Subgrain boundary migration during creep of lif: I. Recombination of subgrain boundaries

Abstract

The multiple-etching method has been applied to observe the migration of subgrain boundaries during compressive creep of pure and 100 p.p.m. MgF₂-doped -oriented single crystals of LiF at 923 K and 2.0 MPa and at 773 K and 9.0 MPa. Groups of neighbouring subgrain boundaries migrate in the same direction. The average number of boundaries per group is 2.9 and > 3 in the steadystate and transient ranges of creep, respectively. Boundaries of opposite sign migrate towards each other at approximately constant speed, until they collide. The collision leads to recombination of the subgrain boundaries. In one case complete dissolution of the colliding boundaries was observed. The dynamic equilibrium of formation and recombination of boundaries keeps the subgrain structure equiaxed during steady-state creep.