Additive manufacturing of stainless steel-to-inconel graded material: Insights into microstructure, defects, and mechanical properties
J. Valilla, M.A. Monclús, P. Rey, I. Sabirov, D. Tourret
Abstract
Additive manufacturing of metallic materials enables the manufacturing of functionally graded materials (FGMs) with a gradual change in composition within a part. Here, we study the microstructure and properties of FGMs graded from a stainless steel (316L) to a nickel-based superalloy (IN718) fabricated using Laser beam-Direct energy deposition (DED-LB) with metallic powder. We explore various gradient configurations to assess their impact on microstructure, mechanical properties, and defect formation. Our results reveal the consistent presence of intergranular cracking within a specific range of the graded region (≈ 10-25 wt.% IN718). The gradient of macroscopic properties (namely hardness, compression stress-strain curves, and thermal expansion) appears relatively smooth, monotonic, and in most cases nearly linear through the graded regions, thus discarding potential mismatch of these properties as the origin of the cracks. Microstructural characterization, nanohardness mapping, and computational thermodynamic (CalPhaD) analyses highlight the role of Nb and Mo microsegregation, triggering the formation of the brittle intermetallic phase C14 Laves as part of a low-melting temperature eutectic structure, which may induce hot (solidification and liquation) cracking. • Graded 316L-IN718 samples were fabricated via Direct Energy Deposition (DED). • Intergranular cracks formed at 10-25 wt% IN718 for all grading configurations. • Grading in fewer steps leads to less cracking and better mechanical performance. • Hardness and thermal expansion varied smoothly across the graded region. • Microsegregation of Nb and Mo led to Laves phase formation in crack-prone areas.