Chapter4c

Chapter4c - Chapter Outline Crystals are like people, it is...

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1 1 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals “Crystals are like people, it is the defects in them which tend to make them interesting!” - Colin Humphreys. Defects in Solids ¾ 0D, Point defects 9 vacancies 9 interstitials 9 impurities, weight and atomic composition ¾ 1D, Dislocations 9 edge 9 screw ¾ 2D, Grain boundaries 9 tilt 9 twist ¾ 3D, Bulk or Volume defects ¾ Atomic vibrations Optional reading (Parts that are not covered / not tested): 4.9 – 4.10 Microscopy 4.11 Grain size determination Chapter Outline 2 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals Why are defects important? Defects have a profound impact on the various properties of materials: Bonding + Crystal Structure + Defects Properties Production of advanced semiconductor devices require not only a rather perfect Si crystal as starting material, but also involve introduction of specific defects in small areas of the sample. Defects are responsible for color (& price) of a diamond crystal. Forging a metal tool introduces defects … and increases strength of the tool. 3 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals Composition Bonding Crystal Structure Thermomechanical Processing Microstructure Defects can be introduced/removed during processing defects introduction and manipulation Processing allows one to achieve the required properties without changes in composition of the material, but just by manipulating the crystal defects . Control (and intentional introduction) of defects is in the core of many types of material processing. 4 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals A 2D representation of a perfect single crystal with regular arrangement of atoms. But … structures of real materials can be better represented by the schematic drawing to the left. Schematic drawing of a poly-crystal with defects by Helmut Föll, University of Kiel, Germany. Defects in Crystals Real crystals are never perfect, there are always defects
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2 5 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals Types of Defects Defects may be classified into four categories depending on their dimension: ¾ 0D, Point defects : atoms missing or in irregular places in the lattice (lattice vacancies, substitutional and interstitial impurities, self-interstitials) ¾ 1D, Linear defects : groups of atoms in irregular positions (e.g. screw and edge dislocations) ¾ 2D, Planar defects : the interfaces between homogeneous regions of the material (e.g. grain boundaries, stacking faults, external surfaces) ¾ 3D, Volume defects : extended defects (pores, cracks) 6 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals How many vacancies are there? Vacancy = absence of an atom
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This note was uploaded on 12/07/2011 for the course MSE 2090 taught by Professor Leoindzhiglei during the Fall '10 term at UVA.

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Chapter4c - Chapter Outline Crystals are like people, it is...

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