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Zhou Y.,CAS Shenyang Institute of Metal Research
Scripta Materialia | Year: 2011

Superalloy CMSX-4 is directionally solidified and initiated by bicrystal seeds. It has been found that diverging boundaries are the most favorable location for stray grain formation. The phenomenon cannot be attributed to nucleation of crystals. A reasonable mechanism is the bending or detachment of side arms during extension of secondary arms and the development of tertiary branches at the diverging boundaries. Solute interaction of the neighboring dendrites increases the likelihood of bending or detachment and thus leads to an enhanced frequency of stray grains. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Wang P.,CAS Shenyang Institute of Metal Research
Dalton Transactions | Year: 2012

Ammonia borane (NH 3BH 3, AB) is a unique molecular crystal containing an intriguingly high density of hydrogen. In the past several years, AB has received extensive attention as a promising hydrogen storage medium. Several strategies have been successfully developed for promoting H 2 release and for suppressing the evolution of volatile by-products from the solid-state thermolysis of AB. Several potentially cost-effective and energy-efficient routes for regenerating AB from the spent fuels have been experimentally demonstrated. These remarkable technological advances offer a promising prospect of using AB-based materials as viable H 2 carriers for on-board application. In this perspective, the recent progresses in promoting H 2 release from the solid-state thermolysis of AB and in developing regeneration technologies are briefly reviewed. © 2012 The Royal Society of Chemistry. Source

Wang S.,CAS Shenyang Institute of Metal Research
Physical Chemistry Chemical Physics | Year: 2011

Information on orbital hybridization is very important to understand the structural, physical, and chemical properties of a material. Results of a comparative first-principles study on the behaviours of orbital hybridization in the two-dimensional single-element phases by carbon, silicon, and germanium are presented. From the well-known three-dimensional hexagonal lonsdaleite structure, in which the atoms are in ideal sp3-bonding, the layer spacing along c-axis is gradually stretched to simulate the evolutions of structural and electronic properties from three-dimensional to two-dimensional lattice configurations in the three materials. A turning point of the total system energy due to the sp3 to sp2 transition is observed during this process in carbon. In contrast, no such phenomenon is found in silicon and germanium. The differences in electronic structure and bonding behaviour are further examined through comparative investigation of atomic angular-momentum projected density of states and electronic energy band spectrums of these materials. We demonstrate that the valence electronic orbital in the two-dimensional hexagonal crystals of Si and Ge shows sp 3-like behaviour for the partial hybridization of s and p z, which leads to their different lattice configurations to graphene. The role of π-bonds in stabilizing the flat configuration of graphene is also discussed. © the Owner Societies 2011. Source

Su D.S.,CAS Shenyang Institute of Metal Research | Su D.S.,Fritz Haber Institute of the Max Planck Society | Perathoner S.,Messina University | Centi G.,Messina University
Chemical Reviews | Year: 2013

Nanocarbon is a term increasingly used to indicate the broad range of carbon materials having a tailored nanoscale dimension and functional properties that significantly depend on their nanoscale features. CNT and graphene belong to this class of materials comprising many more types of carbon materials, such as nanofibers, -coils, -diamonds, -horns, -onions, and fullerene. The field of application of nanocarbon materials is large, because they possess electrical and thermal conductivity, as well as a mechanical strength and lightness that conventional materials cannot match. With the diversity of their structure, these characteristic values can be achieved over an extremely wide range of conditions. For these reasons, they are extensively studied in applications going from photonics and optoelectronics to biotech and nanomedicine, advanced electrodes, and polymer composites. It should be mentioned that for commercial applications a comprehensive understanding of the catalyst structure, bonding, and properties is desirable, but not strictly necessary, provided that the catalysts are well-reproducible and give superior performances. Source

Li S.X.,CAS Shenyang Institute of Metal Research
International Materials Reviews | Year: 2012

The effect of inclusion size on fatigue behaviour of high strength steels in the very high cycle fatigue (VHCF) regime (.10 7-10 9 cycles) is reviewed. Internal fatigue fractures of high strength steels in the VHCF regime initiate mostly at non-metallic inclusions. The critical inclusion size below which it is hard to initiate fatigue cracking of high strength steels in the VHCF regime is found to be about half the critical value characteristic of the high cycle fatigue (HCF) regime (about 10 5-10 7 cycles). A stepwise or duplex S-N curve is observed in the VHCF regime. The shape and form of the S-N curves are affected by inclusion size and other factors including surface condition, residual stress, environment and loading modes. Fatigue strength and fatigue life for high strength steels have been found to obey inverse power laws with respect to inclusion size D of the form σ w∝D -n1 and Nf∝D -n2 respectively. For fatigue strength, the exponent n 1 has been reported to be ∼0·33 in the literature for the HCF regime and, more recently, to fall in the range 0·17-0·19 for the VHCF regime. For fatigue life, the exponent n2 is reported to be ∼3 in the HCF regime, and in the range 4·29-8·42 in the VHCF regime. A special area was often observed inside a 'fish eye' mark in the vicinity of a non-metallic inclusion acting as the fracture origin for specimens having a long fatigue life. The major mechanisms of formation for this special area are discussed. To estimate the fatigue strength and fatigue life, it is necessary to know the size of the maximum inclusion in a tested specimen, and to be able to infer this value using data from a small volume of steel. The statistics of extreme value (SEV) method and the generalised Pareto distribution (GPD) method are introduced and compared. Finally, unresolved problems and future work required in studying the VHCF of high strength steels are briefly presented. © 2012 Institute of Materials, Minerals and Mining and ASM International Published by Maney for the Institute and ASM International. Source

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