纳米金属玻璃脆-塑性的转变

Since the first report by Klement et al. in 1960, the metallic glass (MG) has received extensive attention due to their superior mechanical properties such as high strength and large elastic strain. However, the lack of global plasticity under uniaxial tension at room temperature has been considered the Achilles' heel of MG, significantly undercutting their structural applications. The focus of research on MGs in the last decade, as a consequence, has been on improving their plasticity. Nanoglass (NG) consists of nanometer-sized glassy grains and interfaces between them, called glass−glass interfaces having a reduced density relative to the density in the glassy grains. Up to now, a variety of NGs with chemical compositions Au-Si, Au-La, Fe-Si, La-Si, Pd-Si, Ni-Ti, Ni-Zr, and Ti-P have been synthesized by inert gas condensation. Motivated by this development, in the present project, we will perform molecular dynamics simulations on the tensile fracture of Cu50Zr50 NG with a range of glassy grain size from 15 to 5 nm by using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). This project will focus on simulations on the effect of the size of the glassy grain of NG on its mechanical behavior. We will further investigate that whether controlling the size of the glassy grain of NG can tune the mechanical properties of NG. The project will pave the way for using feature size as a design parameter in attaining superior mechanical properties.

金属玻璃自从1960年被报道以来，由于其高强度大弹性应变等优越的机械性能，从而受到了大量广泛的关注。然而，金属玻璃块体材料几乎没有宏观塑性，这成为其作为结构材料的瓶颈。因此近几年来金属玻璃研究领域的重心即是如何改善其塑性。纳米金属玻璃是一种晶粒和晶界都是金属玻璃的材料(晶界的密度要低于晶粒)。且晶粒大小可以达到纳米级。到目前为止，应用惰性气体冷凝法已能成功合成一系列的不同化学组分的纳米玻璃，例如Au-Si, Au-La, Fe-Si, La-Si, Pd-Si, Ni-Ti, Ni-Zr等等。在本研究中，我们将利用分子动力学模拟晶粒大小界于5-15纳米的纳米金属玻璃Cu50Zr50的拉伸断裂过程。我们的工作旨在探究纳米金属玻璃中晶粒的大小如何影响其力学性能，进而探究控制晶粒大小是否能对纳米玻璃的力学性能进行调控的问题。此工作将为利用特征尺寸作为设计参数以获取优异力学性能材料的发展奠定基础

在室温拉伸载荷作用下，金属玻璃沿着单一剪切带发生断裂，几乎没有宏观塑性，这成为其作为结构材料应用的瓶颈。近十年来，金属玻璃领域的研究重心是如何改善其塑性。纳米金属玻璃是一种晶粒和晶界都是金属玻璃组分的材料(但晶界的密度要低于晶粒)。且晶粒大小在制备中可以达到纳米量级。在本研究中，我们采用开源分子动力学软件LAMMPS模拟晶粒大小分别为5，10，15纳米的纳米金属玻璃Cu50Zr50的拉伸断裂过程。我们的研究表明晶粒大小能有效地调控纳米玻璃的力学性能。当晶粒大于5纳米的时候，纳米金属玻璃以剪切带的形式断裂，剪切带的形成由晶界共同参与；但是当晶粒小于5纳米的时候，纳米金属玻璃呈现出惊人的超塑性，均匀地形变。我们进一步研究了断裂模式转变的内在机制。此工作将为利用特征尺寸作为设计参数以获取优异力学性能材料的发展奠定基础。