Preparation and tribological properties in wide temperature range of Ni-Mo-Y-Gr composites
Ni-Mo-Y-Gr(graphene)self-lubricating composites were prepared by discharge plasma sintering technology,and microstructure,composition,mechanical properties and friction and wear properties of the composites were studied by means of optical microscope,scanning electron microscopy,X-ray diffraction,Raman spectroscopy and high-temperature friction testing machines.The results show that the microstructure of the Ni-Mo-Y-Gr composites is uniform and dense.With the increase of graphene content,the density,hardness and yield strength of the composites show a decreasing trend.The actual density of the composites is higher than that of the calculated theoretical density,indicating that metallurgical fusion and solid solution occur during the preparation process of the composites.The Ni-Mo-Y-Gr composites have low friction coefficient and wear rate in the temperature range of room temperature to 600 ℃,indicating they have good tribological properties.Graphene has a good lubricating effect at room temperature,200 and 400 ℃,and the main lubricating phases at 600 ℃ are graphene,NiO,MoO2,MoO3 and NiMoO4.The formation of NiMoO4 and nickel molybdenum oxides at 800℃ makes it difficult to form a complete and effective lubrication layer,resulting in a decrease in the tribological properties of the composites.
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