Fabrication of the CM247LC Ni-based superalloy using metal-material extrusion additive manufacturing and its microstructure and mechanical properties

Abstract

CM247LC has been widely recognised as a difficult-to-process material for laser-based additive manufacturing processes such as laser powder bed fusion and direct energy deposition. The material extrusion additive manufacturing (MEAM) process involves the melting and extrusion of a feedstock composed of a polymer binder and metal powder to fabricate a green body, followed by debinding and sintering to achieve the final component with the desired geometry. In this study, CM247LC alloy was fabricated using a MEAM process, and its microstructural characteristics and mechanical properties were investigated. The sintered specimens exhibited a relative density exceeding 90%, with inter-layer defects and closed pores observed in the microstructure. Post-sintering analysis confirmed the formation of γ’ precipitates and MC carbides within the matrix, with MC carbides predominantly distributed along grain boundaries and concentrated on the surfaces of closed pores. The fabricated specimens exhibited an increased carbon content compared to the initial powder, attributed to excessive MC carbide formation during sintering. This was caused by the reaction between carbon from the binder and carbide-forming elements in the metal powder. Room temperature tensile tests on defect-free specimens yielded a yield strength of 660.4 MPa, an ultimate tensile strength of 891 MPa, and an elongation of 7.56%, with mechanical properties exhibiting significant variation depending on specimen conditions. This variability was mainly attributed to the susceptibility of inter-layer crack initiation under applied stress. Furthermore, this study discussed the deformation and fracture mechanisms of MEAM-processed CM247LC alloy and assessed the feasibility of fabricating difficult-to-form Ni-based superalloys via the non-fusion MEAM process.