Homework_3 - Introduction To Materials Science, Chapter 1,...

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Unformatted text preview: Introduction To Materials Science, Chapter 1, Introduction Composites Thin crystalline platelets grown fromCr,lut-on ,- Mo ihs voldhis crystal structure so !i Fe cha na f e t back and forth: chain-folded model Spring 2007 Engineering Material Polyethylene Polymer composite materials: reinforcing glass fibers in a polymer matrix. University of Virginia, Dept. of Materials Science and Engineering Homework #3 18 The a erag chain leng h is mu (for Wednesday, v23 eMarch, t2005)ch thickness of the crystallite greater than the University of Virginia, Dept. of Materials Science and Engiineeriing of Virgi24ia, Dept. of Materials Science and Engineering U n v e r s ty n 9 Reading Assignments Chapters 5 Diffusion 1. Below is shown a plot of the diffusion coefficient versus reciprocal of the absolute temperature, for the diffusion of gold in solver. Determine values for the activation energy and the pre-exponential coefficient Figure 1 2. At approximately what temperature would a specimen of iron have to be carburized for 8 hours to produce the same diffusion as when held for 16 hours at Spring 2007 Engineering Material a. 1000˚C b. 900˚C (Note iron transforms from a bcc (α) structure to a fcc (γ) structure on heating at 912˚C)] 3. A mild steel component (carbon content = 0.2%) is to be case hardened by placing it in a furnace at 1100˚C for 10 hours in an atmosphere rich in hydrocarbon gas so that the surface concentration is 0.9% carbon. At the completion of this process, what will be the carbon concentration 1 mm below the surface of the steel 4. Use your knowledge of diffusion to account for the following observations: a. Carbon diffuses fairly rapidly through iron at 100˚C, whereas chromium does not b. Diffusion is more rapid is polycrystalline solver with a small grain size than in coarse-grained solver ...
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