Morphological and tribological studies of thermal plasma jet deposited coatings used in cardan joints

Abstract

All wheels drive (AWD) and railway vehicles require a longitudinal transmission. Double cardan joint is one of the most employed transmission, as it allows misalignments between the shafts. This transmission must support the maximum motor torque and high dynamic loads. In such situation, from tribological viewpoint, cardan joints are subjected to abrasive wear. To increase wear resistance of cardan joints, its rolling elements can be coated with ceramic or metal-ceramic coatings. This paper presents an experimental research on microstructure and dry friction characteristics of two steel samples obtained from cardan crosses (40Cr10 and RUL2), coated by two types of metallic powders (METCO32 and METCO72). Microstructural studies of both surface and cross –section of samples were performed using scanning electron microscopy (SEM). Dry tribological tests at constant speed and load were carried out on AMSLER machine. The micro-structural experiments revealed a structure with a relatively homogeneous character, partially melted particles and several microcracks being detected. Following the tribological tests, it was found that the METCO72 coating provides the lowest coefficient of friction, near values being obtained for both substrates of 40Cr10 and RUL2. The best combination is formed by 40Cr10 substrate and METCO72 coating.