| Phase Boundary Migration in DCB. (cont.) |
Click image to enlarge (~1MB) |
| 52. Forty minutes after the last picture, with the temperature still in the alpha stability field. Further growth of alpha, at the expense of both the pink and dark brown porphyroblasts. See how the phase boundary around (44,23) bears two (brown) fingers or narrow embayments that point opposite to the probable direction of phase boundary migration. Such embayments may form where a migrating phase boundary is "hung-up" or "pinned" on a hole or particle. They may be a useful criterion for the direction of phase boundary migration.See the green twins that have formed in two orientations at (95,5) in the pink grain? Do these reflect the deformation imposed by the motor or some local straining imposed by the phase-change? (ans) |
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| 53. This is the same picture as the previous one but with the center of the field of view shifted a bit. |
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| 54. The
temperature is still around 26°C and an hour and twenty minutes
have elapsed since the last photo. A small amount of dextral bulk
shearing can now be inferred from relative displacement of holes (for
example, the ones at (80,4) and (80,43) in this picture). There has
been further growth of alpha grains at the expense of beta grains. The
pink beta grain is now entirely gone. On the left side of the screen
several pink alpha grains have replaced part of the dark brown beta
grain. There is also a blue alpha grain just coming into the field of
view. Notice the further twinning that has occurred locally in the left-hand part of the old green beta grain. But notice too the UNTWINNING that has occurred in the right-hand part of the same grain. |
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| 55. Further growth of alpha. The main areas of the unstable phase remaining are the dark brown grain at (36,36) and the green grain at (45,10). See how the sublimation pits in this latter grain have grown. Some of them are now holes that completely perforate the grain. |
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