Preparation of Al2O3 nanowires on 7YSZ thermal barrier coatings against CMAS corrosion

The commonly-employed material for thermal barrier coatings(TBCs)is 7 wt.%Y2O3 ZrO2(7YSZ),generally deposited by electron beam-physical vapor deposition(EB-PVD).Due to the increasing demand for higher operating temperature in aero-derivative gas turbines,a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs,which is induced by the microstructure degradation,sintering and spallation after the deposition of infiltrated siliceous mineral(consisting of calcium magnesium aluminum silicate(CaO MgO Al2O3 SiO2,i.e.,CMAS)).A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present.The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs,followed by performing vacuum heat treatment of the Al-deposited TBCs.During the heat treatment,the molten Al reacted with ZrO2 to formα-Al2O3 overlay that effectively hindered CMAS infiltration.Moreover,the Al film could evaporate and re-nucleate,leading to the generation of Al2O3 nanowires,which further restrained the moving of molten CMAS.

Preparation and properties of supersonic atmospheric plasma sprayed TiB2−SiC coating

With the TiB2−SiC powders after spray granulation and vacuum calcination as raw materials,the TiB2−SiC coating was prepared by supersonic atmospheric plasma spraying(SAPS).The effects of spraying power and spraying distance on the properties of the TiB2−SiC coating were investigated and the fabrication processing of SAPS was optimized.The results show that the sprayed powders after calcination have a uniform particle size distribution,good sphericity and enhanced fluidity.The coating prepared by the calcined powders has a dense structure and high deposition efficiency.When the calcined TiB2−SiC powders are used and the spraying power is 95 kW and the spraying distance is 150 mm during supersonic plasma spraying,the obtained TiB2−SiC coating behaves the best comprehensive performance with the porosity,microhardness,bonding strength and resistivity equal to 5.6%,3.57 GPa,18.3 MPa and 10.8 mΩ·cm,respectively.

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.

A comparison between novel Gd_(2)Zr_(2)O_(7)and Gd_(2)Zr_(2)O_(7)/YSZ thermal barrier coatings fabricated by plasma spray-physical vapor deposition

Spherical Gd_(2)Zr_(2)O_(7)hollow powders with a mean size of 8.8μm were fabricated as feedstock for thermal barrier coatings(TBCs)by spray-drying.The single-ceramic-layer(SCL)Gd_(2)Zr_(2)O_(7)TBCs and double-ceramic-layer(DCL)Gd_(2)Zr_(2)O_(7)/YSZ TBCs with quasicolumnar structure were successfully fabricated by plasma spray-physical vapor deposition(PS-PVD).Tensile and water-quenching tests were applied to evaluate TBCs performances.The results show that adhesion strength of SCL Gd_(2)Zr_(2)O_(7)TBCs and DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs is36.5 MPa and 15.4 MPa,respectively.The delamination of SCL Gd_(2)Zr_(2)O_(7)TBCs and DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs in the tensile test takes place at the middle and bottom of Gd_(2)Zr_(2)O_(7)layer,respectively,due to relatively lower fracture toughness of Gd_(2)Zr_(2)O_(7)layer.After 40 cycles of water-quenching test,DCL Gd_(2)Zr_(2)O_(7)/YSZ TBC surface keeps relatively intact,while SCL Gd_(2)Zr_(2)O_(7)TBC surface shows 20%visible destroyed regions,which demonstrates that DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs have a better thermal shock resistance than SCL Gd_(2)Zr_(2)O_(7)TBCs.The cracks in the SCL system propagate near thermally grown oxide(TGO)due to thermal mismatch and TGO growing stress,while cracks in the DCL system propagate in the Gd_(2)Zr_(2)O_(7)layer due to its relatively lower fracture toughness.

Regional characteristic of 7YSZ coatings prepared by plasma spray-physical vapor deposition technique

7 YSZ coating was prepared by plasma sprayphysical vapor deposition(PS-PVD) technique based on a specific experimental design.The microstructure and deposition properties of 7 YSZ coating along the radius of plasma jet were investigated in detail.Results show that the coating presents regional characteristic in the radial direction,which could be divided into three typical zones:In Zone Ⅰ,the coating is all composed of columnar structures with cauliflower structure,and the coating properties including the surface roughness and deposition efficiency(DE) are almost stable;in Zone Ⅲ,the coating is made up of solid particles,droplet and gas phase mixed without columnar structures;Zone Ⅱ is between Zone Ⅰ and ZoneⅢ, in which there are columns with domed top and small particles.Based on experiment results,a model on the state and distribution of particles in plasma jet was proposed to clarify the regional characteristic.This study is helpful to comprehend and control coatings deposition by PS-PVD technique.