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Current gas turbine engines use Yttria-Stabilized Zirconia (YSZ) as the top coat for heat shielding in HP turbines as well as combustors. Unfortunately, YSZ suffers from many drawbacks once the temperature reaches $1200^{\circ }\text{C}$. This limits the long-term application temperature of YSZ, and a few top coat replacements have been suggested and examined. In our study, we make two major changes to the top coat. The first is to use Gadolinium Zirconate (Gd₂Zr₂O₇ or GDZ) which enjoys better thermal properties. The second is to combine it with YSZ in a bilayer configuration, thus, making use of the combined beneficial effects of thermal shielding and mechanical strength of these top coats. In spite of the fact that GDZ/YSZ has been suggested by other authors, no work has been devoted to study the role played by the GDZ–YSZ interphase region, possible interdiffusion, its thermal properties and interphase region strength. In this study, we developed comprehensive atomistic models of the GDZ/YSZ interface using molecular dynamics (MD) with emphasis on thermo-mechanical properties of the GDZ/YSZ interphase region. This allowed us to examine the evolution of the GDZ/YSZ interphase region and compute the interface bond strength with temperature.

From any directed graph E one can construct the graph inverse semigroup $G(E)$, whose elements, roughly speaking, correspond to paths in E. Wang and Luo showed that the congruence lattice $L(G(E))$ of $G(E)$ is upper-semimodular for every graph E, but can fail to be lower-semimodular for some E. We provide a simple characterization of the graphs E for which $L(G(E))$ is lower-semimodular. We also describe those E such that $L(G(E))$ is atomistic, and characterize the minimal generating sets for $L(G(E))$ when E is finite and simple.

In this paper, the brittle fragmentation of an expanding ring is numerically studied by a simple atomistic model. We investigate the statistical distribution of fragment spanned over a wide range of strain rates when damage related to broken bond reaches a steady state. It is shown that at low strain rate limited number of heavy fragments can be generated because of anisotropic behavior while for high strain rate fragment can be well fitted with Weibull distribution. The physical mechanism of fragmentation process reveals that damage accompanying with numerous microcracks is found to initiate in the inner regime of the expanding ring. Furthermore, we discuss the effect of random defect on the fragmentation process.