Oxidation-resistant coating of FeCrAl on Zr-alloy tubes using 3D printing direct energy deposition

Abstract

Zr-alloys are used as nuclear fuel cladding tubes in nuclear reactors. Recently, surface coating of conventional Zr-alloy tubes has been performed to enhance their resistance to corrosion and high-temperature oxidation. FeCrAl is a candidate coating material because of its extremely low oxidation rates and desirable mechanical properties. In this study, FeCrAl was deposited directly on a Zr-alloy using 3D printing technology. The processing conditions, such as laser beam power, scanning speed, and powder/gas feed rates, were optimized to attain a dense and adhesive FeCrAl layer. The minimum beam power required to melt the FeCrAl source powder was found to be 160 W. The FeCrAl layer coagulated when the scanning speed was low and the powder feed rate was high, and it became sparse and porous when the scanning speed was high and feed rate was low. The FeCrAl-coated Zr samples were tested for oxidation at 1200 °C. A thin Al2O3 (2–3 μm) formed on the FeCrAl surface, and a diffusion layer developed between the FeCrAl/Zr interfaces. By comparison, a thick ZrO2 (approximately 120 μm) layer formed in the Zr-alloy without coating. The oxidation resistance of the Zr-alloys increased by approximately 50 times by the formation of FeCrAl layer on their surfaces. This 3D printing method is expected to improve the safety of Zr fuel cladding tubes.