Reversible transformation of a grain-boundary facet into a rough-to-rough ridge in zinc

Abstract

The transition of two first-order facet-to-rough ridges into a single first-order rough-to-rough ridge theoretically predicted for free surfaces has been observed in a slowly migrating grain boundary (GB). The reversible faceting-roughening transition of the tilt GB in a Zn bicrystal has been studied in situ. Above T R+ = 673 K, the slowly migrating GB semi-circle was discontinuously curved, e.g. two rounded (rough) GB portions intersected with a slope discontinuity. Above T R+, a single first-order facet-to-rough GB ridge has been observed. Below T R− = 668 K, a facet appeared and intersected with rounded (rough) GB portions with a slope discontinuity. Below T R−, two first-order facet-to-rough GB ridges existed. The GB facet and tangents to the rounded (rough) GB portions were parallel to the closely packed planes of the constrained coincidence sites lattice. The steady state length of the facet increased with decreasing temperature. A hysteresis of about 5 K between roughening temperatures measured on ...