Coatings toughened with nano-HfO2 fibers to improve the thermal shock resistance of W-26Re alloys

W-Re alloys find wide application in high-temperature measurements and as components of engines and aircraft. However, their low oxidation and thermal shock resistances have limited their application at high temperatures in oxidized atmospheres. In this work, an inner WSi2 coating was first prepared on the surface of the W-26Re alloy by pack cementation. Subsequently, an outer ZrB2-HfO2-SiC (ZHS) coating was prepared by the sol-gel method and blade coating, using self-prepared nano-HfO2 fibers introduced in different ratios (0%, 3%, 6%, and 9%). Following thermal shock tests at 1073-1773 K, the coatings toughened by nano-HfO2 fibers with high melting point (above 3000 K) showed better thermal shock resistance, especially the 6% HfO2-doped coatings. The 6%Hf-ZHS coating underwent the highest number of thermal shock cycles (369), 385.5% and 210.1% higher than those experienced by W-26Re and ZHS. In addition, the thermal shock resistance of ZHS was 56.6% better than of the bare W-26Re alloy. Finally, the protection mechanism of the above coatings was explained by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses.