Characterizing Micromechanical Properties of Friction Welding Interface between TiAl Alloy and GH3039 Superalloy

To explore the macro-fracture mechanism of a friction welded joint between TiAl alloy and GH3039 superalloy, the micromechanical properties of intermediate phases at the joint interface are characterized and the relationship between the macro-fracture and micro-fracture of the joint is established. The indentation technique has been employed to calculate the nano-hardness and fracture toughness of the intermediate phases. The dynamic in-situ tensile test in SEM has been applied to observe the initiation and propagation process of cracks at the interface. It has been found that Al(3)NiTi(2) and AlNi(2)Ti have the highest nano-hardness and elastic recovery rates, while TiAl and GH3039 base metals have the lowest nano-hardness and elastic recovery rates. This indicates that the harder the materials, the more prone they are to elastic deformation. Nevertheless, the fracture toughness of Al(3)NiTi(2) and AlNi(2)Ti are the two lowest, which were 1.7 MPa·m(1/2) and 2.7 MPa·m(1/2), respectively. The cracks sprouted from Al(3)NiTi(2) and AlNi(2)Ti and then spread throughout the entire intermediate phase zone. In other words, the fracture mainly happened in these two phase layers. It has been concluded that Al(3)NiTi(2) and AlNi(2)Ti were the two weakest phases at the interface and their poor fracture toughness results in low joint strength.