This study investigates the precipitation of Fe containing intermetallic compounds in A413 aluminium alloy in the Cr-and Co-modified conditions. The Fe content varied from 0 . 5 to 2 . 5 wt-%. For each amount of Fe, different levels of Cr and Co were added to identify the optimum Fe:Cr and Fe:Co ratios to eliminate the b-phase and obtain microstructures containing well distributed fine intermetallic a-phase in dendritic or Chinese script morphology. It was found that the addition of Cr and Co changes the morphology of Fe rich intermetallic compounds from the harmful plate like b-phase to a less damaging morphology. The critical ratios were Fe:Cr~3 . 0 and Fe:Co~1 . 0 approximately. In addition, it was noted that the addition of Cr or Co promotes the formation of primary Si. The results suggest that the presence and the form of all precipitates (both Fe rich and primary Si) seem to be strongly related to the presence of bifilms (doubled over oxide films) suspended in the liquid alloy.IJC/550
Conventional and nanostructured zirconia coatings were deposited on In-738 Ni super alloy by atmospheric plasma spray technique. The hot corrosion resistance of the coatings was measured at 1050°C using an atmospheric electrical furnace and a fused mixture of vanadium pent oxide and sodium sulfate respectively. According to the experimental results nanostructured coatings showed a better hot corrosion resistance than conventional ones. The improved hot corrosion resistance could be explained by the change of structure to a dense and more packed structure in the nanocoating. The evaluation of mechanical properties by nano indentation method showed the hardness (H) and elastic modulus (E) of the YSZ coating increased substantially after hot corrosion.
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