M. Bahamirian, Sh. Khameneh Asl,
Volume 10, Issue 3 (9-2013)
Abstract
In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior
H. Mohebbi, S.m. Mirkazemi,
Volume 17, Issue 4 (12-2020)
Abstract
Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm-1 and 50 to 200mA.mm-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.
