Preparation And Rapid Solidification Of Mono-sized Metal Microspheres

Metal spherical particles and powders are the basic raw materials for high liquidity,dispersibility and high filling,which are also the basic strategic materials to enhance the comprehensive strength of the industry.They are widely applied to microelectronics packaging,3D printing,new energy and many other fields.China is a big country about production and consumption of microspheres,but high-quality microspheres rely heavily on imports and core technologies is lacking.In microelectronics packaging,mono-sized and high sphericity solder microspheres meet the requirements of package surface flatness and high consistency.In 3D printing,high sphericity makes the powder flowable,which is helpful for subsequent processing,and the narrow particle size distribution is favorable for the uniformity of sintering.In this paper,the mono-sized microspheres of various systems were successfully prepared by the self-developed pulsated orifice ejection method,and the morphology and solidification structure of the obtained microspheres were studied in detail.This paper is divided into seven chapters.The first chapter mainly introduces the application background and preparation method of metal microspheres,the basic theory of rapid solidification,the cooling rate and supercooling calculation model,the main research purposes and contents of this paper;The second chapter mainly introduces the experimental equipment,experimental steps and characterization methods of microspheres;The third chapter to the fifth chapter study the preparation and solidification structure of Al,Cu-13Ni-17Sn and Fe₆₀Ni_7.5Mo_7.5P₁₀C₁₀B₅ microspheres;The sixth chapter discusses the particle size controllability of process parameters;The last chapter summarizes this paper.The specific content and conclusions are as follows:Al metal microspheres,Cu-13Ni-17Sn alloy microspheres and Fe₆₀Ni_7.5Mo_7.5P₁₀C₁₀B₅ metallic glass microspheres were successfully prepared by self-developed pulsated orifice ejection method.These microspheres have uniform particle size with high sphericity,high purity and smooth surface,which also have no impurities,shrinkage holes,defects inside,and satellite drops.A single pulse produces a single droplet,which indicates the method has good stability.Through the regular pulse perturbation,precise control of the droplet volume is achieved.In addition,each droplet drop trajectory is completely consistent with the same thermal history,the finally forming the same solidified structure.The relationship between the cooling rate and the particle size of mono-sized Al metal microspheres was simulated.The results show that as the particle diameter increases,the cooling rate decreases gradually,and the slope of the curve increases with the decrease of the particle size.When the particle diameter is less than 100μm,the cooling rate is higher than 4.83×10⁴ K/s;when the particle diameter is 500μm,the cooling rate is only 8.08×10³ K/s.The solidification structure of Cu-13Ni-17Sn alloy microspheres was studied.It was found that Cu-13Ni-17Sn precipitatedα-（Cu,Ni）dendrites and（Cu,Ni）₃Sn fiber crystals or plate crystals under rapid solidification conditions.The relationship between the cooling rate and particle size of Cu-13Ni-17Sn microspheres was simulated and the results are consistent with those of Al microspheres.When the particle diameter of the microsphere is 87.4μm,the cooling rate is 3.48×10⁴ K/s;when the particle diameter of the microsphere is 105.2μm,the cooling rate is 2.76×10⁴ K/s,and when the particle diameter of the microsphere is 209.0μm,the cooling rate is only 1.23×10⁴ K/s.The relationship between the secondary dendrite arm spacing and particle size of Cu-13Ni-17Sn microspheres was investigated.The results show that the smaller the particle size of the microspheres,the larger the corresponding cooling rate,and the smaller the secondary dendrite arm spacing.The reasons for this structural difference of different particle sizes are that the increase in the diameter of these particles can reduce the heat conduction inside the particles,resulting in the decrease in the cooling rate and the increase in the secondary dendrite arm spacing.In addition,the smaller particles have a higher cooling rate,the development of the secondary dendrite arms is inhibited to some extent,and the secondary dendrite arm spacing is reduced.The XRD patterns of Fe₆₀Ni_7.5Mo_7.5P₁₀C₁₀B₅ metallic glass microspheres are diffuse peaks,and there are no sharp diffraction peaks of any crystals,indicating that the microspheres are amorphous.During the cooling process of the molten alloy,the melt solidifies completely before the atoms have yet to be rearranged to form a crystal lattice,thereby forming a disordered amorphous structure.The effect of micropore aperture on the diameter of Cu-20Sn microspheres was investigated.The results show that the diameter of the microspheres increases linearly with the increase of the pore size of the micropore aperture,and the difference between the diameter of each group of microspheres and the pore size of the micropore aperture is basically the same.When the pore size of the micropore aperture is increased,the obstruction effect of the micropore on the droplet formation can be weakened,the amount of the melt ejected from the micropore is relatively increased,and the amount of the reflowed melt is relatively reduced,thereby resulting in the increase in the particle size of microspheres finally formed.The effect of gas pressure difference on the diameter of Cu and Al microspheres was also investigated.The results show that the particle size of the microspheres increases linearly with the increase of the gas pressure difference.When the gas pressure difference between the inside and outside of the crucible is increased,the volume of the single outward jet of the melt increases,and the particle size of the microsphere increases.In addition,increasing the gas pressure difference will prevent the reflow of the melt to some extent.The volume fraction of the liquid flowing out of the micropores becomes large,resulting in the increase in the particle diameter of the microspheres.