Briefly answer the following questions. (a) Name two diffusion mechanisms in metal alloys, and answer which one occurs more rapidly. (b) To "case harden" the steel gear, carbon atoms diffuse into the surface layer of steel. What is the diffusion mechanism for carbon in steel (mostly iron)? (c) An edge dislocation could be imagined as being created by inserting an extra half- plane of atoms into an otherwise perfect crystal. Is edge dislocation a zero-, one-, two-, or three-dimensional defect? (d) Vacancies and self-interstitials exist in metals as point defects. Which of them, vacancies or self-interstitials, exist at a higher equilibrium concentration? (e) For a tension test illustrated in the figure, what is the strain? Among the following physical quantities: volume, area, length, pressure, mass, force, mathematical constant 7, energy, and acceleration, which one has the same unit of strain? Ap