Interfacial Diffusion And Reaction Of The Contact Of Pb Te-based Thermoelectric Element And Optimization Of The Contact Materials

Pb Te-based thermoelectric devices can directly convert heat into electricity, which are mainly used in power supply for space exploration and automotive or industrial waste heat recovery. Currently, mechanical methods are used to bond Pb Te-based thermoelectric materials to electrode, resulting in increased weight and complex structure of the device. The large electrical and thermal contact resistance of the joint reduces the conversion efficiency of the thermoelectric device. In addition, the Pb Te-based thermoelectric joint requires long-term stability at 550 oC under certain stress conditions. Therefore, it is difficult to fabricate a good performance joint of Pb Te-based thermoelectric electrode. In this paper, the goal is to develop a high-performance Pb Te-based thermoelectric joint.The Ni/Pb Te, Nb/Pb Te, Fe/Pb Te and Mo/Pb Te thermoelectric joints are bonded by using hot pressing method. The interface structures of the joints are studied. The interface diffusions and reaction behaviors of the joints are analyzed. Then the formation mechanisms of the joint interface structures are discussed. For Ni/Pb Te joints, Ni and Pb Te may form a eutectic liquid phase. Ni may react with Pb Te to form Ni3±x Te2 and liquid Pb by liquid-liquid, liquid-solid or solid-solid reaction. In addition, a ternary phase precipitates and a eutectic microstructure may form at the interface between Ni and Pb Te. The eutectic liquid phase and liquid Pb may penetrate into the grain boundaries of Ni foil. For Nb/Pb Te joints, Nb and Pb Te can’t form a eutectic liquid phase. Nb can react with Pb Te to form Nb3Te4 and liquid Pb. The formed liquid Pb does not penetrate into the grain boundaries of Nb foil. The Growth rate of Nb3Te4 reaction layer is controlled by the diffusion rate of Nb atoms into Pb Te through Nb3Te4. For Fe/Pb Te and Mo/Pb Te joints, Fe and Mo can’t form a eutectic liquid phase or react with Pb Te.The Ni Fe Mo/Pb Te and Fe/Ni/Pb Te thermoelectric joints are bonded by using hot pressing method. The interface structures of the joints are studied. The interface diffusions and reaction behaviors of the joints are analyzed. Then the formation mechanisms of the joint interface structures are discussed. The eutectic temperature of Ni Fe Mo/Pb Te joints increases compared to that of Ni/Pb Te joints. There is no obvious interface reaction between Ni Fe Mo and Pb Te, inferring that Fe and Mo atoms in the presence of Ni Fe Mo alloy suppress the interfacial reaction between Pb Te and Ni. For Fe/Ni/Pb Te joints, there may be five kinds of interface structure formed under different bonding parameters:(1) Fe(Ni)/granular(Fe,Ni)1.12Te/Pb Te(Ni)(2) Fe/Fe(Ni)/Ni(Fe)/Pb Te(Ni);(3) Fe/Fe0.88Ni0.12/Ni(Fe)/Ni3±x Te2/Pb Te(Ni);(4) Fe/Fe0.88Ni0.12/(Fe,Ni)1.26Te+Pb/Pb Te;(5) Fe/void Fe0.88Ni0.12/(Fe,Ni)1.26Te+Pb/Pb Te.According to the analysis of interface structure, mechanical properties, thermoelectric and electrical properties of each Pb Te-based thermoelectric joint, Fe/6μm Ni/Pb Te joints bonded at 650℃/150min/40 MPa show a good performance. The formed interface structure Fe/Fe0.88Ni0.12/Ni(Fe)/Ni3±x Te2/Pb Te can not only have a strong bonding strength but also inhibit grain boundary penetration.