Duration of Thermal Stability and Mechanical Properties of Mg2Si/Cu Thermoelectric Joints

Abstract

Preparing an effective and long-term reliable contact between a thermoelectric (TE) element and its electrode is a key issue in integrating TE elements into practical devices. In this work, Cu electrodes were bonded to Mg2Si by using the spark plasma sintering (SPS) technique. To investigate their thermal stability, Mg2Si/Cu joints were annealed in vacuum at different temperatures (500°C, 550°C, and 580°C) for different durations (24 h, 48 h, and 72 h). Scanning electron microscopy (SEM) images illustrated that an intermediate layer with thickness of approximately 10 μm developed between Mg2Si and Cu during the sintering process. Electron probe microanalysis (EPMA) indicated that Mg, Si, and Cu diffused into each other and formed a τ3-phase at the interlayer. After annealing at 500°C for 72 h, the Mg2Si/Cu joints still possessed good adhesion and showed no cracks; the thickness and the elemental fractions within the interlayer did not show an obvious difference due to the thermal treatment. The electrical contact resistance increased slightly while the shear strength of the Mg2Si/Cu joints decreased with increasing aging time. However, when increasing the annealing temperature to 550°C, cracks developed along the boundary of the intermediate layer close to the Cu layer. Severer cracks were observed with higher aging temperature of 580°C. Therefore, it is evident that the Mg2Si/Cu joints exhibited good thermal reliability with stable microstructure, relatively unchanged electrical contact, and sufficient bonding strength at operating temperatures below 500°C.