Microstructure and mechanical properties of Ti2AlNb joints diffusion bonded using Ti foils as interlayer

Abstract

Ti₂AlNb alloy was diffusion bonded using pure Ti as an interlayer at temperatures ranging from 940 °C to 980 °C under a pressure of 80 MPa. A complete metallurgical bond was achieved at all bonding temperatures. It was found that the weld zone (WZ) consistently consisted of α and β phases. A higher bonding temperature promotes significantly enhances elemental diffusion, leading to the formation of a thicker and more uniform WZ. As the bonding temperature increased, the microhardness of the WZ rose, while that of the matrix slightly decreased. With the increasing of bonding temperature, the tensile performance of the joints initially improved and then deteriorated. Meanwhile, the fracture mode of the joints transitioned from quasi-cleavage fracture to ductile fracture, and ultimately to a mixed mode of cleavage fracture and ductile fracture. The joint bonded at 960 °C exhibited the optimal strength-plasticity balance, with an ultimate tensile strength of 979 MPa and an elongation of 18.9 %. It was observed that the premature fracture of the joint bonded at 940 °C was due to an excess of α₂ phase in the WZ, along with the activation of different slip systems in the matrix phase. For the joint bonded at 980 °C, the excessively high temperature deteriorated the matrix microstructure. The dissolution of all primary O phase in the matrix reduced its strength, resulting in fracture within the matrix during tensile testing, which led to a decrease in tensile properties compared to the joint bonded at 960 °C.