Laser Thermal Heating Test Of Thermal Barrier Coatings And Failure Analysis

In modern gas turbine(including power plants and other propulsion turbines),improving engine efficiency by making the engine produce more power and/or reducing fuel consumption are the two most effective ways.The most cost-effective approach to reduce fuel consumption and to increase engine power was the development and application of reliable thermal barrier coatings.As it turns out,the power and efficiency of gas turbine engines typically increase with increasing nominal operating temperature.However,the ability of the turbine engine to operate at increasing higher temperature is limited by the ability of the turbine components;especially the blades,to withstand the heat,oxidation,and corrosion effects of the impinging hot gas stream from the combustor and still maintain enough mechanical strength.Therefore,the development and application of thermal barrier coatings become increasingly important.Thermal barrier coatings(TBC)are used to protect the hot components of gas turbines engines to enhance thermal efficiency and component service life.The coating,based on yttria stabilized zirconia,is used in this study.These buttons are subject to precisely-controlled laser heating on the top side and compressed air cooling on the bottom side.In this paper,laser high heat flux testing with an applied temperature gradient across TBC coated buttons is presented.There are three kinds of ceramic coating were used in this paper: Zr O2-8wt.%Y2O3(8YSZ).8YSZ coating is commonly used in the industry.Analysis of void fraction change before and after the test,thermal conductivity change with respect to heating time,failure assessment,and metallurgical analysis are presented.Based on the horizontal cracks and the thermally grown oxide layer geometry,a finite element analysis is conducted to calculate the residual stress and the strain energy release rate.The heating is cyclic,that is,high temperature is maintained for 15 minutes of dwell time and then laser power is turned off to achieve a short cooling period.In the laser heating,the top surface temperature is maintained at 1150 ? and bottom temperature is at 950?.All key measurements(temperatures,laser power to coupon,compressed air flow rate,etc.)are recorded per second.