Mechanical and dielectric properties of Ni/Al₂O₃ composite coatings prepared by the axial plasma spraying

The nickel-alumina composite coatings were fabricated by the axial plasma spraying method. The effects of the different content of Ni on the microscopic structure, mechanical and dielectric properties of the composite coatings were investigated. The results indicate that with the increase of nickel content, the distribution of Ni particles changes from separated to large but finite interconnected clusters. The relative density and the bending strength decrease gradually, which is attributed to thermal expansion mismatch and non-wettability between alumina and nickel. The increase in the fracture toughness is caused by the Ni particles' extension and deflection of the crack. The complex dielectric constant measurements indicate that the real part shows an increase and then decline trend with the Ni content in the frequency of 8.2-12.4 GHz, while the imaginary part continues increasing. This is ascribed to the bridge structure of Ni particles.