Effect of TiO₂ doping on the fracture toughness and thermal conductivity of HfO₂ ceramic

Abstract Hafnia‐based ceramic coating is considered one of the candidates to substitute yttria partially stabilized zirconia material as thermal barrier coating working above 1200°C. In this work, a series of TiO 2 ‐doped HfO 2 ceramics (Hf 1– x Ti x O 2 , x = 0%, 5%, 10%, 15%, 20%, and 40%) were fabricated by solid‐state reaction. The microstructure, fracture toughness, and thermal conductivity were systematically investigated. The results show that Hf 1– x Ti x O 2 ceramics are comprised of monoclinic HfO 2 and orthorhombic HfTiO 4 phases when Ti 4+ doping amount is between 5% and 20%, and the weight fraction of HfTiO 4 phase linearly increases with the Ti 4+ content and finally reaches 100% for Hf 0.6 Ti 0.4 O 2 . The fracture toughness of TiO 2 ‐doped HfO 2 ceramic is higher than 1.75 MPa m .5 when TiO 2 content is no more than 15% and decreases below 1.5 MPa m 0.5 if TiO 2 content further increases. The thermal conductivity is significantly decreased by TiO 2 doping attributed to the precipitated HfTiO 4 phase. Considering the mechanical properties and thermal insulation capacity, the doping of 15% TiO 2 would be beneficial for the HfO 2 ‐based ceramics.