Study on the Preparation and Microstructure Control of Monodisperse Cu–Sn–Bi Alloy Microspheres by the Pulsated Orifice Ejection Method

In this study, 60Cu40Sn–xBi ( x = 50, 62.5, 75) alloy microspheres were prepared using the Pulsated Orifice Ejection Method (POEM). Their microstructural evolution was systematically characterized by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Under a helium atmosphere, alloys with a wide miscibility gap (50 Bi, 62.5 Bi) exhibited a core–shell structure, whereas the 75 Bi alloy with a narrow miscibility gap, formed a globule‐dispersed structure. Bi surface segregation and the Marangoni effect contributed to both the compositional difference observed in the core–shell structure and the surface roughness induced by solidification shrinkage. By adjusting the pulse waveform step time ( t up ), the convective heat transfer coefficient between droplets and the surrounding gas, together with droplet shape oscillation (DSO), could be regulated, thereby altering the internal temperature field of the microspheres. As t up increased, the droplet cooling rate decreased, accompanied by reduced DSO amplitude. Under the Marangoni effect, (Cu, Sn)‐rich globules in the 75 Bi alloy migrated toward the droplet center, forming a concentric core–shell structure. This study helps to clarify the mechanisms governing microstructural formation in 60Cu40Sn–xBi alloy microspheres and may offer a useful approach to inferring second‐phase globule migration during solidification, thereby contributing to improved control of microsphere microstructural morphology.