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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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CIVE 2700 – Civil Engineering Materials, Winter 2007 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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