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

Abstract

Abstract Dissimilar titanium alloy TC4/304\u2009L 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\u2009L 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\u2009L/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\u2009MPa 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.