CALPHAD-guided interlayer design for crack-free additive manufacturing of copper C18150 – Inconel 625 bimetallic structures

Additive manufacturing (AM) of bimetallic structures combining copper alloys and Ni-based superalloys is critical for extreme environmental applications. However, interface cracking during fabrication persists due to thermophysical property mismatches. By implementing a CALPHAD-based ICME framework (CALPHAD: Calculation of Phase Diagrams; ICME: Integrated Computational Materials Engineering), we decode nonequilibrium solidification and phase stability to predict cracking susceptibility. Liquid phase separation emerges as the dominant mechanism, altering solute redistribution and thermal stress accumulation - a previously underexplored factor in bimetallic systems. Experiments using wire arc additive manufacturing (WAAM) validate model prediction: crack-free interfaces between C18150 and In625 require intermediate layers with 65 wt.% In625. This composition mitigates cracking with the lowest cracking susceptibility coefficient (CSC). Importantly, we establish a quantitative correlation between phase separation and CSC, proposing a way to analyze systems exhibiting these microstructural features. This work uses ICME methodologies by linking thermochemical modeling to process optimization, offering new principles for designing defect-resistant bimetallic components in extreme environments such as rocket engine nozzles.