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Type 316H stainless steel is a primary candidate material for a reactor pressure vessel of a sodium-cooled fast (SFR) reactor which is under development in Korea. The reactor pressure vessel for a SFR is subjected to inelastic deformation induced by cyclic thermal stress. Fully reversed cyclic testing and ratcheting testing at elevated temperatures were performed to characterize the inelastic cyclic deformation behaviors of Type 316H stainless steel at the SFR operating temperature. It was found that cyclic hardening of Type 316H stainless steel was enhanced, and the accumulation of ratcheting deformation of Type 316H stainless steel was retarded at around the SFR operating temperature. The results of the tensile testing and the microstructural investigation for dislocated structures after the inelastic deformation testing showed that dynamic strain aging affected the inelastic cyclic deformation behavior of Type 316 stainless steel at around the SFR operating temperature.

keyword : Type 316H, sodium-cooled fast reactor, dynamic strain aging, inelastic, ratcheting

The effect of the heat treatment condition to introduce the grain boundary (GB) serration on the creep properties was investigated at 950 ℃ in a solid-solution-strengthened Alloy 617. Serrated GBs without carbide at the early stage of slow-cooling were newly observed, and appear to challenge previous models. As the aging temperature for which the specimen was slow-cooled from 1200 ℃ decreased, the amplitude and the fraction of the serration became higher. The serrated GBs with stable planar M23C6 carbides caused a fairly long period of a steady-state stage due to their higher resistance to GB cavitation cracking as well as substantial suppression of recrystallization. The very fine and stable intragranular carbides, which precipitated uniformly throughout the serrated specimen aged at 1000 ℃ during the initial stage of creep, were responsible for the further improvement in the creep rupture life (up to 2.8 times longer) by lowering the creep strain rate.

keyword : alloys, allogs, aging, creep, transmission electron microscopy, TEM, grain boundary serration

SA 508 Gr.3 Mn-Mo-Ni low alloy steel forgings thicker than 200 mm are used for reactor pressure vessels in nuclear power plants. The cooling rate difference along the thickness direction during the quenching process causes variation in the microstructure and mechanical properties. The microstructural variation and its influence on the fracture toughness of RPV steels were investigated in this study. The cleavage fracture toughness in the transition region were evaluated with the ASTM E1921 master curve method for samples at different locations from the inner surface to the center thickness of the RPV steel. The microstructural features, such as the area fraction, and the size and distribution of precipitates were quantitatively evaluated at each sampling position. Microstructure observations showed that at near the surface position, bainite laths are finer, and furthermore, the carbides are smaller and homogeneously distributed. The fracture toughness at the surface was better than those at deeper positions. The reference temperature T0 showed a linear relationship with the area fraction of the carbides bigger than a certain critical size. It is concluded that the size of the precipitates caused by the cooling rate gradient may have a dominant role in controlling the cleavage fracture toughness variation along the thickness direction for a very thick RPV steel.

keyword : low alloy steels, forging, fracture toughness, mechanical properties, SA508 Gr.3

Aluminim pack cementation coatings on Haynes 230 alloys have been developed between 500 and 600 ℃. A single Al3Ni layer was coated on the alloys. The activation energy for growth rate of the coated layer thickness was estimated as 63.1 kJ / mol in the examined temperature range. In order to examine the degradation behaviors, the alloys were subjected to high temperature flame via an LPG / O2 gas torch. In order to test the degradation behaviors, uncoated alloys, coated alloys and oxidized following coated alloys have been prepared. The uncoated Haynes 230 alloys exhibited a weight loss during the torch tests due to the sublimation of chromium oxide on the surface, and the coated allo specimen showed an surface melting due to low melting temperature of the coating layer. However, the coated with oxidation - treated Haynes 230 alloys maintained the original weight due to the presence of an surface in-situalumina layer. The coated microstructures and related coating kinetics are discussed in terms of structural identification and weight changes.

keyword : alloys, coating, oxidation, scanning electron microscopy, SEM

The microstructural evolution and mechanical properties during mechanical milling of pure magnesium powders were investigated as a function of the milling time and processing control agent. Commercially pure magnesium powders were mechanically milled in a SPEX 8000 shaker Mixer/Mill in an inert atmosphere. From the TEM observations and the analysis of the X-ray diffraction patterns, the steady state grain size was approximately 75 nm regardless of the addition of a processing control agent, while the milling time to reach steady state was shorter when a processing control agent (1wt% stearic acid) was added to the pure magnesium. It is noteworthy that the steady state hardness of the pure magnesium with the processing control agent was hardly different from that of the pure magnesium milled without PCA. Hence, we conclude that the oxides present in the magnesium surface function the same as that of the PCA, and their effectiveness is dependent on the characteristics of the magnesium surface oxides broken by mechanical milling.

keyword : mechanical alloying/milling, pure magnesium, X-ray diffraction, transmission electron microscopy, TEM

The optical and electrical characteristics of an ITO film were analyzed by depositing it on a glass substrate using an electron beam evaporator (EBE) for application in thin-film solar cells. The temperature of the substrate during the deposition was adjusted from room temperature to 400 ℃. The optical properties of the ITO film were analyzed with a UV-Vis-NIR spectrometer. A four point probe system was used to measure the electrical characteristics. The surface morphology was studied by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). A high-resolution x-ray diffractometer (HR-XRD) was used to analyze the phases of the ITO film at various substrate temperatures. From the results, ITO whiskers grew at 200 ℃. However, ITO whisker growth changed to ITO nanowire growth above 300 ℃ for the substrate temperature. When the growth changed from whiskers to wires, the morphology of the film and the electrical and optical properties also changed. The ITO nanowires have good transmittance for application in thin-film solar cells above a 300 ℃ substrate temperature.

keyword : optical materials, annealing, optical properties, scanning electron microscopy, SEM, indium tin oxide

The effects of electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes on the interfacial reaction, and the mechanical and electrical reliabilities of a ball grid array (BGA) Sn-0.7Cu lead-free solder bump were systematically investigated. An in-situ annealing test was performed under three different temperatures to obtain the activation energy for the intermetallic compound (IMC) reaction. Additionally, the ball shear test was conducted under various high-speed loading conditions ranging from 10 to 3,000 mm/s. In addition, the electromigration (EM) test was performed at 13 0℃ with a current density of 5.0 × 103 A/cm2. During annealing, (Cu, Ni)6Sn5 IMC formed at the interface of the ENIG surface finish, while at the OSP surface finish, Cu6Sn5 and Cu3Sn IMCs formed. The activation energies for the total IMCs were 0.84 and 0.74 eV for ENIG and OSP, respectively. The maximum shear force increased with increasing shear speed in the ball shear test, while the shear energy decreased. Furthermore, OSP surface finishes have a similar shear strength with the ENIG surface finishes. The EM lifetime of ENIG surface finish was longer than that of the OSP surface finish because the ENIG surface finish acts as an effective diffusion barrier between the Cu substrate and solder.

keyword : electrical/electron materials, soldering, bonding, electromigrtion, strength, scanning electron microscopy, SEM

The effects of heat-treatment temperature on the structural and optical properties of ZnO thin films were investigated with field-effect scanning electron microscopy (SEM), X-ray diffraction analysis, and photoluminescence (PL) measurements. The ZnO thin films were grown on Zn-deposited fluorine-doped tin oxide substrates by sol-gel spin coating. The SEM images of the samples showed that their surfaces had a mountain-chain-like structure. The film annealed at 400 ℃ had the highest degree of alignment along the c-axis, and its residual stress was close to zero. The PL spectra of the ZnO thin films consisted of sharp near-band-edge emissions (NBE) and broad deep-level emissions (DLE) in the visible range. The DLE peaks exhibited a green-to-red shift with an increase in the temperature. The highest INBE/IDLE ratio was observed in the film annealed at 400 ℃. Thus, the optimal temperature for growing high-quality ZnO thin films on Zn-deposited FTO substrates is 400 ℃

keyword : zinc oxide, FTO substrate, Zn buffer layer, spin coating, photoluminescence, post-heat treatment

ZnO thin films were grown on Zn-deposited polyimide (PI) substrates using the sol-gel spin-coating method. The Zn seed layers were annealed at 200, 300, and 400 ℃. The annealing effects of the Zn seed layer on the structural and optical properties of the ZnO thin films were investigated for the first time. By adjusting the annealing temperature of the Zn seed layers, we achieved a significant enhancement in the crystallinity of the ZnO thin films. The ZnO thin film grown on a non-annealed Zn seed layer had a yellow/orange emission, whereas those grown on annealed ones had a green emission as well as lower defect-related deep-level emissions. The narrowest full width at half maximum of the near-band-edge emission was observed for the ZnO thin films grown on the Zn seed layers annealed at 200 and 300 ℃. We found that the structural and optical properties of the ZnO thin films grown on the Zn seed layer annealed at 400 ℃ were deteriorated, which could be attributed to considerable changes in the characteristics of the PI substrate at the annealing temperature of 400 ℃.

keyword : zinc oxide, thin film, sol-gel, Zn Seed layer, optical properties

CeO2 is known as a universal catalyst, and most studies in the literature have concentrated on enhancing the properties of CeO2. In this study, we used amorphous CeO2 to fabricate glass samples and determined their properties. Generally, the catalytic reactions of CeO2 involve redox reactions. To test the reactivity of these glass structures, coverage should increase beyond the limitations of the powder. Glass was chosen rather than conventional materials because it is highly stable and used in a variety of fields.Phosphate systems were selected to analyze the characteristics of the glass samples fabricated with various compositions, and the properties of the glass samples depended on the composition used to fabricate them. The relationship between the ionicity of CeO2 and the catalytic behavior of these systems was determined and analyzed.

keyword : glasses, bonding, optical properties, thermal analysis, catalyst