In this work, Yb4Hf3O12 ceramic, a typical rare-earth hafnate, was exposed to water vapor with Al(OH)3 impurities at 1400 ℃, and microstructural evolution and corrosion mechanisms were investigated. The long-term corrosion can be divided into initial hydration and gasification of Hf4+ and steady-state corrosion after the formation of Al5Yb3O12. In the initial stage, Hf4+ and the surrounding O2- tend to be hydrated and then volatilized in the form of Hf(OH)4, causing a metastable state of Yb4Hf3O12 on the surface. Besides, the preferential corrosion of small grains, grain boundary, and specific crystal plane on the surface and sintered and densified grains result in varied corrosion behavior from the early linear law to the later parabolic law. In the steady-state corrosion stage, due to the consumption of Hf4+, more vacancies promote bonding and diffusion of Al3+ to form corrosion product (Al5Yb3O12), and during this stage, regrowth and shedding of the corrosion layer reach a dynamic balance. 

Corrosion behavior of ytterbium hafnate exposed to water-vapor with Al(OH)3 impurities

The preparation and property analysis of B4C modified inorganic amorphous aluminum phosphates-based intumescent flame retardant coating

High-entropy ferroelastic (10RE0.1)TaO4 ceramics with oxygen vacancies and improved thermophysical properties

Rare-earth phosphates (REPO4) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiCf/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al2O3–SiO2 (CMAS). Nevertheless, a relatively high thermal conductivity (κ) of the REPO4 becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4 (HE (7RE1/7)PO4) has been designed and synthesized for the first time to solve this issue. HE (7RE1/7)PO4 with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO2 up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE1/7)PO4 (5.96×10−6 ℃−1 from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE1/7)PO4 (from 4.38 W·m−1·K−1 at 100&nbsp;℃ to 2.25 W·m−1·K−1 at 1300 ℃) are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m−1·K−1. These results suggest that HE (7RE1/7)PO4 has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

https://www.sciopen.com/article_pdf/1630034412932116481.pdf

Xenotime-type high entropy (Dy
 1/7Ho
 1/7Er
 1/7Tm
 1/7Yb
 1/7Lu
 1/7Y
 1/7)PO
 4: A promising thermal/environmental barrier coating material for SiC
 f/SiC ceramic matrix composites

Ceramic matrix materials have attracted great attention from researchers and industry due to their material properties. When used in engineering systems, and especially in aero-engine applications, they can result in reduced weight, higher temperature capability, and/or reduced cooling needs, each of which increases efficiency. This is where high-temperature ceramics have made considerable progress, and ceramic matrix composites (CMCs) are in the foreground. CMCs are classified into non-oxide and oxide-based ones. Both families have material types that have a high potential for use in high-temperature propulsion applications. The oxide materials discussed will focus on alumina and aluminosilicate/mullite base material families, whereas for non-oxides, carbon, silicon carbide, titanium carbide, and tungsten carbide CMC material families will be discussed and analyzed. Typical oxide-based ones are composed of an oxide fiber and oxide matrix (Ox-Ox). Some of the most common oxide subcategories are alumina, beryllia, ceria, and zirconia ceramics. On the other hand, the largest number of non-oxides are technical ceramics that are classified as inorganic, non-metallic materials. The most well-known non-oxide subcategories are carbides, borides, nitrides, and silicides. These matrix composites are used, for example, in combustion liners of gas turbine engines and exhaust nozzles. Until now, a thorough study on the available oxide and non-oxide-based CMCs for such applications has not been presented. This paper will focus on assessing a literature survey of the available oxide and non-oxide ceramic matrix composite materials in terms of mechanical and thermal properties, as well as the classification and fabrication methods of those CMCs. The available manufacturing and fabrication processes are reviewed and compared. Finally, the paper presents a research and development roadmap for increasing the maturity of these materials allowing for the wider adoption of aero-engine applications. 

/pdf/ceramic-matrix-composites-for-aero-engine-applications-a-esi2aboe.pdf

Ceramic Matrix Composites for Aero Engine Applications—A Review

Abstract Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime. 

Xiaodong Zhao

Papers

Progress in ceramic materials and structure design toward advanced thermal barrier coatings