Mechanical Properties of Oxide Glasses at Constraint Gradients

如果必须将任何材料的特性命名为最相关的，那么选择可能会落在机械性能上。这尤其适用于眼镜，其实际（通常可用）和理论强度相差一个或多个数量级，因此，改进的潜力似乎最有趣。在这里，瓶颈是缺乏对结构组成和力学性能之间相互作用的基本理解，以及潜在的增韧策略。缺陷，主要是表面缺陷及其引发被认为是理论与实践之间巨大差异的主要原因。因此，今天的经验增韧程序侧重于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-对结构-性能关系的理解和定量的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拓扑约束理论的玻璃形成系统在组成接头，其中一个或多个结构参数是已知的急剧变化。作为技术上相关的模型系统，混合网络前硼硅酸盐，铝硅酸盐和可选的钛酸盐玻璃被选择，其中硼和铝的配位分别在相对狭窄的成分区域内急剧变化。除了这两种体系外，还将考虑具有单一网络前体的碲酸盐玻璃（随着网络改性剂含量的变化而改变配位）和磷酸盐玻璃（在共价网络和完全解聚的离子状态之间过渡）。对于每一个体系，弹性性能，硬度，韧性，脆性的依赖关系-与SPP 1594的其他参与者合作-内在强度将在短和中长度尺度上进行实验评估并与相关结构参数相关。关注尖锐结构梯度的成分——“极端成分”——有双重动机：在这样的成分领域，我们期望在识别玻璃机械性能拓扑设计的本构规律方面具有最高的准确性。其次，该方法将促进表面工程工具（特别是阳离子和阴离子交换）的进一步发展，在表面可以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有关机械性能的主要拓扑约束，并推导出将验证和扩展经典约束理论的温度相关函数。预计在与spp1594的平行活动协同作用下，这些功能可以推广到弥合金属和无机氧化物体系之间的知识差距。在准备第二个资助期时，将考虑在玻璃表面建立这种拓扑梯度的工程方法，从而创建机械约束的特定梯度。

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.