Process And Mechanism Research On Brazing Of Skutterudite Thermoelectric Modules

The thermoelectric conversion technology is an area of research focus nowadays. We were aiming at connecting one kind of skutterudite thermoelectric material which used La and Yb as main filler and performed well. The connecting and after using of this material involved a serious of problems and was to be solved in our study.One kind of Ag-Cu-Zn-Sn braze alloy was first taken into use to connect barrier material of thermoelectric with copper. A thin film of Ni coated on barrier material can significantly enhance the compactness of the joint. With means of Mechanics, Performance, Testing, SEM and XRD, the shear strength of our joint can reach up to 72 MPa in condition of 20 min coating time,710℃ brazing temperature and 15 min holding time. The typical microstructure of the joint was: barrier material/Ni/(Cu,Ni)+ Cu Ni2 Sn + small Ag(s,s)/Ag(s,s)+Cu(s,s)+Cu Ni2Sn/Cu(s,s)/Cu. DSC testing was also taken to measure the remelting temperature of the joint which was expected to bear the highest temperature of 650℃. The result supported that remelting temperature was as high as 700℃ and fit the need. A long time of heat aging was also used to the joint and the result came that: after 99 h heat aging, the joint was also compact and had no significant defect. Last, the thermodynamics and kinetics behaviors of Zn were researched to explain our phenomenon.Another kind of non-volatile alloy in Ag-Cu-In-Sn was prepared by vacuum induction melting(VIM). This alloy was reliable Vacuum. In condition of Ni coating, a layer of Cu Ni2 Sn brittle phase appeared and caused cracks and holes in joint. This meant deterioration in electrical performance. And the phase can’t be dispelled by adjusting our brazing temperature and holding time.In the process of coating a layer of Cu on barrier material,it was found that copper can hardly connect with the barrier and also can not be coated homogeneous. A Ni/Cu composite coating was used here to have a good connecting with barrier material as well as prevent Cu Sn Ni2 from occurring. In condition of 660℃,10 min holding time and 20 min Ni coating, 20 min Cu coating, the shear strength of this joint can reach up to 84.3 MPa. The typical microstructure of the joint was: barrier material/Ni/Cu(s,s)+Cu Ni2Sn/Ag(s,s)+Cu(s,s)+Cu3Sn+Cu3.02Sn0.98/Cu(s,s)+Ag(s,s)/Cu.DSC test showed the joint can also bear as high as 700℃. In heat aging experiment, the 20min/20 min layer performed deterioration. A new structure layer of 5min Ni/30 min Cu was conducted and finally generated solid solution that performed well.Finally, the thermoelectric material was sintered and connected by Ag-Cu-In-Sn alloy and 5min Ni/30 min Cu composite coating. The electrical property of a couple thermoelectric module was tested below 200℃. But the module showed also high resistance, for compactness in cold side when it was soldered.