Effects of Ni addition on removing Fe-Ti intermetallic compounds in cold metal transfer arc-brazed TC4/304L dissimilar joints

Abstract

Dissimilar titanium alloy TC4/304 L stainless steel joints suffer from the brittle and inevitable FeTi and Fe2Ti intermetallic compounds. Cold metal transfer (CMT) arc-brazing method was used to join titanium alloy TC4 to 304 L stainless steel by using Cu, CuNi10, and CuNi30 wires. The effects of Ni addition on the microstructure and mechanical property were studied. With the addition of Ni, Fe-Ti intermetallic compounds was removed. TC4/seam interfaces containing TiNiCu, Ti2Cu, TiCu, TiCu4, and TiNi formed instead of those with Fe2Ti, FeTi, Ti2Cu, TiCu, TiCu2Al, and τ4 (Ti37Cu63-xFex). (Fe, Ni) dendritic grains and (Cu) solution formed instead of amount of Fe-Ti intermetallics in the seam and on the 304 L/seam interfaces. The reason is different intermetallic formation enthalpies and solution enthalpies calculated from Miedema model. Due to the thinner and less brittle TC4/seam interface layer, the highest tensile strength was 334 MPa when the CuNi10 wire was used. Excessive Ni content resulted in a reduction of strength due to the formation of an excessively thick and uneven TC4/seam interface. All joints fractured at the TC4/seam interface.