【作者】 王佳明；

【导师】 胡望宇；

【作者基本信息】 湖南大学 ， 凝聚态物理， 2010， 硕士

【摘要】 纳米材料是当前国际材料科学研究的热点之一,纳米技术被认为是21世纪最有前途的研究领域。纳米技术在陶瓷、光电、微电子、生物工程等领域有着广泛的应用。纳米丝作为一种典型的一维纳米材料表现得尤为活跃,其表面原子多,比表面积大,力学性能备受关注。因此,本文对纳米丝力学性能的研究有着重要的实际意义。本文采用改进分析型(EAM)势模型计算原子间的相互作用,利用分子动力学模拟方法,模拟了单晶Mo及Ni3Al纳米丝的单轴拉伸过程,重点分析了纳米丝拉伸过程中的相转变机制以及力学性能,考虑了温度、尺寸等因素对纳米丝力学性能的影响。在相变研究方面,Mo纳米丝在50K下的拉伸过程中共发生两次整体相转变,第一次相变整个纳米丝的构型由bcc结构变为fcc结构,第二次相变纳米丝的构型由fcc结构变为bcc结构。我们计算得到了bcc结构与fcc结构这两种晶格以沿[001]方向双倍层间距为变量的平均原子能量曲线,根据该能量曲线,结合径向分布函数,阐明了由应变驱动的相变机制。在高温下,相变过程更加复杂,相变过程中更多的hcp结构与fcc结构出现,我们的分析表明fcc结构与hcp结构有更好的抗高温性能与抗拉性能。在力学性能研究方面,Mo与Ni3Al纳米丝在不同温度下的模拟结果显示,纳米丝的杨氏模量与屈服强度均随温度的升高而降低。不同尺寸Ni3Al纳米丝的模拟情况表明,纳米丝的杨氏模量与屈服强度都随纳米丝尺寸的增加而增加。在Ni3Al纳米丝中,Re的加入对纳米丝力学性能有很大影响,不同的置换位置对纳米丝力学性能影响差异巨大。我们的研究表明,这种差异与新加入的Re原子和周围原子的结合强弱程度有关。更多还原

【Abstract】 At present, nanomaterials are one of the hottest research points in international materials science. Nanotechnology is considered to be the most promising research area in the 21st century, which is widely used in ceramics, optoelectronics, microelectronics, biotechnology and so on. As a typical one-dimension nanomaterials, nanowires (NWs) which contain a lot of surface atoms and own large surface area to volume ratio is particularly active. The mechanical properties of NWs are the common concerns. Therefore, this article on the mechanical properties of NWs has important practical significance. In present paper, modified analysis embedded-atom method (EAM) is used to describe the interactions between atoms. Using molecular dynamics simulation, we studied the tensile behaviors of Mo and Ni3Al NWs under uniaxial tensile strain. It’s analyzed that the mechanism of phase transitions and mechanical properties under uniaxial tension. The effects of temperature and size on the mechanical properties of NWs are also discussed.The phase transition processes of a single crystal Mo NWs under uniaxial tensile strains were studied at 50K with molecular dynamics simulation. Two phase transitions have been observed during the uniaxial tensile processes. The first one is the configuration of Mo NWs transformed from body-centered cubic (bcc) structure to face-centered cubic (fee) structure and the second one is that transformed from fee structure to bcc structure. The phase structures have also been demonstrated with radial distribution function (RDF) analyses. Two average atom energy curves of bcc structure and fee structure as the function of the double layer space along [001] direction were obtained with the help of embedded-atom method potential calculations, by which the strain-driven bcc-to-fcc and fcc-to-bcc phase transition mechanisms have been clarified clearly for Mo NWs under uniaxial tensile strain. In high temperature, the phase transition processes became more complicated and much more hexagonal close-packed (hcp) structure and fcc structure were found. It’s obvious that hcp and fcc structures are good at high temperature and high pull. At the aspect of mechanical properties, the young’s modulus and yield strengths are decreased with increasing temperature in the tensile processes of Mo and Ni3Al NWs. The young’s modulus and yield strengths are increased with increasing NWs size in the tensile processes of Ni3Al NWs. The mechanical properties of the Ni3Al NWs with Re are different from ones of the Ni3Al NWs. The location of Re in NWs has the obvious effect on the mechanical properties of Ni3Al NWs. According to our study, the difference of mechanical properties is caused by the difference of the bonding strength in Re atom and other atoms around Re atom.更多还原