Thermal behaviour of plasma-sprayed Mo coating on cast-iron substrate

In this study, Mo coatings were fabricated on cast-iron substrate using a plasma-spray technique for diesel engine motors. In order to undergo cyclic heating because of piston element in combustion chamber, thermal behaviour of these coatings were scrutinized through a thermal cycling machine. These Mo coatings were tested at temperature range of 47-600 °C for periods of 303 s under thermal cycling conditions. The effects of thermal cycling on the properties of the samples were characterized by using an optical microscope, image analyzer, SEM, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and microhardness tester. Microstructural observations showed that the coatings possessed lamellae structure with boundaries. XRD, TGA and DSC results revealed that Mo coatings transformed to MoO and MoO₃ during the thermal cycling process. It was found that an increase in porosity and residual thermal stresses after thermal cycling influenced the hardness results of the samples considerably. It was also observed to be a delimination between coating and substrate after thermal cycling.