Microstructural Evolution and Mechanical Properties of Ti2AlNb/GH99 Superalloy Brazed Joints Using TiZrCuNi Amorphous Filler Alloy

Abstract

Dissimilar materials brazing of Ti2AlNb alloy to GH99 superalloy is of great pragmatic importance in the aerospace field, especially the lightweight space aircraft components manufacturing. In this work, TiZrCuNi amorphous filler alloy was used as brazing filler, and experiments were carried out at different brazing temperatures and times to investigate the changes in interfacial structures and properties of the joints. The typical interfacial microstructure was Ti2AlNb alloy/B2/β/Ti2Ni (Al, Nb) + B2/β + (Ti, Zr)2(Ni, Cu) + (Ti, Zr)(Ni, Cu)/(Cr, Ni, Ti) solid solution + (Ni, Cr) solid solution/GH99 superalloy when being brazed at 1000 °C for 8 min. The interfacial microstructure of the joints was influenced by diffusion and reaction between the filler alloy and the parent metal. The prolongation of brazing process parameters accelerated the diffusion and reaction of the liquid brazing alloy into both parent metals, which eventually led to the aggregation of (Ti, Zr)2(Ni, Cu) brittle phase and increased thickness of Ti2Ni (Al, Nb) layer. According to fracture analyses, cracks began in the Ti2Ni (Al, Nb) phase and spread with it as well as the (Ti, Zr)2(Ni, Cu) phase. The joints that were brazed at 1000 °C for 8 min had a maximum shear strength of ~216.2 MPa. Furthermore, increasing the brazing temperature or extending the holding time decreased the shear strength due to the coarse Ti2Ni (Al, Nb) phase and the continuous (Ti, Zr)2(Ni, Cu) phase.