Alloy and Process Development for Additive Manufacturing of Ni-base Superalloys

Currently only a handful of high temperature Ni-base superalloys, such as Inconel 718, can be fabricated mostly defect-free using additive manufacturing (AM). These alloys have upper limit temperature of about 700 C. Higher temperature applications require high volume fraction of gamma-prime phase, and refractory elements for strengthening of the matrix gamma phase. These influence segregation and solidification behavior, as well as residual stresses that lead to cracking of the as-built material. In this work we have focused on an equiaxed superalloy, namely CM247LC, that has so far resisted crack-free AM. We have used CALPHAD and crack susceptibility models, as well as methods to minimize deleterious carbides which form at the beginning of solidification, to minimize cracking behavior with minimum alloy composition changes. The modeling approach is compared with experimental results of single laser line scans of miniature arc melted samples of desired compositions. The purpose of this experimental approach was to minimize major costs associated with procuring of different alloy powders. The results of the approach and their implications will be discussed.