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Metallic glass (MG) additive in brazing paste for high-temperature thermoelectric devices: evaluation of adhesion strength using a push-pull gauge
Hyukjun Youn, Joon Heo, Soonil Lee, Kyu-Mann Lee and Soon-Mok Choi
We designed a metallic glass (MG) additive exhibiting glass transition characteristics for use in a brazing paste for a high-temperature thermoelectric device. Metallic glass (MG) possesses a disordered atomic-scale structure without grain boundaries, offering a significant advantage in exceptional oxidation resistance for high-temperature devices. We fabricated Cu-based MG ribbons (Cu27Mg58Zn5Y10) using the melt spinning process. The combination of high-energy ball mill and planetary mill technologies can optimize the process conditions for pulverizing MG ribbons to <20 micrometers. Using differential scanning calorimetry (DSC), we determined the glass transition temperature (Tg) and crystallization temperature (Tx) of the MG powder. After annealing at a high temperature (over 200°C), we observed a substantial reduction in electrical resistivity resulting from the crystallization of the copper-based MG ribbon. Following the divalent pulverizing processes, we confirmed that the MG powder maintains its amorphous phase using X-ray diffraction. We evaluated the effect of metallic glass addition on the adhesion strength of a brazed junction, comparing two types of pastes with different forms of the MG additive (bulk ribbon and powder). We also developed a foundational process to manufacture a high-temperature brazing paste for bonding applications to evaluate the pulverized metallic glass. The pastes were brazed to form junctions between Cu electrodes at 400°C. The powdertype MG junction exhibited higher adhesion strength than the bulk MG junction due to the powder’s larger surface area, as supported by energy dispersive spectroscopy (EDS).
Keywords: Metallic glass, thermoelectric module, brazing paste, copper electrode
DOI: 10.32908/hthp.v54.1841