Creating Heterostructures via Laser Powder Bed Fusion Using Titanium and Stainless Steel Mixtures

Abstract

This study addresses the challenge of breaking the trade-off dilemma between strength and ductility in additively manufactured Titanium (Ti) products. By leveraging concentration non-uniformity and controlled diffusion during in-situ alloying of unalloyed titanium (CP-Ti) and 316L stainless steel (SS316) powders via laser powder bed fusion (LPBF), we formulated a novel Fe-containing alloy with improved printability and enhanced mechanical performance. The microstructure of the as-built Ti alloy comprises a heterostructure of nano-scaled martensitic α′ within the micro-scaled equiaxed prior-β grains, resulting from rapid solidification inherent in LPBF. Since the modified laser-powder bed fusion in this work lacks a pre-heating function, a stress-relief annealing process was conducted to enhance the mechanical properties of the as-built parts. The annealed in-situ alloyed Ti-Fe achieves a superb balance between strength and ductility, with an ultimate tensile strength (UTS) of approximately 1118.0 MPa and an elongation of ∼9.0 %. This study provides insights for designing high-performance Ti alloys with heterostructures using a mixture of elemental powder and alloyed powders via LPBF. The significance of concentration non-uniformity and diffusion during solidification is highlighted, demonstrating how these factors contribute to the formation of superior heterostructures through additive manufacturing.