Solidification cracking suppression in additively manufactured Hastelloy-X via carbon control

Lowering carbon content (c₀) of powders below the ASTM minimum of 0.05 wt.% is a common approach to producing crack-free additively manufactured Hastelloy-X (HX) alloys by narrowing the solidification range. However, this would compromise the alloys’ mechanical properties. Interestingly, HX alloys with c₀ above 0.09 wt.% remain crack-free. This suggests a Λ-shaped relationship between c₀ and solidification cracking sensitivity (SCS), and reveals that the carbon's effect on SCS extends beyond merely altering the solidification range. Using a combined phase field and Rappaz-Drezet-Gremaud model, we showed that SCS decreases with increasing c₀ in attractive grain boundaries, while it exhibits a Λ-shaped in repulsive grain boundaries, peaking at c₀ around 0.085 wt.%. This behavior originates from the competitive interaction between the secondary dendrite spacing (λ₂) and the carbon concentration in liquid (c_l,C) on SCS, both of which increase with c₀. Increased λ₂ not only narrows the liquid channel width, promoting grain coalescence, but also increases permeability to enhance liquid phase feeding. Both factors contribute to reducing SCS. However, increased c_l,C widens the temperature range prone to cracking, leading to an increase in SCS. As the grain boundary angle increases, λ₂ increases, which diminishes the role of λ₂ in SCS and subsequently alters the trend of c₀-dependent SCS. This study provides valuable insights into the complex role of c₀ in SCS, offering a latent pathway for designing crack-resistant superalloys with excellent mechanical properties.