靜電懸浮條件下液態鋯的熱物理性質與快速枝晶生長

靜電懸浮條件下液態鋯的熱物理性質與快速枝晶生長Thermophysical properties and rapid dendritic growth of liquid zirconium under electrostatic levitation condition

利用靜電懸浮實驗技術研究Zr熔體的深過冷和枝晶生長動力學機制，并測定了液態Zr的密度、黏度和表面張力等熱物理性質。結果表明：液態Zr的超過冷臨界過冷度為524 K(0.25Tm)，平均比熱為41.03 J/(mol？K)。基于熱平衡方程測定出液態Zr在1752~2315 K溫度區間內的輻射率隨溫度升高而增大，熔點處其值為0.312。液態Zr的密度、黏度和表面張力均隨溫度降低呈上升趨勢。同時，通過高速CCD攝像方法測得純Zr的枝晶生長速度隨過冷度以冪函數形式增大，在最大過冷度376 K(0.18Tm)處，枝晶生長速度達到48 m/s。此外對其凝固組織的研究發現，隨著過冷度的增大，純Zr的凝固組織顯著細化且趨于均勻，微觀硬度也隨之增高。

The thermophysical properties and dendritic growth kinetics of undercooled liquid zirconium were investigated by electrostatic levitation method. The results show that the hypercooling limit and specific heat of liquid zirconium are determined to be 524 K(0.25Tm) and 41.03 J/(mol？K), respectively, according to the relationship between undercooling and solidification plateau time. Meanwhile, the measured density, viscosity and surface tension of molten zirconium display a linear increase with the decrease of temperature. The hemispherical total emissivity of liquid zirconium is derived from the thermal equilibrium equation, which exhibits an increase tendency within the temperature range of 1752-2315 K. Besides, the dendritic growth velocity is experimentally measured by using a high speed camera according to the in-situ observation of S/L interface migration during recalescence, which agrees well with the theoretical prediction of LKT/BCT rapid dendritic growth model. The dendritic growth velocity shows a power increase relationship with undercooling, which reaches 48 m/s at the maximum undercooling of 376 K(0.18Tm). In addition, the Vickers microhardness of rapidly solidified pure zirconium is derived as an increase tendency with enhanced undercooling.

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