ME222_Lecture_6_7_Chandraprakash.pdf

ME222_Lecture_6_7_Chandraprakash.pdf - Nature and...

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Nature and Properties of Materials ME 222A Dr. Chandraprakash Mechanical Engineering IIT Kanpur Lecture 6 & 7: Imperfections in Solid
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Stainless Steel Alloy Pure Iron at room temperature and pressure BCC Remaining elements kind of defects Stainless steels can be FCC or BCC Properties different from Iron SS304: FCC
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Outer surface is subjected to heat treatment making the surface hard During heating carbon present in in atmosphere enters/diffuses into the crystal Carbon becomes an interstitial defect The surface becomes hardened Case Hardening Defects alter the properties of materials Flame-hardened Sprocket Courtesy: Wikipedia - lab/metallography-an-introduction/#fancybox-11172-10
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Tetrahedral Voids
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Octahedral Voids
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Octahedral Voids Homework: Identify all kinds of voids present in Simple cubic, FCC, BCC and HCP
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VOIDS Tetrahedral Octahedral Note: Atoms are coloured differently but are the same cell n tetrahedro V V 24 1 cell octahedron V V 6 1 Location of the void: ¼ way along body diagonal {¼, ¼, ¼}, {¾ , ¾ , ¾} + face centering translations Location of the void: At body centre {½, ½, ½} + face centering translations r void / r atom = 0.225 r Void / r atom = 0.414 Calculation shown later
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More views Tetrahedral Octahedral
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Classification of defects Any combination of the above
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Vacancy defect: Missing of atom Atoms around the vacancy displaced from their equilibrium positions Stress fields Stress field generated in the vicinity of the vacancy. Defects generated by quenching from a higher temperature bombardment with high energy particles plastic deformation off-stoichiometry in ordered compounds N v : Number of vacancies N : Number of atomic sites Q v : Energy required to create one vacancy k : Boltzmann constant T : Temperature
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