Preparation And Properities Research Of Ni-Based High Temperature Self-Lubricating Composites

With the high speed development of the food, textile and metallurgical industry, people put forward higher requirements on the friction parts which are runing in high speed and temperature conditions. Because the lubricating grease will cause pollution to the environment inevitably, it has the value of research and practical application to develop the composites with high wear-resisting performance and self-lubricating properties which are used in high temperature environment. Nickel based alloy has wide applications because of the good oxidation resistance, corrosion resistance and high temperature mechanical properties. In this paper, Ni20Cr alloy as the matrix, and adding nickel coated graphite, BN and BaF2/CaF2 eutectic mixture as solid lubricant, the Ni-based high temperature self-lubricating composites are prepared by using powder metallurgy method. The microstructures, morphologies, mechanical properties, friction properties and mechanism were analyzed by OM, SEM, XRD, EDS and the corresponding tests. The results show that:The Ni-based alloy composites have the highest mechanical properties and the best quality of sintering as the sintering temperature of 1220℃, and the sintering time of 3.5h. With the increase of nickel coated graphite content, the density, hardness and crushing strength of the composite materials decrease, and the nickel coating on the graphite surface improves the wettability between the matrix and graphite lubricating phase. The composite with 10wt.%-20wt.% of nickel coated graphite has the higher mechanical properties with hardness of 90HV-110HV and crushing strength of 350MPa-450MPa. The addition of BN makes the density, hardness and crushing strength of composite materials decrease, when the BN content is more than 2wt.%, the composite materials have the best structure and mechanical properties.The microstructure and mechanical properties of Ni-based self-lubricating composite of 2wt.%BN content are improved and the porosity decreased significantly by adding 6wt.%-12wt.% BaF2/CaF2 because of the effect of BaF2/CaF2 filling the pores. The hardness of the composite is 112.9HV-119.6HV, and the crushing strength is 346.47MPa-436.02MPa. The composite has better comprehensive properties with uniform distribution of BaF2/CaF2. When the content of BaF2/CaF2 is 8wt.%, the Ni20Cr-BN-C-BaF2-CaF2 composite with 10wt.% nickel coated graphite and 2wt.%BN has the highest hardness of 66.1HV and crushing strength of 236.64Mpa.Different lubricating phase make the different of friction properties and mechanism of the Ni20Cr based self-lubricating composites. The sample without any lubricating phase shows a serious adhesive worn phenomenon with the friction coefficient of 0.49, and the wear loss of 0.744mg/m. The adhesive wear of Ni20Cr composite was reduced and the friction coefficient and wear loss were decreased after adding 2wt.%BN. Ni coated graphite reduces the tendency of adhesive wear of the composite, and the composite with 10wt.% nickel coated graphite shows a typical characteristic of abrasive wear. The wear loss of Ni-based composite with 2wt.%BN and 8wt.%BaF2/CaF2 is reduced to 0.083mg/m and the friction coefficient of 0.31, and the sample with 10wt.% nickel coated graphite at the same time has the lowest friction coefficient 0.27 and lower wear loss 0.114mg/m. The wear mechanism of the sample is abrasive wear, surface fatigue wear and slight oxidation wear.