Microstructure, mechanical properties and strengthening mechanisms of IN738LC alloy produced by Electron Beam Selective Melting

Abstract

The fabrication of non-weldable nickel-based superalloys is a focus and challenge in additive manufacturing (AM). In this study, IN738LC superalloy specimens are successfully prepared by Electron Beam Selective Melting (EBSM). A new defect-free criterion(which is defined as inner defect criterion) is established and the processing window with a proper energy density to keep the specimens defect-free (pores, lack of fusions less than 50 µm, without crack and linear defect) is determined. The fine γ’ phases with critical sizes of 111–266 nm are directly produced by Electron Beam Selective Melting. Carbide precipitates are observed and classified. The tensile tests at 23 °C, 850 °C, 1000 °C and 1100 °C are conducted on the parallel to building direction (PBD) specimens and the orthogonal to building direction (OBD) specimens respectively. The strengthening mechanisms and fracture mechanisms of the critical size γ’ phases and the carbides at different temperatures (23 °C, 850 °C, 1000 °C and 1100 °C) are identified. Different fracture mechanisms in PBD specimens and OBD specimens are identified by the fractographic analyses.