Study on Solidification and Phase Transformation Behaviors in Ni-based Superalloy IN625

Abstract

The solidification and phase transformation behaviors of IN625 with low C and Fe were investigated through directional solidification and quenching experiments. The primary and secondary dendrite arm spacing decreased exponentially as the solidification rate increased, demonstrating good agreement with theoretical equations. The MC carbide formed at a constant temperature gradient regardless of the solidification rate. It is reasonable to assume that the Laves phase solidified in the final stage of solidification, as it was found at the bottom of the mushy zone. The morphologies and sizes of the MC carbide and the Laves phase were closely related to the solidification rate. Increasing the solidification rate at a constant thermal gradient resulted in the development of the MC carbide from blocky to Chinese script, and eventually spotty shapes, along with decreasing size. As a result of this research, it is believed that the weldability of the alloy could be improved at the expense of mechanical properties, especially with low C and Fe contents and a relatively high solidification rate, which are able to generate the finely distributed MC and Laves phase.