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The superposed structure of double ceramic layer (SDCL) could be an effective means to develop long-life thermal barrier coating (TBC) at high temperatures. In this study, YSZ/LaMgAl 11 O 19 TBC system with double-ceramic layer (DCL) and SDCL structures were prepared on nickel-based superalloy substrates by atmospheric plasma spraying. The thermal cycling behavior of the coatings was investigated using a furnace at 1000 °C and burner-rig facility at 1375 ± 25 °C on the coating surface. Results showed that the thermal cycle life of the SDCL structure was increased by 7.2% for the furnace and 13.2% for the burner-rig facility compared with that of the DCL structure. The relatively long thermal cycle life of the SDCL structure was attributed to the blocking of the propagation of cracks in the LMA layers by the YSZ ceramic layer and the release of residual thermal stresses by the formation of cracks in the LMA layers. [ABSTRACT FROM AUTHOR]

Thermal barrier coating systems with different bond coats were fabricated on polymer matrix composites via the air plasma spray process. During a thermal shock test at 400 °C, Zn and Al interlayers were helpful in improving the thermal shock resistance of coatings due to the low melting point. The coating system consisted of a soft zinc layer as a bond coat, and YSZ as a top coat exhibited the best thermal shock resistance, attributed to the lower residual stress and lower thermal stress in the Zn interlayer. The failure mechanism of the coating system was mainly ascribable to the residual stress derived from the deposition process, thermal stress, and further damage of the substrate. [ABSTRACT FROM AUTHOR]

ZrB 2 -SiC-Al 2 O 3 (ZSA) and ZrB 2 -SiC-Si (ZSS) coatings were prepared on the surface of C/C composites by atmospheric plasma spraying. During oxidation at 1200 ℃ for 10 h, the formation of B 2 O 3 in the ZSA coating volatilizes gradually, no glass phase is able to seal cracks and holes, resulting in poor oxidation resistance. On the other hand, the ZSS coating produces a large amount of borosilicate glass phase and still gains 0.8% weight after 10 h. During oxidation at 1500 ℃, a low viscosity SiO 2 glass phase forms on the ZSA coating, due to the presence of Al 2 O 3 and this glassy phase has a good ability to seal defects. However, the rapid volatilization of B 2 O 3 in the ZSS coating leads to the formation of large holes in the coating, and to progressively increased viscosity of SiO 2 glass phase, resulting in decreased oxidation resistance. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) consisting of yttria-stabilized zirconia (YSZ) as top coat and NiCrAlY as bond coat were deposited on AZ91D magnesium alloy substrate by atmospheric plasma spraying (APS). In order to improve the stability and prolong the thermal shock life of TBCs, a Ni-P/Al/Ni-P sandwich interlayer between the AZ91D magnesium alloy substrate and the NiCrAlY bond coat was fabricated by electroless plating for Ni-P layer and APS for Al layer. The thermal shock behavior of the YSZ TBCs with the Ni-P/Al/Ni-P sandwich interlayer quenched in water at 400 °C was investigated in detail. The results showed that the thermal shock life of YSZ TBCs with the Ni-P/Al/Ni-P interlayer on the AZ91D substrate was about 226 cycles. The failure of YSZ TBCs in thermal shock test was mainly induced by the corrosion of AZ91D substrate. The results of polarization tests and electrochemical impedance spectroscopy showed that the Ni-P/Al/Ni-P interlayer had better corrosion protection for the magnesium alloy substrate than the Ni-P interlayer, which thus enhanced the thermal shock life nearly two times as compared to that of YSZ TBCs with the Ni-P interlayer. • Ni-P/Al/Ni-P sandwich structured interlayer was used between coating and substrate. • The life of TBC with sandwich interlayer was improved to 226 cycles at 400°C. • The thermal shock failure of the as-prepared coatings was investigated. • Corrosion resistance of substrate with Ni-P/Al/Ni-P was effectively strengthened. • The sandwich interlayer reduced the thermal stress between coating and substrate. [ABSTRACT FROM AUTHOR]

Yb 2 SiO 5 and NdMgAl 11 O 19 (NMA) powders were synthesized by solid-state reactions. Triple-layer ceramic coatings based on the Si bond layer, Yb 2 SiO 5 interlayer and NMA top layer were prepared on carbon fiber reinforced silicon carbide ceramic matrix (C f /SiC) composites by atmospheric plasma spraying (APS). The coatings were subjected to thermal shock tests at 1300 °C, 1400 °C and 1450 °C, respectively. The results showed that the Si/Yb 2 SiO 5 /NMA coating significantly improved the oxidation resistance of C f /SiC composites. The failure mechanism of the Si/Yb 2 SiO 5 /NMA coating was closely related to the thermal shock temperature. Below 1400 °C, the failure of the coating was connected with the mismatch of thermal expansion coefficient (CTE) between the coating and substrate, the reaction between Yb 2 SiO 5 and NMA at the interface, the poor sintering property of Yb 2 SiO 5 and NMA and the substrate itself. Above 1450 °C, the coating failed after only one thermal shock cycle due to the temperature higher than the melting point of the silicon. [ABSTRACT FROM AUTHOR]

ZrB 2 – ZrC/Ni composite powders were successfully produced from a Ni – Zr – B 4 C system by self-propagating high-temperature synthesis (SHS), and ZrB 2 – ZrC/Ni cermet coatings were deposited on a magnesium alloy substrate by atmospheric plasma spraying (APS) using the SHS-derived powders as feedstock powders. Microstructure and phase composition of the SHS powders and APS coatings were investigated by scanning electron microscopy and X-ray diffraction, respectively. Microhardness and wear resistance of the coatings were examined by using a Vickers hardness tester and pin-on-desk tribometer. The coatings exhibited lamellar and porous structure, mainly consisting of ZrB 2 , ZrC and Ni in addition to the by-product ZrO 2 . The coatings bonded well to the substrate with the bonding strength as high as 16.27 MPa. Microhardness and wear resistance of the substrate were significantly improved by the coatings. The wear resistance of the coatings for the substrate initially increased and subsequently decreased with the increase in Ni content. The coating with 30 wt% Ni in the feedstock powder displayed the highest microhardness of 525.02±96.08 HV 0.1 and the best wear resistance for the substrate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of TiB2–TiC–Al2O3/Al composite coatings on Mg alloy by RPS. [•] Microstructure and properties of the RPS coatings were characterized. [•] The coatings consist of TiB2, TiC, Al2O3 and/or excess Al without by-products. [•] The coatings display dense structure and good interfacial bonding with substrate. [•] The coatings provide good protection for the Mg alloy against wear and corrosion. [ABSTRACT FROM AUTHOR]

Abstract: TiC–TiB2 composite coatings were successfully synthesized using the technique of reactive plasma spraying (RPS) on a magnesium alloy. Phase composition, microstructure and wear resistance of the coatings were characterized by using X-ray diffraction, scanning electron microscopy and pin-on-disk wear test, respectively. The results showed that the resultant product in the RPS coatings was composed of TiC and TiB2. Depending on the ignition of self-propagating high-temperature synthesis reaction in the agglomerate particles, the RPS coatings displayed porous and dense microstructures. The porosity of the RPS coatings, to some extent, decreased when the feed powders were plasma sprayed with Ni powders. The RPS coatings provided good wear resistance for the substrate under various loads. For high loads (e.g., ≥15N), the wear resistance could be significantly improved by the proper addition of Ni into the RPS coatings. [Copyright &y& Elsevier]