Showing 6 results for Zandrahimi
H. Ebrahimifar , M. Zandrahimi,
Volume 29, Issue 2 (Dec 2010)
Abstract
In order to increase the efficiency and working life of mettalic interconnects used in solid oxide fuel cells, protective coatings with high electrical conductivity are used. In this study, AISI 430 ferritic stainless steel was coated in a cobalt-base pack mixture by pack cementation. The effect of oxide thickness on the area specific resistance (ASR) was investigated by applying isothermal oxidation at 800 °C and non-isothermal oxidation at a temperature range of 400 – 900 ºC. Results showed that the formation of MnCo2O4 and CoCr2O4 Spinels during oxidation improved electrical conductivity. The increase of isothermal oxidation time and temperature increases the oxide thickness, and consequently the ASR increased.
M. Haerifar, M. Zandrahimi,
Volume 34, Issue 1 (Journal of Advanced Materials-Spring 2015)
Abstract
In the present study, 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn-Cu alloy coatings from a bath containing ammonium sulfate. The effects of current density on the microstructure, crystallographic structure, and chemical composition of the deposits were studied. The results showed that at low current densities, discontinuous coatings with a large amount of Cu can be obtained. Further increase in current density resulted in amorphous, compact and heterogeneous coatings with a small amount of Cu. The presence of Cu at low contents in precipitated coatings delayed the phase transformation of as-deposited ductile g-Mn to the brittle and hard a-Mn. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities.
M. Mahmoudi Saleh Abad, M. Zandrahimi, H. Ebrahimi Far,
Volume 37, Issue 3 (Journal of Advanced Materials-Fall 2018)
Abstract
In order to improve the oxidation and hot corrosion resistance of steels, various elements including aluminum, chromium, silicon, titanium or combination of these elements can be diffused on to the surface of steel. In this study, aluminum and titanium were simultaneously co-deposited onto the AISI 430 ferritic stainless steel substrate by the pack cementation process. Coating was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coating consised of two layers with the thickness of approximately 14 microns. The results obtained by XRD showed the existence of FeTi, TiO2, AlTi, Al3Ti and Al5Ti phases in the coating. Isothermal oxidation and cyclic oxidation were carried out at 1000○C. It was showed that the diffusional coating of aluminum-titanium led to the improvement of cycle and isothermal oxidation resistance.
M. Akbarzadeh, M. Zandrahimi, E. Moradpour,
Volume 37, Issue 4 (Journal of Advanced Materials-winter 2019)
Abstract
Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants. In this study, MoS2-Cr composite coatings were deposited onto AISI 1045 steel substrates by direct-current magnetron sputtering. The MoS2/Cr ratio in the coatings was controlled by sputtering the composite targets. The coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and nano-indentation and nano-scratch techniques. The tribological behavior of the coatings was investigated using the pin-on-disc test at room temperature. The results showed that the thickness and the hardness of the coating were 6 µmand 850-1300 HV, respectively. The degree of the crystallization of the composite coatings was enhanced with increasing the Cr contents. The incorporation of Cr into MoSx coatings resulted in the considerable improvement of coating adhesion and hardness. The optimum doping level for MoS2-Cr coatings to show the best tribological propertie was 13 atomic percent. The main wear mechanisms of the coating were delamination, tribochemical and abrasive micro cracking
F. Saeidpour, M. Zandrahimi, H. Ebrahimifar,
Volume 38, Issue 1 (Journal of Advanced Materials-Spring 2019)
Abstract
Crofer 22 APU ferritic stainless steel has been evaluated as one of the favorable materials for utilization in Solid oxide fule cell (SOFC) interconnects. However, there are difficulties in utilizing these metallic interconnects, including the quick decrease of their electrical conductivity and evaporation of Cr species. To overcome the above problems, the application of protective coatings has been proposed. In this work, Co/Y2O3 composite coatings were deposited onto Crofer 22 APU stainless steels by direct current electrodeposition method. Oxidation and electrical properties of uncoated and coated steels were evaluated. Surface and cross-section of the bare and coated steels were characterized using scanning electron microscopy and X-ray diffraction techniques. Results showed that oxidation rate of the coated specimen was reduced by about 4 times, as compared to the uncoated one after 500 h isothermal oxidation in air at 800˚C. Formation of Co3O4 and MnCo2O4 spinel compositions improved electrical conductivity of the coated sample. After 500 h of isothermal oxidation at 800˚C, ASR value of the Co/Y2O3-coated and uncoated steels was 15.8 mΩ·cm2 and 25.9 mΩ·cm2 , respectively.
H. Ebrahimifar, M. Zandrahimi, F. Ekhlaspour,
Volume 38, Issue 3 (Journal of Advanced Materials-Fall 2019)
Abstract
One of the most effective ways to improve oxidation resistance of interconnects used in solid oxide fuel cells (SOFCs) is to apply a layer of conductive protective coating. In this study, Crofer 22APU ferritic steel was coated in a titanium- based powder mixture by pack cementation method. The powder composition for titanium coating was Ti 20 wt.%, NH4Cl 5 wt.% (activator) and Al2O3 75 wt.%. The optimum temperature and time to obtain the best coating quality in terms of adhesion and porosity were 800 °C and 7 hours, respectivly. The obtained titanized coating consisted of TiFe, TiFe2 and TiCr2 phases. The results of isothermal and cyclic oxidation tests carried out at 900 °C, showed that titanium-coated samples had better oxidation resistance than non-coated samples. Microstructural and phase studies of coated and oxidized samples were performed by scanning electron macroscopy (SEM) and X-ray diffraction analysis (XRD). During oxidation process, the coating layer was converted into TiFe, TiFe2, TiFe2O5, TiO2 and TiCr2O4 phases. The coated specimens had lower weight gains relative to uncoated samples showing that coating effectively protects the substrate against oxidation. Moreover, coated samples had higher electrical resistance than uncoated ones.
