1Ionic Metallic Covalent Electrons: Lost Free SharedElements: Positive+negativeMetallic small diff. in electronegativityPrimary bonds & secondary bonds Primary bondsChapter 3ME 201: Materials Science, Z. Hao1Orientation: NondirectionalNondirectionalDirectionalSecondary bondingBonding force is much weaker than primary bondsFluctuating dipole bondsPermanent dipole bonds Lectures are available at: Blackboard.odu.edu Æuse your midas account to log in3.1Three metallic crystal structures: BCC, FCC, HCPChapter 3 Crystal Structures & Crystal GeometriesChapter 3ME 201: Materials Science, Z. Hao23.2Cubic Unit Cells¾Atomic position, direction indices, and miller indices ¾Volume, planar atomic, and linear atomic density 3.3Polymorphism and amorphous materialsA few DefinitionsAtoms, arranged in repetitive 3-Dimensional pattern, in long range order (LRO) give rise to a crystal solid or crystalline material.Examples: metals, alloys, and certain ceramic materials (diamond)Properties of solids depends on crystal structure and bonding forceAn imaginary network of lines, with atoms at intersection of lines,representing the arrangement of atoms is called space lattice.Chapter 3ME 201: Materials Science, Z. HaoUnit cell:the block of atoms which repeats itself to form space lattice.Unit CellSpace LatticeLattice constants a, b, cα,β, γTypes of basic unit cellsTetragonal¾a =b ≠c¾α= β= γ= 900Rhombohedral¾a =b = cMonoclinic¾a ≠b ≠c¾α= β= γ= 900Triclinic¾a≠b≠cSeven different types of basic unit cellsare necessary to create all space lattices. Table 3.1 on Page 75Chapter 3ME 201: Materials Science, Z. HaoCubic Unit Cell¾a = b = c¾α= β= γ= 900¾α= β= γ≠900Orthorhombic¾a ≠b ≠c¾α= β= γ= 900a b ¾α= β= γ= 900Hexagonal¾a = b ≠c¾α= β= γ= 900Variations in basic unit cellsVariations of basic unit cells Æmore atoms added in some way¾Simple ¾Body Centered¾Face Centered¾Base CenteredExample: Orthorhombic unit cellsChapter 3ME 201: Materials Science, Z. HaoSimpleBase CenteredFace CenteredFourteen standard unit cells:describe all possible lattice networks Figure 3.2 on Page 76Body CenteredThree principal unit cellsCubic Unit Cell¾a = b = c¾α= β= γ= 900Body Centered Cubic (BCC)Simple CubicChapter 3ME 201: Materials Science, Z. Hao6Hexagonal¾a ≠b ≠c¾α= β= γ= 900Simple hexagonalFace Centered Cubic (FCC)Hexagonal Close Packed (HCP)
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