Particle penetration during spray forming and Co-injection of Ni3Al + B/Al2O3 intermetallic matrix composite

Intermetallic matrix Ni₃Al + B/Al₂O₃ composite, with 11 vol pct of Al₂O₃ particles incorporated into the matrix, was synthesized using a spray atomization and coinjection method. The penetration behavior of ceramic particles into atomized droplets during spray atomization and coinjection of Ni₃Al + B/Al₂O₃ composite was investigated experimentally and numerically. It was found that the extent of incorporation of Al₂O₃ into Ni₃Al + B droplets depends on the solidification condition of the droplets at the time of droplet/particle interaction. Penetration was observed only in fully liquid droplets or partially solidified droplets. No penetration was observed for droplets smaller than ～40 µm, because droplets in this size range were fully solidified at the point of coinjection, and penetration was not possible for fully solidified droplets. The distribution of penetrated Al₂O₃ in the Ni₃Al + B droplets was, in general, uniform, with no trends of segregation observed. However, it was noted that most Al₂O₃ particles were located at the grain boundaries inside the droplets, while some Al₂O₃ particles were trapped inside the droplets by primary dendrite arms resulting from a fast moving solidification front typically associated with rapid solidification processes such as spray atomization. Finally, it was believed that the Al₂O₃ particles facilitated nucleation upon penetration of the Ni₃Al + B droplets either by means of thermal gradients or compatibility of preferred growth planes.