Directed energy deposition joining of Inconel 625 to 304 stainless steel with direct bonding

Understanding and developing efficient methods to join dissimilar materials is important in additive manufacturing technology. Approaches include functional grading, adding a filler layer, and direct bonding. Each has advantages and disadvantages, but in any, avoiding deleterious brittle phases enhances success. Cracking, attributed to metal carbide formation, has been reported in the Inconel 625 (IN625) to Stainless Steel 304 system when functionally graded. Here, we investigate directly bonded junctions in this material system. Scanning electron microscopy is performed to characterize melt pool composition, substrate interdiffusion and gross defects in single beads and single-layer pads. Cracking and intermetallic formation are not detected at high IN625 content. At lower IN625 content, such gross defects are observed and are attributed to carbide formation. To emulate service conditions, heat treatments are conducted up to 1300 °C. Although oxidation occurs at the highest temperatures, no gross defects develop at junctions in pads with higher IN625 content. Graphic abstract