• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.168-170
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• 2005

Nickel base brazes containing boron and silicon as melting point depressants are used extensively in the joining and repair of hot-section components in next generation nuclear reactor and aero-engine. Therefore, the present study has investigated the preliminary applicability of nickel based alloying nano powders. Nano Ni-based alloying powders synthesized by Pulsed Wire Evaporation (PWE) method. It's powder morphology and phase transformation temperature were analyzed by scanning electron microscopy, transmission electron microscopy, and differential scanning calorimeter(DSC). The powder particle size was approximately 10${\sim}$100nm and exhibits a quite even equiaxed shape. The results of DSC measurement show that both the nano Inconel 625 nano powder and Inconel 718 nano powder presents similar liquidus temperatures approximately $1373^{\circ}C$ and $1380^{\circ}C$ respectively.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.43.2-43.2
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• 2009

니켈기 초내열합금 Inconel 617은 Cr, Mo 등의 첨가물이 함유된 고용 강화된 합금으로써, 우수한 고온 강도, 크립 저항성, 내부식성 및 내산화성을 가지고 있는 것으로 알려져 있다. 또한 Inconel 617의 주된 carbide은 $M_{23}C_6$와 미량의 $M_6C$ carbide로 형성되어있다. 본 연구에서는 냉간 압연 및 고온열화가 carbide의 크기, 분율 그리고 상 변화에 미치는 영향을 평가하였다. 냉간 압연은 50%까지 수행하였으며, 50% 냉간 압연한 시편을 $1050^{\circ}C$에서 1시간 동안 재결정을 수행하였다. 이로 인해 미세한 결정립과 carbide을 가지는 시편을 확보할 수 있었으며, as-received 시편 보다 균일하게 carbide을 분산 시킬 수 있었다. 또한 재결정 후 $950^{\circ}C$에서 고온열화에 의한 carbide의 변화를 평가함으로써, 냉간 압연 및 고온열화에 의한 carbide의 크기, 분율 그리고 상 변화에 미치는 영향을 평가할 수 있었다. Carbide의 분율을 평가하기 위하여 BSE image을 관찰하였으며, Image analyzer을 이용하여 계산되었다. 그리고 carbide의 성분 분석을 통한 $M_{23}C_6$와 $M_6C$의 상을 평가하기 위하여 EPMA 분석을 수행하였으며, carbide의 분산에 의한 균질도를 평가하기 위하여 비커스 경도를 측정하였다.

• 한국항공우주학회지
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• 제46권10호
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• pp.806-813
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• 2018

항공기 엔진을 구성하는 부품 중 하나인 블레이드의 파손에 대해 분석하였다. 블레이드의 파손원인과 그 거동은 다양하지만 크게 일시파단과 피로파손의 두가지 형태로 나뉘어진다. 이 논문에서는 전체 거동은 일시파단으로 진행되고 일부 피로 파손된 블레이드에 대해 기술하였고, 특히 고온에서의 블레이드 손상거동을 분석하므로써 사례의 하나로 제시하고자 한다. 분석한 블레이드는 니켈기 초내열 합금으로 외관, 재질, 미세조직, 고온 크리프 특성, 파단면 형상을 각각의 분석장비를 활용하여 손상원인과 거동을 확인하였고, 원재질에서 재현하였다. 고온에서 니켈 합금은 ${\gamma}^{\prime}$ 형상이 변형되고 조직변형(Alloy Depletion)구간이 관찰되며 재질의 기계적 성질, 물성치 등이 저하되고 연화되어 장시간 운용 시 파손될 수 있다. 니켈합금은 고온특성이 좋으나 함유되는 미량원소에 따라 그 물성치가 다양하므로 니켈합금이라 하여도 그 목적에 맞는 세분화된 소재를 사용해야한다.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1155-1160
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• 2011

니켈기 초내열합금은 높은 강도, 피로 및 산화 저항성이 우수하여 비행기 엔진, 선박 엔진 및 발전용 가스터빈 고온 부품 등을 만드는 소재로 오래전부터 사용되어 왔다. 본 연구에서는 가스터빈 블레이드 소재인 니켈기 초내열합금 IN738LC에 대하여 실제 운전환경과 유사한 조건을 설정하여 다양한 변형률 범위와 온도에서 인장시험을 수행하였다. IN738LC 소재를 $871^{\circ}C$ 및 $982^{\circ}C$에서 각각 1,000 ~ 10,000 시간 동안 열 노출한 시편을 준비하여 기계적 특성 및 미세조직 변화를 관찰하였다. 기계적 특성 변화는 열 노출 시간에 따른 ${\gamma}$의 변화와 관련된 것을 확인하였다.

• Journal of Welding and Joining
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• 제22권2호
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• pp.59-68
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• 2004

Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.

• 한국해양공학회지
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• 제22권6호
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• pp.52-57
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• 2008

The short-term high temperature creep rupture behavior of Ni-based Alloy718 steel was investigated at the elevated temperatures range of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture tim and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 33.5, -24.9, 26.1, -21.2, 16.8, -12.8 and 10, -8.2, respectively. The stress exponent decreased with increasing creep temperature. The creep lift prediction was derived by the Larson-Miller parameter (LMP) method and the resultant equation was obtained as follows: T($logt_r$+20)=-0.00252 ${\sigma}^2$-1.377${\sigma}$+-22718.

• 한국해양공학회지
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• 제22권6호
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• pp.58-63
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• 2008

The short-term high temperature creep rupture behavior of Ni-based Alloy718 steels jointed by friction welding wasinvestigated at the elevated temperatures of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture time and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 26.1, -22.4, 22.5, -18.5, 17.4, -14.3 and 6.9, -8.1, respectively. The stress exponents decreased with increasing creep temperature. The creep life prediction was derived by the Larson-Miller parameter (LMP) method and the result equation obtained is as follows: T(logtr+20)=-0.00148${\sigma}^2$-3.089${\sigma}$+23232. Finally, the results were compared with those of the base metal for Alloy718.

• 한국주조공학회지
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• 제36권5호
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• pp.159-166
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• 2016

The microstructural evolution of a cast Ni base superalloy, IN738LC, has been investigated after long term exposure at several temperatures. Most of the fine secondary ${\gamma}^{\prime}$ particles resolved after 2000 hour exposure at $816^{\circ}C$. At higher temperatures of $871^{\circ}C$ and $927^{\circ}C$, secondary ${\gamma}^{\prime}$ resolved after 1000 hours of exposure, and cuboidal primary ${\gamma}^{\prime}$ grew with exposure time. During the thermal exposure, ${\sigma}$ phase formed at all tested temperatures, and ${\eta}$ phase was observed around interdendritic regions due to carbide degeneration. The influence of microstructural evolution during thermal exposure on the mechanical properties has been analyzed. The effects of ${\gamma}^{\prime}$ particle growth are more pronounced on the high temperature creep properties than on the room temperature tensile properties.

• 대한금속재료학회지
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• 제49권7호
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• pp.535-540
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• 2011

The tensile and creep behaviors of Alloy 263, which is a wrought Ni-base superalloy used for gas turbine combustion systems, was studied. Anomalous increase of yield strength and abrupt decrease of elongation with increasing temperature were observed after tensile testing at an intermediate temperature. Elongation of the superalloy decreased as the temperature increased to and above 540$^{\circ}C$, and it reached a minimum value at 760$^{\circ}C$. It was found that creep strain was also very low at the same temperature. Inhomogeneous deformation with intensive slip bands was observed in the specimens tested at low temperature. A thermally-assisted dislocation climb process was regularly conducted at high temperature. Twinning was found to be an important mechanism of both tensile and creep deformations of the superalloy at an intermediate temperature where ductility minimum was observed.

• 한국정밀공학회지
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• 제26권3호
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• pp.11-18
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• 2009