Thermodynamic Study On The Ag-Cu-Co And Ag-Cu-Ge Systems

Silver-copper-based solder is widely used in the field of electronic welding due to its good properties on flowability,wettability as well as electric and thermal conductivity of welds.In order to further improve the performance of silver-copper-based solder to meet different operating temperatures,it is usually add alloying elements such as Co and Ge.Accurate thermodynamic description can provide basic information for rational composition design of the Ag-Cu-based alloys.In this work,thermodynamic investigation of two ternary systems,Ag-Cu-Co and Ag-Cu-Ge,were investigated by experiments and the CALPHAD（CALculation of PHAse Diagrams）method.The main work content and research results are as follows:（1）No Ag-Cu-Co ternary compound was experimentally observed in this work.At 400°C,the maximum solubility of Cu and Co in fcc（Ag）,Ag and Co in fcc（Cu）,and Ag and Cu in hcp（Co）were measured to be 10.08 at.%and 1.43 at.%,2.37 at.%and 0.98 at.%,as well as 0.22 at.%and 4.15 at.%,respectively.At 650°C,the maximum solubility of Cu and Co in fcc（Ag）,Ag and Co in fcc（Cu）,and Ag and Cu in fcc（Co）were to be 15.74 at.%and0.97 at.%,3.69 at.%and 4.47 at.%,as well as 0.15 at.%and 7.48 at.%,respectively.Isothermal section at 400 and 650°C,liquidus projection and solidification paths of the ternary alloys were then calculated by CALPHAD method.And the calculated results are consistent with the experimental observations,indicating the accuracy of the thermodynamic description of the Ag-Cu-Co ternary system obtained by the CALPHAD extrapolation.（2）Isothermal section of the Ag-Cu-Ge system at 400°C was measured experimentally.No ternary compound was detected,and one three-phase regionε₁+fcc（Ag）+（Ge）and four two-phase regions fcc（Ag）+ξ,fcc（Ag）+fcc（Cu）,ε₁+ξandε₁+（Ge）were observed.The composition ofε₁in the phase region ofε₁+fcc（Ag）+（Ge）was measured to be 3.78Ag-73.41Cu-22.81Ge（at.%）,while the composition ofζin the phase region of fcc（Ag）+ξwas 2.09Ag-87.18Cu-10.37Ge（at.%）.The solubility ranges ofε₁ andξin the Cu-Ge binary system were measured to be 20.13-22.47 at.%Ge and 10.73-14.65 at.%Ge,respectively.Thermodynamic parameters of the Cu-Ge binary system was re-optimized based on the experimental results.Then the thermodynamic optimization of the Ag-Cu-Ge system was carried out,combined with the thermodynamic descriptions of Ag-Cu and Ag-Ge systems reported in literature.Using the obtained thermodynamic parameters of the ternary system,isothermal sections at400,490,520,590,and 650°C,liquidus projection and solidification paths of the ternary Ag-Cu-Ge alloys were calculated and can reasonably reproduce the experimental data.