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To improve the tribological properties of sulfur-containing Ni-based self-lubricating composites, FGH97-WS2-Cr-CeO2 (FWCC) were prepared by spark plasma sintering technique. All composites prepared obtained new phases CrxSy and M6C, originating from the decomposition of WS2. Homogenization and fine microstructure resulted in the best mechanical properties of the FWCC composites, with the microhardness of 542 ± 12 HV, compressive yield strength of 1910 ± 52 MPa, and flexural strength of 954 ± 34 MPa. When the composites exposed to 600 °C, the oxidation of CrxSy dominated the oxidative weight gain. The coefficient of friction and wear rate of FWCC composites both tend to decrease with increasing temperature. The optimum tribological properties of FWCC composites are obtained at 600 °C with the coefficient of friction of 0.23 and the wear rate of 0.22 × 10-5 mm3 N-1 m-1. The wear rate is two orders of magnitude lower than that of FGH97-WS2 composites (FW). This is mainly due to the synergistic effect of Cr and CeO2. The addition of Cr promotes the formation of enough Cr2O3 oxide particles during friction, while the addition of CeO2 not only enhances the adhesion of the oxide enamel layer, but also improves the high-temperature stability of the sulfide. [ABSTRACT FROM AUTHOR]

Metal matrix self-lubricating composites are required to possess well-balanced mechanical and lubricating properties when they are applied as mechanical parts. However, the decomposition of disulfide lubricants usually occurs during the sintering process and unfortunately reduces their mechanical properties. In this work, CeO2 was added to a model Cu/WS2 composite fabricated by spark plasma sintering (SPS). The effect of CeO2 doping on the interfacial microstructure and mechanical and tribological properties was investigated. The results indicated that CeO2 nanoparticles preferentially adsorbed onto the lubricant disulfide, which segmented the Cu/WS2 diffusion layer and reduced Joule heat at the interface while competing with WS2 to intensify the heat dissipation. As a consequence, interfacial overheating was largely suppressed, and WS2 decomposition was successfully prevented. The CeO2-doped Cu/WS2 composite breaks through a trade-off between mechanical and lubricating properties, exhibiting a high bending strength of 295.1 MPa, a hardness of 98.5 HV, a low friction coefficient of 0.19, and a wear rate as low as 4.12 × 10−5 mm3/N m. [ABSTRACT FROM AUTHOR]

The effect of CoO and NiO on the adherence between enamel coating and steel is investigated experimentally in this study. Enamel coatings are applied to the steel using a wet process with slurries. A total of five enamels were prepared including three single layer enamels: blank enamel ( BL), NiO bearing enamel ( MTNi3), CoO bearing enamel ( MTCo3), and two double layer enamels: BL- MTNi3, BL- MTCo3, which consisted an inner layer of BL and an outer layer of MTNi3 or MTCo3. Falling-weights tests were performed and the cross-sections at the enamel/steel interface were analyzed with a scanning electron microscopy ( SEM) coupled with an energy dispersive spectroscopy ( EDS) and electron probe microanalysis ( EPMA). Results show that the increases of adherence for MTCo3 and MTNi3 coated steel are attributed to the micro-alloys precipitation at the enamel/steel interface. These micro-alloy precipitations grow parallel to the steel/enamel interface for MTNi3, while they are dendritic and perpendicular for MTCo3. Compared with MTCo3, the negative reaction energy between NiO and FeO for MTNi3 causes micro-alloy precipitations formed far away from the enamel/steel interface, resulting in different morphology and adherence. [ABSTRACT FROM AUTHOR]