Microstructure, Recovery Stress and Mechanical Property of Direct Energy Deposition Welded Fe-Mn-Si Based Shape Memory Alloy

Direct Energy Deposition (DED) is one of the main methods of additive manufacturing in which a feedstock material in the form of powder or wire is delivered to a substrate while an energy source, such as laser beam or electron beam, is simultaneously applied to melt the feedstock. In addition to fabricating complex three-dimensional shapes using computer aided design, the DED laser welding process can be employed to fill complex shaped gaps between two objects. In this study, 3 mm thick Fe-based shape memory alloy plates with a 45° groove were welded by DED using high manganese steel powder filler. The process parameters including scan speed, hatch spacing, and layer thickness were fixed at values of 840 mm/min, 0.3 mm, 0.15 mm, respectively and laser power was varied during the welding process from 150 W to 300 W. Microstructures of the welds showed different shapes and quantities of defects such as cracks, pores and a lack of fusion depending on the laser power used. Laser power of 150 W showed crack-free weldment with the highest mechanical properties. The tensile strength and recovery stress of the welded sample were higher than the base metal, demonstrating the potential high performance of welding Fe-Mn-Si shape memory alloy components using the L-DED.