Results 1 - 10 of 301657
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[en] Presented are the results of thermal cycling tests carried out on REC and NdFe samples, to determine the irreversible losses in room temperature open circuit magnetic moment. A stabilization prescription was developed for a REC alloy that will allow two 4day/1750C temperature cycles, which simulate two UHV bakeouts, with only a 0.35% average loss and a 0.65% loss variation in the room temperature open circuit magnetic moment after stabilization
[en] Fe atoms, when trapped in frozen NH3 matrixes, react to form the molecules FeNH3 . This species provides a model for the study of the interactions of NH3 with Fe surfaces . The Moessbauer spectrum shows two narrow peaks of equal intensity, which suggests a quadrupole interaction and a well defined Fe site. The Isomer Shift measured is different from that of Fe atoms in rare gas matrixes. Moessbauer experiments in the presence of an external magnetic field reveal a large positive magnetic hyperfine field . We have employed all-electron spin-polarized Discrete Variational Method (DVM) in the local density approximation, as has been described in details elsewhere , to obtain values for the hyperfine parameters, as described below, of FeNH3. (author)
[en] The C1b and Fm-3m phases of CoMnZ (Z=P, As, Sb) were studied via first-principle calculations. The C1b CoMnZ exhibits half-metallicity and is more energetically stable than Fm-3m CoMnZ. Under volume distortions, CoMnP, CoMnAs, and CoMnSb can maintain half-metallicity for volume alterations of -16% to 16%, -20% to 11%, and -32% to 0%, respectively. Under tetragonal distortions, CoMnP, CoMnAs, and CoMnSb can maintain half-metallicity from a change of in-plane lattice constants of 0.500-0.580, 0.515-0.585, and 0.545-585 nm, respectively. - Research highlights: → C1b structure is more energy favored in CoMnZ (Z=P, As, Sb) compounds. → C1b CoMnZ (Z=P, As, Sb) are all half-metals at equilibrium lattice constant. → Half-metallicity in CoMnZ (Z=P, As, Sb) is retained in considerable volume distortion. → Half-metallicity in CoMnP and CoMnAs is more robust than CoMnSb under tetragonal distortion.
[en] A significant exchange bias (EB) training effect has been observed in sputter deposited FeAu/FeNi bilayers, wherein the exchange field (HE) exhibits a special sign-changeable temperature dependence. Very interestingly, despite the absence of multiple easy axes in the FeAu spin glass (SG) layer, HE drops abruptly between the first and second magnetic cycles, which is followed by a more gradual continuous change in the subsequent cycles. This training behavior cannot be described by the empirical n−1/2 law because of the asymmetric magnetization reversal processes. We propose modifying Binek's model to include the asymmetric changes of the pinning SG spins at the descending and ascending branches. This new model successfully describes the EB training effect in FeAu/FeNi bilayers. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
[en] Highlights: • The Al desolated from β-NiAl to react with Cr to produce γ′-Ni3Al + CrAl phases. • The incorporation of Co homogenizes the distribution of β-NiAl phase and Y. • Adhesive wear dominated the wear mechanism of NiCrAlY/Si3N4 tribo-pair. • Abrasive wear was the main wear mechanism for NiCoCrAlY/Si3N4 tribo-pair. • The higher hardness of NiCrAlY may contributed to the lower wear than NiCoCrAlY. In order to explore the mechanical and tribological properties of high-temperature alloy materials, the present study aims to investigate the synthesis, microstructure, composition, mechanical and tribological properties of high-temperature monolithic MCrAlY (M = Ni or NiCo) alloys. The alloys were prepared by spark plasma sintering technique. The microstructure and composition were studied by Scanning Electron Microscopy and X-ray diffractometry. The tribological properties of Ni-based alloys were tested by friction tester against Si3N4 balls at elevated temperatures. The results showed that the NiCrAlY alloy was composed of γ-Ni(Cr) solid solution, β-NiAl, and γ′-Ni3Al with little CrAl. The NiCoCrAlY alloy was consisted of γ-Ni(Cr/Co) solid solution, β-NiAl and γ′-Ni3Al. The hardness of NiCrAlY alloy was higher than that of NiCoCrAlY alloy. However, its flexural strength was lower than the NiCoCrAlY alloy. The more uniform microstructure of NiCoCrAlY alloy along with the evenly dispersed fine reinforced phases and the less pores defects contributed to the higher flexural strength. The μs and WRs of NiCrAlY and NiCoCrAlY alloys increased firstly to reach the highest value at 200 and 400 °C, and then declined with the temperature increasing to 800 °C. The WRs of NiCrAlY were lower than that of NiCoCrAlY for all the temperatures. Adhesive wear dominated the wear mechanism of NiCrAlY/Si3N4 tribo-pair, while abrasive wear was the main wear mechanism for NiCoCrAlY/Si3N4 tribo-pair. At high temperature, oxidation of worn surfaces to a certain extent decreased the wear for both the tribo-pairs. The higher hardness of NiCrAlY may contributed to the lower wear than NiCoCrAlY.