Preparation and solidification process of mono-sized Cu-Ni-Sn microspheres by pulsated orifice ejection method

Cu-Ni-Sn alloys are well known for their excellent properties, including excellent elasticity and high strength, which enable large potentials for applications in microelectronic industry and 3D printing for example. Preparation of the high quality spherical powders should meet the new requirements in these emerging fields. In this work, the mono-sized Cu-13Ni-17Sn (wt%) microspheres with controllable diameters ranging from 84.4 mu m to 212.0 mu m were prepared by pulsated orifice ejection method (POEM). Solidified Cu-Ni-Sn microspheres exhibit good sphericity and remarkably narrowed size distribution. The percentage of microspheres with sphericity of more than 0.9 is high up to 98.6%, and the average sphericity of microspheres is 0.989. The surface of Cu-Ni-Sn microspheres is smooth, and the interior contains no pores and impurities. Furthermore, the cooling rate of Cu-13Ni-17Sn microspheres was estimated in a Newton's cooling model. With decreasing particle diameter, the cooling rate of Cu-13Ni-17Sn microspheres increases gradually. When the particle diameter is less than 84.4 mu m, the cooling rate of microspheres exceeds 3.64 x 10(4) K s(-1). With increasing particle size, the secondary dendrite arm spacing increases gradually owing to the decrease of the sphere cooling rate.