Study on the Strengthening of Unfavorable Composition Zones in 316L‐IN625 Functional Gradient Materials by Nb Element

In this study, 316L‐IN625 functional gradient materials (FGMs) were employed to an innovative dual‐wire + powder plasma arc additive manufacturing (DW + P‐WAAM) process. Various Nb contents (0, 4.00 and 9.77 wt%) were employed to strengthen the 75 wt% 316L zone. The results indicate that the DW + P‐PAAM process has the advantages of high‐precision trace‐element control in powder‐based and high deposition efficiency in wire‐based. The addition of Nb element mainly promotes the precipitation of Laves, and the morphology of Laves undergoes a transition from discrete particles at the grain boundaries to chain structure in grain boundaries to a mesh structure that permeates the dendrites. As the Nb content increases, the microhardness of this region continues to increase continuously. When the Nb element reaches 4.86 wt%, the tensile strength and elongation decrease, due to the precipitation of chain‐Laves at the grain boundaries. When the Nb element is 10.58 wt%, the tensile specimen breaks in the zone of 100 wt% 316L, indicating successful strengthening of specimen #Nb10.58. The tensile results show that #Nb10.58 specimen (UTS, YS and elongation) has the best tensile results, followed by those of Sample #Nb0.90 and #Nb4.86 has the worst results.