• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.871-876
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• 1996

It is believed that fly ash could be suitable for preparing the sialon by carbothermal reduction method because the total amount of SiO2 and Al2O3 is above 80% and the unburned residual carbon is above 5% within the fly ash. The effects of reaction temperature (1350, 1400, 145$0^{\circ}C$) reaction time (1, 5, 10 hours) and the amount of carbon additions (C/SiO2=2, 3, 4 mole) on the $\beta$-sialon synthesis were obserbed, It was conformed that $\beta$-sialon (Z=2.15~2.18) was formed as major phase under all of the synthesis conditions and small amount of Si2ON2 SiC, AlN and Si3N4 was formed depending on the synthesis conditions. FeSix intermetal-lic compound was formed above 140$0^{\circ}C$ reaction temperature due to the large amount of iron oxides within the raw fly ash.

• Journal of Korea Foundry Society
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• v.38 no.6
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• pp.111-120
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• 2018

In this study, the effects of two different casting methods (gravity casting and, diecasting) and various solid-solution conditions on the mechanical properties of ASC (Al-10.5wt%Si-1.75wt%Cu) and ALDC12 (Al-10.3wt%Si-1.72wt%Cu-0.76wt%Fe-0.28wt% Mn-0.32wt%Mg-0.9wt%Zn) alloys were investigated. A thermodynamic solidification analysis program (PANDAT) was used to predict the liquidus, solidus, and phases of the used alloys. In the results of an XRD analysis, ${\beta}$-AlFeSi peaks were observed only in the ALDC12 alloy regardless of the casting method or SST (solid-solution treatment) conditions. However, according to the results of a FE-SEM observation, both ${\theta}(Al_2Cu)$ and ${\beta}$-AlFeSi were found to exist besides ${\alpha}$-Al and eutectic Si in the gravity-casted ASC alloy at $500^{\circ}C$ after a SST of 120min. The ${\alpha}$-AlFeSi and ${\beta}$-AlFeSi phases including the eutectic phases were also found to exist in the ALDC12 alloy. The results of a microstructural observation and analyses by XRD, FE-SEM and EDS were in good agreement with the PANDAT results. The gravity-casted ALDC12 and ASC specimens showed the highest Y.S. and UTS values after aging for three hours at $180^{\circ}C$ after a SST at $500^{\circ}C$ for 30min. At longer solid-solution treatment times at $500^{\circ}C$ in the gravity-casted ALDC12 and ASC specimens, the elongations of the ASC alloys increased, whereas they decreased slightly in the ALDC12 alloys.

• Journal of Korea Foundry Society
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• v.32 no.5
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• pp.219-224
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• 2012

The effects of Mg and Si contents on the microstructure and mechanical properties in Al-Mg alloy (ALDC6) were investigated. The results showed that phase fraction and size of $Mg_2Si$ and $Al_{15}(Fe,Mn)_3Si_2$ phase in the microstructure of Al-Mg alloy were increased as the Mg and Si contents were raised from 2.5 to 3.5 wt%. With Si content of 1.5 wt%, freezing range of the alloy was significantly reduced and solidification became more complex during the final stage of solidification. While there was no significant influence of Mg contents on mechanical properties, Si contents up to 1.5 wt%, strongly affected the mechanical properties. Especially elongation was reduced by about a half with more than 1.0 wt%Si in the alloy. The bending and impact strength were decreased with increased amount of Si in the alloy, as well. The lowered mechanical properties are because of the growth of particle shaped coarse $Mg_2Si$ phase and precipitation of the needle like $\beta$-AlFeSi in the microstructure at the last region to solidify due to presence of excess amount of Si in the alloy.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.6
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• pp.264-271
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• 2016

The effect of the oxygen content and the annealing temperature on the tensile behavior of the Ti-1.5Al-3Fe-0.25Si-(0.1~0.5)O alloy was investigated. The tensile properties were dependent on the volume fraction of the microstructure constituents, i.e. the equixed ${\alpha}$, equixed ${\beta}$ and lamellar ${\alpha}$. The results showed that the O-partitioned equixed ${\alpha}$ had a much higher strength compared to the equixed ${\beta}$. The strength of the lamellar ${\alpha}$ increased with increasing the annealing temperature because the O content of the lamellar ${\alpha}$ increased. Ti-1.5Al-3Fe-0.25Si-0.3O alloy annealed to $900^{\circ}C$ where the volume fraction of lamellar ${\alpha}$ was the highest exhibited an excellent combination of the strength (1198.5 MPa) and ductility (27.5%). The effect of the lamellar ${\alpha}$ on the ductility was discussed.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.477-485
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• 2012

The effect of aging heat treatment on microstructure evolution of the Ti-6Al-4Fe-0.25Si alloy with an initial microstructure of an elongated alpha was investigated. Aging treatments of the samples were carried out at $550^{\circ}C$ for up to 100 hours. The microstructure of the 5 hours heat-treated sample consisted of alpha grains, beta matrix and some TiFe intermetallic compounds that were precipitated from the beta matrix. Increasing the aging time to 10 hours, most of the beta matrix was decomposed to very fine alpha grains (${\sim}0.5{\mu}m$) and TiFe, and thus the volume fraction of the beta matrix was significantly decreased. EBSD analysis revealed that newly formed tertiary-alpha-grains in the vicinity of TiFe had high angle boundaries with respect to the primary and secondary alpha grains. As a result of these phase transformations during aging, the fraction of the alpha/alpha grain boundary was increased while that of the alpha/beta phase boundary was decreased.

• Journal of Korea Foundry Society
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• v.30 no.3
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• pp.100-110
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• 2010

The solidification sequence and formation of intermetallic phase of Fe-rich Al-Si-Cu alloy were investigated by using real-time imaging of synchrotron X-ray radiation. Effects of cooling rate during uni-directional solidification on the resultant solidification behavior was also studied in a specially constructed vacuum chamber in the SPring-8 facility. The series of radiographic images were complementarily analyzed with conventional analysis of OM and SEM/EDX for phase identification. Detailed solidification sequence and formation mechanisms of various phases were discussed based on real-time image analysis. The growth rates of $\alpha$-AlFeMnSi and ${\beta}-Al_5FeSi$ were measured in order to understand the growth behavior of each phase. It is suggested that real-time imaging technique can be a powerful tool for the precise understanding of solidification behavior of various industrial materials.

• 연구논문집
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• s.29
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• pp.163-171
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• 1999

A new titanium alloy system. Ti-xFe-ySi (x,y=0-4 wt%). was designed and characterized with the point at low cost and high strength for casting applications. Fe improved room and elevated temperature mechanical properties owing to solid solution hardening and beta phase stabilization. Si yielded titanium silicides and Si addition over 1 wt% resulted in poor ductility due to coarse silicide chains at prior beta boundaries. The optimum composition was found to be Ti-4Fe-(0.5-1)Si in the viewpoint of tensile strength and ductility which are comparable to the Ti-6Al-4V. The metal-mould reaction was also examined for Ti-xFe and Ti-xSi binary alloy system. The thickness of surface reaction layer w as not affected significantly with Fe content, while it was decreased with Si content. In the Ti-4Si alloy, no reaction layer was found. The depth of surface hardening layer was about $200\mum$ regardless of the mould materials.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.511-516
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• 1992

In this study, SiC powder and Si powder were used as the raw materials. Mixture was prepared with addition of Al2O3 and Fe2O3 at 0.1~0.5wt% respectively. After this step, the mixture was pressed and nitrided for 30 hrs at 140$0^{\circ}C$ under NH3-N2 atmosphere. Mechanical properties of sintered specimens were investigated from measurement of porosity, bulk density and three point bending test. nitration reaction extent was observed at the change of mass before and after reaction, and the microstructure and the change of $\alpha$-Si3N4 and $\beta$-Si3N4 were observed by XRD and SEM. In the current work, the results are as follows 1. When Fe2O3 added, the nitridation increased with the content of Fe2O3, and the bending strength was increased from 0.1 wt% to 0.3 wt%, and decreased to 0.5 wt%. 2. When Al2O3 added, the nitridation and the bending strength increased little by little with the content of Al2O3 3. The bending strength of the specimen added with Fe2O3 were higher than that with Al2O3. Because the specimens contained Fe2O3 had much more the whisker type crystal of Si3N4 contributing to strength than contained Al2O3.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.1-1
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• 1994

;The electronic state calculations for various types of ceramic materials have beell performed by the use of $DV-X\;{\alpha}$ cluster method. The molecular orbital levels and wave functions for model clusters have been computed to study the electronic properties ami chemical bonding of the ceramics. For ${\beta}-sialon(Si_{6-z}Al_zO_zN_{8-z})$ which is a high temperature structural material based on ${\beta}-Si_3N_4$, we have made model cluster calculations to estimate the strength of chemical bonding between atoms by the Mulliken population analysis. It is found that the covalent bonding between Si and N atoms is very strong in pure ${\beta}-Si_3N_4$, but the covalency around solute atom is considerably weakened when Si atom is substituted by AI. This tendency is enhanced by an additional substitution of oxygen atom for N. The result calculated can well explain the experimental data of changes in mechanical properties such as the reductions of Young's modulus and Vickers hardness with increment of z-value in ${\beta}-sialon$. Various model clusters for transition metal oxides which show many interesting physical and chemical properties have also been calculated. High-valent perovskite-type iron oxides EMFe0_3E(M=Ca and Sr) possess very interesting magnetic and chemical properties. In these oxides, iron exists as $Fe^{4+}$ state, but the experimental measurement of Mossba~er effect suggests that disproportionation $2Fe^{4+}=Fe^{3+}+Fe^{5+}$ takes place for $CaFe0_3$ at low temperatures. The model cluster calculations for these compounds indicated the existence of considerably strong covalent bonding of Fe-O. The calculations of hyperfine interaction at iron neucleus show very good agreement with the experimental Mossbauer measurements. The result calculated also implies that the disproportionation reaction is strongly possible by assuming the quenching of breathing phonon mode at low temperatures.tures.

• Journal of Korea Foundry Society
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• v.18 no.5
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• pp.431-438
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• 1998

Microstructure of A356 aluminum alloys cast in the permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. Beryllium addition improved tensile properties and impact toughness of the A356 aluminium alloy, due to the formation of a script phase or a Be-rich phase instead of a needlelike ${\beta}-phase$. The DSC tests indicated that the presence of Be could increase the amount of Mg which is available for $Mg_2Si$ precipitate hardening, and enhance the precipitation kinetics by lowering the ternary eutectic temperature.