Experimental investigations on creep rupture strength and failure mechanism of vacuum brazed joints of a DS superalloy at elevated temperature

Experiments were carried out in order to investigate the creep rupture strength of vacuum brazed joints in a directionally solidified (DS) superalloy. Vacuum brazed joint specimens were tested with and without post-brazing heat treatment. Specimens were crept at 980 °C in laboratory air at applied stress levels between 124. MPa and 318. MPa. After creep testing, specimens were analyzed by means of SEM, OM and EDXS in order to understand failure mechanisms. The results showed that: (1) under the same test conditions, all brazed joints exhibited a lower creep life compared with a typical DS superalloy. In addition, the life of heat treated brazed joints was longer than that of non heat treated braze joints; (2) all the brazed joints fractured in the brazing seam; (3) the Larson-Miller equation can be used to characterize the creep rupture strength of the DS superalloys and the brazed joints. (4) the post-brazing heat treatment had an important impact on the creep behavior and microstructure of brazed joints; and (5) creep loading contributed to interdiffusion of the elements and decrease of the brazing pores in the brazed joints.