e95mtm - Engineering 45 The Structure and Properties of...

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Engineering 45 The Structure and Properties of Materials Midterm Examination November 1, 1995 Problem 1: (a) Almost all of the elements that crystallize in the hexagonal close-packed structure are metallic conductors. Why? (b) There are at least a couple of elements that crystallize in the hexagonal close- packed structure and are electrical insulators. How can this be? (c) The largest sphere that can be placed in a tetragonal void in a face-centered close-packed crystal of rigid, spherical atoms has radius r tet = 0.225 R where R is the radius of the spheres that make up the FCC lattice. What is the radius of the largest sphere that can be placed in a tetrahedral void in an HCP lattice of rigid spheres? Problem 2: (a) Carbon diffuses through BCC iron much more rapidly than nickel does. Why? (b) At low to moderate temperature, nickel diffuses through polycrystalline iron more rapidly than through single crystal iron. Why? (c) If an iron-nickel alloy is quenched from high temperature, the diffusivity of
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This note was uploaded on 04/05/2011 for the course ENGIN 45 taught by Professor Devine during the Spring '07 term at University of California, Berkeley.

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e95mtm - Engineering 45 The Structure and Properties of...

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