ENGR2000_imperfections - Introduction to Engineering...

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Introduction to Engineering Materials ENGR2000 Chapter 4: Imperfections in Solids Dr. Priya Thamburaj Goeser
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The structure of a material - arrangement of its internal components Subatomic structure Atomic structure Microscopic structure Large groups of atoms aggregated together Macroscopic structure Elements that may be viewed with the naked eye
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4.1 Introduction Imperfections or defects in crystal structures ‘mistakes’ in atomic arrangement single atoms (point defects) rows of atoms (linear defects) planes of atoms (planar defects) 3D clusters of atoms (volume defects)
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Point Defects 4.2 Vacancies and Self-Interstitials Vacancy Vacant lattice site (one which is normall y occupied) Self-interstitial Atom that is crowded into an interstitial site (one which is normally not occupied)
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4.2 Vacancies and Self-Interstitials Self-interstitials in metals Atom is significantly larger than the interstitial site Introduces relatively large distortions Exists in small concentrations
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4.2 Vacancies and Self-Interstitials constant. s Boltzmann' the is and Kelvin in re temperatu the is formation, y for vacanc energy activation the is sites, atomic of # total the is where exp : m equilibriu at vacancies of Number k T Q N kT Q N N N v v v v =
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Example 4.1 Calculate the equilibrium number of vacancies per cubic meter for Cu at 1000 C. The energy for vacancy formation is 0.9 eV/atom; the atomic weight and density for Cu are 63.5 g/mol and 8.4 g/cm 3 , respectively.
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Example 4.1 3 25 3 3 28 3 3 / 10 2 . 2 exp : m per vacancies of # / 10 0 . 8 : m per sites atomic of # / 4 . 8 / 5 . 63 / 9 . 0 1273 : Given m vacancies kT Q N N m atoms A N N cm g mol g A atom eV Q K T v v Cu A Cu v × = = × = = = = = = ρ
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4.3 Impurities in Solids Alloys Impurity atoms added intentionally to impart specific characteristics to the material Solid solutions Solute or impurities Solvent or host material
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Solid Solutions Solid solutions are formed when… Solute atoms are added to the solvent Crystal structure is maintained No new structures are formed
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Substitutional solid solutions Solute or impurity atoms substitute for the solvent or host atoms.
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ENGR2000_imperfections - Introduction to Engineering...

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