutions – solid solutions, single phase –M ix tu res – more than one phase Solubility Limit : Max concentration for which only a single phase solution occurs. Question: What is the solubility limit at 20°C? Answer: 65 wt% sugar . If C o < 65 wt% sugar: syrup If C o > 65 wt% sugar: syrup + sugar. 65 Sucrose/Water Phase Diagram Pure Sugar Temperature (°C) 0 20 40 60 80 100 C o =Composition (wt% sugar) L (liquid solution i.e., syrup) Solubility Limit L (liquid) + S (solid sugar) 20 40 60 80 100 Water Adapted from Fig. 9.1, Callister 7e. Components : The elements or compounds which are present in the mixture (e.g., Al and Cu) Phases : The physically and chemically distinct material regions that result (e.g., α and β ). Aluminum- Copper Alloy Components and Phases Components and Phases α (darker phase) β (lighter phase) Adapted from chapter-opening photograph, Chapter 9, Callister 3e.
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3 Effect of Effect of T & Composition ( & Composition ( C o ) • Changing T can change # of phases: Adapted from Fig. 9.1, Callister 7e. D (100°C,90) 2 phases B (100°C,70) 1 phase path A to B . • Changing C o can change # of phases: path B to D . A (20°C,70) 2 phases 70 80 100 60 40 20 0 Temperature (°C) C o =Composition (wt% sugar) L (liquid solution i.e., syrup) 20 100 40 60 80 0 L (liquid) + S (solid sugar) water- sugar system Phase Phase Equilibria Equilibria 0.1278 1.8 FCC Cu 0.1246 1.9 FCC Ni r (nm) electroneg Crystal Structure • Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii ( W. Hume – Rothery rules ) suggesting high mutual solubility. Simple solution system (e.g., Ni-Cu solution) • Ni and Cu are totally miscible in all proportions.
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4 Unary Phase Diagram Unary Phase Diagram Phase Diagrams Phase Diagrams • Indicate phases as function of T , C o , and P . For this course: -binary systems: just 2 components. -independent variables: T and C o ( P = 1 atm is almost always used). Phase Diagram for Cu-Ni system Adapted from Fig. 9.3(a), Callister 7e. (Fig. 9.3(a) is adapted from Phase Diagrams of Binary Nickel Alloys , P. Nash (Ed.), ASM International, Materials Park, OH (1991). • 2 phases: L (liquid) α (FCC solid solution) • 3 phase fields: L L + α α wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T (°C) L (liquid) α (FCC solid solution) L + α l i q u d s o
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5 wt% Ni 20 40 60 80 100 0 1000 1100 1200 1300 1400 1500 1600 T (°C) L (liquid) α (FCC solid solution) L + α l i q u d s o Cu-Ni phase diagram Phase Diagrams : # and types of phases # and types of phases • Rule 1: If we know T and C o , then we know: --the # and types of phases present.
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This note was uploaded on 04/27/2009 for the course MEEN 222 taught by Professor Radovic during the Fall '08 term at Texas A&M.

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Lecture 12 - Phase Diagrams Phase Diagrams ISSUES TO...

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