Binary chromium carbides display excellent wear resistance, extreme stiffness and oxidation resistance under high temperature. The influence of applied pressure on electronic structure, elastic behavior, Debye temperature and hardness of Cr₇C₃, Cr₃C₂ and Cr₂₃C₆ have been investigated by the density functional theory (DFT) method. The results reveal that lattice parameters and formation enthalpy display an inverse relationship with applied pressure, and Cr₃C₂ exhibited optimal structural stability. Moreover, Cr-C orbital hybridization tends to be stronger due to the decreased partial density of states (PDOS) of the Cr atom. The difference in electronic distribution of binary carbides has also been investigated, which confirmed that overall orbital hybridization and covalent characteristics has been enhanced. The theoretical hardness was elevated according to the higher bond strength and bond density. In accordance with structural stability data, Cr₃C₂ has shown maximum theoretical hardness. Furthermore, the anisotropic nature of hardness has been evaluated with external pressure. Cr₃C₂, and the highest isotropic hardness behavior along with an increase in hardness values with increasing pressure has been observed. In addition, the variation in Debye temperatures of binary chromium carbides under applied pressure has also been predicted. The results provide a theoretical insight into electronic, mechanical and thermodynamic behavior of three binary chromium carbides and show the potential of these novel carbides in a wide range of applications.

Thermal barrier coatings (TBCs) are a fundamental technology used in high-temperature applications to protect superalloy substrate components. However, extreme high-temperature environments present many challenges for TBCs, such as the degradation of their thermal and mechanical properties. Hence, highly insulating, long-life TBCs must be developed to meet higher industrial efficiency. This paper reviews the main factors influencing the thermal insulation performance of TBCs, such as material, coating thickness, and structure. The heat transfer mechanism of the coating is summarized, and the degradation mechanism of the thermal insulation is analyzed from the perspective of the coating structure. Finally, the recent advances in improving the thermal insulation and lifetime of coatings are reviewed in terms of advanced materials and structural design, which will benefit advanced TBCs in future engineering applications and provide guidance for the next generation of high thermal insulating TBCs.

Thermal barrier coatings (TBCs) have been developed to protect superalloys against high-temperature heat fluxes, which are required for the development of high-performance gas turbines. TBCs have porous structures, which are densified by sintering. The resulting stiffening is a major cause of TBC failure in service. Therefore, there is a need to reduce the negative sintering effect on the life span of TBCs. In this study, the sintering mechanism and the dominant factors causing changes in stiffening and mechanical properties were revealed experimentally. The experimental results show that the multiscale undulation of the originally smooth two-dimensional (2D) pore inner surface triggers multipoint contact between the upper and lower inner surfaces, resulting in pore healing during thermal exposure. The healing of 2D pores is the main structural characteristic change in TBCs after thermal exposure and the main reason for the stiffening and changes in mechanical properties. Then, the sintering effect on TBCs with vertically cracked structures was designed and simulated. We found that implanting vertical cracks in the topcoat can reduce the sintering effect and driving force for cracking by 87.9% and 79.9%, respectively. The degree of reduction depends on the space between vertical cracks. Finally, the mechanism responsible for the sintering-resistant TBCs was analyzed and discussed. Vertically cracked structures exhibited scale-sensitive stiffening, indicating that macroscopic stiffening is much lower than microscopic stiffening. In other words, the macroscopic sintering effect was lowered, and the TBCs remained highly resistant to global strain during thermal exposure. The resulting strain energy release rates are much lower than those of conventional TBCs. The results of this study contribute to the long-life thermal protection of superalloy-based components used in advanced gas turbines.

A profound overview of the recent development for on-time, on-demand hydrogen production from light metal-based hydrolysis is presented. Hydrogen energy is one of the clean and renewable energy sources which has been recognized as an alternative to fossil fuels. In addition, aluminum is the most suitable light activity metal for hydrolysis materials attributed to its safety, environmental friendliness, high-energy density, inexpensive, and low density with high strength ratio. In general, dense oxide films formed act as a barrier on aluminum surfaces. Accordingly, effective removal of the oxide film is a key measure in solving the Al–water reaction. In this review, recent advances in addressing the main drawbacks including high-purity aluminum with acid–alkali solutions, nano-powders of aluminum or composite with acid–base solutions, ball-milled nano-powders, alloying blocks, and gas atomization powders are summarized. The characteristics of these three technologies and the current research progress are summarized in depth. Moreover, it is essential to promote low-cost aluminum-based materials based on effective hydrogen production efficiency and explore ways for practical large-scale applications.

Micro-arc Oxidation (MAO) is a technology for non-ferrous metal surface treatment through growth ceramic coating in situ. To determine the influence of the power supply mode and the loading parameters on the film forming of magnesium alloy micro-arc oxidation processing, the different power supply modes of pulsed direct current DC, pulsed bipolar current (BC) and the pulsed with a discharge loop current (DLC) was used with MAO technology on the AZ91D magnesium alloy. The power load parameters were optimized. The average energy consumption was calculated. Results showed that the role of the negative voltage in the bipolar pulse power supply is to restrain the large arc tendency. Under the pulse power supply with a discharge loop, the current and energy consumption decreases with the increase of the discharge resistance at the same pulse parameters. The big arc phenomenon can be effectively avoided and the impact of load capacitance could be effectively avoided by using the pulse power supply with a discharge loop. Moreover, the processing of the micro-arc oxidation is stable, the arc point is uniform, the surface of the film is smooth, the hole is uniform and the coating is dense, and the film efficiency is improved effectively.

A Finite-Element Model (FEM) for thermal-barrier coatings was employed to elaborate the temperature distribution on yttria-stabilized zirconia (YSZ) free surface during cracks coalescing, then the influence of sintering of YSZ induced by heat-transfer overlapping on energy release rate was quantificationally evaluated. A three-dimensional model including three layers was fabricated. Two types of cracks, with and without depth variations in YSZ coating, were introduced into the model, respectively. The temperature rise of YSZ coating over the crack is independent of each other at the beginning of crack propagation. As crack distance shortens, the independent temperature-rise regions begin to overlap, while maximum temperature is still located at the crack center before crack coalescence. The critical distance that the regions of temperature rise, just overlapping, is the sum of half lengths of two coalescing cracks (i.e., a₁ + a₂), which is independent of cracking path. The maximum temperature in YSZ sharply increases once cracks coalesce. Compared with one delamination crack, the effective energy-release rate induced by heat-transfer overlapping increases in the range of 0.2%–15%, depending on crack length and crack distance, which is on some level comparable to that of deterioration of thermal expansion misfit induced by temperature jump between crack faces.