The effects of the barium/titanium (Ba/Ti) ratio on the crystalline phase, Curie temperature, and dielectric properties of solid-state-reacted BaTiO3 powder were investigated. The experimental results showed that tetragonality decreased and the Curie temperature shifted to lower temperature when the Ba/Ti ratio strayed from 1.0. The BaTiO3 powder had the maximum dielectric constant when the Ba/Ti approaching 1.0.

A freestanding bulk nanoporous copper with ultralow density has been fabricated through dealloying of as-cast dual-phase Cu1Mn1Al8 alloy, and the dealloying behavior was investigated systematically. The experimental results show that due to different electrochemical activities, the Al11Cu5Mn3 phase of the dual-phase precursor alloy dissolved before AlCu2Mn, which corresponds to the dramatical evolutions of microstructure and composition. Additionally, a formation pattern based upon a mechanism combined “dissolution–redeposition” pattern, “phase-separation” pattern, and “coarsening” process has been built to describe the evolution process, which includes four stages, sequentially defined as “dissolution of Al11Cu5Mn3,” “redeposition of Cu atoms,” “dealloying of AlCu2Mn,” and “coarsening.”

The complex thermochemical and thermomechanical environments in high temperature propulsion and energy generation systems often demand the use of suites of materials with disparate properties. Unique combinations of materials that simultaneously function to optimize mechanical, thermal, and environmental properties can enable breakthroughs in design and system capability. This article focuses on interlayers that function as environmental barriers and promote adhesion of the ceramic thermal barriers to metallic substrates. The structure, composition, processing, and performance of major classes of bond coatings are briefly reviewed. Challenges for the development of new coating systems and for prediction of their performance in service are addressed.

Oxides hold great promise as new and improved materials for thermal-barrier coating applications. The rich variety of structures and compositions of the materials in this class, and the ease with which they can be doped, allow the exploration of various mechanisms for lowering thermal conductivity. In this article, we review recent progress in identifying specific oxides with low thermal conductivity from both theoretical and experimental perspectives. We explore the mechanisms of lowering thermal conductivity, such as introducing structural/chemical disorder, increasing material density, increasing the number of atoms in the primitive cell, and exploiting the structural anisotropy. We conclude that further systematic exploration of oxide crystal structures and chemistries are likely to result in even further improved thermal-barrier coatings.

Molten deposits based on calcium-magnesium alumino-silicates (CMAS), originating from siliceous debris ingested with the intake air, represent a fundamental threat to progress in gas turbine technology by limiting the operating surface temperature of coated components. The thermomechanical and thermochemical aspects of the CMAS interactions with thermal-barrier coatings, as well as the current status of mitigating strategies, are discussed in this article. Key challenges and research needs for developing adequate solutions are highlighted.

Thermal-barrier coatings are complex systems with properties that largely depend on their specific microstructure. Their properties change during operation, typically leading to degradation. A further difficulty arises from the fact that this degradation also depends on specific loading conditions that can be rather complex. Different laboratory setups are described that simulate, at least partially, the actual loading conditions. In addition, sensing and nondestructive methods are described that are targeted toward reliable operation of a gas-turbine engine with thermal-barrier coated components.

Thermal-barrier coatings (TBCs) are complex, defected, thick films made of zirconia-based refractory ceramic oxides. Their widespread applicability has necessitated development of high throughput, low cost materials manufacturing technologies. Thermal plasmas and electron beams have been the primary energy sources for processing of such systems. Electron-beam physical vapor deposition (EBPVD) is a sophisticated TBC fabrication technology for rotating parts of aero engine components, while atmospheric plasma sprays (APS) span the range from rotating blades of large power generation turbines to afterburners in supersonic propulsion engines. This article presents a scientific description of both contemporary manufacturing processes (EBPVD, APS) and emerging TBC deposition technologies based on novel extensions to plasma technology (suspension spray, plasma spray-PVD) to facilitate novel compliant and low thermal conductivity coating architectures. TBCs are of vital importance to both performance and energy efficiency of modern turbines with concomitant needs in process control for both advanced design and reliable manufacturing.

The addition of Al to a Mg–10Gd alloy was found to lead to substantial grain size reduction during casting at concentrations between 0.8% and 1.3%. At these concentrations, Al2Gd particles were found at the center of grains, and the orientation relationship $[112]_{{\rm{Al}}_{\rm{2}} {\rm{Gd}}} \,{\rm{‖}}\,[2\bar 1\bar 10]_{{\rm{\alpha - Mg}}} ,\,(1\bar 10)_{{\rm{Al}}_{\rm{2}} {\rm{Gd}}} \,{\rm{‖}}\,(0\bar 110)_{{\rm{\alpha - Mg}}} $ was found reproducibly between Al2Gd and α-Mg, indicating that these are the heterogeneous nucleant particles that form in situ at these Al contents. Most of these nuclei were between 2 and 7 μm in size. Furthermore, little grain coarsening was observed during solution treatment, particularly compared with an alloy grain refined by Zr particles where substantial coarsening occurred. This appears to be because Al2Gd particles restrict grain boundary motion during solution treatment.