Atomic mechanisms of precipitate plate growth

Space-group analyses of thin precipitates by different convergent-beam electron diffraction procedures

“…It is worthwhile to compare the results from the present CBED space-group analyses of the y' precipitates that were aged for 30 rain at 623 K with an ordered structure proposed for the same y' precipitates by Howe, Dahmen & Gronsky (1986). The present analyses determined the space group of these precipitates to be P63/mmc.…”

Effect of heat treatment on microstructures and mechanical properties in a full lamellar PM TiAl alloy

“…2) Minor addition of boron prevents the grains from growing rapidly during holding in the single α phase field 21 . During cooling from α phase field, the longitudinal and lateral growth of the lamellar precipitates occurs through the "terrace-ledge-kink" mechanism 22 . This mechanism can be described as a lateral growth of the lamellae through the movement of Shockley partials on the habit plane, leading to the formation of ledges on the phase-interfaces.…”

Minimum detectable solute concentration in atomic-resolution transmission electron microscopy

“…However, when large composition changes occur over large spatial regions, for example in spinodal decomposition and growth of highly ordered precipitates, interpretation of image contrast is much more complicated. While the simple results that increasing the atomic number in a column of atoms darkens the column and decreasing the atomic number lightens the column can still be useful for deducing compositional changes in these situations (Howe, Dahmen & Gronsky, 1987), the contrast effects described in this paper can only serve as a guide to possible image contrast rather than as a predictor of contrast.…”

“…Atomicresolution capability is particularly important in the field of materials science, where it is often necessary to understand the atomic structure and composition of a material in order to explain its properties. While many researchers have investigated the possibilities and limitations of structural information that is available by ARM (Spence, O'Keefe & Iijima, 1978;Saxton & Smith, 1985;Self, Glaisher & Spargo, 1985), the compositional information that is contained in atomic-resolution images is just beginning to be systematically examined (Rose & Gronsky, 1986;Ourmazd, Rentschler & Taylor, 1986 Gronsky, 1987;Tanaka & Cowley, 1987). The ability to determine the solute concentration in individual columns of atoms has many important applications in materials science, such as allowing determination of the extent of solute segregation to dislocations, grain and interphase boundaries, permitting characterization of long-range order in small metastable strengthening precipitates, and determining the extent of interdiffusion and abruptness of interfaces in multilayered structures.…”