Abstract
This paper presents an experimental study on simultaneously measuring the elastic modulus and residual stress of a thermal barrier coating (TBC) after different isothermal heat treatments. The elastic modulus and residual stress of TBCs were theoretically analyzed based on composite beam bending theory. Thereafter, an experimental setup was established combining the 3D digital image correlation method with the bending test to obtain the curvature changes in the TBC sample. Finally, the elastic modulus and residual stress of the ceramic layer with different isothermal heat treatments were obtained. The results show that the elastic modulus of the ceramic layer measured under compression is greater than that under tension, and the elastic modulus of the ceramic layer increases first and then tends to be stable as the heat treatment time increases. In addition, the residual stress of the TBCs ceramic layer quickly changes from compressive stress to tensile stress with heat treatment, and the tensile stress increases with the increase in thermal exposure time. Furthermore, the reasons for the change tendency were analyzed according to the variation in porosity and microstructures by processing the scanning electron microscope (SEM) figures. The results demonstrate that simultaneously determining the elastic modulus and residual stress of TBC based on combining the 3D digital image correlation method with the bending test is effective and reliable.
Highlights
The application of thermal barrier coatings (TBCs) to components of gas turbine engines with internal cooling has dramatically increased the turbine entry temperature, thereby improving the performance and efficiency of gas turbine engines
The results indicate that elastic modulus of the topcoat-upward specimen is always greater than that of the topcoat-downward specimen, or elastic modulus in compression is always greater than that in tension, and the mutual difference is significant with the increasing high temperature exposure time
This study focused on the experimental determination of the elastic modulus and residual stress of thermally sprayed TBCs
Summary
The application of thermal barrier coatings (TBCs) to components of gas turbine engines with internal cooling has dramatically increased the turbine entry temperature, thereby improving the performance and efficiency of gas turbine engines. The curvature method has been applied to measure the elastic modulus of plasma-sprayed coatings based on bi-layer beam equilibrium [18]. A progressive layer removal technique is generally unadvisable for ceramic materials where an uncontrolled stress relaxation or modification can occur The destructive techniques such as block sectioning, slitting and hole-drilling with strain gauge rosettes are well established worldwide due to their versatility and reliability. Further research is imperative for the evaluation and design of plasma-sprayed TBCs. The present work aims to develop an experimental method to simultaneously determine the elastic modulus and residual stress of TBCs by a 3D digital image correlation technique. Theoretical studies on composite beam bending were conducted to establish the formulas to determine the elastic modulus and residual stress of TBCs. Second, digital image correlation was employed to obtain curvatures of the TBC specimens with varying high temperature exposure time. Elastic modulus and residual stress of TBCs are obtained followed by discussion and conclusions
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