| dc.description.abstract | Due to the highly increasing demand for energy and the limited reserves of fossil fuels, it is very important to develop alternative energies of other fields. In the field of renewable energy, the development of thermoelectric modules, which can transfer waste heat into electricity, has gained much attention in recent decades. Mid-temperature thermoelectric modules consisting of lead telluride (PbTe) thermoelectric alloys are known for the high thermoelectric performance in the temperature range of 200 to 600 oC. However, because the bonding temperature is higher than the working temperature, it leads to serious interfacial reactions in the joints, which affects the efficiency and even causes the failure of thermoelectric modules. In this study, electroless Ag/Co-P/Ni-P composite layer was applied to PbTe thermoelectric material as diffusion barrier layer, and commercial AgCuZnSn brazing paste was used to braze PbTe with Cu and Ni electrodes in the condition of 630 oC for 10 minutes. By investigating the improvement of severe interfacial reactions in joints and the increase of shear strength, the reliability of the composite layer could be assessed. Severe interfacial reactions occurred between PbTe bulk and brazing paste, which led to continuous crack at the interface; in further thermal aging test at 400 oC for 2 days, the serious consumption of PbTe bulk caused even harsher interfacial reactions and thus critically deteriorated the mechanical strength of joints. With the insertion of the composite layer, the drastic interfacial reaction was avoided, and the shear strength was also improved. Besides, the results of thermal aging test also presented good reliability in maintaining interfaces and shear strength. These results provided that the electroless Ag/Co-P/Ni-P composite layer in the joints of PbTe not only presented effective diffusion barrier layer ability but also enhanced the mechanical strength, even after thermal aging test. | en_US |