Thermal insulation performance of 7YSZ TBCs adjusted via Al modification

ZrO_(2)-7 wt% Y_(2)O_(3)(7YSZ)thermal barrier coatings(TBCs)with three different structures were prepared by atmospheric plasma spraying(APS),electron beam physical vapor deposition(EB-PVD)and plasma spray-physical vapor deposition(PS-PVD).Al films were deposited onto the top 7YSZ TBCs by magnetron sputtering,and the Al-deposited 7YSZ TBCs were subjected to vacuum heat treatment.The effects of Al modification on the thermal insulation properties of 7YSZ TBCs were investigated.The results showed that Al modification could significantly improve the thermal insulation of 7YSZ TBCs at 1000℃.Moreover,the maximum improvement of thermal insulation for PS-PVD 7YSZ TBCs was approximately 100℃,but the improvement decreased with increasing temperature.This is mainly because with increasing temperature,the rate of radiation heat transfer increases,and the effects of convection heat transfer and thermal conductivity on thermal insulation are weakened.At the same temperature,Al modification of PS-PVD7YSZ TBCs provides better temperature insulation than those of APS 7YSZ TBCs and EB-PVD 7YSZ TBCs because of its wider and deeper inter-columnar gaps.When the temperature was 12000C,Al modification still caused a good insulation effect in PS-PVD 7YSZ TBCs;the improvement was approximately 50℃,but in APS and EB-PVD 7YSZ TBCs,the insulation effect disappeared.

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

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.

Low-temperature growth of stoichiometric aluminum nitride films prepared by magnetic-filtered cathodic arc ion plating

A1N films were prepared on Si（100） and quartz glass substrates with high deposition rate of 30 nm-min-I at the temperature of below 85 ℃ by the magnetic-filtered cathodic arc ion plating （FCAIP） method. The as-deposited A1N films show very smooth surface and almost no macrodroplets. The films are in amorphous state, and the formation of A1N is confirmed by Nls and A12p X-ray photoelectron spectroscopy （XPS）. The XPS depth profile analysis shows that oxygen is mainly absorbed on the A1N surface. The A1N film has A1 and N concentrations close to the stoichiometric ratio with a small amount of A1203. The prepared A1N films are highly transparent over the wave- length range of 210-990 nm. The optical transmission spectrum reveals the bandgap of 6.1 eV. The present technique provides a good approach to prepare large-scale A1N films with controlled structure and good optical properties at low temperature.

Pressure infiltration of molten aluminum for densification of environmental barrier coatings

Environmental barrier coatings(EBCs)effectively protect the ceramic matrix composites(CMCs)from harsh engine environments,especially steam and molten salts.However,open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives,and lead to premature failure of EBCs.This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings.These results showed that it was difficult for aluminum to infiltrate spontaneously,but with the increase of external gas pressure and internal vacuum simultaneously,the molten aluminum obviously moved forward,and finally stopped infiltrating at a depth of a specific geometry.Based on the wrinkled zigzag pore model,a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established.The infiltration results confirmed this relationship,indicating that for a given coating,a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.