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SmCo_5-SmCu_5 合金系의 組織과 磁氣特性의 관계를 밝히기 위하여 時效熱處理 및 組成이 이 合金系의 磁氣特性에 미치는 效果를 조사연구하였다. 試料는 알곤(Ar) 분위기의 아크爐를 사용하여 熔解시켰으며 용융상태에서 急激히 냉각 鑄造하였다. SmCo_(5-x)Cu_x(x=1에서 4)의 三元組成을 갖는 合金鑄塊는 다시 400℃와 1000℃사이의 各溫渡에서 燒鈍하였으며 試料合金의 磁氣特性은 SmCo_(3.5)Cu_(1.5)와 SmCo_(3.0)Cu_(2.0)組成에서 가장 뛰어났다. SmCo_(3.5)Cu_(1.5)組成을 갖는 試料合金을 1000℃와 400℃에서 소둔시켜 그 組織을 金屬顯微鏡, X-線回折 및 走査電子顯微鏡으로 조사하여 이것으로부터 合金의 磁氣硬化는 Sm₂Co_(17)相의 針狀形의 많은 析出物에 관계하는 것이라 思慮되었다. X-線回折資料에서 析出相의 格子常數로서는 a=8.402A, C=12.172A을 얻었다. 結論的으로 低溫時效에서 일어나는 析出物은 高溫時效에서 관찰되는 析出物과 同一한 Sm₂Co_(17)相이며 이들 針狀形의 析出物은 400℃와 600℃사이에서 過時效하고 이것은 試料合金系의 磁氣特性이 400℃부근에서 가장 우수하다는것과 관계한다. In order to show the connection between microstructure and magnetic properties, studies have been made of the effect of composition and aging treatment on the magnetic properties of the alloy system SmCo_5-SmCu_5. A number of ingots of the ternary composition SmCo_(5-x)Cu_x (x=1 to 4) were prepared by arc-melting under a protective atmosphere, resulting in a rapid freezing from the molten state. The samples were then annealed at various temperatures between 400℃ and 1000℃. The magnetic properties of these compounds were the highest in the vicinity of the composition SmCo_(3.5)Cu_(1.5) and SmCo_(3.0)Cu_(2.0). When specimens of the composition SmCo_(3.5) Cu_(1.5) annealed at 1000℃ and 400℃ were examined by optical microscope, X-ray diffraction, and electron-probe techniques, there were observed fine needle-shaped precipitates which may be responsible for the magnetic hardening of this compound. Their hexagonal cell constants (a=8.402A, c=12.172A) were obtained from FeKα powder diffraction data. The results indicate that precipitates occurring at the low temperature annealing are the same kind of phase as Sm₂CO_(17) precipitates at the high temperature annealing, and they appear to overage rapidly during the annealing between 400℃ and 600℃. Therefore, annealing at the high temperature over 600℃ does not lead to a further increase in the magnetic properties of SmCo_(5-x)Cu_x alloys.
Superconduction YBa₂Cu₃0_(7-x)./Ag composite thick films on a YSZ substrate were prepared by the screen printing method. Microstructure and supercduction properties such as zero-resistance Tc(Tc^(Zero)), Jc at 77k, and the interface reactions betwean the superconduction thick film and YSZ substrate were investigated. For the YBa₂Cu₃O_(7-x)/Ag composite thick films annealed at 980℃ and 1000℃ in flowing oxygen, Tc^(Zero) and Jc at 77k increased, and the normal state resistivity and the thickness of interface reaction layer decreased strongly with increasing Ag content. The drastic decrease in reaction layer thickness with Ag addition seemed to result from the prevention of interaction between the film and the substrate by liquid Ag which formed during high temperature annealing. SEM analysis showed that the grain size increased as Ag content increased from 7wt% to 24wt%. It seems that the liquid Ag in YBa₂Cu₃O_(7-x)/Ag composite thick films enhances the intergranular coupling of YBa₂Cu_O_(7-x)/Ag grains, which results in the favored sintering process at 980℃.
Al-4%Cu 合金의 析出過程에 미치는 高速性中子의 照射效果를 Vickers 硬度의 測定 및 透過電子顯微鏡으로 관측 고찰하였다. 中性子照射는 日本原子力硏究所材料試驗爐(JMTR)內에서 行하였고 照財中性子量은 各各 2.8×10^(19), 3.4×10^(20), 1.2×10^(21)nvt였다. θ'折出粒子의 成長速度의 觀測은 電子顯微鏡의 hot stage를 사용하였고 測定資料는 析出物의 成長機構에 관한 最近의 ledge 理論式들에 적용 검토하였다. 그 結果 照射한 試料의 擴散係數 및 Arrhenius 振動數項은 未照射試料보다 훨씬 컸고 이것은 照射에 依해서 生成된 過剩空孔(excess vacancies) 또는 interstitials에 기인하는 것이라 믿어진다. 實驗結果는 中性子의 照射가 不均一核生成을 증가시킬 뿐만 아니라 溶質原子의 擴散을 促進시키며 이러한 效果는 照財線量이 많을수록 크며 析出物 成長速度는 보다 커진다는 것을 보여주고 있다. In order to examine the effects of fast neutron irradiation on the precipitation process in Al-4%Cu alloy, hardness measurement and transmission electron microscope were employed. Specimens were irradiated to 2.8×10^(19), 3.4×10^(20) and 1.2×10^(21) nvt neutron doses in the Japan Materials Testing Reactor. Their electron micrographs prior to annealing or at the early stage of annealing at 200℃ showed G. P. 2 and even θ' plates, which it can not normally expect to form. The kinetics of growing of θ'plates in Al-4%Cu alloy were measured by means of hot stage transmission electron microscopy, and the lengthening data of θ'plate measured at each temperature and at each neutron dose have been interpreted in terms of the various equations for recent ledge theories of growth. The calculated diffusivity and frequency factor of Arrhenius' equation of specimen irradiated to 2.3×10^(19) nvt neutron are much larger than the un-irradiated one. This may be attributed to excess vacancies or interstitials produced by irradiation. It is concluded that neutron irradiation does not only bring the enhancement of heterogeneous nucleation, but also give rise to enhanced diffusion of solute atom, and the more the neutron dose increases, the greater the growth rate becomes.
고탄소계 Cr-Ti 합금강 레일재의 용접성에 관한 연구 (1) : 고탄소계 Cr-Ti 합금강 레일재의 용접열영향부의 충격 및 피로특성과 조직 The Microstructure and the Impact and Fatigue Properties fo Welded Heat Affected Zone in High Carbon Cr-Ti alloy Rail Steel
The Enclosed-arc welding simulated at the laboratory level was applied to the rail steel of high carbon Cr-Ti alloy containing 0.1 w/oTi. After welding, the impact toughness and the fatigue properly of the welded zone were investigated in connection with the austenite grain size and microstructure. Also these mechanical properties of the high carbon Cr-Ti alloy rail steel were compared with those of common rail steel. According to the experimental results, the impact toughness and the fatigue property at HAZ, on the whole, increased as the pearlite interlamellar spacing and austenite grain size became finer. And there was little variation in the fatigue property of the welded zone because of the effect of pre-worked notchs at the alloy rail steel. As the cementite spheroidizing phenomena were remarkable at HAZ, both the impact toughness and the fatigue strength increased. Throughout the welded zone of the high carbon Cr-Ti alloy rail steel, austenite grain size showed little variation, and had ASTM No.4.5-5 at a distance of 25㎜ from the bond. The impact and fatigue properties of the high carbon Cr-Ti alloy rail steel were found to be superior to the these of common rail steel.
高硅素의 Fe-Si 合金粉末로 되는 壓粉燒結鐵心의 磁氣的性質과 硬度를 조사하고 그들의 特性을 金屬組織學的인 面에서 고찰하였다. 粒度를 달리하는 各各의 Fe-6.5% Si粉末을 8∼9ton/㎠ 의 壓力으로 成形시켰고 壓粉體는 1250℃∼1400℃의 수소분위기속에서 燒結되었다. Fe-6.5% Si壓粉燒結鐵心의 자기특성은 壓粉體의 밀도가 클수록 向上되었고 소결온도가 높을수록 우수하였다. 特히 保磁力과 기계적성질(硬度)은 鐵粉末鐵心보다 우수하였고 一般硅素電磁鋼板이 比較하여 손색이 없었다. 結論的으로 6.5%Si을 함유하는 高硅素鋼壓粉鐵心의 자기특성은 먼저 壓粉體의 密度를 될수 있는 대로 크게 하고 다음에 높은 은도에서 소결할 때, 보다 우수한 값을 가졌다. 그리고 그 磁化機構는 고온소결에 의한 氣孔의 제거와 조직의 粗大化에 기인하는 것이라 思慮되었다. 그리하여 密度는 壓粉燒結鐵心의 자기적성질과 기계적 성질을 向上시키는 支配的인 因子이라 믿어진다. Magnetic properties and hardness of sintered cores made of Fe-Si alloy powder containing high silicon were studied and the mechanism bringing about their characteristics is examined by metallographic methods. Fe-6.5%Si powders with different particle sizes were compacted under pressures of 8∼9ton//㎠ and sintered at 1250℃∼1400℃ in hydrogen atmosphere. The magnetic properties of Fe-6.5%Si sintered cores were improved with increasing the green density of core and sintering temperature. Especially, coercive force and hardness of sintered cores compared favorably with compressed iron powder cores and were almost comparable to electrial steel sheets. It may be concluded that the higher the density the better the magnetic properties of compacted core, high temperature sintering provides further improvement to them, and their mechanism is attributed to the elimination of porosity and the coarse-grained microstructures. Therefore, it seems that density (or porosity) is the predominant factor controlling magnetic properties and mechanical properties of compacted core.
YBa₂Cu₃O_(7-x) oxide superconductors was fabricated by sintering process and upsetforging method, respectively, and microstructures and conduction properties were compared. There was no difference in crystal structure between the as-sintered and the upset-forged specimens. The upset-forging enhanced the (001) x-ray reflection presumably due to preferred crystal orientation of the YBa₂Cu₃O_(7-x) superconductor. Furthermore, the grain size of the 123-phase increased as the reduction ratio became larger during the upset-forging. The critical temperature for zero resistivity of both samples was almost the same, i.e., about 90K These results have demonstrated the potential of producing YBa₂Cu₃O_(7-x) superconducting wire or tape effectively using a upset-forging method. The critical current density of the upset-forged sample, however, was lower than that of the sintered one, which fact might be ascribed to microcrack formation during fast upset-forging.
A stdy has been made on tempered embrittlement of AISI 4340 steel having martensite-bainite duplex structure, as compared with that in tempered martensite, metallographically. For making martensite-bainite duplex structure, lower bainite formation was achieved in a salt bath held at 315℃, upper bainite at 400℃, and subsequently quenched into iced brine. After the isothermal transformation, they were tempered for lhr in the range between 200℃ and 500℃, and then the mechanical properties were examined. Impact toughness was measured by Charpy Impact Tester, microstructure was examined by means of optical and transmission electron microscope, and fracture surface scanning electron microscope. The lower bainite was precipitated acicularly so as to partition prior austenite grain and the upper bainite was precipitated massively so as to fill prior austenite grain. These shapes of bainite had an effect on the impact toughness, temper embrittlement, and brittle fracture resistance of martensite-bainite duplex structure. The 300℃-tempered martensite embrittlement was greatly improved by martensite-bainte duplex structure and the ductile-brittle transition temperature of martensite-bainite duplex structure was lower than that of martensite. The former, the improvement of tempered martensite embrittlement by martensite-bainite duplex structure, may have been attributed to the shape and distribution of carbide which precipitated differently compared with those of martensite structure during tempering. They also affected on the fracture behavior. And, it seemed that the latter, the increment of brittle fracture resistance, have been due to the partitioning of prior austenite grain, with the result of fining cleavage crack path by lower bainite.