To obtain more in-depth knowledge about the microscopic process during laser sintering, phase change processes including melting, evaporation and resolidification during the irradiation of femtosecond laser on nanosized gold particles were simulated. Laser heat source term was revised to be in accordance with the spherical coordinates and actual situation in a sintering powder bed. The effects of multiple reflection and pulse energy overlapping in small particle size were considered. The results show that, when the particle size is big enough, the simulation results match those of old model. When the particle size is small and laser fluence is high, no resolidification takes place in the time range of the simulation. The laser fluence range to achieve partial melting is narrow when the particle is small. When the diameter is smaller than 400 nm, temperature gradient during the heating period is ignorable, which is different from the large particles. The threshold value of laser fluence to achieve vaporization is about two times higher than that of melting with the same particle size.

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