Cohesive Strength and Structural Stability of the Ni-Based Superalloys

The influence of alloying elements on the cohesive strength of metal heat-resistant alloys (HRAs) is analyzed. Special parameters are introduced to characterize the individual contribution of each alloying element. These are the partial molar cohesion energy of the matrix (χ) and the cohesive strength of the grain boundaries (η) and can be calculated by computer modeling based on the density functional theory. The calculating results of the parameters χ and η in nickel HRAs with mono– and polycrystalline structures alloyed with refractory metals are presented. The calculated data are used to select the chemical composition and develop new nickel (Ni) HRAs with superior creep-rupture properties. It is assumed that a similar approach can be used to search for alloying elements that will contribute to increasing the cohesive strength of additive objects. The resistance of coherent γ-γ’ and lamellar (raft) structures in nickel HRAs to the process of diffusion coarsening during operation is analyzed.

Droplet evaporation method applied to test the efficacy of Zincum metallicum 30c on stressed and non-stressed wheat seeds

Background: The droplet evaporation method (DEM) has been recently proposed as a possible tool to test the efficacy of ultra high dilutions (UHDs) [1]. Here we applied the same methodology consisting in the evaporation of droplets from leakages obtained by placing wheat seeds in UHDs to test whether DEM patterns vary in function of the tested treatment: Zincum metallicum 30c (ZM), lactose 30c as dynamized control (L), and unsuccussed, undiluted water as negative control (C). Since our previous study [1] showed that there is a significant increase in the UHD action in the stressed model, with respect to the non-stressed one, also in the present experiment we tested ZM, L and C on both stressed (s-seeds) and non-stressed wheat seeds (ns-seeds). Aims: The aim of the experiment was to test whether treatments ZM, L, and C applied on ns- and s-seeds influence the DEM pattern characteristics. Materials and methods: Whole, undamaged wheat seeds (Triticum aestivum cv. Inallettabile, harvesting year 2010) were used for the experiment, following the experimental protocol described in [1]. The distinction between s- and ns-seeds is based upon different storing conditions from the harvest until the analysis day: the ns-seeds were kept in controlled conditions at 5°C and in the dark, whereas the s-seeds were kept in lab at varying temperature, humidity and light conditions. As far as treatment preparation is concerned, ZM and L were obtained from triturations 3c (received from the Federal University of Rio de Janeiro) by vertical mechanical succussions and following dilutions; negative control (C) was ultra-pure water from the same water batch used for dilutions. The experiment was repeated on 6 days within one month; each seed lot (ns- and s-seeds) was analyzed on 3 different days (s-seeds on 10th, 11th and 24th February 2014 and ns-seeds on 12th, 26th February and 3th March 2014), with three treatment-replicates for ZM and L and two for C, three repetitions for each treatment-replicate and 5 droplets per repetition (360 patterns for each seed lot). The complexity degree of polycrystalline structures obtained from the evaporating droplets was measured by means of the ImageJ software [2] by calculating their local connected fractal dimensions (LCFD). The data on moon phase, moon position and moon distance from Earth at the beginning of each evaporation process were collected from the online tool virtuelles Telescope [3]. All data were processed by a three-way ANOVA at a significance level of p ≤ 0.05. Correlations between the moon data and LCFD were evaluated by r Pearson coefficient. Results: The effect of the treatment on LCFD values of DEM patterns was significant only in the stressed model: ZM showed a crystallization inhibiting action vs. C on all 3 analysis days, whereas a significant difference between ZM and L could be observed only on first and third analysis day (Fig 1a). ANOVA analysis showed that the overall LCFD means for the s-seed lot differed significantly between each other: 1.33 (a) for C, 1.26 (b) for L, and 1.19 (c) for ZM. Moreover, the LCFD values of both seed lots showed a strong day factor influence. A possible explanation of this finding might be the influence of the moon (position, phase, and distance from Earth) on the crystallization process: strong correlation between the LCFD of the patterns and moon data were found (r values were from -0.72 to -0.97). Figure 1: Graphical representation of the mean local connected fractal dimension values (LCFD) of droplet evaporation patterns obtained from stressed and non-stressed wheat seeds following treatments with Zincum metallicum 30c (ZM), lactose 30c (L), and unsuccussed/undiluted water (C). Discussion: The present study confirms a pre-sensitization effect towards UHD action in stressed models: a significant inhibiting effect of ZM 30c was found in all experimentation day. Furthermore, the strong correlations observed between the LCFD values and moon data indicate that the complexity of polycrystalline structures from evaporating droplets of wheat seed leakages might be affected by tidal forces. Since DEM needs to be standardized, these correlations can be considered only simultaneous and not causal, however their strength gives good reasons for further studies. Conclusions: The results of the present pilot-study seem to encourage further DEM experiments on s-seeds following UHD treatments. For further confirmation of the inhibiting effect of ZM on s-seeds, germination tests should be planned. Finally, the performance of DEM experimentations during days and hours with equal tidal influence on gravity might be helpful for the reduction of the day factor. Keywords:Ultra high dilutions, droplet evaporation method, patterns, Zincum metallicum

Molecular Dynamics Study of Bulk Properties of Polycrystalline NiTi

Molecular dynamics (MD) simulations were carried out to study the bulk polycrystalline properties of NiTi. Thermally driven phase transitions of NiTi between martensite and austenitewere simulated using single crystalline simulation domains. With external stress boundary conditions, MD simulation successfully predicted experimentally observed phase transformation temperatures of bulk polycrystalline. Elastic characteristics of NiTi martensite were simulated using polycrystalline simulation domains that consist of realistic disorientations and grain boundary structures. The existence of grain disorientation and grain boundary lowered the potential energy of the simulation domain, which led to more realistic elastic modulus prediction. Analysis of simulation domains that predicted realistic bulk polycrystalline properties showed that the major difference between single crystalline and polycrystalline structures is atomic stress distribution.

A review on the theory of stable dendritic growth

This review article summarizes the main outcomes following from recently developed theories of stable dendritic growth in undercooled one-component and binary melts. The nonlinear heat and mass transfer mechanisms that control the crystal growth process are connected with hydrodynamic flows (forced and natural convection), as well as with the non-local diffusion transport of dissolved impurities in the undercooled liquid phase. The main conclusions following from stability analysis, solvability and selection theories are presented. The sharp interface model and stability criteria for various crystallization conditions and crystalline symmetries met in actual practice are formulated and discussed. The review is also focused on the determination of the main process parameters—the tip velocity and diameter of dendritic crystals as functions of the melt undercooling, which define the structural states and transitions in materials science (e.g. monocrystalline-polycrystalline structures). Selection criteria of stable dendritic growth mode for conductive and convective heat and mass fluxes at the crystal surface are stitched together into a single criterion valid for an arbitrary undercooling. This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.

Comparative Study and Limits of Different Level-Set Formulations for the Modeling of Anisotropic Grain Growth

In this study, four different finite element level-set (FE-LS) formulations are compared for the modeling of grain growth in the context of polycrystalline structures and, moreover, two of them are presented for the first time using anisotropic grain boundary (GB) energy and mobility. Mean values and distributions are compared using the four formulations. First, we present the strong and weak formulations for the different models and the crystallographic parameters used at the mesoscopic scale. Second, some Grim Reaper analytical cases are presented and compared with the simulation results, and the evolutions of individual multiple junctions are followed. Additionally, large-scale simulations are presented. Anisotropic GB energy and mobility are respectively defined as functions of the mis-orientation/inclination and disorientation. The evolution of the disorientation distribution function (DDF) is computed, and its evolution is in accordance with prior works. We found that the formulation called “Anisotropic” is the more physical one, but it could be replaced at the mesoscopic scale by an isotropic formulation for simple microstructures presenting an initial Mackenzie-type DDF.

Effect of Annealing on the structural, surface morphology and optical properties for CdO:PbO composite thin films

Thin films of pure cadmium oxide films (CdO) and composite with lead oxide (PbO) at different atomic ratios were prepared by pulsed laser deposition under vacuum usingpulsed laser of ND-YAG from CdO and CdO:PbO targets. The prepared thin films were characterized by different technique before and after annealing. The X-ray diffraction shows polycrystalline structures of cubic CdO phase convert tosample of mixed phases for composites. The AFM images illustratedecreasing the particle diameter and increasingsurface roughness with increasing the PbO ratio in composite. While, annealing cause to increase the particle size and reduce roughness. The optical absorbance increased with the PbO ratio, while the absorbance decreased with annealing. The energy gap reduced after annealing and increased with increasing the molar ratio of PbO. These variation in some fundamental properties of the prepared thin films by simplyvarying the components of the started target show the possibilityof controlling the properties of the prepared thin films by pulsed laser depositionfor use in many fields.

Emergence of Rigid Polycrystals from Atomistic Systems with Heitmann–Radin Sticky Disk Energy

We investigate the emergence of rigid polycrystalline structures from atomistic particle systems. The atomic interaction is governed by a suitably normalized pair interaction energy, where the ‘sticky disk’ interaction potential models the atoms as hard spheres that interact when they are tangential. The discrete energy is frame invariant and no underlying reference lattice on the atomistic configurations is assumed. By means of $$\Gamma $$ Γ -convergence, we characterize the asymptotic behavior of configurations with finite surface energy scaling in the infinite particle limit. The effective continuum theory is described in terms of a piecewise constant field delineating the local orientation and micro-translation of the configuration. The limiting energy is local and concentrated on the grain boundaries, that is, on the boundaries of the zones where the underlying microscopic configuration has constant parameters. The corresponding surface energy density depends on the relative orientation of the two grains, their microscopic translation misfit, and the normal to the interface. We further provide a fine analysis of the surface energies at grain boundaries both for vacuum–solid and solid–solid phase transitions. The latter relies fundamentally on a structure result for grain boundaries showing that, due to the extremely brittle setup, interpolating boundary layers near cracks are energetically not favorable.

Multiple stages of serpentinization in mantle derived peridotites of the South Armorican Variscan suture zone

<p>South Armorican mantle peridotites represent a great diversity of protoliths from supra-subduction zone to arc-fore arc ophiolites. In this study, we investigate the serpentinization of these protoliths. Numerous samples were collected in five different units, which represent ophiolitic dismembered pieces (Ty-Lan Peridotites (TLP) from the Audierne Complex, and Pont de Barel Peridotites (PBP), Folies Siffait Peridotites (FSP), l’Orgerais Peridotites (LOP) and Drain Peridotites (DP) from the Champtoceaux Complex). Field and microscopic observations together with Raman spectroscopy and electronic microprobe analysis (EMPA) allowed to identify several stages of serpentinization. All samples display a high rate of serpentinization, up to 80-90 %. Primary assemblage is represented by spinel (TLP, PBP, DP and LOP), olivine (TLP and FSP) and Ti-poor or Cr-rich pargasite (TLP and PBP). In all the samples, lizardite from olivine and bastites from pyroxene and amphibole characterize the first stage of serpentinization. It is associated with magnetite crystallization. No Al-rich lizardite meshe is identified by EMPA suggesting a low temperature (< 340°C) event. This serpentinization is followed by two generations of veins (V1 and V2). The V1 are Al-poor lizardite shear veins and crack-seal chrysotile veins characterize the V2. In PBP, microprobe mapping shows that V2 displays heterogeneous chemical chrysotile composition with significant variations of Al, Fe and Mg contents, suggesting metasomatism and/or variation of fluid composition during serpentinization. All these observations are closely similar to those of oceanic serpentinized peridotites. In the TLP, we identified a second stage of serpentinization characterized by antigorite after lizardite suggesting a high temperature event. In the OP, antigorite after lizardite was also identified. However, compared to the TLP ones, LOP antigorite is related to ductile (i.e., ultramylonite) deformations. This clearly indicates a high temperature stage of serpentinization (up to 500 °C). Furthermore, LOP ultramylonitized samples display one more chrysotile veins generation (V3) characterized by three distinct vein networks. The first one (V3a) is a crack-seal type vein network opened parallel to the main foliation. The second one (V3b) is perpendicular to the first one, whereas the third one (V3c) corresponds to tension gashes connected to C’ plans. This latter is perpendicular to V3a and V3b networks. The mylonitic foliation of LOP is similar to the surrounding micaschists schistosity, suggesting an orogenic high temperature stage of serpentinization. In the FSP, σ-type polycrystalline structures were identified. Lizardite meshes are progressively transposed and recrystallized into the foliation plan. This stage is associated with the crystallization of chlorite after tremolite, suggesting a retrograde stage of serpentinization during serpentinites exhumation. Finally, despite a great diversity of mantle-derived protoliths, our study shows that South-Armorican peridotites recorded a similar first low temperature oceanic stage of serpentinization. According to the Variscan history, it could have started during the Cambro-Ordovician for TLP, and during the Late Devonian for PBP, DP, LOP, FSP. Furthermore, some of these peridotites also recorded an orogenic serpentinization (LOP and FLP). Such observations provide new constraints that could be useful to a better understanding of the tectonometamorphic evolution of the South Armorican suture zones during the Variscan orogeny. </p>

Prospects of Using Small Scale Testing to Examine Different Deformation Mechanisms in Nanoscale Single Crystals—A Case Study in Mg

The advent of miniaturised testing techniques led to excessive studies on size effects in materials. Concomitantly, these techniques also offer the capability to thoroughly examine deformation mechanisms operative in small volumes, in particular when performed in-situ in electron microscopes. This opens the feasibility of a comprehensive assessment of plasticity by spatially arranging samples specifically with respect to the crystal unit cell of interest. In the present manuscript, we will showcase this less commonly utilised aspect of small-scale testing on the case of the hexagonal metal Mg, where, besides dislocation slip on different slip planes, twinning also exists as a possible deformation mechanism. While it is close to impossible to examine individual deformation mechanisms in macroscale tests, where local multiaxial stress states in polycrystalline structures will always favour multiple mechanisms of plasticity, we demonstrate that miniaturised uniaxial experiments conducted in-situ in the scanning electron microscope are ideally suited for a detailed assessment of specific processes.

Facile Template-free Preparation of Silver-coated Cu3SbS4 Hollow Spheres with Enhanced Photoelectric Properties

Hollow polycrystalline structures and noble-metal coating endow ternary sulfides with promising light absorption and electrical properties for solar energy conversion applications. We developed a facile one-pot solvothermal chemical route to...