High pressure wear characteristics of DCI(Ductile Cast Iron) were investigated through unlubricated pin-on-disc wear test. Wear test were carried out at speed of 23m/min, under pressure of 3MPa and 3.3 MPa. Cu and/or Mn were added to examine the effect of alloying elements on the high pressure wear characteristics of DCI. To investigate the relationship between wear characteristics and mechanical properties of DCI, Brinell hardness and V-notched Charpy impact energy were tested. Wear surface of each specimen was observed by SEM to determine the wear mechanism of DCI under high pressure wear condition. In the mild wear region, wear characteristics of alloyed DCI specimens were very similar to that of unalloyed DCI. But mild-severe wear transition was occurred at different wear distance and wear rate of DCI specimens were changed by alloying elements. In severe wear condition, wear rate of DCI was dramatically increased by the addition of Mn. Although the addition of Cu 0.46wt% did not decrease the wear rate of DCI in the severe wear region, but it delayed the mild-severe wear transition. Under high pressure wear condition, wear rate and mild-severe wear transition were not concerned with hardness of DCI specimens, but they were deeply associated with impact energy changed by alloying elements.

Surface layer properties such as composition, phase, hardness, and oxide layer condition are very important if the main failure mechanism of metals is wear. Generally, stable and dense oxide layers are known to decrease the wear rate of metals by prohibition of metallic junction occurred between bare metals. Addition of Si above 4 wt% to DCI(Ductile Cast Iron) is reported to enhance the significant oxidation resistance by forming the silicon-rich surface layer which inhibits further oxidation. And addition of up to 2 wt% Mo to high Si ductile iron produces significant increases in high temperature tensile strength, creep strength, thermal fatigue resistance and oxidation resistance. High pressure wear characteristics of unalloyed DCI(Ductile cast Iron), 4.46 wt% Si ductile iron, 4.3 wt% Si-0.52 wt% Mo ductile iron were investigated through unlubricated pin-on-disc wear test. Wear test was carried out at speed of 23m/min, under pressure of 3 MPa and 3.3 MPa. Wear surfaces of each specimen were observed by SEM to determine the wear mechanism under high pressure wear condition. Addition of Si 4.46 wt% severely deteriorated wear property of ductile iron compared to unalloyed DCI. But combined addition of Si 4.3 wt%andMo0.52wt%decreasedthefrictioncoefficient(${\mu}$)ofductileironsandremarkablydelayedthemild-severeweartransition.

Titanium was melted in the CaO-coated alumina crucible and the reaction between the melt and the coating layer was negligible. The volume fraction of the gas porosity was decreased with increasing pressure and the sound bar castings with no porosity was obtained under the Ar atmosphere of the pressure of $300kN/mm^2$. The surface of the casting obtained from CaO-coated graphite mold was slightly rougher than that from graphite without coating. The reaction product of titanium melt with the layer of CaO was mainly titanium oxide and that with graphite crucible was titanium cabide with small amount of titanium nitride.

Metal matrix composites(MMCs) reinforced with hard particles have many potential application in aerospace structures, auto parts, semiconductor package, heat resistant panels, wear resistant materials and so on. In this work, the effect of SiC partioel sizes(50 and 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on the microstructure and the wear property of $Al-5Mg-X(Si,Cu,Ti)/SiC_p$ composites produced by pressureless infiltration method have been investigated using optical microscopy, scanning eletron microcopy(SEM) with EDS(energy dispersive spectrometry), hardness test, X-ray diffractometer(XRD) and wear test. In present study, the sound $Al-5Mg-X(Si,Cu,Ti)/SiC_p$(50 and 100 ${\mu}m$) composites were fabricated by pressureless infiltration method. The $Al-5Mg-0.3Si-O.1Cu-O.1Ti/SiC_p$ composite with $50 {\mu}m$ size of SiC particle has higher hardness and better wear property than any other composite with $100{\mu}m$ size of SiC particle produced by pressureless infiltration method. The hardness and wear property of $Al-5Mg/SiC_p$(50 and 100 ${\mu}m$) composites were enhanced by the addition of Si, Cu and Ti in Al-5%Mg matrix alloy.

응고 및 마모거동을 연구하기 위하여 Cr, V, Mo 및 W의 조성이 다른 3종류의 백주철을 주조하였다. 고주파유도용해로에서 장입시켜 1873K까지 승온시켜 장입원료들을 모두 용해시킨 후 1823K에서 Y블럭주형에 주입하였다. 얻어진 3종류의 백주철조성은 다음과 같다: Fe-3%C-10%Cr-5%Mo-5%W(합금1), Fe-3%C-10%V-5%Mo-5%W(합금2) 및 Fe-3%C-17%Cr-3%V(합금 3)응고과정을 추적하기 위하여 각 시편으로부터 50g을 채취한 후 알루미나도가니에 넣고 실리콘카바이드로를 사용하여 1723K의 알콘분위기하에서 재용해를 시켰다. 용금을 10K/분의 속도로 냉각시키면서 열분석을 행하였으며 도중 몇 차례 소입 실험을 병행하였다.합금1의 경우 초정오스테나이트, (오스테나이트+$M_7C_3$)공정, (오스테나이트+$M_6C$)공정, 합금2의 경우 초정 MC, 초정오스테나이트, (오스테나이트+MC)공정 , (오스테나이트+$M_2C$)공정, 합금3의 경우 초정 $M7C_3$와 (오스테나이트+$M_7C_3$)공정으로 구성되어 있었다. 주방상태, 균질화열처러상태, 공냉상태, 템퍼링상태에서 내마모시험을 행하였다. 먼저 주방상태시 편을 진공분위기하에서 1223K에서 5시간동안 균질화열처리를 행한후 로냉을 시켰다. 다시 이 시편을 1323K에서 2시간 유지후 강제공냉을 시켰으며 강제공냉된 시편을 573K에서 3시간동안 템퍼링처리를 하였다. 내마모시험은 120 mesh마모지에 10N의 하중을 가하여 실시하였다. 각 사이클마다 무게감소를 측정하였으며 8번 반복실험을 하였다. 마모량은 균질화열처리시편, 주방상태시편, 템퍼링시편, 공냉시편의 순으로 감소하였다. 합금2가 마모량이 가장 적었으며 합금3이 가장 많았다. 합금2의 마모량이 가장 적은 이유는 조직이 초정 MC, 공정 MC 및 공정 M2C로 구성되어 있기 때문으로 사료된다.주방상태에서 기지조직은 퍼얼라이트이었으나 열처리를 통하여 마르텐사이트, 템퍼드마르텐사이트, 잔류오스테나이트로 변태하였다. 이상의 결과를 종합해 보면 MC가 내마모성에 가장 기여하는 조직으로 판단되어진다.

So far, the study on semi-solid process has been carried out to develop and research new advanced materials without some casting defects. In this study, A356 billets consisted of various dendritic shapes were prepared using electro-magnetic stirring process continuously. As-cast respectively has liquidus temperature of $625.6^{\circ}C$ and solidus temperature of $573.55^{\circ}C$ A356 slugs were reheated homogeneously at different temperatures of 580, 590 and $605^{\circ}C$, followed by squeezing in a mold insulated with applied pressures(0, 25, 50 and 70 MPa). In order to investigate on aging responce for casts, 50 MPa squeezed specimen among all specimens was prepared in aging treatments, which conditions are aging temperature of $160^{\circ}C$ and holding times of 0, 45, 90, 270, 360, 720, 1440 and 2880 min after solution treatment ($540^{\circ}C$ for 10 hr). SSM ingot with the output velocity of 150mm/min appeared more spheroidal shape and fine structure than that with the output velocity of 250 mm/min. According to increasing in reheating temperature, numbers of fatigue cycles, U.T.S and elongation increased at same time.

The RP&M (Rapid prototyping and Manufacturing) is the most appropriate technology for the small-lot production system, in which the production cycle is getting shorter owing to various needs from consumers. In this paper, RP&M is applied to a casting process. A casting process has a merit of being able to reflect complicated shapes at one time. But it has not been applied to the precision industry because of bad quality on surface. So we will improve characteristics of aluminum casting process using vacuum sealed casting process and porous ceramic mold which is made by slurry casting process.