chapter 10 - 10/11/11 1 Phase diagrams Chapter 10 10/11/11...

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Unformatted text preview: 10/11/11 1 Phase diagrams Chapter 10 10/11/11 2 A SEM photograph which shows the microstructure of a plain steel containing 0.44 wt % C. The large dark areas are the proeutectoid ferrite. Regions having the alternating light and dark lamellar structure are pearlite, which consists of ferrite and cementite. 10/11/11 3 Why Study Phase diagrams ? Be important to the design and control of heat treating procedures. Because some properties of materials are functions of their microstructures, and, consequently, of their thermal histories. 10/11/11 4 the phase diagram is useful in understanding the development and and preservation of nonequilibrium structures and their attendant properties, whose attendant properties are more desirable than those associated with the equilibrium state, which is illustrated later. Although the phase diagram only considers the equilibrium states, 10/11/11 5 10. 1 Introduction there is a strong correlation between microstructrue and mechanical properties the development of microstructure of an alloy is related to the characteristics of its phase diagram phase diagrams provide valuable information about melting, casting, crystallization, and other phenomena 10/11/11 6 Terminology associated with phase diagrams and phase transformations; Some of the common and relatively simple binary phase diagrams, including that for the Fe-C system; The interpretation of phase diagrams; Topics to discuss: The development of equilibrium microstructures, upon cooling, for several situations. 10/11/11 7 Component: pure metals and/or compounds of which an alloy is composed. e.g., Cu Zn in Cu-Zn brass System-1: 1 May refer to a specific body of material under consideration. e.g., a ladle of molten steel Definitions and Basic Concepts 10/11/11 8 System-2: 2 May relate to the series of possible alloys consisting of the same components, but without regard to alloy composition. e.g., the Fe-C system Definitions and Basic Concepts 10/11/11 9 solid solution: consists of atoms of at least two different types solute atoms occupy either sub- stitutional or interstitial positions in the solvent lattice the crystal structure of the solvent is maintained. Definitions and Basic Concepts 10/11/11 10 10. 2 Solubility Limit Solubility limit: Solubility limit: Maximum concentration of solute atoms which may dissolve in the solvent to form a solid solution at some specific temperature. The addition of solute in excess of solubility limit result in the formation of another solid solution or compound that has a distinctly different composition. 10/11/11 11 e.g., sugar-water system Fig. 10.1 the solubility of sugar (C 12 H 22 O 11 ) composition (wt%) Temperature(C) Sugar Water Temperature(F) 10/11/11 12 10. 3 Phases Phase: Phase: Homogeneous portion of a system that has uniform physical and chemical characteristics....
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chapter 10 - 10/11/11 1 Phase diagrams Chapter 10 10/11/11...

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