Effects of pure Ti or Zr powder on microstructure and mechanical properties of Ti6Al4V and Ti2AlNb joints brazed with TiZrCuNi

Abstract

Ti6Al4V and Ti2AlNb alloys were brazed with three kinds of filler metals, typical commercial filler of TiZrCuNi, TiZrCuNi mixed with Ti or Zr powder. The microstructure evolution, production and growth mechanisms of reaction phases and mechanical properties of the brazing joints were investigated. The results demonstrated that primary dendrites formed by IMCs (Ti,Zr)2(Cu,Ni) and a layer of eutectic β+(Ti, Zr)2(Cu, Ni) products were observed in the TiZrCuNi joint. And the number of IMCs significantly in the joint increased when Zr powder was added in the filler. But if the addition was Ti powder, IMCs can be eliminated a lot. The suppression of ICMs production in the TiZrCuNi + Ti joint was mainly due to two reasons: firstly, the more β phase were firstly formed in the molten filler as the solid solubilities of Cu or Ni in Ti was higher than those in Zr; secondly, owing to the increased melting point of filler by adding the Ti powder, the time spent on the solidification of liquid filler can shorten and the segregation of Cu/Ni then partially repressed. Resulted from the efficient suppression of the detrimental IMCs, the highest tensile strength of 738.7 MPa was obtained by TiZrCuNi + Ti joint, which was higher than those of the TiZrCuNi joint (~136.1 MPa) and TiZrCuNi + Zr joint (~200.1 MPa).