Close-coupled nozzle atomization integral simulation and powder preparation using vacuum induction gas atomization technology

We simulate the gas-atomization process of a close-coupled annular nozzle for vacuum induction gas atomization at a three-dimensional scale.Moreover,the relationship between the simulated droplet type and experimentally metallic powder is established by comparing the morphology of droplets with powders.Herein,the primary atomization process is described by the volume-of-fluid(VOF)approach,whereas the prediction of powder diameter after secondary atomization is realized by the VOF-Lagrangian method.In addition,to completely reflect the breaking and deformation process of the metallic flow,we employ the VOF model to simulate the secondary atomization process of a single ellipsoidal droplet.The results show that the primary atomization process includes the formation of surface liquid film,appearance of serrated ligaments,and shredding of ligaments.Further,gas recirculation zone plays an important role in formation of the umbrella-shaped liquid film.The secondary atomization process is divided into droplet convergence and dispersion stages,and the predicted powder diameter is basically consistent with the experiment.In general,the four main powder shapes are formed by the interaction of five different typical droplets.

Precipitation behavior of γ′ phase in superalloy FGH96 under interrupted cooling test

The precipitation behavior of γ′ phase,under various interrupt cooling tests after 1170℃,solution treatment was examined.The results indicate that the size of secondary γ′ precipitates increases with the decrease of interrupt temperature,and the shape changes from spherical to butterfly like.The fine tertiary γ′ can form either during the post cool air quenching at high interrupt-temperatures,or during the specified 5℃ min-1cooling.Air quenching at high temperatures cannot suppress further nucleation of tertiary γ′ phase.

Effect of oxygen content and heat treatment on carbide precipitation behavior in PM Ni-base superalloys

The influence of oxygen content and heat treatment on the evolution of carbides in a powder metallurgy （PM） Ni-base superalloy was characterized. The results reveal that oxygen content has little influence on the precipitation of carbides inside the particles. However, under the consolidated state, stable Ti oxides on the particle surface act as nuclei for the precipitation of prior particle boundaries （PPB）. Also, oxygen can diffuse internally along grain boundaries under compressive stress, which favors the precipitation of carbides inside the particles. Therefore, a higher amount of carbides will appear with more oxygen content in the case of consolidated alloys. It is also observed that PPB can be disrupted into discontinuous particles at 1200℃, but this carbide network is hard to be eliminated completely. The combined MC-M23C6 morphology approves the nucleation and growth mechanism of carbide evolution.