Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

• Published in: Acta materialia Vol. 177; pp. 209 - 221
• Main Authors: Kontis, Paraskevas, Chauvet, Edouard, Peng, Zirong, He, Junyang, da Silva, Alisson Kwiatkowski, Raabe, Dierk, Tassin, Catherine, Blandin, Jean-Jacques, Abed, Stéphane, Dendievel, Rémy, Gault, Baptiste, Martin, Guilhem
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.09.2019; Elsevier
• Subjects: Electron beam melting; Engineering Sciences; Grain boundaries; Hot cracking; Liquid film; Materials; Superalloys; Hot cracking; Grain boundaries; Liquid film; Electron beam melting; Superalloys; grain boundaries; superalloys; electron beam melting; liquid film
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2019.07.041

There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable nickel-based superalloys. This lack of in-depth understanding of the root causes of hot cracking is an impediment to designing engineering parts for safety-critical applications. Here, we deploy a near-atomic-scale approach to investigate the details of the compositional decoration of grain boundaries in the coarse-grained, columnar microstructure in parts built from a non-weldable nickel-based superalloy by selective electron-beam melting. The progressive enrichment in Cr, Mo and B at grain boundaries over the course of the AM-typical successive solidification and remelting events, accompanied by solid-state diffusion, causes grain boundary segregation induced liquation. This observation is consistent with thermodynamic calculations. We demonstrate that by adjusting build parameters to obtain a fine-grained equiaxed or a columnar microstructure with grain width smaller than 100 μm enables to avoid cracking, despite strong grain boundary segregation. We find that the spread of critical solutes to a higher total interfacial area, combined with lower thermal stresses, helps to suppress interfacial liquation. [Display omitted]