Thermomechanical fatigue damage of silver-silicate composite bonded Ni-Cr joints

In this work, thermal cycling induced mechanical fatigue stresses in silver-silicate composite bonded Ni-Cr joints were estimated first. Then the associated thermomechanical fatigue (TMF) damage at the silver-silicate composite/Ni-Cr interface was investigated. To prepare the conductive composite adhesives, various amounts of silver particles were added into sodium silicate. Ni80Cr20 wires were bonded in parallel by the composite adhesives. The obtained joints were annealed between 20 and 900 °C for various cycles to study the thermomechanical fatigue behavior. Thermomechanical fatigue damage evolution was monitored by measuring the AC impedances of the joints in the frequency range from 1 Hz to 100 kHz. Interface debonding was confirmed by observing the variation of the AC impedance with the increasing of the thermal cycles. The increases in the pore resistance and capacitance shown by Nyquist plots reveal microcrack formation in the joints. Evaluating the fatigue damage evolution of the Ag-silicate/Ni-Cr interface was performed through the debonding area computation.