Hot cracking mechanism affecting a non-weldable Ni-based superalloy produced by selective electron Beam Melting

• Published in: Acta materialia Vol. 142; pp. 82 - 94
• Main Authors: Chauvet, Edouard, Kontis, Paraskevas, Jägle, Eric A., Gault, Baptiste, Raabe, Dierk, Tassin, Catherine, Blandin, Jean-Jacques, Dendievel, Rémy, Vayre, Benjamin, Abed, Stéphane, Martin, Guilhem
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2018; Elsevier
• Subjects: Electron Beam Melting; Engineering Sciences; Grain boundaries; Hot cracking; Liquid film; Materials; Micro-segregations; Ni-based superalloys; Hot cracking; Grain boundaries; Liquid film; Ni-based superalloys; Micro-segregations; Electron Beam Melting; Electron beam Melting; micro-segregations
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2017.09.047

A non weldable nickel-based superalloy was fabricated by powder bed-based selective electron beam melting (S-EBM). The as-built samples exhibit a heterogeneous microstructure along the build direction. A gradient of columnar grain size as well as a significant gradient in the γ′ precipitate size were found along the build direction. Microstructural defects such as gas porosity inherited from the powders, shrinkage pores and cracks inherited from the S-EBM process were identified. The origins of those defects are discussed with a particular emphasis on crack formation. Cracks were consistently found to propagate intergranular and the effect of crystallographic misorientation on the cracking behavior was investigated. A clear correlation was identified between cracks and high angle grain boundaries (HAGB). The cracks were classified as hot cracks based on the observation of the fracture surface of micro-tensile specimens machined from as-built S-EBM samples. The conditions required to trigger hot cracking, namely, presence of a liquid film during the last stage of solidification and thermal stresses are discussed within the framework of additive manufacturing. Understanding the cracking mechanism enables to provide guidelines to obtain crack-free specimens of non-weldable Ni-based superalloys produced by S-EBM. [Display omitted]