Fracture toughness of t′ ZrO2 stabilised with MO1.5 (M=Y, Yb & Gd) for thermal barrier application

Thermal Barrier coatings (TBC's) protect the gas turbine blades at high temperature exposure. The t' phase is metastable and slowly transforms to the high-temperature equilibrium state consisting of tetragonal (t) and cubic (c) during high temperature exposure. A comparative study of the phase stability and fracture toughness of monolithic Y, Yb and Gd stabilised zirconia with composition 8 mol% MO1.5 was studied. Powders were prepared by co-precipitation method with crystallite size similar to 15 nm. Pressureless sintering, Spark plasma sintering (SPS) at 1250 degrees C for 10 min was carried out to produce compacts with >96% relative density for fracture toughness measurements XRD and Raman studies revealed the the initial phase was t'. After sintering, no spontaneous monoclinic phase formed during cooling. The fracture toughness of the sintered pellets of different composition was measured. The results were analysed in terms of the effect of phase constitution on fracture toughness. The role of ferroelastic toughening in these materials was explored.