Through systematic density-functional theory-based ab initio calculations, various performance indicators such as $G/B$, the ratio of shear modulus $G$ over bulk modulus $B$, ${\sigma }_s/{\sigma }_t$, the ratio of ideal shear strength ${\sigma }_s$ over tensile strength ${\sigma }_t$, and the Cauchy pressure defined as $C_{12}\text{−}{C}_{44}$ were evaluated for a selection of fcc metals and assessed in relation to the characteristics of their electronic distributions obtained from the electron localization function. The analysis reveals that the ratio ${\sigma }_s/{\sigma }_t$ is possibly a better indicator of malleability as it discriminates directionally bonded metals in addition to discerning ductile crystals from brittle ones. Furthermore, Al is found to sustain the largest shear deformation among the scrutinized solids due to its directional bonds. Similarly, the surprisingly long range of distortion of Pd is rationalized as a result of the geometric constraints caused by small electron pockets of comparatively high localization in the interionic region. However, the examination of the peculiar case of Ir suggests that, in general, the extent of shear distortion should be the consequence of at least two factors, namely, the angular characteristics of bonding and the bond strength.

In the present work, semiempirical formulae for both bulk $B$ and shear $G$ moduli of diamondlike and zinc-blende covalent crystals are elaborated in terms of bond length and ionicity fraction of the bonding. The resulting expressions can be applied to a broad selection of covalent materials and their modulus predictions are in good agreement with the experimental data and those from ab initio calculations. Furthermore, the correlation between the ratio $G∕B$ and the aforementioned bonding parameters was investigated. The analysis of this relationship demonstrates that compared to the ionicity fraction, the bond length is the predominant parameter responsible for the brittle features of covalent materials.

Beneficial properties achieved by nanostructuring effects in materials have generated tremendous interests in applications in surface engineering, especially in thermal barrier coatings (TBC). Limitations in conventional TBC processing for gas turbines and aero-propulsion systems have been exposed during past decades when rapid progress was made in nano-structuring coating research and developments. The present work is a comprehensive review of the current state of progress in nanostructured TBC (Ntbc) in reference to its microstructure, damage progression, failure mechanisms and a wide range of properties. The review aims to address the comparative performance analysis between the nanostructured and conventional (microstructured) 6–8 wt.% yttrium stabilized zirconia (YSZ) TBC systems. Oxidation resistance and sintering behavior in two TBCs are considered as the central focus of discussion. A few schematics are used to represent major microstructural features and failure progression. A performance analysis is performed for standard 2-layer, as well as functionally graded multilayer, TBC systems. A comparison of TBC characteristics processed by plasma spray and vapor deposition techniques is also made as reference. Compared to the sea of R&D efforts made for conventional TBC (Ctbc), limited experimental studies on Ntbc offers conflicting data, and prediction modeling and computational research are scarce.

To achieve a higher efficiency in gas turbine engine by increasing the inlet-temperature of burning gas is one of the primary goals in aviation industry. The development of thermal barrier coating system (TBCs) continuously raises the inlet-temperature of gas turbine engine in the past decades. Due to the complexity of TBCs and harsh operation environments, the degradation and failure mechanisms of hot section components have not been fully understood, and consequently limits the application of TBCs. It was identified that high-temperature sintering of the topcoat in a typical TBC could be one of the major sources of its failure since the microstructures of the constituent coating layers evolve dynamically during the service period, resulting in significant changes of mechanical and thermal physical properties of the coating system. This paper intends to review recent advances of analytical and numerical modeling of sintering of topcoat in TBCs including the modeling methodology and applications of the models, particularly the implementation of finite element combined with specific materials constitutive functions. Critical remarks on the future development and applications of these models are also discussed in the end.