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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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