THERMO-MECHANICAL STUDY OF THE ROLE OF GD_2ZR_2O_7 (GZ) IN IMPROVING LIFE OF YSZ AND GZ DOUBLE LAYERED THERMAL BARRIER COATINGS

摘要

Thermo-mechanical properties and thermal cycling behavior of gadolinium zirconate Gd_2Zr_2O_7 (GZ) based thermal barrier coatings (TBCs) was investigated in this study in comparison to conventional yttria-stabilized zirconia (YSZ) coatings. This paper presents results focusing on coefficient of thermal expansion (CTE) measurements, thermal cycling tests, measured elastic properties and porosity of the multilayered GZ/YSZ TBCs deposited by atmospheric plasma spraying (APS) on an Inconel 738 (IN738) superalloy substrate. SEM microstructural images of failed TBC specimens are also presented. Samples of different double layer combinations with one layer being either 100% YSZ or 100% GZ and the second containing varying amounts of the two compounds were prepared to determine optimum combination that maintains good insulating properties while reducing the CTE mismatch between the TBC layers. The temperature range of the tests was 25°C to 1300°C. The samples are processed by APS on (Ø -12.7 mm, thickness 3 mm) IN738. Using a dilatometer, CTEs of the as sprayed top coat (TC) combinations are measured and compared. The elastic properties are measured using a Hysitron nanoindenter. Results showed that the 10%GZ/ 90%YSZ+ 100YSZ double layered structure was the best among the tested GZ based TBCs and the delamination of GZ/YSZ coating first initiated in the GZ layer close to the interface of GZ and YSZ layers, which was mainly caused by the sintering effect of the GZ layer.