Laser beam welding properties and microstructural characterization of Kanthal APMT ferritic alloys in the application of accident tolerant fuel cladding

Abstract

Ferritic FeCrAl steel is one of the most promising candidate materials for accident tolerant fuel cladding due to its excellent high temperature mechanical properties, low thermal expansion coefficient, and most importantly, very low void swelling rate under neutron irradiations. Different fuel bundle parts are usually joined together by a variety of joining techniques. These joining processes must allow the cladding to retain acceptable mechanical and accident-tolerant properties. The objective of this study is to assess the feasibility of laser beam welding (LBW) of advanced oxidation-resistant Kanthal APMT Fe-21Cr-5Al-3Mo alloy and to analyze the microstructure of welds. The ultimate tensile strength of FeCrAl weldments reached 78% of the as-received FeCrAl rod, although the ductility of the FeCrAl welds was significantly reduced. Welding-induced cracking and pores were observed in Kanthal APMT alloy welded using high-power laser beam single-side welding technique. Two groups of dispersoids were observed in APMT alloy: smaller particles of Y O, and larger particles of Y-Al-O. Relative abundance of smaller particles can be noted after LBW welding. The particles show slight coarsening, and the number of precipitates increases in comparison with the as-received condition. Based on the results, laser beam welding can be used for joining FeCrAl alloy, but further optimization on welding parameters and post-welding heat treatment are needed to enhance mechanical properties of weldments in the future.