Key Takeaways & Executive Findings
- •• • Friction coefficient and wear rate of plasma-sprayed YSZ-CaF2 coatings decrease monotonically with increasing temperature, reaching minimum values at 800 °C; this enables reliable operation of aero-engine high-temperature moving components up to 800 °C without external liquid lubricants. • • Finite element simulation of wear volume agrees with experimental measurements to within less than 3% error across all tested temperatures, validating the thermomechanically coupled ball/coating model and the temperature-dependent Archard wear simulation method for quantitative wear prediction. • • At elevated temperatures, surface concentrations of ZrO2 and Al2O3 wear-resistant phases and CaF2 lubricious phase increase, producing a continuous protective oxide layer that reduces interfacial contact pressure and promotes more uniform pressure distribution, directly mitigating localized wear and extending component service life. • • The proposed simulation framework, combining Hertzian contact validation with ALE adaptive meshing and temperature-dependent wear coefficients, provides a predictive tool for coating tribological behavior evolution, enabling design optimization and life prediction of YSZ-CaF2 coatings in aerospace applications.
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Abstract
Aero-engine thrust-to-weight ratios and inlet temperatures continue to rise, imposing severe tribological demands on high-temperature moving components. YSZ-CaF2 self-lubricating wear-resistant coatings were deposited by plasma spraying, and ball-on-surface reciprocating sliding tests were conducted from room temperature to 800 °C. Friction coefficient and wear rate both decreased monotonically with increasing temperature, reaching minima at 800 °C. Post-test characterization by SEM/EDS, XRD, and white-light interferometry revealed increased surface concentrations of ZrO2 and Al2O3 wear-resistant phases and CaF2 lubricious phase, accompanied by formation of a continuous protective oxide layer. A finite element model of the ball/coating contact incorporating thermomechanical coupling was developed, and a wear simulation method integrating temperature-dependent friction coefficients and wear rates was implemented using Archard wear theory and Arbitrary Lagrangian-Eulerian adaptive meshing. Simulated contact pressures agreed with Hertzian analytical solutions, and simulated wear volumes deviated from experimental measurements by less than 3% at all tested temperatures. The simulations further showed that contact pressure decreased and became more uniformly distributed as temperature increased. The combination of increased CaF2 lubricious phase and ZrO2/Al2O3 wear-resistant phases, together with oxide layer formation, improved interfacial contact conditions and reduced friction and wear. The proposed simulation methodology is validated as accurate and effective for predicting tribological behavior and wear evolution of YSZ-CaF2 coatings under high-temperature service conditions.
1. Introduction
Aero-engine performance enhancement demands continuous increases in thrust-to-weight ratio and inlet temperature, subjecting internal moving components to increasingly severe tribological conditions. Conventional liquid lubricants degrade rapidly above 300 °C, and uncoated superalloy surfaces exhibit excessive friction and wear at temperatures exceeding 600 °C. Existing solid lubricant coatings, such as those based on MoS2 or graphite, suffer from oxidative degradation above 400 °C, limiting their applicability in the high-pressure turbine and afterburner sections. Yttria-stabilized zirconia (YSZ) offers exceptional thermal stability and wear resistance, but its high friction coefficient at elevated temperatures remains a critical bottleneck. The incorporation of CaF2 as a high-temperature solid lubricant into a YSZ matrix represents a promising strategy to achieve self-lubrication across a broad temperature range, yet the underlying tribological mechanisms and predictive capabilities for wear evolution under thermomechanical coupling remain insufficiently quantified.
This study addresses the lack of validated simulation methodologies for YSZ-CaF2 coatings by integrating high-temperature friction and wear experiments with a thermomechanically coupled finite element model. Plasma-sprayed YSZ-CaF2 coatings were tested in ball-on-surface reciprocating sliding mode from room temperature to 800 °C, and the friction coefficient, wear rate, micromorphology, elemental composition, and phase composition were systematically characterized. A wear simulation method incorporating temperature-dependent friction coefficients and wear rates, based on Archard wear theory and Arbitrary Lagrangian-Eulerian adaptive meshing, was developed and validated against experimental results. The findings establish a quantitative framework for predicting tribological behavior and wear evolution of YSZ-CaF2 coatings, enabling reliable design and life prediction of high-temperature moving components in aero-engines.
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DUAN Ailing, HUANG Xingrui, JING Jiannong, WANG Quan, WANG Zhiwei, MO Jiliang (2026). Friction and Wear Experiment and Simulation of YSZ-CaF2 Coating at High-temperature Conditions. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.11.001
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Frequently Asked Questions
What is the quantitative accuracy of the proposed wear simulation method compared to experimental measurements?
The finite element simulation of wear volume deviates from experimental results by less than 3% across all tested temperatures, as stated in Section B. This error margin validates the thermomechanically coupled ball/coating model and the temperature-dependent Archard wear simulation method, providing confidence for quantitative wear prediction in engineering applications.
How does the friction coefficient and wear rate of YSZ-CaF2 coating vary with temperature, and what is the optimal operating temperature?
Both friction coefficient and wear rate decrease monotonically with increasing temperature, reaching minimum values at 800 °C. This trend is attributed to increased surface concentrations of CaF2 lubricious phase and ZrO2/Al2O3 wear-resistant phases, along with the formation of a continuous protective oxide layer that reduces interfacial contact pressure and promotes more uniform pressure distribution.
What are the primary mechanisms responsible for the reduced friction and wear at elevated temperatures?
At high temperatures, the CaF2 lubricious phase content increases, lowering the interfacial friction coefficient. Simultaneously, ZrO2 and Al2O3 wear-resistant phase contents rise, significantly reducing coating wear and generating a large-area, relatively complete oxide layer. This oxide layer improves the ball/coating interfacial contact state, resulting in more uniform contact pressure distribution and enhanced anti-friction and anti-wear performance.
How does the finite element model account for thermomechanical coupling effects, and how was it validated?
The finite element model incorporates thermomechanical coupling by considering temperature-dependent material properties and thermal expansion. Validation was performed by comparing simulated contact pressures with Hertzian analytical solutions, which showed agreement. Additionally, simulated wear volumes matched experimental results with less than 3% error at all tested temperatures, confirming the model's effectiveness for simulating contact pressure and tribological behavior under varying temperature conditions.
What are the industrial implications of the YSZ-CaF2 coating for aero-engine high-temperature moving components?
The coating exhibits excellent anti-friction and anti-wear performance at high temperatures, with minimum friction and wear at 800 °C. This enables improved service reliability and lifespan of aero-engine high-temperature moving mechanisms, reducing maintenance costs and enhancing operational safety. The validated simulation method supports design optimization and life prediction, facilitating the adoption of YSZ-CaF2 coatings in critical aerospace applications.
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