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 degrees C. Although oxidation occurs at the highest temperatures, no gross defects develop at junctions in pads with higher IN625 content.

Automated summary

This study investigates directly bonded junctions in the IN625 to Stainless Steel 304 system, finding that cracking and intermetallic formation are not detected at high IN625 content, but observed at lower IN625 content due to carbide formation. Heat treatments up to 1300 degrees C are conducted to emulate service conditions, with no gross defects developing at junctions in pads with higher IN625 content even at highest temperatures.