e4510lecture-4

e4510lecture-4 - The Essence of Materials Science The field...

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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 The field can be summarized in two sentences: Properties <= composition + microstructure Microstructure <= composition + processing Composition = kind and fraction of atoms present Microstructure = How those atoms are arranged Microstructure is not only essential to understanding properties It is often much more important than composition The Essence of Materials Science
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Microstructure Microstructure : Type and location of all atoms in solid All atom positions known in only two ideal cases Perfect order (“ crystals ” or “ quasi-crystals ”) Perfect disorder (“ amorphous solids ” or “ glasses ”) Almost all solids prefer the crystalline state But perfect crystals are not possible in nature Describe by basic crystal structure + “ crystal defects
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Atomic Resolution TEM Image: Two Crystals (Grains) of Al grain boundary -Eric Stach NCEM/LBNL
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Atomic Resolution TEM Image: Two Crystals Meet at an Interface NiSi Silicon -Eric Stach NCEM/LBNL
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Importance of Crystal Structure: Diamond vs. Graphite Carbon as diamond Each atom has four neighbors Covalent bonding in 3-D Electrical insulator Ultrahard material Carbon as graphite 3 neighbors in hexagonal plane Strong bond in-plane, weak bond between planes Electrical conductor (in-plane) Mechanically weak (lubricant) Strong if loaded in-plane (fiber)
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Crystal Structure Crystal lattice Periodic grid of positions in space (“ lattice points ”) Crystal structure Identical group of atoms placed at each lattice point Mathematical description : atom positions ( R i ) R i = h i a 1 + k i a 2 + t (h i , k i = integers, t = constant)
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This note was uploaded on 02/09/2010 for the course ENGIN 45 taught by Professor Devine during the Spring '07 term at Berkeley.

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e4510lecture-4 - The Essence of Materials Science The field...

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