Electromechanical Behaviour of Bi-layer Coating Deposited through Thermal Spray Processes on Carbon Fiber Reinforced Composites

The electromechanical behaviour of Ni-20Cr, alumina (Al2O3), and boron nitride (BN) coated on carbon fiber reinforced polymers (CFRP) was investigated. A bilayer coating-substrate system consisting of wire-arc sprayed Ni-20Cr coated on CFRP with flame-sprayed Al2O3 as a dielectric layer was fabricated. Another coating was fabricated in which the dielectric layer was made from aerosol deposition of BN. The electromechanical behaviour of the Ni-20Cr was investigated by subjecting it to cyclic extension loading between 0 and 0.2 mm for 100 cycles and uniaxial tensile loading for each type of dielectric layer while measuring the electrical resistance changes of the Ni-20Cr. Also, a comparative study between the dielectric layers were conducted. The electromechanical tests were correlated with microstructural features observed through scanning electron microscopy images of the pre- and post-loading processes. The nickel alloy showed significant piezoresistive sensitivity for the duration of the loading cycles, with little or no damage to the coating layers under cyclic loading. It also showed considerable sensitivity toward uniaxial tensile loading before failure. The dielectric layers also showed high dielectric breakdown strengths. These results indicated that the nickel alloy coating has great potential as a surface damage detection sensor with Al2O3 or BN as the dielectric layer.