Processing a non-weldable nickel-base superalloy by Selective Laser Melting: role of the shape and size of the melt pools on solidification cracking

The use of laser-based additive manufacturing for the fabrication of parts exposed to very high temperature in the aerospace and energy sectors is still very limited. Indeed, non-weldable superalloys tend to crack during their processing by Selective Laser Melting (SLM). Inconel 738 LC processed by SLM is subjected to solidification cracking. In this study, attention was focused on the influence of size and shape of the melt pools involved in the fabrication on the occurrence of cracking. This approach was motivated by the fact that the size and shape of the melt pools greatly affect the solidification conditions. Samples were fabricated with various fabrication parameters, leading to different melt pool sizes and shapes and different cracking intensity. Cracking was shown to be minimal when the fabrication used narrow melt pools and a strong overlap between adjacent melt pools. These observations were discussed in the light of solidification theory. As the cracks are known to appear primarily at high-angle grain boundaries, the effect of grain structure was investigated. These observations allowed the fabrication of a dense and crack-free material.