Effect of LaB6 on the thermal shock property of MoSi2-SiC coating for carbon/carbon composites

Highlights: ► LaB6-MoSi2-SiC and MoSi2-SiC multi-composition coatings were coated on C/C composites by pack cementation. ► The microstructure and thermal shock resistance of both coatings were investigated. ► The addition of LaB6 can increase the compactness, flexural strength and fracture toughness of the MoSi2-SiC coating simultaneously. ► Both coatings bond well with the substrates before and after thermal cycling oxidation between 1773 K and room temperature. ► The LaB6-MoSi2-SiC coated C/C shows better thermal shock resistance than the MoSi2-SiC coated C/C. - Abstract: LaB6-MoSi2-SiC and MoSi2-SiC coatings were prepared on the surface of carbon/carbon composites by pack cementation method. The crystal structures of the coatings were measured by X-ray diffraction. The morphologies and element distributions were also analyzed by scanning electron microscopy and energy dispersive spectroscopy, respectively. The effect of LaB6 on the microstructure and thermal shock resistance of MoSi2-SiC coating was investigated. The results indicated that the LaB6-MoSi2-SiC coating possessed a denser structure and superior thermal shock resistance. After 25 times of thermal cycling oxidation between 1773 K and room temperature, the weight losses of the LaB6-MoSi2-SiC and MoSi2-SiC coated samples were 0.627% and 2.019%, respectively.