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Under extremely complex conditions, extending the lifetime of thermal barrier coatings (TBCs) is a challenge. In the present study, optimization of the coating structure and selection of coating materials are beneficial for improving the lifetime of TBCs under thermal cycling-CMAS (calcium-magnesium-alumina-silicate) test. It is efficient to obtain different layer thicknesses of multi-layer coating, including the micro-nano dual-scale layer, the dense YbYSZ layer (4.0 mol % Yb 2 O 3 and 0.5 mol% Y 2 O 3 co-stabilized ZrO 2), the porous YbYSZ layer and the laser 3D texturing layer, using the computational model under thermal load. Based on the corresponding coating structure and YbYSZ material, bond strength and thermal cycling-CMAS lifetime are evaluated, and compared with those of YSZ (4.5 mol % Y 2 O 3 stabilized ZrO 2) coating. The results reveal that TBCs with porous embedded particle cluster (PEPC) structure is lower than that of YSZ coating. In addition, the original defects in multi-layer coating with grid texture reduce the bond strength. The lifetime of multi-layer coatings with a punctate texture are significantly improved in the thermal cycling-CMAS test, and their failure behavior includes fragmented and bulk-like exfoliation. This study emphasizes that combination of materials modification and structure optimization are a promising strategy to extend lifetime of TBCs. [ABSTRACT FROM AUTHOR]

SiC reticulated porous ceramic (SRPC) as the key component determined the service life and combustion characteristics of porous burner. The novel multi-layer struts were constructed to synergistically improve the oxidation resistance and infrared radiation of SRPC, including microporous cordierite coating, dense mullite transition layer, SiC skeleton and filling layer. The continuous mullite transition layer significantly improved the resistance to water vapor oxidation of SRPC, also their strength and thermal shock resistance were enhanced because the elimination of strut defects in multi-layer struts. In addition, the microporous cordierite coating generated from the burnt out of pitch increased the burner surface temperature from 764.4 °C to 1061.7 °C, and obviously reduced the CO/NOx emission due to its improved infrared radiation property. Furthermore, the porous cordierite coating enhanced the heat radiation of SRPC, thus increasing the heating rate of the burner from 29.4 °C/min to 33.1 °C/min in the process of water heating. [ABSTRACT FROM AUTHOR]

The present study evaluates the tribological and corrosion behavior of CrN/CrAlN and CrCN/CrAlCN nanostructured coatings applied on 430 stainless steel. These coatings were applied using the physical vapor deposition method from the vapor phase through the cathodic arc technique. X-ray diffraction, field emission scanning electron microscopy, and nano-indentation techniques were utilized for the coatings characterization. Moreover, the adhesion of the coatings to the substrate was evaluated by the adhesion test according to the VDI3198 standard. The corrosion behavior of the coatings was studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt % NaCl solution in 24, 72, and 168 h. It was observed that CrN was the major phase in the coatings. The results of the Rockwell C test indicated the good adhesion of both coatings to the substrate. The hardness of CrCN/CrAlCN coating was 20 GPa and CrN/CrAlN coating was 18 GPa. Concerning the friction coefficient, 430 stainless steel, CrN/CrAlN, and CrCN/CrAlCN coatings showed friction coefficients of 1.049, 0.3, and 0.21, respectively. CrCN/CrAlCN exhibited the lowest friction coefficient, which can be ascribed to the higher ratio of H3/E2, higher hardness, and also reduced surface roughness compared to the CrN/CrAlN sample. The R p value of CrCN/CrAlCN coating is higher than that of CrN/CrAlN coating at different times. The corrosion current density of the CrCN/CrAlCN coating was 0.003 μA cm−2 and for the CrN/CrAlN coating, it was 0.057. The obtained results from both corrosion tests are in an agreement and indicate the better resistance of the CrCN/CrAlCN coating against corrosion which can be due to the dense structure, lower roughness, and low wettability of this coating. [ABSTRACT FROM AUTHOR]

Protective coatings are critical to the successful application of the carbon/carbon (C/C) composites in the thermal protection systems of space vehicles. The damages of such coatings during installation and operation would threaten the safety of flight. In this contribution, an in-field technology based on a multilayer structure was developed to repair the damaged coatings of C/C composites. The multilayer structure contains a silicon buffer inner layer, a mullite heat-resistant middle layer and a borosilicate glass outer layer. The oxidation tests in air at 1300 °C and 1500 °C indicated that the weight loss of the repaired samples was greatly reduced compared with that of the damaged ones. The plasma wind tunnel tests for both repaired and damaged coatings further demonstrated that the multilayer structure could effectively protect the damaged composites from ablation in oxidation environments. [ABSTRACT FROM AUTHOR]