Effect of thermal compensation on microstructure and mechanical properties of electron-beam welded joint for high-Nb containing TiAl/Ti600 alloys

Abstract

High-Nb containing TiAl (TNB) and Ti600 alloys are the alternative materials for the tail-nozzle structure of rocket engines because of their low density, high specific strength and high temperature performance. This paper aims to investigate the microstructure evolution and the change in mechanical properties of the TNB/Ti600 electron-beam welded joints after thermal compensation treatment by electron beam defocusing mode. Compared with the electron beam welding of no-thermal compensation treatment, results showed that the cold cracks of the joint could be eliminated effectively by thermal compensation treatment. The microstructure in the fusion zone was composed of fine rod-shaped α-Ti+α2-Ti3Al phase. Moreover, the precipitated phase in heat affected zone on the TNB alloy side increased noticeably. The hardness of fusion zone considerably diminished to 400HV, at the same time both of the tensile strength of the joints at room temperature and 600°C increased substantially, reached 601 and 613MPa respectively, consisting with the evolution of the microstructure of the joint.