Fukuji Inoko

Nucleation of recrystallized grains in multiple slipped structure without deformation band in aluminum single crystal

Abstract The characteristics of multiple slipped structure and the nucleation of recrystallized grains (RGs) have been investigated using pure aluminum single crystals with an initial tensile axis (TA) orientation of 〈111〉 deformed in tension. By a scanning electron microscope (SEM), very short and wavy slip traces without deformation bands (DBs) were observed, in which the maximum misorientation was only approximately 5°. By a transmission electron microscope (TEM), it is found that a layered dislocation microstructure consisted of cells with dense dislocation walls (DDWs) was developed. Groups of the cells were mutually rotated, by approximately 4°, about an axis normal to the TA as if they maintained tensile strain and compressive strain by turns. After annealing, orientations of RGs were mainly rotated at angles of over 26° about each 〈111〉 axis normal to four kinds of {111} slip planes in each adjacent deformed matrix (DM). It is renewed in more detail that the nucleation of the RGs with the 〈111〉 rotation relationship to each adjacent DM could be explained by the 〈111〉 rotation recrystallization (nucleation) model. The 〈111〉 rotation relationships between the deformation textures and the corresponding annealing textures in FCC metals are selected in both stages of the nucleation of RGs as well as their growth.

Crystal orientations before and after annealing in an Al single crystal strained in tension

Abstract A single crystal of initial [ 10 1 ] tensile axis orientation was extended 70% in uniaxial tension. The deformed crystal exhibited a macroscopic deformation band structure consisting of deformed matrix bands (DM), domains in which slip occurred predominately on a single slip plane, and special bands of secondary slip (SBSS), which were subdivided into smaller domains in which slip was predominately on one or the other critically stressed slip planes. These slip patterns produce crystal orientations in the deformation structure that are rotated about ±[101] from the initial crystal orientation. After annealing, the SBSS are almost completely recrystallised and the DM are not recrystallised. The recrystallised grains in SBSS have crystal orientations that are rotated in a positive sense about [101] from the initial crystal orientation. The orientations of recrystallised grains in SBSS are near the periphery of the range of orientations found in the deformation microstructure prior to annealing. The orientation and morphology of recrystallised grains in SBSS are consistent with the hypothesis that domains rotated in a positive sense about [101] from the initial crystal orientation have higher stored energy density than domains rotated in a positive sense about −[101]. Recrystallised grains with new orientations were also detected, these have a twin relationship to crystal orientations present in the deformation microstructure; the critically stressed slip planes being twin planes.

Deformation band evolution in [110] Al single crystals strained in tension

Several types of deformation bands form during uniaxial extension of Al single crystals for which the tensile axis is initially parallel to [110]. The objectives of the present work are to analyse crystal orientation evolution in the deformation bands and adjoining regions, and to integrate the experimental observations with a crystal mechanics model. The most prominent deformation bands contain secondary slip traces and exhibit crystal rotations consistent with unpredicted slip on a secondary slip system. These special bands of secondary slip (SBSS) become more closely aligned with the tensile axis as extension increases. The evolution of SBSS inclination with extension indicates that SBSS form initially as kink bands and that SBSS boundaries are immobile. SBSS grow during straining by expansion of the volume of material in which secondary slip operates. Deformed matrix (DM) bands are zones between SBSS; primary slip predominates in DM bands. Small intra-DM bands result from spatial variation of the shear amplitudes for the two primary slip systems. The evolution of intra-DM band inclination with extension indicates that intra-DM bands form initially as kink bands and that the band boundaries are mobile, at least to some extent.

Grain boundary premelting in thin foils of deformed copper bicrystals

Abstract The grain boundary premelting temperature (GBPMT) T m in thin foils of 99.99 mass% copper bicrystals deformed in tension to a strain of 0.4 increased from approximately 0.5 T M up to near the bulk melting point T M with increasing oxidation time. The GBPMT T m in thin foils of the bicrystal whose grain boundary plane was parallel to active screw dislocations was lower than that to active edge dislocations. The difference between the GBPMT in 99.99 and 99.9999 mass% copper polycrystals were not so significant. The difference between the GBPMT T m (Al)[ ≑ T M (Al)] of aluminum bicrystals and the T m (Cu)[ ≑ 0.5T M (Cu)] of copper bicrystals depends upon the difference between the properties of the corresponding oxide films and would probably be related to the difference in the elastic anisotropy between them. Plastic strain would decrease the GBPMT at least in copper.

Crystallographic defects under surface morphological defects of 4H-SiC homoepitaxial films

Transmission electron microscopy (TEM) was applied to characterize the crystallographic defects associated with “device-killing” surface morphological defects of 4H-SiC homoepitaxial films. Typical surface defects exhibit elongated shape along the off-cut direction [11-20] and are classified into “comet”, “triangular defect” and “carrot” according to their morphological features. The “comet” is accompanied by 3C-SiC of zinc blende structure. The “triangular defect” and “carrot” are associated with stacking faults on the (0001) plane. From observations of the samples in which their homoepitaxial films had been partially or completely removed prior to the TEM sample preparation, it was suggested that the defects were not directly inherited from the substrate.

Morphology of [011]-tilt Σ3 boundaries in pure copper and copper-aluminum alloy tricrystals

Abstract Tricrystals of pure Cu, Cu-3at.%Al and Cu-9at.%Al having [011]-tilt Σs=3, 3 and 9 CSL boundaries were grown and the morphology of the grain boundaries was investigated. In pure Cu and Cu-3at.%Al tricrystals, the Σ3 boundaries were composed of flat planar surfaces of the {111} coherent plane and short incoherent segments. Frequently observed incoherent steps are {322} and {311}. As the aluminum content of the alloy was increased to 9at.%, the morphology of the Σ3 boundaries changed drastically. The average step height became larger and the ratio of the incoherent segments in the total length of the Σ3 boundary increased to about 40%. To explain these experimental results, a simple model is proposed which attributes the step formation to the nucleation and subsequent sidewise growth of microscopic twins close to the Σ3 boundary during the solidification process.

Strain Induced Grain Boundary Premelting along Twin Boundaries in Copper Polycrystals

A polycrystalline copper sample was compressed at room temperature, then the temperature was raised to 873 K in a vacuum and annealed without unloading. Grain boundary cracks were found at Σ 3 coherent twin boundaries. The formation of these cracks can be interpreted based on the idea of strain induced grain boundary premelting (SIGBPM). It is emphasized that Σ 3 twin boundaries can be one of the most dangerous boundaries for crack formation when certain experimental conditions are satisfied.

Some crystal boundary phenomena in aluminum bicrystals

Abstract The authors have found that in the melt growth of aluminum bicrystals under certain conditions, the crystal boundary rotates about the direction of heat flow during progressive solidification, even though the crystal boundary area increases. This crystal boundary phenomenon may not be analogous to that found by Chalmers in tin and lead. It is suggested that the former occurs in the bicrystals the boundaries of which have twist components, and in which a cellular substructure grows appreciably so that there will be a variation in the thermal conductivity for different directions. In the high purity aluminum bicrystals this boundary phenomenon does not occur.

Transmission Electron Microscopy of Sublimation-Grown GaN Single Crystal and GaN Homoepitaxial Film

A GaN film with nominal thickness of 0.6 µ m was homoepitaxially deposited on a sublimation-grown GaN single-crystal substrate. An electron-transparent area of 10 µ m×10 µ m prepared by focused Ga ion beam machining was examined by transmission electron microscopy. In addition to the dislocations on the basal plane of the wurtzite unit cell, another type of dislocation, near pure edge in character and aligned close to the c-axis direction, was found in the GaN substrate crystal. Neither type of dislocation threaded to the top surface. Dislocation-free growth was achieved in the GaN homoepitaxial film.

Effect of Surface on Recrystallization

It is shown using aluminum single crystals with kink bands like a plate through the depth that the nucleation and growth of recrystallized grains (RGs) on/in the surface precede those in the interior.