Effects of Y₂O₃ on mechanical, dielectric, and microwave-absorbing properties of short carbon-fiber/Al₂O₃ composites

Short carbon-fiber (C_sf) reinforced alumina ceramics with MgO-Y₂O₃ as additives were fabricated by pressureless sintering at 1500 °C for 2 h. The mechanical, dielectric and microwave properties of the composites in the X band (8.2-12.4 GHz) were evaluated. The flexure strength and HRA of the ceramic increased with increasing Y ₂O₃ content and the maximum values of 293 MPa and 98 were obtained by the addition of 1.0 wt% Y₂O₃, which were about 33.2% and 12.6% higher than the composite without Y₂O₃, respectively. Both the real and imaginary parts of the complex permittivity increased with increasing Y₂O₃ content. The composite containing 0.5 wt% Y₂O₃ showed that reflection loss exceeded -10 dB in the frequency of 9.6-11.6 GHz and the minimum value was -33 dB at 10.38 GHz. The results showed that the addition of Y₂O ₃ allowed both mechanical and microwave absorbing properties of the composite to be enhanced and it indicates that the C_sf/Al ₂O₃ ceramic prepared by pressureless sintering with a small quantity of Y₂O₃ is a promising microwave absorber with satisfactory mechanical properties.