Study On The Bulk And Grain Boundary Phase Diagram Of The Cu-based Key Ternary Alloys

Cu-based alloys are extensively utilized in electronic industry,mechanical brazing and railway transportation as they display high strength brazing,excellent electronic properties,thermal conductivity and process performance.As high strength and high conductivity materials,the addition of alloying elements in Cu-based alloys can enhance their ductility,abrasive and corrosion resistance.Cr,Nb,Si,Sn,Ti and Zr as the common additional elements in Cu-based alloys lead to a considerable enhancement of electrical and mechanical properties in fabrication processing though solid solution strengthening and precipitation hardening mechanisms.Knowledge of the phase equilibria and thermodynamic properties of the Cu-based alloys is essential in developing the new Cu-based high-temperature structural materials.The phase equilibria and thermodynamic calculation of the Cu-Cr-Si,Cu-Ti-Nb,Ag-Sn-Zr and Ag-Cu-M(M=Nb,Fe,Pb)were carried out by the CALPHAD(CALculation of PHAse Diagrams)approach coupled with key experiments by using X-ray diffraction(XRD)and scanning electron microscopy with energy dispersive Xray spectroscopy(SEM/EDS).The Miedema-type macroscopic-atom model which further developed by Benedictus,Bottger,and Mittemeijer was adopted in the present work to estimat the interfacial energies(35)?,the CALPHAD method was adopted to construct the grain boundary phase diagram of Cu-Ag system.The main results are as following:(1)The phase equilibria of the Cu-Cr-Si ternary system were investigated via thermodynamic modeling coupled with key experiments.Seventeen ternary alloys were prepared to determine the isothermal sections of the Cu-Cr-Si system at 700 and 800 ℃ by combining XRD and SEM/EDS.No ternary compound was found.The solubilities of the third element in binary compounds in the Cu-Si and Cr-Si systems were measured.Based on the thermodynamic descriptions of three constitutive binary systems available in the literature as well as the experimental phase equilibria data obtained from the present work and literature,thermodynamic re-assessment of the Cu-Cr-Si system was carried out by the CALPHAD approach.The substitutional model and sublattice model were used to describe the solution phases and intermediate phases,respectively.A set of thermodynamic parameters of the Cu-Cr-Si system was obtained.The calculated isothermal sections and vertical section are in good agreement with most of the reliable experimental data.The liquidus projection and reaction scheme of the Cu-Cr-Si system over the whole composition were also presented.(2)The phase equilibria of the Cu-Ti-Nb ternary system were investigated via thermodynamic modeling coupled with key experiments.Fourteen equilibrated alloys were prepared to determine the isothermal sections of the Cu-Ti-Nb system at 600 and 700 ℃ combining XRD and SEM/EDS,and four as-cast alloys were prepared to study the alloys solidification behavior.The solubilities of Nb in binary compounds of the Cu-Ti system and Cu in the(βTi,Nb)phase were measured.No ternary compound was found.The thermodynamic assessment of the Cu-Ti-Nb system was carried out by the CALPHAD approach based on the thermodynamic descriptions of three constitutive binary systems as well as the experimental phase equilibria data obtained from the present work and literature.A set of self-consistent thermodynamic parameters of the Cu-Ti-Nb system was obtained.The calculated isothermal sections are in good agreement with most of the reliable experimental data.The liquidus projection and reaction scheme of the Cu-Ti-Nb system over the whole composition were also presented.The solidification behaviors of as-cast alloys were described under Gulliver-Scheil non-equilibrium condition.The simulated and experimental results are consistent with each other(3)The phase equilibria of the Ag-Sn-Zr ternary system were investigated over the whole composition via thermodynamic modeling coupled with key experiments.Twenty-two equilibrated alloys were prepared to determine the isothermal sections of the Ag-Sn-Zr system at 500,700 and 900 ℃ by combining XRD and SEM/EDS,and eight as-cast alloys were prepared to study the alloys solidification behavior.The solubilities of Zr,Sn and Ag in binary compounds of the Ag-Sn,Ag-Zr and Sn-Zr systems were measured.No ternary compound was found.Based on the thermodynamic descriptions of three constitutive binary systems as well as the experimental phase equilibria data obtained from the present work and literature,thermodynamic assessment of the Ag-Sn-Zr system was carried out by the CALPHAD approach.A set of thermodynamic parameters of the Ag-Sn-Zr system was obtained.The calculated isothermal sections are in good agreement with most of the reliable experimental data.The liquidus projection and reaction scheme of the Ag-Sn-Zr system over the whole composition are also presented.The solidification behaviors of as-cast alloys are described under Gulliver-Scheil nonequilibrium condition.The simulated and experimental results are consistent with each other.(4)Sixteen ternary alloys were prepared to determine the isothermal sections of the Ag-Cu-Nb system at 500,600,700 and 800 ℃ by XRD and SEM/EDS.The thermodynamic assessment of the Ag-Cu-M(M = Nb,Fe,Pb)ternary systems were carried out by the CALPHAD approach,and a set of thermodynamic parameters of the Ag-Cu-M(M = Nb,Fe,Pb)ternary systems were obtained,respectively.The calculated isothermal sections are in good agreement with most of the reliable experimental data.The liquidus projection and reaction scheme over the whole composition were also presented.(5)The Benedictus-Bottger-Mittemeijer modified model was used to estimate the reference interface energy of Cu-Ag and Cu-Cr systems and the volume free energy consumed to form the supercooled liquid phase was calculated based on CALPHADtype thermodynamic database in the present work.The parameter of λ was introduced to correlated the reference interface energy and the volume free energy in terms of the trade-off relationship that exists in the phase diagrams of Cu-Ag and Cu-Cr systems.The λ phase diagrams of Cu-Ag and Cu-Cr systems were constructed by Matlab algorithm combining the bright interface model of coupled GB premelting and prewetting with CALPHAD method.The results show that the value of λ in the(Cu)+(Ag)two-phase region are constant at constant temperature and the value of λincreases with the increased Ag content at Cu-rich region,which indicates that Ag can promote grain boundary disorder,then the addition of Ag can promote the sintering of Cu alloy.The active sintering experiments of Cu with at 5,10 and 15 at.% Ag were carried out to determine the relation between the relative density of Cu-Ag alloy and sintering time.The relative density of alloy samples increases gradually as the increase of sintering temperature and time.Figure [154] Table [21] Reference [205]...