Abstract
There are about sixty percent of energies consumed as waste heat in the process of energy conversion. Therefore, recycling of waste heat is now considered as an important issue of energy. Thermoelectric module can convert heat into electricity directly. The reliability of thermoelectric materials depends on the working temperature of soldering. During heat treatment, intermetallic compound forms and it may affect mechanical property of the joint. In this research, low-melting-point metals are chosen as solder. We observe what intermetallic compound forms at the interface while doing the process of transient liquid phase bonding. In the research of In/Co interfacial reactions, we only find CoIn3 intermetallic phase formed at 200oC, 350oC and 500oC for 26, 12 and 24 hours, and the thickness of CoIn3 phase are 9 m, 53 m and 80 m, respectively. As we increase the reaction time, the thicknesses of CoIn3 phase is proportional to the square root of reaction time. We can conclude that they are diffusion-controlled. In In/Ni interfacial reactions, Ni3In7 phase is formed at 200oC and 350oC for 24 hours, and its thickness is 31 m and 120 m. Besides, NiIn and Ni2In3 phases are formed at 500oC for 12 hours, and their thickness are 57 m and 39 m, respectively. In In/Ni interfacial reactions at 500oC, the results show that only Ni2In3 phase is formed with shorter reaction time, and NiIn phase is formed when we increase the reaction time above 1 hour. Both of In/Ni interfacial reactions at different temperatures are diffusion-controlled. In In/Cu interfacial reactions, the -Cu7In3 and '-Cu2In are formed at 350oC and 500oC for 24 hours and 12 hours, and Cu11In9 and Cu11In9+In-rich are formed at 200oC. There are the same phases at these temperatures when we changed the reaction time. The thicknesses of reaction layer is proportional to the square root of reaction time. Compare with binary system interfacial reactions, in Co/In/Cu interfacial reactions, there are CoIn3 phase at In/Co side at 200oC and 350oC. it is similar to binary system, but CoIn2 phase is formed at 500oC because of Cu dissolution. At In/Cu side, there are Cu11In9 and Cu11In9+In-rich phase at 200oC, and -Cu7In3 and '-Cu2In are formed at 350oC and 500oC. In Ni/In/Cu interfacial reactions, at In/Ni side, Ni3In7 are formed at 200oC and 350oC. At In/Cu side, there are Cu11In9 and Cu11In9+In-rich phase at 200oC, but there are Cu11In9+In-rich phase at 350oC. when the temperature increasing to 500oC, the NiIn, Ni5In21Cu24, '-Cu2In, and -Cu7In3 are formed. All of Co/In/Cu and Ni/In/Cu interfacial reactions are diffusion-controlled, and we calculate the liquid Indium consumption rate to manipulate thickness of pieces of Indium. In addition, series of ternary of Co-In-Cu alloys are designed, fabricated and heat-treated at 200oC, 350oC, and 500oC. And new ternary compound are found at 350oC.