Effect of cryogenic laser surface modification on the microstructure evolution and corrosion resistance of accident-tolerant FeCrAl alloys

Accident-tolerant FeCrAl alloys require a thinner cladding wall than zirconium cladding to overcome the extra neutron loss, thus requiring enhanced corrosion resistance. Surface treatment was used in this study to address this issue via cryogenic laser surface modification. A finite element model based on heat-transfer theory was raised to reveal the temperature field change during cryogenic laser treatment. The relationship between the laser processing parameters and surface morphology was studied with various characterizations to better understand the process mechanism and verify the correctness of the model. Hydrothermal corrosion test was proceeded in an autoclave at 290 °C and 7.5 MPa for 150 h to examine the enhancing corrosion resistance. STEM observations were used to study the microstructure evolution by cryogenic laser processing and corrosion. Electrochemical tests were performed to analyze the relationship between processing parameters and corrosion resistance before and after corrosion. The oxide film thickness and corrosion rate of the cryogenic laser-modified sample were 66 % and 80 % smaller than the as-received sample. The enhanced corrosion resistance was attributed to the microcrystalline layer and the thin duplex passive film that formed during the cryogenic laser process.