A secondary liquid phase with a droplet shape is separated from the primary liquid phase in Cu–Ni–Fe–Mo–Si alloy during Laser Metal
Deposition process. In the subsequent quenching process, the secondary liquid phase solidifies into hard particles that are dispersed in the primary
matrix phase. The increase in Ni content suppresses the coarsening of the hard particles, but the mechanism of the phenomenon has not been
clarified. In this study, we investigated the effects of Ni content on the hard particle sizes, mainly focusing on Marangoni effect controlled by the
temperature variation of interfacial energy. The effects of Ni content on the hard particle size were analyzed based on the change in the start
temperature of the separation of two liquid phases (L1 and L2) and the temperature dependence of interfacial energy with Ni content calculated by
thermodynamic calculations. The results showed that Ni content had little effect on the temperature variation of interfacial energy. On the other hand, an increase in Ni content decreases the temperature of L2 droplet formation and shortens the time to solidification, resulting in reduced moving
distance of the droplet. Therefore, the collision frequency of L2 droplets caused by the Marangoni effect was reduced and coarsening of the droplets was suppressed.