Papers by Author: Wen He

Abstract: The influence of La2O3 on the phase and microstructure evaluation and mechanical properties of La2O3-Al2O3 ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that La2O3 could densify the pure alumina with a lower sintering temperature and a short sintering time. La2O3 reacted with Al2O3 to form LaAl11O18 completely and the amount of LaAl11O18 increased with the increasing content of La2O3, distributing at the Al2O3 grain boundaries. 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 La2O3-Al2O3 ceramics.

Abstract: The influences of Nb₂O₅ on the phase, microstructure and hydrochloric acid corrosion behaviors of Nb₂O₅-Al₂O₃ ceramics sintered with 2.45 GHz microwave energy were investigated. The results showed that Nb2O5 reacted completely with Al₂O₃ to form AlNbO₄ and densified the pure Al₂O₃ at a lower sintering temperature and in a short sintering time. Nb₂O₅-Al₂O₃ ceramic samples were corroded in diverse concentration hydrochloric acid for different time. Weight loss rate of Nb₂O₅-Al₂O₃ ceramic rose dramatically when the corrosion time was not longer than 4 h, and it increased slowly beyond 24 h. After Nb₂O₅-Al₂O₃ ceramic 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.

Abstract: Primeval TC4 titanium alloy was subjected to solution treatment at 1150°C for 1h, followed by water quenching, oil quenching, air cooling and furnace cooling, respectively. The pulse-echo method was carried out to measure ultrasonic longitudinal wave velocities (ν) and attenuation coefficients (α) of these heat-treated samples. The relationship between microstructures of different cooling rates and ultrasonic parameters such as ultrasonic longitudinal wave velocities (ν) and attenuation coefficients (α) was investigated. The results show that the microstructures of heat-treated TC4 alloy were α phase and β boundaries, and the ultrasonic longitudinal velocities and attenuation coefficients of these heat-treated samples, in turn, increased with reducing the cooling rate from water quenching to furnace cooling.

Abstract: The green bodies of LaNbO4/MoSi2 composite materials were compacted by warm pressing and cold pressing processes, and then the composites were prepared by microwave sintering. Effects of the two different compaction processes on sintering process and sintered samples were analyzed. The results show that the density of the microwave sintered sample by cold pressing (5.599g/cm3) is similar to that of warm pressing (5.593 g/cm3). But cold pressing has some disadvantages, such as longer sintering time, incomplete sintered samples, peeling easily on the surface and delaminating, existing internal stress, having microcrack and impurities, and occurring distortion easily in sintered samples. The samples compacted by warm pressing have higher heating rate in the microwave sintering process, which have more homogeneous structures, no clear microcrack and big cavities, and higher fracture toughness after sintering. Compared with cold pressing, the comprehensive properties of warm pressing are better.