In Situ Observation of the Dissolution, Collision, and Aggregation Behavior of Nitride Inclusions in GH4169 Nickel-Based Superalloy

In this study, the dissolution, collision, aggregation, and separation behaviors of nitride inclusions at the melt interface of GH4169 nickel-based superalloy were investigated via thermodynamic calculations combined with in situ observation via high-temperature confocal laser scanning microscope (CLSM). The results showed that the nitride inclusions were able to dissolve completely during the alloy melting process, and boundary layer diffusion was the limiting factor for dissolution. Nitride inclusions from the remelting process were reprecipitated during solidification. As the melt temperature increased, the degree of dissolution of the inclusions increased, and the dissolution rate of the inclusions increased. Second, the results of in situ observation by CLSM showed that nitride inclusions were more likely to aggregate with oxide inclusions, that separation may still occur between nitride inclusions after aggregation. The attraction of nitride–oxide inclusions was greater than that of nitride–nitride inclusions. The ability of the inclusions in the collision zone to aggregate together in contact depends on the interaction forces between the inclusions. The calculation results showed that the cavity bridge force was much greater than the capillary force and van der Waals force, which were the main forces leading to aggregation between the inclusions. Once a stable cavity bridge was formed between the inclusions, the aggregated inclusions no longer separated. In contrast, if cavity bridges formed between inclusions were substable, then fluctuations in the alloy melt would cause the substable structure to rupture, leading to the separation of inclusions.