Synchrotron diffraction characterization of dislocation density in additively manufactured IN 718 superalloy

In the present study, 3-dimensional (3D) parts of Inconel 718 (IN 718) have been fabricated using laser powder bed fusion (L-PBF) processing. Synchrotron diffraction experiments have been carried out on 0.5 mm thick specimens extracted from the as-built 3D parts at an incident energy level and wavelength of 30.05 keV and 0.41377 Å, respectively. The dislocation density (ρ) of additively manufactured IN 718 superalloy (AM IN 718) has been characterized using modified Warren-Averbach methodology. Fourier transformation of the synchrotron diffraction data corresponding to the first six reflections i.e., 111, 200, 220, 311, 222 and 400 and using its Fourier coefficients considering modified Warren-Averbach methodology enabled the evaluation of ρ. The ρ in conventionally processed wrought IN 718 (W IN 718) has also been characterized to compliment the results of AM IN 718. The synchrotron diffraction data was also studied considering classical Williamson-Hall and modified Williamson-Hall methodology to understand the influence of strain anisotropy on the peak broadening. The ρ was found to be very high (1.85 ± 0.24 × 1015 m−2) in AM IN 718 which corroborated well with the dislocation substructure observed using transmission electron microscope (TEM). The average dislocation contrast factor (C¯), as a part of modified Williamson-Hall methodology, was found to account for the strain anisotropy in both AM and W IN 718.