Evaluation of LaAlO3 as top coat material for thermal barrier coatings

Abstract

Perovskite is a versatile group of oxide materials allowing their properties to be tailored by composition towards specific requirements. LaAlO3 was prepared to study and report its properties in the context of its potential in thermal barrier coatings (TBCs) technology. A citric acid method was used for synthesis and the perovskite structure was confirmed using XRD and FT-IR. Viscosity of the solution precursor was checked as well as the particle size by laser particle size analysis. Densification behavior of the material was followed by conventional sintering and by spark plasma sintering. Apparent porosity by the Archimedes method, thermal conductivity and thermal expansion coefficient were studied. Mechanical and fracture properties were measured at elevated temperatures up to 1300 °C. For samples sintered at 1200−1400 °C, coefficient of thermal expansion ranged from 5.5×10−6 to 6.5×10−6 K−1 and thermal conductivity ranged between 2.2 and 3.4 W/(m·K). Elastic modulus and ultimate stress were measured at 1000−1300 °C, while by micro-indentation, fracture toughness was found to be 3 MPa·m1/2. As the sintering temperature increased from 1200 to 1500 °C, significant densification from 3.21 to 5.81 g/cm3 was found, indicating that material annealing should be made at least at 1400 °C. Under this condition, negligible dimensional change in phase transition temperature of LaAlO3 from the rhombohedral (R3c) to the ideal cubic (Pm3m) is found. Data reported in this work can be useful for comparing the mechanical and fracture behaviours of different TBCs developed involving LaAlO3 as well as input for numerical simulations.