Chiang Mai Journal of Science

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This research aims to study feasibility of applying powder liquid coating process to form nickel aluminide layer which is superior for oxidation resistance on nickel.  In powder liquid coating process, mixture slurries of Al and Al₂O₃ powders were pasted onto samples and heat treated.  The microstructures of coated samples were analyzed by SEM and optical microscope. GIXD, EDS and EPMA were employed to investigate phase formations and element distributions in the coating layer.  Thickness of  the coating layer was also measured. The coating layer can be either single-phase (Ni₂Al₃) or multi-phases (NiAl, (Al) and Ni₂Al₃) coating layer depending on the coating condition.  Thickness and homogeneity of the coating layer are used as the criteria to determine quality of  the coating layer. Increasing of  Al content in mixture slurries produces thicker coating layer with less degree of homogeneity. To increase homogeneity, longer aluminizing time is required.  The thickness uniformity depends on Al powder distribution in the mixture slurries which can be controlled by adding appropriate amount of  Al₂O₃ powder into the mixture slurries.  In this experiment, the optimum condition to achieve uniformly thick single-phase (Ni₂Al₃) coating layer is to use slurry with Al:Al₂O₃ ratio of 7:3 and 4 hours aluminizing time at 1,000^oC.

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