A comprehensive review of microstructural heterogeneities in the laser powder bed fusion of nickel-base superalloys with high γ′ content
M. Velasco-Castro, Fernando D. León-Cázares, E.I. Galindo-Nava
Abstract
Additive manufacturing (AM) offers significant advantages in fabricating complex three-dimensional metallic components, which are traditionally difficult to fabricate using subtractive methods. However, the AM of nickel-base superalloys poses significant challenges due to their high susceptibility to various weld-cracking mechanisms, particularly in precipitation-strengthened systems with a high volume fraction (60 - 70%) of γ ′ phase. Despite progress in reducing crack formation through optimised scanning strategies, a comprehensive understanding of how distinct weld-cracking phenomena develope in the as-fabricated microstructure remains limited. Additionally, the role of microstructural heterogeneities in crack formation and their impact on mechanical performance has not been thoroughly explored. This review examines recent findings on the formation of microstructural heterogeneities during laser powder bed fusion (LPBF) processing of nickel-base superalloys with high γ ′ content. It identifies key discrepancies in the literature regarding the mechanisms behind these heterogeneities and highlights the need for further research into their connection with weld-cracking phenomena. Gaining insights into these heterogeneities is crucial for enhancing mechanical performance and extending the life service of LPBF-processed superalloy components. This review also aims to provide guidance for future alloy development, as similar heterogeneities may affect a range of novel superalloy systems with high γ ′ content. • Microstructural heterogeneities in as-fabricated structures have been thoroughly reviewed. • Reports on γ / γ ′ eutectic formation remain inconsistent. • No consensus on the bimodal distribution of nano-scaled γ ′ precipitates. • Comprehensive examination of metastable carbides is lacking. • Impact of heterogeneities on mechanical performance and cracking is underexplored.