• Journal of Surface Science and Engineering
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• v.39 no.3
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• pp.110-114
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• 2006

In this work, comparative studies on microstructure and mechanical properties between $Mo_2N$ and Mo-Si-N coatings were conducted. Ternary Mo-Si-N coatings were deposited on AISI D2 steel substrates by a hybrid method, where AIP technique was combined with a magnetron sputtering technique. Instrumental analyses of XRD, HRTEM, and XPS revealed that the Mo-Si-N coatings must be a composite consisting of fine $Mo_2N$ crystallites and amorphous $Si_3N_4$. The hardness value of Mo-Si-N coatings significantly increased from 22 GPa of $Mo_2N$ coatings to about 37 GPa with Si content of 10 at.% due to the refinement of $Mo_2N$ crystallites and the composite microstructure characteristics. The average friction coefficient of the Mo-Si-N coatings gradually decreased from 0.65 to 0.4 with increasing Si content up to 15 at.%. The effects of Si content on microstructure and mechanical properties of Mo-N coatings were systematically investigated.

• Journal of the Korean Ceramic Society
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• v.32 no.9
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• pp.1033-1039
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• 1995

The current experiment has quantitatively investigated the effect of the content of CaO and SiO2 on the microstructure, density, electrical resistivity, power loss and initial permeability of manganese zinc ferrites. The density increased initially with CaO and SiO2 content and the further addition showed an adverse effect. The excess addition of CaO and SiO2 developed a discontinuous grain growth with numerous pores inside grains and lowered the electrical resistivity. The initial permeability decreased with increasing the content of SiO2. The samples with relatively low power loss showed that half of the total loss at 10$0^{\circ}C$, 100 kHz and 2000 Gauss was due to the eddy current loss.

• Journal of Korea Foundry Society
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• v.26 no.6
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• pp.241-248
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• 2006

The effects of silicon content and melt treatment on the fluidity of Al-Si alloys during squeeze casting were investigated. The fluidity of Al-3.0 wt%Si alloy was found to be lower than that of Al-1.0 wt%Si and the fluidity of the alloy with more than 3.0 wt%Si increased with the silicon content upto 13.0 wt% and rather decreased with15.0 wt%. The fluidity was also increased by the separated treatment of grain refinement or eutectic modification, and even more by the simultaneous treatment of both. The fluidity of hypereutectic alloy was increased by the refinement of primary silicon particle.

• Polymer(Korea)
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• v.38 no.5
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• pp.602-612
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• 2014

Polyurethanes containing poly(dimethyl siloxane) (PDMS) unit, PU-Si, were synthesized and their thermal and shape memory properties were investigated. Various amounts of PDMS units were incorporated via a solution polymerization method using mixed diols of poly(tetramethylene ether glycol) (PTMEG) and PDMS-diol as the soft segment (SS) and methylene diphenyl diisocyanate and 1,4-butanediol as the hard segment (HS). Two series of PU-Si samples with an HS content of 23% or 32% were prepared and analyzed. For PU-Si with an HS content of 23%, both the cold crystallization temperature ($T_{cc}$) and melt crystallization temperature of the SS domain moved higher temperature with increasing PDMS content, while the melting temperature ($T_m$) of the SS domain remained unaffected. The increase in HS content from 23% to 32% resulted in the increased $T_m$ and disappearance of $T_{cc}$. The shape recovery of PU-Si flim with an HS content of 32% increased while its shape retention decreased as PDMS content increased.

• Journal of Surface Science and Engineering
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• v.36 no.2
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• pp.109-115
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• 2003

Quaternary Ti-Al-Si-N films were deposited on WC-Co substrates by a hybrid deposition system of arc ion plating (AIP) method for Ti-Al source and DC magnetron sputtering technique for Si incorporation. The synthesized Ti-Al-Si-N films were revealed to be composites of solid-solution (Ti, Al, Si)N crystallites and amorphous Si3N4 by instrumental analyses. The Si addition in Ti-Al-N films affected the refinement and uniform distribution of crystallites by percolation phenomenon of amorphous silicon nitride, similarly to Si effect in TiN film. As the Si content increased up to about 9 at.%, the hardness of Ti-Al-N film steeply increased from 30 GPa to about 50 GPa. The highest microhardness value (~50 GPa) was obtained from the Ti-Al-Si-N film haying the Si content of 9 at.%, the microstructure of which was characterized by a nanocomposite of nc-(Ti,Al,Si) N/a$-Si_3$$N_4$.

• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.388-394
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• 2004

Composites of Si$_3$N$_4$-SiC containing up to 30 wt% of dispersed SiC particles were fabricated via hot-pressing with an oxynitride glass. To determine the effect of sintering time and SiC content on the mechanical properties and the cutting performance, the composites with fixed 8hr-sintering time and 20 wt% SiC content were fabricated and tested. Fracture toughness of the composites increased with increasing sintering time, while the hardness increased as the SiC content increased up to 20 wt%. The hardness of the composites was relatively independent of the grain size and the sintered density. For machining heat-treated AISI4140, the insert with 20 wt% SiC sintered for 8hr showed the longest tool life while the insert with 20 wt% SiC sintered for 12hr showed the longest tool life for machining gray cast iron. An effort was made to relate the mechanical properties, such as hardness, fracture toughness and wear resistance coefficient with the tool life. However, no apparent relationship was found between them. It may be stated that tool life is affected by not only the mechanical properties but also other properties such as surface roughness, density, grian size and the number of the inherent defects in the inserts.

• Advances in materials Research
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• v.3 no.1
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• pp.259-269
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• 2014

The boron-nitrogen-containing phenol-formaldehyde resin (BNPFR)/$SiO_2$ nanocomposites (BNPFR/$SiO_2$) were synthesized in-situ, and structure of BNPFR/$SiO_2$ nanocomposites was characterized by FTIR, XRD and TEM. The loss modulus peak temperature $T_p$ of BNPFR/$SiO_2$ nanocomposites cured with different nano-$SiO_2$ content are determined by torsional braid analysis (TBA). The thermal degradation kinetics was investigated by thermogravimetric analysis (TGA). The results show that nano-$SiO_2$ particulate with about 50 nm diameter has a more uniformly distribution in the samples. The loss modulus peak temperature $T_p$ of BNPFR/$SiO_2$ nanocomposite is $214^{\circ}C$ when nano-$SiO_2$ content is 6 wt%. The start thermal degradation temperature $T_{di}$ is higher about $30^{\circ}C$ than pure BNPFR. The residual rate (%) of nanocomposites at $800^{\circ}C$ is above 40 % when nano-$SiO_2$ content is 9 %. The thermal degradation process is multistage decomposition and following first order.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.364-372
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• 1998

Effects of Si and Ca additions on the mechanical properties of AM60 based Mg alloys have been investigated. Hardness of the AM60 based Mg alloys reached a maximum value after aging for approximately 33 hours but the amount of hardness increase was negligible. The poor age hardening response of the alloys was due to low Al content, which implies that Al content must be >6 wt.% to observe age hardening effect. The tensile and yield strength increased with increasing Al, Si, and Ca content but elongation decreased with increasing Al and Si content. The best mechanical properties obtained in AM 40-2.5Si-0.2Ca alloy after T4 heat treatment were as follows; tensile strength 193.4 MPa, yield strength 79.2 MPa, and elongation 11.2%. High temperature property obtained from creep test was also improved by introducing $Mg_2Si$ which has high hardness, high melting temperature and low thermal expansion coefficient.

• Journal of Korea Foundry Society
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• v.12 no.4
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• pp.335-345
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• 1992

Aluminum alloy matrix composites reinforced with various amounts of SiC particles have been produced by rheo-compocasting followed by hot extrusion. A relatively uniform distribution of SiC particles in the composites was obtained. The amounts of pore and SiC particles cluster were relatively small in the composites. Particle free zones were observed in the hot extruded composites when the amount of SiC particles was less than 20 vol%. However, the width of particle free zone decreases with the increase of SiC particle content. Eutectic Si phase play an important role for improving bonding between SiC particle and matrix. Tensile and yield strength increased with the increase of SiC particle content. the strenthening effect of SiC particle addition was effective even at relatively high temperature of 573 K.

• Fibers and Polymers
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• v.2 no.3
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• pp.135-140
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• 2001

Organic-inorganic hybrid composites consisting of poly(vinylidene fluoride) (PVDF) and SiO$_2$ were prepared through a sol-gel process and the crystallization behavior of PVDF in the presence of $SiO_2$ networks was investigated by spectroscopic, thermal and x-ray diffraction measurements. The hybrid composites obtained were relatively transparent, and brittleness increased with increasing content of tetraethoxysilane (TEOS). It was regarded from FT-lR and DSC thermal analyses that at least a certain interaction existed between PVDF molecules and the $SiO_2$ networks. X-ray diffraction measurements showed that all of the hybrid samples had a crystal structure of PVDF ${\gamma}$-phase. Fresh gel prepared from the sol-gel reaction showed a very weak x-ray diffraction peak near 2$\theta$=$21^{\circ}$ due to PVDF crystallization, and Intensity increased grade-ally with time after gelation. The crystallization behavior of PVDF was strongly affected by the amount of $SiO_2$ networks. That is, $SiO_2$ content directly influenced preference and disturbance fur crystallization. In polymer-rich hybrids, $SiO_2$ networks had a favorable effect on the extent of PVDF crystallization. In particular, the maximum portent crystallinity of PVDF occurred at the content of 3.7 wt% $SiO_2$ and was higher than that of pure PVDF. However. beyond about 10 wt% $SiO_2$, the crystallization of PVDF was strongly confined.