Effect on residual stresses in plasma sprayed Al-Si/B₄C composite coatings subjected to thermal shock

Al-Si/B₄C composite coatings were deposited on metallic substrates using an atmospheric plasma spray technique for diesel engine motor applications. The effect on residual stresses of the reinforcement particle (B₄C) content, coating thickness and porosity of Al-Si/B₄C coatings on Al-Si alloy substrate were investigated by the finite element method (FEM). The coatings were characterized by means of optical microscope. Thermal loads were applied to the model at a temperature of 550 °C using FEM. Metallographic analysis of the coatings proved the existence of porosity and reinforcement particle. It was found that the volume content of the B₄C phase was in the range of 5-25%, and the porosity had a content at 0-14 vol.%. The coating thickness was in the range of 100-1000 μm. Finite element calculations demonstrated that the thermal shock resistance decreased with the increase of the reinforcement particle content, the increase in coating thickness and with porosity contents of over 4 vol.%. Of the coating systems, Al-Si/20% B₄C coating possess the highest thermal shock resistance.