An investigation on diffusion bonding of TZM alloy and Nb-Zr alloy using Ni foil as an interlayer

Diffusion bonding of TZM alloy and Nb-Zr alloy without and with Ni interlayer was carried out at the temperature ranging from 1000 °C to 1100 °C for 30min under a pressure of 10 MPa. The effects of bonding temperature and the thickness of Ni interlayer on the microstructure and mechanical properties of the diffusion bonded joints were investigated systematically. Compared with the direct diffusion bonding method, sound TZM/Nb-Zr joints were obtained with Ni interlayer at a low bonding temperature of 1000 °C. When the bonding temperature was 1100 °C, sound joints could be achieved for both methods. But the joint shear strength with 30 μm Ni interlayer reached 228 MPa, which was 60% higher than that bonded without Ni interlayer. The diffusion-induced reaction layers were determined to be NiMo, Ni3Mo + Ni4Mo, Ni8Nb, Ni3Nb and Ni6Nb7, whose thickness and micro-hardness were measured at different bonding conditions to establish a correlation between the interfacial microstructure and joint properties. It was found that the thickness of Ni3Nb layer and the remained Ni foil were beneficial to the joint shear strength. By changing Ni foil from 0 to 45 μm, the shear strength was improved obviously, and then kept at around 250 MPa with further increasing Ni foil to 120 μm. The maximum shear strength was 264 MPa when the joint was bonded at 1100 °C for 30min with 45 μm Ni foil. Cracks were initiated from NiMo and Ni6Nb7 diffusion layers, and then propagated across the central diffusion layers.