Nanoscratching of metallic glasses – An atomistic study
Nanoscratching of metallic glasses – An atomistic study
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DOI：
10.1016/j.triboint.2019.06.017
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发表时间：
2019-08
影响因子：
6.2
通讯作者：
Karina E. Avila;Stefan Kuchemann;I. A. Alhafez;H. Urbassek
中科院分区：
文献类型：
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作者：
Karina E. Avila;Stefan Kuchemann;I. A. Alhafez;H. Urbassek
材料的摩擦学性能在工程应用中起着重要的作用。到目前为止，许多实验研究已经确定了摩擦学参数与力学响应之间的相关性。采用分子动力学模拟方法，研究了cu64.5 zr35.5金属玻璃的纳米刮擦磨损行为。法向力和横向力以及硬度值的演变遵循了众所周知的晶体基底的行为。特别是，正面堆积的产生削弱了材料对划痕尖端的响应，导致横向硬度与正常硬度相比下降。然而，金属玻璃随着温度的升高而软化，特别是在玻璃化转变温度以上，因此在施加应力时显示出更高的结构松弛趋势。这种塑性响应的分析重点是原子的局部区域，这些区域经历了强的冯-米塞斯应变，因为这些是剪切转变区和剪切带的基础。这些原子所占的体积随着温度的升高而增加，但只有在玻璃化转变温度以上才能观察到较大的增加。我们通过塑性效率的概念来量化塑性的产生，它将样品内部塑性体积的产生与外部损伤（即划痕槽）的形成联系起来。与纳米压痕相比，纳米划痕过程中塑料体积的生成速率与温度有很大的关系，这使得玻璃内部在较低温度下更能承受损伤，但在高温下更容易受到损伤。
Tribological properties of materials play an important role in engineering applications. Up to now, a number of experimental studies have identified correlations between tribological parameters and the mechanical response. Using molecular dynamics simulations, we study abrasive wear behavior via nanoscratching of a Cu64.5Zr35.5metallic glass. The evolution of the normal and transverse forces and hardness values follows the behavior well known for crystalline substrates. In particular, the generation of the frontal pileup weakens the response of the material to the scratching tip and leads to a decrease of the transverse hardness as compared to the normal hardness. However, metallic glasses soften with increasing temperature, particularly above the glass transition temperature, thus showing a higher tendency to structurally relax an applied stress. This plastic response is analyzed focusing on local regions of atoms which underwent strong von-Mises strains, since these are the basis of shear-transformation zones and shear bands. The volume occupied by these atoms increases with temperature, but large increases are only observed above the glass transition temperature. We quantify the generation of plasticity by the concept ofplastic efficiency, which relates the generation of plastic volume inside the sample with the formation of external damage, viz. the scratch groove. In comparison to nanoindentation, the generation rate of the plastic volume during nanoscratching is significantly temperature dependent making the glass inside more damage-tolerant at lower temperature but more damage-susceptible at elevated temperatures.