Study On Microstructure And Tribological Properties Of Plasma-sprayed Nanostructured Sulfide Coatings

Nanoscale FeS, FeS-SiC, MoS2 powders were prepared by mechanical milling. Before spraying, the powers were reconsititued to form granules ranging from 20 to 80 u m with excellent flowability and were suitable for plasma spraying process. Nanostructured FeS coating, nanostructured FeS-SiC composite coating and nano- and submicron-structured coating were deposited by atmospheric plasma spraying. The microstructure and phase composition of the coatings were characterized with SEM and XRD, respectively. It was found that: the nanostructured FeS coating was mainly composed of FeS, a small quantity of Fe₁-xS and oxide were also found. The grain size of the coating was 50¹00nm; the plasma-sprayed nanostructured FeS-SiC composite coating exhibited a bimodal distribution with small grains (30-80nm) and large grains (100-200nm). The coating was mainly composed of FeS and SiC, a small quantity of Fe₁-xS and oxide were also found. The porosity of the coating was about 19%; Nano-and submicron-structured M0S2 coating was mainly composed of M0S2, a small quantity of Mo, Mo₂S₃ and MoO₃ were also found. The grain size of the coating was 100⁴00nm. The nano-grains resulted from the re-crystallization of melted and partially melted nanoscale powders and some unmelted nanoscale powders preserved in the coating. The friction and wear experiment results showed that: the tribological properties of the plasma-sprayed nanostructured Iron sulfide coating were more superior to the GCr15 steel. Especially under oil lubrication condition, the friction coefficient of the nanostructured iron sulfide coating was half of that of GCr15 steel, the wear volume of the coating was also reduce to nearly half of that of GCr15 steel under high load; the friction coefficient of the nano- and submicron-structured M0S2 coating was half of that of GCr15 steel under oil lubrication condition, the wear volume of the coating was also reduce to nearly half of that of GCr15 steel under high load. In addition, the effect of the content of SiC on the microstructure and tribological properties of the nanostructured FeS-SiC composite coating was investigated. It was found that the larger the content of SiC, the more roughenss and looseness the coating was. The nanostructured FeS-SiC composite coating exhibit the best friction-reduction and wear-resistance properties when the content of SiC reach to 20%.