Microstructural and thermophysical properties of Dy2Hf2O7-HfO2 composite for thermal barrier coating applications

Abstract A novel biphasic Dy2Hf2O7-HfO2 composite was synthesized via a solid-state reaction route for potential thermal barrier coating (TBC) applications. X-ray diffraction confirmed that the reaction between Dy2O3 and HfO2 at 1500 °C yields a dense composite comprising ∼81 wt% cubic pyrochlore Dy2Hf2O7 and ∼19 wt% cubic fluorite HfO2. Microstructural analysis revealed a hierarchical architecture of nanoscale crystallites (25–34 nm for Dy2Hf2O7 and ~ 13 nm for HfO2) agglomerated into faceted microparticles (~ 1.1 μm). Williamson-Hall analysis indicated significant lattice strain within the Dy2Hf2O7 phase due to its complex pyrochlore framework and cation-size mismatch, whereas HfO2 remained nearly strain-free. The thermophysical properties of Dy2Hf2O7–HfO2 composites were studied from room temperature to 1200 °C. The thermal expansion coefficient increased from 7.6 × 10− 6 K− 1 to 9.2 × 10− 6 K− 1 between room temperature and 1200 °C, while thermal diffusivity and conductivity decreased due to enhanced phonon–phonon scattering and interfacial disorder. The specific heat capacity rose from 0.35 to 0.50 Jg−1K− 1, consistent with Debye behavior approaching the Dulong-Petit limit. The composite’s low thermal conductivity (~ 1.3 W/mK at 1200 °C) and moderate thermal expansion, indicating its excellent thermal stability and suitability for high-temperature insulation and thermal barrier coating applications.