• 한국재료학회지
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• 제10권2호
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• pp.128-137
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• 2000

가스터빈 블레이드 재료로 사용되는 IN738LC 니켈기 초합금 주조재에 대하여 고온등압압축(HIP) 공정에 의한 미세조직 변화와 고온 피로수명에 미치는 영향을 조사하였다. 세부적으로 HIP 처리에 따른 주조결함 제거와 피로변형 열화재의 물성재생효과 확인에 중점을 두었으며, 이를 위하여 회전굽힘 피로시험을 실시하고 변형전후의 미세조직을 광학 및 주사전자현미경으로 관찰하였다. HIP 처리 전후의 미세조직과 피로수명을 비교, 평가한 결과, 주조재와 열처리재의 피로수명 차는 크지 않았으나 HIP 처리재의 피로수명은 이들과 비교하여 평균 60배 이상 증가한 것으로 나타났다. 또한 인위적으로 고온 피로변형을 가한 열화재를 대상으로 반복 HIP 처리한 결과, 열화 변형조직이 신재 상태로 거의 완전히 재생될 뿐만 아니라, 재료내에 미세하게 잔존하던 주조결함까지 부가적으로 제거됨에 따라 반복 HIP 처리에 의한 피로수명 연장 효과가 크게 나타났다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2008년도 추계학술대회 초록집
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• pp.56-56
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• 2008

연소화학증착법(CCVD)를 이용해 IN738LC 합금에 $SiO_2$ 보호피막 코팅을 행하였다. 소스물질인 TEOS 첨가량과 증착 시간을 변화시키면서 $SiO_2$ 보호피막을 제조하였다. 증착된 코팅층은 SEM, EDX, XPS 분석을 통해 $SiO_2$층임 을 확인하였고 TGA(Thermogravimetric analysis)를 이용하여 합금의 내산화 특성을 평가하였다.

• 한국재료학회지
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• 제14권1호
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• pp.28-34
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• 2004

IN 738LC, the major material for gas-turbine for power generation, was heat treated at $750^{\circ}C$, $850^{\circ}C$, $950^{\circ}C$ for 1000, 2000, and 4000 hrs and the microstructural evolution and mechanical properties were examined using optical microscope, XRD, SEM/EDS. The results showed ${\gamma}$', the main strengthening elements in this alloy, was about 300 nm in size and was about 56% by area fraction in as-cast samples. The area fraction of ${\gamma}$' peaked at 2000 hours at $750^{\circ}C$. The average diameter of the ${\gamma}$' which was about 300 nm at ascast specimen increased to about 1 $\mu\textrm{m}$ after heat treatment at $950^{\circ}C$ for 4000 hrs. Carbides were formed at dendrite, cell or grain boundaries which was ascribed to the segregation caused by solute redistribution during solidification. It was found that MC type carbides formed at low temperature, whereas carbides of $M_{23}$ /$C_{ 6}$/ type formed at higher temperature or at longer degradation. The hardness and impact energy decreased as the heat treatment temperature or time of retention increased, which was inaccrodance with the area fraction of ${\gamma}$'.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.188-193
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• 2000

A more accurate life prediction for gas turbine blade takes into account the material behavior under the complex thermo-mechanical fatigue(TMF) cycles normally encountered in turbine operation. An experimental program has been carried out to address the thermo-mechanical fatigue life of the IN738LC nickel-base superalloy. In the first phase of the study, out-of-phase and in-phase TMF experiments have been performed on uncoated and coated materials. In the temperature range investigated. the deposition of NiCrAlY air plasma sprayed coating did not affect the fatigue resistance. In the second phase of the study, a physically-base life prediction model that takes into account of the contribution of different damage mechanisms has been applied. This model was able to reflect the temperature and strain rate dependences of isothermal cycling fatigue lives, and the strain-temperature history effect on the thermo-mechanical fatigue lives.

• 한국주조공학회지
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• 제19권5호
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• pp.427-432
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• 1999

Most investment castings contain some porosities and microcavities. In this study, we investigated the elimination trends of various internal defects in IN738LC investment castings for industrial gas turbine blade by hot isostatic pressing. The results showed that cylindrical defects which are under $0.6mm{\Phi}{\times}7mm$ size are mostly eliminated and aspect ratio of defects is more sensitive factor than their cross section shape in removing these defects. Increasing hot isostatic pressure and holding time doesn't affect the elimination trend of cylindrical defects over $0.6mm{\Phi}{\times}7mm$ size because first step(plastic deformation) of HIP densification doesn't occur under these HIPping conditions.

• 한국공작기계학회논문집
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• 제10권2호
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• pp.73-78
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• 2001

In this study, the friction weldability and properties of inconel alloy(IN738LC) to stainless steel (STS304) was investigat-ed. Upset length increased according to increment of friction pressure and time. The tensile strength of the friction weld-ing reached 85% of the STS304 base metal strength under the conditions of 8 sec friction time, 50MPa friction pressure and 150 MPa upset pressure. From the result of fracture surface analysis, IN738LC section can be joined with STS 304 materials in shape of a convex lens. Also, the temperature of welded interface was measured with k-type thermocouple. Finally the plastic flow confirmed at the welded interface STS304 by micro test.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.193-198
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• 2000

The small punch test have been developed to evaluate the material strength of the power plant components. This small punch test specimen is very small than the conventional strength test specimens. Korea Electric Power Research Institute (KEPRI) have been applying this test to assess accurately the life of thermal power plant and enhancing the reliability. The small punch test for gas turbine blades is under development. It's possible to compare the relative strength among the same materials having different operation histories. In this paper, the strength reductions of gas turbine materials are investigated by the small punch tests. All materials shows the almost same strength and deformation with the allowable deviation. At the same test temperature, the damaged material has the maximum load value. The strength reduction is not shown in this small punch test results.

• 한국재료학회지
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• 제31권7호
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• pp.409-419
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• 2021

The effect of solidification rate on micro-segregation in investment casting of IN738LC superalloy was studied. In Ni-based superalloys, the micro-segregation of solute atoms is formed due to limited diffusion during cast and solidification. The microstructure of cast Ni-based superalloys is largely divided into dendrite core of initial solidification and interdendrite of final solidification. In particular, mosaic shaped eutectic γ/γ' and carbides are formed in the interdendrite of the final solidification region in some cases. The micro-segregation phenomena formed in regions of dendrite core and interdendrite including eutectic γ/γ' and carbides were analyzed using OM, SEM/EDS and micro Vickers hardness. As a result of analysis, the lack of (Cr, W) and the accumulation of Ti were measured in the eutectic γ/γ', and the accumulation of (Cr, Mo) and the lack of Ti were measured in the interdendrite between dendrite and eutectic. Carbides formed in interdendritic region were composed of (Ti, W, Mo, C). The segregation applied to each microstructure is mainly due to the formation of γ' with Ni₃(Al,Ti) composition. The Ni accumulation accompanied by Cr depletion, and the Ti accumulated in the eutectic region as a γ' forming elements. The Mo tends to diffuse out from the dendrite core to the interdendrite, and the W diffuse out from the interdendrite to the dendrite core. Therefore, the accumulation of Mo in the interdendrite and the deficiency of W occur in the eutectic region located in the interdendrite. Heat treatment makes the degree of the micro-segregation decrease due to the diffusion during solid solution. This study could be applied to the heat treatment technology for the micro-segregation control in cast Ni-based superalloys.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2007년도 추계학술대회 논문집
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• pp.47-47
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• 2007

• 한국분말재료학회지
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• 제19권3호
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• pp.215-219
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• 2012

An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of ${\gamma}^{\prime}$ precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of ${\gamma}^{\prime}$ precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.