Microstructure and mechanical properties of stainless steel 316L-Inconel 625 bimetallic structure fabricated by laser wire direct energy deposition

This study explores the laser wire direct energy deposition (LW-DED) process to manufacture bimetallic SS316L and Inconel 625 alloy. The microstructure and mechanical properties of as-printed SS316L, Inconel 625, and the bimetal were analyzed. Notably, the LW-DED bimetal exhibited superior mechanical properties and a robust metallurgical bond compared to wire arc additive manufacturing. The bimetallic interface demonstrated epitaxial grain growth, a columnar coarse grain structure, and a gradual transition with a zone thickness of 55 μm, as revealed by elemental mapping analysis. Electron backscatter diffraction (EBSD) analysis confirmed low angle grain boundaries leaning towards Inconel 625 deposition, ensuring uniform grain growth from SS316L to Inconel 625 with a consistent crystallographic direction. The EBSD analysis indicated a strong fabric texture with a <001> orientation towards the build direction. However, with increasing layer deposition, the morphology of δ-ferrite in SS316L transformed to skeletal, without interface defects and minimal laves phase. Higher layer deposition revealed the presence of laves phase, as observed in the SEM and EDAX analysis. Microhardness and nano-hardness measurements illustrated that the hardness values in the interfacial region fall between those of individual materials, showcasing a gradual transition at the interface. The tensile properties are higher in the Inconel 625, while SS 316L exhibits comparable properties to the bimetallic sample.