Selective Laser Melting of Ni-Based Superalloy IN 738LC: Studying the Compositional Effect on Hot Cracking by Modelling.

Selective laser melting (SLM), as one of the most widely used metal additive manufacturing methods, can enable more efficient designs in aerospace engines. For the high temperature sections of the engines, there are however only a handful of relatively low strength superalloys usable due to the high crack tendency in the SLM process. High-strength Ni-based superalloys such as IN738LC can be prone to hot cracking. Although some of the compositional effects from experimental studies were reported in literature, detailed metallurgical study and modelling work are still lacking in explaining the unusually high cracking tendency of certain elements. In our research, several solidification crack theories were used to model the SLM crack susceptibilities with the aid of Calculation of Phase Diagram (CALPHAD) techniques. The modelling results are compared to the experiments from over 12 powder batches with slightly different compositions, either from literature or in-house experiments. The comparisons indicate that the SLM cracking tendency of IN738LC can generally be modelled, provided that the CALPHAD modelling assumptions and settings are appropriate. The compositional effects from individual elements are also investigated by the models. The findings coincide with some of the known effects in similar processes to SLM such as laser welding with also rapid solidification conditions. The segregation patterns were also modelled and compared with the result from microstructural study, showing in general acceptable agreements with some interesting discrepancies. This research can provide better understanding in the cracking issues from the metallurgical perspective, as well as insights into future research useful for alloy modifications specialized for SLM process.