Solidification Cracking Susceptibility Modelling of Nickel Based Superalloys by Selective Laser Melting

Most high-strength Ni-based superalloys additively produced by Selective Laser Melting (SLM) are prone to cracking, especially the solidification type, and it seriously limits the available compared to the conventional manufacturing process. One key obstacle is the lack of fundamental understanding and reliable modelling technique in evaluating the cracking susceptibility in the SLM process. In many cases, the unique rapid solidification behaviour during SLM process renders many classic indicators of solidification cracking unreliable, for example the freezing range. In this presentation, we are reporting a large scale experimental and metallurgical studies on the gamma prime forming IN738LC superalloys as a classic case of studying the solidification cracking susceptibility specifically in the SLM process. Several classic and new solidification crack theories were used to model the SLM crack susceptibilities with the aid of Calculation of Phase Diagram (CALPHAD) techniques. The rapid solidification behaviour and its physics were specifically considered in some of the models to increase their modelling accuracies. 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 origins of some of the high impact elements in crack susceptibility will also be discussed. This research can provide better understanding in the solidification cracking issues from the metallurgical perspective, as well as general insights into modifying and designing alloys specialized for SLM process.