The influence of aging times at 650 °C on the microstructure of dissimilar laser welded joints of GH159/GH4169 superalloy

This study explored the aging time-dependent microstructures and strengthening mechanisms of dissimilar welds between GH159 and GH4169 superalloy. The joint consisted of ?-Ni matrix, nano-scale ?' and ?? phases, granular MC carbides, and Laves phase after welding and aging at 650 degrees C. The aging time mainly affects the precipitation, size, and transformation of the strengthening phase. The weld joints aged for short times (= 25 h); the content of small-sized strengthening phases ?' and ?? increased gradually with the increased aging time. It can increase the microhardness of the weld center from 252 HV (unaged) to 396 HV (aged for 25 h). With a longer aging time (= 600 h), the Laves phase produced during welding and the nano-scale phases precipitated by aging are severely coarsened. With increasing aging time to 2000 h, the nano-scale phase ?' increasingly transforms into the d phase, resulting in its performance degradation. However, the d phase has the effect of "cutting" the Laves phase, which can refine the Laves to a certain extent.