Influence of glass topology and medium range order on the deformation mechanisms in borosilicate glasses, a multiple length scale approach

本项目采用多重尺度方法研究了NBS_1和NBS_2两种类型的硼硅酸盐玻璃的拓扑结构和中程有序对其力学性能的影响。对于NBS1，聚合程度取决于玻璃制备过程中的压力。玻璃状态可以通过激光或离子照射等局部处理进一步改变。在NBS2中，尽管基本玻璃形成实体保持不变，但玻璃的中程顺序可以在整体和局部尺度上改变。经过处理后，用红外光谱和拉曼光谱对玻璃的形貌进行了表征。此外，通过添加少量的结构指示离子，如Mn2+或Cr3+，可以用荧光显微镜检测结构的变化。结合不同玻璃态的制备和表征，从多尺度的角度研究了它们的力学性能。通过原位微悬臂梁变形实验和扫描电子显微镜中的柱子压缩实验，以及纳米压痕和冲击测试方法，评估了材料在一系列长度尺度和变形条件下的弹性、塑性和断裂性能。塑料在玻璃中的流动和致密化效应将通过压痕来研究，因为由于周围材料提供的限制，裂缝可以被抑制。通过改变压头或试件的几何形状(Berkovich、立方角压头或微柱和小玻璃球)，研究了应力状态或试件体积对变形机制的影响。在这种情况下，微柱提供了一种测试，其中流体静压应力分量被最小化。利用微悬臂梁，还可以得到具有不同拓扑结构的玻璃的最大抗弯强度以及在缺口悬臂梁的情况下的局部断裂韧性。通过改变冲击和压痕试验中的应变率和试验温度，量化了不同玻璃结构中断裂和塑性变形机制的动力学。变形后的激活致密化和流动机制由塑性变形体积的光谱和显微镜(原子力显微镜、扫描电子显微镜和透射电子显微镜)表征，特别值得关注的是控制玻璃变形和损伤行为中长度尺度的结构参数。通过将观察到的变形机制与大块金属玻璃或其他玻璃系统的结果进行比较，将获得理解玻璃中局域变形和断裂行为的一般概念。

In this project, the influence of topology and medium range order on the mechanical properties of the NBS1 and NBS2 type borosilicate glasses is studied following a multiple length scale approach. For NBS1, the degree of polymerisation depends on the pressure during glass preparation. The glass state can be further modified by local treatments like laser or ion irradiation. In NBS2, the medium range order of the glass can be changed in the bulk as well as on the local scale, despite the fact that the basic glass forming entities remain the same. After processing, the topology of the glass is characterised by Infrared and Raman spectroscopy. Moreover, by using small additions of structure indicator ions, such as Mn2+ or Cr3+, it is possible to detect structural changes by fluorescence microscopy.In conjunction with the preparation and characterisation of the different glass states, their mechanical properties are studied in a multi-scale approach. With in-situ micro-cantilever deformation experiments and pillar compression tests in the SEM, as well as the nanoindentation and impact testing methods, the elastic, plastic and fracture properties of the materials are assessed over a range of length scales and deformation conditions. Plastic flow in the glass and densification effects will be studied by indentation, as cracking can be suppressed, due to the confinement provided by the surrounding material. By changing the indenter or the specimen geometry (Berkovich, cube-cornerindenter or micropillars and small glass spheres), the effect of the stress state or sample volume on the deformation mechanism is studied. In this context, micropillars provide a test in which the hydrostatic stress component is minimised. Using microcantilevers, the maximum bending strength and, in the case of notched cantilevers, the local fracture toughness of glasses with different topology is also accessible. By varying the strain rate and test temperature in impact and indentation testing, the dynamics of the fracture and plastic deformation mechanisms in the different glass structures is quantified. After deformation, the activated densification and flow mechanisms are characterised by spectroscopy and microscopy (AFM, SEM and TEM) of the plastically deformed volumes.Of particular interest are the structural parameters which govern the length scales in the deformation and damage behaviour of the glasses. By comparison of the observed deformation mechanisms with the results on bulk metallic glasses or other glass systems, general concepts for the understanding of localised deformation and fracture behaviour in glasses will be obtained.