Effect of chromium content on the mechanical and dielectric properties of Al₂O₃/Cr composites

Al₂O₃/Cr composites were prepared by hot pressing, and the relationship among their microstructure, mechanical and dielectric properties with Cr particle content was studied. SEM photographs show that some Cr particles are slightly elongated in the direction perpendicular to the pressing direction and are arranged in such a way to form large but finite interconnected clusters which do not span the entire specimen up to a volume fraction higher than 30 vol%. By increasing the amount of metal in the composite, the relative density and the bending strength decreased gradually. For composite, maximum fracture toughness values were 5-6 MPa·m^1/2 which was about double the value for alumina. The complex dielectric constant measurements indicate that the imaginary part and the real part increase greatly with the Cr content in the frequency of 8.2-12.4 GHz. The imaginary part of dielectric constant of Al₂O₃-30 vol%Cr is negative in value within specific frequency because a properly formed, well-bonded network of chromium actually occurs.