Demonstration and Analysis of Conditions to Obtain a High Strength Inconel 625 to Stainless Steel 304L Interface by Directed Energy Deposition

Functional grading (FG) is often used to bond dissimilar metals. However, that approach is complicated from a manufacturing perspective, and the associated challenges can outweigh the benefits of FG. Here, we investigate a directly bonded interface by transitioning from stainless steel 304L (SS304L) to Inconel 625 (IN625) using powder-feed directed energy deposition with a laser beam energy source (DED-LB). Both cracking and the presence of carbide phases have been reported in this multi-materials system. Conditions that unambiguously achieve crack-free joints have not yet been established. With DED-LB, we consistently observe solidification cracking in melt pools containing > 50 wt pct SS304L, while no cracking is observed in melt pools with < 40 wt pct SS304L. Variations on the most up-to-date solidification cracking model are applied to gain insight into the cracking dependencies. Parameters that give rise to defect-free single layers also enable defect-free multilayer prints despite the additional thermal cycling. Upon printing and testing full-sized ASTM E8 tensile specimens, the interface is sufficiently strong that failure occurs solely within the SS304L region, indicating a joint strength of > 650 MPa. Thus, a simple method to attain high strength joints for these dissimilar metal alloys is demonstrated.