Effect of Gd content on mechanical properties and erosion durability of sub-stoichiometric Gd2Zr2O7

Abstract

Advanced thermal barrier coating materials are necessary to improve the efficiency of next-generation gas turbine engines. As such, different TBC chemistries must be developed with enhanced temperature stability above that of 7YSZ (~1200°C) while maintaining thermal and mechanical reliability. The present study investigates the effect of rare-earth content on the mechanical properties of ZrO 2 TBCs. Various cubic compositions in the ZrO-GdO 1.5 system were investigated in the form of monolithic pellets and coatings with stoichiometric GZO

Durable aluminate toughened zirconate composite thermal barrier coating (TBC) materials for high temperature operation

“…This is important as it enables some flexibility in the processing of the materials. Additionally, previous research has shown that reducing the rare earth content in GZO can slightly increase the fracture toughness and erosion durability with minimal impact on the thermal conductivity . Thus, the compositional flexibility enables fine tuning of the composites for higher durability (lower RE content) or higher CMAS resistance (higher RE content).…”

“…GZO also has a significantly lower bulk thermal conductivity (1.4 W/m·K) than 7YSZ (2.2 W/m·K), good thermal cyclic durability (when utilizing the appropriate 7YSZ interlayer to prevent interaction with the Al 2 O 3 TGO), and improved resistance to calcium‐magnesium‐alumino‐silicate (CMAS) degradation, a necessary criterion for materials operating above the ~1200°C capability threshold of 7YSZ. The primary drawback of GZO is that it possesses a low fracture toughness of ~1 MPa√m which reduces erosion durability by an order of magnitude compared to that of 7YSZ . Therefore, a means of improving the erosion durability of pyrochlore materials must be developed if they are to be adapted for TBC applications in particulate laden environments.…”

“…A direct comparison of these approaches has been carried out by the authors and demonstrated the strengths and weaknesses of each method . For the intrinsic approach, several authors have investigated the effects of RE zirconate chemistry and stoichiometry on toughness . Unfortunately, the changes are not well understood and still result in toughness values significantly lower than that of 7YSZ, ultimately limiting their applicability.…”

Thermal cycling performances of multilayered yttria‐stabilized zirconia/gadolinium zirconate thermal barrier coatings

“…In order to ensure reliability of results, 15 indentations with 1 N load were made on each sample. The elastic modulus of the sample can be obtained with the following equation:where is the elastic modulus (MPa); is the effective elastic modulus (MPa) obtained from the unloading slope of displacement‐load curve; is the Poisson's ratio; for GZO was applied …”

“…where E is the elastic modulus (MPa); E eff is the effective elastic modulus (MPa) obtained from the unloading slope of displacement-load curve; is the Poisson's ratio; = 0.22 for GZO was applied. 38 To measure fracture toughness of coating, a Vickers indenter with a load of 3 N was applied on a metallographic cross-section of the coatings to generate proper cracks. As all the generated cracks were Palmqvist cracks, the following equation was used to calculate the fracture toughness:…”