Microstructure and ablation behavior of TiAl alloy with in-situ HfSi2-HfO2-SiO2 nanocomposite ceramic coating by LPDS technique

Abstract

In this study, a HfSi2-HfO2-SiO2 nanocomposite coating is prepared on a TiAl alloy via a one-step liquid plasma-assisted particle deposition and sintering (LPDS) method to enhance its ablation resistance. For comparison, a conventional plasma electrolytic oxidation (PEO) coating is fabricated on the substrate. The phase composition, microstructure, and elemental distribution of the coatings are investigated via scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Moreover, the ablative resistance of the coated samples under flame (> 1500 °C) ablation is evaluated using a methyl acetylene polypropylene gas spray gun. The results show that numerous HfSi2 particles are incorporated into the coating with partial oxidation to HfO2 during the LPDS, thus resulting in a larger thickness by approximately eight folds compared with the thickness of the PEO coating. After ablation for 360 s, 15.4 % of the PEO coating peeled off, whereas no exfoliation occurred on the HfSi2-HfO2-SiO2 nanocomposite coating. The nanocomposite coating exhibits the smallest thickness after ablation. The superior high-temperature ablation resistance of the nanocomposite coating is primarily attributed to the presence of an oxygen-consuming HfSi2 phase. Furthermore, the formation of HfO2 during high-temperature ablation effectively anchors the ceramic coating, thereby impeding crack propagation and hindering oxygen diffusion. Hence, LPDS is a prominent strategy for the design and fabrication of multifunctional ceramic coatings that incorporate various functional particles, which can enhance the thermal protection of alloy substrates.