• 열처리공학회지
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• 제19권5호
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• pp.249-256
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• 2006

Structural studies have been performed on precipitation hardening found in $L1_2$ ordered ${\gamma}^{\prime}-Ni_3(Al,Ti)$ alloys using transmission electron microscopy. A uniform solid solution of ${\gamma}^{\prime}-L1_2$ ordered phase supersaturated with Ni can be obtained by solution annealing in a suitable temperature range. The ${\gamma}^{\prime}$ phase hardens appreciably by the fine precipitation of disordered ${\gamma}$. The shape of ${\gamma}$ precipitates formed during aging is initially spherical or round-cubic and grow into platelets as aging proceeds. High resolution electron microscopy revealed that the ${\gamma}$ precipitates are perfectly coherent with the matrix ${\gamma}^{\prime}$ as long as the ${\gamma}$-precipitates are plates. The loss of coherency initiates by the introduction of dislocations at the ${\gamma}/{\gamma}^{\prime}$ interface followed by the step formation at the dislocations. The ${\gamma}$ precipitates become globular after the loss of coherency. The strength of ${\gamma}^{\prime}-Ni_3(Al,Ti)$ increases over the temperature range of experiment by the precipitation of fine ${\gamma}$ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature.

• 분석과학
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• 제6권5호
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• pp.515-520
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• 1993

Rene 80 주조블레이드가 고온에서 사용중인 사용 온도에 의해 ${\gamma}^{\prime}$이라는 석출물이 기지(${\gamma}^{\prime}$) 내에서 생성되기 때문에 고온강도는 그 석출물에 좌우된다. 즉, 석출물의 격자상수는 기지의 격자상수보다 크기 때문에 석출물이 생성되거나 성장할 때에 ${\gamma}-{\gamma}^{\prime}$ 격자어긋남(lattice misfit)에 의해 전위가 발생한다고 일반적으로 알려져 있다. 이러한 격자어긋남은 석출물(${\gamma}^{\prime}$)의 크기가 클수록 원형${\rightarrow}$사각형${\rightarrow}$판상형으로 바뀌어 가면서 증가한다. 따라서 본 연구에서는 이러한 격자어긋남의 양을 주사투과전자현미경에서 수렴성 빔전자 회절(CBED)을 사용하여 측정하여, 석출물과 인접한 기지의 전위밀도의 증가가 기지 내에서 석출물이 생성하고 성장함에 따른 격자어긋남이 원인인가를 관찰하였다.

• 한국재료학회지
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• 제25권9호
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• pp.468-474
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• 2015

Evaluations of the microstructure and mechanical properties of age hardenable Cu-2.0wt%Be alloy are performed in order to determine whether it can be used as a welding electrode for projection welding. The microstructure examinations, hardness measurements, and tensile tests of selective aging conditions are conducted. The results indicate that the aging treatment with the fine-grained microstructure exhibits better hardness and high tensile properties than those of the coarse-grained microstructure. The highest hardness value and high tensile strength are obtained from the aged condition of $300^{\circ}C$ for 360 min due to the presence of the metastable ${\dot{\gamma}}$ precipitates on the grain boundaries. The values of the highest hardness and tensile strength are measured as 374 Hv and 1236.2 MPa, respectively. The metastable ${\dot{\gamma}}$ precipitates are transferred to the equilibrium ${\gamma}$ precipitates due to the over-aged treatment. The presence of the ${\gamma}$ precipitates appears as nodule-like precipitates decorated around the grain boundaries. The welding electrode with the best aging treated condition exhibits better welding performance for electrodes than those of electrodes used previously.

• 열처리공학회지
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• 제22권1호
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• pp.8-15
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• 2009

Structural studies have been performed on precipitation hardening found in $Ni_{3}Al$ based ordered alloys using transmission electron microscopy (TEM). Tilt experiments by the weak-beam method were made to obtain some information concerning the cross slip mechanism of the superlattice dislocation. The strength of ${\gamma}'-Ni_3$(Al,Ti) increases over the temperature range of experiment by the precipitation of fine $\gamma$ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature. Over the whole temperature range, the interaction between dislocation and $\gamma$ precipitates is attractive. On the temperature range of 773 K to 973 K, the dislocations in ${\gamma}'$ matrix move on (111) primary slip plane. When the applied stress is removed, the dislocations make cross slip into (010) plane, while those in $\gamma$ precipitates remain on the (111) primary slip plane. The increase of high temperature strength in ${\gamma}'-Ni_3$(Al,Ti) containing $\gamma$ precipitates is due to the restraint of cross slip of dislocations from (111) to (010) by the dispersion of disordered $\gamma$ particles.

• 대한금속재료학회지
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• 제49권2호
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• pp.137-144
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• 2011

Strengthening mechanisms in an ordered intermetallic compound containing coherent precipitates of lower antiphase boundary energy than the matrix were investigated on the basis of the interaction between the deformation induced dislocations and the disordered precipitates in an $Ll_2$ ordered $Ni_3Al$-based alloy. Extra work was needed to pull out the dislocations from the precipitate, which was dependent on the difference in the antiphase boundary energy between the matrix and the precipitate, as well as the size and volume fraction of the precipitate. The strength of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase containing fine precipitates of the disordered ${\gamma}$ phase was examined using the proposed model. The model can explain almost quantitatively the age hardening behavior of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2001년도 춘계학술발표강연 및 논문개요집
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• pp.43-43
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• 2001

• 한국재료학회지
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• 제10권7호
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• pp.515-521
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• 2000

주소용 718합금의 고온 인장 성질에 미치는 석축물의 영향을 상추출법과 미세조직관찰을 통해 고찰되었다. 고온 인장시험에서 $760^{\circ}C$까지는 인장강도와 연신율이 동시에 감소하였고, 그보다 높은 온도에서는 인장강도는 급격히 감소하고 연신율은 증가하였다. 고온 인장시험에의한 응력의 영향으로 인하여 ${\gamma}',{\gamma}"$석출물의 양은 $760^{\circ}C$에서 최대의 값을 나타내었다. 미세한 ${\gamma}',{\gamma}"$상의 석출이 최대로 일어나는 온도에서 석출물에의한 유동응력의 증가로 인해 항복강도의 저하폭이 작았으며, 연신율은 가장 낮은값을 나타내었다. $760^{\circ}C$보다 높은 온도에서는 전체적인 석출물의 양도 감소하였고, 특히 강화석출상의 양이 적어 연화현상이 급격히 나타났다. 급격히 나타났다.

• Journal of Welding and Joining
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• 제21권2호
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• pp.89-96
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• 2003

The change of microstructures in the base metal during transient liquid phase bonding process of directionally Ni base superalloy, GTD-111 was investigated. Bonds were fabricated using a series of holding times(0-7.2ks) at three different temperatures(1403, 1418 and 1453K) under a vacuum of 13.3mPa. In raw material, ${\gamma}$- ${\gamma}$' eutectic phases, platelet η phases, MC carbide and PFZ were seen in interdendritic regions or near grain boundary and size of primary ${\gamma}$' precipitates near interdendritic regions were bigger than core region. The primary ${\gamma}$' precipitates in dendrite core were dissolved early in bonding process, but ${\gamma}$' precipitates near interdendritic regions were dissolved partially and shape changed. The dissolution rate increased with increasing temperature. Phases in interdendritic regions or near pain boundary continually changed with time at the bonding temperature. In the bonding temperature of 1403K, eutectic phases had not significantly changed, but η phases had transformed from platelet shape to needle morphology and PFZ region had widened with time. The interdendritic region and near pain boundary were liquated partially at 1423k and fully at 1453k by reaction of η phases and PFZ. In the bonding temperature of 1453K, interdendritic region and near pain boundary were liquated and then new phases which mixed with η phases, PFZ and MC carbide crystallized during cooling. Crystallized η phases transformed from rod shape to platelet shape with increasing holding time.

• 한국분말재료학회지
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• 제9권6호
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• pp.455-462
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• 2002

The microstructures and properties of TiC dispersed nickel-base alloy were studied in this work. The alloy prepared by powder metallurgical processing was solution treated, 1st-aged at $880^{\circ}C$ for 16 hours, and then 2nd-aged at $760^{\circ}C$ for 4 hours. Microstucture of sintered specimen showed that TiC particles are uniformly dispersed in Ni base alloy. In the specimen aged at $880^{\circ}C$ for 8 hours, the fine $\gammaNi_3$(Al,Ti) precipitates with round shape are observed and the very fine $\gammaNi_3$(Al,Ti) particles with round shape are precipitated in the specimen aged at $760^{\circ}C$ for 4 hours. The presence of ${\gamma}$precipitates in TiC/Ni base alloy increased the hardness and wear resistance of the specimen. The hardness and wear resistance of the Ni-base with TiC are higher than those of conventional Ni-base superalloy X-750 because of dispersion strengthening of TiC particles. The hardness, transverse rupture strength and resistance of the specimen 2nd-aged at $760^{\circ}C$ for 4 hours are higher than those of 1st-aged specimen due to ultrafine $\gammaNi_3$(Al,Ti) precipitates.

• 한국분말재료학회지
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• 제2권3호
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• pp.208-215
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• 1995

The aging effects on the characteristics of the melt spun Cu based shape memory alloys have been investigated by the microhardness test, X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. After aged for specific times, hardness of the ribbons began to increase and shape memory capacity diminished. At the initial stage of aging the austenitic transformation temperatures increased gradually, but at last became nearly constant: That is, the aging deteriorated the thermal stability. The increase in hardness was due to the formation of the $\gamma_2$ precipitates. The loss in the shape memory capacity was due to the decrement of solute atoms in the matrix by the formation of the $\gamma_2$ precipitates. In this study, it was confirmed that Mn is an effective element for Improving the thermal stability.