Application of a Numerical Method for the Analysis of Metglas 2826 MB Crystallization Kinetics

Crystallization kinetics of y-FeNiMo solid solution in Metglas 2826 MB was studied by isothermal differential scanning calorimetry (DSC). The Johnson-Mehl-Avrami (JMA) equation was used to describe the crystallization process. In order to calculate the kinetic parameters, a new model of the numerical analysis of isothermally obtained DSC data was successfully applied. For the purposes of method evaluation, the classical analytical method of data analysis was also performed. The apparent activation energies obtained were (280 ± 22) kJ mol-1 and (296 ± 23) kJ mol-1 for the analytical and numerical methods, respectively. The Avrami exponents obtained by both methods lie between 1.75 and 1.95

Microstructure and Flux Pinning of Reacted-and-Pressed, Polycrystalline Ba0.6K0.4Fe2As2 Powders

The flux pinning properties of reacted-and-pressed Ba0.6K0.4Fe2As2 powder were measured using magnetic hysteresis loops in the temperature range 20 K ≤ T ≤ 35 K. The scaling analysis of the flux pinning forces (Fp = jc × B, with jc denoting the critical current density) following the Dew-Hughes model reveals a dominant flux pinning provided by normal-conducting point defects (δl-pinning) with only small irreversibility fields, Hirr, ranging between 0.5 T (35 K) and 16 T (20 K). Kramer plots demonstrate a linear behavior above an applied field of 0.6 T. The samples were further characterized by electron backscatter diffraction (EBSD) analysis to elucidate the origin of the flux pinning. We compare our data with results of Weiss et al. (bulks) and Yao et al. (tapes), revealing that the dominant flux pinning in the samples for applications is provided mainly by grain boundary pinning, created by the densification procedures and the mechanical deformation applied

Microstructure analysis of electrospun La0.8Sr0.2MnO3 nanowires using electron microscopy and electron backscatter diffraction (EBSD)

The microstructural properties of electrospun La0.8Sr0.2MnO3 (LSMO) nanofibers were investigated using electron microscopy and electron backscatter diffraction (EBSD). By means of EBSD, it is possible to measure the crystallographic orientation of the LSMO grains within an individual nanofiber. As the LSMO grains within the nanofibers are in the 10-nm range, we employ here parts of the recently developed transmission Kikuchi diffraction technique in order to enhance the Kikuchi pattern quality to enable an automated mapping of the crystallographic data. The diffraction results demonstrate that the grain orientation is not random, but there is a texture induced by the shape of the polymer nanofiber formed after the electrospinning step. Within an individual nanofiber section, the dominating grain boundaries are high-angle ones, which play an important role in the current flow through the sample (low- and high field magnetoresistance). The data obtained allow further an analysis of the grain shape aspect ratio, and elucidate the grain and grain boundary arrangement within electrospun LSMO nanofibers

On the process of co-deformation and phase dissolution in a hard-soft immiscible CuCo alloy system during high-pressure torsion deformation

In this study, dual phase Cusingle bondCo composites with a total immiscibility in the solid state and a very different initial phase strength are deformed by severe plastic deformation. Nanocrystalline supersaturated solid solutions are reached in all Cusingle bondCo composites independent of the initial composition. The deformation and mechanical mixing process is studied thoroughly by combining scanning electron microscopy, transmission electron microscopy, three-dimensional atom probe tomography and nanoindentation. The indentation hardness of the Cu and Co phase and its evolution as a function of the applied strain is linked to deformation and mechanical mixing process to gain a better understanding how the phase strength mismatch of the Cu and Co phase effects the amount of co-deformation and deformation-induced mixing. Our results show that co-deformation is not a necessary requirement to achieve mechanical mixing

Thermal stability, phase decomposition, and micro-fatigue properties of pulsed electrodeposited nanocrystalline Co-Cu

Nanocrystalline (nc) immiscible Co-Cu alloys system is a promising material where the decomposition of the super-saturated solid solution can be used to obtain nano-structured materials. In this research, homogenous and solid nc Co-Cu thick films were synthesized through the pulsed electrodeposition technique in complex sodium tartrate electrolyte. Annealing procedures were conducted to evaluate its thermal stability and induce phase decomposition of cobalt and copper, which can be utilized to enhance mechanical properties and thermal stability. Initial cyclic micro-bending experiments were also conducted to observe micro-fatigue properties and structural evolution during mechanical loading

Analysis of the carbide precipitation and microstructural evolution in HCCI as a function of the heating rate and destabilization temperature

Microstructural modifcation of high chromium cast irons (HCCI) through the precipitation of secondary carbides (SC) during destabilization treatments is essential for improving their tribological response. However, there is not a clear consensus about the frst stages of the SC precipitation and how both the heating rate (HR) and destabilization temperature can afect the nucleation and growth of SC. The present work shows the microstructural evolution, with a special focus on the SC precipitation, in a HCCI (26 wt% Cr) during heating up to 800, 900, and 980 °C. It was seen that the HR is the most dominant factor infuencing the SC precipitation as well as the matrix transformation in the studied experimental conditions. Finally, this work reports for frst time in a systematic manner, the precipitation of SC during heating of the HCCI, providing a further understanding on the early stages of the SC precipitation and the associated microstructural modifcations

On the process of co-deformation and phase dissolution in a hard-soft immiscible Cu Co alloy system during high-pressure torsion deformation

In this study, dual phase CuCo composites with a total immiscibility in the solid state and a very different initial phase strength are deformed by severe plastic deformation. Nanocrystalline supersaturated solid solutions are reached in all CuCo composites independent of the initial composition. The deformation and mechanical mixing process is studied thoroughly by combining scanning electron microscopy, transmission electron microscopy, three-dimensional atom probe tomography and nanoindentation. The indentation hardness of the Cu and Co phase and its evolution as a function of the applied strain is linked to deformation and mechanical mixing process to gain a better understanding how the phase strength mismatch of the Cu and Co phase effects the amount of co-deformation and deformation-induced mixing. Our results show that co-deformation is not a necessary requirement to achieve mechanical mixing

General Synthesis of Alkyl Amines via Borrowing Hydrogen and Reductive Amination

Amines are a very important class of compounds and the selective synthesis of differently substituted primary, secondary and tertiary alkyl amines is challenging. Here we present the synthesis of primary, secondary, and tertiary alkyl amines from ammonia and alcohols, aldehydes, ketones and hydrogen by combining borrowing hydrogen or hydrogen autotransfer and reductive amination with hydrogen. The key is a nanostructured, bimetallic Co/Sc catalyst able to mediate both reactions or concepts efficiently. We observe a broad product scope, a very good functional group tolerance, upscaling is easily accomplished and our catalyst is reusable

Magnetoresistance and Structural Characterization of Electrospun La1−xSrxMnO3 Nanowire Networks

Nanowire network fabrics of La1−xSrxMnO3 (LSMO) with different doping levels x = 0.2, 0.3, and 0.4 were fabricated by means of electrospinning. The resulting nanowires are up to 100 μm long with a mean diameter of about 230 nm. The nanowires form a nonwoven fabric-like arrangement, allowing to attach electric contacts for magnetoresistance (MR) measurements. The resistance in applied magnetic fields and the MR effect were measured in the temperature range 2 K < T < 300 K in magnetic fields up to 10 T applied perpendicular to the sample surface. An MR ratio of about 70% is obtained for x = 0.2 at 10 T applied field and T = 20 Kr. The highest low-field MR of 5.2% (0.1 T) is obtained for the sample with x = 0.2. Magnetization measurements reveal the soft magnetic character of the samples. A thorough analysis of the microstructure of these nanowire networks is performed including scanning electron microscopy (SEM) and transmission electron microscopy (TEM)