Fabrication And Numerical Simulation Of Mono-sized Copper Spherical Particles

Due to its excellent properties,spherical metal particles are widely used in additive manufacturing,powder metallurgy,electronic packaging and other fields.Copper and its alloys have attracted extensive attention worldwide due to their excellent corrosion resistance,excellent electrical conductivity and thermal conductivity.The internal structure of the Cu particles prepared by the traditional method is volatile due to the uncontrollable preparation process and solidification heat history,which is difficult to meet the requirements of electronic packaging and additive manufacturing,etc.In this study,mono-sized spherical Cu particles were prepared by pulsated orifice ejection method(POEM)under Ar and He gas.The results show that the Cu particles prepared by POEM have the advantages of uniform particle diameter,high sphericity,no satellite particles and consistent thermal history.The variation of particle size and distribution under different process parameters was studied.The experimental results show that the particle size decreases with the time of t_up,and increases with the applied pressure.When the diameter of the orifice is 300?m,the time of t_up=200?s,and applied pressure is 3 k Pa,the particle distribution is the smallest,and the particle size is the most uniform.When the orifice diameter is the same,the distribution of particle size increases with the increase of orifice depth.The effect of different experiment conditions in the size of crystal grain was cleared.Some particles with the size of155.1?m,247.6?m,355.4?m were prepared by POEM in Ar atmosphere,the grain size is56.7?m,92.6?m,118.3?m,respectively.Meanwhile,the size of some particles prepared by POEM in He atmosphere is 353.6?m and the grain size is 63.9?m,which is much smaller than in Ar atmosphere.A numerical simulation was established to study the relationship between cooling rate and crystal grain by finite difference method.According to calculated results,the cooling rate in Ar gas is 8.4×10³ K·s^-1,4.9×10³ K·s^-1,2.4×10³ K·s^-1,respectively,for different grain size mentioned above,the cooling rate in He gas is 5.2×10³ K·s^-1.Accordingly,the variation of the grain size meets well with the relationship of the cooling rate of Cu particles.The solidification process of different particle sizes were studied.The calculation results show that the convective heat transfer coefficient of particles increases with the increase of falling time in the solidification process,and the convective heat transfer coefficient of particles with smaller particle size is large under the same conditions.During the solidification process of particles,the increase rate of solid phase rate increases with time,which is consistent with the variation trend of the distance between the solidification section and the particle surface.During the solidification process,the convective heat flux changes of particles with different sizes show a trend of first decreasing,then increasing and then decreasing,and the radiation heat flux changes show a trend of first decreasing,then remaining unchanged,and finally continuing to decrease.