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Effect of Ti Content on Creep Properties of Ni-Base Single Crystal Superalloys
최백규,김인수,홍현욱,도정현,정중은,조창용 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5
The effect of Ti content on the creep properties and microstructures of experimental Ni-base single crystal superalloyshas been investigated. The experimental alloys were designed to provide better high temperature propertiesthan the commercial single crystal alloy CMSX-4. The creep properties of the experimental alloys, Alloy 2 andAlloy 3, were superior to those of CMSX-4. Alloy 3 showed a longer creep life than Alloy 2 at 900 °C and 950 °C,while it has similar creep life with Alloy 2 at 982 °C. Transmission electron microscopy micrographs of the experimentalalloys after the creep test showed distinct deformation features as a function of temperature and Ti content. The dissociation of dislocations into partial dislocations with stacking faults in Alloy 3 was found to improve resistanceto creep deformation at 950 °C. The effect of Ti on the creep deformation mechanism was not evident at 982 °C,which resulted in similar creep properties in both experimental alloys. The transition of the γ′ cutting mechanismfrom dislocations coupled with stacking faults to anti-phase boundary coupled pairs occurred both in Alloy 2 andAlloy 3. However, the transition temperature was higher in Alloy 3 than in Alloy 2 because of the difference in Ticontents.
다결정 니켈기 초내열 합금 CM247LC의 온도에 따른 인장특성 변화
최백규,김인수,도정현,정중은,석우영,이유화 한국주조공학회 2020 한국주조공학회지 Vol.40 No.4
Microstructural evolution during a heat treatment and high-temperature tensile properties have been investigated in conventionally cast CM247LC. In as-cast specimens, MC carbides with high amounts of Ta, Ti, Hf, and W were found to exist in the interdendritic regions, and γ' was observed in the form of cubes and octocubes prior to decomposition into cubes. In the heat-treated condition, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in both interdendritic regions and dendrite core. Three types of carbides with different stoichiometries and compositions were found at the grain boundaries. MC carbides with high Hf contents were observed in the vicinity of eutectic γ-γ'. The highest tensile strength value was found at 750o C, whereas the greatest ductility appeared at 649o C. The effect of the temperature on the tensile properties was closely related to the dislocation structure. With increase in the test temperature, the density of dislocations inside γ' decreased, whereas that in the γ matrix increased. Stacking faults generated in γ' at 750o C had a strengthening effect, whereas thermally activated dislocation motion at a high temperature was considered to have the opposite effect.
IN738LC 합금의 열간 노출 및 재생 열처리에 따른 미세조직과 응력 파단 특성의 변화
최백규,주동원,김인수,장중철,조창용,Choe, Baek-Gyu,Ju, Dong-Won,Kim, In-Su,Jang, Jung-Cheol,Jo, Chang-Yong 한국재료학회 2001 한국재료학회지 Vol.11 No.10
Effects of thermal exposure and rejuvenation treatment on the microstructural evolution and the stress-rupture properties of IN738LC have been investigated. The role of precipitates on the stress- rupture properties has been analyzed through microstructural observations. Thermal exposure at $982^{\circ}C$ for 1000 hours gave rise to precipitation of $\sigma$ phase and coarsening of ${\gamma}$'. The microstructural degradation with thermal exposure at $982^{\circ}C$ deteriorated stress rupture properties of the alloy. All the existing phases except MC carbides have completely dissolved into the matrix with homogenization treatment at $1200^{\circ}C$ for 2 hours. Microstructure and stress-rupture properties of the thermal exposed specimens have been successfully rejuvenated by the proposed treatment.