Frontiers of Materials Science (v.3, #3)

Like all sponges (phylum Porifera), the glass sponges (Hexactinellida) are provided with an elaborate and distinct body plan, which relies on a filigree skeleton. It is constructed by an array of morphologically determined elements, the spicules. Schulze described the largest siliceous hexactinellid sponge on Earth, the up to 3 m high Monorhaphis chuni, collected during the German Deep Sea Expedition ”Valdivia“ (1898–1899). This species develops an equally large bio-silica structure, the giant basal spicule (3 m × 10 mm). Using these spicules as a model, one can obtain the basic knowledge on the morphology, formation, and development of silica skeletal elements. The silica matrix is composed of almost pure silica, endowing it with unusual optophysical properties, which are superior to those of man-made waveguides. Experiments suggest that the spicules function in vivo as a nonocular photoreception system. The spicules are also provided with exceptional mechanical properties. Like demosponges, the hexactinellids synthesize their silica enzymatically via the enzyme silicatein (27 kDa protein). This enzyme is located in/embedded in the silica layers. This knowledge will surely contribute to a further utilization and exploration of silica in biomaterial/biomedical science.
Keywords: sponge; Porifera; Hexactinellida; spicule; giant basal spicule; silicatein; biomaterial science

Preparation and cytocompatibility of silk fibroin/chitosan scaffolds by Zhen-ding She; Wei-qiang Liu; Qing-ling Feng (241-247).
One challenge in soft tissue engineering is to find an applicable scaffold, not only having suitable mechanical properties, porous structures, and biodegradable properties, but also being abundant in active groups and having good biocompatibility. In this study, a three-dimensional silk fibroin/chitosan (SFCS) scaffold was successfully prepared with interconnected porous structure, excellent hydrophilicity, and proper mechanical properties. Compared with polylactic glycolic acid (PLGA) scaffold, the SFCS scaffold further facilitated the growth of HepG2 cells (human hepatoma cell line). Keeping the good cytocompatibility and combining the advantages of both fibroin and chitosan, the SFCS scaffold should be a prominent candidate for soft tissue engineering, for example, liver.
Keywords: silk fibroin; chitosan; scaffold; cytocompatibility; HepG2 cell

Biogenic nanoparticles and mineral composition in the radula of chiton Acanthochiton rubrolineatus by Chuan-lin Liu; Xiao-jie Cheng; Jian-gao Zhao; Xia Qian; Cheng-hua Guo; De-jiao Yu; Xi-guang Chen (248-254).
Magnetite particles were confirmed to deposit in the radula of chiton Acanthochiton rubrolineatus, and these magnetite particles presented as chip-shaped pieces which were 150 nm in width. Many nano-scale crystals constructed each piece of the magnetite particles. The mean size of a single crystal was 52 nm in diameter. Calcium composites were found to coexist with iron minerals. The total amount of magnetite in the chiton radula was 10% (w/w) of the radula weight, and 41% (w/w) of the total minerals. Eight metal elements were measured in the chiton radula, among which iron was a major element (14.6%, w/w) of the radula, followed by sodium, magnesium, calcium, potassium, chromium, manganese and cobalt in turn.
Keywords: biomineralization; nanoparticle; magnetite; radula; chiton

Preparation and comparison study of hydroxyapatite and Eu-hydroxyapatite by Xian-ying Cao; Feng Wen; Wei Bian; Yang Cao; Su-juan Pang; Wan-ke Zhang (255-258).
Hydroxyapatite (HA) is the main component of inorganic minerals in animal sclerous tissues. Nano HA has been used as an inorganic drug for many years in laboratories. In this paper, nano HAwas at frist synthesized by the coprecipitation method. The element europium was then doped to HA to obtain a new kind of product with fluorescence. Both products of doped and of non-doped HA were analyzed by IR, XRD, TEM and fluorescence microscope. It was proven that Eu-HA had fluorescence.
Keywords: hydroxyapatite (HA); nanometer; europium; dope

A low viscosity urethane diacrylate monomer of 2-(acryloyloxy) ethyl bis (2-(acryloyloxy) ethyl)carbamate (AEBAC) was prepared via a nonisocyanate route. The photopolymerization kinetics of this urethane acrylate was studied by real-time FTIR. The influences of light intensity, photoinitiator type, and concentration on the polymerization kinetics were discussed. The photopolymerization kinetic results indicated that the relationship between the polymerization rate (R p) and the incident light intensity (I 0) was R pI 0 0.5 and the maximum rate of polymerization (R p,max) was proportional to [A]0.5 ([A] was the molar concentration of initiator). The dynamic mechanical analysis (DMA) results indicated that the glass transition temperature (T g) of the curing product of AEBAC was about 80°C.
Keywords: kinetics; photopolymerization; RTIR; urethane diacrylate

Interfacial friction damping characteristics in MWNT-filled polycarbonate composites by Yu-hong Man; Zheng-cao Li; Zheng-jun Zhang (266-272).
The effects of strain, temperature, test frequency, and multi-walled nanotube (MWNT) weight percentage on the interfacial sliding at the tube-polymer interfaces were investigated by dynamic mechanical tests. The storage modulus first increased slightly then reached a plateau and finally decreased sharply with further increasing strain (temperature, frequency) amplitude. Moreover, the changing of the storage modulus of the nanocomposite lagged the loss modulus as a function of strain (temperature, frequency). Furthermore, with the increase of MWNT weight percentage interfacial slip was activated at relative smaller strain, lower temperature, or lower frequency. The possible influence of polymer wrapping carbon nanotubes in the interfacial area on interfacial friction was introduced.
Keywords: carbon nanotube; polycarbonate; damping; interfacial friction

Laminated ZrB2/Mo composites, alternately consisting of matrix layers of 80 vol.% ZrB2 + 10 vol.% nano-SiC whiskers + 10 vol.% SiC particles and Mo interlayers, with the addition of Si and B as interlayer adjusting agent, were prepared by roll-compaction and spark plasma sintering (at 1600°C) process. XRD and SEM techniques were used to characterize the phases and microstructure of the obtained composites. The results showed that without the addition of Si and B in the interlayer, interfacial debonding between the matrix layer and interlayer often occurred due to the thermal mismatch between the two kinds of layers. However, the interfacial mismatch could be effectively inhibited by the addition of Si and B to the Mo interlayers. The laminated ZrB2/Mo composites with 6 at.% Si and 4 at.% B in the interlayers showed the highest bending strength at (451±20) MPa and the highest fracture toughness at (7.52±0.12) MPa·m½. MoB, ZrB and Mo5SiB2 were formed by the reactions among ZrB2, Mo and the additions.
Keywords: zirconium diboride (ZrB2); ceramics matrix composites; laminated; spark plasma sintering (SPS)

Surface-hardening effect of B implantation in 6H-SiC ceramics by Heng Du; Zheng-cao Li; Tian Ma; Wei Miao; Zheng-jun Zhang (281-284).
This study was conducted on the surfacehardening effect of boron ion implantation in 6H-SiC ceramics. The SiC samples prepared by pressureless sintering were carefully polished, and 500 keV B+ implanted in 6H-SiC ceramics at room temperature and four implantation doses, namely, 1×1015, 5×1015, 1×1016, and 5×1016 cm−2, were chosen. The implanted samples were analyzed by scanning electron microscope and Raman spectra. The Vickers hardness of the samples was evidently increased. The thickness of the damage layer was about 1 μm, which is consistent with the simulated results. The structure of the damage layer was different from the internal part and severely damaged at high doses.
Keywords: 6H-SiC; boron; ion implantation; surface-hardening

The vibrational dynamics of some Zr-based bulkmetallic glasses were studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). The well recognized model potential is employed successfully to explain electron-ion interaction in the metallic glass. The present findings of phonon dispersion curve are found to be in fair agreement with available theoretical as well as experimental data. The thermodynamic properties obtained by the HB and TG approaches are found to be much lower than those obtained by the BS approach.
Keywords: pair potential; Zr-based bulk metallic glasses; phonon dispersion curves; thermal properties; elastic properties

Simulation analysis of thermal stress during casting process of large-sized alloy steel ingot by Yi-tao Yang; Wei Luo; Meng Chen; Guang-jie Shao (301-305).
To quantitatively analyze the main reasons of common crack in the surface of alloy steel ingot with 5% Cr during production and to propose the direction of improvement, a physical model system, which consisted of steel ingot mold, casting, riser of heat insulation, slag layer, sprue pipe, and runner, was primarily established by three-dimensional CAD software. The joint simulation method concerned with pouring, solidification, temperature field, and cast stress was determined by using ADSTEFAN cast simulation software. The stress distribution of casting and the quantitative effect of shake-out timing were analyzed in detail. An effective plan of decreasing stress was proposed in cooling mode.
Keywords: alloy steel; solidification; thermal stress; crack

Numerical simulation of weld tab length influence on welding residual stress and distortion of aero-engine disk by Xue-qiu Zhang; Jian-guo Yang; Xue-song Liu; Xu-hui Chen; Hong-yuan Fang; Shen Qu (306-309).
In order to control the welding residual stress and distortion to the greatest extent, based on the MSC. MARC software platform and adopting the impending critical value methods gradually, the welding residual stress and distortion are calculated through varying the weld tab length values. The results show that different weld tab lengths only have a slight effect on welding residual stress but a significant effect on welding distortion. According to the calculation results with different weld tab lengths, the critical length value for the 100 mm-length TC4 alloy weld for electron beam welding of an integral disk should be 50 mm or so.
Keywords: weld tabs; temperature field; residual stress; distortion

Elemental powders of Fe and Al were mechanically alloyed using a high energy rate ball mill. A nanostructure disordered Fe(Al) solid solution was formed at an early stage. After 28 h of milling, it was found that the Fe(Al) solid solution was transformed into an ordered FeAl phase. During the entire ball milling process, the elemental phase co-existed with the alloyed phase. Ball milling was performed under toluene to minimise atmospheric contamination. Ball milled powders were subsequently annealed to induce more ordering. Phase transformation and structural changes during mechanical alloying (MEA) and subsequent annealing were investigated by X-ray diffraction (XRD). Scanning electron microscope (SEM) was employed to examine the morphology of the powders and to measure the powder particle size. Energy dispersive spectroscopy (EDS) was utilised to examine the composition of mechanically alloyed powder particles. XRD and EDS were also employed to examine the atmospheric and milling media contamination. Phase transformation at elevated temperatures was examined by differential scanning calorimeter (DSC). The crystallite size obtained after 28 h of milling time was around 18 nm. Ordering was characterised by small reduction in crystallite size while large reduction was observed during disordering. Micro hardness was influenced by Crystallite size and structural transformation.
Keywords: nanostructured powder; mechanical alloying; FeAl; disorder; order

Effect of powder particle size on green properties and stress wave by Jian-zhong Wang; Hai-qing Yin; Xuan-hui Qu (319-324).
In the powder metallurgy (PM) industry, high velocity compaction (HVC) technique is a new way to obtain higher density parts. In this study, three reduced pure iron powders with different particle sizes were pressed by HYP35-2 High Velocity Compaction Machine. A computer controlled universal testing machine was used to measure the bending strength of the green body. The relationships among the particle size, the impact velocity, the green density, the stress wave, the bending strength and the radial springback were discussed. The results show that the powder of −200 mesh is the best option among the three powders for the HVC process. At the identical impact velocity, the green density for the powder of −200 mesh is higher than the other two types of powders, while the bending strength and the radial springback for the powder of −300 mesh is the highest. In addition, the stress waves exhibit similar, pulsed waveforms. As the impact velocity rises up, the duration of the first peak decreases gradually, while that of the stress wave increases slowly. The response time for the powder of −200 mesh is shorter than the other two types of powders.
Keywords: high velocity compaction (HVC); particle size; green properties; stress wave; iron powder

Amorphization and crystallization characteristics of TiNi shape memory alloys by severe plastic deformation by Jun-tao Li; Wei-dong Miao; Yu-ling Hu; Yan-jun Zheng; Li-shan Cui (325-328).
Differential scanning calorimetry (DSC) was used to determine the crystallization fraction and rate in TiNi alloys by severe plastic deformation. Results showed that the reverse martensitic transformation peak was not observed during the first heating at the rate of 40 K/min in the as-rolled samples, but one exothermic peak was observed at 620 K, which was associated with the amorphous crystallization process. During the second heating, reverse martensitic transformation was recovered. The onset crystallization temperature was low in the initial stage of crystallization with lower heating rates, but the crystallization fraction was found to increase with increasing temperature. However, the crystallization fraction was almost constant in the initial stage of crystallization with a relatively high heating rate. In all heating rates, the amorphous crystallization rates almost always reached maximum as the volumetric fraction of amorphous crystallization rose to 50%.
Keywords: shape memory alloy; cold deformation; nanocrystallization; amorphization

Processing of Fe-6.5wt.%Si alloy foils by cold rolling by Yong-feng Liang; Jun-pin Lin; Feng Ye; Yan-li Wang; Lai-qi Zhang; Guo-liang Chen (329-332).
Thin foils of 50 μm in thickness of Fe-6.5wt.%Si alloy were obtained by conventional hot-cold rolling method. The rolling texture and basic mechanical properties of the foils were examined. The foils were heavily work-hardened and exhibited high tensile fracture strength with some extent of plastic elongations. Their bending ductility was more remarkable.
Keywords: Fe-6.5wt.%Si; fabrication; cold rolling; tensile; bending

Adhesion behavior of plasma sprayed thermal barrier coatings on Al-6061 and cast iron substrates by N. Krishnamurthy; S. C. Sharma; M. S. Murali; P. G. Mukunda (333-338).
In this work an investigation was carried out on adhesion strength and micro-hardness of plasma sprayed coatings on Al-6061 and cast iron substrate materials. For the adhesion test, ASTM C633, and for the micro hardness, ASTM E384 standards were used. From the results obtained it was found that the main failure locations were in the bond coat-substrate interface, which is considered as adhesion strength. The various parameters affecting adhesion strength are also discussed.
Keywords: adhesion strength; micro-hardness plasma spraying; thermal barrier coating

The microstructures and dry sliding wear behaviour of an Al-2Si alloy cast centrifugally are studied. Results indicate that at optimum speed the cast has a microstructure consisting of uniformly distributed α-Al grains and fine eutectic silicon grains. The cast exhibited better wear resistance compared to the same cast prepared at different rpms. This paper attempts to investigate the influence of the microstructural changes in the Al-2Si alloy by varying the rotational speed of the mould and its combined action on the dry sliding wear behaviour.
Keywords: rotational speed; dry sliding wear; Al-Si alloy