l8 - CIVE 2700 – Civil Engineering Materials Winter 2007...

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Unformatted text preview: CIVE 2700 – Civil Engineering Materials, Winter 2007 1 Crystal Defects Professor George Hadjisophocleous, Ph.D., P.Eng. Carleton University Department of Civil and Environmental Engineering Ottawa, Ontario CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.2 Outline • Crystal defects • Point defects • Linear defects • Planar and bulk defects • Crystal slip CIVE 2700 – Civil Engineering Materials, Winter 2007 2 CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.3 Objectives • Define point defects. • Define line defects. • Define planar defects. • Define edge, screw, and mixed dislocations. CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.4 Defects in Crystals • What is a defect? • An imperfection or "mistake" in the regular periodic arrangement of atoms in a crystal • Can involve an irregularity in – location of atoms – type of atoms • Type and number of defects depends on the material, its environment, and the conditions under which it is processed. CIVE 2700 – Civil Engineering Materials, Winter 2007 2 CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.3 Objectives • Define point defects. • Define line defects. • Define planar defects. • Define edge, screw, and mixed dislocations. CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.4 Defects in Crystals • What is a defect? • An imperfection or "mistake" in the regular periodic arrangement of atoms in a crystal • Can involve an irregularity in – location of atoms – type of atoms • Type and number of defects depends on the material, its environment, and the conditions under which it is processed. CIVE 2700 – Civil Engineering Materials, Winter 2007 3 CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.5 Types of Defects • Point defects : Irregularity in structure extending over only a few atoms in size • Linear defects : Irregularity extends across a single row of atoms (1-D) • Planar defects : Irregularity extends across a plane of atoms (2-D) • Volumetric defects : Irregularity extends over 3-D cluster of atoms CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.6 Why are Defects Important? • Defects, even in very small concentrations, can have a dramatic impact on the properties of a material. • Without defects: – solid-state electronic devices could not exist – metals would be much stronger – ceramics would be much tougher – crystals would have no color CIVE 2700 – Civil Engineering Materials, Winter 2007 4 CIVE 2700 – Civil Engineering Materials, Winter 2007, 8.7 Vacancies • Simplest point defect is a vacancy: An atom is missing from its position • For most metals the fraction of vacancies just below the melting temperature is in the order of 10-4 , meaning one lattice out of 10,000 will be empty....
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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l8 - CIVE 2700 – Civil Engineering Materials Winter 2007...

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