Dislocation Structures in Low-Angle Grain Boundaries of α-Al2O3

Abstract

Alumina (α-Al 2 O 3) is one of the representative high-temperature structural materials. Dislocations in alumina play an important role in its plastic deformation, and they have attracted much attention for many years. However, little is known about their core atomic structures, with a few exceptions, because of lack of experimental observations at the atomic level. Low-angle grain boundaries are known to consist of an array of dislocations, and they are useful to compose dislocation structures. So far, we have systematically fabricated several types of alumina bicrystals with a low-angle grain boundary and characterized the dislocation structures by transmission electron microscopy (TEM). Here, we review the dislocation structures in 1120 /[0001], 1120 / 1100 , 1100 / 1120 , (0001)/ 1100 , 1104 / 1120 , and (0001)/[0001] low-angle grain boundaries of alumina. Our observations revealed the core atomic structures of b = 1/3 1120 edge and screw dislocations, 1100 edge dislocation, and 1/3 1101 edge and mixed dislocations. Moreover, the stacking faults on 1120 , 1100 , and (0001) planes formed due to the dissociation reaction of the dislocations are discussed, focusing on their atomic structure and formation energy.

Evaluation of Mechanical Properties and Microstructures of Direct‐Quenched and Direct‐Quenched and Tempered Microalloyed Ultrahigh‐Strength Steels

“…For 0.5Mo and Mo–Nb steels, there was no such decrease and the low‐angle boundaries can be assumed to be composed of an array of dislocations. [ 20,21 ] In our study, EBSD data further verified that microalloying with Mo and Mo–Nb hindered the annihilation and movement of dislocations during the tempering process. As mentioned previously, the strongest pinning effect of dislocations was achieved with the combined alloying of Nb and Mo.…”

A Review of Grain Boundary and Heterointerface Characterization in Polycrystalline Oxides by (Scanning) Transmission Electron Microscopy

“…Polycrystalline materials comprise grains in a wide range of crystallographic orientations and therefore characters. Researchers have synthesized and studied bicrystals to manually change the GB character and study its influence on properties [36,53,54]. We will discuss experimental examples of bicrystals in the following sections.…”

“…Bicrystals are composed of two specific single crystals with controllable interfacial structure. Because many single crystals are and have been commercially available, bicrystals are crucial tools for research on interfaces and have been extensively explored in undoped/doped single phase polycrystalline systems [6,7,54,[57][58][59][60][61][62][63][64][65][66][67][68][69]. They are often used to analyze individual interfaces at atomic scale, such as CSL boundaries and their relation to properties [6,33].…”

“…Nanomilling is an effective tool for final thinning and cleaning of TEM specimens following other preparations by low voltage Ga + FIB milling or mechanical polishing. Nanomilling uses a focused Ar beam to polish both sides of the TEM specimen [54,133]. The spot size of an Ar beam is as small as 1 µm-smaller than the size of TEM lamella-so there will be no milling or redeposition of the specimen grid material (e.g., copper or molybdenum) if correct milling procedures are used [134].…”

Crystal Dislocations: Their Impact on Physical Properties of Crystals

“…One way of producing such dislocations is to fuse crystals with surfaces having controlled crystallographic planes to make low-angle grain boundaries for subsequent characterization. Tochigi et al [11] reviewed the dislocation structures in α − Al 2 O 3 , obtained using systematically fabricated alumina bi-crystals with low-angle grain boundaries and characterized using transmission electron microscopy (TEM). Wang et al [12] examined the interface effects on screw dislocations in Al/TiC hetero-structures, which was used as a model interface to study the unstable stacking fault energies and dislocation properties of interfaces.…”