Discovering the crack formation criteria for Rene 80 superalloys in Laser Blown Directed Energy Deposition

Nickel based super alloys with high volume fraction of $\gamma{'}$ such as Rene 80 possess the desirable properties of high strength and ductility, and it can also be used in high temperature environments. This makes them good candidates for building components in jet engines and gas turbines that may operate at higher efficiencies \cite{acharya2015additive, seidel2018additive, ramakrishnan2019direct}. However, additive manufacturing (AM) of these high-strength alloy geometries leads to cracking, including both hot cracking and solidification cracking. Crack formation in the crack-susceptible Rene 80 can be avoided for single-pass walls built using laser blown powder directed energy deposition (DED-LB/M) for certain input process parameters but there is lack of understanding about the crack formation mechanism. Thus, this work focuses on predicting hot cracking in R80 thin walls built with DED-LB/M using a physics based hybrid approach. Furthermore, the goal is extend this understanding to other geometries like hatch and cube specimens. The approach is developed based on a series of single-pass walls builds that result in both cracked and crack-free walls. We attempt to first generalize the crack prediction approach by using a simplified RDG criterion and link thermal features to crack formation. The thermal feature information is provided by a multi-source 2D Rosenthal model calibrated against process monitoring data. The classification accuracy is assessed and we try to add the missing physics in the crack formation criterion to improve the prediction accuracy. Specifically, an explicit expression of classification (crack/no crack) boundary is discovered which is a function of the process parameters and thermal features.