The Research On The Preparation And Tribological Properties Of Cu-Ni-Sn Self Lubricating Composites

Cu-Ni-Sn alloy has high strength,good mouldability,excellent wear resistance and corrosion resistance.But the segregation of Sn appeared easily in traditional casting method because of the cooling speed is too slow.As a result,the mechanical properties of the alloy is deteriorated.Powder metallurgy can suppress the segregation of components and the formation of non-uniform microstructures during sintering,and can compound multiple materials.In this thesis,Cu-7.5Ni-x Sn alloy and Cu-7.5Ni-5Sn-0.75Fe-x Gr composite materials added with solid lubricant were prepared by pressureless sintering of powder metallurgy process,and the sintering and aging process of the alloy were also explored.In addition,Cu-2Ni-5Sn-?Gr.+Pb O?composite self-lubricating material was prepared.The composition,microstructure,mechanical properties and tribological properties at room temperature to 500?of the alloy and its composites were analyzed by XRD,SEM,universal material testing machines and high temperature friction and wear testing machines.The main results are as follows:?1?The addition of Sn can form Cu Ni₂Sn compounds.The formation of lamellar and twinning structure is the main reason for the increase of alloy strength.The optimum temperature of pressureless sintering is 870?.The optimum temperature of aging treatment is 350?and the time is 4 h.?2?The element Ni can be solid-solubilized with Cu.It's intermetallic compound Ni₃Sn₂,fomed with Sn,distributed in the Cu matrix can provide dispersion strengthening and improve the mechanical behaviour of the material.?3?Cu-2Ni-5Sn-?Gr.+Pb O?self-lubricating composite has a relatively low friction coefficient from 25?to 500?.The wear rate increases with the increase of temperature.At 300?,the dense and lubricious film composed of graphite,Pb O?Fe₂O₃?₆ and Cu₂O is the main reason for the good lubricity of the composite material.The wear mechanism mainly includes the plastic deformation,local exfoliation and slight adhesive wear of composites.At 500?,the composite lubricating film composed of Pb O?Fe₂O₃?₆,graphite,Cu₂O and Cu O plays a role in lubrication,the main wear mechanism is the peeling off of the matrix of graphite surrounding area,peeling off caused by the plastic deformation and oxidative wear.