tailieunhanh - Material Science_ Vol 1 of 2 - US DOE (1993) WW Part 4

Tham khảo tài liệu 'material science_ vol 1 of 2 - us doe (1993) ww part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Structure of Metals COMMON LATTICE TYPES DOE-HDBK-1017 1-93 Face-centered Cubic In a face-centered cubic FCC arrangement of atoms the unit cell consists of eight atoms at the corners of a cube and one atom at the center of each of the faces of the cube. Hexagonal Close-packed In a hexagonal close-packed HCP arrangement of atoms 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 hence the name close-packed. Most diagrams of the structural cells for the BCC and FCC forms of iron are drawn as though they are of the same size as shown in Figure 2 but they are not. In the B C C arrangement the structural cell which uses only nine atoms is much smaller. BODY-CENTERED CUBIC FACE-CENTERED CUBIC HEXAGONAL CLOSE PACKED Figure 2 Common Lattice Types Rev. 0 Page 7 MS-01 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 Y-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 . Summary The important information in this chapter is summarized below. Common Lattice Types Summary 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 .

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