Hierarchical architecture and mechanical behavior of K418 Ni-based superalloys manufactured by laser powder bed fusion

Abstract

Laser powder bed fusion (LPBF) has great potential in the manufacturing of difficult-to-cut Ni-based superalloys with complex geometries. The approach endows the alloys with multi-scale microstructure hierarchy, while its formation mechanism and contribution to mechanical properties are poorly understood. In this work, the hierarchical architecture in LPBF-fabricated K418 Ni-based superalloys, in terms of 3D interlocked grains, low-angle grain boundaries (LAGBs), cellular structure, inter-cellular segregation, and nano-sized γ′ precipitates and carbides, is comprehensively investigated. The formation of cellular structure is governed by the rapid solidification condition, and the 3D interlocked grain structure is associated with the cell growth behavior regulated by locally varied temperature gradient in the melt pool. The LPBF K418 alloys show a higher tensile strength but a slightly lower ductility at both room temperature and 600 °C than their conventional cast counterparts. The superior strength of LPBF alloys is dominantly attributed to the strengthening effect of interlocked grain boundaries and cellular microstructure. This work demonstrates the capability of LPBF to manufacture Ni-based superalloys with hierarchical microstructures and high performance for the application of hot-section gas turbine components.