Intermetallic phase evolution and strengthening mechanisms of the titanium and stainless steel lap joints welded by interrupted pulsed arc welding

Abstract

The study is focused on analyzing the intermetallic phase evolution and strengthening mechanisms of the titanium alloy and stainless steel (Ti-SS) seam-welded joints using interrupted pulsed arc welding (IPAW). The precise adjustment of welding parameters for the IPAW technique allowed for the successful creation of two different joining modes for Ti-SS joints: contact reactive brazing and fusion modes. The homogeneous composition in the brazing joints was achieved by the formation of a diffusion-driven eutectic liquid phase at the joining contact, resulting in an unusual eutectic structure consisting of β-Ti and TiFe. The molten pool at high temperatures caused an uneven distribution of composition and energy throughout the fusion joints. The fusion joints consisted of a Ti-rich layer, containing β-Ti and TiFe phases near the TC4 side, and a Fe-rich layer, containing TiFe2/TiCr2 and α-Fe phases near the 304SS side. The shear-bearing capacity of the joints exhibited an initial increase and subsequent decrease as the heat input increased. The low heat input resulted in the formation of the unwelding zone, which significantly reduced the shear resistance of the joints. With the increase of the heat input, a reduction in shear strength occurred due to the accumulation of TiFe2 brittle phases associated with the shift of the joining mode from the brazing to the fusion. The shear force decreased after reaching its maximum value, despite the joints being fully joined and the joining area expanding.