Additive manufacturing (widely known as 3D printing) is a promising route to repair of single crystal Ni-based superalloy turbine blades, but a formidable obstacle is that the residual stress and inhomogeneous gamma prime morphologies in the single-crystalline fusion zone after AM process are unacceptable, prone to cracking or recrystallization that degrade the high-temperature performances.
To this end, Dr. Yao Li and collaborators design a post-3D-printing recovery protocol that eliminates the driving force for recrystallization, prior to standard solution treatment and aging. The recovery is rendered possible by the rafting of gamma prime particles that facilitates dislocation rearrangement and annihilation. The rafted microstructure is removed after solution treatment, leaving behind a damage-free and residual stress free single crystal with uniform gamma prime precipitates. This discovery offers a practical means to keep 3D-printed single crystals from cracking due to unrelieved residual stress, or stress-relieved but recrystallizing into a polycrystalline microstructure, paving the way for additive manufacturing to repair, restore and reshape any single crystal superalloy product.
The result is published on Advanced Materials, titled as Rafting-Enabled Recovery Avoids Recrystallization in 3D-Printing Repaired Single-Crystal Superalloys.
link to this paper: https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201907164
