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남수우 대한금속재료학회(대한금속학회) 1977 대한금속·재료학회지 Vol.15 No.1
고순도철 (Ferrovac E iron)에 전기분해 방법으로 수소를 주입시키는 경우 수소 주입 기구에 대하여 조사하였다. 실험 결과로부터, 수소가 철 속으로 확산되기 위하여 철 표면에 충분한 수소 원자 농도가 형성되어야 하며 이러한 수소 농도의 형성은 불순물로 첨가된 arsenic이 비정질 상태로 시편 표면에 전착되는 현상에 영향을 받는 것으로 생각된다. Using the Ferrovac E iron specimens cathodically charged with hydrogen, investigations of the mechanism of hydrogen entry into the alpha-iron were carried out. According to the experimental results, the delaying time due to the formation of hydrogen concentration at the metal surface was investigated in terms of the amount of amorphous arsenic electrodeposited on the cathode surface.
Nb 이 첨가된 A286 초내열합금의 고온저주파 피로에서 피로균열의 천이에 영향을 미치는 인자에 관한 연구
남수우,노병섭 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.5
Continuous low cycle fatigue tests have been conducted on Nb-A286 Fe-base superalloy in an air atmosphere at the temperature range of 25 to 650℃ to investigate the transition of fatigue cracking with test temperature and applied strain range. The intergranular fatigue cracking at high temperatures was due to the precipitation of the η phase at the grain boundary assisted by the applied stress during low cycle fatigue. It is investigated whether the precipitate at the grain boundary provides the site for the grain boundary cavitation, which induces the intergranular cracking in low cycle fatigue. The fatigue cracking mode changes from the transgranular mode to the predominantly intergranular mode with the applied strain range. The change of the fatigue cracking with strain range is induced by the combination of mutually competing factors involving the grain boundary precipitate, the density of the slip band, and the concentration of stress at points where the slip bands impinge upon the grain boundaries.
남수우,진근찬,신동혁 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.9
Primary creep tests were performed on commercially pure aluminum in the temperature range of 0.32 - 0.38 T_m. The activation energies were obtained by usual method using different specimens (Q_c) and the temperature cycling method (Q_(T.C.)). The relation of activation energy with effective stress, σ_e, has been analysed. The activation length, ℓ_c^*, obtained from Q_c is linearly proportional to the inverse of affective stress. But no such relationship is observed in ℓ_(T.C).^* obtained from Q_(T.C.). The Q_c seems to have better physical meaning compared to Q_(T.C).
남수우,신동혁,최대순 대한금속재료학회(대한금속학회) 1984 대한금속·재료학회지 Vol.22 No.8
The cyclic creep behavior of pure aluminum is investigated for two different types of testing machine, one is the creep testing machine having constant values of peak stress, stress amplitude and frequency, and the other is Instron machine controlling peak load constant. Temperature range of the tests is around 0.33 T_m. Both results from the two different machines show the cyclic creep acceleration for which the constant load condition is more significant. The activation energies for the creep and the measured internal stress are increasing with the strain but the values are always higher for the constant peak stress test. Since the lower internal stress is one of the representatives of softer substructure, it probably accounts For the more accelerated cyclic creep and the lower apparent activation energy for the creep test under constant peak load. It is thought that the significant deviation of the creep behaviors with Instron machine is due to the increasing stress amplitude and peak stress, and the difference in the initial loading rate.
1Cr-Mo-V 강에서 고온저주파 피로의 균열 전파속도에 관한 연구
남수우,정창열 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.3
Smooth cylindrical specimens of 1Cr-Mo-V steel were tested under HTLCF( high-temperature low-cycle fatigue) conditions to investigate the growth behavior of microcracks. HTLCF crack growth rate is analyzed based on the concept of J-integral by monitoring the hysteresis loop. A new approach that the crack growth rate is measured by the striation counting from the observation of SEM(scanning electron microscope) fractographs was shown to be successful in determining the LCF crack growth rate as well as the LCF life. It is shown that ΔJ is reasonable in characterizing the growth rate of fatigue microcracks at elevated temperatures but results in unacceptable deviations for the hold time cycling owing to the relative contribution of time dependent processes at the crack tip. Approach of C(t) correlated with ΔJ gives recommendable results for interpreting the crack growth rate with hold time.
남수우,임성택 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.5
This work investigates the hardening mechanism of the low carbon steel by adding NiAl inter-metallic compound. The specimens was carted to have 0.15C-Ni-Al component in which the amount of NiAl was varied. These specimens were air cooled after solution treatment at 1100℃ for 1.5 hours and aged for various holding periods at 550℃. Mechanical testings have been performed to find out the proper heat treatment condition for the best mechanical properties. X-ray diffraction and electron diffraction techniques, and transmission electron microscopic observation show that NiAl particles have been precipitated and the particles maintained coherency with the matrix. It has been concluded that the maximum strength was obtained when the specimens were aged at 550℃ for 8 hours. The strength and hardness values are increasing with the amount of NiAl component in the steel but the maximum impact strength was obtained in the sample in which 3% of NiAl component was contained.
Al-Zn-Mg 합금에서 Cr 이 기계적 성질에 미치는 영향
남수우,전주매,박동석 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.10
The mechanical behaviors of a wrought high strength aluminium alloy containing 4.5 Zn, 2.0 Mg, and 0.12 Zr in wt.% have been examined as a function of the concentration of chromium in the range of 0.02∼0.2wt.%. It has been reported that the chromium forms Cr-dispersoids called E-phase(Al_(18)Mg₃Cr₂) in AI-Zn-Mg alloys. The size of these Cr-dispersoids is known to be depended on the content of chromium. The alloy containing 0.1 wt.% Cr has the small spherical Cr-dispersoids. However, the Cr-dispersoids are long rod-Like in the alloy with 0.2wt.% Cr. Because these Cr-dispersoids inhibit the motion of dislocations within the grain, the strength is increased. However, increment in strength is higher in the alloy with 0.1 wt.% Cr than in that with 0.2 wt.% Cr. The reason of the above phenomena may be resulted from the decrease of planar slip and increase cross slip due to the spherical Cr-dispersiods in the alloy with 0.1 wt.% Cr. The fracture toughness of the alloy depends on the shape and size of the Cr-dispersoids. The small spherical dispersoids increase the fracture toughness but the long rod-like dispersoids reduce it.