Microstructure and properties of friction welding joint of Ti–45Al-8.5Nb-0. 2W-0. 2B-0. 02Y alloy

Abstract

Abstract High Nb containing TiAl alloys have prospect to be used for turbo wheel and exhaust valve for vehicle engine. Friction welding is a suitable process for fabricating these components. For investigating the weldability of these alloys, cylindrical samples of Ti–45Al-8.5Nb-0.2W-0.2B-0.02Y (in at%) alloy with a diameter of 10\u202fmm were welded by continuous drive friction welding process, and the microstructures and the mechanical properties of the joints were analyzed in this paper. The results showed that the weldability of the present alloy was very good. At parameters of rotational speed of 2400 r/min, friction pressure of 320\u202fMPa, burn-off distance of 3\u202fmm and upset pressure of 360\u202fMPa, completely metallurgical bonding interfaces were obtained. The joint had a severely plastic deformation zone (SPDZ) with a biconcave lens geometry. The thicknesses of the center and periphery of SPDZ were about 40\u202fμm and 800\u202fμm, respectively. There existed a transition zone (TZ) between parent metal (PM) and SPDZ. SPDZ exhibited the deformation flow lines and had a randomly-oriented recrystallized duplex (DP) microstructure with the average grain size of 2.5\u202fμm, in contrast, PM presented a nearly lamellar (NL) microstructure with a colony size of 150\u202fμm. TZ showed a mixture microstructure combining deformed lamellar colonies and partially recrystallized grains. At room temperature, 750\u202f°C and 800\u202f°C, welding joints had better tensile properties than PM.