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Abstract: This study examines the effect of ytrria stabilized zirconia (YSZ) dispersion on hot corrosion behaviour of NiCrAlY bond coat. Hot corrosion studies were conducted on NiCrAlY and NiCrAlY containing 25, 50 and 75 wt.% YSZ coatings obtained through the air plasma spray technique, in Na2SO4 +10 wt.% NaCl environment at 800°C. The results show that YSZ dispersion lowers the overall hot corrosion tendency of the NiCrAlY, though it enhances the inherent hot corrosion tendency of its metallic constituent (NiCrAlY). Furthermore, there exists a threshold oxide level beyond which it adversely affects the hot corrosion of the coating. [Copyright &y& Elsevier]

Electroslag remelted cast iron aluminides were investigated to understand the effect of C (0.05–1 wt.%) and Al (16–8 wt.%) on their sulfidation behaviour in SO2+O2 environment at 800 °C. Irrespective of the C content for a given Al content, sulfidation behaviour of the aluminides was found to be the same. The sulfidation rate of these iron aluminides was much lower than that of 310 SS, which was used a reference alloy. With variation of the Al content in iron aluminides, the sulfidation rate was influenced by the matrix phase rather than the carbide phase. [Copyright &y& Elsevier]

Abstract: Oxide dispersed NiCrAlY bond coatings have been developed for enhancing thermal life cycles of thermal barrier coatings (TBCs). However, the role of dispersed oxides on high temperature corrosion, in particular hot corrosion, has not been sufficiently studied. Therefore, the present study aims to improve the understanding of the effect of YSZ dispersion on the hot corrosion behaviour of NiCrAlY bond coat. For this, NiCrAlY, NiCrAlY+25wt.% YSZ, NiCrAlY+50wt.% YSZ and NiCrAlY+75wt.% YSZ were deposited onto Inconel-718 using the air plasma spraying (APS) process. Hot corrosion studies were conducted at 800°C on these coatings after covering them with a 1:1 weight ratio of Na2SO4 and V2O5 salt film. Hot corrosion kinetics were determined by measuring the weight gain of the specimens at regular intervals for a duration of 51h. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques were used to determine the nature of phases formed, examine the surface attack and to carry out microanalysis of the hot corroded coatings respectively. The results show that YSZ dispersion causes enhanced hot corrosion of the NiCrAlY coating. Leaching of yttria leads not only to the formation of the YVO4 phase but also the destabilization of the YSZ by hot corrosion. For the sake of comparison, the hot corrosion behaviour of a NiCrAlY+25wt.% Al2O3 coating was also examined. The study shows that the alumina dispersed NiCrAlY bond coat offers better hot corrosion resistance than the YSZ dispersed NiCrAlY bond coat, although it is also inferior compared to the plain NiCrAlY bond coat. [Copyright &y& Elsevier]

The oxide films formed during early stage of oxidation at 800 °C on dendritic and interdendritic regions of the cast Fe–16Al–1C (wt.%) alloy were studied using scanning Auger electron spectroscopy. Microhardness measurement and elemental depth profiles by Auger spectroscopy reveal that the carbide, Fe3AlC0.69, is the major constituent of the interdendritic region, while dendrites are predominantly Fe3Al phase. Between the two, the interdendritic region is found to be more prone to oxidation than the dendritic region, which was attributed to presence of carbides with low-Al content. In spite of the difference in oxide film thickness exhibited by both the phases, they consist of an inner aluminium oxide layer and an outer iron oxide layer. [Copyright &y& Elsevier]