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

Abstract

AbstractHafnia‐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 TiO2‐doped HfO2 ceramics (Hf1–xTixO2, 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 Hf1–xTixO2 ceramics are comprised of monoclinic HfO2 and orthorhombic HfTiO4 phases when Ti4+ doping amount is between 5% and 20%, and the weight fraction of HfTiO4 phase linearly increases with the Ti4+ content and finally reaches 100% for Hf0.6Ti0.4O2. The fracture toughness of TiO2‐doped HfO2 ceramic is higher than 1.75 MPa m.5 when TiO2 content is no more than 15% and decreases below 1.5 MPa m0.5 if TiO2 content further increases. The thermal conductivity is significantly decreased by TiO2 doping attributed to the precipitated HfTiO4 phase. Considering the mechanical properties and thermal insulation capacity, the doping of 15% TiO2 would be beneficial for the HfO2‐based ceramics.