Reparation And Tribological Properties Of Nickel-based Self-lubricating Composites At Wide Temperature Range

With the development and progress of society,People have put forward higher requirements for friction parts operation.Traditional grease-based lubricants are difficult to provide effective lubrication at wide temperature range,so it has high value to develop composite materials with good tribological and self-lubrication performance at wide temperature range.Nickel-based alloys have excellent corrosion resistance,friction resistance and high-temperature mechanical properties,making them widely used in the field of high-temperature friction.Ni-Mo alloy was used as the matrix to prepare Ni-Mo-Y alloy with higher mechanical properties through adding rare earth element Y.Ni-Mo-Y-CaF₂ and Ni-Mo-Y-Gr composite materials were prepared by adding solid lubricants CaF₂ and graphene（referred to as Gr）using Ni-Mo-Y alloy as the matrix.The mechanical properties,microstructure and tribological properties of the matrix and composite materials were tested by XRD,SEM,EDS,Raman and high-temperature friction testing machines.The effects of CaF₂ and graphene on the tribological properties of composites were discussed,and the self-lubricating mechanism of composites at wide temperature was revealed.This article uses Spark-Plasma-Sintering（referred to as SPS）to prepare four sets of Ni-Mo alloys with different Mo contents.By analyzing their mechanical properties and metallographic structure,NM-3 is selected as the matrix alloy.By conducting friction tests on the matrix alloy at room-temperature,400℃,600℃and 800℃.The results showed that the average friction coefficients were 0.70,0.45,0.41,and 0.42 at these four temperatures,respectively,showing a trend of first decreasing and then increasing.And their average wear rates were 1.06×10^-5 mm³/N·m,2.86×10^-5mm³/N·m,2.95×10^-5 mm³/N·m,7.27×10^-5 mm³/N·m,showing a trend of increasing with temperature.Adding rare earth elements on the basis of NM-3 to prepare Ni-Mo-Y alloy,the results showed that the Y element effectively improved the mechanical properties of the alloy.The tribological properties of NM-2 as a matrix alloy were studied through research and comparison.The alloy was subjected to friction tests at room-temperature,200℃,400℃,600℃,and 800℃,respectively.The experimental results showed that the average friction coefficients were 0.77,0.67,0.50,0.40 and 0.42 at these five temperatures,showed a trend of first decreasing and then increasing.And their wear rates were 1.26×10^-5 mm³/N·m,18.39×10^-5 mm³/N·m,28.06×10^-5 mm³/N·m,7.85×10^-5 mm³/N·m and 7.57×10^-5 mm³/N·m,showing a trend of first increasing and then decreasing.Ni-Mo-Y-5CaF₂,Ni-Mo-Y-10CaF₂ and Ni-Mo-Y-15CaF₂ composite materials were prepared by adding different amounts of CaF₂ to the Ni-Mo-Y alloy matrix.The experiment showed that the mechanical properties showed a decreasing trend with the increase of CaF₂ content.Friction tests were conducted on these three groups of composite materials at room-temperature,400℃,600℃,and 800℃.The friction coefficient of Ni-Mo-Y-CaF₂ composite material showed a trend of first rapid decrease,then stable and then slow decrease with the increase of temperature.The wear rate of Ni-Mo-Y-CaF₂ composite material shows a trend of first increasing and then decreasing.The composites showed good tribological properties at high temperature,this is mainly due to the formation of Ni Mo O₄,CaMo O₄ Mo O₃ and Mo O₂ on the friction surface during high-temperature friction.These molybdate and molybdenum oxides form a dense oxide layer,which plays a role in lubrication,thus making the composites show good tribological properties.Comprehensive research has found that Ni-Mo-Y-10CaF₂composite material has the best tribological performance.Ni-Mo-Y-1Gr,Ni-Mo-Y-5Gr and Ni-Mo-Y-10Gr composite materials were prepared by adding different amounts of graphene to the Ni-Mo-Y alloy matrix.The mechanical properties showed a decreasing trend with the increase of graphene content.Then,friction tests were conducted on these three composite materials at room-temperature,200℃,400℃,600℃,and 800℃.The research results showed that the Ni-Mo-Y-Gr composite material had lower friction coefficient and wear rate at lower temperatures,exhibiting good friction and wear properties.This was mainly attributed to the good lubrication effect of graphene at low temperatures.