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M Pyda - One of the best experts on this subject based on the ideXlab platform.
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thermal expansivity of polystyrene determined by multi frequency Dilatometry
Thermochimica Acta, 2005Co-Authors: Pawel Kamasa, P Myślinski, M PydaAbstract:Abstract Thermal expansibility and heat capacity of solids in general are linked by the first Gruneisen parameter. While the thermal expansion results from molecular motion in an anharminic potential, contribution to the heat capacity results from all kinds of motion. Similar to the temperature modulated DSC, thermal expansion can be measured by modulated temperature Dilatometry (MT-DIL). One component corresponding to the reversing dilatation contributes to both the total and the modulated dimension change, while the non-reversing gives a characteristic easily distinguishable spike. In the present work a multi-frequency temperature modulated program was applied in push-rod dilatometer to measure a coefficient of thermal expansion (CTE) of polystyrene in the temperature range up to glass transition. At the temperature just below glass transition, the frequency dependence of CTE is observed, similar to the heat capacity behavior by MT-DSC.
Roland Wurschum - One of the best experts on this subject based on the ideXlab platform.
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quantitative volumetric identification of precipitates in dilute alloys using high precision isothermal Dilatometry
Philosophical Magazine Letters, 2018Co-Authors: Elisabeth Hengge, Wolfgang Sprengel, Robert Josef Enzinge, Marti Luckabaue, Roland WurschumAbstract:ABSTRACTThe present case study demonstrates that high-precision Dilatometry serves as sensitive tool for quantitatively characterising precipitation processes down to small relative length changes ...
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kinetics of vacancy annealing upon time linear heating applied to Dilatometry
Journal of Materials Science, 2018Co-Authors: Robert Josef Enzinger, Wolfgang Sprengel, Chr Neubauer, Jaromir Kotzurek, Roland WurschumAbstract:A kinetic model for the diffusion-controlled annealing of excess vacancies under the experimentally relevant, non-isothermal condition of time-linear heating is presented and applied to Dilatometry. The evolution of the vacancy concentration with time is quantitatively analyzed, considering as ideal sinks either dislocations or grain boundaries of spherical- or cylindrical-shaped crystallites. The validity of the model is tested using Dilatometry data that were obtained for ultrafine-grained Ni prepared by high-pressure torsion. The entire two-stage annealing curve of the dilatometric length change can be analyzed by combining the present kinetic model of vacancy annealing at grain boundaries with established non-isothermal kinetics of recrystallization.
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internal stress and defect related free volume in submicrocrystalline ni studied by neutron diffraction and difference Dilatometry
Philosophical Magazine Letters, 2017Co-Authors: Jaromi Kotzurek, M Hofma, Sanja Simic, Pete Pol, Anto Hohenwarte, Reinhard Pippa, Wolfgang Sprengel, Roland WurschumAbstract:A combined study of neutron diffraction and difference Dilatometry on submicrocrystalline Ni prepared by high pressure torsion aims at studying the anisotropic behaviour during Dilatometry and its relation to internal stress and structural anisotropy. Macroscopic stresses were undetectable in the dilatometer samples. Along with specific tests such as post cold-rolling, this shows that an observed anisotropic length change upon annealing is not caused by internal stress, but can be explained by the inherent microstructure, i.e. the anisotropic annealing of relaxed vacancies at grain boundaries of shape-anisotropic crystallites.
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direct measurement of vacancy relaxation by Dilatometry
Applied Physics Letters, 2016Co-Authors: Jaromi Kotzurek, Anto Hohenwarte, Reinhard Pippa, Wolfgang Sprengel, Eva Maria Steyskal, Ernd Oberdorfe, Roland WurschumAbstract:A model is proposed for directly determining the volume of lattice vacancies by means of dilatometric measurements of the anisotropic irreversible length change which occurs during annealing of lattice vacancies at grain boundaries of shape-anisotropic crystallites. The model is tested using nanocrystalline Ni after the high-pressure torsion deformation which exhibits excess concentration of lattice vacancies and elongated crystallite shape. Different length changes upon annealing parallel and perpendicular to the elongation axis occur from which a vacancy volume can be derived.
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Dilatometry a powerful tool for the study of defects in ultrafine grained metals
Journal of Materials Science, 2012Co-Authors: Wolfgang Sprengel, Eva Maria Steyskal, Ernd Oberdorfe, Roland WurschumAbstract:Vacancies, dislocations, and interfaces are structural defects that are deliberately introduced into solids during grain refinement processes based on severe plastic deformation (SPD). Specific combinations of these defects determine the improved mechanical properties of the obtained ultrafine-grained materials. High-precision, non-equilibrium Dilatometry, i.e., measurement of the irreversible macroscopic length change upon defect annealing, provides a powerful technique for the characterization and the study of the kinetics of these defects. It is applied to determine absolute concentrations of vacancies, to characterize dislocation processes, and to assess grain boundary excess volume in pure, FCC and BCC ultrafine-grained metals processed by SPD.
Randall M German - One of the best experts on this subject based on the ideXlab platform.
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analysis of the effect of solubility on the densification behavior of tungsten heavy alloys using the master sintering curve approach
International Journal of Refractory Metals & Hard Materials, 2013Co-Authors: Seong Jin Park, Youngsam Kwon, John L Johnson, Yunxin Wu, Randall M GermanAbstract:Abstract The densification behavior of 88W–8.4Ni–3.6Fe, 88W–8.4Ni–3.6Cu, and W–15Cu during heating is compared using the master sintering curve (MSC) approach. The MSC parameters, such as the work of sintering, activation energy, and densification ratio, are calculated from Dilatometry tests, based on which the densification is classified into three regions with different sintering mechanisms. This approach enables contrast and comparison of the densification sensitivity to solubility, temperature, and heating rate. The master sintering curves are combined into a master sintering surface that includes integral work and the solubility of tungsten in the liquid phase.
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microstructural evolution of injection molded gas and water atomized 316l stainless steel powder during sintering
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Pavan Suri, Ryan P Koseski, Randall M GermanAbstract:The present study investigates the microstructural evolution and densification behavior of water- and gas-atomized 316L stainless steel powder. Dilatometry and quenching studies were conducted to determine the extent of densification and corresponding microstructural changes. Results indicate that water-atomized powder could be sintered to 97% of theoretical density, while gas-atomized powders could be sintered to near-full density. The difference in the densification behavior is examined in terms of the particle morphology, initial green density and the particle chemistry.
J D Escoba - One of the best experts on this subject based on the ideXlab platform.
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austenite reversion kinetics and stability during tempering of a ti stabilized supermartensitic stainless steel correlative in situ synchrotron x ray diffraction and Dilatometry
Acta Materialia, 2017Co-Authors: J D Escoba, G A Faria, J P Oliveira, Paulo Roberto Mei, Antonio J RamirezAbstract:Abstract Correlative physical simulation, synchrotron x-ray diffraction and laser Dilatometry were used to characterize the surface and volumetric austenite reversion kinetics and stability in a Ti-stabilized supermartensitic stainless steel. A fast heating rate of 500 °C s−1 was used to minimize any martensite to austenite reversion related to the heating stage. This allowed the characterization of the austenite reversion kinetics and its corresponding thermal stability on cooling for tempering temperatures between 600 and 700 °C. In all cases, a soaking time of 9000 s and a cooling rate of 5 °C s−1 were used. The isothermal transformation was divided in two regimes: At and above 625 °C, the kinetics of the transformation was faster and the austenite equilibrium volume fraction was reached. Below 625 °C, the transformation was slower and incomplete. The reverted austenite was stable during cooling after tempering at and below 610 °C, partially stable for temperatures between 625 and 650 °C, and unstable for temperatures between 670 and 700 °C. The austenite Ni content should be higher than 8 wt % in order to effectively stabilize austenite at room temperature. Correlated bulk (Dilatometry) and surface (diffraction) analyses showed very good agreement during the isothermal stage. However, martensitic transformation at the sample surface was evidenced at higher temperatures related to the bulk due to the free surface effect. A reversion TTT diagram and the austenite stability curve were constructed from the in situ x-ray diffraction data, providing tools for microstructural and performance optimization of this material.
Pete Van Puyvelde - One of the best experts on this subject based on the ideXlab platform.
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development of a method for pressure free volumetric Dilatometry of polymer melts and solids
Polymer Testing, 2018Co-Authors: Leande Verbele, Ja Van Humbeeck, Pete Van PuyveldeAbstract:Abstract The tendency of polymers to shrink upon cooling and to expand upon heating strongly affects polymer processing operations. Therefore, quantifying these properties through Dilatometry is crucial. Existing setups to measure Dilatometry are, however, mostly limited to solid samples, or are expensive and impractical to use. Moreover, upcoming forms of polymer processing such as additive manufacturing techniques or more commonly named 3D-printing techniques require these properties to be measured under atmospheric pressure, which is not possible with most of the existing setups. Therefore, this paper describes a novel method for pressure-free volumetric Dilatometry that is able to characterize samples in both liquid and solid phase, and during liquid-solid transitions. The principle of the method is based on the use of a highly viscous confining fluid that, in combination with a simple piston-die sample container, offers a cheap, easy-to-use and safe method to measure volumetric Dilatometry on a variety of samples. The method is verified by comparison with standards and data from literature.