Microstructural evolution of the interfacial layer in the Ti–Al/Yb0.6Co4Sb12 thermoelectric joints at high temperature

A thermoelectric (TE) device is basically fabricated by joining p- and n-type thermoelectric materials with electrodes. For skutterudite (SKD) based TE devices, Ti and alloys like Co–Fe–Ni are widely used as the barrier layer joining the SKD and the electrode. In this paper, TE joints composed of Yb0.6Co4Sb12 (Yb-SKD) and a Ti–Al barrier layer with various Al contents (0–15 at.%) were fabricated by a one-step SPS process. The influence of the Al content on the evolution of the interfacial microstructure during accelerated aging at 600 °C was studied. During sintering and aging, Ti and Al diffused into each other and formed inert Ti–Al alloys, which hindered the interfacial diffusion and resulted in a lower growth rate of the diffusion layers. On the other hand, excess Al at the Ti–Al/Yb-SKD interface encouraged the interfacial diffusion. The interplay of the above two mechanisms decides the inter-diffusion behaviors at the interface. In this work, the two mechanisms reached balanced when the Al content was 6 at.%, which resulted in the best interfacial stability and the highest shear strength after aging. At the same time, with the increase of the Al content in the Ti–Al barrier layer, the CTE mismatch between the Yb-SKD and the Ti–Al barrier layer was reduced, consequently the interfacial integrity after aging was improved. As a result, the contact resistivity of the Ti–Al/Yb-SKD joints (Al: 6–12 at.%) remained below 12 μΩ cm2 after 16 days of aging.