Abstract

Additive manufacturing of nickel based super alloys such as IN718 is highly desirable since they have a wide range of applications in high performance structures. Compared to conventional methods, laser processing allows for near net shaping of complex geometries. However, laser processing can result in very complex microstructures including meta-stable phases, grain boundary segregation of precipitates, dendritic grains and cellular microstructure. Describing elastic properties of such structures can be quite challenging due to these features. This article explores the use of resonant ultrasound spectroscopy (RUS) to characterize the elastic properties of IN718 samples fabricated using Laser Directed Energy Deposition (DED). For initial estimates of the elastic constants, ultrasonic wave (longitudinal and shear) velocities measured at 5MHz and 2.25 MHz respectively. The initial assumption was that the eventual structure will be orthotropic and the 9 elastic constants were determined using a combination of RUS and propagating wave experiments. A finite element approach was adopted to model this system and to minimize the values of elastic constants. The results seem to suggest that the secondary phases such as Laves will influence the eventual anisotropy of the bulk structure.

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