Although the effect of the deformation field size on the mechanical strength of metallic glasses (MGs) has been investigated thoroughly, a few studies have investigated the effect of the deformation field size on the kinetic creep deformation behavior for these materials. This issue is addressed in the current work by investigating the nanoindentation creep kinetics of La-based MGs under the application of spherical indenters with two different tip radii and three different loading rates. The experimental data are fit to a viscoelastic model to extract the activation volume and relaxation time characteristics of the kinetic nanoindentation creep deformation of the samples. The results demonstrate that the nanoindentation creep kinetics are not only strongly dependent on the loading rate, but also vary significantly with the indenter tip radius. The deformation dynamics is interpreted by the stretched exponent β, indicating its relatively small value at a large loading rate along with a large indenter tip radius. Furthermore, the observed effect of the deformation field size can be attributed to an interplay between the deformation field under the spherical indenter and flow defects associated with the excess free volume, shear transition zone, or shear band embryo with an evolution that is essentially dependent on the loading rate. The current findings contribute to a fundamental understanding of the mechanism of shear softening during creep deformation in MGs.

中文翻译：

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球形压头半径和加载速率对La基金属玻璃动力学纳米压痕蠕变行为的影响

尽管已经充分研究了形变场大小对金属玻璃（MGs）机械强度的影响，但是一些研究已经研究了形变场大小对这些材料的动力学蠕变变形行为的影响。通过研究具有两个不同尖端半径和三个不同加载速率的球形压头，研究了基于La的MG的纳米压痕蠕变动力学，从而解决了该问题。实验数据适合于粘弹性模型，以提取样品的动力学纳米压痕蠕变变形的活化体积和弛豫时间特征。结果表明，纳米压痕蠕变动力学不仅强烈依赖于加载速率，而且还随着压头尖端半径的变化而显着变化。β，表明它在较大的加载速率下相对较小的值以及较大的压头尖端半径。此外，观察到的变形场大小的影响可归因于球形压头下的变形场与流动缺陷之间的相互作用，该流动缺陷与过量的自由体积，剪切过渡区或剪切带胚胎相关，而其演化主要取决于加载率。目前的发现有助于对MGs蠕变变形过程中的剪切软化机理有基本的了解。