Kyeong Ho Baik

Effects of Plasma Nitriding on the Erosion Behavior of AISI 403 Stainless Steel Solid State Particles

This study investigated the effects of plasma nitriding on the erosion behavior of AISI 403 stainless steel solid state particles at ambient temperature and 620 °C using Fe3O4 erodent particles at impact angles of 15-90 . The plasma nitriding formed a thick hardened layer which had a high microhardness of 1210 ± 15 Hv. At ambient temperature, AISI 403 suffered from severe erosion damage at low impact angles and exhibited ductile erosive behavior, while the nitrided layer experienced no significant damage at any impact angles. For AISI 403, the erosion rates at 620 °C were ~2 times higher than those obtained at ambient temperature. When eroded at 620 °C, the nitrided layer exhibited a ductile erosive manner, with a maximum erosion rate occurring at a low impact angle of 30 . The results from high temperature hardness measurement and the observation of the eroded surface are discussed to explain the high-temperature erosion behavior of the nitrided AISI 403 stainless steel. †(Received October 18, 2013)

Nanostructured WC-Co Coatings from Different Feedstock Powders

Nanostructured WC-Co coatings have been manufactured by high velocity oxyfuel (HVOF) spraying using commercially available nanocomposite powders. The effect of feedstock powder characteristics on coating microstructure has been investigated. A significant loss of carbon occurred during HVOF spraying, which was much greater for a porous, irregular powder than for a dense, spherical powder. The decarburization promoted the formation of several additional phases in the coating, including W2C, W and CoxWxC. The microstructural differences in each coating arose from the different extent of feedstock powder melting because of initial powder morphology.

La0.8 Sr 0.2 Ga 0.8 Mg 0.2-x Zn x O 2.8 (X = 0.0 ~ 0.05) 전해질의 저온 소결 특성

La 0.8 Sr 0.2 Ga 0.8 Mg 0.2-x Zn x O 2.8 (LSGMZ, X = 0-0.05) was prepared using a solid state reaction method. Two secondary phases (LaSrGaO₄ and LaSrGa₃O 7 ) of powders were identified by X-ray diffraction analysis. The relative amount of these secondary phases depended on the calcination conditions (temperature and time) and Zn content. The sintering density of LSGMZ was enhanced by increasing the Zn content and calcination temperature at the low sintering temperatures (1250-1300℃). The relationship between the sintering density of LSGMZ and the synthesis conditions was discussed considering the phase analysis results.

Transmission electron microscopy analysis of octanethiol-coated Cu powders

In this study, microstructures of Cu powders coated with octanethiol were analyzed using (scanning) transmission electron microscopy. Moreover, aging process of the octanethiol-coated layer as time passes by was analyzed using the electron energy loss spectroscopy technique. The octanethiol layer coated on the surface of Cu powders was kept until it was exposed to air for around 30 days. As days passes by, the coating layer had been decomposed and then a Cu(2)O layer was formed on the surface of powders.

The Effects of Process Parameters on Mechanical Property and Visual Aspect of Plasma Sprayed Y2O3 Coating

The effects of process parameters on the mechanical property and visual aspect of Y203 coating formed by plasma spraying were investigated. For the experiments, granular Y203 powders were plasma sprayed using plasma gun with external powder-feeding system. When an asymmetric spraying was introduced by one-side powder-feeding, bigger pores and more frequent black spots were found in the region formed in opposite side from powder feeding direction, where the droplets of relatively lower temperature and lower flying velocity impinged to form coating. The optimum conditions for highest Vickers hardness were found to be different from those for white visual aspect of the Y203 coatings. Among the process parameters such as Ar flow rate, H2 flow rate, 02 contents, spraying distance, spraying distance was known to be most important for the formation of black spots in Y203 coating. The black spots formed in Y203 coating are thought to have relationship with the breakdown of stoichiometry between Y and O during plasma spraying. Consequently, the processing route not to form black spots in Y203 coating is described.

Processing Conditions and Mechanical Properties of Fine Grained Mg by Equal Channel Angular Pressing

Mg and Mg alloys are promising materials for light weight high strength applications. In this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing (ECAP) at various processing temperatures were investigated experimentally. ECAP of channel angle of 90o and corner angle of 0o was successful without fracture of the samples at 300 oC. The hardness of the ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of temperature on the hardness and microstructure of the ECAP processed Mg were explained by the dislocation glide in the basal plane and non-basal slip systems and the dynamic recrystallization and recovery.