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이효수,남태운,이병권 ( H . S . Lee,T . W . Nam,B . K . Lee ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.2
It has been investigated that the ion nitriding effects of a STD61 steel in various time conditions of 3 to 9 hours, and the microstructure of compound and diffusion layers of the ion nitrided specimen for 6 hours and subsequently reheated for 1 hour at various temperatures of 400∼800℃. As the nitriding time increased, the thickness of compound and diffusion layers was increased, but the hardness of surface was not considerably increased (Max Hv=1045 at 9hrs). Some of the nitrogen was denitrided out of the surfac and diffused into the core, and also the oxides (Fe₃O₄, Fe₂O₃) were formed on the surface of the specimen during repeating. The compound layer was partially decomposed at about 600℃ but the diffusion layer was increased up to 800℃. With increasing repeated temperture, the hardness of the surface was decreased, whereas the hardness depth of diffusion layer (0.25㎜) was increased up to 600℃ more than that of ion nitrided (0.18㎜). The blend-heat treated STD61 steel by ion nitriding is therefore expected to hold on the characteristics of ion nitriding up to 600℃.
전기방전소결을 이용한 Ti-Ni-Zr 준 결정상의 상변화 연구와 Ti, W 다공체 제작
조재영,송기안,이민하,이효수,이원희,김기범,Cho, J.Y.,Song, G.A.,Lee, M.H.,Lee, H.S.,Lee, W.H.,Kim, K.B. 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.2
Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.
자기펄스 압축성형법으로 성형된 Ag-SnO<sub>2</sub> 접점소재의 미세조직 및 특성
박종석,김영재,이민하,이효수,홍순직,이진규,Park, J.S.,Kim, Y.J.,Lee, M.H.,Lee, H.S.,Hong, S.J.,Lee, J.K. 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.4
In this study, we reported the microstructure and properties of Ag-$SnO_2$ contact materials fabricated by a controlled milling process with subsequent consolidation. The milled powders were consolidated to bulk samples using a magnetic pulsed compaction process. The nano-scale $SnO_2$ phases were distributed homogeneously in the Ag matrix after the consolidation. The relative density and hardness of the Ag-$SnO_2$ contact materials were 95~96% and 89~131 Hv, respectively.