【作者】 李峰伟；

【导师】 董星龙； 董闯； 羌建兵；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2013， 博士

【摘要】 成分设计和力学性能研究是块体金属玻璃研究的基础问题。开发具有大玻璃形成能力和高强度、大塑性的块体金属玻璃是该领域的研究目标之一。团簇加连接原子模型作为一种成分设计思想,已被成功应用到许多体系的块体金属玻璃成分设计中。该模型将金属玻璃看作由团簇和连接原子两类结构单元构成,团簇为基于特定原子的第一近邻配位多面体,而连接原子填补团簇间的间隙,相应的,金属玻璃的成分与结构信息可用团簇成分式统一表述成：[团簇](连接原子)x～1,3。本论文以该模型为指导,系统研究了Zr-Ni-Al三元基础非晶体系合金的玻璃形成能力和力学性能,并从团簇加连接原子模型角度探讨了该体系块体金属玻璃合金的力学性能与结构的关系。同时,对Zr-Al-Ni-Cu-(Nb)多组元Zr基块体金属玻璃的力学性能进行了研究。论文主要内容如下：首先,基于团簇加连接原子模型,从Zr-Ni-Al系金属玻璃的三种常见晶化相——-Al2NiZr6、NiZr2(NiTi2-type)和NiZr2(Al2Cu-type)中提取可代表各相结构特征的三类团簇(即CN11Ni3Zr9、CN12Ni4Zr9和CN10Ni3Zr8)作为基础团簇,建立团簇式进行成分设计,获得三个系列合金成分：Ni3Zr9Alx、Ni4Zr9Alx和Ni3Zr9Alx,x=1、1.5、2、3,同时,类比配制Ni3Zr6Alx、Ni3Zr7Alx和Ni3Zr10Alx系列合金作为比较成分。利用不同内径铜模通过真空吸铸法制备上述六系列合金的铸态合金棒,对其进行结构和热分析测试与表征。结果表明,除Ni3Zr6Al3成分外,其余合金金属玻璃形成的临界直径都达到3mm以上。其中,Ni4Zr9Al2(即Zr60Ni26.7Al13.3, at%)玻璃形成能力最佳,其形成玻璃的临界直径达10mm,在同等制备条件下高于已报道的Zr60Ni25Al15最优成分；其过冷液相宽度⊿Tx、约化玻璃转变温度Trg和γm值分别为68K、0.579和0.689,也优于Zr60Ni25Al15(△TX=68K, Trg=0.568, γm=0.676)。进一步电子浓度和团簇式解析表明,Ni4Zr9Al2符合基于Ni3Zr9团簇加三个连接原子的金属玻璃通用团簇式：[Ni3Zr9](Al2Ni)。其次,3mm样品的室温压缩和维氏硬度结果表明,随Al、Ni含量的增加,Zr-Ni-Al块体金属玻璃的屈服强度σy、杨氏模量E和维氏硬度Hv增大。同时发现,这些合金的力学性能与其玻璃转变温度Tg、晶化温度Tx、摩尔体积V以及原子密度ρa存在密切关联。依据电子浓度和金属玻璃通用团簇式判据,总体上可将本文涉及的Zr-Ni-Al块体金属玻璃成分分成两种类型：一种是基于Ni3Zr9团簇加三个连接原子团簇式的；另一类属于Ni3Zr8团簇加一个连接原子的形式；结合元素间混合焓数据,可估算各合金三类键合的相互作用强度I,分别为：团簇的中心原子与壳层原子间的键合Icenter-shell、相邻团簇壳层原子间的键合Ishell-shell和连接原子与壳层原子键合Iglue-shell。研究表明Zr-Ni-Al块体金属玻璃的力学性能与其键合参数(1/Icenter-shell+1/Ishell-shell+1/Iglue-shell)呈良好的线性关联,其中最弱的Ishell-shell是决定块体金属玻璃力学性能的主因。据此,本论文提出一种并联弹簧振子模型阐释了金属玻璃的结构与其强度间的关联。最后,研究了满足Ni4Zr9团簇加一个连接原子团簇式的Zr基Zr-Al-Ni-Cu-(Nb)多元块体金属玻璃的力学性能。探讨了合金化元素Nb对Zr65Al10Ni10Cu15块体金属玻璃力学性能的影响规律,研究了(Zr65Al10Ni10Cu15)97Nb3块体金属玻璃在不同结构状态下的热学与力学性能。结果表明,Nb的加入可有效提高合金屈服强度并影响变形能力,其中含2at.%Nb的块体金属玻璃室温变形能力最高,其压缩时的塑性变形达12.7%。(Zr65Al10Ni10Cu15)97Nb3块体金属玻璃经退火处理,导致其玻璃态结构逐步失稳并引发初始晶化温度下降和过冷液相区变窄,而屈服强度和杨氏模量稍有增大,但室温塑变能力明显下降,其压缩塑变由8%降至几乎消失。更多还原

【Abstract】 Composition design and mechanical properties are two basic issues in the study of bulk metallic glasses (BMGs). Developing BMGs with high glass forming abilities (GFAs) and excellent mechanical properties (e.g. high strength and large plasticity) is one of the targets in this field. Cluster-plus-glue-atoms model, a composition design method developed in our group, has been successfully applied in several metallic glass systems. This model dissociates a glassy structure into a cluster part and a glue atom part. The cluster is the nearest neighbor coordination polyhedron constituted by specific atoms and glue atoms are located between the clusters. The composition and structure information of BMGs can be expressed by a universal cluster formulas [cluster](glue atoms)1,3resulted from this model. In this thesis, the GFAs and mechanical properties of the Zr-Ni-Al and Zr-Al-Ni-Cu-(Nb) BMGs were studied, and the relationship between mechanical properties and glassy structure were discussed from the perspective of the cluster-plus-glue-atom model.The first step for the composition design is to determine the principal clusters, as exemplified by clusters CN11Ni3Zr9, CN12Ni4Zr9, and CN10Ni3Zr8respectively derived from three common devitrification phases Al2NiZr6, NiZr2(NiTi2-type) and NiZr2(Al2Cu-type) in Zr-Ni-Al BMGs. Three alloy series were thus designed, namely Ni3Zr9Alx, Ni3Zr8Al and Ni4Zr9Alx,(x=1,1.5,2,3). Analogically, Ni3Zr6Alx, Ni3Zr7Alx and Ni3Zr10Alx alloy series were designed for comparisons. Alloy rods with different diameters of these compositions were prepared by copper mould suction casting, and their structure and thermal glass parameters were investigated. The experimental results showed that all the rods, except Ni3Zr6Al3, were in amorphous state within a rod diameter of3mm. Composition Ni4Zr9Al2(Zr60Ni26.7Al13.3, at%) could be cast into rods with a critical glass forming diameter of10mm, whose GFA was even higher than that of the reported best glass former Zr6oNi25Al15prepared in the same preparation conditions. Its supercooled liquid region△Tx, reduced glass transition temperature Trg and γm were respective68K,0.579and0.689, which were also higher than those of Zr6oAl15Ni25(△TX=68K,Trg=0.568, γm=0.676). After analysis for electron concentration (e/a) and cluster formula, Ni4Zr9Al2was shown to satisfy a cluster formula based on the Ni3Zr9cluster plus three glue atoms [Ni3Zr9] Al2Ni.Room temperature compression and Vickers hardness tests of the3mm-diameter BMGs were carried out. Their yield strength (σy), Young’s modulus (E) and Vickers hardness (Hv) increased with increasing contents of Al and Ni and were closely related with glass transition temperature (Tg), crystallization temperature (Tx), molar volume (V) and atomic density (ρa). The e/a and cluster formula analysis of these Zr-Ni-Al BMGs showed that they belonged to two glass series respectively expressed by cluster formulas [Ni3Zr9](glue atom)3and [Ni3Zr8](glue atom)1. An estimation of the bonding strength, I, between the three kinds of bonds prescribed by the cluster formulas, i.e. the bonds between the cluster center and the cluster shell (Icenter-shell), between the cluster shells (Ishell-shell), and between the glue atom and the shell (Iglue-shell), were calculated in terms of the enthalpy of mixing. It was found that the mechanical properties of the Zr-Ni-Al BMGs were linearly correlated with1/Icenter-shell+1/Ishell-shell+1/Iglue-shell.The mechanical properties of the Zr-Ni-Al BMGs were mainly dominated by the weakest shell-shell interaction. A spring model was therefore proposed to explain the relationship between structure and strength of metallic glasses.Finally, the mechanical properties of Zr-based Zr-Al-Ni-Cu-(Nb) BMGs which satisfy cluster formula of Ni4Zr9cluster plus one glue atom, and the effect of alloying element Nb on the mechanical properties of Zr65Al10Ni10Cu15BMG, and the thermal properties and mechanical properties of (Zr65Al10Ni10Cu15)97Nb3BMG under different structural conditions were studied. It was shown that the yield strength increased effectively and affect deformation ability with Nb addition. The compression plasticity reached12.7%in the sample with2at.%Nb addition. With annealing treatment, the structure of (Zr65Al10Ni10Cu15)97Nb3BMG became unstable, and the initial crystallization temperature and supercooled liquid region decreased. Meanwhile, the yield strength and Young’s modulus increased, but the compression plasticity decreased from8%to nearly0%.更多还原