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Fe-Aluminide합금의 미세조직과 기계적 특성에 관한 연구
조종춘,이도인,이성재,최병학,김학민,Jo, Jong-Chun,Lee, Do-In,Lee, Seong-Jae,Choe, Byeong-Hak,Kim, Hak-Min 한국기계연구원 1992 硏究論文集 Vol.22 No.-
Mechanical properties and microstructure were investigated on vacuum induction melted $Fe_3A1$base alloys of $DO_3$ structure. Specal emphasis were put on the effect of alloy chemistry, grain size and process(rolling, directional solidification) on mechanical properties of Fe-22.5-39at.%Al at elevated temperature between room temperature and $800^{\circ}C$. grain size of as-cast alloys is refined by rolling from 1mm to $80\mum$. Tensile strength of Fe-24.lat.%AI was about 404MPa at the critical ordering temperature, and the fracture strain of the alloy was 1-2% at room temperature. An inverse temperature dependence of the strength is noticed as-cast $Fe_3A1$. The presence of Cr and Zr do not affect the room temperature ductility and high temperature strength. Fracture strain of directionally solidified(DS) $Fe_3A1$ is about 1%at room temperature, but is about 60%at. $T_C$(550^{\circ}C)$. Tensile strength of DS alloy is lower than that of as-cast alloy at $530^{\circ}C$ and $430^{\circ}C$. Failure mode at room temperature varies from transgranular fracture to intergranular fracture with the addition of Al. the failure mode also varies from mixed(transgranular+ intergranular) mode between room temperature and $500^{\circ}C$ to intergranular mode above $550^{\circ}C$
최병학(Byung-Hak Choe),김진우(Jin-Woo Kim),김광호(Kawng-Ho Kim),김우식(Woo-Sik Kim),고영태(Young-Tai Kho),김학민(Hak-Min Kim),조종춘(Chong-Chun Cho) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
This paper presents the main finding of cracking in a Ni-base alloy tube of Hastelloy C-276. It was developed as inter-granular cracking in the heat affected zone (HAZ) or weld metal that occurs during the exposure of welded assemblies to the elevated temperatures. Crack propagation along grain boundaries caused leak failure in the HAZ of socket welding tube. In the HAZ of socket welding, the cracking was not accompanied by carbide precipitation such as Cr₂₃C? and Cr depleted zone in grain boundary. The intra-grain, however, was inflicted by highly dense dislocations and severe elastic strain fields by thermal stress or strain caused in welding ad cooling. These may be caused by carbon diffusion during heating service, and result in construction of high-strengthened matrix in HAZ. The cracking may occur in relatively weak grain boundaries due to grain boundary sliding of the creep condition.
($NiAl+Ni_3Al$) 2상 합금의 미세 조직과 기계적 특성에 관한 연구
이종훈,최병학,이남진,김학민,이진형,Lee, Jong-Hun,Choe, Byeong-Hak,Lee, Nam-Jin,Kim, Hak-Min,Lee, Jin-Hyeong 한국기계연구원 1994 硏究論文集 Vol.24 No.-
The Ni-Al intermetallic compound that has the greatest potential to be commercialized shows the high ductility at room temperature with the addition of boron, but has extremely low ductility at high temperature and oxidation environment. On this research work, the changes of microstructure and compressive fracture properties were studied in ($NiAl+Ni_3Al$) two-phase alloys. The precipitation behavior of $Ni_3Al$ after solution treatment at $1300^\circC$ for 14hrs and aging treatment at $800^{\circ}C$ for 14hrs was varied with Al content in ($NiAl+Ni_3Al$) two-phase alloys. These microstructure could be modified dramatically by suitable heat treatments. Martensite or martensite plus $Ni_3Al$ microstructure was obtained upon oil quenching from $1300^\circC$. Aging of Martensite at $800^\circC$ resulted in the $Ni_3Al$ plus NiAl phase. The compressive fracture strength and compressive fracture strain were improved by the $Ni_3Al$ plus NiAl phase mixtures at room temperature and $1100^\circC$. Microcracks are observed mostly in the region of NiAl and the interface of $NiAl-Ni_3Al$ phase after compressive test at room temperature. In the case of high temperature compressive test, microcracks are formed in the region of $Ni_3Al$ phase.