Microstructures of thin and thick slurry aluminide coatings on Inconel 690

Two slurry aluminide coatings are produced on the Ni-base super alloy Inconel 690 by applying two different thicknesses of the same slurry on to the 690 substrate, followed by a two-step heat-treatment. The resulting thin aluminide coating consists of a single layer of Ni-rich β-NiAl matrix containing few large Cr precipitates with a high P content. The thick aluminide coating has a precipitate free inner layer of Ni-rich β-NiAl. An outer layer of Al-rich β-NiAl with many α-Cr precipitates has formed as well. The present metallurgical characterization shows a significant influence of slurry thickness on the morphology and composition of the coatings formed during heat treatment.