Project Details
Projekt
Mechanical Properties of Oxide Glasses at Constraint Gradients
Subject Area
Mechanical Properties of Metallic Materials and their Microstructural Origins
Term
from 2012 to 2016
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 224699528
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.
DFG Programme
Priority Programmes
