Cu-Zr和Cu-Ag合金溶体结构动力学表征及非晶动态力学性能研究

发布时间：2018-04-29 23:01

本文选题：难混溶合金熔体 + 结构不均匀性　；参考：《山东大学》2017年硕士论文

【摘要】：本文采用分子动力学模拟的方法,运用修正的镶嵌原子势(MEAM),研究了易混溶的Cu-Zr和难混溶的Cu-Ag合金熔体的结构及动力学特征的差异并探讨了两种体系非晶的动态力学性能。以上研究对于认识金属玻璃的本质、玻璃转变机制以及变形机制具有重要意义。对于Cu-Zr合金熔体,当温度低于1200K,MSD曲线上出现一个平台,并且随着温度的降低,平台逐渐明显。而对于Cu-Ag体系,平台出现的时间较短,甚至可以忽略。对扩散系数研究发现Cu-Zr体系的扩散系数远远低于Cu-Ag体系。非相干散射因子Fs(q,t)的计算结果与MSD曲线呈现相同的趋势,说明Cu-Zr体系比Cu-Ag体系具有更明显的β弛豫现象。根据MCT理论对扩散系数和弛豫时间进行了拟合,发现由两者拟合得到的临界温度Tc值差别不大,说明扩散系数与弛豫时间之间的相关性。对两个体系的结构分析,发现Cu-Zr体系中0 0 12 0、0 2 8 1和0 2 8 0等正二十面体和五次对称性强的类二十面体的数量远远高于Cu-Ag体系,并且这些团簇数量随着温度的降低逐渐增加;Cu-Ag体系中的多面体主要是0 3 6 3、0 3 6 4和0 2 8 2等一些非二十面体团簇和类晶型团簇。二十面体和类二十面体团簇易形成骨架阻碍原子运动,原子运动减慢,原子扩散系数降低,弛豫时间增加,从而导致Cu-Zr体系的扩散能力远远低于Cu-Ag体系,非晶形成能力远远高于Cu-Ag体系。两种体系在过冷条件下弛豫时间与五次对称符合关系τα=τ0expM/(1-W)σ扩散系数与五次对称符合关系D=A*(T*W)B,揭示了微观结构与动力学的内在联系。对两者非晶动态力学性能的研究,发现Cu-Zr和Cu-Ag两种体系的β弛豫都是以过剩尾的形式在损耗模量曲线体现出来的,但是Cu-Ag体系在αα弛豫峰左侧部分高于Cu-Zr体系,这表明Cu-Ag体系的β弛豫比Cu-Zr体系更容易激活,这是由于Cu-Zr非晶的二十面体团簇的数量远远高于Cu-Ag非晶。研究了机械应变对两种体系动态力学性能的影响,发现升高温度和增大振幅对两种体系来说对应的弛豫过程是很相似的,说明机械应变和温度对体系的弛豫动力学起到相似的作用,机械应变对弛豫动力学的影响具有普遍性。同时研究了α弛豫与结构不均匀性的相互关系,发现对于Cu-Zr体系,在α弛豫峰峰值温度,原子最可能的位移距离与平均最近邻原子间距的比值(up/rp)接近一个常数,约为23%,而对于Cu-Ag体系,up/rp的数值约为21%。说明α弛豫通常发生在原子移动距离是平均原子间距的约为21%-23%处,这与文献结果一致。进一步研究了两者内耗关系,发现内耗与快原子近似地满足一次线性关系,由于Cu-Zr体系中正二十面体数量远远多于Cu-Ag体系,抑制了原子运动,使快原子数量减少,因此导致了 Cu-Zr体系的内耗小于Cu-Ag体系。
[Abstract]:In this paper, the structure and dynamic characteristics of the melt of easily miscible Cu-Zr and inmiscible Cu-Ag alloy are studied by means of molecular dynamics simulation and modified inlay atomic potential. The dynamic mechanical properties of the two systems are also discussed. The above studies are of great significance in understanding the nature, glass transition mechanism and deformation mechanism of metallic glass. For the melt of Cu-Zr alloy, a platform appears when the temperature is below 1200kg, and with the decrease of temperature, the platform becomes more and more obvious. For the Cu-Ag system, the platform appears in a short time, even can be ignored. The diffusion coefficient of Cu-Zr system is much lower than that of Cu-Ag system. The calculated results of the incoherent scattering factor (FslQ) show the same trend as the MSD curve, which indicates that the 尾 -relaxation of Cu-Zr system is more obvious than that of Cu-Ag system. According to the MCT theory, the diffusion coefficient and relaxation time are fitted. It is found that there is little difference between the critical temperature T _ c obtained from the two fitting results, which indicates the correlation between diffusion coefficient and relaxation time. It is found that the number of normal icosahedron and icosahedron with strong quintic symmetry in Cu-Zr system is much higher than that in Cu-Ag system, and the number of icosahedron and icosahedron in Cu-Ag system is much higher than that in Cu-Ag system. Moreover, the number of these clusters increases with the decrease of temperature, and the polyhedron in Cu-Ag system is mainly composed of some non-icosahedron clusters and crystal like clusters such as 0.363N 0.364 and 0.282. Icosahedron and icosahedron clusters are easy to form skeletons that hinder the movement of atoms, slow down the atomic movement, decrease the atomic diffusion coefficient and increase the relaxation time, resulting in the diffusion ability of the Cu-Zr system being much lower than that of the Cu-Ag system. The ability of amorphous formation is much higher than that of Cu-Ag system. The relaxation time and the quintic symmetry coincidence relation 蟿伪 = 蟿 0expM / l W) 蟽 diffusion coefficient of the two systems under undercooling conditions and the five-order symmetry coincidence relation D _ (a) A ~ (1) T _ (T) W _ (B) reveal the intrinsic relationship between microstructure and dynamics. It is found that the 尾 -relaxation of both Cu-Zr and Cu-Ag systems is reflected in the loss modulus curve in the form of excess tail, but the Cu-Ag system is higher than the Cu-Zr system on the left side of 伪 relaxation peak. This indicates that 尾 -relaxation in Cu-Ag system is easier to activate than that in Cu-Zr system, which is due to the fact that the number of Cu-Zr amorphous icosahedron clusters is much higher than that of Cu-Ag amorphous. The effect of mechanical strain on the dynamic mechanical properties of the two systems is studied. It is found that the relaxation process corresponding to the two systems is very similar to the increase of temperature and amplitude. The results show that mechanical strain and temperature play a similar role in the relaxation kinetics of the system, and the influence of mechanical strain on the relaxation kinetics is universal. At the same time, the relationship between 伪 relaxation and structural inhomogeneity is studied. It is found that for Cu-Zr system, the ratio of the most probable displacement distance of atoms to the average nearest neighbor distance is close to a constant at the peak temperature of 伪 relaxation peak. About 23, and for the Cu-Ag system uprp is about 21. It is shown that 伪 -relaxation usually occurs at a distance of about 21% to 23% of the average atomic distance, which is consistent with the results in the literature. It is found that the linear relationship between internal friction and fast atoms is approximately linear. Because the number of normal icosahedrons in Cu-Zr system is much larger than that in Cu-Ag system, the atom motion is restrained and the number of fast atoms is reduced. Therefore, the internal friction of Cu-Zr system is smaller than that of Cu-Ag system.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139.8

【参考文献】