Electrochemically enhanced wetting of 3YSZ and Mn1.5Co1.5O4 by Ag−CuO and their application in flash joining

Ag−CuO is a widely used air braze sealant for joining ceramic electrolytes and stainless-steel interconnects in solid oxide fuel cells (SOFCs). Balancing the amount of CuO in a braze is challenging because it enhances wettability and also aggravates steel surface degradation. Manganese cobaltite spinel (MCO) is widely used as a protective coating for SOFC steel interconnects. Therefore, we herein propose a strategy for enhancing the wetting of an Ag−CuO alloy with a low concentration of CuO (4 mol%) on 3 mol% yttria-stabilized zirconia (3YSZ) and MCO by applying a direct current to the 3YSZ/Ag−CuO/MCO system. It was discovered that the wetting of 3YSZ improved regardless of the current polarity; however, the wetting of MCO was selectively improved by the current flowing from MCO to 3YSZ. The underlying mechanisms are discussed based on the current-induced interfacial electrochemical reactions and dissolution. Furthermore, the flash joining of 3YSZ to MCO-coated Crofer22APU was achieved, and an optimized shear strength of 62 ± 11 MPa was obtained. A correlation between the interfacial microstructure, mechanical properties, current polarity and current intensity was also established.