Low-temperature joining of YSZ and Crofer 22 APU via femtosecond laser fabricated micro-cone arrays

The joint strength of ceramic/metal interfaces has become one of the major technical difficulties in the development of solid oxide fuel cells. Hence, a method to fabricate 3D cone structure arrays on the surface of yttria-stabilized zirconia (YSZ) and stainless steel (Crofer 22 APU) by femtosecond laser machining technique is proposed to improve its shear strength. Compared to the shear strength of flat substrate (5 MPa), the optimized strength (23.4 MPa) is 4.7 times that of the original strength. Increasing the sintering temperature from 200 °C to 350 °C enhances the mobility and sintering of Ag nanoparticles, leading to a denser Ag layer and consequently improving the interfacial connection strength. Cross-sectional analysis of the sintered joint reveals that the 3D cone structure forms a mechanical interlock with the Ag layer, enhancing the interfacial shear strength. A finite element analysis model is also established for revealing the shear stress distribution in the Ag layer with microstructure.