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Al-Li-Cu-Mg-Zr 합금에 있어서 δ' 상 조대화를 위한 Lithium의 확산계수 평가
정동석,김은석,조현기( D . S . Chung,E . S . Kim,H . K . Cho ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.1
The evaluation and analysis of diffusivity of lithium for coarsening and coarsening kinetics of δ` precipitate in Al-Li-Cu-Mg-Zr alloy aged at 170℃ have been investigated by transmission electron microscopy. With ageing time, δ` precipitate coaesened to followed γ ̄∝t^(1/3) and coarsening kinetics was found to be obeyed to the Lifshitz-Slyozov-Wagner(LSW) theory and diffusivity of lithium for coarsening of δ` precipitate in Al-Li-Cu-Mg-Zr alloy was obtained to be 5.85×10^(-17)∼1.53×10^(-16) by experimental coarsening rate constant and various coarsening kinetic theory. Diffusivity of lithium measured by using various model but MLSW and Tsumuraya(VI) et al. model in Al-Li-Cu-Mg-Zr alloy is similar to that calculated by the Costas`s diffusivity equation. It was, therefore, suggested that additing to the Cu, Mg and Zr element in Al-Li system have no great effect on diffusivity of lithium for coarsening of δ` This suggest that in matrix.
Ni/Ni-aluminide//Ti/Ti-aluminide 구조경사형 층상재료의 균열 전파 거동
정동석,김진곤,조현,Chung, D.S.,Kim, J.K.,Cho, H. 한국결정성장학회 2005 한국결정성장학회지 Vol.15 No.6
Ni/Ni-aluminide//Ti/Ti-aluminide 경사기능 층상 복합재료를 박막 hot press법을 이용하여 제작하였다. NiAl과 $TiAl_3$ 금속간화합물 층이 자전고온합성반응을 통해 비교적 두껍게 형성되었고, 얇고 연속적인 $Ni_3Al$과 TiAl 층이 고상 확산을 통해 형성되었다. 파괴저항은 하중 방향이 crack arrester인 경우가 금속 층이 균열의 성장을 방해하기 때문에 crack divider 방향인 경우보다 높다. $Ni_3Al$과 NiAl 금속간화합물 층은 각각 벽개파괴와 입계파괴 거동을 보였고, $TiAl_3$층의 파괴 형태는 입내벽개파괴이었다. Ni/Ni-aluminide 층에서 관찰되는 기공과 금속 층과 금속간화합물 층의 미결합 부위가 낮은 파괴저항의 원인으로 판단된다. Acoustic emission (AE) 원파형 해석을 통해 제작된 복합재료의 파괴특성을 고찰하였다. Ni/Ni-aluminide/Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and $TiAl_3$ were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous taters of $Ni_3Al$ and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the interruption of crack growth in metal layers. The $Ni_3Al$ and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of $TiAl_3$ layer was found to be an intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance. With the results of acoustic emission (AE) source characterization the real time of failure and the effect of AE to crack growth could be monitored.
Cu , Mg을 함유한 Al-Li 합금의 기계적 성질과 전기저항 변화에 미치는 기본 및 추가 강화상들의 역할
정동석,송기호,우기도 ( D . S . Chung,K . H . Song,K . D . Woo ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.2
Roles of fundamental and additional hardening precipitates on the changes of mechanical properties and electrical resistivity during precipitation decomposition in binary Al-Li, ternaty Al-Lieu and multi-Li-Cu-Mg-Zr alloys have been investigated by the detailed measurement of electrical resistivity, hardness and tensile strength and the observation of transmission electron micrographs. Peek hardness and tensile strength in multi-component Al-Lieu-Mg-Zr Alloy had higher than that of the other alloys and the results of measurement of hardness, strength and electrical resistivity in each alloys aged at 90 and 190℃ precipitation behaviors and mechanical properties in binary, ternary and multi component Al-Li alloys were contributed to the δ`, precursory phase of δ`, T₁, G.P.B. zone and S`phases, respectively.
Mg 합금의 발화 및 연소특성에 미치는 Ca 첨가의 영향
정동석,조현,김진곤,Chung, D.S.,Cho, H.,Kim, J.K. 한국결정성장학회 2009 韓國結晶成長學會誌 Vol.19 No.6
Mg 합금에서 Ca 첨가가 발화 및 연소 특성에 미치는 영향을 조사하였다. 주조 상태에서 순 Mg은 표면과 내부에 균열과 게재물들이 관찰되었지만 Ca이 첨가된 Mg-Ca 합금에서는 관찰되지 않았다. Mg 합금에 Ca가 첨가됨에 따라 1.5 wt%Ca까지는 발화 온도가 급격히 증가하다가 포화되는 경향을 보였다. 이러한 경향은 Mg-Ca 합금에서 Ca의 고용도와 관련이 있었다. Mg-Ca 합금의 연소 표면에 형성된 MgO 산화층이 발화와 연소를 억제하는 역할을 하였다. In the present study, the effect of Ca additions on the ignition and combustion behaviors of Mg alloys has been investigated. Cracks and inclusions were observed at the free surface and interior in as-cast pure magnesium but not in Ca-bearing Mg alloys. There was a tendency that ignition temperature rapidly increased with increasing Ca content in Mg-Ca alloy. Saturated composition for increasing of ignition temperature was related with solid solubility of Ca in Ca-bearing Mg alloys. The protective oxide layers, MgO, could also be found on the combustion surface of Ca-bearing magnesium alloy.
Al-Li-Cu-Zr합금의 시효에 따른 인장파괴모드변화에 미치는 미세조직의 영향
정동석 ( D . S . Chung ),이수진 ( S . J . Lee ),조현기 ( H . K . Cho ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.3
To clarify the influence of precipitation microstructure and inclusion on the monotonic tensile fracture behaviors in 2090 alloy aged at 180℃, the detailed measurement of hardness, tensile strength, elongation and the observation of scanning electron micrography, transmision electron micrography have been carried out. The transgranular shear ductile fracture has been observed in specimen quenched after solution treatment at 500℃ for 45min. While the undet-aged specimen was fractured in both transgranular shear ductile and intergranular fracture.mode, the fracture mode of peak-aged and over-aged alloy was predominantly intergranular fracture. The fracture behavior of each ageing condition was influenced by the change of precipitation microstructural features. In the case of peak-aged and over-aged alloys, the coarse and heterogeneous slip band caused by both shearable nature of the δ`(Al₃Li) precipitates and PFZ along the high angle grain boundary aid the localization of deformation, resulting in low energy intergranular fracture. It was also estimated that the fractured T-type intermetallic phases (inclusion) and the equilibrium δ(AlLi) phases which were formed at grain boundaries palyed an important role in promoting intergranular fracture mode.
Al-Cu-Li-Mg-Ag-Zr합금의 시효에 따른 전기화학적 분극 거동과 공식특성
민병철,정동석,손태원,조현기 ( B . C . Min,D . S . Chung,T . W . Shon,H . K . Cho ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.2
In this paper, we studied on both electrochemical polarization behaviors and pitting characteristics of ultra high strength Al-Cu-Li-Mg-Ag-Zr alloys(named C1 and C2) and 2090 alloy according to their treatments in the deaerated 3.5% NaCl, using by the potentiodynamic and the potentiostatic method; SEM micrograph and surface roughness including depth of pitting attack. With the cyclic polarization curves, the hysteresis of the C1 and C2 alloys appeared more remarkably than that of the 2090 alloy, because of precipitation microstructural difference between C1, C2 alloys and 2090 alloy. In the pitting experiments, the correlations between pitting growth and aging conditions were analyzed with the SEM micrograph and measurement of the pit depth.
응력제거 열처리한 Mg-AX31B합금 TIG 용접부의 기계적 특성과 미세조직 변화에 미치는 용접조건의 영향
김용길 ( Yong Gir Kim ),정동석 ( Dong Seok Chung ),배차헌 ( Cha Hurn Bae ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.4
N/A Present work was carried out to investigate the influence of welded conditions, such as welding cur-rent, diameter of welding wire on the microstructural change and mechanical properties of TIG welded joint in AZ31B Mg alloy. It was found that good and sound welded joint was achieved in all welding conditions. The grain size decreased with increasing welding current and decreasing diameter of welding wire. Also, the second phases were homogeneously distributed in the grain and grain boundary as decreasing welding current and diameter of welding wire. The β discontinuos precipitates were observed in the welded joint, but this microstructure has not been reported by previous researchs in AZ31B Mg alloy. The hardness value is affected by the existence state of the second phase and the hardness of the welded joint region is lower than the other regions in welded AZ31B Mg alloy. The strength of the welded joint region was influenced by the grain size and has more than 90%, compared to that of ASTM standard specification.