Common Lattice Types Summary

Hexagonal Close-Packed

GRAIN STRUCTURE AND BOUNDARY

Material Science Volume 1 of 2
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COMMON LATTICE TYPES DOE-HDBK-1017/1-93 Structure of Metals Metals such as a-iron (Fe) (ferrite), chromium (Cr), vanadium (V), molybdenum (Mo), and tungsten (W) possess BCC structures. These BCC metals have two properties in common, high strength and low ductility (which permits permanent deformation). FCC metals such as g-iron (Fe) (austenite), aluminum (Al), copper (Cu), lead (Pb), silver (Ag), gold (Au), nickel (Ni), platinum (Pt), and thorium (Th) are, in general, of lower strength and higher ductility than BCC metals. HCP structures are found in beryllium (Be), magnesium (Mg), zinc (Zn), cadmium (Cd), cobalt (Co), thallium (Tl), and zirconium (Zr). The important information in this chapter is summarized below. A crystal structure consists of atoms arranged in a pattern that repeats periodically in a three-dimensional geometric lattice. Body-centered cubic structure is an arrangement of atoms in which the unit cell consists of eight atoms at the corners of a cube and one atom at the body center of the cube. Face-centered cubic structure is an arrangement of atoms in which the unit cell consists of eight atoms at the corners of a cube and one atom at the center of each of the six faces of the cube. Hexagonal close-packed structure is an arrangement of atoms in which the unit cell consists of three layers of atoms. The top and bottom layers contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The middle layer contains three atoms nestled between the atoms of the top and bottom layers. Metals containing BCC structures include ferrite, chromium, vanadium, molybdenum, and tungsten. These metals possess high strength and low ductility. Metals containing FCC structures include austenite, aluminum, copper, lead, silver, gold, nickel, platinum, and thorium. These metals possess low strength and high ductility. Metals containing HCP structures include beryllium, magnesium, zinc, cadmium, cobalt, thallium, and zirconium. HCP metals are not as ductile as FCC metals. MS-01 Page 8 Rev. 0

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