International Journal of Advanced Engineering Application

Thermomechanical Fatigue Life Prediction, Spallation Resistance Characterisation, and Microstructural Degradation Analysis of Gadolinium Zirconate / Yttria-Stabilised Zirconia Bilayer Thermal Barrier Coatings for Advanced Gas Turbine Blade Applications

Author(s):Rajmohan Venkatesh

Affiliation: Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India Collaborating Institution: Gas Turbine Research Establishment (GTRE), Defence Research and Development Organisation (DRDO), Bengaluru, Karnataka, India

Page No: 21-27

Volume issue & Publishing Year: Volume 3, Issue 6, 2026/06/05

Journal: International Journal of Advanced Engineering Application (IJAEA)

ISSN NO: 3048-6807

DOI:

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Abstract:
Next-generation aero gas turbine engines targeting turbine inlet temperatures (TIT) exceeding 1700°C require Thermal Barrier Coating (TBC) systems whose thermal insulation capacity and spallation resistance surpass those of the current industry-standard 7 wt% Yttria-Stabilised Zirconia (7YSZ) single-layer system, which undergoes destabilising tetragonal-to-monoclinic phase transformation above 1200°C with attendant volume change and accelerated sintering-driven stiffness increase that precipitates coating spallation after 300–500 thermal cycles at service temperatures. Gadolinium Zirconate (Gd₂Zr₂O₇, GZO) has emerged as the leading candidate top-coat material for next-generation TBC systems owing to its intrinsically lower thermal conductivity (1.2–1.6 W/m·K vs. 2.0–2.2 W/m·K for 7YSZ at 1000°C), superior phase stability to 1450°C, and resistance to calcium-magnesium-alumino-silicate (CMAS) glass infiltration that is the dominant degradation mechanism for TBCs in engines operating in particulate-laden environments. However, GZO's low fracture toughness (0.9–1.1 MPa√m vs. 2.0–2.3 MPa√m for 7YSZ) makes single-layer GZO TBCs susceptible to spallation during the high thermal gradient transients associated with engine start-stop cycles, motivating the bilayer architecture in which a dense GZO top-coat is deposited over a standard 7YSZ bond-coat-compatible interlayer that provides fracture toughness bridging while preserving the thermal insulation benefit of GZO.
This study presents a comprehensive experimental characterisation of GZO/7YSZ bilayer TBC systems deposited by Electron Beam Physical Vapour Deposition (EB-PVD) on René 80 nickel-superalloy substrates with NiCoCrAlY bond coats, evaluating three GZO thickness fractions (25%, 50%, 75% of total TBC thickness at constant 250 μm total thickness) against a 100% 7YSZ control. Thermal cycling fatigue life (furnace cycle testing, 1100°C hot-side, 100°C cold-side, 1-hour cycles), thermomechanical fatigue life (in-phase and out-of-phase TMF, 400–1100°C, 60-second period), CMAS infiltration resistance (75 mg/cm² CMAS powder deposit, 1250°C/24-hour isothermal exposure), and thermal conductivity evolution over 100 cycles (laser flash diffusivity, 25–1100°C) are reported. Results demonstrate that the 50% GZO bilayer configuration achieves 2.3 times the furnace thermal cycle life of the 7YSZ control (1,148 vs. 502 cycles to 20% area spallation), 1.8 times the out-of-phase TMF life, 94% CMAS penetration depth reduction relative to 7YSZ, and 31% lower steady-state thermal conductivity — establishing the 50% GZO bilayer as the optimal architecture for GTRE's Kaveri engine derivative programme targeting 1650°C TIT.

Keywords: thermal barrier coating, gadolinium zirconate, yttria-stabilised zirconia, bilayer TBC, EB-PVD, thermomechanical fatigue, CMAS degradation, spallation resistance, gas turbine blade, thermal conductivity, nickel superalloy, GTRE Kaveri

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