Microstructure evolution and mechanical properties of diffusion bonding Al_5(TiZrHfNb)_(95) refractory high entropy alloy to Ti_2AlNb alloy

摘要

In this study, the refractory high entropy alloy Al_5(TiZrHfNb)_(95) was diffusion bonded (DB) with the intermetallic compound (IMC) Ti_2AlNb under 5 MPa at 970-1100 °C in vacuum. The microstructure and element distribution were analyzed using a scanning electron microscope (SEM) and mechanical properties were evaluated by nanoindentation and shear tests. The typical microstructure of DB joint was Ti_2AlNb substrate/solid solution/ scattered A13Zr5/solid solution/Al_5(TiZrHfNb)_(95) substrate, which the discrete brittle Al_3Zr_5 phase was arranged along a straight line in the bonding surface, and gradually elongated and dissolved as the bonding temperature increased from 970 °C to 1100 °C. The formation of Al_3Zr_5 was attributed to the lowest Gibbs energy of all the possible IMCs in the range of the welding temperature. In the joining region, the IMC Al_3Zr_5 had the highest hardness (9.01 GPa) and modulus (143.37 GPa) but the lowest elastic recovery (20.37%), thus, it tended to cause stress concentration at the phase interface and induced crack initiation, which had a detrimental effect on the shear strength of joints. The shear strength of DB joints improved with the increase of bonding temperature and reached the highest (427 MPa) at 1100 °C owing to is lowest Al_3Zr_5 content. As the bonding temperature increased, the fracture of the joint transformed from intergranular brittle to ductile.