Effect of MoSi ₂ content on dielectric and mechanical properties of MoSi ₂/Al ₂O ₃ composite coatings

Molybdenum disilicide (MoSi ₂) sheath and aluminum oxide (Al ₂O ₃) core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray (APS) technology. The effects of MoSi ₂/Al ₂O ₃ mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi ₂ content of the composites increases from 0 to 45, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa·m ^1/2 then decline to 310 MPa and 4.67 MPa·m ^1/2, respectively. The dielectric loss tangent increases with increasing MoSi ₂ content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi ₂ particles and the increase of the electrical conductivity with increasing MoSi ₂ content.