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Droplet-Based Manufacturing 공정에 의해 제조된 무연 솔더볼의 제조공정 변수 연구
엄호천,조경목,송인혁,한유동 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.1
Uniform droplet of lead-free solder balls was produced by using the Droplet-Based Manufacturing(DBM) process. Compositions of solder were Sn, Sn-3.6 wt.% Ag, and Sn-3.8 wt.%Ag-0.6 wt.% Zn. Effect of parameters such as orifice size, pressure difference, and frequency on the solder ball production was also investigated. Mean size, size distribution, and surface defect of solder balls were analyzed with variations of the parameters. Droplet spacing decreased with increasing frequency and decreasing pressure difference. Thus the size of solder ball decreased with increasing frequency and decreasing pressure difference. Size distribution fell within the narrow range of ±5% from the mean diameter of solder balls. The experimentally measured diameter of the solder balls fabricated by DBM process coincided quite well with the theoretically anticipated value of d_d=A d_o^2/3.
박판주조법으로 제조된 Zr계 벌크 비정질 합금의 미세파괴기구
이정구,이동근,이성학,김낙준,조경목,박익민 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.2
The mechanical property improvement of a strip-cast Zr-base bulk amorphous alloy was explained by clarifying fracture mechanisms. Effects of crystalline phase particles formed in the amorphous matrix during strip casting on strength, ductility, and fracture toughness were explored in detail by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber. The compressive and fracture toughness test results indicated that ductility, strength, and fracture toughness of the atrip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5 vol. %) of hard, brittle crystalline particles. This improvement of mechanical properties in the strip-cast alloy could be plausibly explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles. Such property improvement presents new applicability of the strip-cast amorphous alloy containing crystalline particles to structures and components requiring excellent fracture toughness.
Fe-0.1C-(V, Nb) 제어압연강의 미세조직 및 기계적 특성
조경목 ( Kyung Mox Cho ),김수영 ( Su Young Kim ),박인애 ( In Ae Park ),이영중 ( Young Jung Lee ),강남현 ( Nam Hyun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 대한금속·재료학회지 Vol.45 No.5
Following the trend of industrial high strength and toughness structural steel manufacturing, it is evolving and increasing needs of basic research and development efforts. One of the examples is, due to the high cost of vanadium, the replacement of Fe-V steel to Fe-Nb steel. However, there still exist difficulties for commercial production of Fe-Nb steel because of poor impact toughness of this steel comparing with Fe-V steel. In this study, a fundamental investigation was carried out to analyze the microstructure, tensile properties and impact toughness of Fe-Nb steel as a function of the rolling conditions with no post heat treatment. The steel samples were prepared with three different compositions, i.e., Fe-V steel (Fe-0.05V-0.001Nb), Fe-V-Nb steel (Fe-0.014V-0.03Nb), Fe-Nb steel(Fe-0.003V-0.033Nb). The steels were deformed with controlled rolling conditions, namely start rolling temperature(SRT) 1150℃ for the all experiment, but two different finish rolling temperature(FRT); 950℃ and 860℃. Ferrite grain size decreased and thus impact toughness was measured higher at FRT of 860℃ than at FRT 950℃ treated steels. Even though the impact toughness of Fe-Nb steel was quite low due to inhomogeneous distribution of ferrite grain size, Fe-V-Nb steel exhibited impact toughness improved with controlled rolling at FRT 860℃. Application of the controlled rolling process showed one of the possibilities to replace Fe-V steel with Fe-V-Nb and/or Fe-Nb steel.
Effect of Mn addition on corrosion properties of biodegradable Mg-4Zn-0.5Ca-xMn alloys
Cho, Dae Hyun,Lee, Byoung Woo,Park, Jin Young,Cho, Kyung Mox,Park, Ik Min Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-
<P><B>Abstract</B></P> <P>The corrosion properties of biodegradable Mg–4Zn–0.5Ca–xMn alloys (x = 0, 0.4, 0.8 wt%) in Hank's solution were investigated. According to the electrochemical measurements, the corrosion resistance of the alloys was effectively improved by Mn addition. In addition, the analysis of corroded surface with high resolution transmission electron microscopy (HR-TEM) and time of flight secondary ion mass spectrometry (ToF-SIMS) revealed that the depth of the corrosion product was decreased by Mn addition. It was observed that the microstructural changes had little effect on corrosion properties and Mn oxide film acts as a helpful barrier against chloride ions penetration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Biodegradable as-cast Mg–4Zn–0.5Ca–xMn (x = 0, 0.4, or 0.8 wt%) alloys are prepared. </LI> <LI> The corrosion properties are investigated by immersion tests in Hank's solution. </LI> <LI> The corrosion films formed on the alloy surface are analysed by HR-TEM and ToF-SIMS. </LI> <LI> The corrosion resistance of the alloys is improved with increasing Mn addition. </LI> </UL> </P>
조경목,이희태,김수영,조영기 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4
In the present study, wear properties, of cast Al-SiC_p composites were characterized. Wear tests were performed as a function of teat conditions including applied load, sliding speed and sliding distance under dry wear condition employing a block-on-roller type wear test machine. Wear mechanism of Al-SiC_p composites was also investigated by the analysis of worn surfaces and wear debris. Results show that wear resistance of Al alloy is improved with reinforcement of SiC_p especially with severer wear conditions such as high applied load and long sliding distance. Weight loss of Al-SiC_p composites almost linearly increases with applied load and sliding distance. There exists a transition point of wear behavior at which a minimum wear rate encountered in terms of the sliding speed. Wear mechanism is abrasive at the low speed and at .the transition speed, and adhesive/abrasive wear at the high speed range. It was found that uniform distribution of SiC_p reinforcement is desirable to improve the wear resistance of Al-SiC_p composites.
조경목,박익민,최일동,송대현,최홍석 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.6
In the present study, Al-SiC_p FGMs containing 10 layers with different volume fraction of Al and SiC_p, and different geometry in thickness (3 ㎜, 5 ㎜ and 7 ㎜) were fabricated by employing the pressureless infiltration technique. Optimum condition was established to obtain the enough strength of preforms by controlling the forming pressure and binder added. Al-10%Mg was properly infiltrated into the preforms at 920℃ with N₂ atmosphere within a tube furnace. Analysis of microstructure and mechanical properties revealed that Al-SiC_p FGMs were fabricated successfully. Curvature of Al-SiC_p FGMs plates was measured to predict the internal stress distribution via a theoretical model for the analysis of thermo-mechanical deformation.
조경목,이후철,현태욱 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.1
A study on the fracture toughness of WC-Co using alloys is made single-edge notched beam specimens pre-cracked by electron-discharge machining. The microstructural parameters are determined on the electron micrographs by linear analysis. The relations between K_(IC) and the microstructural parameters show that K_(IC) tends to increase with increased binder volume fraction and cobalt mean free path and tends to decrease with increases in WC contiguity, but cannot be related only to one microstructural parameter. A structure model is sugested to estimate the fracture path in WC-Co alloys and the critical strain energy release rate is evaluated from this fracture model.