Study On Thermal Physical And Mechanical Properties Of Ceramic Thermal Barrier Coatings

As a typical multi-layer structural composite material,thermal barrier coatings are widely used in aerospace,transportation and large-scale hydropower fields due to their low thermal conductivity,good fracture toughness and impact resistance.However,with the increasing service temperature of aero-engine hot end components and the harsher working environment,the internal defects of the material are easy to form initial cracks.With the expansion and collection of cracks,the coating falls off and even the material breaks down.This seriously hinders the application and development of thermal barrier coating materials.Therefore,it is urgent to improve the service life of thermal barrier coatings.It is of great significance to develop new thermal barrier coatings with high temperature phase stability,low thermal conductivity and high fracture toughness.In this paper,ZYTO system composite ceramic materials were prepared by solid-state reaction method,and the high-temperature phase stability,thermophysical properties and mechanical properties were studied.The specific research contents are as follows:（1）In this paper,zirconia,yttrium oxide,tantalum oxide,erbium oxide,titanium oxide and niobium oxide powder were used as raw materials,and the concept of high-entropy ceramics was introduced.The composite ceramic materials were prepared by high-temperature solid-state synthesis method.The thermophysical and mechanical properties of ZYTO system composite ceramic materials were studied,and the factors affecting the performance were explored.The phase composition and high-temperature phase stability of ceramic materials were analyzed by XRD and SEM.The specific heat,thermal diffusivity and thermal conductivity of the composite ceramics were measured by laser thermal conductivity instrument,and the influencing factors of the thermal physical properties of the composite materials were explored.The hardness and Young’s modulus of the ceramic samples were tested by micro indentation instrument,and the main reasons affecting the fracture toughness of the samples were analyzed by transmission electron microscopy（TEM）.Among the seven kinds of composite ceramics,（Zr0.544Y0.114Ta0.114Ti0.114Er0.114）O composite ceramics show excellent mechanical properties and thermal physical properties,and can be sintered at1600°C for a long time to maintain phase stability.The results can provide guidance for the regulation of thermal physical properties and mechanical properties of thermal barrier coatings.（2）The high temperature phase stability,thermophysical properties and mechanical properties of（Zr YTa Ti Er）O composite ceramics were studied by changing the ratio of elements.The results show that the（Zr YTa Ti Er）O composite ceramics sintered at 1300-1600°C for 20 h have good high temperature phase stability,similar thermal expansion coefficient and low thermal conductivity to YSZ,especially the thermal conductivity of（Zr0.544Y0.114Ta0.114Ti0.114Er0.114）O is 2.17 W/m K.This is because the multi-element doped materials form complex structure and lattice distortion,which hinders the propagation of phonons and photons in the crystal,and makes the thermal conductivity of ZYTO system composite ceramic materials low.The Young’s modulus and Vickers hardness of（Zr YTa Ti Er）O composite ceramics decrease with the increase of zirconia content,indicating that the inhibitory effect of other rare earth elements on tetragonal zirconia phase transition is weakened.Among them,（Zr0.544Y0.114Ta0.114Ti0.114Er0.114）O has the best mechanical properties.Under the effect of ferroelastic toughening,its fracture toughness can reach 4.29 MPa·m^1/2,which is 1.5 times higher than that of the traditional YSZ thermal barrier coating.（3）The Ti and Er elements in（Zr YTa Ti Er）O composite ceramic materials were replaced by Nb,and the properties of the materials were studied.Among them,the thermal conductivity of（Zr0.544Y0.114Ta0.114Ti0.114Nb0.114）O was the lowest,only 0.98 W/m K.The results of mechanical properties show that（Zr0.544Y0.114Ta0.114Ti0.114Nb0.114）O and（Zr0.544Y0.114Ta0.114Ti0.114Er0.114）O have lower fracture toughness than 8YSZ,but their lower Young’s modulus and higher hardness can still be used as a potential thermal barrier coating material for further development.Through the corrosion resistance study of three groups of composite ceramic materials,it was found that（Zr0.544Y0.114Ta0.114Ti0.114Er0.114）O corrosion rate was only 3.16μm/h,showing excellent corrosion resistance.