Flash joining of BaTiO3 ceramic to NiCrFe medium-entropy alloy by using an electric field

Joining of barium titanate (BaTiO3, BT) ceramics to metals plays an important role in their wide applications. However, conventional joining methods, including solid state diffusion joining and liquid state joining, have several drawbacks. In this paper, BT ceramic was flash joined to NiCrFe medium-entropy alloy (MEA) in seconds with an electric field (E-field) using current density of 10-80 mA/mm2 at 700-1000 degrees C. Shear strength of the joint first increased with applied current density and dwell time of the E-field and then decreased. It exceeded 40 MPa when the temperature was above 900 degrees C with current density of 60 mA/mm2 for 60 s. Both the real part (epsilon') and imaginary part (epsilon") of complex permittivity of the joined sample were larger than those of the as-sintered BT ceramic at high frequency range. Microstructure of the joint suggests that a layer of chromium oxide was formed at faying surfaces, achieving effective bonding of BT and MEA. This research provides an efficient method for the manufacturing of BT based devices.