Enhancing Ti-6Al-4V Microstructure Prediction in Additive Manufacturing via Integrated Heat Transfer and Phase Transition Kinetics Modeling

• Macro temperature simulations and experiments linked process parameters to microstructure. • Developed two predictive models for α lath width in DEDed Ti-6Al-4V. • Coarsening of α lath in the DED is explained with multiple dissolution-precipitation mechanisms. • Phase fraction and dissolution-precipitation both crucial in α lath width prediction. • The study aids in optimizing DED parameters and improving mechanical properties control. The α lath width is a crucial microstructural feature size that influences the mechanical properties of Ti-6Al-4V components produced by laser directed energy deposition. Predicting the α lath width in as-deposited Ti-6Al-4V improves the control of the microstructure and mechanical properties. However, quantitative evaluation regarding the correlation between the reciprocal thermal cycles in additive manufacturing and the α lath size remains inadequate, and relevant phase-transition kinetics models require further modification to account for multiple heating–cooling cycles. This study combines macroscopic temperature field simulations with univariate controlled experiments to establish the qualitative relationship between the process parameters, thermal history, and microstructural evolution. According to the experimental and simulated correlation, two predictive models for the α lath width based on the phase fraction and the multiple dissolution–precipitation mechanism are developed and optimized by coupling phase transition kinetics. Model accuracy validation experiments reveal that the phase fraction model (27.3%) slightly outperforms the multiple dissolution–precipitation model (28.6%) in terms of the α lath width prediction accuracy. However, the multiple dissolution–precipitation model is valuable for assessing the trend of the α lath width evolution and coarsening with the deposition height during thermal cycles, demonstrating the plausibility of multiple dissolution–precipitation mechanisms in elucidating α lath coarsening during DED.