Research Of The Microstructure And Tribological Properties Of Cu-Pb Immiscible System Bearing Alloys Prepared By Mechanical Alloying

In this thesis,Cu-(10,15,20)wt%Pb nanocomposite alloys were prepared by mechanical alloying assisted with isothermal annealing process.The calculation of thermodynamics about the formation mechanism of the metable structures in Cu-Pb binary immiscible alloys during non-equilibrium process mechanical alloying was carried out.Microstructure and tribological properties of mechanical alloying Cu-(10,15,20)wt%Pb immiscible alloys were systematically investigated by X-ray diffraction,scanning electron microscopy and differential scanning calorimeter.At the beginning of the thesis,A comprehensive review of bearing alloys and the preparation method of Cu-Pb immiscible bearing alloys was carried out.In particular,the principle and influencing factor were summarized.In addition,the hardness and tribology properties of Cu-Pb immiscible bearing alloys were briefly introduced.Single-phase nanocrystalline supersaturated solid solution Cu(Pb)that the Pb was completely dissolved in Cu was observed in Cu-(10,15)wt%Pb alloys prepared by mechanical alloying.The coexistence microstructure of Pb and nanocrystalline supersaturated solid solution Cu(Pb)were observed in Cu-20wt%Pb alloy prepared by mechanical alloying.The thermodynamic calculation result shows that there is no thermodynamic driving force in Cu-Pb binary immiscible system to form supersaturated solid solution,the expanded solid solubility comes from dynamic driving.In other words,the existence of dislocations and the increase of grain boundaries promotes the expansion of solid solubility.The second phase Pb uniformly dispersed in the Cu matrix was obtained in as-milled Cu-(10,15,20)wt%Pb alloys isothermal annealing.With the increase of sintering temperature,the density,relative density and microhardness of MA Cu-(10,15,20)wt%Pb alloys first increases and then decreases,these properties reached the maximum values at 623 K.With the increase of Pb content,the density,relative density and microhardness of Cu-Pb alloy increases.With the increase of annealing temperature,the wearing capacity decreased firstly and then increased,at 623 K,Cu-(10,15,20)wt%Pb alloys showed the best wear resistance capability.With the increase of Pb content,wearing capacity gradually decreased,the wear resistance of the alloy gradually increased.Compared with the ungrinded samples of the same composition,the samples after ball milling showed a higher carrying capacity and anti-friction.