Study on microstructure evolution and failure behavior of Ni3Al-based single crystal superalloy joints brazed with Ni-based filler

Abstract

The microstructural characteristics of brazing seams significantly influence the mechanical properties of brazed joints. In this study, a novel Ni3Al-based single crystal superalloy(Alloy 1) with high Mo content was brazed with a Ni-B-Si-Ti filler. The evolution of microstructure and mechanical properties of brazed joints were investigated after thermal exposure at 1000°C up to 300h. The brazed joint was mainly composed of the athermally solidified zone (ASZ), isothermal solidification zone (ISZ), diffusion affected zone (DAZ), and base metal (BM). As the increase of thermal exposure time, the tensile strength of the joint at 980°C decreases from 625MPa at 0h of thermal exposure to 443MPa after 300h of thermal exposure. It is suggested that as the duration of thermal exposure increases, the skeleton phases gradually aggregate at the ASZ/ISZ interface, reducing the relative barrier effect of the skeleton in ASZ. Simultaneously, the ASZ/ISZ interface becomes smoother over time, which in turn leads to rapid crack propagation.