Effects on performance of Cr₂O₃ layers produced on Mo/cast-iron materials

The principle aim of this paper is to investigate effects on performance of protective multilayer coatings with Cr₂O ₃/Mo/cast iron architecture in order to use in an internal combustion engines. With this regard, Cr₂O₃ powders were deposited on Mo coated cast iron substrates using an atmospheric plasma spray system. The coated samples were characterized by means of an optical microscope, image analyzer (LUCIA), scanning electron microscope (SEM) and X-ray diffraction. Mechanical properties of the multilayers were determined by using standard and dynamic ultra microhardness machines. Wear tests were conducted with the Cr₂O₃/Mo and Mo coated cast iron substrates at 89 N under dry sliding conditions through a pin-on-plate arrangement against AISI 303L steel counterbody. The microstructural analysis of worn surfaces were examined by SEM. Thermal behavior of the Cr₂O₃/Mo coatings was scrutinized using a thermal cyclic machine without external load. The microstructural observations showed that the multilayers contain some inhomogeneities such as porosity, crack-like defects, unmelted particles, oxides and inclusions. The structures with the inhomogeneities strongly influenced their mechanical, wear/friction and thermal properties. It was also found that Cr₂O₃ layer significantly increased the performance of Mo coated cast iron substrate as a protective layer.