Preparation And Properties Of Thermal Barrier Coatings For YSZ And CYSZ Agglomerated Powder

PS-PVD has obvious advantages in the preparation of thermal barrier coatings,but the technology has a high demand for spray powder.Agglomerated powder is the preferred powder for PS-PVD spraying because it is easy to gasify in plasma flame.In this paper,YSZ agglomerated powder for PS-PVD was prepared by spray drying technique,and the effect of calcination temperature on the agglomerated powder as well as coating properties was investigated.Further,the CYSZ composite powder was prepared by spray drying technique,and the effect of CeO₂doping content on the coating properties was investigated.The main conclusions of the full paper are as follows.(1)YSZ agglomerated powders is mainly composed of t-Zr O₂phase and a small amount of m-Zr O₂phase.It has high sphericity,uniform particle size distribution and good flowability.The powder calcined at 500?is easier to gasify in the spraying process,but the weak bonding between primary particles makes the powder easier to compact,resulting in insufficient fluidity.On the contrary,the powder calcined above900?can form strong bonds between the primary particles,even partial sintering,and ensure the fluidity of the powder.However,too strong cohesion makes it difficult to gasify the powder and obtain columnar structure coating.(2)YSZ agglomerated powder deposited columnar structure coating before and after low temperature calcination,and uniform cauliflower head structure was formed on the coating surface.However,with the increase of calcination temperature,the coating becomes dense and the columnar structure disappears.The m-Zr O₂in the calcined powder is completely transformed into t-Zr O₂with better high temperature properties after PS-PVD deposition.At 700?,the special composite structure of dense columnar dense was formed,and the bonding strength of the coating was significantly improved.The coatings deposited before and after calcination show excellent thermal shock resistance..(3)The successful preparation of CYSZ agglomerated powder proves that the agglomerated process design is reasonable.XRD results show that the agglomerated CYSZ powder is composed of c-CeO₂,t-Zr O₂and a small amount of m-Zr O₂,and there is no phase transformation.The agglomerated CYSZ powder is physically agglomerated by binder.With the increase of CeO₂content,the surface of agglomerated powder changes from rough surface with small particles agglomerated to smooth surface with compact agglomerations.EDS analysis showed that CYSZ agglomerated powder contained Y,Zr,Ce,O and other major elements.Y and Zr elements were evenly distributed in the agglomerated powder,while CE element existed in the form of second phase CeO₂,and the powder had good overall fluidity.(4)CYSZ coatings with columnar structure were successfully prepared by PS-PVD using YSZ agglomerated powders with different CeO₂content as spray powder.The results show that Ce⁴⁺in the coating has been completely dissolved into the Zr O₂lattice,forming a composite t-Zr O₂structure,which improves the structural stability of the coating at high temperature.In addition,the bonding strength of the prepared CYSZ coating is low,and the tensile fracture failure is mainly located in the columnar crystal.In 1100?thermal shock test,after 100 times of water-cooled thermal shock,the coating can still remain intact,showing high thermal shock resistance.