Materials Structure & Micromechanics of Fracture VI

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Authors: Zbigniew Marciniak, Dariusz Rozumek
Abstract: The paper contains the fatigue test results of rectangular cross-section specimens made of 10HNAP steel. The specimen height to width ratio was 1.5. Bending with torsion tests were carried out for the following ratios of bending to torsional moments MaB / MaT = 0.47, 0.94, 1.87 and the loading frequency 26.5 Hz. The tests were performed in a high cycle fatigue regime for the stress ratio R = - 1 and phase shift between bending and torsion loading equal to  = 0.
187
Authors: Chi Ping Lai, Luen Chow Chan, Tai Chiu Lee
Abstract: This paper aims at presenting an experimental investigation to compare the rolling behaviors of selected materials under profile rolling process. Copper alloy (C37700), aluminum alloy (AA6063) and stainless steel (AISI304) in 6 mm diameter were selected as rolling specimens. The process parameters, i.e. spindle speed, forward speed, and fractorgraphic analysis were carried out to determine the deformation behaviours of selected materials. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality precision components efficiently.
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Authors: Jenő Gubicza, Nguyen Q. Chinh, Sergey V. Dobatkin, E. Khosravi, Terence G. Langdon
Abstract: The thermal stability of ultrafine-grained (UFG) microstructure in face centered cubic metals processed by severe plastic deformation (SPD) was studied. The influence of the SPD procedure on the stability was investigated for Cu samples processed by Equal-Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT), Multi-Directional Forging and Twist Extrusion at room temperature (RT). It is found that HPT results in the lowest thermal stability due to the very high dislocation density. Furthermore, the effect of the low stacking fault energy of Ag on the stability is also investigated. It is revealed that the UFG microstructure produced in Ag by ECAP is recovered and recrystallized during storage at room temperature. The driving force for this unusual recovery and recrystallization is the high dislocation density developed during ECAP due to the high degree of dislocation dissociation caused by the very low stacking fault energy of Ag.
195
Authors: Alena Michalcová, Dalibor Vojtěch, Pavel Novák, Ivan Procházka, Jakub Čížek, Jan Drahokoupil, Kateřina Wienerová, Karel Saksl, Pawel Rokicki, Zdeněk Spotz
Abstract: An alloy containing Al – 3wt.% Cr – 3wt.% Fe – 0.8wt. % Ce, was prepared by melt spinning. Structure of obtained ribbons was observed by light, scanning and transmission electron microscopy. It was found out that the structure is very fine. Microhardness of cross sectioned ribbons was also measured. Defects in structure were determined by positron annihilation spectroscopy. The thermal stability of the alloy was observed by comparing rapidly solidified ribbons and ribbons annealed at 400°C and at 500°C for 100 h
199
Authors: L. Hong, A.K. Soh
Abstract: A three dimensional phase field model has been devised to account for the manipulation of domain states in individual ferroelectric (PbTiO3) nanoparticles. Vortex structures and dipole flux domain patterns were obtained by applying tensile and compressive strains, respectively. The direction of the two domain configurations was found to correlate with the plane on which the strains were applied, mainly due to dipole-strain coupling and depression of depolarizing field.
203
Authors: Matthias Funk, Christoph Eberl
Abstract: In this paper data on fatigue lifetime of nanocrystalline (nc) Ni samples is presented. The nc-Ni samples show high lifetimes and can resist large stress amplitudes. Furthermore a new method to determine the fatigue limit based on a Fourier analysis [7] is presented. First results of a load increase test suggest strong parallels to thermal and resistive measurements which can be used to determine the fatigue limit. Microstructural investigations on as received and failed samples show a strong increase in grain size induced by the cyclic loading. The processes behind this are not understood so far and will be investigated in the future.
207
Authors: A.V. Pak, Nikolay G. Lebedev
Abstract: The results of theoretical quantum-statistical research of atomic hydrogen adsorption on the graphene surface within the framework of the periodic Anderson’s model have been presented. The band structure of graphene with adsorbed hydrogen atoms is calculated by the Green's function method. The work is supported by The Education Ministry of Russian Federation (project No. NK-16(3)).
211
Authors: Jenő Gubicza, E. Khosravi, Vladimir V. Stolyarov
Abstract: Ultrafine-grained (UFG) CP titanium (Grade-4) sample was processed by electroplastic rolling (EPR) at room temperature which was compared to a specimen processed by conventional cold rolling (CR). EPR was performed using pulsed unidirectional current with a current density of 95 A/mm2, pulse duration of 10-4 s and frequency of 1000 Hz. It was found that the sample processed by EPR has slightly higher dislocation density and smaller crystallite size than for the CR specimen resulting in a higher tensile strength for the former specimen. In the case of EPR sample, the relative fraction of dislocations is lower than for CR specimen. During annealing the relative fraction of dislocations decreased for both samples which can be explained by the fact that the dislocations have larger Burgers-vector and consequently higher formation energy than the other two types.
215
Authors: Grzegorz Moskal, Andrzej Grabowski
Abstract: This article describes the microstructures, chemical and phase compositions, surface morphologies, and internal structures of three ZrO2 x 8Y2O3-type of powders obtained by different manufacturing methods. The first of the analyzed powders was a conventionally prepared form of the material obtained by the spraying method. The second powder was a spherically shaped form of the material obtained from the spray drying process. It displayed a distinctive surface morphology characterized by a rough structure with visible cavities. The particle sizes of these two powders were comparable. The third form of the powder was classified as “nano” and was obtained by a grinding and crushing method. The shapes of individual particles were generally polyhedral with smooth surfaces and no visible porosity. A study of the chemical composition of each form of the powder did not show significant differences, similar to the results obtained from the phase composition study. The results of thermal diffusivity and electrical impedance studies indicated that the electrical and thermal properties of the powders with spherical structures, i.e., sprayed and spray drying, were very similar. The thermal diffusivity and impedance properties of these two powders were greater than those of the ground powder with a finer grain size.
219
Authors: Anja Weidner, Maxime Sauzay, Werner Skrotzki
Abstract: Cyclic slip irreversibility is one of the most important features of fatigue processes in ductile metals because it induces surface relief evolutions during cycling which are mainly responsible for crack initiation. The reversible and irreversible parts of the slip within persistent slip bands (PSBs) in polycrystalline nickel are measured directly after half-cycle deformation and one full cycle on specimen surfaces once more well-polished after 60% of fatigue life using atomic force microscopy (AFM) and different techniques of scanning electron microscopy as electron channelling contrast imaging and electron backscattered diffraction. Using AFM measures on the same slip steps after half-cycle and full cycle, the cyclic slip irreversibility factor is directly evaluated and discussed with respect to the literature.
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