静电悬浮条件下液态锆的热物理性质与快速枝晶生长

Thermophysical properties and rapid dendritic growth of liquid zirconium under electrostatic levitation condition

利用静电悬浮实验技术研究Zr熔体的深过冷和枝晶生长动力学机制,并测定了液态Zr的密度、黏度和表面张力等热物理性质。结果表明:液态Zr的超过冷临界过冷度为524 K(0.25T_m),平均比热为41.03 J/(mol?K)。基于热平衡方程测定出液态Zr在1752～2315 K温度区间内的辐射率随温度升高而增大,熔点处其值为0.312。液态Zr的密度、黏度和表面张力均随温度降低呈上升趋势。同时,通过高速CCD摄像方法测得纯Zr的枝晶生长速度随过冷度以幂函数形式增大,在最大过冷度376 K(0.18T_m)处,枝晶生长速度达到48 m/s。此外对其凝固组织的研究发现,随着过冷度的增大,纯Zr的凝固组织显著细化且趋于均匀,微观硬度也随之增高。

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.