Microstructure Evolution and Mechanical Properties of Linear Friction Welded Ti2AlNb/Ti60 Dissimilar Joint
GUO Zhenguo1, MA Tiejun1, CHEN Xi1, YANG Xiawei1, LI Wenya1, TAO Jun2
1. Key Laboratory of Friction Welding Engineering Technology of Shaanxi Province, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China;
2. Aeronautical Key Laboratory for Welding and Joining Technologies, AVIC Manufacturing Technology Institute, Beijing 100024, China
The linear friction welding (LFW) experiment of Ti2AlNb and Ti60 alloys was conducted. The microstructure evolution of the joint was analyzed by using an optical microscope and scanning electron microscope, and the mechanical property of the joint was tested as well. The results reveal that the microstructures of thermo-mechanically affected zones (TMAZ) on both sides of the joint deform along the direction parallel to weld interface. α2→B2 and O→B2 transformations occur in TMAZ of the Ti2AlNb side joint in which the fraction of B2 phase is higher than that of base metal; β→metastable β→α transformations occur in TMAZ of the Ti60 side joint, resulting in fine lamellar secondary α precipitation. Dynamic recrystallization happens in weld zones (WZ) on the two sides of the joint. During welding, the WZ of Ti2AlNb side joint completely transformed into B2 phase and retained after rapid cooling; the WZ of Ti60 side joint is firstly transformed into high-temperature β, and then β→α′ transformation occurs during fast cooling, leading to α′ martensite precipitation. In addition, interdiffusion of solute elements occurs at the weld interface, forming an element diffusion layer about 1 μm in width, and the grains on two sides of the weld interface are intergrowth. Under the coupling effects of strain strengthening and precipitation strengthening of TMAZ and fine grain strengthening and precipitation strengthening of WZ, the tensile strength (939 MPa) of the joint is not lower than that of Ti60 base metal, and the fracture mode is ductile fracture.