Materials
| About the Journal of Materials Science Robert W. Cahn Best Paper Prize
About the Journal of Materials Science Robert W. Cahn Best Paper Prize
The Editors and Publisher are pleased to announce the launch of the Journal of Materials Science Robert W. Cahn Best Paper Prize (the “Cahn Prize”). The Cahn Prize has been named in honor of the Journal’s founding editor, the late Professor Robert Wolfgang Cahn. This annual prize will recognize a truly exceptional original research paper published in the journal in a particular calendar year. The selection process will follow that adopted for Sapphire Prize, which was awarded in 2011 to mark the Journal’s 45th anniversary. Each month the Editors will select a paper published in that month's issues via a rigorous nomination and voting procedure. The winning paper will be selected from the twelve finalists by a separate panel of distinguished materials scientists. The authors of the winning paper will receive an award of $5,000.
The winning paper was announced on November 27th, 2012, at the Fall 2012 Materials Research Society Meeting
(Those who experience difficulties accessing these papers on SpringerLink.com or link.springer.com may download them here.)
WINNING PAPER October: Room temperature fracture processes of a near-α titanium alloy following elevated temperature exposure
A. L. Pilchak (Air Force Research Laboratory, Materials and Manufacturing Directorate), W. J. Porter (University of Dayton Research Institute), and R. John (Air Force Research Laboratory, Materials and Manufacturing Directorate)
From the issue entitled "Sintering and Microstructural Development"…In this work, monotonic and fatigue fracture mechanisms of Ti–6Al–2Sn–4Zr–2Mo–0.1Si samples exposed to laboratory air at 650 °C for 420 h were identified by means of a combination of quantitative tilt fractography, metallographic sectioning, and electron backscatter diffraction. These mechanisms were compared and contrasted with those operative during similar tests performed on material is the as-received condition with uniform oxygen content. While faceted fracture was not observed during quasi-static loading of virgin material, locally elevated concentrations of oxygen near the surfaces of exposed samples were shown to change the fracture mode from ductile, microvoid coalescence to brittle facet formation and grain boundary separation at stresses below the macroscopic yield point. Similar features and an increased propensity for facet formation were observed during cyclic loading of exposed samples…
December: Wetting of calcium fluoride by liquid metals
Shmuel Barzilai, Natalya Froumin, Eugene Glickman, David Fuks, and Nahum Frage
The results of wetting experiments for the CaF2/Me and CaF2/Me–Ti systems (Me = Cu, Ge, Al, In, Ga, Sn, and Au) are presented and discussed. It was found that pure metals do not wet the CaF2 substrate, while a small quantity of Ti added to the melt improves the wetting. The effect of Ti depends on its thermodynamic activity in the melts. According to the thermodynamic analysis and experimental observations, Ti dissolved in the metals does not react with the substrate to form any new condensed phase at the interface and its effect cannot be attributed to the “reactive wetting” phenomenon. Density functional theory (DFT) was applied to focus on the nature of chemical bonding between the atoms in the melt and the surface of the substrate in these systems. It was demonstrated that partly filled d-states of Ti stimulate its adsorption onto F ions. Ab initio calculations show that Ti may segregate to the interface, decreasing the energy of CaF2/Me–Ti system. Based on the results of thermodynamic and DFT analyses, it is proposed that Ti segregation at the interface may be considered as the source of the improved wetting.
November: First principles calculations of oxygen vacancy-ordering effects in resistance change memory materials incorporating binary transition metal oxides
Blanka Magyari-Köpe, Seong Geon Park, Hyung-Dong Lee, Yoshio Nishi
...We have employed first principles simulations based on density functional theory to elucidate the effect of oxygen vacancies on the electronic structure of rutile TiO2 and NiO using the local density and generalized gradient approximations with correction of on-site Coulomb interactions (LDA + U for TiO2 and GGA + U for NiO). We find that an ordered oxygen vacancy filament induces several defect states within the band gap of both materials, and can lead to the defect-assisted electron transport. This state may account for the “ON”-state low resistance conduction observed experimentally in rutile TiO2 and NiO. As the filament structure is perturbed by oxygen ions moving into the ordered chain of vacancies under applied electric field, charges are trapped and the conductivity can be significantly reduced. We predict this partially disordered arrangement of vacancies may correspond to the “OFF”-state of the resistance change memories.
September: The effect of indentation-induced microcracks on the elastic modulus of hydroxyapatite
X. Fan, E. D. Case, M. J. Baumann
…In this study, an array of Vickers indentation-induced microcracks was placed on the surfaces of two hydroxyapatite (HA) specimens with totals of 391 and 513 indentations per specimen. This study tests the validity of theoretical studies of microcrack damage-induced changes in E and υ, where the changes are expressed either by (i) the volumetric crack number density, N and (ii) the crack damage parameter, ε. All elasticity measurements were done via resonant ultrasound spectroscopy. For both the HA specimens included in the study and alumina specimens indented in an earlier study [J Mater Sci 38:1910. doi: 10.1007/BF00595764, 1],E and υ decreased approximately linearly with increasing microcrack damage. The slopes of the Eand υ versus N and ε are also computed and compared to the available theoretical models.
August: Phase transformations and segregation in Fe–Ni alloys and nanoalloys
M. Byshkin, Marc Hou
Ordering and segregation properties of Fe–Ni alloys and nanoalloys are investigated by means of Metropolis Monte Carlo (MMC) and molecular dynamics (MD) simulations. The model is based on an embedded atom potential which, according to thermodynamic integration, only stabilizes those phases that are observed experimentally. This stability is confirmed by MMC and the same phases are found stable in truncated octahedral nanoparticles containing no more than 201 atoms. At given composition, Ni segregates at {100} and nanoparticle surfaces on the Fe-rich side of the phase diagram, Fe segregates at intermediate compositions and no significant trend is predicted on the Ni-rich side. A BCC to L10 transition is observed to occur at a Ni fraction close to 0.32, both in bulk alloys and in nanoparticles. The transition gives rise to a change in the nanoparticle aspect ratio by a factor 21/2. Using MD, by varying temperature, it was possible to monitor a BCC to FCC transition in solid solution nanoparticles reversibly.
July: Dislocation structure at a {1210}/⟨101−0⟩ low-angle tilt grain boundary in LiNbO3
Atsutomo Nakamura, Eita Tochigi, Jun-nosuke Nakamura, Ippei Kishida and Yoshiyuki Yokogawa
LiNbO3 is a ferroelectric material with a rhombohedral R3c structure at room temperature. A LiNbO3 bicrystal with a {1−21−0}/⟨101−0⟩ 1° low-angle tilt grain boundary was successfully fabricated by diffusion bonding. The resultant boundary was then investigated using high-resolution TEM. The boundary composed a periodic array of dislocations with b=1/3⟨1−21−0⟩ . They dissociated into two partial dislocations by climb. A crystallographic consideration suggests that the Burgers vectors of the partial dislocations should be 1/3⟨011−0⟩ and 1/3⟨1−100⟩ , and a stacking fault on {1−21−0} is formed between the two partial dislocations. From the separation distance of a partial dislocation pair, a stacking fault energy on {1−21−0} was estimated to be 0.25 J/m2 on the basis of isotropic elasticity theory.
June: Preparation of mesoscopic gold rings and split rings by selective wetting of the contact points between the spheres within colloidal crystals
Sabine Kaufmann, Herbert Schletter, Daniel Lehmann, Francisc Haidu, Dietrich R. T. Zahn, Michael Hietschold and Werner A. Goedel
Rings and split rings of sub-micrometer size are prepared by the infiltration of colloidal crystals of spherical silica particles with diameters of about 1 μm by diluted solutions of tetrachloroauric acid in butanone, followed by the evaporation of the butanone, the annealing of the samples at elevated temperatures and the removal of the silica spheres with hydrofluoric acid. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and electron backscatter diffraction investigations reveal that the obtained rings and split rings are made out of metallic gold.Electronic supplementary material The online version of this article (doi:10.1007/s10853-012-6307-4) contains supplementary material, which is available to authorized users.
May: Quasi chemical and defect correlation models for intermetallic compounds with B2-structure: new applications
Olga Semenova, Regina Krachler
...Both modeling approaches were applied for description of thermodynamic activities and vacancy concentrations over composition range and temperature in non-stoichiometric B2 ordered intermetallic compounds with triple-defect mechanism (PdIn, NiGa, and CoGa), as well as with substitutional (anti-structure) defect mechanism (FeCo, NiZn, AgMg). The (hypothetical) critical temperatures of the order–disorder transformations were derived from the model calculations. Comparison with a wealth of experimental data provided in the literature confirms the viability of these simple models.
April: Connecting the macro and microstrain responses in technical porous ceramics. Part II: microcracking
Giovanni Bruno, Alexander M. Efremov, Chong P. An, Bryan R. Wheaton, Darren J. Hughes
...Confirming our previous study, we observed that macrostrain relaxation occurs at constant load, which is not observed in non-microcracked compounds, such as SiC. This relaxation effect increases as a function of porosity. Moreover, we generally observed a linear dependence of the diffraction modulus on porosity. However, for low and very high applied stress, the lattice strain behavior versus stress seems to be influenced by microcracking and shows considerable strain release, as already observed in other porous microcracked ceramics. We extended to microcracked porous ceramics (cordierite) the macro to microstrain and stress relations previously developed for non-microcracked ceramics, making use of the integrity factor (IF) model. Using the whole set of data available, the IF could also be calculated as a function of applied stress. It was confirmed that highly porous microcracked materials have great potential to become stiffer and more connected.
March: Surface form memory in NiTi shape memory alloys by laser shock indentation
Xueling Fei, David S. Grummon, Chang Ye, Gary J. Cheng, Yang-Tse Cheng
An indentation-planarization method for NiTi shape memory alloys has been developed that produces a robust surface topographical memory effect that we call "surface form memory", or SFM... In the dynamical case however, relative cyclic two-way displacements are found to be significantly larger, when normalized to the initial indent depth, than is the case with quasistatic indentation. This confers certain processing and boundary condition advantages. Analysis of the shock dynamics is found to be consistent with the observed surface displacements.
February: Structure of multilayer ZrO2/SrTiO3
Wei Li Cheah, Michael W. Finnis
Multilayered oxide heteroepitaxial systems, including that of a 1-nm-thick Y2O3-stabilised ZrO2 (YSZ) sandwiched between layers of SrTiO3 (STO) [1], have been a subject of much interest lately due to their significantly enhanced ionic conductivities as compared to the bulk materials... We find that the fluorite ZrO2 phase is unstable as a coherently strained epitaxial layer in the multilayer system. Instead, anatase-, columbite-, rutile-, and pyrite-like ZrO2 epitaxies are found to be more stable, with the anatase-like epitaxy being the most stable structure over a wide range of chemical potential of the components. We also find a high energy metastable structure resembling the tetragonal fluorite structure which is predicted by DFT to be stabilised by SrO-terminated STO but not by TiO2-terminated STO.
January: Studying grain boundary regions in polycrystalline materials using spherical nano-indentation and orientation imaging microscopy
Siddhartha Pathak, Johann Michler, Kilian Wasmer, Surya R. Kalidindi
... [W]e demonstrate that it is possible to investigate the role of grain boundaries in the mechanical deformation of polycrystalline samples by systematically studying the changes in the indentation stress–strain curves as a function of the distance from the grain boundary. Such datasets, when combined with the local crystal lattice orientation information obtained using orientation imaging microscopy, open new avenues for characterizing the mechanical behavior of grain boundaries based on their misorientation angle, dislocation density content near the boundary, and their propensity for dislocation source/sink behavior.