ZrO2 doped with 7.5% (volume percent) nanoalumina ceramics were prepared by microwave sintering processes. The effects of nanoalumina additions and various sintering temperature on densification, phase composition, microstructure and mechanical properties of Al2O3-ZrO2 ceramics were investigated. The results show that the m-ZrO2 phase transformed into t-ZrO2 during the process of microwave sintering. Relative densities between 95% and 99% were attained in the different conditions. In any cases the grain size was maintained at a submicron scale at a processing microwave sintering. The presence of Al2O3 grains had an effect of hindering grain growth of ZrO2 grains. When the microwave sintering temperature was 1500°C, 7.5Al2O3-ZrO2 composite ceramics presented excellent mechanical properties: HV=12.0 GPa, σf=715.7 Mpa, KIC=11.9 MPa·m1/2. Compared with that of pure ZrO2 ceramic, the bending strength and the fracture toughness were improved 45% and 23% at least, respectively. The fracture mode was associated with sintering temperature: when the sintering temperature was 1350°C~1450°C, the intergranular fracture and transgranular fracture coexisted; when the sintering temperature was 1500°C, intergranular fracture was the main fracture mode.
Al2O3(x)/ZrO2composite ceramics were successfully prepared by microwave sintering. The influence of variety content of nanoAl2O3on mechanical properties and microstructure of ZrO2dental materials were studied, and analysied the mutual relations of chemical composition, mechanical properties and microstructure to investigate the reason of strengthening and toughening. Results indicated that The relative density of the Al2O3(x)/ZrO2composite ceramics reached more than 96.8%.The HV hardness ,bending strength and fracture toughness presented excellent mechanical properties as 12.5GPa, 753.8MPa and 11.8MPa·m1/2with the content of nanoAl2O3was 7.5%. Compared with that of pure ZrO2ceramics, the bending strength and the fracture toughness were improved 19% and 96%, respectively. The main crystal phases in this composite ceramics were t-ZrO2and α-Al2O3.The nanoAl2O3have a obvious effect on the strength and toughness of ZrO2based ceramics. The reason of strengthening and toughening mainly the additions reduced the ZrO2grains growth and promoted grains size uniformity, and changed the fracture mode from transgranular fracture to intergranular fracture characteristics.
Annealing treatment of cold compression deformation red copper was heated by microwave. The feasibility of microwave heating technology applied to heat treatment of metallic materials, and the effect of annealing process on microstructure were discussed. The results show that the phenomenon of arc discharge do not occur during the process of microwave heating red copper, which illustrates that microwave can be used as heat source for heat treatment of metallic materials. When annealing condition is 510°C for 30min, the grains of deformation red copper undergo a transition from fibrous grain to equiaxial grain, and it completes recrystallization. Compared with traditional annealing treatment, microwave annealing treatment can prevent oxidation phenomenon of specimen surface effectively, reduce annealing temperature, shorten heating and holding time, reduce the consumption of energy greatly, and the degree of hardness decline is smaller under the same annealing condition.
The influence of Nb2O5 and La2O3 on the phase and microstructure evaluation and mechanical properties of composite ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that Nb2O5 could densify the pure alumina with a lower sintering temperature and a short sintering time. Nb2O5 reacted with Al2O3 to form AlNbO4 completely and the amount of AlNbO4 increased with the increasing content of Nb2O5, distributing at the Al2O3 grain boundaries. The specimen doped with 10 Vol.% Nb2O5 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:3. La2O3 reacted with Al2O3 to form LaAl11O18 completely, the specimen doped with 10 Vol.% and 15 Vol.% La2O3 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:4. The existence of columnar grains enhanced the microhardness and fracture toughness of composite ceramics.
The influences of Nb2O5on the phase, microstructure and hydrochloric acid corrosion behaviors of Nb2O5-Al2O3ceramics sintered with 2.45 GHz microwave energy were investigated. The results showed that Nb2O5 reacted completely with Al2O3to form AlNbO4and densified the pure Al2O3at a lower sintering temperature and in a short sintering time. Nb2O5-Al2O3ceramic samples were corroded in diverse concentration hydrochloric acid for different time. Weight loss rate of Nb2O5-Al2O3ceramic rose dramatically when the corrosion time was not longer than 4 h, and it increased slowly beyond 24 h. After Nb2O5-Al2O3ceramic samples were corroded for 1 h, pitting corrosion was observed by scanning electric microscope, which was consistent with the analysis results of the scanning Kelvin Probe.
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