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Choi, Hanshin,Byun, Jong Min,Lee, Wonsik,Bang, Su-Ryong,Kim, Young Do The Korean Powder Metallurgy Institute 2016 한국분말재료학회지 (KPMI) Vol.23 No.2
Additive manufacturing (AM) is defined as the manufacture of three-dimensional tangible products by additively consolidating two-dimensional patterns layer by layer. In this review, we introduce four fundamental conceptual pillars that support AM technology: the bottom-up manufacturing factor, computer-aided manufacturing factor, distributed manufacturing factor, and eliminated manufacturing factor. All the conceptual factors work together; however, business strategy and technology optimization will vary according to the main factor that we emphasize. In parallel to the manufacturing paradigm shift toward mass personalization, manufacturing industrial ecology evolves to achieve competitiveness in economics of scope. AM technology is indeed a potent candidate manufacturing technology for satisfying volatile and customized markets. From the viewpoint of the innovation technology adoption cycle, various pros and cons of AM technology themselves prove that it is an innovative technology, in particular a disruptive innovation in manufacturing technology, as powder technology was when ingot metallurgy was dominant. Chasms related to the AM technology adoption cycle and efforts to cross the chasms are considered.
Nano-Attached Tungsten Particle Synthesis and Sintering Behaviors
Chulwoong Han,Hanshin Choi,Byoungmoon Kim 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5
The reduction of sintering temperatures in industrial processes is advantageous for both energy efficiency and material properties in powder metallurgy. Based on the well-known size effects of nano-particles on sintering processes, nano-particles were intentionally used as a homogeneous sintering activator for micro-particles in this study. Two kinds of tungsten bimodal feedstocks which consisted of nano-particles and microparticles were prepared and sintered by spark plasma sintering processed. Even at the low sintering temperature of 1,250 °C and the short sintering time of 300 sec, relatively high densities could be achieved. Depending on the content of the nano-particles in the charged feedstock, the sintered body exhibited different morphological features. Density, field emission scanning electron microscopy, transmission electron microscope was used for analysis.
벌크 비정질 Ni_(57)Ti_(18)Zr_(20)Si₃Sn₂ 입자 산화거동에 따른 HVOF 코팅 상변화 거동
이상용,최한신,김길영,이창희,김용진 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.9
Bulk amorphous Ni_(57)Ti_(18) Zr_(20)Si₃Sn₂ feedstock was sprayed using a high velocity oxy-fuel spraying process. In order to evaluate the amorphous formability ign view of chemical instability, the oxygen to hydrogen gas flow rate ratio was changed at the constant total gas flow rate. Flame gas enthalpy was increased with the O₂/H₂ gas ratio. In-flight particle melting state was improved with the increase of oxidizer flow rate. Fthe amorphous phase fraction within an as-sprayed coating was decreased with the oxygen flow rate. From the thermal analysis and x-ray diffraction, the effects of 0₂/H₂ gas ratio on the crystallization of HVOF sprayed bulk amorphous Ni_(57)Ti_(18) Zr_(20)Si₃ could be divided into two categories. One is due to the solid-state crystallization during flight along the low gas enthalpy The other results from the of bulk amorphous feedstock due to the chemical composition change resulting from in-flight particle oxidation at the higher oxygen gas flow rate.
Na, Hyunwoong,Choi, Hanshin,Oh, Ji-Won,Jung, Ye Seul,Cho, Yong Soo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.28
<P>There have been extensive efforts to develop competitive electrocatalysts using carbon black (CB) supports for high-performance proton-exchange membrane fuel cells with less usage of Pt. Herein, we propose a very promising electrocatalyst architecture based on the three-dimensional Pt/indium tin oxide (ITO)/CB support structure which was enabled by a nonconventional deposition process ensuring very uniform impregnation of Pt and ITO nanoparticles into the CB network. The unusual scales of the Pt (∼1.9 nm) and ITO (∼5.6 nm) nanoparticles were directly related to unexpectedly better performance of the electrocatalytic activities. As a highlight, the electrochemical surface area of the electrocatalyst was maintained very well after the 3000 cycle-accelerated durability evaluation by demonstrating an excellent retention of ∼74.9%. Particularly, the CO tolerance exhibited a low value of ∼0.68 V as the absorption current peak, compared to ∼0.79 V for a commercial Pt/CB catalyst containing twice more Pt.</P> [FIG OMISSION]</BR>
대기 열플라즈마를 이용한 NiCr-Cr₂O₃-Ag-BaF₂/CaF₂ 코팅미세조직과 상조성에 대한 고찰
한창민,최한신,김길영,이창희,황순영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.6
A blended NiCr-Cr₂O₃-Ag-CaF₂/BaF₂ feedstock was sprayed using an atmospheric plasma spraying. Physical and thermophysical properties of each constituent phase are quiet different and resulting interactions of each constituent with the plasma jet can be expected to be different. Thus, an attempt to change the plasma jet characteristics by changing the hydrogen gas flow rate in view of the thermophysical properties of the plasma jet was tried. According to the hydrogen gas flow rate, phase compositions and microstructures were evaluated. The effects of phase composition and microstructure on the Vickers microhardness and bond strength were also evaluated. For empirically tracing the each constituent particle trajectory, spot spraying bead was produced. Finally, particle temperature and velocity according to the hydrogen gas flow rate was measured using alumina-titania particle instead of the blended feedstock. (Received January 19, 2004)
Cho, Hoon,Choi, Hanshin,Jo, Hyungho,Lim, Sungchul,Kim, Byoungmoon,Lee, Changhee Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>Effects of isothermal oxidation on the chemical instability which triggers crystallization of Cu<SUB>54</SUB>Zr<SUB>22</SUB>Ti<SUB>18</SUB>Ni<SUB>6</SUB> (numbers indicate at.%) bulk metallic glass were investigated. Comparing the isothermal heat flux of Cu<SUB>54</SUB>Zr<SUB>22</SUB>Ti<SUB>18</SUB>Ni<SUB>6</SUB> bulk metallic glass within the supercooled liquid region in differential scanning calorimetry, it could be observed that the isothermal oxidation did decrease the incubation time for crystallization. What is further, this amorphous phase instability was enhanced with the decrease of particle size. Through this study, chemical instability due to preferential oxidation of alloying element and resulting deviation of chemical composition in intact metallic region needs to be considered in phase evolution of bulk metallic glass during material processing.</P>
Jang, Jin Woo,Choi, Hong Je,Kwon, Oh Hyeon,Na, Hyunwoong,Oh, Hyo Chan,Choi, Hanshin,Cho, Yong Soo Elsevier 2018 THIN SOLID FILMS - Vol.660 No.-
<P><B>Abstract</B></P> <P>Nanocomposite thick-film electrodes are investigated for highly integrated microcircuit devices that require retarded densification in order to match potential co-fireable ceramic sheets. In this study, we introduce carbon nanotube (CNT) as an ingredient to retard the densification of the conducting Ni paste while minimizing the decrease in the electrical resistivity of the Ni paste. Well dispersed CNT/Ni pastes containing various amounts of CNT ranging from 1 to 5 wt% were screen-printed on a regular alumina substrate and fired at 800–1200 °C for 1 h in a reducing atmosphere. The retardation effect was evident even with 1 wt% CNT that exhibited late full densification at 1100 °C, which corresponds to the target firing temperature for ceramic sheets. Electrical resistivity was not significantly influenced by the low content of CNT, which corresponds to 3.39 × 10<SUP>−5</SUP> Ω cm when compared to 2.97 × 10<SUP>−5</SUP> Ω cm for pure Ni paste processed at the same temperature of 1100 °C. The results indicate that the Ni-CNT composite thick films are potentially useful as a competitive co-fireable electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CNT/Ni nanocomposite thick films are printed on an alumina substrate. </LI> <LI> CNT addition delays the densification of Ni. </LI> <LI> 1 wt% CNT was sufficient to hinder grain growth by ~200 °C </LI> <LI> Electrical resistivity of Ni was almost maintained at 1100 °C with 1 wt% CNT. </LI> </UL> </P>
Yoon, Sanghoon,Lee, Changhee,Choi, Hanshin Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>A bulk amorphous Ni–Ti–Zr–Si–Sn powder produced using an inert gas atomization was sprayed by a kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate and they were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the sprayed Ni–Ti–Zr–Si–Sn bulk metallic glass coatings, a partially crystallized coating and a fully crystallized coating were prepared by isothermal heat treatments. Tribological properties were investigated—friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscopy and α-step. From the examination of the scratch wear track microstructure, transition from ductile-like deformation micro-cutting to brittle-deformation micro-fracturing in the scratch groove was observed with the increase of the crystallinity.</P>
Kim, Juneseob,Lee, Changhee,Choi, Hanshin,Jo, Hyungho,Kim, Hwijun Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>In this study, vacuum plasma spraying (VPS) was chosen for making Ni–Ti–Zr–Si–Sn bulk metallic glass (BMG) coating and the process parameters were optimized in view of phase composition of as-sprayed BMG overlay. When it comes to the phase evolution of BMG particle in thermal spraying process, the crystallization does occur by chemical instability and/or thermal instability. For the VPS process, the chemical instability such as in-flight particle oxidation can be neglected and thus the crystallization of BMG feedstock can be considered to result from the thermal instability. Actually, the crystalline phase fraction of the as-sprayed coatings was largely affected by the plasma gas composition which determines the plasma jet characteristics and also in-flight particle melting state. As the gas enthalpy is increased with the increase of hydrogen gas flow rate, number density of unmelted particle within the coating and crystalline phase fraction were consistently decreased. It implied that the phase composition of VPS BMG coating was largely dependent on the melting state of the impacting BMG particle.</P>