Microstructure evolution and mechanical properties of rotary friction welded TC4/SUS321 joints at various rotation speeds

The dissimilar joints between TC4 titanium alloy rod and SUS321 stainless steel rod were produced by rotary friction welding (RFW). The influence of rotation speed was investigated on the morphologic distribution of intermetallics (IMCs) formed at the interface and on the mechanical properties that were assessed by tensile test and microhardness. Results showed that the morphology of IMCs, mainly TiFe₂ and TiFe formed on SUS321 side, transforms from dispersive pattern to laminar pattern as the rotation speed increases from 400 to 1800 rpm with a transition point around 600 rpm. The joint strength increases and then decreases after reaching a maximum value with increasing rotation speed. The highest tensile strength of 468 MPa, corresponding to the joint efficiency of 90%, was achieved at 600 rpm, where the valley value of equilibrium interfacial temperature was obtained. All of the dissimilar RFWed joints failed completely in cleavage fracture mode along the boundary between IMCs layers and TC4 matrix.