Preparation And Properties Of Rare Earth Oxides Co-doped Zirconia Ceramics And Coatings

With the aviation turbine developing to high-flow ratio,high thrust-weight ratio,the gas temperature and pressure of combustion chamber constantly improve.However,for hot components of aircraft engine and gas turbine,conventional ZrO₂ partially stabilized with Y₂O₃?YSZ?coatings,which can only be used below 1473K,can not meet the demand.It is important to find new thermal barrier coatings with lower thermal conductivity,stable performance in the high temperature,good sintering resistance.In this paper,0/0.5/1.0 LGY-YSZ rare earth co-doped zirconia ceramic powders were prepared by high temperature solid-phase synthesis method.The LGY-YSZ thermal barrier coatings were prepared by air plasma spraying.Thermal stability,thermal and physical properties of the bulks and the coatings were investigated.The influence of concentration of La₂O₃ on the phase stability,thermal conductivity and sintering resistance was investigated.The effects of La₂O₃ content on the thermal shock resistance.Evolution of the coating structure as well as the failure mechanism under thermal shock was investigated.The studies on crystal characteristion of the powders reveal that the powders were composed of cubic phase?c?phase and tetragonal phase?t"?phase.No phase transformations occur in the 0/0.5/1.0LGY-YSZ bulks after 150h of testing at 1400?,which proved that LGY-YSZ have excellent phase stability.Compared to 8YSZ,the thermal conductivity of LGY-YSZ are much lower.The grain sizes of the heat treated bulks were obeserved.It is proved that La₂O₃ has a significant role on the inhibition of grain growth.The powder for plasma spraying was prepared by Spray granulation method.Difference of ion radius between La³⁺and Zr⁴⁺has obvious effect on grain boundary migration and grain growth,and it has obvious effect against material diffusion under high temperature sintering condition.Compared to 8YSZ and 0/0.5LGY-YSZ,1.0LGY-YSZ coating has lower thermal conductivity and better sintering resistance.During the thermal shock process,the thermal stress caused by the mismatch between the thermal expansion coefficient of the ceramic layer and the adhesive layer is the reason for the crack in the inner porosity of the coating,which causes the coating to gradually peel off and eventually fail.The substrate temperature has a significant influence on the thermal shock life of the coating.When the thickness of 1.0LGY-YSZ coating is around 200?m,the substrate temperature is over 1150?,the thermal shock lifetime of the coating is only 13times.When the coating thickness is up to 400?m,the substrate temperature is reduced to900?,difference between the coating surface and the back of the substrate is about470⁵00?,he thermal shock lifetime of the coating is 468 times.The thickness of TGO is about 5?m,composed of Al₂O₃,Cr₂O₃,and spinel.Three is a strong oxidation in the bonding layer after the process.The crack mainly occurs at the LGY-YSZ/TGO interface and extends in the ceramic layer?TC?.The thermal stress of the interface caused by the growth of TGO is the main cause of failure.