• 한국주조공학회지
• /
• 제25권3호
• /
• pp.128-133
• /
• 2005

The effects of Mn and Cr on the crystallization behaviors of Fe-bearing intennetallics in A356 alloy were studied. Coarse and acicular ${\beta}-Al_{5}$FeSi phase in A356-0.20wt.%Fe alloy was modified into small ${\alpha}$-Al(Fe,Mn)Si and ${\alpha}$-Al(Fe,Cr)Si phases in response to Mn and Cr addition, respectively. Increasing of Mn addition amount elevates the crystallizing temperature of ${\alpha}$-Al(Fe,Mn)Si and the Mn/Fe ratio in the ${\alpha}$-Al(Fe,Mn)Si. Cr is more effective to modify ${\beta}-Al_{5}$FeSi in comparison with Mn. ${\alpha}$-Al(Fe,Mn)Si phase had BCC/SC dual structure.

• 한국분말재료학회지
• /
• 제10권2호
• /
• pp.118-122
• /
• 2003

Alpha-SiAlON ceramics having various compositions and modifying cations were investigated with respect to their phase stability, transformation kinetics. and resulting microstructures. Each composition was heat treated at 150$0^{\circ}C$ for 1h and measured the $\alpha$-SiAlON transformation. The phase-boundary composition in the single-phase $\alpha$-SiAlON region showed sluggish transformation from $\alpha$-$Si_3N_4$ to $\alpha$-SiAlON compared to the phase-center composition in the diagram. Using the different rare earth modifying cations, dependence of transformation kinetics on the phase stability in a fixed composition was also explained. By changing size of the stable u-phase region with exchanging cations, systematic change in transformation was observed. Transformation rate of $\alpha$-SiAlON at low temperature has an important role on controlling the final microstructure. Less transformation gives more chances to develop elongated grain in the microstructure.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
• /
• pp.183-195
• /
• 1997

The micorstructural characteristics, particularly $\alpha$-halo formation, in semi-solid state processed hypereutectic Al-Si alloy was investigated. The microstructural changes during reheating of wedge type mold cast ingot, hot-rolled sheet, and Si particulate reinforced Al composite was compared with those occurred during stirring of semi-solid state hypereutectic alloy. In the case of semi-solid state reheating of wedge type ingot and hot-rolled sheet, fine particles of Si as well as $\alpha$-halo formed after heat treatment. Although there seemed to be no coarsening with variations of holding time, the region of $\alpha$-halo decreased due to homogenization. Nucleation and recrystallization was accelerated with the addition of alloying elements during hot rolling resulting in primary Si particle size decrease and $\alpha$-halo formation. In the case of extruded specimens, very little morphological change of reinforcing Si particles was observed. Almost no $\alpha$-halo formed during reheating because of the oxide film formed on the reinforcing Si particles which acted as a diffusion barrier between the matrix and the primary Si particles.

• 한국주조공학회지
• /
• 제33권3호
• /
• pp.103-112
• /
• 2013

Effect of Fe and Mn contents on the tensile properties of Al-4 wt%Mg-0.9 wt%Si alloy system has been studied. Common phases of Al-4 wt%Mg-0.9 wt%Si alloy system were ${\alpha}$-Al, $Mg_2Si$, ${\alpha}-Al_{12}(Fe,Mn)_3Si$ and ${\beta}-Al_5FeSi$. As Fe content of Al-4 wt%Mg-0.9 wt%Si alloy system increased from 0.15 wt% to above 0.3 wt%, ${\beta}-Al_5FeSi$ compound appeared. When Mn content of the alloy increased from 0.3 wt% to 0.5 wt%, morphology of plate shaped ${\beta}-Al_5FeSi$ compound changed to chinese script ${\alpha}-Al_{12}(Fe,Mn)_3Si$. As Fe content of Al-4 wt%Mg-0.9 wt%Si-0.3 wt%Mn alloy increased from 0.15 wt% to 0.4 wt%, tensile strength of the as-cast alloy decreased from 191 MPa to 183 MPa and, elongation of the alloy also decreased from 8.0% to 6.2%. Decrease of these properties can be explained as the formation of plate shape, ${\beta}-Al_5FeSi$ phase with low Mn/Fe ratio of the alloy. However, when Mn content of Al-4 wt%Mg-0.9 wt%Si-0.3 wt%Fe alloy increased from 0.3 wt% to 0.5 wt%, tensile strength of as-cast alloy increased from 181 MPa to 194 MPa and, elongation of the alloy increased from 6.8% to 7.0%. These improvements attribute to the morphology change from ${\beta}-Al_5FeSi$ phase to chinese script, ${\alpha}-Al_{15}(Fe,Mn)_3Si_2$ phase shape-modified from with high Mn/Fe ratio of the alloy.

• 한국세라믹학회지
• /
• 제30권3호
• /
• pp.243-249
• /
• 1993

Coated type Al2O3-SiC composite powders were synthesized by surface modification method. Transformation temperature to $\alpha$-Al2O3 of Al2O3 monolith was 115$0^{\circ}C$ whereas increased to 1200, 1250, 130$0^{\circ}C$ with increment of SiC content to 5, 15, 25wt%. Transformation temperature to $\alpha$-Al2O3 was lowered by $\alpha$-Al2O3 seeding. FTIR data analysis and electron micrographs showed that Al2O3 particles were effectively coated on SiC particles.

• 한국주조공학회지
• /
• 제33권6호
• /
• pp.233-241
• /
• 2013

Effect of Fe and Mn contents on the castability of Al-9wt%Si-xMg-yFe-zMn alloy has been studied. The alloy was composed of ${\alpha}$-Al phase, Al+eutectic Si phase, ${\beta}$-Al5FeSi compound and chinese script ${\alpha}$-$Al_{15}(Mn,Fe)_3Si_2$ compound. ${\beta}$-$Al_5FeSi$ and ${\alpha}$-$Al_{15}(Mn,Fe)_3Si_2$ compounds assumed to effect the fluidity and shrinkage behaviors of the alloy during solidification due to the crystallization of ${\alpha}$-$Al_{15}(Fe,Mn)_3Si_2$ and ${\beta}$-$Al_5FeSi$ compounds above eutectic temperature. As Fe and Mn contents of Al-9wt%Si-0.3wt%Mg system alloy increased from 0.15wt% to 0.6wt% and from 0.3wt% to 0.7wt%, fluidity of the alloy decreased by 5.7% and 3.3%, respectively. And as Mg content of Al-9wt%Si-0.45wt%Fe-0.5wt%Mn system alloy increased from 0.3wt% to 0.4wt%, fluidity of the alloy decreased by 8.6%. When Fe content of the alloy increased from 0.15wt% to 0.6wt%, macro shrinkage ratio decreased from 6.1% to 4.1%, and micro shrinkage ratio increased from 0.04% to 0.24%. Similarly, Mn content of the alloy increased from 0.3wt% to 0.7wt%, macro shrinkage ratio decreased from 6.0% to 4.5% and micro shrinkage ratio increased from 0.12% to 0.18%. Judging from the castability of the alloy, Al-9wt%Si-0.3wt%Mg alloy with low content of Fe and Mn, 0.1wt% Fe and 0.3wt% Mn, is recommendable.

• 한국세라믹학회지
• /
• 제28권7호
• /
• pp.561-567
• /
• 1991

Submicron ${\alpha}-SiC$ powder with $Al_2O_3$ addition was hot-pressed under the controlled heating and pressurizing schedule. $SiO_2$ layer on ${\alpha}-SiC$ powder was effective for the sintering of ${\alpha}-SiC$ powder when $Al_2O_3$ was used as an additive. Applying of pressure under the controlled schedule accelerated the rearrangment of SiC grains, yielding 98% of theoretical density of SiC even at $1900^{\circ}C$. Flexural strength of the specimen containing 2 wt% $Al_2O_3$ was increased as increasing the hot-pressing temperature up to $2050^{\circ}C$ and maximum value was 800 MPa, while the flexural strength of the specimen containing 10 wt% $Al_2O_3$ was decreased as increasing the hot-pressing temperature above $2000^{\circ}C$ due to the formation of continuous grain boundary phase. Fracture toughness of the specimens was in the range of $3.5~4.5\;MNm^{-3/2}$ regardless of the amount of $Al_2O_3$ addition.

• 한국세라믹학회지
• /
• 제33권2호
• /
• pp.169-176
• /
• 1996

The specimens which were prepared from $\alpha$-Si3N4 with additions of YAG(3Y2O3.5Al2O3)-10 wt% and various AlN contents were sintered in N2 atmosphere at 1$700^{\circ}C$ The effect of $\alpha$,$\beta$-solid solution contents and sintering time on mechanical properties were investigated. As the content of $\beta$-solid solution and sintering time increased the hardness is reduced but the hardness of specimen sintered over 10 hours is constant irrespective of sintering time. While the fracture toughness increased with increasing of $\beta$-solid solution and sintering time. The fracture toughness of specimen with 80% $\beta$-solid solution content increased from 3.89 to 6.66 MPam1/2 with sintering sintering up to 20 hours/ But the amount of increased fracture toughness of specimen with below 20% $\beta$-solid solution content is not significant.

• 한국세라믹학회지
• /
• 제50권4호
• /
• pp.280-287
• /
• 2013

Plate-type phosphor is a promising substitute in overcoming the issues related to the powder phosphor paste mixed with resin. In this research, $Ca-{\alpha}-SiAlON:Eu^{2+}$ plate phosphor ($Ca_xSi_{12-(m+n)}Al_{m+n}O_nN_{16-n}:Eu_y$) was investigated for the varied compositions (m,n) of the host crystal with the fixed Eu content (y). Densification was promoted for the compositions with increasing 'm' values for the m=2n relationship. Dictated by the Eu concentration inside the phosphor crystal, photoluminescence intensity was stronger in ${\alpha}2$ specimen (m = 3.0, n = 1.5) containing the second phases when compared to ${\alpha}1$ specimen (m = 1.5, n = 0.75) comprising a single-phase ${\alpha}$-SiAlON. The concentration of Eu in the non-emitting amorphous interfacial glass phase was 2~4 times of the designed Eu concentration inside the ${\alpha}$-SiAlON crystal.

• 한국결정성장학회지
• /
• 제7권4호
• /
• pp.658-664
• /
• 1997

자기질 도자기 소지조성에 필수적으로 함유되는 부산화물들($K_2O, MgO, CaO,Al_2O_3$, 그리고 $TiO_2$)이 순수한 $SiO_2$의 상형태에 미치는 영향을 조사하였다. 또한 장석, 도석, 카올린, 그리고 점토를 이용하여 조합된 자기질 도자기 소지 조성에서 $SiO_2/Al_2O_3$의 비를 조정하여 안정화된 $\beta$-cristobalite 상을 갖는 도자기 소지 조성을 개발하였으며, 여기에 첨가된 부산화물들이 $SiO_2$의 상형태에 미치는 영향을 조사하였다. $SiO_2$에 $K_2$O와 MgO를 첨가할 경우 준안정한 주상은 $\alpha$-cristobalite, CaO와 $Al_2$O$_3$를 첨가할 경우 $\alpha$-quartz, 그리고 $TiO_2$를 첨가할 경우는 비정질상이었다. 장석, 도석, 카올린, 그리고 점토를 사용하여 조합한 도자기 소지에서 $SiO_2/Al_2O_3$비가 작아질 수록 $\beta$-cristobalite 상의 안정화가 촉진되었으며, $\beta$-cristobalite 상이 안정화되는 임계의 $SiO_2/Al_2O_3$의 비는 68.10/22.75이었다. Cristobalite 상이 안정화된 실용 도자기 조성에 부산화물들이 첨가될 경우 $\alpha$, $\beta$-cristobalite 상생성이 억제되었다.