Microstructure And Properties Of Atmospheric Plasma Sprayed 5wt.%YSZ And 8wt.%YSZ Nanostructured Coatings

Because of the high melting point,low thermal conductivity,high thermal expansion coefficient and chemical stability,yttria-stabilized zirconia(YSZ)ceramics are widely used in aviation,aerospace,energy and other fields as thermal barrier coatings.In order to meet the needs of the continuous development of equipment properties,exploration and optimization on the YSZ coating performance has become an important research direction in related fields.In this study,atmospheric plasma spraying was used to spray the 5wt.%Y2O3-ZrO2 and 8wt.%Y2O3-ZrO2 nano-agglomerated powders,5YSZ and 8YSZ coatings were successfully deposited.The as-sprayed coatings were observed and compared.In order to compare the high temperature resistance of 5YSZ and 8YSZ coatings,YSZ samples were heat treated at 1400℃,the microstructure of 5YSZ and 8YSZ coatings after heat treated were compared.The differences between Vickers hardness,phase composition and thermal insulation property were analyzed.The influences of heat treatment on the structural features and properties of coatings were characterized.In the study,the thermal shock tests were carried out by heating and quenching,and the reasons of YSZ failure after thermal shock were discussed.The experimental results showed that the bimodal structure of 5YSZ and 8YSZ coatings were obtained with a spraying current of 375A,and the content of nanostructure in the coatings were 50%±1%and 52%±1%respectively.As-sprayed YSZ coatings are consisted of t and t’phase.The t→m phase transformation of YSZ happened at 1400℃ heat treatment.As the heat treatment continues,the content of m phase in 5YSZ and 8YSZ coatings gradually increased to 63%and 33%,respectively.Comparing with the heat-treated coatings,5YSZ shows better resistance on densify/shrinkage and grain growth,as well as higher fracture toughness.The Vickers hardness value of 5YSZ coating is 14%lower than 8YSZ after heat treated.When the thermal shock test was performed at 1000℃,the thermal cycling life of the 5YSZ coating was over 25%longer than the 8YSZ.The better sintering resistance of 5YSZ may results in a better thermal shock resistance.After thermal shock,the residual compressive stress values in the 5YSZ and 8YSZ coatings were 92 MPa and 454 MPa,respectively.A higher residual stress may cause the failure of the 8YSZ coating.