Inheritance of microstructure and mechanical properties in laser powder bed fusion additive manufacturing: A feedstock perspective

Abstract Correlation between the feedstock powder and the as-printed products is well expected in laser powder bed fusion (LPBF). However, the inheritance/heredity relationship between the feedstock powder and the products remains broadly overlooked since most atomized powders are printed without any modification. This study addresses the inheritance issue through comparing the hydrogenation/dehydrogenation (HDH) Ti powder with the ball-milled (BM) Ti powder, as well as the respective as-printed samples. Rietveld refinement, focused ion beam, electron backscatter diffraction, and transmission electron microscopy are employed to characterize the microstructure; uniaxial tensile tests and fractographic observation are performed for the mechanical analysis; single-track finite element simulations are conducted to reveal the varied powder-bed properties. A “core-shell” powder structure has been generated through the ball milling modification. Nano-crystallites in the “shell” and stress-induced twins have brought significant grain refinement to the BM powder. A β-to-αm massive transformation has been observed in the samples printed using HDH powder, whereas the microstructure changes to fully-martensitic when using BM powder as the feedstock. Excellent mechanical performance (∼1000 MPa tensile strength with ∼20% ductility) have been achieved through inheriting the fine microstructure and oxygen content from the BM powder, which are induced by the powder modification process. This study has therefore unveiled the comprehensive correlation between the feedstock powder and the as-printed Ti, highlighting a novel methodology for developing additively-manufactured, cost-effective, and high-performance materials through tailoring the feedstock powder.