Evaporation‐Induced Composition Evolution in Metal Additive Manufacturing

In fusion‐based metal additive manufacturing (MAM), the high‐intensity energy input leads to serious evaporation, but how evaporation induces composition evolution and variation and further impacts microstructure and mechanical properties remain a knowledge gap. Here a model integrating composition evolution with molten pool dynamics is developed to reproduce temperature‐ and composition‐dependent evaporative losses and subsequent transport during laser melting. Together with comprehensive experimental characterizations and tests, the simulation results illustrate varying evaporation rates of different elements altering compositions, resulting in a 3D cirrus‐shaped concentration distribution, which significantly impacts the mechanical properties. The simulations reproduce the detailed composition evolution from surface evaporation to molten pool transport and reveal underlying mechanisms relating the composition, temperature, fluid flow, and cracking, which is challenging to observe experimentally. This study elucidates the critical role of evaporation‐induced composition evolution in determining microstructure and mechanical properties. In future alloy design for MAM, integrating initial composition and manufacturing parameters is imperative, where composition evolution simulation offers valuable guidance.