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9-12% Cr강의 용접부에 미치는 δ-ferrite의 영향
안성용,강남현,Ahn, Sung-Yong,Kang, Namhyun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6
As the energy consumption increases rapidly, power generation needs the high energy efficiency continuously. To achieve the high efficiency of power generation, the materials used have to endure the higher temperature and pressure. The 9-12%Cr steels possess good mechanical properties, corrosion resistance, and creep strength in high temperature due to high Cr contents. Therefore, the 9-12%Cr steels are widely used for the high-temperature components in power plants. Even though the steels usually have a fully martensitic microstructure, they are susceptible to the formation of ${\delta}$-ferrite specifically during the welding process. The formation of ${\delta}$-ferrite has several detrimental effects on creep, ductility and toughness. Therefore, it is necessary to avoid its formation. As the volume fraction of ${\delta}$-ferrite is less than 2% in microstructure, it has the isolated island morphology and causes no significant degradation on mechanical properties. For ${\delta}$-ferrite above 2%, it has a polygonal shape affecting the detrimental influence on the mechanical properties. The formation of ${\delta}$-ferrite is affected by two factors: a chemical composition and a welding heat input. The most effective ways to get a fully martensite microstructure are to reduce the chromium equivalent less than 13.5, to keep the difference between the chromium and nickel equivalent less than 8, and to reduce the welding heat input.
Electromigration에 의한 Sn-0.7Cu 솔더 금속간화합물 성장 예측
허민혁 ( Min-hyeok Heo ),강남현 ( Namhyun Kang ),박성훈 ( Seonghun Park ),김준기 ( Jun-ki Kim ),홍원식 ( Won Sik Hong ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.12
The reliability of printed circuit boards (PCB) has emerged as a critical concern as the size of solder bump decreases and current density to solder bump increases by fine pitch formation. The main failure mode of solder bumps is open-circuits due to void formation as intermetallic compounds (IMC) grow, mainly due to electromigration. This study modeled IMC growth by electromigration in Sn-0.7Cu solder bumps. The IMC produced in the reflow process grew again significantly due to electromigration upon application of electric current. The thickness of the IMC under electromigration increased as the current increased from 1 A (current density: 1.3 × 104 A/cm2) to 1.5 A (current density: 1.9 × 104 A/cm2). For the current density applied in the study, IMC growth of Cu6Sn5 was faster than that of Cu3Sn. The Nernst-Einstein relation was used to model the IMC growth induced by electromigration. The modeling results of Cu3Sn and Cu6Sn5 thickness showed good agreement with the experimental observations of IMC growth under electromigration. Specifically, a good prediction for Cu3Sn growth was derived for the current density of 1.3 × 104 A/cm2. However, the modeling values of 1.9 × 104 A/cm2 and Cu6Sn5 thickness showed a minor difference as compared with the experimental IMC thickness results. As the current density increased from 1.3 × 104 A/cm2 to 1.9 × 104 A/cm2, the solder bump probably evolved under heat generation, and the further effects of aging and thermomigration should be incorporated in the IMC growth. †(Received April 7, 2016; Accepted June 17, 2016)