Abstract
AbstractBetter understanding of the effect of multimode‐microwave sintering of zirconia‐toughened alumina (ZTA) was investigated. A comparative dilatometric analysis was conducted between conventional and microwave heating processes, to clarify the influence of zirconia on the densification of ZTA under electromagnetic field. The thermal gradient on sample measurements indicates the change to the microwave volumetric heating is improved by zirconia which adsorbs microwave energy better, thus acting as a susceptor. The most beneficial effect on microstructure, toughness, and hardness were observed at the optimal zirconia content of 10 vol%. The results with both microwave and conventional sintering illustrate the strengthening effect on the composite by zirconia. Of special interest, multimode microwave sintering creates a finer homogeneous microstructure, with resulting hardness and toughening comparable to those obtained for conventional sintering, as well as improved densification, and at lower cost.
Highlights
For many years, reducing the environmental impact of industrial processes has been the focal point of research
This phenomena improves the mechanical properties of composite. These results show the feasibility of applying microwave heating process to produce ceramic materials with high density and fine/homogeneous microstructure
Rigorous comparison of densification behavior under identical thermal cycles between conventional and microwave sintering showed a expected delaying effect of zirconia on densification for both heating modes. This comparative dilatometric study demonstrated the beneficial effect of the electromagnetic field on densification of alumina and zirconiatoughened alumina (ZTA): under microwave, maximum densification rate occurs at lower temperature, leading to an increase in the sample density for any given temperature
Summary
For many years, reducing the environmental impact of industrial processes has been the focal point of research. Microwave can target only or almost only the matter: the ceramic material has a direct interaction with the microwave field depending on its dielectric properties This offers several advantages over conventional methods,[1] for example, high heating rate, lower sintering temperature, enhanced diffusion for densification, finer and/or uniform microstructure, potential optimized final properties of the sample, etc. The first is stress-induced transformation toughening: under external tensile stress, the metastable tetragonal zirconia phase will transform to a stable monoclinic phase; this is followed by a volume expansion (~4%) and shear strain (~6%) which can provide a compressive stress leading to a reduction and a stop in crack propagation.[4] The second is due to “microcracks” in the composite: when the phase transformation appears during the cooling after sintering temperature, microcracks occur inside the material (mainly caused by the volume expansion) These microcracks can absorb fracture energy, and improve strongly the mechanical properties of composite. On the basis of this research, we tried to show the possible differences in densification behavior as well as in mechanical properties between conventionally sintered and multimode microwave-sintered Al2O3–ZrO2 composites with different amounts of ZrO2
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