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 ½10 " 10 tilt GB in a Zn bicrystal has been studied in situ. Above T Rþ ¼ 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 Rþ , a single first-order facet-to-rough GB ridge has been observed. Below T RÀ ¼ 668 K, a facet appeared and intersected with rounded (rough) GB portions with a slope discontinuity. Below T RÀ , 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 heating, T Rþ , and on cooling, T RÀ , was observed. The facet reaches its steady-state length not immediately after a change of sample temperature but with a specific retardation.

Review: grain boundary faceting–roughening phenomena

“…Two intersecting facets lie in the closely packed planes of the CCSL with coincidence parameter R = 15. In the asgrown sample, flat grain boundary facets formed the sharp first-order ridge with the break of the first derivative qy/ qx of the grain boundary shape similar to those observed previously for GB faceting in Zn [109,113,114]. However, above 350°C, the sharp first-order ridge is substituted by the smooth GB portion (Fig.…”

“…It has been observed in Zn how two first-order facet-to-rough ridges separated by a GB facet merge together with the increasing temperature and form a first-order rough-to-rough GB ridge (Fig. 12) [113,114]. This phenomenon was observed in tilt 10 10 ½ GB with h = 30°.…”

“…The tangents to the rough GB portions in the ridge point remain parallel to the to closely packed CCSL planes (Fig. 12c, d) [113,114]. The transformation of the facet into the first-order rough-to-rough GB ridge proceeds at T R?…”

Interface Faceting-Defaceting Mediated by Disconnections

“…2b, for which the capillarity driving force is constant, leading to steady-state GB migration. This has been exploited in a wide range of experimental [10,38,39] and atomistic simulation [40] studies [36]. We exploit this geometry to observe the influence of elastic interactions on interface faceting-defaceting transitions and migration.…”

“…Figure 6 shows the evolution of a half-loop grain boundary in a hexagonal close-packed Zn bicrystal that undergoes a faceting-defaceting transition with temperature. The CSL of the [10 10] tilt misoriented crystals corresponds to 2-reference interfaces; the (0001) closepacked plane and the ∼ 76 • inclined from the (0001) plane [38]. Referring to Figs.…”