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정봉용,주대헌,박주승,김명호 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.9
This paper reports an investigation of the characteristics of plasma duplex treated ductile cast irons during thermal fatigue tests on a thermal cycling rig. The thermal fatigue cracking behaviors and microstructure of untreated and plasma surface treated ductile cast irons have been investigated. Both ferrite and pearlite matrix ductile cast irons were evaluated. During the tests, 60 mm long cylinders with 20 mm diameter were subjected to 1,000 high frequency induction heating and water cooling cycles, lasting 7 and 5 sec, respectively. The thermal fatigue damage was evaluated by analyzing different crack dimensions and distribution by light microscopy. The results showed that the plasma surface treatment increased thermal fatigue cracking resistance. When thermal fatigue cracking occurs, the cracks always initiate at the surface of the specimen. The major path of crack propagation is generally along the ferrite grain boundaries. The hardened layer had an effect on the thermal fatigue property. In addition, the ductile cast iron with an pearlite matrix has a better resistance to thermal fatigue than that of ferrite matrix.
Cu-Ag 합금의 전기전도도와 기계적 특성에 미치는 P , Mg 의 영향
정봉용,김기태,정운재,김명호 ( Bong Yong Jeong,Ki Tae Kim,Woon Jae Jung,Myung Ho Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2
N/A Effects of P and Mg on the electrical conductivity and mechanical properties of Cu-Ag alloys were investigated experimentally. Small addition of these alloying elements decreased the electrical conductivity of Cu alloy greatly, especially for P addition. The maximum amounts of P addition to obtain the electrical conductivity being over 90%IACS was found to be about 0.019wt.%, and in this case recrystallization temperature of the addition was about 450˚C. The tensile strength was not changed significantly by the addition of P. However, for Cu-Ag-P-Mg alloys, P-Mg compound was precipitated by heat treatment at 450˚C for 1 hour. Such a precipitation of P-Mg compound increased the electrical conductivity of the alloy from 47~57%IACS to 72.3~86.6%IACS. (Received January 15, 1998)
용탕단조한 미세강선 보강 알루미늄 복합재료의 미세조직에 대한 고찰
정봉용,이인우,박흥일,김준수,김명호 ( Bong Yong Jeong,In Woo Lee,Heung Il Park,Jun Su Kim,Myung Ho Kim ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.5
N/A Aluminum matrix composites reinforced by fine steel wires were fabricated by squeeze casting process. Preforms made of fine steel wires were prepared with different surface conditions, namely uncoated(TN), carbo-nitriding treated(TT), and brass coated(TA). Squeeze casting were performed under the pressure of 1500㎏/㎠ for 3min. during solidification, and pouring temp. of the melt being 750℃ and the steel mold being preheated at 250℃. Microstructural characteristics were evaluated, particularly concerned with the effect of the surface conditions of the preforms. The results obtained from this study are like these. TN specimens show partially non-wetted regions, due to easy formation of oxides on the surface of the fine steel wires. TT specimens show no interfacial reaction between the steel wires and the aluminum alloy matrix, possibly due to the formation of carbo-nitrided zone on the surface of the steel wires. TA specimens show excellent wettabillity between the reinforced steel wires and the aluminum alloy matrix and very thin interfacial zone is formed between them. During the solution hardening treatment of TA specimens, thickness of the interfacial reaction zones were increased with the solution treating time. TA specimens show typical ductile fracture in tensile test, but TT specimens show brittle fracture possibly due to the formation of the brittle hard surface on the steel wires during carbo-nitriding treatments. TA specimens which were reinforced with 40 vol.% of the fine steel wires exhibit high tensile strength of 77.l㎏f/㎟ and impact value of 8.l㎏f-m/㎠.
NaF 전해질 양극산화에 의한 마이크로콘 구조 니오븀 산화물 제조
정봉용,정은혜,Jeong, Bong-Yong,Jung, Eun-Hye 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.6
In this study, we show that by anodization of Nb in NaF electrolytes microcone niobium oxide layers can be formed under a range of experimental conditions. It is found that a single NaF electrolyte leads to the formation of microcones. At 1 M NaF, 40 V, 1 h, well-ordered microcones were generated on Nb discs. XRD results show that the initially formed anodic oxide is amorphous, but an amorphous to crystalline transition occurs during anodization. For the formation of favorable microcones, it is considered that proper parameters such as electrolyte concentration, voltage, anodizing time are necessary according to the kind of electrolytes.
정봉용,Eun Hye Jung 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.3
Niobium oxide produced by an anodization process for application in a high-efficiency dye-sensitized solar cell (DSSC) has been reported. In order to increase the energy conversion efficiency of the cell, we demonstrated niobium oxide micro-mountain and nano-forest pancake structures that contained nanowires on the surface. The increase in efficiency is attributed to the significantly enhanced surface area, which allows for more dye loading and light harvesting, as well as the reduced charge recombination, which provides direct conduction pathways along the crystalline Nb2O5 micro-mountain structures with nanowires. We observed that the photovoltaic performance of the Nb2O5 DSSC increased from 1.03% to 3.35% when the oxide thickness was increased from 9.3 μm to 27.7 μm. Since the anodization process is very cheap and takes place at low temperatures, it has substantial potential for the further development of DSSCs with metal-oxide nano-materials. Anodized oxide advantage is that essentially any form of a niobium surface can be treated in a quick and low-cost approach with Nb2O5 coating.
정봉용,Min Ryou,이종무,김명호 한국전기전자재료학회 2014 Transactions on Electrical and Electronic Material Vol.15 No.1
Dual phase steels have a microstructure comprising of a polygonal ferrite matrix together with dispersed islands ofmartensite. There are clear differences between the image quality (IQ) map of the dual phase and the correspondingferritic/pearlitic structures, both in the as-heat treated and cold rolled conditions. Electron backscatter diffraction(EBSD) techniques were used to study the evolution substructure of steel due to plastic deformation. The martensiteferriteand ferrite-pearlite interfaces were observed. The interface can be a source of mobile dislocations which thebands seem to originate from the martensite islands. In particular, the use of image quality is highlighted.