Ultrasonic Nondestructive Qualification of IN718 Fabricated Using Laser DED

Qualification of AM structures using nondestructive methods has been of interest to the wider AM community. The nondestructive nature of these methods allows for rapid qualification, thus increasing the number of samples/structures that can be qualified achieving a tighter quality control. Ultrasonic testing has several advantages including microstructural characterization, which makes it a good candidate for qualification. However, the complex microstructure that results from AM processes such as Laser directed energy deposition can be very difficult to characterize using ultrasonic testing. Specifically, we show that the ultrasonic response of the fabricated structure is spatially heterogenous due the presence of large macrograins, which makes traditional ultrasonic parameters such as velocity, attenuation and backscatter very difficult to implement. We have previously shown that this is somewhat specific to IN718, which is highly desirable in the aerospace industry for a variety of high temperature applications. This presentation will identify and test potential qualification parameters that qualitatively and quantitatively describe the microstructural state of the sample. To test the effectiveness of these parameters, the as-fabricated samples were subjected to four different heat treatments that will result in different microstructures. The rational behind these heat treatments is the resulting microstructure, which can vary from wrought condition to homogenized microstructural state. The ability of ultrasonic parameters to track microstructural evolution in a nondestructive manner will be explored. These findings were also validated using destructive analysis including optical and electron microscopy.