Preparation Of 8YSZ Nano-agglomerated Powder For PS-PVD And Its Effect On Thermal Barrier Coatings

Thermal barrier coatings(TBCs)are a key technology in the core components of advanced aeroengines.As aeroengines move toward higher thrust-to-weight ratios,the demand for highperformance thermal barrier coatings has increased.Plasma Spray-Physical Vapor Deposition(PS-PVD)is the hottest and most promising thermal barrier coating technology due to it has advantages of atmospheric plasma spray(APS)and electron beam-physical vapor deposition(EB-PVD).At present,the application of PS-PVD deposited thermal barrier coatings has achieved certain results,but those researches mainly focused on process improvement and coating performance characterization.The research on the influence of powder intrinsic properties on coating structure and properties is rare.Based on the status quo,this paper studies the controllable preparation of YSZ nano-agglomerated powder for PS-PVD.In this paper,8YSZ nano-powders were used as raw materials to prepare corresponding agglomerated powders by spray drying method.The effects of polyacrylic acid(PAA,dispersant),polyvinylpyrrolidone(PVP,binder)and solid content on agglomerated powder were studied.After that,a series of columnar thermal barrier coatings was prepared by PS-PVD,and the influence of the particle size of the agglomerated powder and the original grain size on the structure and properties of the coating was investigated.The main research results are as follows:(1)As the PAA content increases,the viscosity of the suspension decreases first and then increases;When the PAA addition amount is 6 wt.% and the pH value is 6.4,the suspension has a maximum zeta potential of 33.6 mV,and the dispersion effect of PAA is the best.The viscosity of the suspension increases with the addition of PVP.And it is beneficial to increase the sphericity and particle size of the agglomerated powder to increasing the amount of PVP.When the solid content is low,the solid phase content in the liquid droplets is small,and it is difficult to agglomerate into a ball;when the solid content is high,the agglomerated powder is dense and has a large particle size.When the solid content is more than 35 wt.%,the agglomerated powder has good fluidity.(2)The thermal barrier coating after deposition includes a dense layer and a columnar layer.The thickness of the coating increases as the particle size of the agglomerated powder increases;The bonding strength of the coating decreases with the increase of the particle size of the agglomerated powder,and the failure mode is mainly caused by intergranular fracture and cohesive failure;(3)As the original grain size increases,the thickness of the deposited coating of the agglomerated powder increases.And the bond strength decreases and the dense layer is thinned.When the original grain size is 150 nm,the dense layer basically disappears.At this time,the bottom and top indentation hardness and Young’s modulus of the coating section tend to be uniform.When the original grain size is 150 nm,the thickness of TGO in the coating is reduced by 3.6 μm after high temperature oxidation for 200 h.However,since there is no dense layer to relieve the stress,a through crack occurs at the interface.(4)The change in particle size of the agglomerated powder does not affect the gasification efficiency at the time of spraying.But changes in the original grain size will change the powder gasification efficiency: As the original grain size increases,the particles undergo a force change in the radial direction of the plasma jet.As a result,the number of particles entering the center of the flame flow increases,and the powder gasification efficiency is improved.In this paper,the deposition of thermal barrier coatings is mainly the process of condensation of gas phase particles to form clusters of equiaxed crystals,which then grow on the surface of the substrate.When the gas phase concentration is high,the cluster crystals grow sufficiently,the dense layer of the coating is thin,and the columnar crystals are slender and uniform;When the gas phase concentration is low,the cluster crystals are difficult to grow,and the columnar crystals preferentially grow on the surface of the liquid phase YSZ and spherical particles,and the columnar crystals are short and thick.