Crack initiation and propagation within nickel-based high-temperature alloys during laser-based directed energy deposition: A review

Laser-based directed energy deposition (L-DED) has a broad application prospect in the preparation of complex structural parts, the repair of critical parts, and other aspects of Ni-based high-temperature alloys. However, the rapid solidification rate of the melt pool during the L-DED forming process, as well as the forming process characteristic of track-by-track overlapping of the cladding tracks and layer-by-layer stacking of the cladding layers, make it easy for defects, such as cracks, to appear in the multi-layer cladding layer of Ni-based alloys. Crack initiation brings hidden danger to the multi-layer cladding layer in subsequent service, and the propagation of the crack after initiation determines the final mechanical properties of the cladding layer. This paper reviews and discusses the initiation mechanisms of hot and cold cracks during the L-DED forming process, reviews and analyzes the propagation mechanisms after crack initiation in combination with the process characteristic of L-DED, and summarizes the influencing factors of crack initiation and propagation. Based on this, the main methods to inhibit crack initiation and propagation are further reviewed. The work in this paper aims to provide reference and guidance for realizing effective inhibition of crack initiation and propagation during L-DED forming of Ni-based high-temperature alloys.