Enhancing the high temperature oxidation behavior of Cr2AlC coatings by reducing grain boundary nanoporosity

Abstract

The oxidation behavior of Cr2AlC MAX phase coatings with columnar and equiaxed morphologies is compared. After oxidation at 1100°C for 240 min the Cr2AlC MAX phase coatings with equiaxed grains showed a 20% lower scale thickness and a 52% larger scale grain size as the coatings with columnar grains. Transmission electron microscopy data suggests that this is primarily caused by nanopores (2–25 nm) present in the columnar grain boundaries. As their presence has previously been overlooked, a 20% improvement of the high temperature oxidation behavior of Cr2AlC coatings is obtained if the formation of nanopores is avoided. IMPACT STATEMENT: This is the first report on the formation of nanopores at grain boundaries of Cr2AlC coatings and their implications for the oxidation behavior. Avoiding the previously overlooked presence of nanopores at the grain boundaries of the as grown coatings enables a significant improvement in high temperature oxidation behavior of Cr2AlC coatings.