Effect of bonding temperature on the microstructure and mechanical properties of the diffusion-bonded joints of Zr705 alloy

Abstract

Research on the diffusion bonding of ( )similar joints of zirconium (Zr) alloys is limited as compared to that on the diffusion bonding of ( )dissimilar joints. The similar Zr alloys are difficult to bond together owing to its high melting point; however, an added interlayer can solve this problem. This study demonstrated the successful vacuum diffusion bonding of the Zr-2.5Nb (Zr705) alloy with a Cu interlayer at 900–960 °C and analyzes the microstructure and mechanical properties of the diffusion-bonded joints. The layered morphology of the joints at 900 °C and 920 °C is attributable to the formation of intermetallic compound layers ( ). In contrast, no such formation was observed at 940 °C and 960 °C owing to the complete diffusion of Cu atoms into the Zr substrate. The base material at the bonding temperatures of 900 °C and 920 °C exhibited two different microstructures i.e., a Widmanstätten microstructure near the bonding interface and a duplex microstructure away from the bonding interface. However, the temperatures at 940 °C and 960 °C exhibited an entirely Widmanstätten microstructure. The tensile strength of the joints increased with the bonding temperature, from 78 MPa at 900 °C to a maximum of 603 MPa at 960 °C (joint efficiency = 104.8%), and the elongation first increased and then decreased with the increasing temperature; at 940 °C, it reached 54% that of the original Zr705 alloy.