Research Of The Microstructure And Properties Of Cu-Sn Immiscible System Alloys Prepared By Mechanical Alloying

In this thesis,the variation of microstructure,properties and thermal behavior of Cu-Sn immiscible system alloys during high energy ball milling and subsequent annealling were systematically investigated by X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,and differential scanning calorimetry?DSC?.In addition,the calculation of thermodynamics about the formation mechanism of supersaturated solid solutions in Cu-Sn immiscible system during mechanical alloying?MA?was carried out.At the beginning of the thesis,a comprehensive review of bearing alloys was carried out.In particular,the mechanical alloying and its application on the preparation of nanocomposite alloys were summarized.In addition,the effect of nanocomposite microstructure on the properities of immiscible system alloys was introduced.The microstructure variation of Cu-?5,10,15?wt%Sn alloys prepared by high energy ball milling investigated by XRD,SEM,and TEM.The results show that single-phase nanocrystalline supersaturated solid solutions Cu?Sn?was obtained in Cu-5wt%Sn alloy,and the Sn was dissolved completely in Cu.The coexistence microstructure of Sn and nanocrystalline supersaturated solid solutions Cu?Sn?were obtained in Cu-10wt%Sn and Cu-15wt%Sn alloys.The thermodynamic calculation result shows that there is no thermodynamic driving force in Cu-Sn binary immiscible system to form supersaturated solid solutions at all alloy compositions,the expanded solid solubility comes from dynamic driving.That is to say,the existence of high density of dislocations and a large fraction of grain boundaries promotes the expansion of solid solubility.The melting point of the Sn phase in the Cu-?5,10,15?wt%Sn alloys prepared by MA is significantly decreased,which is related to the interfacial energy produced during high energy ball milling.The Cu₁₀Sn₃ particles with nano-meter size embedded in Cu matrix were obtained in as-milled Cu-?5,10,15?wt%Sn alloys after isothermal sintering.The density and therelative density of Cu-Sn bulk alloys increased with the increase of sintering temperature.In addition,the relative density of Cu-Sn bulk alloys increased with the increase of Sn content.And the microhardness of Cu-Sn bulk alloys increased gradually with the increase of sintering temperature.The microhardness of the bulk alloys sintered at 573 K reached the maximum values.When the sintering temperature further increases,the microhardness of bulk alloys decreases slightly.