Faceting of migrating 〈110〉 coincidence boundaries in aluminium bicrystals

2004

Polycrystalline alumina specimens with and without MgO doping show smoothly curved grain boundaries after heat treatment at 1400°C indicating their rough structure. When heat‐treated at 1400° and 1500°C for 24 h after packing in an alumina–YAG powder mixture, many grain boundaries (without any liquid phase) develop kinks of large and small scales as observed by scanning electron microscopy and transmission electron microscopy. The addition of Y2O3 at concentrations close to the solubility limit is thus shown to induce the grain boundary transition to singular structures.

Section: Resultsmentioning

confidence: 83%

Section: Resultsmentioning

confidence: 89%

Kinked Grain Boundaries in Alumina Doped with Y₂O₃

Kim

2004

“…Kinked grain boundaries were observed also in metallic bicrystals. 6,7,9,10,12,13,18,19 These observations thus show that at least some of the grain boundaries in alumina undergo reversible roughening-singular transition at temperatures below about 1100°C. It is possible that most of the grain boundaries still do not show the singular transition because of slow kinetics.…”

Section: March 2004mentioning

confidence: 68%

“…G RAIN boundaries of hill-and-valley (h&v) shapes with alternating parallel segments or kinked shapes (as observed at cross sections) with flat or curved segments intersecting at joints have been observed in many metals (Au, [1][2][3] Ni, 4,5 Al, 2,6,7 Ag, 8 -10 Cu, 11 Zn, 12,13 316L stainless steel, 14,15 a Ni-base superalloy, 16 Si-Fe, [17][18][19] Cu-Bi, 20 -22 and Fe-Te 23,24 ) and some oxides (MgO, 25 MgO⅐2Al 2 O 3 , 26 NiO, 27 Al 2 O 3 , 28 -34 and BaTiO 3 35-39 ) with both special and general misorientation angles between the grains. Some flat segments of the h&v boundaries were parallel to low-index planes of one or both of the grain pairs 1,3,28,32,34 -39 and likely to be singular corresponding to cusps in the polar plot of the boundary energy ␥ against the normal direction.…”

Section: Introductionmentioning

confidence: 99%

Facet–Defacet Transition of Grain Boundaries in Alumina

Kim

2004

Grain boundaries in pure alumina powder compacts sintered at 1400°C are smoothly curved, indicating that they have atomically rough structures. When these specimens are heat‐treated at temperatures between 900° and 1100°C, a small fraction of the grain boundaries develop either hill‐and‐valley or kinked shapes with flat segments. Some of these flat boundary segments lie on the {011[Twomacr]} plane of one of the grain pairs. These grain boundaries thus appear to become singular at these temperatures. When a corundum crystal with a basal surface is sintered in alumina powder at 1400°C, all grain boundaries formed between the corundum basal surface and small grains, as well as those between the small grains, are smoothly curved, indicating their rough structure. When heat‐treated at 900°C for 3 days, about 30% of the grain boundaries between the corundum basal surface and the small grains develop kinks with flat boundary segments, and some of these flat segments lie on the basal plane of the corundum. When heat‐treated again at 1400°C, all grain boundaries are curved, indicating that they become reversibly rough. These observations show that at least some of the grain boundaries in alumina undergo roughening‐singular transitions at temperatures between 900° and 1100°C.

“…F ACETED grain boundaries with hill-and-valley (h&v) shapes have been observed in many metal bicrystals (Au, [1][2][3][4][5] Ag, 6,7 Al, 2,8,9 Cu, 10,11 Cu-Bi, 12 Zn 13,14 ) with special misorientation angles corresponding to relatively high densities of coincidencesite-lattice (CSL) points (as indicated by low-inversity density, ⌺, of coincident lattice points). Such faceted grain boundaries indicate that the reciprocal polar plots (the ␥ Ϫ1 plots) of the grain boundary energy ␥ against the boundary inclination angle have concave segments, 15 and it is likely that some of the facet planes are singular corresponding to convex cusps in the ␥ Ϫ1 plots.…”

Section: Introductionmentioning

confidence: 99%

Faceting of High‐Angle Grain Boundaries in Titanium‐Excess BaTiO₃

2004

The grain boundaries in BaTiO3 with excess Ti of 0.5, 0.3, and 0.1 at.% sintered at 1300° or 1250°C have been examined by scanning electron microscopy (SEM), electron backscattered diffraction pattern (EBSP), and transmission electron microscopy (TEM). In the 0.1% Ti‐excess specimen, large grains growing abnormally form high‐angle grain boundaries when they impinge on each other as verified by EBSP. A large fraction of these grain boundaries are faceted with hill‐and‐valley shapes. In the 0.5% Ti‐excess specimen, large grains growing abnormally are elongated in the directions of their {111} double twins. These grains often form flat grain boundaries parallel to their {111} planes with the fine matrix grains, and the grain‐boundary segments between the large impinging grains with high misorientation angles are often also parallel to the {111} planes of one of the grains. These grain boundaries are expected to be singular. Most of the grain boundaries between the randomly oriented fine‐matrix grains in the 0.3 at.% Ti‐excess specimen are also faceted with hill‐and‐valley shapes at finer scales when observed under TEM. The facet planes are parallel to {111}, {011}, and {012} planes of one of the grain pairs and are also expected to be singular. These high‐angle grain boundaries lying on low index planes of one of the grain pairs are similar to those observed in other oxides and metals.