Microwave joining of 48% alumina–32% zirconia–20% silica ceramics

Abstract

Microwave heating leads to generation of an inverted temperature profile and provides selective heating within a ceramic. However, most ceramics are almost transparent to microwaves at room temperatures and frequencies reserved for industrial usage. With rising temperature, however, most ceramics became increasingly susceptible to microwave energy. Impurities within ceramics make them susceptible more to microwave heating, when compared with high-purity ceramics. Microwave joining techniques attempt to raise ceramics to fusion temperatures and provide effective joining at targeted regions. Thorough studies have been conducted to characterise zirconia–alumina–silica ceramics at high temperatures. Time–temperature behaviour of alumina–zirconia–silica ceramics at different powers has also been studied. On-line load matching techniques using a six-port impedance analyser coupled to a motorised three-stub tuner, have been utilised to optimise power transmission and energy deposition rates to the material. Microwave joining trials of alumina–zirconia–silica and high-purity alumina ceramics have yielded joint strengths in excess of the base material strength. Moreover, impure interlayers between mating surfaces, which tend to decrease joint strengths, have been totally eliminated. These results are discussed in this paper.