Mechanical Properties of Oxide Glasses at Constraint Gradients

如果任何材料的属性必须被命名为最相关的，选择可能会落在机械行为。这尤其适用于玻璃，其中实际（通常可用）和理论强度相差一个或多个数量级，因此，改进的潜力似乎最吸引人。在这里，瓶颈是一方面对结构组成和机械性能之间的相互作用以及另一方面潜在的增韧策略缺乏基本的理解。缺陷，主要是表面缺陷和它们的产生被认为是理论和实践之间巨大差异的主要原因。因此，今天的经验韧化程序集中在工程特定的表面结构，主要依赖于残余压缩的产生。在本项目中，这两个问题-结构-性能关系的理解和定量，表面靶向增韧策略将共同处理。拟议的项目将侧重于扩展和实验应用的拓扑约束理论的玻璃形成系统的组成关节，其中一个或多个结构参数已知急剧变化。作为技术相关的模型系统，已选择混合网络形成剂硼硅酸盐、铝硅酸盐和任选的钛酸盐玻璃，其中已知硼和铝配位分别在相对窄的组成区域中急剧变化。除了这两个系统，碲酸盐玻璃与一个单一的网络形成（网络改性剂含量的函数改变配位）和磷酸盐玻璃（共价网络和完全解聚，离子状态之间的过渡）将被考虑。对于这些系统中的每一个，弹性性能，硬度，韧性，脆性和-与SPP 1594的其他参与者合作-固有强度的依赖性将通过实验进行评估，并与短和中等长度尺度上的相关结构参数相关。在尖锐的结构梯度的组合物的重点-“极端组合物”-动机是双重的：在这样的组成领域，我们期望最高的准确性，在确定本构关系的拓扑设计的玻璃的机械性能。其次，该方法将能够进一步开发表面工程工具（特别是阳离子和阴离子交换），其中可以在表面产生专用的拓扑梯度，扩展化学增韧的经典观点。第一个资助期的主要目标是感知与力学性能相关的主要拓扑约束，并推导出温度相关函数，这将验证和扩展经典约束理论。预期与SPP 1594的平行活性协同，这些功能可被推广以弥合金属和无机氧化物系统之间的知识差距差距。在筹备第二个供资期时，将考虑在玻璃表面上建立这种拓扑梯度的工程方法，从而建立特定的机械约束梯度。

If any materials property had to be named the most relevant, the choice would probably fall to mechanical behavior. This holds especially for glasses, where practical (commonly available) and theoretical strength differs by one or more orders of magnitude and, hence, the potential for improvement appears most intriguing. Here, the bottleneck is the significant lack of fundamental understanding of the interplay between structural constitution and mechanical properties on the one side, and potential toughening strategies on the other side. Defects, primarily surface defects and their initiation are known as the primary reason for the large difference between theory and praxis. Today's empirical toughening procedures therefore focus on engineering specific surface architectures, mostly relying on the generation of residual compression. In the present project, both problems - the understanding of structure - property relations and quantitative, surface-targeting toughening strategies will be treated jointly. The proposed project will focus on extending and experimentally applying the theory of topological constraints to glass forming systems at compositional joints, where one or more structural parameters are known to change sharply. As technologically relevant model systems, mixed-network-former borosilicate, aluminosilicate and, optionally, titanate glasses have been chosen where boron and aluminum coordination, respectively, are known to sharply change in relatively narrow compositional regions. In addition to these two systems, tellurite glasses with a single network former (changing coordination as a function of network modifier content) and phosphate glasses (on the transition between covalent network and fully depolymerized, ionic state) will be considered. For each of those systems, the dependence of elastic properties, hardness, toughness, brittleness and - in cooperation with other participants of SPP 1594 - intrinsic strength will be assessed experimentally and related to relevant structural parameters on short and intermediate length scale. The focus on compositions at sharp structural gradients - "extreme compositions" - is motivated twofold: in such compositional areas, we expect the highest accuracy in identifying constitutive laws for the topological design of the mechanical properties of glasses. Secondly, the approach will enable further development of surface engineering tools (especially cation and anion exchange) where dedicated topological gradients can be generated at the surface, extending the classical view of chemical toughening. Primary objective of the first funding period is to perceive the dominant topological constraints with respect to the mechanical properties and to deduct temperature-dependent functions which will verify and extent the classical constraint theories. It is anticipated that in synergy with parallel activities of SPP 1594, these functions can be generalized to bridge the gap of knowledge between metallic and inorganic oxide systems. In preparation of the second funding period, engineering approaches to establish such topological gradients on glass surfaces and, hence, to create specific gradients of mechanical constraints will be considered.