Research On Fatigue Properties Of TC4 Diffusion Bonding Joints

With the increasing and widely application of welding structure in Aeroengine components, the mechanical properties especially the fatigue performance has drawn scholars’ attention. The static performance and fatigue performance of TC4 diffusion bonding joints are studied, in order to provide the theoretic support for engineering application of diffusion bonding components.Metallographic test and static strength test of TC4 diffusion bonding joints were carried out to verify the feasibility of processes parameters and the bonding quality of the joints. The ability to resist deformation and crack extension was studied by fracture toughness test and nano indentation test.Three kinds of specimens were designed with different inclined angles of diffusion bonding line. Tensile fatigue test was performed to establish the load-life(S-N) curves. The influence of different ratio of normal stress and shear stress on the fatigue properties of diffusion bonding joints was discussed. The fatigue performance is weakened in the order:TC4 raw material, TC4 base metal and diffusion bonding line The fatigue life of diffusion bonding joints was evaluated based on the critical plane method and good expectation results are obtained. Double lap specimens were designed and shear load-life(S-N) curves were established through shear fatigue test. There are three kinds of failure modes of double lap joints,which are fracture of baseplate dominanted by normal stress, fracture of baseplate after sealing off of welded area and completely sealing off of the baseplate dominanted by shear stress. Those three failure modes change with the changing of fatigue load.The macro and micro morphology observation of fatigue fracture shows that the macro fracture appears no obvious plastic deformation and fatigue crack initiates on the surface of specimens. The fracture is of cleavage type during the process of crack propagation. A lot of dimples are found in the final fracture region. In general, the crack surface of diffusion bonding joints is brittle intergranular fracture.