Microwave glazing of alumina-titania ceramic composite coatings

The application envelop of atmospheric plasma sprayed ceramic composites ca n be widened considerably by reducing/eliminating inherent surface defects by treating them through techniques like microwave irradiation. In microwav e processing, microwave energy is directly applied to the material. High-fr equency microwaves (> 1 GHz usually) penetrate into the bulk of the materia l and the volumetric interaction of the electromagnetic fields with the mat erial results in dielectric (volumetric) heating. This leads to higher heat ing efficiency with faster processing. Ceramics are transparent to microwav es at low temperatures, however, start absorbing microwaves at higher tempe ratures resulting change in microstructure and material characteristics. Th is paper presents microwave processing of atmospheric plasma sprayed alumin a-titania ceramic composite coatings in conventional microwave heating syst em and evaluation of the processed materials through XRD, SEM, microhardnes s survey and surface finish with illustrations. Results indicate microwave irradiation induces densification of the material and possible flow of domi nant gamma-alumina phase that leads to glazing of coated surface. Glazed su rfaces exhibit enhanced microhardness as well as surface finish. (C) 2001 E lsevier Science B.V. All rights reserved.