Thermodynamic Pathways of Nonequilibrium Solidification in Wire‐Arc Additive Manufacturing Fe‐Based Multicomponent Alloy Structures

Multicomponent alloys offer high strength, thermal stability, and corrosion resistance; however, their complex chemistries make phase formation under nonequilibrium additive manufacturing conditions difficult to predict. This study examines the thermodynamic pathways of an Fe‐based 140MXC multicomponent alloy fabricated by wire‐arc additive manufacturing (WAAM). Two geometries, a thin‐wall deposit (TWD) and a bulk‐wall deposit (BWD), were designed to impose distinct thermal gradients and reveal their influence on solidification. Multiscale microscopy, diffraction, and compositional mapping revealed that TWD exhibited strong heterogeneity, with refractory elements segregating to top layers and forming coarse NbC and W/Mo‐rich carbides due to reduced entropy stabilization. In contrast, BWD exhibited homogenized carbide distributions due to enhanced interlayer reheating, which stabilized mixing entropy and moderated segregation. Entropy calculations confirmed that decreasing entropic stabilization with cooling rate drives segregation–precipitation competition, consistent with Gibbs free energy predictions. Mechanical testing of TWD revealed higher hardness in carbide‐rich regions and a progressive increase toward the top. These findings demonstrate that geometry‐driven thermal gradients, rather than alloy chemistry alone, govern phase stability and mechanical response. The results establish a framework for optimizing the WAAM of multicomponent alloys through thermal management strategies, enabling the development of reliable, high‐performance components for aerospace, energy, and defense applications.