This study was aimed at developing an integrated fabrication process for solid oxide fuel cells (SOFC) with radio-frequency plasma spraying (RFPS) and/or hybrid plasma spraying (HYPS). Fundamental studies concerning particle velocity and deformation showed that the novel plasma spraying processes were mainly characterized by their superior capability for homogeneous heating and spraying of large size powders with relatively low particle velocity, and that even the lower particle velocities in RFPS (20 m s -' ) and HYPS (40-70 m s -' ) compared with those in direct current plasma spraying (Zooms-l) were found to be sufficient for deformation of impinging molten particles on the substrate. However, RFPs imposed a severe limitation on the substrate position because it led to a short flying distance for the molten particles. In this respect, HYPS was considered to be superior to RFPS. With 75pm Ysz powder, use of HYPS made it possible to get not only dense vszcoating with relative density higher than 98% but also good gas permeability, lower than 5.7 x 10-'cmAg-'s-' (2500 mm H,O). Moreover, porous NiO and chemically stable LaCoO, could be prepared as electrodes by Ar-0, HYPS. Though the cell performance has not been investigated yet. these experimental results have proved that HYPS must be a strong candidate for new aspects of the production of SOFC. especially from economic and engineering points of view.
Low Pressure Plasma Spraying (LPPS) is a promising coating method for Functionally Graded Material (FGM) expected to be able to reduce the thermal stress in high temperature environments such as a gas turbine. In this paper, we report the effect of the composition profile and coating density of LPPS sprayed FGM, consisting of ZrO 2-8 wt%Y 2 O 3 (YSZ) top coating, YSZ-Ni-20 wt%Cr (NiCr) FGM coating, NiCr under coating and copper substrate, on the thermal shock resistance evaluated by a modified temperature difference test. The density of YSZ and NiCr coating was successfully controlled by the chamber pressure and initial particle size in the range from 5.43 to 5.79 g/cm 3 and from 7.89 to 8.09 g/cm 3 , respectively. For an YSZ composition profile from NiCr under coating to YSZ top coating (in FGM), the highest thermal shock resistance was obtained when the fraction of YSZ increased with gentle slope just over NiCr coating and acute slope just under YSZ coating. Also, the higher density coatings tended to perform the higher thermal shock resistance. Initial cracks formed in the YSZ top coating propagated into YSZ parts in FGM coating through the grain boundary of YSZ and/or the interface between flattened NiCr and YSZ particles. After the cracks connected, the coupled cracks caused the coating spallation.
Ultra-fine grained steel (UFGS) with an average grain size of less than 1μm has been
developed and is expected to demonstrate superior properties. However, its welded heat-affected zone,
HAZ, substantially affecting the strength of a welded joint, will be easily softened after welding.
Therefore, minimization of UFGS’s HAZ size during laser welding was carried out using the cooling
conductor liquid nitrogen. It was found that a shielding gas with adequate flow rate for the liquid
nitrogen depth was used to displace nitrogen on the area of laser beam irradiation to stabilize the weld
bead. Also, because YAG laser system was mainly used because it has a lower laser induced plasma or
plume temperature, which results in a decreased occurrence of pit and blowhole. HAZ size
minimization strongly depends on the initial plate temperature. Reduced initial plate temperature
shrinks the specific heated temperature range in which softening occurs. However, due possibly to
decreasing thermal conductivity under room temperature, which prevents heat removal, the benefit of
reducing the initial plate temperature is limited. The optimal initial temperature to minimize the HAZ
size, in the present work, was found to be 123K.
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