Laser-processed additive manufacturing (laser-AM) is a technology that allows the direct fabrication of metallic three-dimensional parts from a CAD model, with the particularity of using a laser as its energy source. The application of this technology to nickel-based superalloys (Ni-superalloys) attracts interest from the aircraft, aerospace, or power generation industry due to the outstanding strength at high temperatures and exceptional resistance to fatigue, hot corrosion, and wear under extreme conditions shown by these materials. However, the main drawbacks that prevent the implementation at a large scale of laser-AM nickel-based superalloys are the uncertainty of the mechanical integrity, quality and reproducibility of mechanical properties that can occur due to porosity, bonding defects, anisotropy, or heterogeneity present in the microstructure, which in turn is affected by the processing parameters. Furthermore, one of the principal aspects that prevents the adoption of this technology is the lack of a unified qualification standard that contemplates the needs of the aforementioned industries. Although several efforts are currently on track in the field of destructive testing for the characterization of AM materials in general, non-destructive techniques have merely been utilized for the detection of defects and their capability as a material characterization tool has not been deeply explored. In particular, ultrasonic non-destructive evaluation (ultrasonic NDE) stands out among other NDE techniques given its straightforward application and its sensitivity to microstructural variations that can be applied to complex materials such as Ni-superalloys fabricated with laser-AM technologies. The aim of this work is to show our efforts in the ultrasonic NDE characterization of as-fabricated Laser-Directed Energy Deposition Inconel 718 (laser-DED IN718) and to derive parameters that can be further applied in a unified qualification standard for the acceptance of this material.First, we present a baseline ultrasonic NDE comparison of Inconel 718 samples fabricated with Laser-Directed Energy Deposition and with hot-rolled to show their difference in ultrasonic velocities, ultrasonic attenuation, and ultrasonic backscattering and to further correlate the contributions of the laser-DED IN718 microstructure to these parameters. Then, utilizing the ultrasonic response of the hot-rolled sample and two laser-DED samples fabricated with different processing parameters, we derived for the first time ultrasonic NDE qualification parameters to quantify anisotropy, heterogeneity, grain, and grain clusters contributions to attenuation, and grain cluster sizes. Finally, we utilize ultrasonic NDE to characterize laser-DED multi-material structures of Inconel 718 and Stainless steel 420. The ultrasonic velocities, attenuation and backscatter coefficients responses are measured, and their values are compared to theoretical values derived from a simple rule of mixtures.
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