Effects of Ni Content on Particle Size of Secondary Phase in Cu-Based Alloys with Liquid Immiscibility by Laser-Melting

A secondary liquid phase with a droplet shape is separated from the primary liquid phase in Cu-Ni-Fe-Mo-Si alloy during laser cladding processing. During the subsequent quenching process, the secondary liquid phase solidifies into hard particles that are dispersed in the primary matrix phase. An increase in Ni content suppresses coarsening of the hard particles, while the mechanism of the suppression has not been clarified. In this study, we investigated the effect of Ni content on hard particle size, mainly emphasizing the Marangoni effect controlled by the temperature dependence of interfacial energy. The effects on the hard particle size were analyzed based on changes in the starting temperature of the separation of two liquid phases (L1 and L2) and the temperature dependence of interfacial energy, calculated for various Ni contents using CALPHAD software. Our findings revealed that the Ni content had little effect on the temperature dependence of interfacial energy. However, an increase in the Ni content decreases the temperature of L2 droplet formation and shortens the time to solidification, thereby reducing a moving distance of droplet. Therefore, the collision frequency of L2 droplets caused by the Marangoni effect was reduced, and coarsening of the droplet was suppressed.