<p>Metal additive manufacturing using Laser Powder Bed Fusion (LPBF) often induces selective evaporation of alloying elements, leading to significant chemical composition changes in the printed parts. Changes in composition can affect the microstructural features, mechanical properties, and performance of the final part. This research investigates the selective evaporation and composition change during LPBF of a NiTi binary alloy. A novel computational framework that combines 3D transient heat transfer simulations of LPBF, thermodynamic calculations, and Langmuir evaporation modeling, is developed to predict composition changes. The model is validated by LPBF experiments at various processing conditions. The results show, using process maps, that Ni loss is minimal at low heat input but significantly increases at higher laser powers and slower scanning. For example, Ni loss is enhanced by almost two times when the laser power is increased from 400 to 500&#xa0;W. In addition, this work provides a new, combined theoretical and experimental understanding of the effects of composition change on the phase formation and solidification morphology of NiTi alloy. Ni loss at high powers reduces the Ni composition and increases the Ti composition. This change results in precipitation of Ti rich NiTi₂ precipitates, which is proved by both thermodynamic calculations of phase formation and BSE imaging of samples. LPBF using higher powers results in larger pools with a lower temperature gradient. This condition results in a mixed solidification morphology with columnar and equiaxed grains compared to a fully columnar morphology at low powers. Since Ni variations can affect transformation temperatures, shape memory properties, and superelastic behaviors of NiTi, the effects of evaporation-driven composition change on those aspects need to be studied in the future.</p>