Inhomogeneous interface structure and mechanical properties of rotary friction welded TC4 titanium alloy/316L stainless steel joints

Abstract

The inhomogeneous interface structure and mechanical properties along the radius direction of rotary friction welded TC4 titanium alloy/316 L stainless steel dissimilar joints were investigated under as-welded and post-weld heat treated conditions. The interface in the joint is convex-shaped on TC4 titanium alloy side and concave-shaped on 316 L stainless steel side. The mechanical properties of joints are highly correlated with the inhomogeneous interface structure and the dimension of tensile samples. The tensile strength of the as-welded entire joint was 117 MPa, while it dramatically increased to 419 MPa after post-weld heat treatment at 600 °C for 2 h due to homogenization of aggregated atoms. However, the sliced samples was relatively weak even after post-weld heat treatment, because the internal defects became surface crack sources after machining, and caused stress concentration and sharply reduced the strength of samples. All tensile samples failed through the interface. The X–ray diffraction patterns of TiC, Cr23C6, Fe2Ti, FeTi, FeNi3, AlTi3, CrTi4, NiTi and TiCr phases and the river-like features on fracture surfaces indicate a brittle quasi-cleavage fracture mode. C and Cr aggregated around the interface under as-welded condition. Nonetheless, elemental homogenization occurred in the joint after post-weld heat treatment.