Unravelling heterogeneities in sub-grain cellular structure and micromechanical response of additive manufactured Ti-Nb alloys

Abstract

Additive manufactured (AM) metallic components often exhibit unique hierarchical and heterogeneous microstructure. Recently, exploiting the heterogeneities in sub-grain cellular structure and associated micromechanical response has been considered as a novel strategy to achieve unprecedented mechanical properties of AM-fabricated parts. In-depth understanding of such heterogeneities is critical for AM process control and optimization. In this work, laser powder bed fusion (LPBF) of a Ti-35Nb alloy is investigated with focus on unravelling and controlling the heterogeneities in site-specific cellular structure and associated micromechanical response. The experimental results reveal significant changes in such heterogeneities across the melt pool as affected by LPBF conditions. For in-depth investigation, a computational framework integrating a finite element thermal model, a phase-field grain growth model and a crystal plasticity micromechanical model is developed. The integrated experimental and computational effort is utilized to investigate the process-microstructure-property relationship at the sub-grain scale. In specific, the effects of process-induced thermal conditions on sub-grain cellular structure, thereby micromechanical response, are investigated. Spatial distribution maps of cell size and microhardness are constructed to demonstrate the heterogeneities within the melt pool. The roles of individual processing parameters on the spatial control of sub-grain cellular structure and micromechanical response are evaluated.