Alloy Design of Gamma/Gamma' Ni-base Superalloy for 3D printability

High temperature g/g' Ni-base superalloys have been difficult to fabricate microcrack-free using additive manufacturing (AM). Their high g' volume-fraction and associated poor weldability have been cited as possible reasons. However, the solidification rate during laser powder bed fusion printing is orders of magnitude higher than welding. Consequently, it requires a more careful examination of the mechanisms involved in cracking and alloy formulations that can mitigate such problems. We have used CALPHAD and the non-equilibrium Scheil Model to understand the basis of cracking. Experimental observations have found microstructural defects, such as microcracks, occurring at high angle grain boundaries. These experimental results were obtained from laser line scans of arc melted buttons of CM247LC, a conventional high-temperature superalloy, as well as alloy compositions that were designed to minimize microcracking at grain boundaries. This approach circumvents the high cost of procuring powders of different chemistries until the final selection stage. Analytical results such as EDS, elemental spectra, and EBSD texture will be presented to highlight the microcracking location and microstructural segregation, while also drawing attention to differences from predictions based on non-equilibrium solidification models. We will demonstrate that alloys with reduced strong carbide formers are beneficial to microcrack-free printability. More recently, we have procured powders of the standard and screened alloy composition, and results from those 3D printed samples will be presented to validate our design approach for a microcrack-free superalloy with high g' content.