无序态材料在极端条件下的表现行为

发布时间：2018-04-19 18:47

本文选题：氧族化合物 + 高熵合金　；参考：《浙江大学》2016年博士论文

【摘要】：通过理论与实验的结合,本文对无序的氧族化合物(如非晶As_2Se_3和非晶AsSe)在高压下的行为、化学无序高熵合金在高温高压下的性质以及Zr基金属玻璃在极端压力和温度下动力学行为进行了系统研究,简单介绍了常用的实验方法,详细研究了在高压力和高温极端条件下材料的表现行为及性质。对非晶As_2Se_3施加高压后,我们观察到了可逆的中程序(IRO)断裂过程和对应网状结构转变,发现这样的网络转变是渐进的,并没有观察到密度的突然跳跃。同样在非晶态As_2Se_3中,我们观察到了压力诱导的可逆晶化过程。我们发现,FCC相在高压下超过其自由能总量而变成了亚稳相,对其进行卸压后,非晶相又得以回复。令人惊讶的是,无论是实验结果还是理论模拟,实验前As_2Se_3样品的非晶相和从高压晶体相通过完全卸压回复后得到的非晶相是一致的。我们首次发现,对于一种非晶态材料在加压诱导其晶化和完全卸压后非晶化这两个过程中,局部结构回复到未加压之前的结构,与前人研究有很大的不同而且具有很大的新颖性。与非晶态As_2Se_3类似,对非晶AsSe进行加压,我们也观察到了可逆的中程序(IRO)断裂过程和对应网状结构转变。同样发现这样的网络转变也是渐进的,并没有密度的突然跳跃。我们也对化学无序高熵合金(HEA)在高温和高压下的行为进行了研究。高熵合金在高压下的状态方程发和在高温下的体积热膨胀均为线性变化,表明高熵合金在高温和高压下十分稳定,并没有发生相变。本文也进行了Zr基金属玻璃的低温动力学和玻色峰的研究,建立了Zr基金属玻璃中玻色峰和局部结构的关联性,发现该玻色峰的产生原因是金属玻璃在密度涨落区的回复性波动。
[Abstract]:By combining theory with experiment, the behavior of disordered oxygen compounds (such as amorphous As_2Se_3 and amorphous AsSes) at high pressure is studied. The properties of chemical disordered high entropy alloy under high temperature and high pressure and the kinetic behavior of Zr-based metallic glass under extreme pressure and temperature were systematically studied. The common experimental methods were introduced briefly. The behavior and properties of the materials under high pressure and high temperature extreme conditions were studied in detail. After applying high pressure to amorphous As_2Se_3, we observed the reversible mid-order IRO-fracture process and the corresponding network structure transition. It is found that the network transition is gradual, and no sudden jump of density is observed. The reversible crystallization process induced by pressure was also observed in amorphous As_2Se_3. It is found that the FCC phase becomes metastable phase when it exceeds its free energy at high pressure, and the amorphous phase can be recovered after unloading the pressure. It is surprising that both experimental results and theoretical simulations show that the amorphous phase of the As_2Se_3 sample is consistent with the amorphous phase obtained from the high pressure crystal phase after complete pressure relief recovery before the experiment. We found for the first time that the local structure of an amorphous material reverted to the structure before compression during the process of pressure-induced crystallization and complete post-decompression non-crystallization. It is very different from previous studies and has great novelty. Similar to the amorphous As_2Se_3, the reversibly meshwork fracture process and the corresponding network structure transformation are also observed when the amorphous AsSe is pressurized. It is also found that such a network shift is gradual, and there is no sudden jump in density. We also studied the behavior of chemical disordered high entropy alloy (HEAA) at high temperature and high pressure. Both the equation of state at high pressure and the volumetric thermal expansion at high temperature are linear, indicating that the high entropy alloy is very stable at high temperature and high pressure, and no phase transition occurs. The low temperature kinetics and the Bose peak of Zr-based metallic glass are also studied, and the correlation between the Bose peak and local structure in Zr-based metallic glass is established. It is found that the reason of the Bose peak is the recovery fluctuation of metallic glass in the density fluctuation region.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139

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