Thermo-mechanical evaluation of plasma sprayed YSZ-based multi-layered thermal barrier coatings

The multi-layered YSZ, NiCoCrAlY, Cr2O3 and Al2O3 coatings of varying thickness (200 μm-400 μm) have been investigated for thermal barrier coating (TBC) application. Plasma spray technique has been utilised on piston crown to optimise the thermal fatigue life in view to reduce the heat losses. Four types of TBC overlay each with a 100 μm NiCrAlY bond coat were deposited on the A336 aluminium alloy substrate cut out of the diesel engine piston. The phase composition of coatings before and after the thermal shock testing was analysed by XRD and the lattice strain analysis was performed by Williamson-Hall analysis. It was observed that among the considered multi-layered coating configurations, those with 300 μm YSZ and 200 μm Cr2O3 top coat exhibited acceptable thermal shock resistance as the specimens sustain up to 298 and 325 thermal cycles respectively. The microstructural analysis suggested against the formation of any major deformity or structural changes at the higher temperature as investigated by thermal shock experiment.