Abstract
Strain rate dependent deformation behaviours of selective laser melted Alloy 718 (IN718) are systematically studied at 550 and 650 °C by slow strain rate testing, with a forged counterpart as a reference. Selective laser melted IN718 shows significant susceptibility to intergranular cavitation, resulting in ductility degradation with decreasing strain rate. Detailed fractography and cross section inspections are employed to identify the damage mechanisms. Creep rates are also estimated and compared with the conventional counterparts. The possible critical factors for the inferiority of time dependent damage resistance of selective laser melted IN718 are discussed.
Highlights
During the past years, manufacturing nickel-base (Ni-base) superalloys components via additive manufacturing (AM) for high temperature applications has attracted significant interests in the aero and energy industries
With the years of development, one can see in the literature that the focus of selective laser melting (SLM) IN718 research changes from the microstructure and monotonic mechanical property studies (Jia and Gu, 2014; Lu et al, 2015; Zhang et al, 2015; Chlebus et al, 2015; Trosch et al, 2016; Deng et al, 2018) to fatigue (Balachan dramurthi et al, 2018, 2019; Witkin et al, 2019a; Pei et al, 2019) and creep (McLouth et al, 2020; Popovich et al, 2018; Xu et al, 2018; Kuo et al, 2018a; Shi et al, 2019; Witkin et al, 2019b) studies
Even though a homogenization step of 1080 ◦C for 1 h is included in the heattreatment routine for the SLM material, recovery or grain growth is barely found in the as heat-treated SLM microstructure, and the cell/subgrain structure completely remains
Summary
During the past years, manufacturing nickel-base (Ni-base) superalloys components via additive manufacturing (AM) for high temperature applications has attracted significant interests in the aero and energy industries. With comparison in the cited literature above, one can find that the monotonic tensile properties of SLM IN718 are comparable to the wrought counterparts, while time-dependent properties (Kuo et al, 2018b; Witkin et al, 2019b), especially min imum creep rate and ductility at elevated temperature, are rather inferior to wrought counterparts. The enhanced nanoscale creep is dominated by surface diffusion, since free surface has 200 higher times of diffusion coef ficient than grain boundary (Choi et al, 2013; Yoo et al, 2012) Such a possibility is not applicable to the activation of creep at 550 ◦C for SLM IN718, given that the test sample size is at millimetre scale in Deng et al (2019). The present study will be able to 1) map the mechanical properties of SLM IN718 with regards to strain rates and temperatures, and 2) identify the time-dependent damage mechanism active and responsible for inferior creep properties with comparison of a forged counterpart
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