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석출경화형 Al-0.55wt%Zr 합금의 고온 변형에서의 Threshold 응력과 Orowan 응력과의 관계
김병일,길영일출남 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.6
To clarify the character of the relationship between the threshold stress and coherence, Al-Al₃Zr alloy with coherent particles was chosen in this work. High temperature creep test particle strengthened Al-Al₃Zr alloy was carried out by means of stress relaxation test at 573K, 623K and 673K. For the experiments, an Al-0.55wt%Zr alloy was melted in Ar gas atmosphere and then chilled to an ingot. The alloy was strengthened by coherent particles, β'(Al₃Zr) with Ll₂ structure. It was found that there exist the threshold stress during stress relaxation test and the threshold stress, σ_(th) results from the presence of β'(Al_Zr) particles. It was also obtained that the stress are approximately equal to Orowan stress, σ_(or) at 573K but 0.4σ_(or), at 673K. The temperature dependence of threshold stress might be due to the interaction between dislocations and particles. The ratio of σ_(th) and σ_(or) decreases gradually with increasing temperature. During local climb a considerable amount of length of dislocation increase lead to the threshold stress which depends on particle shape and is roughly estimated by σ_(th) =(0.4∼0.9)σ_(or). The activation energy for relaxation creep is found to be very close to that for pipe diffusion of pure Al. Observation of deformed specimens by transmission electron microscopy(TEM) suggests that dislocation and particles interact as a repulsive type.
Al-Mg-Mn 합금의 고온 연성 저하에 미치는 분산입자의 효과
김병일,중도영치,길전동수,길영불남 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.9
The dependency of the ductility of Al-Mg-Mn alloy containing Al_6Mn particles on temperature and strain rate was examined by using standard tensile test. The ductility minimum was found to be at 773K for 2.7×10^(-3), 5.5×10^(-3) and 1.1×10^(-2) strain rates, and the reduction of area decreased with increasing temperature 'irrespective of strain rates. The rate of ductility loss increased significantly at lower strain rate and at higher temperature. However, the maximum ductility drop occurred at the same temperature, 773K, for various strain rates. For 2.7×10^(-3) and 5.5×10^(-3) strain rates, ductility was determined uniquely by the parameter Z=ε˙ exp(Q/RT) at Z= ≥10^6s^(-1). Brittle fracture showing the ductility loss at higher temperature was associated with cavity growth as well as interlinkage of cavities, while a number of dimples were observed on the fracture surface at lower temperatures.
논문 : 기계적 성질 ; Al-Mg-Be 합금의 고온 연성저하 현상
김병일 ( Byung Il Kim ),길전동수 ( Fuyuki Yoshida ),중도영치 ( Hideharu Nakashima ),길영일출남 ( Hideo Yoshinaga ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.6
The high temperature ductility behaviors of Al-Mg-Be alloy containg particles in grain have been studied using a tensile test and scanning electron microscopy. The results show that the reduction of area increased with increasing temperature up to 523K and the minimum ductility was found to be at 573K for 8.3 × 10-5s-1 strain rate. The rate of ductility loss of the Al-Mg-Be alloy deformed at 573K under strain rate, 8.3 × 10-4s-1 was higher than that of under a strain rate, 8.3 × 10-5s-1 However, the maximum ductility drop was occured at the same temperature, 573K for various strain rate. The reduction of area was not determined uniqely by Zenner-Hollomon parameter, Z=εexp(Q/RT). The cleavage fracture showing the ductility loss at higher temperature was associated with cavity growth as well as interlinkage of cavities. On the other hand, ductile fracture was observed on the fracture surface at lower temperature.