Microstructure Characterization and Failure Mechanism of Laser Welded Nuclear-grade FeCrAl Alloy

Abstract

FeCrAl alloy is considered a new type of promising accident-tolerant fuel cladding material. Laser welding technology, which has been widely applied in the connection of various metal materials, uses a high energy density laser heat source with the advantages of efficiency and precision. However, due to the inherent characteristic of high speed, the laser weld is generally exposed to rapid solidification, resulting in the inevitable formation of defects such as coarse grain size and porosity in the weld. The presence of pores is a troublesome question because they will reduce the bearing area of the joint and accelerate the initiation of cracks, resulting in a significant reduction of the tensile strength. Based on these considerations, in this study, the effect of pores on laser-welded nuclear-grade FeCrAl alloy is investigated by quasi-in-situ tensile testing, and the fracture mechanism of the joint is revealed. The maximum ultimate tensile strength measured by the experiment is 550 MPa, and the elongation of welds is 9.6%. In addition, there are obvious stress concentrations and cracking phenomena generated in the vicinity of a pore. The joint is eventually fractured in the fusion line near the fusion zone. A large number of pores can be found at the fracture failure position from the fracture morphology observation, indicating that the pores are presumably to be the intrinsic reason for the cracking of the welded joints.