[en] A method is described of determining the material granulation, which eliminates the mechanical sorting of granular material and simplifies the analysis. The method also permits a continuous process of individual operations required for the determination of material granulation. (V.V.)

[en] This study focuses on characterizing and modeling advanced oxide dispersion strengthened (ODS) NiAl intermetallics with improved high temperature creep strength driven by incorporating a high number density (∼10²⁴ m^-3) of very thermally stable Y-Ti-O nano-clusters, akin to those recently observed to improve creep strength and radiation resistance in nano-structured ferritic alloys. The motivation of the study was; what structure and composition do the nm-scale features/precipitate clusters have and what processing variables control their formation. To answer these questions, advanced experimental characterization techniques, combined with atomic modeling, were used to investigate the material microstructure and strength following processing. In particular, the size, number density and composition of nano-clusters were assessed. There was a clear indication that milling for 5-15 hrs was sufficient to produce good mixing during the mechanical alloying process, as determined by XRD, SEM, and EDS results. Powder consolidation was carried out by spark plasma sintering. Fully dense NiAl alloy materials were produced by SPS. A distribution of 10-20 nm precipitates was found in NiAl-Y₂O₃ and NiAl-Y₂O₃-Ti alloys, and those precipitates were identified as Y-Al-O (garnet) particles in the NiAl-Y₂O₃, while both garnet (Y₂Al₄O₇) and Y₂Al₉Ti₂O₆ phase particles were found at the NiAl-Y₂O₃-Ti alloy. The Al composition of a particle increases as the particle size increases, and Y was dominantly found at the particles size of less than 50 nm while Ti was found at the relatively larger particles with size larger than 100 nm. The Al incorporation believed detrimental to the formation of nanoscale Y-Ti-O precipitates. The effect of Hall-Petch grain size and dispersion strengthening mechanisms in ODS NiAl alloys will be semi-quantatively assessed. The LMC simulations indicate that larger than 10% lattice strain required to form coherent nano-clusters

[en] The effect of the magnetic anisotropy at temperatures above the blocking temperature of a uniaxial, randomly oriented, nanoparticulate magnetic system has been studied. If anisotropy is disregarded in fitting the magnetization curves, apparent particle-size distributions emerge from the calculations, even for monodisperse systems. Apparent mean grain size increases with temperature, with a saturation value corresponding to the actual particle size. This evolution collapses to a master curve for anisotropy energy terms up to the fourth order

[en] The consolidation behavior of tungsten powders with different particle size (ranging from submicron size to several microns) have been investigated by using a novel method combining resistance sintering with ultra-high pressures. The densification effects of the consolidation parameters, including pressure, input power and sintering time, have been investigated. High density is achieved for consolidation of micron sized tungsten powder and the microstructure retained its fine-grain size. The sintered samples achieve higher hardness and bending strength when the finer powder is used. The sintering mechanism of this method was quite different from other sintering techniques

No abstract available

[en] The main aim of the present investigation was to study the flow behaviour of two medium carbon microalloyed steels under hot forming conditions, and to analyse their microstructural evolution. the dependence of recrystallized grain size (D_rec) on the Zener-Hollomon parameter Z shows a bimodal behaviour with transition from single to cyclic dynamic recrystallization. We also observed that the variation of D_rec normalized by the Burgers vectors (b) with the steady state stress σ_ss normalized by shear modules (μ) shows the same bimodal behaviour cited above. the Derby's universal equation reported in the literature for recrystallized grain sizes was not followed; it seems that the presence of fine precipitated particles has a clear effect on this disagreement. (Author)

[en] The remanent state of truncated conical particles is investigated as a function of their size, aspect ratio, and anisotropy, using a micromagnetic model based on the Landau - Lifshitz - Gilbert equation. Particles with a base diameter smaller than three times the exchange length show a 'flower' state, while larger particles show a 'vortex' magnetization state. The critical size for this transition increases with increasing anisotropy. Small flower-state particles show abrupt reorientation from out-of-plane to in-plane magnetization at a critical aspect ratio of 0.9. For vortex-state particles, the axial remanence gradually increases as the aspect ratio increases, and high aspect ratio particles have significant remanence even at larger diameters. [copyright] 2001 American Institute of Physics

[en] In this work, we try to answer the following question: What is the effective characteristic length of a mixture of Cosserat continua? More generally, homogenization methods for heterogeneous Cosserat media are proposed and applied to the case of linear elasticity. They first application deals with a beam network regarded as a discrete Cosserat medium and the second with a continuous heterogeneous Cosserat continuum. (orig.)

[en] Particle size and specific surface area measurements are conventional characterization techniques for ceramic powders to predict sintering behaviour. Dilatometry is one of the most popular techniques in ceramics to study the sintering characteristics for optimization of firing processes. Uranium dioxide (UO_2) powders from different sources were characterized by conventional techniques and these characteristics were correlated with sintering behaviour, as measured with a dilatometer. The suitability of dilatometry to correlate the sintering characteristics of UO_2 powder with variations in the O/U ratio, particle size and green density was discussed. Explanations of features in the sintering profiles for UO_2 powders have been presented. (author)

[en] The mineralogic variation of clay minerals in the Araruama Lagoon is demonstrated by X-ray diffraction analysis of 45 samples of clay-sized material. (L.H.L.L.)