Fracture toughness of reactive bonded Co–Mn and Cu–Mn contact layers after long-term aging

Creating a tough bond for the electrical contact between metallic interconnects and ceramic solid oxide cells (SOC) in a stack is challenging due to restrictions on the assembly temperature. The reactive oxidation bonding in the formation of Co2MnO4 (CoMn) and Cu1.3Mn1.7O4 (CuMn) spinel oxides from metallic precursors could provide a potential solution for achieving tough and well-conducting contact layers. These contact layers are deposited from metallic precursors onto CoCe-coated AISI441 substrates to achieve high toughness even after aging for 3000 h at typical operating temperatures for SOCs. The interface fracture energy of CoMn and CuMn contact layers was measured for as-sintered and aged samples by using a modified four-point bending test. After the fracture test, X-ray diffraction, electron microscopy, and energy-dispersive X-ray spectroscopy were used to determine phase evolution and possible reactions at the contact layer/interconnect interface. The results show that the interface fracture energy of sintered CoMn contact layer (6.1 J/m2) decreased to 2.9 J/m2 after aging at 850 ○C for 3000 h while the fracture energy for CuMn increased from 6.4 J/m2 to 19.7 J/m2.