Hot cracking behavior and mechanism of a third-generation Ni-based single-crystal superalloy during directed energy deposition

• Published in: Additive manufacturing Vol. 34; p. 101228
• Main Authors: Lu, Nannan, Lei, Zhenglong, Hu, Kuan, Yu, Xingfu, Li, Peng, Bi, Jiang, Wu, Shibo, Chen, Yanbin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2020
• Subjects: Additive manufacturing; Directed energy deposition; Hot cracking; Microstructures; Nickel-based superalloy; Hot cracking; Nickel-based superalloy; Additive manufacturing; Microstructures; Directed energy deposition
• ISSN: 2214-8604; 2214-7810
• DOI: 10.1016/j.addma.2020.101228

[Display omitted] •Crack-free nickel-based single crystal superalloy samples were fabricated via directed energy deposition.•Hot cracking occurred at high-angle grain boundaries and especially at low-angle grain boundaries.•The existence conditions of the liquid film for hot cracking in CMSX-10 are calculated with analysis models.•Re-rich precipitations promote cracks initiation by the pinning effect on the liquid feeding.•The hot cracking mechanism is related to the stability of liquid film, stress concentration and Re-rich precipitations. Hot cracking is a frequent and severe defect that occurs during the directed energy deposition (DED) of single-crystal superalloys. Understanding the cracking behavior and mechanism is key to avoiding these defects. Thus, in this study, a third-generation single-crystal superalloy, CMSX-10, was investigated. Hot cracking occurred at high-angle grain boundaries and especially at low-angle grain boundaries. Cracks were formed beyond a critical misorientation angle of 6.9°. Hot cracking was determined to be caused by a stable liquid film, stress concentration, and Re-rich precipitates. The stability of the liquid film depended on dendrite coalescence undercooling which was related to the misorientation angle. The dendrite coalescence undercooling at low-angle grain boundary (misorientation angle 6.9°) was 178 K, which was far higher than the vulnerable temperature interval 38 K for hot cracking within a single dendrite. Stress concentration provided the driving force for crack initiation and propagation. Re-rich precipitates promoted crack initiation by a pinning effect on the liquid feed. These findings provide technical support for achieving high-quality additive manufacturing and repair of non-weldable Ni-based single-crystal superalloys.