Dissimilar welding between Ti-6Al-4V and 17-4PH stainless steel using a vanadium interlayer

In this study, electron beam welding, continuous laser welding, and pulsed laser welding were used to join Ti-6Al-4V alloy and 17-4PH stainless steel with a 1 mm pure V sheet interlayer. In addition, the effect of V composition on the mechanical properties of the welded joint by shifting the laser towards the 17-4PH was examined. Vanadium bonded well with Ti, and the weld metal was characterized by a (beta Ti,V) solid solution. In the V-steel welded joint, similar phases ((Fe,V)ss) but with different compositions were found in the MZs, which affected the mechanical properties. The cracked region was visible at the V-steel interface of the pulsed-laser welded joint and contributed to its low tensile strength. Electron beam welding showed a good intact joint with no defects, and failure occurred in the vanadium interlayer. A common MZ was created for the three metals in EB1, which formed Fe2Ti and FeTi intermetallic compounds that acted as crack initiation sites and led to the failure of the welded joint during machine processing. Variation in V composition had a significant impact on the mechanical properties of the welded joints. Hardness increased incrementally with the V concentration, and joints with a composition of less than 35 at% V, which corresponded to alpha-Fe + (Fe,V)sigma and alpha-Fe phase formation ranges, had better tensile properties than those with more than 35 at% V, which corresponded to the single (Fe,V)sigma phase. However, care should be taken in regulating the laser beam in order to avoid a very low V content, since this could lead to the formation of unfused regions.