S. R. Bakhshi, M. Salehi, H. Edris, G. H. Borhani,
Volume 29, Issue 1 (6-2010)
Abstract
In this study, Mo-14Si-10B and Mo-57Si-10B (at%) elemental powders were separately milled using an attritor mill. Mechanically alloyed powders were agglomerated and annealed. Then, powders of Mo-Si-B as alloyed (with composites) and agglomerated (without composites) were plasma sprayed onto plain carbon steels. The samples, both coated and non-coated, were subjected to isothermal oxidation tests. Metallurgical characteristics of powders and coatings were evaluated by SEM and XRD. Plasma-sprayed Mo-Si-B coatings (with phases of MoSi2, Mo5Si3, MoB and Mo5SiB2) greatly improved the oxidation resistance of the plain steel substrates, but plasma-sprayed Mo-Si-B coatings (without any phases) did not significantly improve the oxidation rate of substrates. Also, the kinetics and composition of the oxide-scale have been found to depend on the alloy composition.
S. N. Hosseini, F. Karimzadeh, M. H. Enayati,
Volume 39, Issue 4 (2-2021)
Abstract
The bare and pre-oxidized AISI 430 pieces were screen printed by copper ferrite spinel coatings. Good bonding between the coating and the substrate was achieved by the reactive sintering process of the reduced coating. The energy dispersive X-ray spectroscopy (EDS) analysis revealed that the scale is a double layer consisting of a chromia-rich subscale and an outer Cu/Fe-rich spinel. The results showed that the spinel protection layer not only significantly decreased the area specific resistance (ASR), but also inhibited the subscale growth by acting as a barrier to the inward diffusion of oxygen. ASRs of 19.7 and 32.5 mΩ.cm2, much lower than that of the bare substrate (153.4 mΩ.cm2), at 800 °C after 400 h oxidation were achieved for the bare and pre-oxidized copper ferrite spinel coated samples, respectively. Excellent, stable ASR (20.5 mΩ.cm2) was obtained with copper ferrite coating after 600 h of exposure at 800 °C. The high electrical conductivity of CuFe2O4 and its doping by Mn, the growth reduction of Cr2O3 oxide scale and the good coating to substrate adherence are proposed to be responsible for substantial improvement in electrical conductivity.
