• 한국주조공학회지
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• 제20권1호
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• pp.13-20
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• 2000

In the present study,($10%Al_2O_3+5%Si$)/AZ91 Mg hybrid composite was fabricated using the squeeze casting method. During squeeze casting, Molten Mg was infiltrated into the preform of $10%Al_2O_3+5%Si$ and reaction product of $Mg_2Si$ intermetallic compound was formed by the reaction between molten Mg and Si Powder. Microstructure has been observed and mechanical properties were evaluated for the reaction squeeze cast(RSC) hybrid composite. It was found that Si powder totally reacted with molten Mg to form $Mg_2Si$. Reinforcement($Al_2O_3$) and the reaction product ($Mg_2Si$) are fairly uniformly distributed in Mg Matrix for the squeeze cast hybrid composite. Mechanical Properties were improved with hybridization of reinforcements, namely higher hardness and enhanced wear resistance comparing squeeze cast($15%Al_2O_3$)/AZ91 Mg composite.

• 한국주조공학회지
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• 제17권4호
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• pp.393-401
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• 1997

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a $CO_2$ laser to produce the wear resistant composite layer. From the experimental results of this study, it was possible to composite TiC particles on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of laser remelted cast iron substrate without titanium coating was about $1{\times}10^4$ K/s to $1{\times}10^5$ K/s in the order under the condition used in this study. The microstructure of alloyed layer consisted of three zones, that is, TiC particule crystallized zone (MHV $400{\sim}500$), the mixed zone of TiC particule+ledebulite (MHV $650{\sim}900$) and the ledebulite zone (MHV $500{\sim}700$). TiC particules were crystallized as a typical dendritic morphology. The secondary TiC dendrite arms were grown to the polygonized shape and were necking. And then the separated arms became cubic crystal of TiC at the slowly solidified zone. But in the rapidly solidified zone of fusion boundry, the fine granular TiC particules were grouped like grape.

• 한국주조공학회지
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• 제17권4호
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• pp.365-370
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• 1997

The effects of changes in microstructure of Si phase on the thermal expansion coefficients(CTEs) and tensile properties of the hypereutectic Al-Si foundry alloy(A390) were investigated experimentally. Specimens were prepared by various fabrication processes, such as a permanent mold casting, a squeeze casting and a spray casting process, and subsequently hot-extruded. CTEs of the spray-cast specimen were found to be about 10% lower than those of the permanent mold-cast specimen, and the CTEs of the hypereutectic Al-Si alloy(A390) were changed proportionally with the size of Si phase. Ultimate tensile strength of the spray-cast and hot-extruded specimen was dramatically improved about 100% with improved elongation, compared to that of permanent mold-cast specimen. These improvements are mainly attributed to the reduction in size and aspect ratio of the brittle Si phase, and the elimination of the microvoids/porosities formed during casting.

• 한국주조공학회지
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• 제13권2호
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• pp.175-186
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• 1993

In this study, the effect of Mo addition on the microstructure and mechanical properties of ductile cast iron have been investigated. The amounts of Mo and the thickness of specimen have been varied from 0 to 4.79wt% and 13mm, 10mm and 6mm, respectively. As the casting thickness decreases, the average size of spheroidal graphite is decreased and the hardness increases. By increasing the Mo content, the tensile strength of ferrite and pearlite matrix increases and shows maximum which is about $30{\sim}40%$ higher than ordinary ductile cast iron. After the maximum, adding more Mo results in gradual transformation of ferrite and pearlite to bainite and thus tensile strength decreases again. The elongation decreases continueously with Mo content. The addition of Mo about $0.5{\sim}1.0wt%$ improves the wear resistance and tensile strength of thin ductile cast iron.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.553-556
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• 1999

This paper presents a proper condition to achieve above 19 % conversion efficiency using PC1D simulator. Cast poly-Si wafers with resistivity of 1 $\Omega$-cm and thickness of 250 ${\mu}{\textrm}{m}$ were used as a starting material. Various efficiency influencing parameters such as rear surface recombination velocity and minority carrier diffusion length in the base region, front surface recombination velocity, junction depth and doping concentration in the Emitter layer, BSF thickness and doping concentration were investigated. Optimized cell parameters were given as rear surface recombination of 1000 cm/s, minority carrier diffusion length in the base region 200 ${\mu}{\textrm}{m}$, front surface recombination velocity 100 cnt/s, sheet resistivity of emitter layer 100 $\Omega$/$\square$, BSF thickness 5 ${\mu}{\textrm}{m}$, doping concentration 5$\times$10$^{19}$ cm$^3$ . Among the investigated variables, we learn that a diffusion length of base layer acts as a key factor to achieve conversion efficiency higher than 19 %. Further details of simulation parameters and their effects to cell characteristics are discussed in this paper.

• 보존과학연구
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• 통권23호
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• pp.131-147
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• 2002

Kkonmoe relic located in Jangan-gu, Suwon-si, Gyeonggi-do Provinceis an example of the wide chronology from the Three Kingdoms Period to Joseon Dynasty. Examinations on a forged iron ax, a cast iron ax and an iron sickle excavated from this relic revealed the microstructure structure of the metal and the manufacturing technologies. Microstructure investigation was carried out with a metallurgical microscope and a Vickers hardness tester was used to measure the hardness of the micro structures. The test results show that the forged iron ax has a ferrite and pearlitestructure. It is made of low carbon steel and then carbonized to increase carbon content. After carbonization, the surface grains are reworked and the surface decarbonized. In case of the iron sickle, it is forged from low carbon steel, then carbonized and hardened, to increase overall strength. The sickle blade is carbonized and quenched after forging, resulting in afirm, solid blade. Heat treatment to remove brittleness is not applied to the cast ironartifact, which is manufactured by solidifing hypo-eutectic cast iron with a3-4% carbon content and white cast iron. All artifacts are produced from steel and subjected to a carbonization process. To increase hardness of the blade, additional heat treatment is applied.

• Tribology and Lubricants
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• 제28권5호
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• pp.233-239
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• 2012

The engine of a large ship operates under wet conditions using a fuel such as bunker C oil, which includes sulfur and many impurities. A cylinder liner made of cast iron is very susceptible to damage such as scuffing on the surface. This scuffing can reliably be attributed to the destruction of the oil film and the corrosion wear caused by water and sulfur included in the fuel, along with abrasion impurities and poor lubricants. In this study, a reciprocating friction and wear test was carried out with a cast iron specimen, which was used to simulate an engine cylinder in a corrosive environment. Base-oil and stirred oil containing distilled water, NaCl solution, and dilute sulfuric acid were used as lubricants. The friction surface was analyzed using a microscope and EDAX, and the friction coefficient was measured using a load-cell under each experimental condition. We then attempted to investigate the damage to the cylinder liner using the results.

• 한국정밀공학회지
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• 제5권1호
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• pp.50-62
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• 1988

An experimental investigation of the machining characteristics of compact vermicular cast iron whose matrix were formulated under two kinds of annealing conditions has been conducted. The various characteristics of the machinability of CA cast iron depending upon its matrix and cutting condition have been obtained from the experiment. The results are as follow. As depth of cut increases, the shear stress slightly decreases in order $P_1, \P_2, \P_3$ which are classified by ferrite matrix of CV cast iron. As depth of cut increases, the normal stress increases, and annealing effect in heavy cutting is smaller than that in light cutting. The cutting energy slightly decreases, as depth of cut increases and the effect of annealing on cutting energy in light cutting is higher than that in heavy cutting. The cutting equation in this study are as follow. $P_1\:\2{\phi}\ + \1.49({\beta} - {\alpha} )=84^{\circ}$ $P_2\:\2{\phi}\ + \1.36({\beta} - {\alpha} )=82^{\circ}$ $P_3\:\2{\phi}\ + \1.34({\beta} - {\alpha} )=79^{\circ}$ Machining constants in this study for $P_1, P_2, P_3$give $74^{\circ} , 66^{\circ}, 61^{\circ}$ Tool wear increases as depth of cut increases, and decreases as ferrit matrix increases.

• 열처리공학회지
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• 제10권1호
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• pp.47-54
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• 1997

Flake graphite cast irons with the high damping capacity have been used for the control of vibration and noise occuring in the members of various mechanical structures under vibrating conditions. However, the damping capacity which is morphological characteristics of graphite is one of the important factors in reducing the vibration and noise, but hardly any work has deal with this problem. Therefore, the authors have examined the damping capacity of various cast irons with alloying elements and studied the influences of the matrix, mechanical properties and morphological characteristics of graphite. The main results obtained are as follows: Effects of Ni on the damping capacities and mechanical properties are investigated in 3.9%C-0.3% Cu gray cast iron. At 0.2% Ni content, specific damping capacity showed the maximum value, and decreased with further increase in Ni content, Graphite continuity also showed same behavior. This indicates that the specific damping capacity has a close relation with graphite continuity. On the other hand, the damping capacity in pearlite matrix showed superior to that in ferrite. In contrast, with increasing the Ni content, both tensile strength and hardness increased due to the decrease of graphite length and eutectic cell size.

• 열처리공학회지
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• 제31권5호
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• pp.231-236
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• 2018

The purpose of this study was to investigate the microstructural characteristics and hardness distribution of AZ91 magnesium alloy furnace-cooled to room temperature after solution treatment, and to compare the results with those of as-cast condition. The as-cast alloy showed a partially divorced eutectic ${\beta}(Mg_{17}Al_{12})$ phase and discontinuous precipitates (DPs) with a lamellar morphology, while only DPs were observed in the furnace-cooled alloy. The DPs in the furnace-cooled AZ91 alloy had various apparent interlamellar spacings, which would be ascribed to the different transformation temperatures during the furnace cooling. The average hardness for the furnace-cooled alloy is similar to that for the as-cast alloy. It is interesting to note that the hardness values of the furnace-cooled alloy were distributed over a narrower range than those of the as-cast alloy. This is likely to be caused by the relatively more homogeneous microstructure of the furnace-cooled alloy in comparison with the ascast one.