High-temperature strengthening mechanisms of optimized L-PBF IN718 superalloys with interpretable machine learning

Abstract

Laser powder bed fusion (L-PBF) fabricated IN718 alloy is subject to a strength-ductility trade-off at elevated temperatures owing to its intrinsic defects and anisotropic microstructure. In this study, the high-temperature strengthening mechanisms of optimized L-PBF-processed IN718 alloy were elucidated through the integration of in situ synchrotron X-ray tomography and interpretable machine learning. Optimization of the volumetric energy density (VED) during L-PBF established a critical processing window (47–60 J/mm³) that minimized defects (porosity <1 %) and refined grains. Specimens IN718 fabricated at 230 W/1000 mm/s (VED = 52.27 J/mm³) exhibited superior high-temperature tensile properties (YS = 1017 MPa, UTS = 1184 MPa, EL = 21.3 %). In situ X-ray tomography revealed that strain-induced void nucleation, rather than pre-existing defects, was the primary cause of damage at elevated temperatures. Grains oriented along < 111 > with low Schmid factors were found to impede dislocation slip, thereby enhancing strength while simultaneously accelerating defect-driven premature failure. The XGBoost-SHAP model quantitatively assessed the microstructure-property relationships, demonstrating that grain size and Σ3 boundaries predominantly govern strength, whereas porosity constituted a critical limiting factor for ductility. This study presents a causal framework linking process, microstructure, and property relationships, thereby providing fundamental insights into defect-aware grain boundary engineering in additively manufactured superalloys.