Kazuhiko Yoshida

The Thickness Dependence of Plastic Behaviors of Copper Whiskers

Stress-strain curves of 150 copper whiskers, whose thickness ranges from 4 to 30µ and growth orientations are parallel to the three principal crystallographic orientations, have been investigated by an Instron-type tensile machine at room temperature. Thinner whiskers have shown characteristic sharp yield points. The upper yield stress of some thinner whiskers reaches nearly the theoretical strength of an ideal perfect crystal, but it decreases as the thickness increases. In the subsequent “easy glide” region, corresponding to the propagation of one or a few Luders bands, pronounced serrations appear, and both of flow stress and Luders strain vary approximately in inverse proportion to the thickness. The hardening rate in the most rapid hardening stage of the stress-strain curve increases with increasing thickness. In whiskers, thicker, than about 20µ, the sharp yield point and serrated “easy glide” region are scarcely observable, and their Stress-strain curves are similar to those of bulk crystals.

Cubic Crystals in Ti Films Evaporated on NaCl Substrates

The growth and structure of Ti films evaporated on NaCl substrates have been studied by electron microscopy. The film showed cubic or fcc-like diffraction spots of three types in the early growth stage, depending on the preparation method and temperature of the substrate and film thickness. The lattice parameters corresponding to those spots taken from 2 nm-thick films formed on the substrate at 260°C were a=0.441 nm, 0.418 nm and 0.426 nm, which were determined to be those of CaF2-type TiH1.5, NaCl-type TiO1.0 and some titanium compound, respectively. The former two grew on the substrate cleaved in vacuum while the last one grew on that cleaved in air, only. When the film was thicker than 3 nm, hcp diffraction spots also appeared. The formation mechanism of the cubic and hcp crystallites is discussed.

Electron microscope study of the Ti4O7 phase in an annealed titanium oxide evaporated film

Abstract Interpretable images of the structure of Ti4O7 have been obtained with a high-voltage electron microscope at a resolution of approximately 4·5 A. The Ti4O7 phase including defects was observed to grow quickly in an evaporated film made from TiO17middot;0 during in situ annealing and oxidation in the electron microscope. The basis for interpretation of the images is first investigated using a computer-simulation technique. Then, it is possible to analyse three different types of defect which occur within the Ti4O7 phase, i.e. coherent twin boundaries having (104) composition planes, coherent intergrowth of Ti n O2n−1 (n = 5, 6) parallel to the (002) plane of Ti4O7 and a new, possibly metastable, type of Ti5O9 structure which forms coherent boundaries parallel to the (102) plane of Ti4O7.

Transmission electron-microscopic study on the growth of copper whiskers by halide reduction

Abstract Transmission electron-microscopic observations have been made, using 100, 500 and 1000 kV electron microscopes, on many thin copper whiskers grown directly on small Cu meshes-as used commonly for electron-microscopic observations — which were obtained by the reduction of CuI melt with a H 2 atmosphere. Various observational facts are reported, but dislocations which might play an important roˆle in the growth process involving the screw-dislocation mechanism have not been detected. Further, the experimental results give no conclusive evidence supporting any other available growth mechanisms. Thus, it is concluded that systematic transmission electron-microscopic or any other “atomic-scale” observations of “growing” whiskers are necessary to make clear the mechanism and kinetics of the reduction growth of metal crystals. It may be that metal whiskers grow from their roots and bases in the hydrogen reduction of their halides of solid and melt states, respectively.

Mechanism of oxidation of the crystallographic shear phase Ti4O7

Abstract High-resolution electron microscope images of Ti4O7 show lamellae of Ti5O9 and Ti6O11 attached to (104) twin boundaries and (102) lamellae of a new (metastable) Ti5O9 phase. Structural models for the coherent accommodation of oxidation lamellae in Ti4O7 and their coherent intersections with both the twin boundaries and the (102) lamellae are readily deduced from the images. Consideration of the atomic diffusion mechanisms responsible for the observed mobility of all three types of defects offers an explanation for the hysteresis and other non-equilibrium phenomena observed in thermogravimetric studies of reduced rutiles.

Growth and Structure of Titanium Oxide Thin Films. II.

Films formed by evaporating TiO1.0 and TiO1.25 onto NaCl cleavage surfaces held at about 470°C in a vacuum of about 10-8 Torr have been studied by electron microscopy. The compositions of the films measured by Auger electron spectroscopy were TiO0.5 and TiO0.74 when TiO1.0 and TiO1.25 were evaporated.The film made from TiO1.25 consists mainly of fcc epitaxial crystallites of (001)- and (110)-orientation having square and rectangular shapes respectively. In the film made from TiO1.0, fcc epitaxial crystallites of the same orientations as above appear in the early growth stage and then fcc crystallites which have Ti2O structure begin to grow on the {111}planes of the fcc crystallites, with the increase of the film thickness. In both films made from TiO1.0 and TiO1.25, however, little evidence for the presence of twinned fcc crystallites grown on the {111} planes of the crystallites of (001)-orientation has been found.

Thickness and Orientation Dependence of Plastic Behaviors of Iron Whiskers

Stress-strain curves of iron whiskers, of which thickness ranges from 5 to 80 µ, have been measured using an Instron-type tensile machine at room temperature. All of the whiskers show “work-softening”, of which softening rate decreases with increasing thickness. “The lower yield stress” decrease with increasing thickness in and whiskers thinner than about 35 µ. Marked thickness and orientation dependence of the stress-strain curve have been found. The whiskers thinner than about 8 µ show no appreciable plastic deformation after the sharp yielding, as already known in very thin whiskers. Those, 8∼17 µ in thickness, show nearly flat regions in their stress-strain curves after yielding and those thicker than about 17 µ reveal “work-hardening” after about 5% strain.

Electron Microscopic Study of the δ-Phase in Titanium Oxide Evaporated Films

The phase transformation of evaporated films of TiO0.5 into transition structure I has been demonstrated by in situ heating using an electron microscope. Single crystals of the δ-phase precipitate in the film during the transformation. Anderssons hexagonal model of the crystal structure of the δ-phase is verified by analysing diffraction patterns taken from these single crystals. The lattice parameters measured are ad=5.022 A and cd=2.869 A. The structural relationships among the α-phase, the δ-phase and transition structure I are examined.

Stress-Strain Curves and Slip Bands of KCl Whiskers

Tensile tests were made, at room temperature, on KCl whiskers grown on outer surfaces of thin cellophane bags containing saturated aqueous solution. It was found that their stress-strain curves consist of four deformation stages. Slip bands were straight in the early stage of deformation, but rumpled surfaces were observed in the later stages under an optical microscope. Deformed specimen showed several Luders bands where the slip was single. From etch pit study, it was deduced that most of dislocations generated during deformation slipped out from surfaces. In thicker specimens the hardening rate was larger and the strain value for the beginning of each stage was smaller as compared with those of thinner specimens. Cross-slip seems to play important role for development and increasing of slip bands, and also for work hardening and size effect.

Distribution of Etch Pits on KCl Whiskers

The distribution of etch pits on slightly deformed KCl whiskers is examined. Linear alignments are observed in edge dislocation bands, but a diffuse distribution is observed in screw dislocation bands at the initial stage of deformation. The distribution of etch pits in screw bands rapidly becomes linear when strain is increased. The length of edge bands is about 4 times larger than that of the corresponding screw bands on the average. This result may indicate that the velocity of edge dislocations Ve, is larger than that of screw dislocations Vs. However, the value of Ve/Vs for KCl whiskers seems to be far smaller than that for LiF crystals. These experimental results are consistent with the prediction deduced from the preceding studies.