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.

GRAPHICAL ABSTRACT

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.

KEYWORDS:

• MAX phases
• nanoporosity
• oxidation behavior

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors gratefully acknowledge financial support from the Euratom research and training program 2014–2018 under grant agreement number [740415 (H2020 IL TROVATORE)]. JMS gratefully acknowledges the Max Planck Fellow Program.