27 research outputs found
Stability of Cu-precipitates in Al-Cu alloys
No full textWe present first principle calculations on formation and binding energies for Cu and Zn as solute atoms forming small clusters up to nine atoms in Al-Cu and Al-Zn alloys. We employ a density-functional approach implemented using projector-augmented waves and plane wave expansions. We find that some structures, in which Cu atoms are closely packed on (100)-planes, turn out to be extraordinary stable. We compare the results with existing numerical or experimental data when possible. We find that Cu atoms precipitating in the form of two-dimensional platelets on (100)-planes in the fcc aluminum are more stable than three-dimensional structures consisting of the same number of Cu-atoms. The preference turns out to be opposite for Zn in Al. Both observations are in agreement with experimental observations.Peer reviewe
DLTPulseGenerator: a library for the simulation of lifetime spectra based on detector-output pulses
No full textThe quantitative analysis of lifetime spectra relevant in both life and materials sciences presents one of the ill-posed inverse problems and, hence, leads to most stringent requirements on the hardware specifications and the analysis algorithms. Here we present DLTPulseGenerator, a library written in native C++ 11, which provides a simulation of lifetime spectra according to the measurement setup. The simulation is based on pairs of non-TTL detector output-pulses. Those pulses require the Constant Fraction Principle (CFD) for the determination of the exact timing signal and, thus, the calculation of the time difference i.e. the lifetime. To verify the functionality, simulation results were compared to experimentally obtained data using Positron Annihilation Lifetime Spectroscopy (PALS) on pure tin
Thermo-optical-measurement device for sintering of pm products under atmospheric control
No full textTesting and inspection of Additive Manufactured PM Parts Using Thermo-Optical Measuring Technique
No full textFollowing the shrinkage of powder metallurgical samples of unusual shape is possible employing our thermo-optical measurement device with atmospheric control (TOM-AC). Its accuracy of better than 0.5 microns resolution reached during contact-less measurements and its robust contour-detection algorithm allow a data quality making a numerical derivative of the shrinkage possible. Hence, we present here shrinkage and shrinkage rates for spheres of carbonyl iron, metallic foams and a grid produced by screen printing of stainless steel powder. The TOM-AC allows not only measuring samples of arbitrary shapes but also changing the sintering atmospheres (vacuum, inert gas or reducing gases like hydrogen mixtures) during the heat treatment at chosen temperatures. The whole control during the heat treatment is realised via a specific code on a standard PC
Update (v1.2) to DLTPulseGenerator: A library for the simulation of lifetime spectra based on detector-output pulses
No full textIn the last update of DLTPulseGenerator library (v1.1), we realised the simulation of distributed specific lifetimes as can be found for the lifetimes of positrons (PALS) in porous materials due to the pore size distribution.However, in this update v1.2, the DLTPulseGenerator library was modified to allow the simulation of lifetime spectra consisting of non-Gaussian distributed and linearly combined Instrument Response Functions (IRF), since a Gaussian shaped instrumental response of a lifetime spectroscopy setup more likely represents an approximation as it reflects the experimentally obtained results. Eventually, this provides an improved modeling of the experimental instrumental response and, finally, leads to a more realistic simulation of lifetime spectra
DDRS4PALS: a software for the acquisition and simulation of lifetime spectra using the DRS4 evaluation board
No full textLifetime techniques are applied to diverse fields of study including materials sciences, semiconductor physics, biology, molecular biophysics and photochemistry.
Here we present DDRS4PALS, a software for the acquisition and simulation of lifetime spectra using the DRS4 evaluation board (Paul Scherrer Institute, Switzerland) for time resolved measurements and digitization of detector output pulses. Artifact afflicted pulses can be corrected or rejected prior to the lifetime calculation to provide the generation of high-quality lifetime spectra, which are crucial for a profound analysis, i.e. the decomposition of the true information. Moreover, the pulses can be streamed on an (external) hard drive during the measurement and subsequently downloaded in the offline mode without being connected to the hardware. This allows the generation of various lifetime spectra at different configurations from one single measurement and, hence, a meaningful comparison in terms of analyzability and quality. Parallel processing and an integrated JavaScript based language provide convenient options to accelerate and automate time consuming processes such as lifetime spectra simulations
Following shrinkage and exothermic processes by thermo-optical measurement techniques
No full textCode 13160
Data on pure tin by Positron Annihilation Lifetime Spectroscopy (PALS) acquired with a semi-analog/digital setup using DDRS4PALS
No full textPositron annihilation lifetime spectroscopy (PALS) provides a powerful technique for non-destructive microstructure investigations in a broad field of material classes such as metals, semiconductors, polymers or porous glasses. Even though this method is well established for more than five decades, no proper standardization for the used setup configuration and subsequent data processing exists. Eventually, this could lead to an insufficiency of data reproducibility and avoidable deviations.
Here we present experimentally obtained and simulated data of positron lifetime spectra at various statistics measured on pure tin (4N-Sn) by using a semi-analog/digital setup, where the digital section consists of the DRS4 evaluation board, “Design and performance of the 6 GHz waveform digitizing chip DRS4” [1]. The analog section consists of nuclear instrument modules (NIM), which externally trigger the DRS4 evaluation board to reduce the digitization and, thus, increase the acquisition efficiency. For the experimentally obtained lifetime spectra, 22Na sealed in Kapton foil served as a positron source, whereas 60Co was used for the acquisition of the prompt spectrum, i.e. the quasi instrument response function. Both types of measurements were carried out under the same conditions.
All necessary data and information regarding the data acquisition and data reduction are provided to allow reproducibility by other research groups
Sintering nickel and iron: Are there indications for defect-activated sintering?
No full textDefects in powder metallurgical samples may enhance diffusion processes during sintering. Samples of high purity nickel reduction powder and pure carbonyl iron are prepared by interrupted sintering, i.e. removing the furnace at the target temperature and rapidly cooling the samples, which are then investigated by analytical methods like positron annihilation lifetime spectroscopy (PALS). Thus, we can follow the sintering process by changes in the microstructure. These results are compared to heavily deformed reference samples (iron taken from literature) to determine the recovery temperature (0.4 of the melting temperature), i.e. annealing of dislocations. We estimate an effective powder particle size, which can be used to model the shrinkage by a modified two-particle model. The results for the two systems will be compared. For larger samples (10-30mm in diameter) we follow the shrinkage by thermo-optical measurements to determine influences of the pressing tools by monitoring the shrinkage at different height positions during one run
Using a novel microstructure generator to calculate macroscopic properties of multi-phase non-oxide ceramics in comparison to experiments
No full textS.325-333A novel method to generate microstructures and calculate thermal and elastic properties in non-oxide ceramics, namely in Aluminum Nitride (ALN), Silicon Nitride (Si3N4), and Silicon Carbide (SiSiC) is presented. Structural features like dihedral angle (ALN), anisotropic material properties of grains (Si3N4), and multiscale structure (SiSiC) are considered. To ensure that the simulated structures are close to the real materials, several samples of all ceramics were prepared by the artifact-free method of cross section polishing and imaged by scanning electron microscopy (SEM). By image analysis chord lengths, phase fractions, connectivity between grains or elongation of grains were obtained. The same parameters were extracted from 2-dimensional sections of 3-dimensional representative volume elements produced by a structure generator. Structure generation followed closely the structure formation in the real process. It was repeated until close agreement between experimental and theoretical structures was obtained. Then, thermal and mechanical properties were calculated by finite element simulations. The calculated material properties showed good agreement to the obtained experimental data.42Nr.1, Pt.
