Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys. (15th September 2019)

• Record Type: Journal Article
• 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
• Is Part Of: Acta materialia. Volume 177(2019)
• Page Start: 209
• Page End: 221
• Publication Date: 2019-09-15
• Subjects: Hot cracking -- Grain boundaries -- Electron beam melting -- Superalloys -- Liquid film; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2019.07.041
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: 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. Graphical abstract: Image 1