Chapter_9 - ENGINEERING MATERIALS (MECH203) TYPES OF...

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1 ENGINEERING MATERIALS (MECH203) TYPES OF MATERIALS * The metals / alloys are the most important engineering materials to be used over 90% of the total materials. Chapter 9-11 Chapter 12-13 Chapter 14-15 Chapter 16
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2 CHAPTER 9 : PHASE DIAGRAMS ( 相圖 ) Examples for solid phases : 2. C has a limited solubility in Fe 3. Cu has a limited solubility in Ag Solvent ( 溶劑 ) - host component ( 組元 ) Solute ( 溶質 ) - minor component Solubility limit ( 溶解度 ) : Max. concentration for which only a solution occurs.
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3 Components : Elements ( e.g. Phases : The physically & chemically distinct material regions that result ( e.g. α & β ). A phase may contain one or more components. • Single-phase system = homogeneous system ( e.g. Cu-Ni) • System with 2 or more phases = heterogeneous system ( e.g. Ag-Cu) Microstructure ( 顯微組織 ) is given by no. of phases, their proportions Ag-Cu alloy Adapted from Fig. 9.0, Callister 3e. α (darker phase) β (lighter phase)
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4 • System is in equilibrium ( 平衡 ) if it is at constant temperature, pressure & composition the system is stable , not changing with time. • Equilibrium is achieved given sufficient time , but that may be very long. System may appear to be stable = metastable state ( 穩態 ) . metastable equilibrium Free Energy
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5 Fig. 9.2(a). The Cu-Ni phase diagram. BINARY ISOMORPHOUS SYSTEMS ( 二元勻晶相圖 ) e.g. Cu-Ni Complete solubility occurs because both Cu & Ni have same crystal structure, FCC, 3 regions : 1. Liquid (L) 2. Solid + liquid ( α +L) 3. Solid ( α ) Liquidus line separates L from α +L Solidus line separates α from α +L (L) (fcc solid solution) P = 1 atm
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6 Fig. 9.2(a). The Cu-Ni phase diagram. Rule 1 : o are known, - # & types of phases present are also known. e.g. Cu-Ni Systems • Point A (1100 o C, 60 wt%) single phase : α (fcc solid solution) • Point B (1250 o C, 38 wt%) 2 phases : L + α (L) (fcc solid solution)
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7 Rule 2 : o are known, - then the composition of each phase is also known. e.g.
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This note was uploaded on 11/28/2010 for the course FST 55 taught by Professor Kowk during the Winter '10 term at University of Macau.

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Chapter_9 - ENGINEERING MATERIALS (MECH203) TYPES OF...

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