Synergistically achieving low friction and high wear resistance over wide-temperature-range in a composite coating for ceramic matrix composites

Designing the composite sealing coating towards synergistically achieving low friction and high wear resistance over wide-temperature-range is critical for stable application of ceramic matrix composite(CMC) turbine outer ring component. Hence, in this work, a multi-phase composite coating is fabricated on C/SiC composites by using Supersonic Atmospheric Plasma Spraying (SAPS) for the application of sealing. A dense layered microstructure and a low coefficient of thermal expansion mismatch with the substrate enable superior thermal shock resistance, sustaining 110 cycles at 800 °C. In addition, the optimized coating exhibited a stable and low coefficient of friction (∼ 0.3) and an ultralow wear rate (∼ 10⁻⁷ mm³/N·m) across a broad temperature range (from room temperature to 800 °C). The low friction can be attributed to the in-situ formation of a temperature-adaptive lubricating film containing CaF₂, CaMoO₄, and Ag phases. The outstanding wear resistance is due to the formation of a layered friction structure, including a third-body layer(TBL) and a plastic deformation layer(PDL). The TBL rejects heat and resists plastic deformation, whereas the PDL has the appropriate plastic deformation capacity to carry and release stresses. This work can provide valuable insights into the development of low-friction and wear-resistant composite sealing coatings for high-temperature CMC applications.