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Analysis of the residual stress and bonding mechanism in the cold spray technique using experimental and numerical methods
No full textIn the current study, numerical solutions were used to simulate multi-particle deposition in the cold spray (CS) process, and to investigate some of the physical attributes of the deposition process of AA-6061-T6 particles deposited on an AA-6061-T6 substrate. Earlier experimental results are presented, with varying substrate and cladding combination; a subset of these results is analysed using single particle impact simulation, a more traditional approach in simulations of cold spray, and the smooth particle hydrodynamic (SPH) formulation to simulate multi-particle deposition. In a single particle impact simulation, a strong correlation between temperature and plastic deformation of the CS particles during the deposition process was found. The authors were able to correlate the onset of adiabatic shear instability with pronounced reduction in the flow stress with an inversely proportional relation exhibited for both temperature rise and plastic deformation. In the simulation of multiple particle impact, 400 particles, several bulk characteristics were extracted as through-thickness functions: density, equivalent plastic strain and stress profile. Stress profile from the simulation was contrasted against neutron diffraction measurements of residual stress, along with the analytical model of Tsui and Clyne, and is shown to achieve good correlation and providing validation of the results of simulations. Furthermore it was found that these stresses originate from a delicate balance between (a) the strain rate hardening and thermal softening and (b) the shot peening effects induced by the impact of CS particles. Analysis of particle morphologies in the simulation suggests a strong influence of temperature rise at the periphery of CS particles during deposition and dynamic recrystallization with the strong jetting of molten metal allowing for inter particle mixing and substrate adhesion. © 2014, Elsevier B.V
The thermal decomposition of hydronium jarosite and ammoniojarosite
No full textThe thermal decomposition of hydronium jarosite and ammoniojarosite was studied using thermogravimetric analysis and mass spectrometry, in situ synchrotron X-ray diffraction and infrared emission spectroscopy. There was no evidence for the simultaneous loss of water and sulfur dioxide during the desulfonation stage as has previously been reported for hydronium jarosite. Conversely, all hydrogen atoms are lost during the dehydration and dehydroxylation stage from 270 to 400 °C and no water, hydroxyl groups or hydronium ions persist after 400 °C. The same can be said for ammoniojarosite. The first mass loss step during the decomposition of hydronium jarosite has been assigned to the loss of the hydronium ion via protonation of the surrounding hydroxyl groups to evolve two water molecules. For ammoniojarosite, this step corresponds to the protonation of a hydroxyl group by ammonium, so that ammonia and water are liberated simultaneously. Iron(II) sulfate was identified as a possible intermediate during the decomposition of ammoniojarosite (421–521 °C) due to a redox reaction between iron(III) and the liberated ammonia during decomposition. Iron(II) ions were also confirmed with the 1,10-phenanthroline test. Iron(III) sulfate and other commonly suggested intermediates for hydronium and ammoniojarosite decomposition are not major crystalline phases; if they are formed, then they most likely exist as an amorphous phase or a different low temperature phases than usual. © 2013, Akadémiai Kiadó, Budapest, Hungary
Direct evidence of Ni magnetic moment in TbNi2Mn—X-ray magnetic circular dichroism.
No full textWe have investigated the individual magnetic moments of Ni, Mn and Tb atoms in the intermetallic compound TbNi2Mn in the Laves phase (magnetic phase transition temperature TC ~131 K) by X-ray magnetic circular dichroism (XMCD) studies at 300 K, 80 K and 20 K. Analyses of the experimental results reveal that Ni atoms at 20 K in an applied magnetic field of 1 T carry an intrinsic magnetic moment of spin and orbital magnetic moment contributions 0.53±0.01 μB and 0.05±0.01 μB, respectively. These moment values are similar to those of the maximum saturated moment of Ni element. A very small magnetic moment of order <0.1 μB has been measured for Mn. This suggests that Mn is antiferromagnetically ordered across the two nearly equally occupied sites of 16d and 8a. A magnetic moment of up to ~0.3 μB has been observed for the Tb atoms. Identification of a magnetic moment on the Ni atoms has provided further evidence for the mechanism of enhancement of the magnetic phase transition temperature in TbNi2Mn compared with TbNi2 (TC~37.5 K) and TbMn2 (TC~54 K) due to rare earth–transition metal (R–T) and transition metal–transition metal (T–T) interactions. The behaviour of the X-ray magnetic circular dichroism spectra of TbNi2Mn at 300 K, 80 K and 20 K – above and below the magnetic ordering temperature TC ~131 K – is discussed. © 2014 Elsevie
A novel silicon microdosimeter using 3D sensitive volumes: modeling the response in neutron fields typical of aviation
No full textA 4th generation silicon microdosimeter has been designed by the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong using three dimensional (3D) Sensitive Volumes (SVs). This new microdosimeter design has the advantage
of well-defined 3D SVs as well as the elimination of lateral charge diffusion by removal of silicon laterally adjacent to the
3D SVs. The gaps between the sensitive volumes are to be backfilled
with PolyMethyl MethAcrylate (PMMA) to produce a surrounding tissue equivalent medium. The advantage of this design
avoids the generation of secondary particles from inactive silicon lateral to SVs. The response of the microdosimeter to the neutron
field from , Pu-Be sources and an avionic radiation environment were simulated using the Geant4 Monte Carlo toolkit for design
optimisation. The simulated energy deposition in the SVs from
the neutron fields and microdosimetric spectra is presented. The simulation study shows a significant reduction in silicon nuclear recoil contribution to the energy deposition for the novel microdosimeter
design. The reduction of silicon recoil events from outside of the SV’s will consequently reduce the uncertainty in the calculateddose equivalent. The simulations have demonstrated that a 3D silicon microdosimeter surrounded by PMMA can produce
microdosimetric spectra similar to those of a tissue equivalent microdosimeter. © 2014, IEEE
Martensitic Phase Transformation and Deformation Behavior of Fe–Mn–C–Al Twinning-Induced Plasticity Steel during High-Pressure Torsion
No full textThe transformation between the face centered cubic austenitic and hexagonal close-packed martensitic
phases during high-pressure torsion processing was observed in a Fe–Mn–C–Al twinning-induced
plasticity steel. This phase transformation was not found in the same material processed by
unidirectional compressive and tensile deformation. Initiated by the high-pressure loading, the
martensite phase initially increased with torsional strain but diminished subsequently. Texture
evolution of the austenitic phase was compared with the ideal texture distribution of face-centered cubic
materials after shear deformation.© 2014, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Electronic and vibrational properties of yttria-stabilised zirconia from first-principles for 10–40 mol% Y2O3
No full textDensity-functional theory calculations are performed to investigate the electronic and vibrational density-of-states (DOS) for a series of recently predicted stable and metastable structures of yttria-stabilised zirconia (YSZ) with yttria (Y2O3) concentrations of 14, 17 and 20 mol%. Analogous quantities are also studied for the so-called δ-phase, which forms for 40 mol% yttria, as well as for model structures with ≈10.3 mol% yttria. These calculated results, together with those for the cubic, tetragonal and monoclinic phases of ZrO2, afford a comparison of structural, electronic and vibrational properties as a function of yttria concentration. With increasing yttria content, the electronic DOS exhibit a decrease in the valence band-width (of about 2.0 eV relative to the cubic phase) and a corresponding increase of the band-gap of 0.73 eV (from cubic to 40 mol% yttria containing ZrO2). Regarding the vibrational DOS (vDOS), the addition of yttria causes the peaks in the vDOS of ZrO2 to become less distinct, reflecting the more dense occupation of states due to the larger number of atoms in each primitive cell, and to the lower symmetry. The vDOS of the various YSZ structures appear qualitatively similar with contributions from O atoms spanning the whole frequency range and cation related contributions present for frequencies View the MathML source. With increasing yttria content, more Zr atoms become seven-fold coordinated as in monoclinic ZrO2, concominantly the vDOS increasingly resembles that of m-ZrO2, but with notable contributions from Y atoms, which has a main peak at about 17 meV, similar to that of Zr atoms. © 2014 Elsevier Ltd
Preface for Special Issue of Marine Geology: In the wake of the 2011 Tohoku-oki tsunami – three years on
No full textThe 2011 Tohoku-oki event that devastated the northeast coast of Japan gives us a rare opportunity to improve our knowledge about tsunami deposits. Before this event the geological evidence of historical and prehistoric tsunamis was generally not included in tsunami mitigation plans. The 2011 event clearly forces all those working on tsunami disaster mitigation to rethink the importance of geological data as a key line of evidence for understanding magnitudes intervals and magnitudes.
The geological work related to this tsunami is of global interest. It is the appropriate time to produce a special issue that includes papers presenting a more in-depth analysis of the deposits, more highly developed numerical modeling, and analysis of high-resolution pre- and post-tsunami DEM data for the 2011 Tohoku-oki tsunami. The papers in this special issue provide many new insights to help us better understand the nature of the tsunami deposits, both onshore and offshore.
This special issue includes 11 original papers and 1 review paper related to the 2011 Tohoku-oki tsunami event. The papers comprising this special issue of Marine Geology are focused on four primary topics:
1)
Onshore sedimentation and erosion (Nandasena et al., 2013 (reprinted); Fujiwara and Tanigawa, 2014, Goto et al., 2014a, Koiwa et al., 2014, Schneider et al., 2014 and Yamada et al., 2014)
2)
Offshore sedimentation and erosion (Ikehara et al., 2014--this issue and Kitahashi et al., 2014)
3)
Linkage of offshore and onshore sedimentation by modeling (Sugawara et al., 2014)
4)
Reinterpretation of beach ridge formation (Goff and Sugawara, 2014)
5)
Terminology and social relevance (Goff et al., 2014 and Goto et al., 2014b
The 2011 Tohoku-oki tsunami — three years on
No full textThe 2011 Tohoku-oki tsunami that devastated the Pacific coast of Tohoku, Japan was a turning point for modern research. As a result of this event it was recognized that paleotsunami research is vital to help understand the size and recurrence interval of low-frequency large tsunamis. This paper reviews the progress of geological research on the 2011 Tohoku-oki tsunami and summarizes new questions that are arising out of this work. For example, recent work suggests that the landward extent and thickness of the sandy deposit, as well as the presence or absence of marine microfossils in the sediment are most likely to be mainly controlled by the initial wave properties, sediment source, offshore bathymetry and onshore topography. This in turn implies that there are certain relationships between the characteristics of a tsunami deposit and the wave properties and it may be possible to reconstruct the latter from the deposits.
Offshore tsunami deposits related to the 2011 Tohoku-oki tsunami have also been well described. This recent research indicates that sedimentation and erosion in inner bay and open ocean (~ 20 m water depth) locations can be in the order of several meters, suggesting that the tsunami shear force was strong in the nearshore zone. On the other hand, sandy to muddy deposits a few centimeters thick were observed at about 100 to 6000 m water depth. It is likely that the tsunami resulted in resuspension of sea bottom sediments and that suspended material flowed downslope as a turbidity current or suspended flow, although many authors recognize the possibility that strong earthquake groundshaking might have also generated turbidity currents.
Studies of the 2011 Tohoku-oki event have led researchers back to two of the fundamental issues of tsunami geology: understanding the linkage between onshore and offshore sedimentation and erosion, and establishing identification criteria for tsunami deposits. Moreover though, beyond the issue of simple tsunami geology, it is important for all researchers to communicate with governments and the general public in order to reduce future casualties by using risk assessments based on our understanding of infrequent large tsunamis.© 2014, Elsevier B.V
Intermolecular interactions in solid-state metalloporphyrins and their impacts on crystal and molecular structures
No full textA variable-temperature (VT) crystal structure study of [Fe(TPP)Cl] (TPP2– = meso-tetraphenylporphyrinate) and Hirshfeld surface analyses of its structures and previously reported structures of [M(TPP)(NO)] (M = Fe, Co) reveal that intermolecular interactions are a significant factor in structure disorder in the three metalloporphyrins and phase changes in the nitrosyl complexes. These interactions cause, for example, an 8-fold disorder in the crystal structures of [M(TPP)(NO)] at room temperature that obscures the M–NO binding. Hirshfeld analyses of the structure of [Co(TPP)(NO)] indicate that the phase change from I4/m to P1̅ leads to an increase in void-volume percentage, permitting additional structural compression through tilting of the phenyl rings to offset the close-packing interactions at the interlayer positions in the crystal structures with temperature decrease. X-ray and neutron structure studies of [Fe(TPP)Cl] at 293, 143, and 20 K reveal a tilting of the phenyl groups away from being perpendicular to the porphyrin ring as a result of intermolecular interactions. Structural similarities and differences among the three complexes are identified and described by Hirshfeld surface and void-volume calculations.© 2014, American Chemical Society
Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)
No full textAnalysis of the CO2 adsorption properties of a well-known series of metal–organic frameworks M2(dobdc) (dobdc4− = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe, Co, Ni, Cu, and Zn) is carried out in tandem with in situ structural studies to identify the host–guest interactions that lead to significant differences in isosteric heats of CO2 adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO2 within many of these materials while systematically varying both the amount of CO2 and the temperature. Unlike previous studies, we show that CO2 adsorbed at the metal cations exhibits intramolecular angles with minimal deviations from 180°, a finding that indicates a strongly electrostatic and physisorptive interaction with the framework surface and sheds more light on the ongoing discussion regarding whether CO2 adsorbs in a linear or nonlinear geometry. This has important implications for proposals that have been made to utilize these materials for the activation and chemical conversion of CO2. For the weaker CO2 adsorbents, significant elongation of the metal–O(CO2) distances are observed and diffraction experiments additionally reveal that secondary CO2 adsorption sites, while likely stabilized by the population of the primary adsorption sites, significantly contribute to adsorption behavior at ambient temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO2 angles and trends in relative geometric properties and heats of adsorption in the M2(dobdc)–CO2 adducts. © 2014, The Royal Society of Chemistry