Microstructure, mechanical properties and fracture behavior of GH3535 alloy joints brazed with Au–18Ni filler metal

Abstract

Vacuum brazing of GH3535 alloy was conducted using Au–18Ni (wt%) filler metal. The effect of brazing temperature on the microstructure and mechanical properties was investigated. Furthermore, the microstructural evolution and fracture mechanisms of brazed joints were discussed. The cross section of brazed joint could be divided into two distinctive reaction zones. The typical microstructure of the joint brazed at 1030 °C/10min was GH3535 substrate/Ni (s.s) + Mo-rich Ni (s.s) + Au-rich phase/Au (s.s) + FeNi3/Au-rich phase + Mo-rich Ni (s.s) + Ni (s.s) + GH3535 substrate. Raising the brazing temperature promoted the diffusion of elements, Ni (s.s) and Au (s.s) gradually increased, and the second phase particles consisting of FeNi3 gradually decreased. With the increase in brazing temperature, the shear strength of brazed joints first increased and then decreased. The maximum room shear strength of 420 MPa was obtained at 960 °C/25min and the high temperature shear strength of 153 MPa was obtained at 600 °C. Fracture analysis indicated that cracks initiated at the interface of Au (s.s) and then propagated along the zone of FeNi3 with dimple and tearing ridges patterns.

Keywords

• Vacuum brazing
• Au–18Ni filler
• Microstructure
• High temperature
• Fracture mechanism