块体非晶合金的形成、结构与流变性能研究

发布时间：2018-05-16 04:23

本文选题：块体非晶合金 + 非均匀性　；参考：《湘潭大学》2016年博士论文

【摘要】：块体非晶合金(BMG)因具有独特而优异的物理、化学和力学性能引起了人们极大的关注。BMG不仅在国防、航空航天、机械和电子电力等领域有着广阔的应用前景,同时它也是研究非晶材料的结构、玻璃转变和变形机理等基本科学问题的理想研究对象。目前人们已成功开发了众多的非晶合金系,有的已在工程中得到了应用。然而较低的玻璃形成能力(GFA)和室温塑性仍然是很多非晶合金系应用的主要障碍。洞悉非晶合金的微观结构是理解玻璃形成和变形本质,并进一步开发性能更优的非晶合金的关键。本文以Zr-Cu-Al、Zr-Ni-Al和Zr-Cu-Al-Nb等Zr基块体非晶合金为研究对象,应用第一性原理分子动力学(AIMD)模拟结合实验结果的方法,对非晶合金的微观结构与玻璃形成以及流变行为的关系进行了系统深入的研究。全文工作和主要结果总结如下:1、基于经典结晶理论研究了非晶合金的流变性能与GFA的影响。结果表明,合金的等温转变曲线“鼻尖”温度T_n处的黏度与GFA成正比,同时晶化开始温度Tx处的黏度与GFA成反比或液相线温度T_l对应的黏度与GFA成正比。由此得到了新的GFA参数ψ0=(T_g-T_0)/(T_n-T_0)+(T_g-T_0)/(T_l-T_0),其中T_g为玻璃转变温度,T_0为理想玻璃转变温度。2、用AIMD研究了Zr_(55-x)Cu_(45)Al_x(x=3,7,12 at.%)非晶合金的玻璃转变过程,并用Honeycutt-Andersen的键型指标和Voronoi多面体等方法分析了其原子结构,以及结构变化对微观流变性能和玻璃形成的影响。我们发现该合金系中添加少量(x=3,7)Al时,以Al为中心的二十面体团簇比以Cu或Zr为中心的团簇要稳定。不管是在热起伏还是在外力作用下,这些以Al为中心的团簇都是最稳定的团簇,可视为该合金系中的基本结构单元;当x=7时,这些稳定原子团簇以共点、共线或共面的方式互相连接形成的二十面体中程序的空间骨架结构,使其整体结构更稳定,原子平均扩散能力更低,GFA更强。3、对(Zr_(0.5)Cu_(0.4)Al_(0.1))_(100-x)Nb_x(x=0,3,6 at.%)非晶合金的实验和AIMD模拟研究结果表明,少量的(3 at.%)Nb的添加后,形成了以Nb为中心的(类)二十面体以及以Al为中心的(类)二十面体原子团簇稳定结构。这两种稳定团簇在合金中互相联接和匹配形成了一种更稳定紧密的结构,而且也增加了结构总体的非均匀性程度,导致其弹性模量、强度以及宏观塑性的提高;而较多的(6 at.%)Nb添加后,一些稳定Nb团簇取代了Al团簇,一定程度降低了这种结构的非均匀性程度,并导致其宏观强度的下降和微观流动性能的提高。4、对Zr_(67)Ni_(33-x)Al_x(x=8,15,21 at.%)非晶合金的AIMD研究表明:该合金系内部存在着以Ni为中心和以Al为中心的两类团簇,其中以Ni为中心的团簇主要为0 3 6、0 3 6 1、0 2 8和0 2 8 1这几种Bernal多面体。而以Al为中心的主要为配位数为12的0 2 8 2、0 3 6 3、0 0 12 0和配位数为13的0 110 2、0 3 6 4等(类)二十面体。(类)二十面体的稳定性一般高过这些Bernal多面体,随着Al含量的提升,以Al为中心的(类)二十面体含量也在不断提高。这就使得合金的强度和弹性模量逐渐提高,而结构的非均匀性程度和流动性能逐渐降低。5、对Zr-Cu-Al(-Nb)和Zr-Ni-Al非晶进行单轴压缩的第一性原理模拟结果显示,合金塑性流动时应力-应变关系出现了原子尺度的“锯齿流变”状的变化。我们发现,随着应变的增加,1551键对和(类)二十面体团簇含量不断减少。1551键对含量变化与这种锯齿状的应力变化具有一定的对应关系。进一步的分析表明在外应力作用下,相对稳定的(类)二十面体团簇转变成为更易流动的无序或类似液态的原子团簇,应力的陡降直接原因是合金内这些稳定团簇含量的减少。这说明具有五次对称结构的(类)二十面体稳定团簇在合金抵抗塑性流动时扮演了类似骨架的角色。
[Abstract]:The bulk amorphous alloy (BMG) has attracted great attention because of its unique and excellent physical, chemical and mechanical properties..BMG not only has a broad application prospect in the fields of national defense, aerospace, mechanical and electronic power, but it is also ideal for the study of the basic scientific problems of the structure of amorphous materials, glass transition and deformation mechanism. At present, many amorphous alloys have been developed successfully, and some have been applied in engineering. However, the low glass forming ability (GFA) and room temperature plasticity are still the main obstacles for many amorphous alloys. The microstructure of the amorphous alloys is the essence of the formation and deformation of the glass, and the further development of the amorphous alloy. The key of amorphous alloys with better performance is to study the relationship between the microstructure of amorphous alloys and the relationship between the microstructure of amorphous alloys and the rheological behavior of Zr based bulk amorphous alloys, such as Zr-Cu-Al, Zr-Ni-Al and Zr-Cu-Al-Nb, with the method of first principle molecular dynamics (AIMD) simulation combined with experimental results. The full text work and the main results are summarized as follows: 1, based on the classical crystallization theory, the influence of the rheological properties of amorphous alloy and GFA is studied. The results show that the viscosity of the temperature T_n at the tip temperature of the alloy is proportional to the GFA, and the viscosity of the Tx at the beginning of the crystallization temperature is inversely proportional to the GFA or the viscosity of the liquid phase temperature T_l. The new GFA parameter 0= (T_g-T_0) / (T_n-T_0) + (T_g-T_0) / (T_l-T_0) is obtained, in which T_g is the glass transition temperature, T_0 is the ideal glass transition temperature.2. The glass transition process of the amorphous alloy of 45 is studied AIMD, and the key type index and the polyhedron are used. The atomic structure and the effect of structural changes on the microrheological properties and glass formation were analyzed. We found that when a small amount of (x=3,7) Al was added to the alloy system, the twenty - hedral clusters centered on the Al were more stable than the clusters centered on Cu or Zr. These clusters of Al centered clusters, regardless of the thermal fluctuations and external forces, were in the center. The most stable cluster is considered as the basic structural unit in the alloy system. When x=7, these stable clusters are interconnected with each other in a common, coplanar or coplanar way to form the space skeleton of the twenty plane. The overall structure is more stable, the atomic average diffusion capacity is lower, the GFA is stronger.3, and (Zr_ (0.5) Cu_ (0.4) Al_ (0) (0). The experimental and AIMD simulation results of Nb_x (100-x) Nb_x (x=0,3,6 at.%) amorphous alloys show that a small amount of (3 at.%) Nb is added to form a Nb centered (class) twenty - hedral and a Al centered (class) twenty - hedral cluster stable structure. The two stable clusters are linked and matched in the alloy to form a more stable form. The tight structure is fixed, and the degree of inhomogeneity of the structure is increased, which leads to the increase of its modulus, strength and macro plasticity; and after adding more (6 at.%) Nb, some stable Nb clusters replace the Al clusters, which reduces the uneven uniformity of the structure to a certain extent, and leads to the decrease of the macro intensity and the microscopic flow. The improvement of dynamic performance.4, the AIMD study of Zr_ (67) Ni_ (33-x) Al_x (x=8,15,21 at.%) amorphous alloy shows that there are two clusters of clusters with Ni centered and Al centered in the alloy system, of which Ni centered clusters are mainly 03 6,0 36, 28 and 0281. 12 028 2,0 36 3,0 0120 and 0110 2,0 364 (class) twenty of the coordination number 13. (class) the stability of the twenty face is generally higher than these Bernal polyhedron. With the increase of Al content, the content of the Al centered (class) twenty surface body is also increasing. This makes the strength and modulus of the alloy increase gradually, and the structure of the structure. The inhomogeneity and flow performance gradually decrease.5. The first principle simulation of the uniaxial compression of Zr-Cu-Al (-Nb) and Zr-Ni-Al amorphous shows that the stress strain relationship in the plastic flow of the alloy appears at the atomic scale "sawtooth rheology". We find that with the increase of strain, 1551 bond pairs and (class) twenty sides mass Further analysis shows that under the action of external stress, the relatively stable (class) twenty - face clusters change into more easily disordered or similar liquid clusters, and the direct cause of the stress drop is in the alloy. This shows that the content of stable clusters decreases. This shows that the (class) twenty - hedral stable cluster with five symmetric structures plays a similar role as a skeleton in the alloy resistance to plastic flow.

【学位授予单位】：湘潭大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8

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