Fast joining of 8YSZ to NiCrFe medium-entropy alloy by using an electric field

In this study, yttria-stabilized zirconia (8YSZ, 8 mol%) was flash joined to Ni-Cr-Fe medium-entropy alloy (MEA) within seconds under an electric field (E-field), where the current density was above the threshold (about 100 mA·mm−2) at 750–1000 °C. The maximum joint strength of 103 MPa was achieved at joining temperature of 900 °C under current density of 100 mA·mm−2 for 30 s. The impedance spectrum of the joined sample revealed that there was no impedance barrier to charge transfer between the metal electrode and the ceramic, indicating that the interface was well bonded. Scanning electron microscopy and transmission electron microscopy results show that the joint was formed mainly due to the fast diffusion of Ni into 8YSZ and reduced Zr into MEA. The diffusion of these elements does not change the crystal structure of the ceramic and metal, and leads to only slight increase in the lattice spacing of MEA.