Effects of brazing temperature and testing temperature on the microstructure and shear strength of γ-TiAl joints

Abstract

Ti–47Al–2Nb–2Cr–0.15B (at%) alloy was brazed with an amorphous Ti–25.65Zr–13.3Cu–12.35Ni–3Co–2Mo (wt%) alloy foil in vacuum furnace. The effects of brazing temperature and testing temperature on the interfacial microstructure and mechanical property of the TiAl joints were investigated in detail. Sound TiAl brazed joints are obtained at brazing temperature of 925–1050°C for 5min. The joint is mainly composed of two zones, and the intermetallic phases in the joint are (Ti, Zr)2, (Cu, Ni) and Ti3Al. The brazing temperature has a significant effect on the interfacial microstructure of the TiAl joint. The room temperature shear strength of the joint first increases and then decreases with the brazing temperature. The highest room temperature shear strength of the joint is 211MPa when the TiAl alloys were brazed at 1000°C for 5min. The shear strength decreases with the testing temperature and maintains above 155MPa at a temperature below 700°C. However, solid-state diffusion and serious oxidation in the central brazed layer II lead to the sharp reduction of the joint shear strength when the testing temperature exceeds 700°C. All the failures of the joints occur in the central brazed layer II and the (Ti, Zr)2 (Cu, Ni) intermetallic compounds occupy most of the fracture surfaces.