ENGR2000_phasediagrams1

ENGR2000_phasediagrams1 - Introduction to Engineering...

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Introduction to Engineering Materials ENGR2000 Chapter 9: Phase Diagrams I Dr. Priya Thamburaj Goeser
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Definitions and Basic Concepts •A component is a chemically distinct and essentially indivisible substance. – Fe, Si, C are single component systems –H 2 O is a single component system – window glass (SiO 2 , Na 2 O & CaO) is a three- component system
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9.3 Phases •A phase is a chemically and structurally homogeneous region of a material. Liquid Solid Gaseous
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Phase and Component • Pure FCC Al is a single component, single phase system • A mixture of pure ice and pure water is a single component, two phase system • A mixture of BCC Fe and FCC Fe is a single component, two phase system. • A solid solution of Cu and Ni is a two component, single phase system • A solid solution of NiO and MgO is a two component, single phase system
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9.2 Solubility Limit • Maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution – At a specific temperature – For a specific alloy system
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10-09-08
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9.4 Microstructure • Microstructure in metal alloys – # of phases – Proportions of phases – Distribution or arrangement of phases • Microstructure depends on – Alloying elements – Concentrations – Heat treatment
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9.5 Phase Equilibrium • Free energy = function (internal energy, randomness or disorder of the atoms) • A system is at equilibrium if its free energy is at a minimum under some specified combination of temperature, pressure and composition. • Phase equilibrium is reflected by a constancy with time in the phase characteristics of a system.
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Sugar-water solution + solid sugar at 20 C in equilibrium
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Equilibrium Phase Diagrams • Phase diagrams presented here are for a constant pressure of 1 atm.
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9.6 Binary Isomorphous Systems •B i n a r y – 2 components • Isomorphous – Complete liquid and solid solubility
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pure component Cu pure component Ni Melting Temperature of pure Cu
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Substitutional solid solutions Cu & Ni solution - Isomorphous Atomic radii for Cu & Ni are 0.128 nm & 0.125 nm. Both have FCC crystal structure EN values are 1.9 & 1.8 Valences are +1 & +2.
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9.7 Interpretation of Phase Diagrams Phases Present 60 wt % Ni – 40 wt % Cu alloy at 1100 C 35 wt % Ni – 65 wt % Cu alloy at 1250 C
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Determination of Phase Compositions 60 wt % Ni – 40 wt % Cu alloy at 1100 C Ni wt C .% 60 = α
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Determination of Phase Compositions - Tie line 35 wt % Ni – 65 wt % Cu alloy at 1250 C Ni wt C Ni wt C L .% 5 . 31 .% 5 . 42 = = α
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Determination of Phase Amounts 60 wt % Ni – 40 wt % Cu alloy at 1100 C % 100 = α W
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Determination of Phase Amounts - Lever rule 35 wt % Ni – 65 wt % Cu alloy at 1250 C 1 : Note 68 . 0 32 . 0 .% 35 .% 5 . 31 .% 5 . 42 0 0 0 = + = = = = = = = L L L L L L W W C C C C W C C C C W Ni wt C Ni wt C Ni wt C α
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Reading Assignments • Section 9.7 – Tie line – Lever rule – Example 9.1 – Volume fractions & mass fractions
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9.8 Development of Microstructure in Isomorphous Alloys • Equilibrium cooling – Cooling occurs very slowly – Phase equilibrium is continuously maintained
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9.8 Development of Microstructure in
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ENGR2000_phasediagrams1 - Introduction to Engineering...

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