Evaluation of Tribological Properties of Plasma Sprayed Ni(5Al)-Al2O3-MoS2 Composite Coating on Plain Carbon Steel

The aim of this research is evaluation of tribological properties of Ni(5Al)-Al2O3-MoS2 composite coating deposited by atmospheric plasma spray process on the CK45 steel substrate. For this purpose, three powder materials composed of 60wt%Ni(5Al)-40wt%Al2O3, 60wt%Ni(5Al)-35wt%Al2O3-5wt%MoS2 and 60wt%Ni(5Al)-25wt%Al2O3-15wt%MoS2 were prepared by mechanical milling and then spray drying processes. Plasma spray treatment was done by a plasma spray apparatus equipped with a gun of PS50 model. The coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), wear and coefficient of friction tests. In order to study the tribological properties of the coating, wear tests were performed by using a high temperature pin on disk machine. The tests were performed at temperatures of 25, 300 and 6000C, under 5N load and pin rotation speed of 0.1m/s. The wear test results at 25oC showed the presence of brittle phase of NiAl2O4 and lack of MoS2 lubricate in the 60wt%Ni(5Al)40wt%Al2O3 coating led to delamination wear. In this case, coefficient of friction decreased from 0.98 to 0.80. Significant weight loss was not observed during the wear test at 25oC in the coating contains 15wt% lubricant, due to the presence of Ni solid solution and absence of brittle phase of NiAl2O4. Due to the simultaneous presence of NiO and MoO3, 15wt%MoS2 coating showed the best lubricant performance at 600oC, thus, coefficient of friction was reduced from about 0.95 to 0.25.