Initial γ' phase formation mechanism in a GH4099 precipitation strengthened nickel-based superalloy

The strengthening phases in Ni-based superalloys are the key structures for providing excellent high-temperature mechanical properties, and a current lack of understanding of the very initial step-to-step formation mechanisms for these phases hinders their applications in advanced manufacturing. Here we report the initial formation mechanism of the γ' phase in the GH4099 Ni-based superalloy, which differs from the reported classical and non-classical nucleation theories. Based on the experimental observations, preferable bondings between γ' elements will induce the Al-Al and Ti-Ti clustering, acting as the starting mechanism in the chemical homogeneous superalloy. This spinodal-like chemical modulation causes the uphill diffusion of the γ' elements into the clusters and reduces the energy barrier of the chemical ordering of the γ' phase in them. This transitional initial formation mechanism of the strengthening phase in this alloy will provide a foundamental theory to design the novel superalloys for advanced manufacturing and processing.