l6 - CIVE 2700 Civil Engineering Materials, Winter 2007...

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CIVE 2700 – Civil Engineering Materials, Winter 2007 1 STRUCTURE OF METALS AND CERAMICS Professor George Hadjisophocleous, Ph.D., P.Eng. Carleton University Department of Civil and Environmental Engineering Ottawa, Ontario CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.2 Outline • Objectives • Crystal structures – Metals – Ceramics
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CIVE 2700 – Civil Engineering Materials, Winter 2007 2 CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.3 Objectives • Learn the different crystal structures of metals • Learn to calculate various properties of the different structures CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.4 Introduction • Properties of materials are directly related to their crystal structures. • For example, non-crystalline ceramics and polymers are optically transparent and the same materials in crystalline form tend to be opaque. • A crystalline material is one in which the atoms are situated in a repeating or periodic array over large atomic distances. – repeated 3-D pattern in which an atom is bonded to its nearest neighbouring atoms
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CIVE 2700 – Civil Engineering Materials, Winter 2007 3 CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.5 Introduction • When describing crystalline structures, atoms or ions are thought of as being solid spheres having well-defined diameters. - atomic hard sphere model • Lattice : a 3-D array of points coinciding with atom position • Unit cell : the repeating pattern of atoms (repeat entities). • Unit cells for most crystal structures are parallelepipes or prisms having three sets of parallel surfaces. CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.6 Unit Cell • Units cells are the smallest repeating units within a crystal structure. • The geometry of a unit cell is described in terms of six lattice or cell-parameters: Cell-lengths: a, b, c Cell-angles: ! , " , #
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4 CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.7 Introduction • Metallic crystal structure : atomic bond in this group of materials is metallic. • Three crystal structures are found for most common metals: – FCC – face centered cubic packing – BCC – body-centered cubic packing – HCP – hexagonal close-packing CIVE 2700 – Civil Engineering Materials, Winter 2007, 6.8 Face Centered Cubic Crystal Structure • Unit cell has cubic geometry with atoms located at each of the corners and the centers of all its cube faces. -
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l6 - CIVE 2700 Civil Engineering Materials, Winter 2007...

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