The effect of pressure on the crystallization of rapidly supercooled zirconium melts
The effect of pressure on the crystallization of rapidly supercooled zirconium melts
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压力对快速过冷锆熔体结晶的影响
DOI：
10.1039/c7cp00865a
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发表时间：
2017
影响因子：
3.3
通讯作者：
Hou Zhaoyang
中科院分区：
文献类型：
--
作者：
Zhang Haitao;Mo Yunfei;Tian Zean;Liu Rangsu;Zhou Lili;Hou Zhaoyang
采用分子动力学模拟方法研究了压力（P）对快速冷却条件下锆（Zr）晶化过程的影响。用系统能量、对分布函数和最大标准聚类分析方法分析了结构演化。结果发现，在零压下Zr熔体通过bcc中间态晶化为hcp晶体的冷却速率为1.0 × 1011 K s-1时，玻璃化的临界压力（Pc）约为28.75 GPa，压力越大，玻璃化转变温度Tg越高。当P < Pc时，Ostwald阶梯规则适用于Zr熔体。在压力下快速过冷Zr熔体的晶化总是从bcc相开始，在hcp晶体中结束;压力越高，晶化的起始温度（Tc）越低。与零压下的单中间态结晶（SisC）不同，在压力下通常观察到多中间态结晶（MisC）。结构分析表明，如果成核基本上是在第一结晶（bcc为主）阶段结束时完成，MisC将发生;否则，SisC发生。并从压力对热力学和动力学因素的影响讨论了这种现象的起因。这些结果有助于全面理解金属在压力下的凝固过程。
Molecular dynamics simulations have been performed to explore the effect of pressure (P) on the crystallization of zirconium (Zr) under rapid cooling. The structural evolutions have been analysed in terms of the system energy, the pair distribution function and the largest standard cluster analysis. It was found that at the cooling rate of 1.0 × 1011 K s−1, which can crystallize Zr melts into hcp crystals via the bcc intermediate state under zero pressure, the critical pressure (Pc) for vitrification is about 28.75 GPa, and the larger the pressure, the higher the glass transition temperature Tg. At P < Pc the Ostwald's step rule is applied to Zr melts. Crystallization of rapidly super-cooled Zr melts under pressure always begins with the bcc phase and ends in the hcp crystal; the higher the pressure, the lower the onset temperature (Tc) of crystallization. Unlike the single-intermediate-state crystallization (SisC) under zero pressure, multiple-intermediate-state crystallization (MisC) is usually observed under pressure. Structural analysis reveals that if nucleation is essentially completed at the end of the first crystalline (bcc-dominated) stage, MisC will occur; otherwise, SisC occurs. The origin of such an observation is also discussed from the effect of pressure upon the thermodynamics and kinetics factors. These findings are useful for comprehensively understanding the solidification of metals under pressure.