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

Kontis, P. and Chauvet, E. and Peng, Z. and He, J. and da Silva, A.K. and Raabe, D. and Tassin, C. and Blandin, J.-J. and Abed, S. and Dendievel, R. and Gault, B. and Martin, G.

Volume: 177 Pages: 209-221
DOI: 10.1016/j.actamat.2019.07.041
Published: 2019

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. © 2019 Acta Materialia Inc.

« back