The Mechanical Performance Parameters Determination And Analysis Of Thermal Barrier Coating Material Under The High Temperature

Thermal barrier coatings(TBCs) have been widely used in the fields of military and nation defense due to their thermal insulation, wear resistance and corrosion resistance. In practice, however, Mismatch stresses in multiple-layers TBCs lead to the nucleation, propagation of the cracks, and result in the failure of TBCs, which strong restricts the reliability and application of TBCs. Therefore, determination of the material mechanical parameters for the thermal barrier coating under the serving temperature is of great importance, even for the guidance of the coating material design and process improvement. In this paper, A material high temperature testing system based on the digital image correlation have been designed and developed. For the analysis of the thermal expansion coefficient, modulus of elasticity, fracture strength and fracture toughness and other performance parameters, thermal deformation of the thermal barrier coating material was measured under different high temperature. Developed an experimental characterization method for mechanical parameters of the high temperature materials, The main research content is summarized as follows:Firstly, a set of high temperature material mechanical performance test system based on digital image correlation method have been designed and developed independently. This system is assembled with 1600 °C high temperature furnace, Aramis deformation measurement system, lighting system and infrared filter system and so on. A kind of high temperature resistant speckle applied to the digital image correlation method was finished and meet the requirements. After debugging the high temperature furnace, the temperature error was controlled in ±1 °C. Provided a suitable experimental method and reliable experimental instruments, thermal barrier coating material mechanical performance test is proceed under the high temperature environment.Secondly, within the range of 1600 °C, through the thermal deformation test of the thermal barrier coating material, the thermal expansion coefficient of the ceramic layer and substrate materials were analysis under different temperature. Combined the high temperature furnace with Aramis deformation measuring system, the digital images on the sample surface were real-time monitored and gathered under different temperature. On the basis of the surface full thermal deformation information, the thermal expansion was calculated. The results show that, at the range of 25 °C and 1600 °C, the thermal expansion coefficient of the freestanding ceramic 8wt%Y2O3-ZrO2(8YSZ) coating and the high temperature alloy substrate changes from 8.837×10-6/°C to 14.332×10-6/°C and 12.37×10-6/°C to 18.03×10-6/°C, respectively. The accuracy of the digital image correlation method was verified by experiment, and the results provided reliable theoretical and experimental basis for the appearance of the high temperature thermal mismatch stress.Thirdly, the elastic modulus and fracture strength of the thermal barrier coating material were tested under the high temperature. With the digital image correlation method, uniaxial tension method and three point bending method were carried on fracture experiments under different high temperature. The experimental results were conducted for the substrate alloy and freestanding coating indicated that the elastic modulus of the alloy substrate changes from 143 GPa to 129 MPa, and the tensile strength changed from 156 MPa to132 MPa between 1000 °C and1100 °C by uniaxial tension method. The elastic modulus of the ceramic coating varies from 26.2 GPa to 16.9 GPa and the bending strength was between 33.55 MPa and 29.64 MPa at the range of 1100 °C and 1200 °C by three point bending method.Fourthly, the fracture toughness of the thermal barrier coating material was estimated with the unilateral incision beam method under the high temperature. Coupled with digital image correlation method, the bending process and the crack expense path were monitored and recorded currently. From the Time-Strain curve and Time-Stress curve of the 8YSZ freestanding coating, the critical load was determined. Experimental and theoretical studies turned out that the fracture toughness of the freestanding coating is reduced from 1.98 MPa·m1/2 to 1.04 MPa·m1/2 with the increase of the temperature from 1100 °C to1200 °C. This measurement provide a reliable experimental characterization method to research the crack propagation and fracture failure of the ceramic coating under the high temperature.