Papers by Keyword: FCC

Abstract: The strain rate exerts a profound influence on the mechanical characteristics of nanomaterials. To investigate this phenomenon, the molecular dynamics approach was employed to examine the impact of uniaxial compression along the [100] crystallographic direction in monocrystalline Al. The purpose of this research was to determine the differences in reactions observed during the elastic and plastic phases. It employed the Embedded Atom Method (EAM) as well as the Modified Embedded Atom Method (MEAM) potentials at 300 K. A comparative analysis of the outcomes from these potentials demonstrated considerable disparities. The results encompassed the percentage distribution of crystal structures (fcc, hcp, bcc, and others) as well as their atomic configurations. Several analytical factors were examined, including the strain-stress curve, the radial distribution function (RDF), the common neighbor analysis (CAN). The applied MEAM potential represents a subsequent occurrence of transitions following EAM, encompassing both increasing and decreasing phase transitions.

Abstract: Orientation microscopy, based on electron backscattered diffraction (EBSD) has been used to study the regularities of formation of the crystallographic texture in materials with BCC and FCC lattices in the hot rolling process throughout the whole thickness of the strips. It has been established that the texture of the central layers of all samples consisted of the discrete sets of stable orientations corresponding to the cold rolling texture. In the surface layers of the samples Fe-3%Si and Al, the texture consisted of sets of discrete orientations corresponding to the shear structure. In the samples of Mo and austenitic steel, the set of discrete orientations of the surface layers matched the texture of the central layers. The difference in textures of the central and surface layers was the result of a certain stress state. The amount of friction has notably influenced the texture of the surface layer. In "hard" materials (Mo, γ-Fe), the friction was minimal, i.e. the difference in stress states of the surface and central layers was insignificant.

Abstract: In this study, a framework to predict the onset of plastic flow localization is introduced. The Marciniak-Kuczyński type approach, which is a classical method to predict the strain localization, and a crystal plasticity model with a homogenization-based finite element method are combined, and forming limit strains that are defined as the onset of plastic flow localization for FCC polycrystals are computed. The forming limit strains with several kinds of textures are evaluated with the present approach, and the results are compared with those obtained by the Taylor model, which is a widely used conventional polycrystalline model. Within the present application, the present method and the classical Taylor model give similar forming limit strains for FCC polycrystal sheets. According to the present results, the use of the Taylor model in the sheet necking analysis might be justified, at least for FCC polycrystal sheets with various textures.

Abstract: The influence of strain rate over domains involving the thermal activation and the viscous drag behavior of the dislocations has been investigated for a series of face centered cubic metals. The effect of grain size on the strain rate threshold delimitating the two domains in compression was examined with grains sizes ranging from 0.1 to 100 μm for nickel and copper. The tensile strengthening occurring at high strain rates for an austenitic stainless steel was also investigated.

Abstract: Gas-solid two-phase flow of the quick-contact cyclone reactor used in FCC was simulated with the multi fluid Eulerian model, especially the velocity field and volume fraction of solid in the mixing chamber was researched. The results show that flow pattern and catalyst particles concentration are non-uniform in the direction of axial, radial and tangential. The tangential gas admission increases turbulent intensity, it has a great benefit on spreading the catalyst particles uniformly, enhancing gas-solid contact effect. This work could offer a base for the structure optimization of the quick-contact reactor.

Abstract: The CO2 capturing technologies as applied to FCC flue gas in order to reduce GHG (green house gases) were evaluated and compared in this review. Although the CCS (carbon capture and storage) idea has been proposed for more than 30 years, there has been little commercial success of CCS projects. The largest issue is where to store the massive amount of captured pure CO2 every year. Therefore, the review will focus on the efficient use of power or heat to reduce CO2 emission and how to recycle the use of produced CO2 before it is emitted to the atmosphere rather than being captured and stored. The scenarios with oxyfiring, microalgae-cofiring or biogas burning to treat FCC flue gas are introduced and discussed.

Abstract: {111} fiber textured face centered cubic (fcc) titanium has been found to coexist with the {0002} fiber textured hexagonal close packed (hcp) titanium in polycrystalline titanium (Ti) thin films (thickness: 144 nm to 720 nm) deposited on Si (100) substrate by magnetron sputtering. X-ray diffraction investigation confirms that relative phase fraction of such metastable fcc Ti phase decreases with increasing film thickness indicating thickness dependent fcc-hcp phase transformation of titanium. Texture development in hcp Ti phase was due to film microstructure (thickness effect) rather than the phase trans-formation. Diffraction stress analysis (by d-sin2 method) indicates that fcc to hcp phase transformation is also accompanied by the reduction of compressive stress in the hcp Ti phase with increasing film thickness. Strain energy calculations for both phases of titanium indicate that fcc Ti is a more stable phase compared to hcp Ti at relatively low film thickness (144 nm to 432 nm). It has been concluded that film stress favours fcc to hcp phase transformation towards the higher film thickness. Reverse transformation (hcp to fcc) occurs towards the lower film thickness.

Abstract: The Stacking fault energy (SFE) is an important parameter for metals and alloys. The plastic deformation behavior of face centered cubic (FCC) metals and alloys is directly related to the SFE values. The several methods for determining SFE are critically discussed. The values reported in the 1960s and early 1970s are, in general, 20-30% overestimated. The node dislocation method, due to Whelan, overestimates the SFE. The method based on the critical resolved shear stress is not reliable. The most accurate method is the direct observation of dissociated partials by weak beam in TEM or using HREM (High resolution electron microscopy). Indirect methods based in X-Ray Diffraction and texture may provide reasonable estimates since reliable SFE values of reference metals are available. Selected SFE values for Ni, Cu, Ag, Cu and Al are presented.

Abstract: The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.

Abstract: The stress-strain characteristics and plastic behavior of aluminum alloy were examined by tensile test and infrared thermo-viewer. This thermo viewer is a device for converting a thermal radiation pattern from an object into visible images. Al-Mg alloy plates with different crystal grain size subjected to a uni-axial tensile load were measured continuously by this thermo viewer. The strain concentration pattern was analyzed by the differential thermal image and the macroscopic estimation method by the thermal image processing was proposed and the propriety of FE simulation based on polycrystalline plasticity model was shown.