• 열처리공학회지
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• 제10권4호
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• pp.219-231
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• 1997

Inconel alloys used as nuclear power plant components have experienced intergranular stress corrosion cracking problems inspite of their good corrosion characteristics. In order to investigate the effects of heat treatments on carbide precipitation and intergranular stress corrosion cracking(IGSCC) in Inconel alloys, DSC(Differential Scanning Calorimeter), TEM, EDXS and static potential corrosion tests were carried out. Thermal treatment at $750^{\circ}C$ for 15hours in Inconel alloys increased the density of intergranular carbide. The carbides are mainly $Cr_7C_3$ in Inconel 600, and $Cr_{23}C_6$ in Inconel 690. The Cr depletion around grain boundary is not crucial factor on IGSCC. The carbides in grain boundary play an important role as acting dislocation source, and as decreasing stress around growing crack.

• E2M - 전기 전자와 첨단 소재
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• 제7권4호
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• pp.300-305
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• 1994

We determined the alloy composition of the liquid-phase epitaxy(LPE) grown $Al_{x}$G $a_{1-x}$ As by the photoreflectance(PR), and observed the variation of PR signal by changing the condition of annealing and thickness of epilayer. As the measuring temperature was decreased, the broadening parameter was decreased, and the amplitude of PR signal was increased. When the temperature of annealing was increased, the surface carrier concentration was decreased and then the shape and amplitude of PR signal were affected by the surface electric field. The structure change was observed when the specimen was annealed for long time at a high temperature. We found that the surface electric field increased when the thickness of epilayer was decreased by etching, because the band bending was increased by the decreased of the width of depletion layer....

• 한국주조공학회지
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• 제15권3호
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• pp.272-282
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• 1995

Iron-based metal matrix composites have been recently investigated for the use of inexpensive abrasion resistance material. This paper carried out to investigate the in-situ reaction effects on the microstructural characteristics and the formation mechanism of tungsten carbides in a white cast iron matrix. The specimens of Fe-3.2%C-2.8%Si alloy cast-bonded with tungsten wire were cast in the metal mold and isothermally heat treated at $950^{\circ}C$ up to 48 hours. The typical microstructure of heat treated specimens showed the reaction layer of WC at the interface of tungsten wire and the carbon depletion zone between the WC layer and the matrix. During the formation of WC layer, if the carbon supply is insufficient due to the decarburization of matrix or the isolation of matrix by cast-bonded W wires, the reaction layer develops coarse hexagonal crystalline WC. From the microstructural investigation, it was found that the volume of WC layer and the carbon depletion zone increased linearly with the isothermal heat treating time. This results supported that the formation rate of WC in the white cast iron matrix is controlled by the interfacial reaction with a constant reaction rate.

• Corrosion Science and Technology
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• 제2권1호
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• pp.18-25
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• 2003

Effects of the precipitation of $\sigma$ phase on the metastable pitting as a precursor of stable pitting corrosion and also on the progress of stale pitting of the 25Cr-7Ni-3Mo-0.25N duplex stainless steel were investigated in chloride solution. Electrochemical potential and current noises of the alloy were measured in 10 % ferric chloride solution ($FeCl_3$) with zero resistance ammeter (ZRA), and then analyzed by power spectral density (PSD) and by corrosion admittance ($A_c$) spectrum. With aging at $850^{\circ}C$, the passive film of the alloy was found to get significantly unstable as represented by power spectral density (PSD) and a transition from metastable pitting state to stable one was observed. In the corrosion admittance spectrum, the number of negative $A_c$ corresponding to the state of localized corrosion increased with aging, suggesting that the precipitation of $\sigma$ phase considerably degraded the passive film by depleting Cr and Mo around it at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries, thereby leading to the initiation of the pitting corrosion. However, the Cr and Mo at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries which were once depleted due to the precipitation of the $\sigma$ phase were partly replenished by the diffusion of Cr and Mo from the surrounding matrix with aging time longer. The initiation of pitting seems to be associated with the precipitation density of the $\sigma$ phase with an effective size needed to induce the sufficient depletion of Cr and Mo around it.

• Corrosion Science and Technology
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• 제20권6호
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• pp.426-434
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• 2021

The effect of two different annealing temperatures on the level of the second phase precipitated in the microstructure and the corrosion behaviors of super austenitic stainless steel were examined. The sample annealed at a higher temperature had a significantly lower fraction of the sigma phase enriched with Cr and Mo elements, showing more stable passivity behavior during the potentiodynamic polarization measurement. However, after the welding process with Inconel-type welding material, severe corrosion damage along the interface between the base metal and the weld metal was observed regardless of the annealing temperature. This was closely associated with the precipitation of the fine sigma phase with a high Mo concentration in the unmixed zone (UMZ) during the welding process, leading to the local depletion of Mo concentrations around the sigma phase. On the other hand, the fraction of the newly precipitated fine sigma phase in the UMZ was greatly reduced by post-weld heat treatment (PWHT), and the corrosion resistance was greatly improved. Based on the results, it is proposed that the alloy composition of welding materials and PWHT conditions should be further optimized to ensure the superior corrosion resistance of welded super austenitic stainless steel.

• 한국주조공학회지
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• 제17권1호
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• pp.28-35
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• 1997

SiC whisker and $Al_2O_3-SiO_2$ short fiber reinforced AC8A, AC8B and AC8B(J) marix composites were fabricated by squeeze casting method. Preform deformation, change of reinforcement volumefraction and formation of macro-segregation in two composites were investigated by using micro Vickers hardness test, analysis of macro and micro structures with OM, SEM and EDAX. $Al_2O_3-SiO_2$ short fiber preform manufactured with 5% $SiO_2$ binder in this study was considerably deformed and cracked, nevertheless, the short fibers were distributed homogeneously in the composites. In SiC whisker reinforced composites, on the other hand, preform deforming and cracking were not occurred, however, macro segregation zone formed along the infiltration routes by interface reaction during infiltration of molten metal into the preform was observed at center-low area in the composites. The decrease of hardness in the macro segregation zone resulted from the depletion of Si and Mg atoms.

• 한국재료학회지
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• 제14권12호
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• pp.829-834
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• 2004

Annealing of $Cu(B)/Ti/SiO_2$ in vacuum has been carried out to investigate the effects of Ti underlayer on microstructure in $Cu(B)/Ti/SiO_2$ structures. For comparison, $Cu(B)/Ti/SiO_2$ structures was also annealed in vacuum. Three different temperature dependence of Cu growth can be seen in $Cu(B)/Ti/SiO_2$; B precipitates- pinned grain growth, abnormal grain growth, normal grain growth. The Ti underlayer having a strong affinity for B atoms reacts with the out-diffused B to the Ti surface and forms titanium boride at the Cu-Ti interface. The formation of titanium boride acts as a sink for the out-diffusion of B atoms. The depletion of boron in grain boundaries of Cu films, as results of the rapid diffusion of B along the grain boundaries and the insufficient segregation of B to the grain boundaries, induces grain boundaries to migrate and causes the abnormal grain growth. The increased bulk diffusion coefficient of B within Cu grains can be responsible for the normal grain growth occurring in the annealed $Cu(B)/Ti/SiO_2\;at\;600^{\circ}C$. In contrast, the $Cu/SiO_2$ structures show only the abnormal growth of grains and their sizes increasing as the temperature increases above $400^{\circ}C$.

• 헤리티지:역사와 과학
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• 제52권1호
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• pp.4-21
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• 2019

영남지역에서 출토된 6~7세기 신라 금제 귀걸이 23점에 대한 성분 분석을 실시하고, 금판에 포함된 은(Ag) 함량을 기준으로 세 가지 유형으로 분류하였다. I 유형(20~50wt%), II 유형(10~20wt%), III 유형(10wt% 이하)으로 구분하였는데, I II 유형의 귀걸이 금판은 금(Au) 함량이 상대적으로 높은 부분에서 미세한 기공이 집중적으로 분포되는 현상이 관찰되었다. 금판 표면의 성분 차이 발생 원인을 네 가지로 구분하여 1) 표면 처리, 2) 제작 과정에서 열 확산, 3) 사금의 성분 차이, 4) 금의 정련 방법 측면에서 검토하였다. 금판 표면의 금 함량이 상대적으로 높은 부분에서는 미세한 기공이 집중적으로 관찰되며, 이와 관련하여 금 합금 표면에 의도적으로 금을 제외한 금속 성분을 제거하면서 금 함량을 높이는 고갈 도금(depletion gilding) 가능성을 제시하였다. 의도적인 표면 처리와 더불어 제작 과정에서 금판과 금속 봉 사이에 열 확산이 일어나 금판의 구리 함량이 높아진 사례를 세환이식의 분석 결과로 확인되었다. 금판의 재료적인 측면에서 살펴보면 금판에 포함된 은(Ag)이 자연금에 포함된 것인지, 합금에 의해 추가된 것인지를 국내에서 채취된 사금 분석을 통해 살펴보았다. 분석 결과 평균적으로 13wt% 정도의 은이 포함된 것으로 미루어 보아 II 유형은 자연금의 범주에 포함되고, III 유형은 정련 과정을 거친 금, I 유형은 자연금에 은이 합금된 것으로 보인다. 여기에서 III 유형의 경우 정련 과정을 거쳐 순수한 금을 만든 뒤 은을 합금했을 가능성에 대해 국내외 고대 문헌에 소개된 금 정련 방법을 조사하였다. 고대 정련 방법은 자연금에 포함된 은이 염화물 또는 황화물과 반응하여 결합됨으로써 제거되는 방법이었는데, 이러한 방법을 통해 순수한 금을 얻기 위해서는 장시간의 노력과 기술이 요구된다는 것이 밝혀졌다. 따라서 정련 과정을 통해 순금을 만든 후에 강도를 높이기 위해 소량의 은을 첨가했을 가능성은 낮아 보인다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권6호
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• pp.698-703
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• 2014

최근 기존 화석연료의 고갈로 인하여 대체에너지로써 천연액화가스의 수요 증가와 함께 LNG 운반선의 수요가 증가하고 있으며, 그로인해 극한의 환경에서 사용할 수 있는 LNG 선박용 벨로우즈의 수요 또한 증가할 것으로 예상된다. 현재 LNG 선박용 벨로우즈에 사용되는 재료는 저온취성과 해수부식에 강한 INCOLOY 825와 STS316L합금이다. 본 연구에서는 극저온에 사용되는 LNG용 벨로우즈 재질인 INCOLOY 825과 STS316L 합금에 대하여 최적의 용접조건을 설정하고, 에릭센 시험을 통하여 용접부의 성형성을 분석하였다. 최적 조건에서의 용접시 용접부의 인장강도는 모재에 비하여 90% 이상의 강도값을 나타내었다. 또한 에릭센 시험을 통한 성형성 분석의 결과, 용접부가 아닌 모재에서 파단이 발생하는 매우 양호한 용접부를 얻을 수 있었다.

• Applied Microscopy
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• 제32권1호
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• pp.31-37
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• 2002

[ $Mg_{68}Zn_{28}Y_4$ ] 합금의 응고 조직은 primary solidification phase, primary solidification phase로부터 성장된 ${\alpha}-Mg$ dendrite, 그리고 응고 말기에 형성된 eutectic structure의 세 가지형태 조직으로 구성되어져 있다. Primary solidification phase에는 매우 큰 정도의 phason strain이 존재하고 있으며, $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$의 격자상수를 갖는 1/1 rhombohedral approximant가 존재한다. 이와 같은 rhombohedral approximant의 구조는 six dimensional face centered hyper-cubic lattice에 phason strain을 도입함에 의해 얻어질 수 있다. Decagonal phase는 icosahedral phase로부터 방위 관계를 가지며 형성되며, $Mg_4Zn_7$는 decagonal phase로부터 방위관계를 가지며 성장한다. 이는 세 상간에 구조적 유사성이 존재하고 있음을 의미하며, 응고시 용질원자의 분배에 의해 이들 세 상이 순서대로 형성되어진다.