THE EFFECT OF SILICON ADDITIONS ON THE THERMAL STABILITY AND MORPHOLOGY OF CARBIDES IN A Ni-Mo-Cr SUPERALLOY

摘要

The effect of silicon additions on the thermal stability and morphology of carbides has been investigated in a Ni-Mo-Cr superalloy. It is found that granular M_6C carbides form at the grain boundaries in the standard heat. The size and morphology of M_6C carbides remain unchanged in the aging treatment at 700-800°C up to 1000 h. While in the non-silicon heat, the intergranular carbides are examined as M_2C type carbides by TEM at the initial stage of the aging treatment. With the aging time increasing, the fine granular M_2C carbides transform into coarse planar M_6C carbides. It can be concluded that silicon additions can lead to the more stable intergranular carbides in the Ni-Mo-Cr superalloy.