Lecture note 7 (09-27-2011)

Lecture note 7 (09-27-2011) - MAE 581 Advanced Materials...

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1 MAE 581 Advanced Materials Science Lecture note 7 Microstructure and phase, grain and phase boundaries Definitions Bulk metal materials and metal alloys Consist of many microscopic crystal “grains” Required by thermodynamics in materials Homogeneous system The material, in which its grains only differ from one another in orientation, is regarded as a homogeneous system. Example: iron
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Heterogeneous system The material, in which its grains not only differ from one another in orientation but also in crystal structure or composition, is regarded as a heterogeneous system. Example: steel (Steel is a metal alloy whose major component is iron, with carbon content between 0.02% and 2.14% by mass) Phase In a heterogeneous material, its constituents, which are in themselves homogeneous, are defined as phases. Question: Is there any phase existing in a homogeneous system? Answer: No In materials, the crystal structure, composition and volume fraction of each vary in such a way that the free enthalpy of the system in equilibrium is a minimum. The free enthalpy of materials under the thermodynamic equilibrium
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Lecture note 7 (09-27-2011) - MAE 581 Advanced Materials...

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