MSE 2034 Lecture 4: Chapter 3 - Part 2
22 Feb 2017
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Went over : sc, bcc, fcc, hcp, n, a, cn, apf, rho, ld, pd. Ld of [100] in bcc = (# of radii)/(length) = 2r/a = 1 atom/a for wiley plus. Diffraction gratings must have spacing comparable to the wavelength of diffracted radiation. Spacing is the distance between parallel planed of atoms. Transition from lattice of one region to that of the other. Low density in grain boundaries: high mobility, high diffusivity chemical reactivity. Grains can be: equiaxed (roughly same size is all directions, columnar (elongated grains) Grain refiner - added to make smaller, more uniform, equiaxed. Many of the properties of material (particular metals and mechanical properties) are due to imperfections. Vacancies: vacant atomic sites in a structure. Self-interstitials: extra atoms positioned between atomic sites. Equilibrium concentrations varies with temperature: with heat there will be more vacancy, with cold there will be more interstitials. When atom leaves the crystal structure it goes to the surface of sample.
