Self-healing YSZ-La-Mo-Si heterogeneous coating fabricated by plasma spraying to protect carbon/carbon composites from oxidation

To protect carbon/carbon (C/C) composites against oxidation, YSZ-La-Mo-Si (YSZ-LMS) heterogeneous coating was prepared by the plasma spraying using YSZ (Y₂O₃-stabilized ZrO₂), MoSi₂ and LaB₆ as raw materials. Microstructure and surface chemistry of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Moreover, the thermogravimetric and isothermal oxidation results indicated that the YSZ-LMS coating revealed superior oxidation protective ability at elevated temperatures, which protected the C/C composites from oxidation for 50 h at 1773 K with a mass loss of 0.58%. The generation of SiO₂, ZrSiO₄, Y₂SiO₅ and La₂O₃ expanded the volume of solid phase and decreased the volatilization of SiO₂, forming a denser Zr-Y-La-Si-O oxide glass layer. Such volume expansion promoted the formation of compressive stress within the coating at high temperature, which restrains the initiation and propagation of cracks and facilitates the oxidation resistance of the coatings for C/C composites. The corresponding high temperature oxidation activation energy of the coated C/C composites at 1573–1773 K is calculated to be 74.466 kJ mol⁻¹.