Microstructural Aspects in the Diffusion Bonding of Zr702 to A516 Steel with Ni/Mo/Ti Multi-Interlayer

The bonding of zirconium to various grades of steel has found increasing applications in different industries. Due to their fusion welding problems, the solid state bonded joints of these alloys have received more attention from researchers. In this study, diffusion bonding between zirconium alloy Zr702 and low-alloy steel A516 was performed using a multi-layer interlayer consisting of titanium, molybdenum, and nickel. The bonding process was carried out at a temperature range of 900-1050 ℃ for 30 minutes using the spark plasma diffusion bonding method. The microstructure and interdiffusion of elements at different interfaces were examined using a field emission scanning electron microscope (FESEM) equipped with EDS analysis. The results showed that a suitable bonded joint was successfully established with the interlayers arranged as Zr702/Ti/Mo/Ni/Steel. At the interface of the interlayers with the base metals, no harmful phases, cracks, or discontinuities were observed. In the Zr/Ti joint interface, diffusion zones were identified as (α+β) (Zr,Ti), β(Ti,Zr), and α(Ti,Zr). In the Ti/Mo interface, two solid solution diffusion zones were present, while the Mo/Ni interface showed two areas that included solid solutions and intermetallic phases. In the Ni/A516 joint interface, a solid solution combination and an intermetallic composition were identified. EDS Linear analysis results indicated that the maximum diffusion occurred in the Zr/Ti layer, while the lowest diffusion was observed in the Ti/Mo layer.