Zr基非晶合金微观结构与玻璃形成能力的关联性研究
本文选题:非晶合金 + 玻璃形成能力 ; 参考:《南京航空航天大学》2016年博士论文
【摘要】:非晶合金具有长程无序短程有序的结构特点,因此其拥有许多比晶态合金更加优异的宏观性能,但也使其微观结构的研究充满挑战。而非晶合金微观结构的研究对理解其宏观性能具有重要的意义。非晶合金的玻璃形成能力(GFA)对于成分的改变十分敏感,改变一点成分配比或者微量掺杂都会导致GFA的显著变化,而且由于影响GFA的微观结构因素目前尚不清楚,因此很难从根本上解决GFA对成分的高度依赖性。为了能够开发具有高GFA的非晶合金,澄清微观结构与GFA之间的关联性就显得尤为重要。在本工作中,我们选择Zr基合金体系作为研究对象,寻找影响非晶合金GFA的微观结构层面的因素与机制。基于同步辐射X射线衍射实验和X射线吸收实验,结合理论模拟计算研究了Zr Cu二元合金体系的微观结构。在选取的五种成分中,不同样品之间的微观原子团簇的化学或几何特征没有显著区别,但是可以探测到在GFA最佳点Cu64Zr36成分处的非晶相中Zr原子(溶质原子)为中心团簇具有更高的原子堆积效率,并且相对于以溶剂原子为中心团簇,以溶质原子为中心团簇为更加致密的结构单元。通过对团簇的规则度分析发现GFA最佳点Cu64Zr36成分处的非晶相中的团簇具有相对较高规则度。以上结构特征使得非晶结构更为稳定,因此对比其他成分相近的非晶相,Cu64Zr36具有最高GFA。利用同步辐射X射线衍射实验和同步辐射X射线吸收实验并结合RMC模拟、Voronoi分形分析等方法系统研究了Zr50Cu50二元非晶合金与Zr48Cu45Al7三元非晶合金的微观结构特征。发现Al原子与其近邻的Zr和Cu原子之间存在强的杂化相互作用,导致了Al-Zr、Al-Cu原子对间距的缩短,进而引起Zr48Cu45Al7微观团簇体积的收缩,使得非晶合金局部结构在团簇尺度存在致密堆积,导致Zr48Cu45Al7 GFA显著增强。利用同步辐射技术与理论模拟方法从结构层面揭示了在Zr Cu Al大块非晶合金的基础上分别进行Gd、Ag和Fe元素掺杂从而导致其GFA显著提高的原因。在Zr Cu Al Gd四元体系中,Zr45Cu46Al7Gd2样品中由于添加2%含量Gd元素,使得以溶质原子为中心团簇的数量与稳定性都有所增加,并且导致在原子和团簇层面其结构具有相对更高的堆积效率,可以显著增强其GFA。但在Zr42Cu46Al7Gd5样品中,由于出现Al-Gd(溶质原子-溶质原子)直接键合,原子结构的堆积效率降低,导致GFA的降低;在Zr Cu Al Ag四元体系中,发现Ag掺杂于Zr Cu Al体系之后,不仅增加了Al原子周围的类二十面体局域结构的含量,而且使得Zr和Cu原子为中心的团簇更规则。这些结构因素使得玻璃态结构更加稳定,显著增强了合金体系的GFA。然而,当加入过量Ag时,以上结构因素起到的作用被削弱,导致了GFA的降低;在Zr Cu Al Fe四元体系中,发现Zr60Cu25Fe5Al10样品中含有大量具有高五次对称性特征的结构,其团簇也更规则,原子堆积效率更高,在异种原子之间存在强的相互作用。以上结构特点导致Zr60Cu25Fe5Al10具有更高的GFA。而当Fe掺入过量时,以上结构特点被削弱,导致GFA的降低。选用大块非晶合金成分Zr48Cu45Al7在不同冷却速率下得到棒状(低冷却速率)和条带(高冷却速率)样品,利用同步辐射技术结合模拟计算研究了两种样品的微观结构。在改变冷却速率的情况下,非晶合金中的以Zr原子为中心的局域结构没有发生明显的变化,而Al原子和Cu原子周围的局域结构发生了较大的变化,主要表现为在棒状样品的Cu原子周围的近邻配位数小于条带样品,而Al原子周围的近邻配位数则大于条带样品;棒状样品的Al原子周围的近邻原子更趋向于分布在相对局域化的位置。棒状样品中Al和Cu原子为中心的团簇的原子堆积效率高于条带样品,特别是以Al原子为中心团簇的原子堆积效率的差别最大,达到1.6%;相对于条带样品,棒状样品中Al原子周围的局域结构更规则。而Al原子因为其浓度较低,可被视为溶质原子,所以可以推断溶质原子为中心的局域结构比溶剂原子为中心的局域结构对冷却速率更为敏感。
[Abstract]:Amorphous alloys have the structural characteristics of long range disorder and short range order, so they have a lot of better macroscopic properties than crystalline alloys, but it also challenges the study of their microstructure, and the study of the microstructure of amorphous alloys is of great significance for understanding its macroscopic properties. The glass forming ability (GFA) of amorphous alloys is of great importance. The change of the fraction is very sensitive. Changing a bit of composition or trace doping will lead to significant changes in the GFA, and it is difficult to fundamentally solve the high dependence of the GFA on the composition because of the microstructural factors affecting the GFA. In order to develop the amorphous alloy with high GFA, the microstructure and GFA can be clarified. In this work, we choose the Zr based alloy system as the research object and find the factors and mechanisms to influence the microstructure of amorphous alloy GFA. Based on the X ray diffraction experiment of synchrotron radiation and the X ray absorption experiment, the microstructure of the Zr Cu two element alloy system is studied and studied in theory. In the selected five components, there is no significant difference in the chemical or geometric characteristics of the microscopic atomic clusters between different samples, but it can be detected that the Zr atom (solute atom) of the Zr atom (solute atom) at the amorphous phase of the Cu64Zr36 component at the best point of the GFA has a higher atomic accumulation efficiency, and is soluble in relation to the solvent atom as the central cluster. The mass atom is the denser structural unit of the central cluster. By the analysis of the regularity of the cluster, it is found that the clusters in the amorphous phase of the GFA best point Cu64Zr36 have relatively high regularity. The above structural features make the amorphous structure more stable, so Cu64Zr36 has the highest GFA. utilization compared to the other amorphous phase. Synchrotron radiation X ray diffraction (synchrotron radiation) and synchrotron radiation X ray absorption experiments, combined with RMC simulation and Voronoi fractal analysis, have been used to systematically study the microstructure characteristics of Zr50Cu50 two element amorphous alloy and Zr48Cu45Al7 three element amorphous alloy. It is found that there is a strong hybrid interaction between Al atoms and their adjacent Zr and Cu atoms, resulting in Al-Z. The shortening of the space between R and Al-Cu atoms causes the contraction of the size of the Zr48Cu45Al7 cluster, which makes the local structure of the amorphous alloy dense accumulation in the cluster scale and leads to the significant enhancement of the Zr48Cu45Al7 GFA. Using the synchrotron radiation technique and the theoretical simulation method, the amorphous alloy of Zr Cu Al is revealed on the basis of the structure layer. The doping of Gd, Ag and Fe leads to the significant improvement of its GFA. In the Zr Cu Al Gd four element system, the number and stability of the solute atoms as the central cluster increases with the addition of 2% Gd elements in the Zr45Cu46Al7Gd2 sample, and the structure has a relatively higher accumulation effect at the atomic and cluster level. Rate can significantly enhance its GFA., but in Zr42Cu46Al7Gd5 samples, due to the direct bonding of Al-Gd (solute atom), the accumulation efficiency of the atomic structure is reduced and the GFA is reduced. In the Zr Cu Al Ag four element system, it is found that Ag doping in Zr Cu Al system not only increases the local structure of the class twenty surface around the atom, but also the Zr Cu Al system. Content, and make Zr and Cu atoms centered clusters more regular. These structural factors make the glass structure more stable and significantly enhance the GFA. of the alloy system, however, when excess Ag is added, the role of the above structural factors is weakened, resulting in the decrease of GFA; in the Zr Cu Al Fe four element system, the discovery of Zr60Cu25Fe5Al10 samples is found. It contains a large number of structures with high five times symmetry, and its clusters are more regular, with higher atomic accumulation efficiency and strong interaction between dissimilar atoms. The above structural characteristics cause Zr60Cu25Fe5Al10 to have a higher GFA. and when Fe is overdoped, the above structural characteristics are weakened, resulting in the reduction of GFA. The microstructures of the two samples were studied by the synchrotron radiation technique combined with the synchrotron radiation technique at different cooling rates. In the case of changing the cooling rate, the local structure of the Zr precursor in the amorphous alloy has not changed significantly. The local structure around the Al atom and the Cu atom has been greatly changed, which mainly shows that the adjacent neighbour coordination number around the Cu atom in the bar like sample is smaller than the strip sample, while the adjacent neighbour coordination number around the Al atom is larger than the strip sample, and the adjacent adjacent atoms around the Al atoms of the bar like samples tend to be distributed in the relative localization. The accumulation efficiency of the clusters of Al and Cu atoms centered in the rod like samples is higher than that of the strip, especially the accumulation efficiency of the atomic clusters with Al atoms is the largest, reaching 1.6%. Compared with the strip samples, the local structure around the Al atom in the bar like samples is more regular. And the Al atom can be considered as a solute because of its low concentration. Therefore, it can be deduced that the local structure of solute atom centered is more sensitive to the cooling rate than the local structure centered on solvent atoms.
【学位授予单位】:南京航空航天大学
【学位级别】:博士
【学位授予年份】:2016
【分类号】:TG139.8
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