Mechanical Properties Durability of Sc2O3-Y2O3 Co-Stabilized ZrO2 Thermal Barrier Materials for High Temperature Application

Wei Fan,Yanfen Liu,Qi Liu,Yiqi Wang,Yu Bai,Yu Wang

doi:10.3390/coatings12020155

Abstract

The poor phase stability of conventional 6–8 wt.% yttria-partially stabilized zirconia (YSZ) results in the formation of detrimental cracks in thermal barrier coatings (TBCs) as well as the decrease of fracture toughness, limiting its long-term application above 1200 °C. Here, we try to prove that a higher t′-phase stability is the prerequisite for the mechanical properties durability of ZrO2-based TBC materials. Compared with YSZ ceramic, 7.0 mol.% Sc2O3 and 0.5 mol.% Y2O3 co-stabilized ZrO2 (ScYSZ) shows a superior t′ phase stability at 1300 °C. In addition, the fracture toughness of ScYSZ is nearly stable after being annealed at 1300 °C for 0–40 h, while the value of YSZ gradually declines during the aging process. The stable fracture toughness of ScYSZ is closely related to its prominent t′ phase stability. The elastic modulus of ScYSZ is nearly unchanged and lower than that of YSZ. The excellent stability of the phase structure and mechanical properties makes ScYSZ a great potential material for next generation high-temperature TBCs.

Highlights

Thermal barrier coatings (TBCs) are indispensable in protecting the key hot-section components of high-temperature gas turbines as well as high-power diesel engines [1,2,3,4]
The TBC system deposited on the super-alloys includes a metallic bond coating layer, a thermally grown oxide (TGO) layer that forms as a result of in-service bond-coat oxidation, and a thermal barrier ceramic layer [5,6,7]. 6–8 wt.% yttria-partially stabilized zirconia (YSZ) is employed intensively as thermal barrier material due to its relatively low thermal conductivity, proper coefficients of thermal expansion and prominent mechanical properties [8,9,10]
The previous research demonstrated that 7.0 mol.% scandia and 0.5 mol.% yttria co-stabilized zirconia (ScYSZ) was fully t phase, even when annealed for 336 h at 1500 ◦C, while t -YSZ fully changed to the m phase and c phase under the same conditions [24]

Summary

Introduction

Thermal barrier coatings (TBCs) are indispensable in protecting the key hot-section components of high-temperature gas turbines as well as high-power diesel engines [1,2,3,4]. The t-phase further transforms into the monoclinic (m) phase during cooling, resulting in a 3–5% volume expansion and the degradation of the fracture toughness [11,12,13,14,15,16] These changes are the main reasons for the easy generation and propagation of detrimental cracks as well as the premature failure of TBCs [17,18,19]. The mechanical properties durability of dense YSZ and ScYSZ bulk materials after a high-temperature heat treatment was comparatively studied by selecting an appropriate annealing temperature and time to control the phase composition and grain size. This study further confirmed that t phase stability was a prerequisite for the mechanical properties durability of ZrO2-based thermal barrier coatings, and provided a very promising future for the generation of high-temperature thermal barrier coating materials

Samples Preparation

Findings

Phase Composition