The effect on residual stresses of porosity in plasma sprayed MgO-ZrO₂ coatings for an internal combustion diesel engine

The effect on residual stresses of porosity in MgO-ZrO₂ coatings on Al-Si alloy substrate was investigated. The MgO-ZrO ₂ coatings were deposited on metallic substrates using an atmospheric plasma spray technique. The coatings were characterized by means of optical microscopy and environmental scanning electron microscopy. Thermal loads were applied to the model at the temperature of 550 °C using finite element method. Metallographic examinations pointed out that coatings possessed porosity, unmelted and semi-melted particles, and the porosity values changed between 5 and 20%. Finite element calculations demonstrated that the highest thermal shock resistance was reached in the coating system with 7.5% small size sphere shape and uniformly distributed porosity. It was also found that the coating with above 7.5% porosity had maximum values in radial, axial and shear stresses.