SUMMARY

Directed energy deposition-laser beam-powder blown (DED-LB-PB) additive manufacturing can be used to fabricate geometrically complex parts and from metals that are difficult to machine. Such metals include refractory alloys, whose high heat- and corrosion-resistance make them desirable for propulsion applications and in-space structures. However, refractory metal powders are expensive, and components are prone to stress cracking during printing due to the steep thermal gradients experienced across layers. Therefore, completed parts are often rejected due to cracking and other defects discovered during post-manufacturing inspection, long after the powder, energy, and hours have been invested into making the part. Current in-situ process monitoring efforts for DED-LB-PB are largely directed toward meltpool monitoring via thermal imaging, which is very data intensive and difficult to analyze in real-time. This work proposes acoustic emission (AE) monitoring as an alternative approach to in-situ DED-LB-PB monitoring to enable the development of a real-time crack detection and early warning system. Features in the AE will be mapped to changes in printing process parameters through parameter screening studies in order to differentiate the AE contributions from different noise sources. AE due to cracking in printed coupons will then be identified through comparison with ground truth in-situ thermal imaging and post-manufacturing x-ray computed tomography, which will also allow for the identification of defect healing. A real-time warning system will be developed through statistical modelling based on the dataset generated through the coupon printing experiments. This work is supported by the NASA Space Technologies Graduate Research Opportunities program, award number 80NSSC23K1213.