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Pressureless-sintering of non-stoichiometric barium titanate (BaTiO3) powder of TiO2-excess compositions has been investigated. Crystalline phases were analysed by X-ray diffractometry. Attention has been paid to the analysis of the corresponding sintered microstructure by adopting scanning and transmission electron microscopy. Large plate-like grains grown abnormally containing {111} double twin lamellae are commonly found in low-temperature (1332oC) sintered BaTiO3, by presence of a liquid phase, or by twinning, or as discussed in this experiments by partial dislocations. Samples were sintered in air at 1250oC for 1¡B4 and 50 h. In this respect, the emphasis is discussed about the role of the partial dislocations in the early stage of twin formation. Both analytic dislocations exist on the {111} double twin lamellae within abnormal grain and the interface between abnormal grain and normal grain. In the experimental process, dislocation type with the Burgers vector ‹110› and ‹112› has been found except for the ‹111›. For the Burgers vector ‹110› in the perovskite structure, it is possible to envisage that edge dislocations with [100] Burgers vector can be dissociated in their climb plane ([100] ¡÷ 1/2[101] + 1/2[10 ]). Moreover, the perovskite structure has been deformed form ‹110› dislocation (perfect dislocation). Oppositely, the [112] Burgers vector has been formed both partial dislocation type and perfect dislocation type. For sintering at 50 h, we can conjecture the grain growth mold by Shockley or Frank partial dislocation affect on the macroscopic step. Experimental results show that Shockley and Frank partial dislocations have not been found on the {111} double twin lamellae.

Electromigration (EM) describes the mass transport in a metal driven by the momentum transfer from electron scattering with metal ions. This can develop into a degradation process due to void growth for on-chip interconnects when subjected to high electric current densities and eventual interconnect line failure. The mass transport occurs in decreasing order of magnitude along interfaces grain boundaries and in bulk. The diffusivities along interfaces and grain boundaries are determined by crystallographic orientation. Diffusion discontinuities can create flux divergent sites that control void growth kinetics and failure characteristics. Most of the earlier studies of EM modeling have assumed an averaged diffusivity measured across the underlying crystallographic microstructure. The objective of this thesis is to study the effect of microstructure on EM reliability by modeling of the diffusivity corresponding to grain orientation at the interface and to project the EM lifetime and the standard deviation (sigma) of the failure statistics. The simulation consists of two parts. First, the microstructure is generated using a Monte Carlo algorithm based on the Potts model. In the second stage, the void formation and growth induced by electromigration is modeled until a maximum time elapsed. During the void growth, the electrical resistance is monitored to search for EM failure subjected to a 400% (5 times the initial value) resistance increase failure criterion. The simulated electromigration lifetimes were found to follow a log-normal distribution. The computations were carried out on a parallel computer, simulating a population of 100 interconnect segments with random microstructure configurations. In this way, the 100 interconnect segments form the basis for statistical analysis of a special simulation run. Simulation runs were carried out with microstructures varying over a range of grain sizes and diffusivity for the top interface. In the simulation, four cases were studied and compared to results from EM experiments. These four cases were large and small grains combined with slow and fast diffusing top interfaces. Results from the simulation revealed a consistent trend in that large grains prolong the electromigration lifetime, especially for the case of a slow diffusing top interface. This trend is also consistent with the experimental results where the lifetime was found to increase in the order of small grain/fast interface, large grain/fast interface, small grain/slow interface and large grain/slow interface. The overall agreement, however, is only qualitative. For instance, the EM experiment showed a lifetime improvement of more than 100 fold whereas the simulation only showed an improvement of 6 fold from fast to slow interface for large grains. / text

Dynamic abnormal grain growth (DAGG) in commercial-purity molybdenum sheets was investigated through a series of tensile tests at temperatures between 1450°C and 1800°C. DAGG is abnormal grain growth (AGG) which requires the presence of concurrent plastic strain. Most AGG phenomena previously documented in the literature can be categorized as static abnormal grain growth (SAGG) because they occur during static annealing, sometimes following plastic strain, but do not occur during plastic deformation. The DAGG boundary migration rate is much faster than the SAGG boundary migration rate, and DAGG may be utilized to obtain large single crystals in the solid state. Dynamic abnormal grains were found to exhibit a crystallographic orientation preference with respect to the specimen geometry, generally described as derivative from a <101> fiber texture. DAGG was found to prefer growth on the surface of the specimen rather than the interior. The growth of dynamic abnormal grains, which initiated and grew during plastic straining, generally ceased when the application of plastic strain was removed. The DAGG boundary migration rate was found to be a direct function of plastic strain accumulation, regardless of the strain-rate. Therefore, it is hypothesized that the rapid boundary migration rate during DAGG results from an enhanced mobility of certain boundaries. A model is proposed based on the rate of boundary unpinning, as mediated by the emission of dislocations from pinning sites. / text

Dynamic abnormal grain growth (DAGG) is a phenomenon that produces abnormal grain growth at elevated temperatures during plastic deformation. It is distinct from classically studied static abnormal grain growth phenomena in that it only occurs during plastic deformation. Previous investigations of DAGG in a Mo sheet material produced using powder metallurgy techniques observed DAGG grains to grow more rapidly near the sheet surface than near the sheet center. This phenomenon is explored in the present study. A Mo sheet material produced using arc melting techniques is also studied to determine the morphology of DAGG grains. A preference for growth near the sheet center is observed in this material. The through-thickness variations in texture and grain size for both the arc-melted and powder-metallurgy Mo sheet materials are investigated. The preference for growth near the surface in the powder-metallurgy material is due to a through-thickness variation in grain size, with smaller grains near the surface and larger grains near the center. The preference for DAGG grain growth at the center of the arc-melted sheet material is because of very large grains that grow near the sheet surface. These large grains may be the product of multiple abnormal grains occurring near the sheet surface because of texture variation through the sheet thickness. Regardless, the DAGG grain cannot consume these large grains and leaves them as island grains decorating the region near the sheet surface. These results suggest that DAGG is driven primarily by grain boundary curvature. Microstructures that include DAGG grains are investigated with electron backscatter diffraction (EBSD). A new method to evaluate geometrically necessary dislocation densities using EBSD data is derived. DAGG grains are relatively undeformed compared to the polycrystalline microstructure. DAGG grains are not oriented either favorably or unfavorably for slip. Results of the analysis of the grain boundaries between DAGG grains and normal grains do not indicate any special character preference for these grain boundaries. / text

Secondary abnormal grain growth (SAGG) during sintering of barium titanate has been explained in terms of twin plane re-entrant edge (TPRE) growth mechanism by {111} double twin lamellae. But during sintering of Ti-excess barium titanate, {111} double twins lamellae are observed with out SAGG. In our group, Lin founded that when combine two different Ba/Ti ratio of powder to sintering above the eutectic temperature, the SAGG is observed in the interface between two different powders. Therefore, this thesis consists of three major researches: (a) {111} double twin, (b) Ba/Ti ratio, (c) liquid phase. In the experiment, we follow Lin¡¦s experiment to sinter the specimen contain with SAGG. And in this specimen, it can observe the specimen divided into three type of growth grain: (a) top surface with normal grain growth (NGG), (b) intermediate layer with abnormal grain growth (AGG), (c) bottom layer with secondary abnormal grain growth. It can all observed {111} double twin in these three different type of layer. This result confirmed that SAGG are not induced by TPRE growth mechanism. Then we used SEM/EDS to analysis the Ba/Ti ratio in the different type of grain growth layer. The Ba/Ti ratio in this analysis is not differing in NGG, AGG and SAGG. Therefore, we used OM, SEM, TEM to observe the grain boundary and triple grain junction in NGG, AGG and SAGG. It can observe that only the grain boundary and triple grain junction in SAGG are complete wetting. The experimental results shows that the grain growth behavior controlled by the liquid phase wetting degree.