Local Temperature Gradient Laser Pulse Triggered Nucleation Experimental Technology under Electrostatic Levitation

The containerless and solidification method of electrostatically suspended deep subcooled samples is of great significance for materials science research and materials preparation, and this paper proposes to realize the experimental study of triggered nucleation and solidification and measurement of materials under deep subcooling based on the local temperature gradient field of the laser pulse. By triggering the laser pulse to generate a local temperature, a temperature gradient is formed around the sample, and the temperature gradient triggers convection to increase the probability of structural and energy undulation inside the experimental sample and deepen the degree, so that the crystals change from a molten liquid phase to a solid phase, realizing high-quality and controllable deep-subcooling laser pulse-triggered nucleation under electrostatic levitation. By means of finite element simulation methods, the effect of laser heating with different spot diameters and a power of 9 W, a power density of $ 2.86\times {10}^{8}\;\mathrm{W} \cdot {\mathrm{m}}^{-2} $ and $ 1.146\times {10}^{7}\;\mathrm{W} \cdot {\mathrm{m}}^{-2} $ on the temperature gradient field was investigated. The distribution results of the local temperature gradient field in the molten sample under different laser spot diameters were obtained. A zirconium sample with a diameter of 2 mm was used in the experiment to study the time scale of triggered nucleation of molten samples with different laser pulse widths and subcooling degrees under smaller laser beam spot diameters. Based on the classical nucleation theory, the time required for the zirconium samples to move from the substable state of the mother phase melt to the solid phase under different supercooling degrees was obtained by statistically analyzing the data from 16 groups of 20 spontaneous nucleations at different supercooling degrees. On this basis, the experimental study of laser pulse triggered nucleation was carried out at a wavelength of 936 nm with a laser pulse spot diameter of 0.2 mm and a sample of zirconium material. The experimental results show that the time required for nucleation and solidification of zirconium material at a low subcooling of 195 K ± 3 K is 3/4 times lower than that required for spontaneous nucleation, and that high quality and controllable nucleation can be triggered for molten samples at different subcooling levels.