| dc.description.abstract | In this study, the wear resistance of thermally sprayed Ni-MoS2 composite coatings on an AISI 1020 steel substrate was investigated. Ni-MoS2 composite powder (size: 60-90 μm) containing 25 wt.% of dispersed MoS2 was prepared by electroless plating. Ni-MoS2 composite coatings were then prepared by HVOF thermal spraying. The coatings were characterized by structural, surface morphologies and compositional analyses by means of microhardness tests, SEM/EDS, XRD, and ICP-AES. For the evaluation of their anti-wear properties, the composites were subjected to ball-on-disk dry wear tests based on the ASTM G99 standard at room temperature.
Experimental results showed that some of the MoS2 content dispersed in the Ni-based composite coating burnt away during the high-temperature spraying process, thereby reducing the MoS2 concentration in the coating. In the wear test, the weight loss in the Ni-MoS2 composite coating was minimal under a low load (< 15 N) but increased rapidly with increasing load (> 30 N). The average wear rate of the coatings was found to be ~1/40 times that of a pure Ni coating, showing that the wear resistance of the composite coatings was significantly improved by MoS2 addition.
The coatings were then subjected to heat treatments. Various surface inspection techniques including hardness test, scanning electron microscopy, and X-ray fluorescence were then used to characterize the composition and mechanical properties of the composite HVOF coating. In addition, ball-on-disc tests were carried out under dry abrasive conditions, on specimens that were heat treated at different temperatures, according to the ASTM G99 standard. The wear of each specimen was observed and recorded, and the measurements were used to provide a comprehensive assessment of the coating’s wear resistance. When the Ni-MoS2 composite coating was heat treated at 500°C, the growth of MoO2 crystals evaporates from the inward, and condenses as the protruding oxide crystals on the surface, which led to an increase in porosity and structural looseness. Consequently, the hardness and structural strength of the coating decreased significantly, which dramatically decrease its wear resistance. | en_US |