Microstructural evolution and mechanical properties of the niobium alloy/GH4099 diffusion-bonded joints

Niobium alloy and nickel-based superalloy exhibit high strength and remarkable corrosion resistance, joining them to fabricate composite structures could help to realize their potential. Nevertheless, research attention devoted to the joining of niobium alloy with nickel-based superalloy remains scarce. This study investigates direct diffusion bonding of these two materials. The microstructure of the joint is characterized in detail, with the typical joint microstructure being identified as GH4099 / (Ni, Cr)_ss + Ni₃Nb + Cr₂Nb / Ni₃Nb / Ni₆Nb₇ /Nb alloy. With holding time fixed at 60 min and diffusion pressure maintained at 15 MPa, the effects of diffusion bonding temperature on the microstructure and mechanical properties of joints are examined within the range of 900–1150 ℃. An increase in bonding temperature results in the formation of different intermetallic compounds within the joint. The primary cause of joint fracture is the presence of Cr₂Nb and Ni₆Nb₇. The tensile strength of the joint initially increases and then decreases with increasing temperature, reaching a maximum value of 204 MPa. This work expands the range of methods for joining niobium alloys to nickel-based superalloys, enabling bonding without the introduction of additional elements.