The following data were obtained for creep of a polycrystalline oxide having a grain size of 10 m. Stress (MPa) 10 20 30 40 50 60 70 80 90 100 at T = 1700 K 2.0 10-8 4.0 10-8 6.0 10-8 8.0 10-8 2.3 10-7 5.0 x 10-7 9.9 10-7 1.8 x 10-6 3.1 x 10-6 4.9 10-6 Strain rate () at T = 1810 K 7.0 10-8 1.4 x 10-7 2.1 x 10-7 2.8 x 10-7 8.0 10-7 1.8 x 10-6 3.5 x 10-6 6.3 x 10-6 1.1 x 10-5 1.7 x 10-5 at T=1940 K 4.2 x 10-7 8.4 x 10-7 1.3 x 10-6 1.7 x 10-6 4.8 x 10-6 1.1 x 10-5 2.1 x 10-5 3.8 x 10-5 6.5 x 10-5 1.0 10-4 a Plot (logarithmic coordinates) creep rate vs. stress for the three temperatures. Iden- tify on your plot the stress regions that correspond to diffusional creep and those that correspond to power-law creep. b Does the diffusional creep region correspond to Nabarro-Herring creep or to Coble creep? (Hint: Recall that the activation energies for NH creep and power-law creep are the same, and greater than that for Coble creep.) e On the graph you developed for part (a), plot creep rate vs. stress at 1700 K for this material if the grain size were increased to 20 m.