Abstract
In this study, the Ni-based superalloy IN718, fabricated using an electron beam melting process, was investigated in as-built and various heat-treated conditions. The relationships between the microstructure characteristics and creep properties were elucidated. Under testing conditions of 650 °C and 650 MPa, the direct-aged specimen exhibited the lowest steady-state creep rate, at 0.15 × 10−8 s−1. The superior creep resistance can be attributed to the higher volume fraction of γ’/γ”-strengthening precipitates within the grain and fine δ precipitates along the grain boundaries. Being coherent to the γ matrix, the nano-sized γ’/γ” precipitates effectively hindered the dislocation motion in the grain interior. In addition, controlled grain boundary δ precipitates inhibited grain boundary sliding and decelerated the steady-state creep strain rate during creep deformation.
Highlights
Developed in the early 1960s, the nickel-iron based IN718 alloy features high-temperature strength and outstanding corrosion resistance up to 700 ◦C
additive manufacturing (AM) is a new advanced manufacturing process that enables the fabrication of components with complex designs, which are problematic in manufacturing using traditional methods
We focus on the creep properties of Electron beam melting (EBM)-fabricated IN718 heat-treated at various conditions
Summary
Developed in the early 1960s, the nickel-iron based IN718 alloy features high-temperature strength and outstanding corrosion resistance up to 700 ◦C. IN718 derives its high-temperature strength from the ordered body-centered tetragonal γ” phase (Ni3Nb, D022, ordered BCT) and face-centered cubic γ’ phase (Ni3 (Al, Ti), L12, ordered FCC), which are both coherent to the matrix. As an age-hardenable alloy, IN718 possesses excellent weldability due to its retarded γ” precipitation-hardening rate and low cracking susceptibility, making IN718 suitable for various additive manufacturing (AM) processes [4,5]. Powder preheating in the EBM process relieves the residual stress in the final built parts by lowering the thermal gradient between the layers [7]. Considering its benefits, EBM was applied to manufacture high-performance IN718 with complex components for various applications, especially aerospace applications
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