Study On The Characteristics And Deposition Mechanism Of Yb₂O₃ Stabilized ZrO₂ Nano Coatings By Liquid Plasma Spray

With the increasing demand for thermal barrier coatings（TBCs）,nano-coatings have become one of the most promising thermal barrier coatings.At present,the methods and materials for preparing nano-thermal barrier coatings are mainly atmospheric plasma sprayed Y₂O₃ partially stabilized ZrO₂（YSZ）.However,when the YSZ coating is used for a long time in a high temperature environment of 1200°C or higher,the stability of the high temperature phase is poor,phase transformation and sintering are prone to occur,and the conventional atmospheric plasma sprayed crystal grains tend to grow,making it difficult to prepare nanostructure coatings..In this paper,Yb₂O₃ with better stability is used as stabilizer.Solution precursor plasma spraying（SPPS）and suspension plasma spraying（SPS）are used to prepare Yb2O3stabilized ZrO₂（YbSZ）nano-coating.Morphology,phase composition,crystallinity and porosity were studied to find the influence law,and the optimal process parameters were obtained.Finally,the deposition mechanism of SPPS/SPS coating was discussed.The results show that the SPPS coatings contain three microstructures:spherical YbSZ nanoparticles,agglomerated particles and pores.With the increase of spraying distance and spraying power,the number of spherical nanoparticles increases,and the number of uniform pore increases,the deposition efficiency increases;grain size first decreases and then increases with the increase of spraying distance,and then decreases with the increase of spraying power.There are longitudinal cracks in the coating and a large number of closed pores,the particles tend to grow in clusters.When the spraying power is 36 kW and the spraying distance is 60 mm,m-ZrO₂ is detected.As the distance increases and the spraying power increases,only a single t-ZrO₂ exists in the coating.In comparison,it can be found that a concentration of the precursor solution of 0.8mol/L is most suitable.The thermal conductivity and thermal expansion coefficient of the substrate affect the morphology and bonding strength of the coating.The formation mechanism of SPS coatings is that the solvent evaporates rapidly,then the nanoparticles melt and spread flat and stack,and some of the nanoparticles don’t melt at a lower temperature zone,resulting in the inclusion of many unmelted nanospheres in the coatings.The average porosity of the YbSZ coating by SPPS increases with the increase of the spraying distance and the reduction of the spraying power,up to 40.2%.Within a certain range of parameters,the effect of spray distance on crystallinity is greater than the effect of spray power on crystallinity.The SPPS/SPS coating has good high temperature phase stability,which increases the thermal cycle life of the coating.In addition,according to the coating morphology,the formation mechanism of SPPS coatings is that the atomized droplets undergo solvent evaporation,precipitation solid phase,chemical reaction,sintering,melting,etc.in the plasma flame flow,and finally collide with the substrate to form the coating.The higher the spray power and the longer the flight time,the more the atomized droplets change in the plasma flame flow,which affects the effect of the deposited coating.