Development of shear band structure during deformation of a Zr57Ti5Cu20Ni8Al10 bulk metallic glass
Development of shear band structure during deformation of a Zr57Ti5Cu20Ni8Al10 bulk metallic glass
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DOI：
10.1016/s1359-6462(00)00527-3
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发表时间：
2000-11-27
影响因子：
6
通讯作者：
Vinci, RP
中科院分区：
文献类型：
--
作者：
Hufnagel, TC;El-Deiry, P;Vinci, RP
能够以大块形式形成金属玻璃的合金的发展(1)使得在更大范围的加载条件下进行机械测试成为可能，而不是使用早期的玻璃形成合金（只能生产成薄带）。这促使了最近几项关于力学性能的研究，包括在准静态和高应变率下的单轴压缩行为（2-3），施加静水应力对流动和断裂的影响(4)，以及断裂韧性（5-9）。因此，我们对金属玻璃力学行为的基本方面的理解正在迅速提高。即使在这些最近的研究之前，从早期的工作中众所周知，金属玻璃中的塑性变形集中在称为剪切带的狭窄区域，除非温度足够高，允许均匀流动（10）。在某些几何形状（如单轴拉伸）中，产生的变形是不稳定的，在屈服开始后不久就会发生破坏。在其他几何形状中，例如弯曲和单轴压缩，可以形成多个剪切带，从而导致明显的“弹塑性”行为（10）。我们在环境扫描电子显微镜（ESEM）下原位检测了非晶Zr57Ti5Cu20Ni8Al10在三点弯曲试验中的变形，同时记录了载荷-挠度数据。我们观察到，第一个剪切带的出现与塑性变形的开始一致；没有“均匀”塑性变形的证据。随着荷载的增加，剪切带数量急剧增加，直至最大荷载点。我们在荷载-位移曲线中看到屈服下降或“锯齿状流动”，这似乎与新剪切带的开始有关。超过最大荷载点的持续变形主要是由于沿现有剪切带的滑移；这种滑移似乎是连续的，而不是间歇性的（在我们实验的时间分辨率范围内）。随着滑移的发生，新的次级剪切带在原有的主剪切带上产生。破坏发生在最大拉应力表面的一个主剪切带上。
The development of alloys capable of forming metallic glasses in bulk form (1) makes it possible to conduct mechanical testing under a much wider range of loading conditions than was possible with earlier glass-forming alloys (which could only be produced as thin ribbons). This has prompted several recent studies of mechanical properties, including behavior under uniaxial compression at quasistatic and high strain rates (2–3), the effect of applied hydrostatic stress on flow and fracture (4), and fracture toughness (5–9). As a result, our understanding of fundamental aspects of the mechanical behavior of metallic glasses is rapidly improving.Even before these recent studies, it was well known from earlier work that plastic deformation in metallic glasses is concentrated into narrow regions called shear bands, except at temperatures sufficiently high to allow homogeneous flow (10). In certain geometries (such as uniaxial tension) the resulting deformation is unstable and failure follows shortly after the onset of yielding. In other geometries, such as bending and uniaxial compression, multiple shear bands can form, resulting in behavior that is apparently “elastic-perfectly plastic”(10). We have examined the deformation of amorphous Zr57Ti5Cu20Ni8Al10 in situ in an environmental scanning electron microscope (ESEM) during a three-point bend test, while simultaneously recording load-deflection data. We observe that the appearance of the first shear bands coincides with the onset of plastic deformation; there is no evidence for “homogeneous” plastic deformation. As the load increases, the number of shear bands increases dramatically up to the point of maximum load. We see yield drops or “serrated flow” in the load-displacement curve which appear to be correlated with the initiation of new shear bands. Continued deformation beyond the point of maximum load occurs primarily as the result of slip along existing shear bands; this slip appears to be continuous, rather than intermittent (within the time resolution of our experiment). As slip occurs, new secondary shear bands initiate at the previously existing primary bands. Failure occurs by fracture initiated on one of the primary shear bands on the surface of maximum tensile stress.