Study On Preparation And Solidification Mechanism Of Monodisperse Copper-based Microspheres

Monodisperse Cu-based metal microsphere has a basic strategic material to enhance the comprehensive strength of industry.Compared with metal microspheres prepared by traditional production process,the uniformity of microsphere size and high sphericity are important indicators for evaluating high-quality microspheres.Based on this,the preparation device of metal microspheres was built,and copper-based metal microspheres with different systems were prepared.The relationship between microsphere microstructure and solidification parameters was discussed,which provided theoretical basis for the research and development of high-performance metal microspheres.The main contents of this paper are as follows:(1)A metal microsphere preparation device was built,including metal melting system,piezoelectric drive system,differential pressure control system and microsphere collection system.Based on the theory of local pulse micropore perturbation,piezoelectric driving combined with the pressure difference inside and outside the crucible could control the droplet volume at the crucible micropore.On the other hand,container-free solidification technology is used to effectively avoid wall contamination and heterogeneous nucleation during the preparation of microspheres,ensuring the uniformity of microsphere size,high sphericity and the same microstructures from the preparation mechanism.(2)Using the above-mentioned preparation device,the Cu Microsphere with diameter ranging from 120.6 to 437.0 μm were prepared,which have good spherical morphology and narrow size distribution.The particle size of Cu microspheres increases with the increase of the pore size of the crucible.When the pressure difference increases,the particle size of Cu microspheres also increases.The upper and lower limits of the pressure difference are 0.8KPa and 0.29KPa.The cooling rate decreases and the grain size increases with the increase of particle diameter during the rapid solidification.(3)Cu-20Sn microspheres with diameter ranging from 70.6 to 334.0 μm were prepared,which have high sphericity and narrow particle size distribution.The phase composition of Cu-20Sn microspheres is composed of(Cu)phase and β phase.The y phase,δ phase and ε phase of eutectoid reaction at low temperature have not been detected because of the low temperature of phase transformation reaction and weak thermal effect.The cooling rate of Cu-20Sn microspheres decreases with the increase of particle size,and the secondary dendrite spacing increases with the increase of particle size.(4)Sn-1.0Ag-0.5Cu microspheres with diameter ranging from 124.0 to 337.4 μm were prepared which have high sphericity and narrow particle size distribution.The main phase composition of Sn-1.0 Ag-0.5Cu microspheres is primary(β-Sn)phase.Binary eutectic and ternary eutectic can be detected only in large particle size microspheres.With the increase of the particle size of microspheres,the cooling rate decreases and the content of primary crystalline phase(β-Sn)increases gradually.The reason is that the bigger the particle size of microspheres,the smaller the cooling rate,the less easy the eutectic reaction occurs;the products of binary eutectic and ternary eutectic increase gradually,because the larger the particle size,the smaller the cooling rate of microspheres,the binary eutectic reaction β-Sn→Cu6Sn5+β-Sn and ternary eutectic reaction.The increase of reaction time of L(?)(β-Sn+η-Cu6Sn5+Ag3Sn)was initiated.