Characteristics Of APS Coating Based On Spherical Thin-walled Hollow Shell Fully Stabilized Nano T′-TSZ Powder

The microstructure of 7-8 wt%Yttria Stabilized Zirconia（YSZ）coatings plays a key role in improving its durability.The adjustments of the spray process to improve the coating durability have been extensively studied,but few on the microspheres of feedstock.The distance of air plasma spraying（APS）gun and the coating base decided that the plasma time of the powder was extremely short,so the durability and performance of the coatings largely depended on the property of powder.The structure and performance of APS coatings prepared with spherical thin-wall hollow shell fully stable t′-YSZ powder were investigated by XRD,SEM,Vickers hardness tester and laser scintillation techniques et al.The purpose of this work was to prepare a long-term durability and low-cost Thermal barrier coatings（TBCs）.1.The structure and properties of the powder were studied,and the results indicated that powder had a high sphericity,smooth surface,the distribution of particle size was 14-105μm,the wall thickness was 4-6μm,the grain size was 9 nm;the bulk density was 1.37 g/cm³,the fluidity was 30 s/100 g.The powder of t′-phase gradually transformed into m and Y-rich c phase above 1200℃,and the c-phase was the main phase.The critical appearing time for the m-phase was～180h after heating at 1200℃,when the powder still contained 73 mol%of t’-phase;2.The structure and properties of the APS coatings were studied,the results indicated that coatings maintained the same phase structures and YO_1.5 concentrations with the powder.The coatings without any multilayer structure had 21.5%closed pores with a dispersion distribution size of 0.5-4.0μm.The thermal conductivity of the coatings was 1.0 W/mK between room temperature and 800℃,Vickers hardness value was 6.16 GPa,with only a little peeling occurs after 101 times of 1050℃water quenching thermal shock cycles;3.The high temperature phase stability of the coatings was studied,and the results indicated that the m phase was observed in the coatings neither after heat treatment at 1200℃ for 1000 h nor after elevated temperature at 1600℃for 30h,but observed after grinded into powder.In addition,the c phase appeared with m phase in coatings and the content also had the same trend at the same time,which implied that the harmful m phase could be judged by detecting the appearance of c phase in coatings;4.The activation energy of the diffusion phase transition of the coatings was studied.The activation energy Q for the diffusion phase transition of the t′-YSZ coatings was calculated to be 260 k J/mol,which based on the thermal kinetics of superalloy creep,using the analogy method and according to the experimental data;5.The sintering resistance of the coatings was studied.The porosity after sintering at1300℃ for 200 h was as same as the initial powder,the shrinkage rate of the coatings didn’t not change significantly even after heating at 1500℃ for 100 h.The reason for the difficulty of sintering in coatings were large number of closed pores inside the coatings.The above results indicate that the coatings performance can be improved significantly with changing the powder structure.The temperature-bearing capacity of the fully stable t’-YSZ coatings prepared with the spherical thin-walled hollow shell powder can be increased at least 400°C,which is very important to the use of the engine.