Influence of pre-existing defects on corrosion performance of Cr coatings

THis is a poster presented at the 2024 Annual MIDAS meeting held at the Henry Royce Institute, University of Manchester, on the 16th of September 2024.

The poster covers a study looking a tthe impact of pre-existing cracks on the corrosion performance of chromium coated zirconium alloy cladding tubes.

Cracks were introduced to the coating by mehcanical deforming cladding tubes under uniaxial tension in the axial direction up to a strain of 2%. Four different coatings candidtates were exmained including a Nitrogen Cold Spray (NCS) and three differnt Magnetron Sputtered Physical Vapour Deposited (MS-PVD) coatings, labeled PVD a, b and c. PVDa and b had been produced using the same susbtrate bias but with different coating thicknesses, whilst PVD c was produced at a different substrate bias. 

The samples were autoclaved in pressurised water reactor (PWR) chemistry at 360 degrees celcius for 25 days with a subsequent autoclave test performed at the same temperature and with the same chemistry but using deuterium spiked water for 28 days.

The samples were then cross sectioned to reveal the circumferential cracks and were imaged using electorn microscopy to analyse crack density, crack opening and oxide area.

The cross sectioned samples were anaylsed using NanoSIMS to invesitgate the relative location of Deuterium within the microstrucutre as a result of the second autoclave tests. 

The coatings demonstrated enhanced oxidation resistance compared to the uncoated cladding. While larger oxides can lead to blistering and increase the risk of delamination, they are typically associated with large crack openings in PVD coatings. A  reduced crack density can lead to fewer cracks with a greater cack opening that allow for larger oxide formation, whereas higher crack densities contribute to a greater overall area of oxide islands at the Cr-Zr interface. The complex crack networks observed in NCS coatings, however, appear to reduce oxide size and limit deuterium presence at the interface.