铝基金属玻璃的形成及其局域原子结构的研究

发布时间：2018-02-27 20:09

本文关键词： Al基金属玻璃玻璃形成能力热稳定性局域原子结构二十面体团簇　出处：《浙江大学》2016年硕士论文　论文类型：学位论文

【摘要】：金属玻璃(Metallic glasses, MGs)是非晶态材料大家庭的新成员,具有长程无序而短程有序的原子排列,呈现出许多相对于传统晶态金属材料更加优异的性能。其中Al基金属玻璃由于密度低强度高等特性,一直是新材料研究的热点之一。然而其较低的玻璃形成能力(Glass forming ability, GFA)以致目前仅能得到较小的临界尺寸是制约Al基金属玻璃工业应用的主要因素。因此,本论文主要针对Al基金属玻璃的玻璃形成能力和局域原子结构两个方面开展研究,取得了以下研究成果：(1)在Al基合金中,通过Y元素与La元素的相互替换以及Co元素对Ni元素的替换,研究了相似元素的添加对玻璃形成能力的影响。此外,通过Ca元素的添加,研究Al86-xNi7Y4.5Co1La1.5Cax (x= 0-5 at.%)金属玻璃的热稳定性和玻璃形成能力的变化。结果表明Al89Y11比Al91.5La8.5具有更强的玻璃形成能力。随着Y/La配比的改变,发现二元Al91.5La8.5合金中部分La元素被Y元素替换后玻璃形成能力显著提升,而通过La元素对Al89Y11中Y元素的部分替换,其对玻璃形成能力的影响十分有限。通过Co元素对(Al90Y6.6La3.4)92Ni8成分中Ni元素的部分替换,结果表明Co元素的添加并不能提升其玻璃形成能力；由于Ca原子与Al原子之间存在着较大的原子半径尺寸差和较大负的混合热,所以Ca元素的添加能够有效抑制fcc-Al晶体相的析出,较大提升A186-XNi7Y4.5CoLa1.5Cax金属玻璃的热稳定性和玻璃形成能力。(2)通过对Al89Y11、Al90Y6.5La3.5和Al82.8Y6.07Ni8La3.13三种成分的金属玻璃进行示差扫描热分析,高能X射线衍射和X射线吸收谱等实验,并结合从头算分子动力学模拟与反蒙特卡洛模拟系统研究了这三种铝基金属玻璃中的局域原子结构特征,并对原子结构与玻璃形成能力之间的关联性进行了探讨。结果表明Al89Y11、Al90Y6.5La3.5和Al82.8Y6.07Ni8La3.13金属玻璃中占主导作用的近邻原子对为X-Al(X=Al、Y、La或Ni)配对。二元Al89Y11中存在着一定的Y-Y原子对,随着La的添加在三元Al90Y6.5La3.5中少量La原子分布在了Y的周围形成了La-Y配对；四元Al82.8Y6.07Ni8La3.13中至少有1个Ni原子分布在Y或La的近邻周围从而形成少量的Ni-Y和Ni-La的配对；La元素的添加虽然提升了体系局域原子的混乱度或无序度,同时以La为中心的高配位原子团簇的存在导致了有利于非晶形成的二十面体或类二十面体团簇的减少,因此总体上看La的加入对Al-Y体系GFA的影响十分有限。四元成分的Al82.8Y6.07Ni8La3.13金属玻璃中,Ni原子与Al、Y和La原子之间都存在着一定的近邻配位关系,从而大大增加了局域原子的无序度。此外,四元体系中形成了以Ni为中心的类二十面体原子团簇,从而相比三元Al90Y6.5La3.5金属玻璃,Ni的存在提高了原子团簇之间的联结性和紧密度,抑制了晶体相的析出,从而能够提高玻璃形成能力。
[Abstract]:Metallic glasses (MGs) is a new member of the amorphous material family with long range disordered and short range ordered atomic arrays. The Al-base metallic glass is characterized by its low density and high strength. However, its low glass-forming ability and its ability to obtain only small critical size are the main factors restricting the industrial application of Al-based metallic glass. In this thesis, the glass-forming ability and local atomic structure of Al-base metallic glasses were studied. The following results were obtained: 1) in Al-base alloys. The influence of the addition of similar elements on glass forming ability was studied by the substitution of Y element and La element and the substitution of Co element to Ni element. The thermal stability and glass-forming ability of Al86-xNi7Y4.5Co1La1.5Cax glass were studied. The results showed that Al89Y11 had stronger glass-forming ability than Al91.5La8.5. It was found that the glass-forming ability of partial La element in binary Al91.5La8.5 alloy was significantly improved after the substitution of Y element, but the partial substitution of Y element in Al89Y11 was achieved by La element. The effect of Co on glass-forming ability is very limited. Through the partial substitution of Ni in Al90Y6.6La3.4Ni8 by Co element, the results show that the addition of Co element can not improve the glass-forming ability of Al90Y6.6La3.4Ni8. Due to the large atomic radius difference and negative mixing heat between Ca atom and Al atom, the addition of Ca can effectively inhibit the precipitation of fcc-Al crystal phase. The thermal stability and glass-forming ability of the metal glass A186-XNi7Y4.5CoLa1.5Cax were greatly improved. The thermal stability and glass-forming ability of the metallic glass were studied by differential scanning calorimetry (DSC), high energy X-ray diffraction (HXXRD) and X-ray absorption spectroscopy (XRD). Using ab initio molecular dynamics simulation and anti-Monte Carlo simulation system, the local atomic structure characteristics of the three aluminum-based metallic glasses were studied. The relationship between atomic structure and glass-forming ability is also discussed. The results show that the nearest neighbor pairs in Al89Y11Al90Y6.5La3.5 and Al82.8Y6.07Ni8La3.13 metallic glass are X-AlXX Alyyni-La or Ni) pairs. There are some Y-Y pairs in binary Al89Y11. With the addition of La, a small amount of La atoms distribute around Y in ternary Al90Y6.5La3.5 to form La-Y pairing. At least one Ni atom in the quaternary Al82.8Y6.07Ni8La3.13 is distributed around the nearest neighbors of Y or La to form a small amount of Ni-Y and Ni-La pairing La elements, although the degree of confusion or disorder of the local atoms in the system is increased. At the same time, the existence of high coordination atom clusters centered on La leads to the decrease of 20 hedrons or 20 hedrons which are favorable to the formation of amorphous crystals. Therefore, the effect of La addition on the GFA of Al-Y system is very limited. There is a close neighbor coordination relationship between Ni atom and Alniy and La atoms in Al82.8Y6.07Ni8La3.13 metallic glass with quaternary composition. Therefore, the disorder degree of local atoms is greatly increased. In addition, a kind of 20 hedron atom cluster centered on Ni is formed in the quaternary system. Compared with the existence of Ni in ternary Al90Y6.5La3.5 metallic glass, the connectivity and compactness of the clusters are improved. The precipitation of crystal phase was inhibited and the glass forming ability was improved.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG139.8

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