Development of cost-effective repair and rejuvenation processes for Directionally Solidified (DS) Ni-based superalloy blades are of great economic and technological meanings. Laser deposition is a promising rejuvenation candidate for DS blades due to its precise controllability on heat input, solidification conditions, deposition geometry and microstructure. However, one of the challenges for rejuvenating DS blade is the extremely high liquation and cracking susceptibility. Boundary liquation and interface cracking frequently occur during laser deposition on the DS Ni-based superalloy blade. It is not clear the real mechanism of liquation happened in DS blade during laser deposition, to clarify the liquation mechanism on DS blade is then vital for developing a practical laser deposition technology for crack-free rejuvenation.
Based on systematic experimental results and analyses on laser deposition on DS Ni-based substrate, this paper exhibits the boundary liquation and interface cracking phenomena, and approves that the liquation during laser deposition on DS substrate originates from the melting of the periphery of small WC carbides in grain boundary in the heat affected zone, instead of the as-believed melting of eutectics in the grain boundary. The melting of the carbide periphery further develops, connects with each other, propagates along the grain boundary and finally forms a liquid film and then the cracking. Based on this understanding, two approaches were then proposed to achieve crack-free laser deposition rejuvenation for DS superalloy blades.