Influence of Heat Input on Solidification Cracking in Additively Manufactured CM247LC Ni-based Superalloy

Solidification cracking in a laser powder bed fusion (LPBF) manufactured CM247LC is studied as a function of heat input ranging from 0.27 to 0.44 J/mm using a single process variable, scan speed. The 0.44 J/mm sample exhibited a large fraction of high angle grain boundaries (HAGBs) ~ 68 pct with significant solidification cracks (2.33 mm/mm²). On the other hand, the 0.27 J/mm sample showed minimal cracking (0.08 mm/mm²) and was characterized by < 52 pct HAGBs. While the grain sizes were 31 to 35 μm in both cases, the 0.44 J/mm sample showed double volume fraction of 50 to 80 nm sized (MC, M = Ta/W/Hf) carbides and a larger dislocation density compared to the 0.27 J/mm. In both samples, 2 to 5 nm coherent γ′-Ni₃Al(Ti) precipitates were present in the as-printed condition. A 3-dimensional sequential coupled thermo-mechanical model showed that a wider mushy zone (49 μm\()\) and lower thermal gradient (\(\sim \) 39,130 K/mm) for the 0.44 J/mm specimen resulted in a higher tensile longitudinal stress (\(\sim \) 210 MPa) at the solidus–liquidus zone that primarily governed the solidification cracking. The results show that the numerical model is able to explain the tendency for solidification cracking in LPBF processed CM247LC as a function of scan speed, and can be extended to predict the effect of other process parameters, overcoming the necessity for a full factorial design of experiments.