Nonequilibrium thermodynamics perspective for shear localization in additive manufacturing

Shear localization during deformation of additively manufactured Ti-6Al-4V alloy leads to macroscopic strain softening and premature failure, severely limiting component performance in aerospace applications, yet its underlying physical mechanisms remain unclear. This study systematically investigates the formation mechanism of shear localization through experiments and constitutive modeling. Monotonic tensile tests and microscopic characterization results reveal a strong correlation between shear localization and intrinsic microstructural heterogeneity. To elucidate the mechanism, a constitutive model is developed within an irreversible thermodynamic framework, incorporating local non-equilibrium configuration characteristics, dislocation evolution, and cumulative plastic damage. The comparison of the predicted results with the experiments demonstrated the effectiveness of the new constitutive model. Analysis of modeling results revealed that interactions between pore defects and heterogeneous microstructures induce local damage, which ultimately contributes to pronounced shear localization. Furthermore, more significant structural heterogeneity caused by severe local shear promotes dislocation accumulation, which subsequently facilitates the propagation and diffusion of shear bands. This work clarifies the physical origin of shear localization in additively manufactured titanium alloys, providing a new theoretical perspective for understanding their deformation and failure mechanisms.