Creep and fatigue lifetime analysis of directionally solidified superalloy and its brazed joints based on continuum damage mechanics at elevated temperature

Experiments are carried out at elevated temperature to investigate the effect of brazing itself and post-brazing heat treatment on the lifetime of directionally solidified (DS) superalloy. Meanwhile, a new lifetime prediction methodology based on continuum damage mechanics (CDM) is proposed to predict the lifetime of DS superalloy and its brazed joints. After creep and fatigue testing, the fractured specimens are observed by means of Optical Microscope (OM) and Scanning Electron Microscope (SEM) with the Energy Dispersive X-ray Spectrometer (EDXS) to understand their failure mechanisms. The results showed that: (1) under the same test condition, all the brazed joints exhibited a lower creep and fatigue lifetime compared with a typical DS superalloy; (2) the creep and fatigue lifetime of heat treated brazed joint was longer than that of non heat treated one; (3) the developed CDM method can be used to predict the lifetime of all the specimens; (4) all the brazed joints fractured in the brazing seam; and (5) there were many distinctive differences between the failure mechanics of DS superalloy and its brazed joints.

► The brazed joints showed lower creep and fatigue life compared with DS superalloy. ► The heat treatment affected the creep and fatigue rupture of the brazed joints. ► The brazing seam was the weakest location of the brazed joints. ► The failure mechanism of the brazed joints had been analyzed. ► The test data were modeled by continuum damage mechanics with a developed method.