Integrating In-situ Two-Wavelength Pyrometry with Thermal Field Modeling to Elucidate Solidification Microstructure in LPBF of IN718

This initial study combines experimentally measured melt pool surface temperatures using a novel single-camera two-wavelength imaging pyrometry (STWIP) system with COMSOL numerical simulation to investigate the relationship between thermal evolution and microstructure formation during laser powder bed fusion (LPBF) of IN718. Using the Kurz-Fisher dendritic growth model, quantitative solidification microstructure metrics, such as primary dendrite arm spacings (PDAS), are linked to local solidification interface characteristics, including thermal gradient and growth velocity. By integrating STWIP temperature measurements with post-mortem SEM imaging of solidified microstructures and constraining numerical thermal-field simulations with these experimental data, the framework enables location-specific estimation of solidification interface properties and their influence on microstructure evolution. This work presents a preliminary, experimentally grounded framework that directly leverages measured melt pool thermodynamics—rather than relying on purely simulated temperatures—to analyze the interplay between laser processing parameters, melt pool dynamics, and resulting microstructure. While demonstrated for IN718, the approach is broadly extensible to other alloys and LPBF conditions, highlighting the potential of high-acquisition-rate, emissivity-independent in-situ pyrometry to support microstructure prediction, process understanding, and data-driven parameter optimization in additive manufacturing of high-performance alloys.