Adrian Goldstein

Microwave sintering and mechanical properties of Y-TZP/20 wt.% Al2O3 composites

Abstract Y2O3-stabilized t-ZrO2 (Y-TZP)/20 wt.% Al2O3 composites were fabricated using microwave (MW) and conventional sintering techniques at temperatures in the 1200–1500°C range. A considerable difference in the densification behavior between conventional and microwave sintered specimens up to 1300°C was observed. The microwave sintered composites attain a bulk density ∼97% theoretical density (T.D.) at 1200°C, while the conventional fired materials attain only ∼95% T.D. at 1500°C. The average bulk density of the specimens, made by microwave sintering at 1500°C, was ∼99% T.D. At a given sintering temperature, microwave fabricated composites exhibited superior bending strength, fracture toughness and Vickers hardness when compared with conventionally sintered materials. For example, the composites fabricated at 1500°C exhibited a KIC of ∼7.7 MPa m and bending strength of ∼990 MPa. For comparison, specimens made by conventional sintering exhibited KIC of ∼6.5 MPa m and bending strength of ∼820 MPa. This is due to a better densification of the MW-sintered specimens.

Liquid assisted sintering of SiC powders by MW (2.45 GHz) heating

Abstract The feasibility of densifying α-silicon carbide powder compacts—based on a liquid assisted sintering approach—by the use of microwave powered furnaces, is examined. Despite the low penetration depth of GHz radiation, it is possible to obtain microwave sintering of SiC. Spatial uniformity of fired state density and warpage/cracking tendency are more dependent on size than in the case of conventional heating. Electromagnetic field intensity spatial variation—related to both the low penetration depth of the carbide and the inherent non-uniformity of the MWs distribution within the applicator—is one of the main factors which negatively affect densification uniformity. Nonetheless, fired state bulk density of 98% t.d. may be achieved in the case of small components. The phase composition of MWed and respectively conventionally sintered specimens is similar and so is the grain size distribution. A larger fraction of the oxide second phase is accumulated in triple points than in the case of resistive furnace firing. While MW sintering of SiC is feasible, it does not seem to generate practical advantages over conventional heating.