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Materials | About the 2014 Journal of Materials Science Robert W. Cahn Best Paper Prize

About the 2014 Journal of Materials Science Robert W. Cahn Best Paper Prize

The Editors and Publisher are pleased to announce the monthly finalists for the 2014 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.

Each month the Editors selected 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.

January: The control of crack arrays in thin films 

Jiexi Huang, Byoung Choul Kim, Shuichi Takayama, and M. D. Thouless

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...The control of crack arrays depends on the nature of the intrinsic flaw population. If there is a relatively large density of long flaws, as commonly assumed in fracture mechanics analyses, reliable crack patterns can be obtained fairly robustly using relatively blunt geometrical features to initiate cracks, provided the applied strain is carefully matched to the properties of the system and the desired crack spacing. This process is analyzed both for cracks confined to the thickness of a film and for cracks growing into a substrate. The latter analysis is complicated by the fact that increases in strain can either drive cracks deeper into the substrate or generate new cracks at shallower depths. If the intrinsic flaws are all very short, the geometrical features need to be very sharp to achieve the desired patterns...

February: Evolution of tin whiskers and subsiding grains in thermal cycling 

Ying Wang, John E. Blendell, and Carol A. Handwerker

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The evolution of surface morphology, including whisker formation, grain boundary cracking, and subsiding grains, was studied in Sn thin films on Si substrates with a Cu interlayer during thermal cycling from −40 to 85 °C in air for up to 250 cycles and was compared with surface morphologies resulting from room temperature aging. Multiple areas were tracked, and the areal density of whiskers and the grain morphologies within these areas were monitored over time for room temperature aging and with increasing number of thermal cycles. During room temperature aging, the whisker density increased with time until saturation ~3 weeks after plating. As for thermal cycling, the whisker density was observed first to increase but then to decrease as a result of a whisker pinch-off phenomenon. The characteristic features of whiskers formed during thermal cycling included the formation of deep grooves along the in-plane grain boundaries of whiskers (“whisker root”), a decrease in whisker radii as they grew, striation rings on whiskers perpendicular to the whisker growth direction, corresponding striations along grooved surfaces in the film, albeit at different spatial periodicities than those on their corresponding whiskers, and whisker pinch-off as whiskers became prone to fracture as their radii decreased. Whiskers formed during room temperature aging did not display such grooving or pinch-off. A whisker pinch-off model was proposed to explain the observed morphological changes and the resulting decrease in whisker density during thermal cycling, with a calculated whisker growth rate that agrees with the experimental observation.

March: Mechanical characterization of hollow ceramic nanolattices 

by Lucas R. Meza and Julia R. Greer

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...In situ uniaxial compression experiments performed in combination with finite element analysis on individual unit cells revealed that the TiN was able to withstand tensile stresses of 1.75 GPa under monotonic loading and of up to 1.7 GPa under cyclic loading without failure...

April: Impact of different coating processes of microfibrillated cellulose on the mechanical and barrier properties of paper 

Nathalie Lavoine, Isabelle Desloges, Bertine Khelifi, Julien Bras

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This study presents a comparison of the mechanical and barrier properties of papers coated with microfibrillated cellulose (MFC) by two different coating processes: (i) bar coating and (ii) size press. Due to the high water content of MFC, water-treated papers were taken as references to highlight the effects of MFC on the properties of papers. Structural, mechanical and barrier properties of the ensued materials were performed respectively with SEM, tensile and stiffness testers, and air and oxygen permeability equipments. The properties of the water-treated papers were considerably damaged compared to those of the base paper that underlined the negative impact of both coating processes on the papers structure. With MFC, the air barrier and the bending stiffness were considerably improved (+90 and +50 % respectively), especially when the bar coating was used, i.e. with 7 g m−2 of MFC. Size press was indeed not able to considerably improve papers properties as the MFC coat weight barely reached 4 g m−2 resulting from ten successive MFC layers.

May: Localized strain and heat generation during plastic deformation in nanocrystalline Ni and Ni–Fe 

T. Chan, Y. Zhou, I. Brooks, G. Palumbo, and U. Erb

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...For all materials, higher loads or higher strain rate generally resulted in higher peak temperature with the highest temperatures recorded in the fracture regions. The maximum temperature for the nanocrystalline materials was just over 80 °C, which is significantly below the reported temperatures for the onset of thermally activated grain growth. Therefore, the previously reported grain growth observed on similar materials after tensile deformation is likely not thermally activated but a stress-induced phenomenon...

June: The effect of nanoparticle on microdomain alignment in block copolymer thin films under an electric field 

Joonwon Bae, Seon Joo Park, Oh Seok Kwon, and Jyongsik Jang

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...It was revealed that the microdomain orientation of BCP/nanoparticle thin films under electric field was suppressed by the introduction of gold nanoparticles. Thus, it can be inferred that gold nanoparticles can show a shielding effect under external electric field...

July: Critical conditions for the occurrence of quench cracking in an Al–Zn–Mg–Cu alloy 

by D. K. Xu, P. A. Rometsch, L. Li, L. M. Shen, N. Birbilis

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The occurrence of quench cracking in small cuboidal samples of aluminium alloy AA7150 was determined to be related to the maximum temperature difference (∆T max) between various locations within samples during quenching... Moreover, quench cracks can penetrate through the whole thickness of a sample quenched from 495 into 20 °C water. Fractography reveals that no constituent particles exist in the quench fracture region, indicating that, unlike impact fracture, the occurrence of quench cracks is not dependent on the presence of coarse particles.

August: Multi-scale 3D imaging of absorbing porous materials for solid oxide fuel cells 

Julie Villanova, Peter Cloetens, Heikki Suhonen, Jérôme Laurencin, François Usseglio-Viretta, Elisa Lay, Gérard Delette, Pierre Bleuet, David Jauffrès, Denis Roussel, Aaron Z. Lichtner, Christophe Louis Martin

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...Here, the X-ray nano-holotomography technique is used to image various multi-phase and absorbing solid oxide fuel cell electrodes. Different porous structures for typical commercial cells and innovative electrode designs obtained using a freeze-casting process are studied. Taking advantage of the geometrical setup and the use of high energy X-rays, both large reconstructions (field of view: 150 µm) and local tomography at higher resolution (field of view: 50 µm) can be performed on the same sample to have a multi-scale approach...

September: Phase stabilization principle and precipitate-host lattice influences for Al–Mg–Si–Cu alloy precipitates 

F. J. H. Ehlers, S. Wenner, S. J. Andersen, C. D. Marioara, W. Lefebvre, C. B. Boothroyd, R. Holmestad

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...This strongly supports a connection of the geometries with a bulk phase stabilization principle. We relate our findings to the Si network substructure commonly observed in all Mg–Al–Si(–Cu) metastable precipitates, showing how this structure can be regarded as a direct consequence of the local geometries. Further, our proposed phase stabilization principle clearly rests on the importance of metal-Si interactions. Close links to the Al–Mg–Si precipitation sequence are proposed.

October: Electrophoretic deposition of alumina, yttria, yttrium aluminium garnet and lutetium aluminium garnet 

Michael Bredol, Joanna Micior, Stephan Klemme

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... The obtained green bodies were studied by surface area analysis, scanning electron microscopy, optical transmittance measurements, determination of pycnometric density and sintering behaviour. The effect of colloid-chemical dispersion properties on green and sintered ceramics is discussed as well. The green ceramics received are nanoporous and dense, providing excellent properties for further processing under mild conditions to optical materials. For comparison, EPD-formed green bodies were either processed directly to ceramic bodies or after additional compacting by hot-pressing in a piston-cylinder apparatus.

November: Phase stabilization principle and precipitate-host lattice influences for Al–Mg–Si–Cu alloy precipitates 

F. J. H. Ehlers, S. Wenner, S. J. Andersen, C. D. Marioara, W. Lefebvre, C. B. Boothroyd, R. Holmestad

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...A small set of local geometries is found to fully explain all structures. Density functional theory based calculations have been carried out on a larger set of structures, all fully constructed by the same local geometries. The results reveal that experimentally reported and hypothetical Cu-free phases from the set are practically indistinguishable with regard to formation enthalpy and composition. This strongly supports a connection of the geometries with a bulk phase stabilization principle. We relate our findings to the Si network substructure commonly observed in all Mg–Al–Si(–Cu) metastable precipitates, showing how this structure can be regarded as a direct consequence of the local geometries. Further, our proposed phase stabilization principle clearly rests on the importance of metal-Si interactions. Close links to the Al–Mg–Si precipitation sequence are proposed.

December: Fabrication of two-dimensional zinc oxide nanorod patterns and their application for optical diffraction grating effect 

Un Jeong Kim, Sun Il Kim, Sungwoo Hwang, Jaehyun Hur

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We present a novel method for fabricating two-dimensional arrays of zinc oxide (ZnO) nanorod patterns. Vertically aligned ZnO nanostructure patterns were synthesized by hydrothermal growth on a two-dimensional seed layer pattern formed by atomic layer deposition. Various characteristics of ZnO seed films were experimentally studied in order to optimize the fabrication of ZnO rod structures in terms of their uniformity and vertical alignment on the two-dimensional-patterned surfaces. Using these ZnO structures as hierarchical electrodes, we demonstrate that localized electric fields in the proximity of ZnO rod patterns can be used for periodic alignment of liquid crystal molecules, resulting in the optical diffraction grating effect. Process conditions for creating ZnO rod patterns that best enhance diffraction efficiency are further discussed. The current study is the first demonstration of hierarchical ZnO rod patterns as electrodes for optical modulation of a medium. We believe this will be beneficial for future optical applications.