Chapter9

Chapter9 - Chapter Outline: Phase Diagrams Microstructure...

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1 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Microstructure and Phase Transformations in Multicomponent Systems Chapter Outline: Phase Diagrams ± Definitions and basic concepts ± Phases and microstructure ± Binary isomorphous systems (complete solid solubility) ± Binary eutectic systems (limited solid solubility) ± Binary systems with intermediate phases/compounds ± The iron-carbon system (steel and cast iron)
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2 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Component -chem ica l ly recogn izab le spec ies (Fe and C in carbon steel, H 2 O and Sucrose in sugar solution in water). A binary alloy contains two components, a ternary alloy – three, etc. Phase –a po r t ion o f a sy s tem tha t ha s un i fo rm phy s l and chemical characteristics. Two distinct phases in a system have distinct physical and/or chemical characteristics (e.g. water and ice, water and oil) and are separated from each other by definite phase boundaries . A phase may contain one or more components. A single-phase system is called homogeneous , systems with two or more phases are mixtures or heterogeneous systems. Definitions: Components and Phases
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3 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Solvent -ho s t o r ma jo r compon en t in so lu t ion , solute - minor component. Solubility Limit of a component in a phase is the maximum amount of the component that can be dissolved in it (e.g. alcohol has unlimited solubility in water, sugar has a limited solubility, oil is insoluble). The same concepts apply to solid phases: Cu and Ni are mutually soluble in any amount (unlimited solid solubility), while C has a limited solubility in Fe. Definitions: Solubility Limit
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4 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Microstructure The properties of an alloy depend not only on proportions of the phases but also on how they are arranged structurally at the microscopic level. Thus, the microstructure is specified by the number of phases, their proportions, and their arrangement in space. Microstructure of cast Iron Phase diagrams will help us to understand and predict microstructures like the one shown in this page The long gray regions are flakes of graphite. The matrix is a fine mixture of BCC Fe and Fe 3 C compound. http://www2.umist.ac.uk/material/research/intmic/ (link is dead)
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5 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams A system is at equilibrium if at constant temperature, pressure and composition the system is stable, not changing with time. Equilibrium is the state that is achieved given sufficient time. But the time to achieve equilibrium may be very long (the kinetics can be slow) that a state along the path to the equilibrium may appear to be stable. This is called a metastable state .
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This note was uploaded on 03/05/2012 for the course MSE 209 taught by Professor Kelly during the Spring '08 term at UVA.

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Chapter9 - Chapter Outline: Phase Diagrams Microstructure...

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