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Effect of Additional Zn on Plasticity of Large-Scale Mg-Based Nanostructure-Dendrite Composites
송기안,J. S. Lee,박준식,김기범 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.2
Large-scale Mg90Cu10 and Mg90Cu3Zn7 nanostructure-dendrite composites were successfully fabricated using a water-cooled squeeze casting. The Mg90Cu3Zn7 nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and tetragonal MgCuZn phases has plasticity up to 8.4 % in excess of that of the Mg90Cu10 nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and orthorhombic Mg2Cu phases. This implies that phase selection plays an important role in controlling the strength and plasticity of largescale Mg-based nanostructure-dendrite composites.
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.
CuCrFeMnNi 고엔트로피 합금의 열처리에 따른 미세조직 및 기계적 물성 변화 연구
송호섭,송성호,조재영,송기안 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.6
High entropy alloys (HEAs) are defined as a multi-element alloy including more than 4 elementswith near equi-atomic percentage. In general, the configurational entropy of the HEAs is known to besufficient to stabilize a single solid solution, such as body-centered cubic (BCC), face-centered cubic (FCC) andhexagonal-closed pack (HCP). Compared to BCC single-phase alloys, FCC single-phase alloys draw extensiveattention because they are advantageous in manufacturing and processing. FCC-based HEAs show excellentductility but limited strength, so many research on improving strength has been conducted. Outstandingmechanical properties with a balance of strength and ductility are rarely achieved in single-phase FCC-basedHEAs. This is why most alloys for structural applications exhibit a multi-phase microstructure. In this study,we aimed to develop multi-phase FCC-based HEA with superior mechanical properties than single-phaseCoCrFeMnNi HEA, via Co substitution in CoCrFeMnNi HEA by Cu, which has a high mixing enthalpy. Itwas found that the CuCrFeMnNi HEA is composed of two FCC phases and one BCC phase. The CuCrFeMnNiHEA was cold-rolled, and subsequently aged at 500, 700, 900 oC for 1 hour. As the annealing temperatureincreased, the volume fraction of the FCC phase (FCC1 + FCC2) increased and the residual stress wasgradually relieved by recrystallization. Furthermore, small amount of sigma phase was formed at 900 oC. Theeffect of the microstructural evolution on the mechanical properties, such as hardness and tensile propertiesat room temperature, will be discussed.
Nd-Fe-B 소결자석의 소결 후 열처리 조건에 따른 미세조직 및 자기적 특성 변화
정윤종,홍순직,김동환,배경훈,송기안 한국열처리공학회 2024 熱處理工學會誌 Vol.37 No.1
Nd-Fe-B permanent magnets have been utilized on various industrial fields such as electric vehicles, generator, robots with actuator, etc, due to their outstanding magnetic properties even 10 times better than conventional magnets. Recently, there are many researches that report magnetic properties improved by controlling microstructure through adjusting alloying elements or conducting various processing. Especially, post-sintering annealing (PSA) can significantly improve the coercivity by modifying the distribution and morphology of Nd-rich phase which formed at grain boundaries. In this study, Nd-Fe-B sintered magnets were subjected to primary heat treatment followed by secondary heat treatment at 460oC, 500oC, and 540oC to investigate the changes in microstructure and magnetic properties with the secondary heat treatment temperature. EBSD analysis was conducted to compare anisotropic characteristics. Through the SEM and TEM observation for analyzing the morphology and distribution of Nd-rich phase, we investigated the relationship between microstructure and magnetic properties of sintered Nd-Fe-B magnets.