Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Diffusion induced grain boundary migration (DIGM) and liquid film migration (LFM) have been studied in an Al-2.07wt%Cu alloy by isothermal annealing after down and up quenching from an equilibrated state at 620°C in the α+L phase field. During "down quench" DIGM at 520, 540 and 560°C, the grain boundaries were observed to migrate against their curvature from one grain into another, leaving behind alloyed zones. During "down quench" LFM at 590 and 605°( and "up quench" LFM at 630 and 640°C, the liquid films were observed to migrate, leaving behind alloyed and dealloyed zones, respectively. The migration of grain boundaries was also observed during "down quench" LFM. The migration distances (s) for both DIGM and LFM were observed to have power law dependencies s = Ktn on time (t) with the values of n falling from 0.20 and 0.25. For a given annealing time the migration rates of liquid films by LFM were about twice as fast as those of grain boundaries by DIGM. Finally, the coherency strain energy of the coherency strain theory seems not adequate to drive the reactions. The thermodynamic free energy change according to the Fournelle theory available for both reactions is shown to be more than sufficient
to drive the migrations of boundaries and liquid films against their curvature.