Yangsan, South Korea
Yangsan, South Korea

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Ha J.W.,Pusan National University | Ha J.W.,KOS Ltd | Seong B.S.,Korea Atomic Energy Research Institute | Jeong H.W.,Korea Institute of Materials Science | And 3 more authors.
Materials Characterization | Year: 2014

Inconel X-750 is a Ni-based precipitation-hardened superalloy having large tensile and fracture strengths. In the study, X-750 wires were cold drawn to different extents. Small angle neutron scattering was employed to quantitatively measure the size and volume fraction of the γ′ phase as a function of the cold drawing ratio (DR) and aging temperature. The presence and size of γ′ precipitates were confirmed by transmission electron microscopy. The drawing ratio had an important effect on the volume fraction of the γ′ precipitates. However, the size of the precipitates was independent on the drawing ratio. The specimen with the minimum drawing ratio (DR0) produced the largest volume fraction of γ′ as compared with large drawing ratio (DR) specimens such as DR17 and DR42. The small volume fraction of the γ′ phase for a sizeable drawing ratio was associated with the large amount of nucleation sites for secondary carbides, M 23C6, and the fast diffusion path, i.e., dislocation, needed to form M23C6. A Cr depletion zone around the secondary carbides raised the solubility of γ′. Therefore, the significant drawing ratio contributing to the large volume fraction of the secondary carbides decreased the volume fraction of the γ′ precipitates in Inconel X-750. © 2014 Elsevier Inc.


Oh C.,Korea Electronics Technology Institute | Kim A.,Korea Electronics Technology Institute | Kim J.,Korea Electronics Technology Institute | Bang J.,Korea Institute of Industrial Technology | And 2 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2015

The requirement for environmentally friendly technology has led to considerable efforts to develop photovoltaic (PV) modules. The copper (Cu) ribbon interconnects of PV modules require alternative bonding materials to replace the current solder that contains lead. Several candidate lead-free solder materials have been developed that are inexpensive and reliable. In this study, we evaluate Cu ribbon interconnection bonding with Sn–0.7Cu and Sn–48Bi–2Ag solder materials to address their feasibility for use in PV modules by investigating material degradation during thermal cycling. After thermal cycling, in the Sn–0.7Cu solder, considerable intermetallic compound (IMC) growth occurred at both interfaces, while Bi-rich grains coarsened with IMC growth in Sn–48Bi–2Ag solder. However, the degradation of the electrical performance of the PV modules was similar for those containing both solder materials. Cracks that appeared at the interface propagated from the fractures of the Ag3Sn IMC layers. This suggests that preventing IMC growth at the interface between the Cu ribbon and Ag sintered electrode is important to improve the reliability of interconnects in PV modules. The use of Pb-free solder in PV modules opens up a novel opportunity to realize high reliability at low cost. © 2015 Springer Science+Business Media New York


Ha J.W.,Pusan National University | Ha J.W.,KOS Ltd | Seong B.S.,Korea Atomic Energy Research Institute | Jeong H.W.,Korea Institute of Materials Science | And 2 more authors.
Journal of Nuclear Materials | Year: 2015

Inconel X-750 is a Ni-based precipitation-hardened superalloy typically used in springs designed for high-temperature applications such as the hold-down springs in nuclear power plants. γ' is a major precipitate in X-750 alloys which affects the strength, creep resistance, and stress relaxation properties of the spring. In this study, a solution-treated X-750 wire coiled into a spring was used that was aged at various temperatures and submitted to stress relaxation tests with and without loading. Small angle neutron scattering was employed to quantify the size and volume fraction of γ' phase in the springs as a function of the aging temperature and the application of a load during stress relaxation. The volume fraction of γ' precipitates increased in the specimen aged at 732 °C following stress relaxation at 500 °C for 300 h. However, the mean size of the precipitates in the samples was not affected by stress relaxation. The specimen aged at the lower temperature (620 °C) contained a smaller γ' volume fraction and gained a smaller fraction of γ' during stress relaxation compared with the sample aged at the higher temperature (732 °C). The smaller increase in the γ' volume fraction for the sample aged at 620 °C was associated with a larger increase in the M23C6 secondary carbide content during relaxation. The Cr depletion zone around the secondary carbides raises the solubility of γ' thereby decreasing the volume fraction of γ' precipitates in Inconel X-750. In terms of stress relaxation, a larger increase in the γ' volume fraction was measured with loading rather than without. This is probably associated with the dislocation accumulation generated under loading that facilitate the nucleation and growth of heterogeneous γ' phase due to enhanced diffusion. © 2014 Elsevier B.V. All rights reserved.


The use of thermoplastic technology and fabrication techniques to provide cost effective alternatives to existing structures used


PubMed | Daegu Gyeongbuk Institute of Science and Technology, Yonsei University, KOS Ltd., Korea Institute of Materials Science and 4 more.
Type: | Journal: Scientific reports | Year: 2015

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse -Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface -Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications.

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